Abstract:
The inkjet recording head comprises: a plurality of ink chambers aligned, each of the plurality of ink chambers having a nozzle; and a piezoelectric element arranged on an outer side of the plurality of ink chambers, the piezoelectric element using displacement in d31 direction, piezoelectric strain absorbing holes being formed through the piezoelectric element in regions of outer perimeters of active sections of the piezoelectric element, wherein when voltage is applied to one of the active sections of the piezoelectric element, corresponding one of the plurality of ink chambers is compressed by the piezoelectric element, and ink filled in the one of the plurality of ink chambers is discharged through the nozzle toward a recording medium.

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2003-332470 filed in Japan on Sep. 24, 2003, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to inkjet recording head, an inkjet recording apparatus and a method for manufacturing an inkjet recording head, and more particularly, to an inkjet recording head, an inkjet recording apparatus, and a method for manufacturing an inkjet recording head, whereby no cross-talk is generated. 
     2. Description of the Related Art 
     An inkjet printer used as an image forming apparatus, such as a printer, a facsimile apparatus, a copying apparatus, or the like, forms images on paper by discharging ink from nozzles of pressure chambers, in accordance with image forming data. 
     Ink discharging devices based on a piezo-actuator using a piezoelectric element, which deforms in accordance with an electric signal, are known. In a piezo-actuator method, a pressure wave is applied to a pressure chamber by deforming the wall of the pressure chamber by means of a piezoelectric element, thereby causing ink to be discharged from the nozzle of the pressure chamber, and therefore it is possible to generate a strong pressure wave by means of a low drive energy. In recent years, inkjet printers have been required to form images of high precision and resolution, and it has become necessary to eliminate differences in the flight characteristics of ink droplets, when one nozzle is driven and when a plurality of nozzles are driven, and to eliminate the generation of accidental droplets due to cross-talk between one pressure chamber and an adjacent pressure chamber. As a method for resolving these requirements, Japanese Patent Application Publication No. 10-329320 discloses that cross-talk is prevented by forming strain absorbing holes in two or three of the outer edges of the pressure chamber of the piezoelectric element. 
     In the recording head disclosed in Japanese Patent Application Publication No. 10-329320, the piezoelectric elements corresponding to respective nozzles are connected partially with the adjacently positioned piezoelectric elements, and hence a problem arises in that cross-talk cannot be completely eliminated. Moreover, the recording head disclosed in Japanese Patent Application Publication No. 10-329320 is formed by stacking green sheets in multilayer on which strain absorbing holes have been formed, and it is difficult to register the small strain absorbing holes in position, and hence productivity declines. Moreover, in an inkjet printer head based on a method wherein ink is discharged by using a bimorph effect between a vibration plate and a piezoelectric body, as in the present example, since the displacement of the piezoelectric body in a lateral direction is utilized, there is a very significant effect on adjacent nozzles if a structure is adopted wherein all of the piezoelectric bodies are connected. 
     SUMMARY OF THE INVENTION 
     The present invention is contrived in view of such circumstances, and an object thereof is to provide an inkjet recording head, an inkjet recording apparatus and a method for manufacturing an inkjet recording head whereby cross-talk is prevented, whilst also achieving excellent productivity. 
     In order to attain the above-described object, the present invention is directed to an inkjet recording head, comprising: a plurality of ink chambers aligned, each of the plurality of ink chambers having a nozzle; and a piezoelectric element arranged on an outer side of the plurality of ink chambers, the piezoelectric element using displacement in d31 direction, piezoelectric strain absorbing holes being formed through the piezoelectric element in regions of outer perimeters of active sections of the piezoelectric element, wherein when voltage is applied to one of the active sections of the piezoelectric element, corresponding one of the plurality of ink chambers is compressed by the piezoelectric element, and ink filled in the one of the plurality of ink chambers is discharged through the nozzle toward a recording medium. 
     According to the present invention, since the piezoelectric strain absorbing holes passing through the piezoelectric element are formed in the piezoelectric element in the regions of the outer perimeters of the active sections (i.e., the discrete electrodes, the pressure chambers), then stress generated by piezoelectric strain is eliminated by means of the piezoelectric strain absorbing holes and hence cross-talk can be prevented. 
     Preferably, the inkjet recording head further comprises a vibration plate which defines the plurality of ink chambers, grooves being formed on the vibration plate at positions opposing the piezoelectric strain absorbing holes in the piezoelectric element. According to this, it is possible further to alleviate the stress generated in the vibration plate by piezoelectric strain, and hence elimination of cross-talk is promoted. 
     Preferably, the vibration plate and the piezoelectric element are bonded by means of adhesive, and the piezoelectric strain absorbing holes form escape regions for surplus adhesive during bonding. According to this, any surplus adhesive enters into the piezoelectric strain absorbing holes, thereby enabling stable bonding of the vibration plate and the piezoelectric element. Moreover, the drying time for the adhesive can also be shortened by means of the piezoelectric strain absorbing holes. 
     The present invention is also directed to an inkjet recording apparatus, comprising: a plurality of ink chambers aligned, each of the plurality of ink chambers having a nozzle; and a piezoelectric element arranged on an outer side of the plurality of ink chambers, the piezoelectric element using displacement in d31 direction, piezoelectric strain absorbing holes being formed through the piezoelectric element in regions of outer perimeters of active sections of the piezoelectric element, wherein when voltage is applied to one of the active sections of the piezoelectric element, corresponding one of the plurality of ink chambers is compressed by the piezoelectric element, and ink filled in the one of the plurality of ink chambers is discharged through the nozzle toward a recording medium. 
     The present invention is also directed to a method for manufacturing the inkjet recording head, comprising the steps of: forming a common electrode onto a first surface of a single green sheet by means of a screen printing; then forming discrete electrodes onto a second surface of the green sheet by means of screen printing; then forming the piezoelectric strain absorbing holes in the green sheet in the regions of the outer peripheries of the discrete electrodes by means of a pressing machine; then calcining the green sheet to form the piezoelectric element using displacement in d31 direction; and then bonding the piezoelectric element to a vibration plate. 
     According to the present invention, since the piezoelectric strain absorbing holes are processed after forming the common electrode and the discrete electrodes, whereupon the vibration plate is bonded, it is possible to prevent strain or damage to the vibration plate, which is liable to the vibration plate, during forming and processing, and hence productivity can be increased. 
     In the present specification, the term “recording” indicates the concept of forming images in a broad sense, including text. Furthermore, “recording medium” indicates a medium on which an image is formed by means of a recording head (this medium may be called an image forming medium, recording medium, image receiving medium, recording paper, or the like), and this term includes various types of media, irrespective of material and size, such as continuous paper, cut paper, sealed paper, resin sheets, such as OHP sheets, film, cloth, and other materials. 
     According to the present invention, cross-talk can be prevented, and productivity can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein: 
         FIG. 1  is a side view showing an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a plan view showing an inkjet recording head according to an embodiment of the present invention; 
         FIG. 3  is a partial enlarged cross-sectional view showing the detailed structure the inkjet recording head; 
         FIGS. 4A to 4E  are plan views showing other embodiments of piezoelectric strain absorbing holes; 
         FIGS. 5A to 5E  are descriptive diagrams showing a method for manufacturing the inkjet recording head; 
         FIG. 6  is a detailed cross-sectional diagram showing the inkjet recording head; 
         FIG. 7A  is a detailed plan view showing an inkjet recording head according to another embodiment of the present invention, and  FIG. 7B  is a cross-sectional view of  FIG. 7A ; and 
         FIG. 8  is a detailed plan diagram showing an inkjet recording head relating to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, an embodiment of an inkjet recording head, an inkjet recording apparatus and a method for manufacturing an inkjet recording head are described with reference to the accompanying drawings.  FIG. 1  is a side view showing a schematic illustration of the composition of an image forming apparatus  10  to which an inkjet recording head, an inkjet recording apparatus and a method for manufacturing an inkjet recording head according to a first embodiment are applied. 
     The image forming apparatus  10  comprises: a recording head  12 ; a belt conveyance unit  18  for conveying recording paper  16  whilst maintaining the recording paper  16  in a flat state, disposed in a position opposing the recording head  12 ; a paper supply unit  20  for supplying recording paper  16 ; and a paper output section  22  for outputting recording paper externally, once an image has been formed thereon. 
     The recording head  12  is constituted by a so-called full line type head, wherein a line type head having a length corresponding to the width of the recording paper  16  is disposed in a fixed position, in a direction orthogonal to the paper conveyance direction. Recording heads  12 K,  12 C,  12 M,  12 Y corresponding to respective ink colors are disposed in the order, black (K), cyan (C), magenta (M) and yellow (Y), from the upstream side, following the direction of conveyance of the recording paper  16  (arrow A). Nozzles (not shown) are formed in each of these recording heads, and a color image, or the like, is formed on the recording paper  16  by discharging ink of the colors from the nozzles, onto the recording paper  16 , whilst conveying the recording paper  16 . The details of the recording head  12  are described hereinafter. 
     Roll paper  26  is set in place detachably on a paper supply unit  20 . Pickup rollers  21  for picking up the recording paper  16  from the roll paper  26  are provided in the vicinity of the paper supply unit  20 . The force of a motor (not shown) is transmitted to at least one of the pick-up rollers  21 , and the recording paper  16  picked up thereby is conveyed from right to left in  FIG. 1 . Reference numeral  24  is a shearing cutter disposed between the rollers  21 , and the recording paper  16  picked up from the roller paper  26  is cut to a prescribed size by means of the cutter  24 . 
     The belt conveyance unit  18  has a structure wherein an endless belt  38  is wound about rollers  30 ,  32 ,  34  and  36 , and is composed in such a manner that at least the portion opposing the recording head  12  is a horizontal surface. This belt  38  has a broader width dimension than the width of the recording paper  16 , and the recording paper  16  can be suctioned onto the surface of the belt. The drive force of a motor (not shown) is transmitted to at least one of the rollers  30 ,  32 ,  34 ,  36  about which the belt  38  is wound, whereby the belt  38  is driven in a counterclockwise direction in  FIG. 1 , and hence the recording paper  16  suctioned onto the belt  38  is conveyed from right to left in  FIG. 1 . 
     Reference numeral  82  denotes a recording determination unit for reading in the position, size, and the like, of the recording paper, reference numeral  84  denotes a recording position determination unit for determining the timing of ink discharge onto the recording paper  16 , and reference numeral  88  denotes a recording paper end detection unit for detecting a stacking of the recording paper  16  and for determining the supply timing of the next sheet. Furthermore, the image forming apparatus  10  has a system controller (not shown) which controls the whole image forming apparatus  10  on the basis of the detection results from these detection units. The system controller is constituted by a central processing unit (CPU) and peripheral circuits, and the like, and it generates, for example, drive signals and control signals for the motors for conveying the recording paper  16 , and image forming signals for the recording head  12 , and the like. 
     Next, the structure of the recording head  12  will be described. Since the structure of the recording heads  12 K,  12 C,  12 M and  12 Y provided for the ink colors are similar, each of the recording heads is denoted with the reference numeral  12  hereinafter, as a representative example of the recording heads.  FIG. 2  is a plan view of the recording head  12 , and  FIG. 3  is a partial enlarged cross-sectional view of the recording head  12 . 
     As shown in  FIG. 3 , the recording head  12  is composed of a nozzle plate  42  formed in a square plate shape, partitions  43 , a vibration plate  44 , a common electrode  46 , a piezoelectric element  48 , discrete electrodes  50 , and the like. As shown in  FIG. 3 , pressure chambers  54  are formed by the empty spaces enclosed by the nozzle plate  42 , the plurality of partitions  43 , and the vibration plate  44 , and the pressure chambers  54  are disposed in a staggered matrix arrangement in the positions indicated by the reference numerals  50  in  FIG. 2 . The pressure chambers  54  are connected to an ink supply passage (not shown), whereby ink is supplied to the interior of the pressure chambers  54 . 
     A nozzle  56  connected to the lower face of the nozzle plate  42  is formed through the nozzle plate  42  in a position corresponding to the lower portion of each of the pressure chambers  54 . The vibration plate  44  is arranged on the ceiling face of the pressure chambers  54  in such a manner that the vibration plate  44  seals the pressure chambers  54 , and the grounded common electrode  46  is arranged on the upper face of the vibration plate  44 . 
     The piezoelectric element  48  is a single plate, and has a rectangular shape similar to the nozzle plate  42 . The piezoelectric element plate  48  is arranged on the upper face of the common electrode  46 . The discrete electrodes  50  are arranged on the upper face of the piezoelectric element  48 , in positions opposing the pressure chambers  54 . When an electric field is applied to the piezoelectric element  48  in the vertical direction in  FIG. 3 , by means of the discrete electrode  50  and the common electrode  46 , the piezoelectric element  48  deforms in a lateral direction (mode d31), in other words, in the directions of arrows B in  FIG. 3 . The piezoelectric element  48  is connected on the vibration plate  44  through the common electrode  46  and when the piezoelectric element  48  deforms in the lateral direction, both the piezoelectric element  48  and the vibration plate  44  bend downwards as represented with alternate long and two short dashes lines in  FIG. 3 , thereby causing the volume of the pressure chamber  54  to change, and thus applying a pressure wave to the pressure chamber  54 . 
     In the regions of the four outer edges of the discrete electrodes  50  on the piezoelectric element  48 , a plurality of piezoelectric strain absorbing holes  52  are formed. The piezoelectric strain absorbing holes  52  are formed passing in a direction orthogonal to the sheet of  FIG. 2 . 
     When a drive voltage is applied to the discrete electrode  50 , the vibration plate  44  deforms due to the deformation of the piezoelectric element  48  as shown with the alternate long and two short dashes lines in  FIG. 3 , thereby causing the volume of the pressure chamber  54  to change, and thus applying a pressure wave to the pressure chamber  54 , in response to which ink is discharged from the nozzle  56 . A connection circuit board (not shown) for providing electrical connections to a drive circuit for applying drive voltage to the discrete electrodes  50  provided inside the image forming device  10 , is installed in the recording head  12 . 
     Next, the action of the recording head  12  having the composition described above will be explained. 
     In order to form an image on the basis of an image forming pattern, drive voltages are applied to the discrete electrodes  50  from the drive circuit, in accordance with a system controller. As shown in  FIG. 3 , the piezoelectric element  48  deforms in a lateral direction (the directions of the arrows B in  FIG. 3 ), and the vibration plate  44  forming the ceiling face of the pressure chamber  54  bends projectingly towards the pressure chamber  54  as shown with the alternate long and two short dashes lines in  FIG. 3 , whereby a pressure wave is applied to the pressure chamber  54 . Upon application of the pressure wave, ink is discharged from the pressure chamber  54  through the nozzle  56 . The ink thus discharged is deposited onto the recording face of the recording paper  16 , whereby an image is formed on the recording paper  16 . When the application of the drive voltage is terminated, the piezoelectric element  48  and the vibration plate  44  which had deformed revert to their state prior to deformation. When they revert in this manner, new ink of approximately the same volume as the ink that has been discharged is supplied to the pressure chamber  54  from the ink supply passage (not shown). This ink discharging operation is performed repeatedly, and an image based on an image forming pattern is formed on the recording paper  16  as it is conveyed. 
     Here, when the piezoelectric element  48  is deformed in the lateral direction, internal stress arises in the piezoelectric element  48  to the outer sides of the discrete electrode  50 , but this internal stress is eliminated by means of the piezoelectric strain absorbing holes  52 . More specifically, since the piezoelectric strain absorbing holes  52  are formed in the piezoelectric element  48 , which bends and deforms together with the vibration plate  44 , in the region of the outer perimeter of the discrete electrode (active element)  50 , then it is possible to eliminate cross-talk to the piezoelectric element  48  at other adjacently positioned pressure chambers. 
     As shown in  FIGS. 4A to 4E , various shapes and positional configurations may be adopted for the piezoelectric strain absorbing holes  52 . In an example shown in  FIG. 4A , piezoelectric strain absorbing holes  52   a  are disposed along the four outer edges of each discrete electrode  50  as in the above-described embodiment. In an example shown in  FIG. 4B , rectangular shaped piezoelectric strain absorbing holes  52   b  are disposed along the four outer edges of each discrete electrode  50 . In an example shown in  FIG. 4C , piezoelectric strain absorbing holes  52   c  are disposed in a staggered matrix arrangement along the four outer edges of each discrete electrode  50 . In an example shown in  FIG. 4D , oval-shaped piezoelectric strain absorbing holes  52   d  are disposed along the four outer edges of each discrete electrode  50 . In an example shown in  FIG. 4E , piezoelectric strain absorbing holes  52   e  of different sizes are disposed along the four outer edges of each discrete electrode  50 . 
     The piezoelectric element  48  according to the present embodiment is constituted by a single plate, and hence costs are low and processing is straightforward. 
     Next, a method for manufacturing the piezoelectric element  48  used in the recording head  12  according to the present embodiment is described with reference to  FIGS. 5A to 5E . This process advances sequentially from  FIG. 5A  to  FIG. 5E . 
     Firstly, in  FIG. 5A , a green sheet  60  is laid provisionally on a base plate  62 . 
     As shown in  FIG. 5B , a common electrode  46  is printed onto the surface of the green sheet  60 , by means of a screen printing technique. 
     As shown in  FIG. 5C , the green sheet  60  is turned over from the state in  FIG. 5B , and discrete electrodes  50  are then printed onto the other surface (i.e., reverse to the surface on which the common electrode  46  has been formed) of the green sheet  60 , by means of a screen printing technique. The positions at which the discrete electrodes  50  are formed are previously set in such a manner that they correspond to nozzles  56  arranged in a matrix configuration. 
     As shown in  FIG. 5D , piezoelectric strain absorbing holes  52  are then pierced in the green sheet  60 , by means of a pressing machine  64 . 
     As shown in  FIG. 5E , after degreasing the green sheet  60 , it is calcined, thereby forming a plate of piezoelectric element  48 . Thereupon, the plate of piezoelectric element  48  is bonded to a vibration plate  44  ( FIG. 3 ), whereby the formation process for the piezoelectric element  48  relating to the present embodiment is completed. 
     Here, as shown in  FIG. 6 , the vibration plate  44  and the piezoelectric element  48  are bonded by means of adhesive  66 . In this case, the piezoelectric strain absorbing holes  52  form escape regions for surplus adhesive  66   a , and as shown in  FIG. 6 , stable bonding of the vibration plate  44  and the piezoelectric element  48  is achieved by means of the surplus adhesive  66   a  entering into the piezoelectric strain absorbing holes  52 . 
     Next, the inkjet recording head relating to a second embodiment of the present invention is described with reference to  FIGS. 7A and 7B . Elements which are the same or similar to those of the first embodiment illustrated in  FIG. 2  and  FIG. 3  are denoted with similar reference numerals and detailed description thereof is omitted here. 
     As shown in  FIGS. 7A and 7B , in the recording head  100  relating to the present embodiment, grooves  102  for absorbing piezoelectric strain are formed in the vibration plate  44  in positions opposing the piezoelectric strain absorbing holes  52 . 
     According to the recording head  100  composed as described above, it is possible further to alleviate any stress generated in the vibration plate  44  by piezoelectric strain, and therefore, the elimination of cross-talk can be promoted. 
     The composition of the inkjet recording head, the inkjet recording apparatus and the method for manufacturing an inkjet recording head indicated in the embodiments described above are not limited to the foregoing embodiments. For example, as shown in  FIG. 8 , it is also possible to solder electrode lead sections  112  for the discrete electrodes  50  onto the sections where no piezoelectric strain absorbing holes  52  are formed, by means of a ball grid array, or the like, as in the recording head  110 . In this way, the electrodes from the discrete electrodes  50  can be wired in an integrated fashion, by means of these electrode lead sections  112 . 
     Moreover, although the discrete electrodes  50  are formed by screen printing before calcining in the above-described embodiments, the invention is not limited to this, and they may also be installed by sputtering, vapor deposition, or the like, after calcining. 
     It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.