Abstract:
According to one embodiment, an ink jet head includes a base portion and a plurality of nozzles configured to discharge ink formed in one end side of the base portion, an actuator including a plurality of pressure chambers corresponding to the plurality of nozzles, is provided on a first surface which is an end surface of the one end side of the base portion, ink guides which form ink channels are formed on a second surface which is a main surface of the base portion and crosses with the first surface, and a wiring connected to the actuator is formed on a third surface which is another main surface opposite to the second surface of the base portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-214972, filed on Sep. 16, 2009; the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    Embodiments described herein relate generally to an ink jet head including an ink-discharging nozzle. 
       BACKGROUND 
       [0003]    With regard to circulation-type ink jet heads, such a structure is known, which comprises a nozzle plate including a plurality of nozzles, a plurality of pressure chambers provided to correspond respectively to the nozzles, on a main surface of a plate-shaped substrate, a base substrate in which ink channels and liquid chambers communicating to the pressure chambers are built, and a printed circuit board on which wiring which drives the pressure chambers are formed. 
         [0004]    In such an ink jet head, grooves are formed by mechanical processing in a piezoelectric member provided on the main surface of the plate-shaped base substrate. 
         [0005]    However, the above-described technique entails the following problem. That is, a plate-shaped piezoelectric member has a low stiffness in its thickness direction and the piezoelectric member in many cases deforms while being subjected to mechanical processing on its main surface, which applies a load on the member in its thickness direction. Due to this drawback, it is difficult to form the pressure chambers at a high accuracy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view showing an ink jet head according to the first embodiment; 
           [0007]      FIG. 2  is an exploded perspective view showing a base structure portion of the ink jet head according to the first embodiment; 
           [0008]      FIG. 3  is an enlarged perspective view showing a portion A shown in  FIG. 2 ; 
           [0009]      FIG. 4  is an enlarged side view showing a portion B shown in  FIG. 3 ; 
           [0010]      FIG. 5  is a plan view showing the base structure portion of the ink jet head according to the first embodiment; and 
           [0011]      FIG. 6  is a side view showing the ink jet head according to the first embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     The First Embodiment 
       [0012]    In general, according to one embodiment, an ink jet head  1  according to the first embodiment will now be described with reference to  FIGS. 1 to 6 . In these figures, arrows X, Y and Z indicate 3 directions normally crossing with each other. Further, in these figures, structures are enlarged, contracted or omitted as need for the sake of explanation. 
         [0013]      FIG. 1  is a perspective view showing the ink jet head  1  according to the first embodiment.  FIG. 2  is an exploded perspective view showing a structural portion of the ink jet head  1  of this embodiment, while partially omitting the structural portion. In these figures, the head is inverted upside down such that nozzles  11   a  are arranged upwards and the ink discharging direction faces upwards for the convenience of explanation. 
         [0014]    In  FIG. 2 , a set of a first actuator unit  12  and a first cover  14  and a set of a second actuator unit  13  and a second cover  15  are shown to be developed while these sets are rotated by 90 degrees with respect to each other. A pair of the actuator units  12  and  13  have the same structure and therefore common explanations will not be repeated. In  FIG. 2 , a rear side (one side in the X direction) of the first actuator unit  12  and a front side (the other side in the X direction) of the second actuator unit  13  are shown. 
         [0015]    The ink jet head  1  of this embodiment is the so-called circulation type ink jet head in which ink is circulated at all times. As shown in  FIGS. 1 and 2 , the ink jet head  1  comprises a nozzle plate  11  in which a plurality of nozzles  11   a  are formed, A pair of the actuator units  12  and  13  arranged to face each other on a lower surface side of the nozzle plate  11 , and a pair of covers  14  and  15  formed to cover both sides of the pair of these actuator units  12  and  13 . 
         [0016]    The nozzle plate  11  is formed into a plate shape comprising a plurality of nozzles  11   a  respectively corresponding to a plurality of pressure chambers  23 . The nozzle plate  11  is provided to cover a base structure portion  10  from an upper side, which comprises the pair of the actuator units  12  and  13  and the pair of the covers  14  and  15 . 
         [0017]    Each of the actuator units  12  and  13  comprises a base portion  20  of a rectangular parallelepiped shape having upper and lower surfaces normally crossing the Z axis, front and rear surfaces normally crossing the X axis and both side surfaces normally crossing the Y axis. The base portion  20  is formed of a material selected from, for example, a metal, ceramics and resin, and is placed in such a manner that its thickness direction goes along the X-axis, its longitudinal direction along the Y-axis, and its width direction along the Z-axis. For example, the base portion  20  is formed to have such dimensions of several tens of millimeters in width, 18 mm in thickness and about 60 mm in length. 
         [0018]    A piezoelectric actuator  21  is formed via an adhesive layer  27  on an upper surface (first surface) of the base portion  20 , which is an end face close to the nozzle  11   a.    
         [0019]    As shown in  FIGS. 3 and 4  enlarged, the piezoelectric actuator  21  (actuator) comprises a plurality of driver elements  22  arranged in the Y direction. Each portion sandwiched from both sides by a respective adjacent pair of driver elements  22  forms a respective pressure chamber  23  corresponding to a respective nozzle  11   a . In other words, driver elements  22  which drive each nozzle  11   a  to discharge ink are arranged both sides of each pressure chamber  23 . Ink is reserved inside each of the pressure chambers  23 . 
         [0020]    Each of the driver elements  22  comprises two piezoelectric elements  24   a  and  24   b  formed of, for example, a PZT-based piezoelectric ceramic material. Each of the driver elements  22  comprises the first piezoelectric element  24   a  at a position close to the nozzle  11   a  and the second piezoelectric element  24   b  at a position distant from the nozzle  11   a . The first piezoelectric element  24   a  and the second piezoelectric element  24   b  are subjected to a polarization process such that the polarization directions of the elements are reverse to each other, and they are adhered to each other via an adhesive layer  25 . An electrode  26  is formed on an inner surface of each pressure chamber  23  formed between an adjacent pair of driver elements  22 . 
         [0021]    As shown in  FIG. 2 , an ink guide  30  is formed in a surface (the second surface) of the base portion  20 . The ink guide  30  comprises a T-shaped guide rib  31  which stands from the second surface in the X direction, and a cylindrical guide pipe  32  which extends from the Y-axial central portion of the guide rib  31  downwards, which are integrated as one unit. 
         [0022]    The guide rib  31  is formed as integrated with the base portion  20  by, for example, molding when forming the base portion  20 . The guide rib  31  comprises an outer rib  33  formed along the longitudinal edge of the base portion  20  to each both the upper and lower ends, and an inner rib  34  which extends in the Y direction at the Z-axial central portion of the base portion  20 . On an distal end surface of the outer rib  33 , a plurality of alignment projections  33   a  are formed. 
         [0023]    The guide pipe  32  are continuously formed from the central position of the inner rib  34  downwards, and an ink channel is formed within the guide pipe  34  from a common liquid chamber formed on an upper side of the guide rib  31  to reach below the ink jet head  1 . 
         [0024]    A plurality of driver ICs  41  which drive the operation of the piezoelectric actuator  21  and a plurality of wirings  42  (electrodes) which connect the driver ICs  41  and the electrode  26  to each other are formed on the rear surface (third surface) of the base portion  20 . That is, the rear surface of the base portion  20  functions as a printed circuit board. The wirings  42  are formed to respectively correspond to the driver elements  22  by a one-to-one manner. Further, the rear surface comprises electric connection portions  43  formed continuous to the wirings  42 , respectively. 
         [0025]    It should be noted that the wirings  42 , the driver ICs  41  and the electric connection portions  43  are arranged at positions which detour the opposing ink guide  30 . 
         [0026]    A plurality of alignment recess portions  20   a  are formed on a Y-axial one end side of the rear surface of the base portion  20 . 
         [0027]    Further, at the edge of the Y-axial other end side of the rear surface of the base portion  20 , an outer rib  36  is formed to stand up in the X direction. The outer rib  36  is formed to reach both the upper and lower ends of the base portion  20 , and a plurality of alignment projections  36   a  are formed on the distal end surface thereof. 
         [0028]    The first cover  14  is provided on the front surface side of the first actuator unit  12 , and is formed into an L-shape in its plan view to comprise a plate portion  51  which covers the surface of the first actuator unit  12  while interposing the liquid chambers and ink channels, and an outer rib  52  which stand up from the edge of the Y-axial other end side of the plate portion  51 . A alignment recess portion  51   a  is formed in the edge of the Y-axial one end side of the plate portion  51 . The outer rib  52  is formed to bent from the plate portion  51  in the X direction and stand towards the first actuator unit  12 . When the outer rib  52  is assembled onto the actuator unit  12 , a liquid chamber is formed. A plurality of alignment projections  52   a  are formed on the outer rib  52 . 
         [0029]    The second cover  15  is provided on the rear surface side of the second actuator unit  13 , and is formed to comprise a plate portion  61  which covers the rear surface of the second actuator unit  13  while interposing the liquid chambers and ink channels, and an ink guide  62  formed on the inner surface of the plate portion  61 . Alignment recess portion  61   a  are formed in the edge of the Y-axial other end side of the plate portion  61 . 
         [0030]    An ink guide  62  is formed comprises an L-shaped guide rib  63  which stands from the inner surface in the X direction, and a cylindrical guide pipe  64  which extends from the Y-axial central portion of the guide rib  63  downwards, which are integrated as one unit. With this structure, liquid chambers and ink channels are formed. The guide rib  63  comprises an outer rib  65  formed along with the edge of the Y-axial one end side of the second cover  15  to reach the upper end from the center, and an inner rib  66  which extends in the Y direction at the Z-axial central portion of the second cover  15 . The guide rib  63  is formed as integrated with the second cover  15  by, for example, molding when forming the base portion  20 . On the outer rib  65 , a plurality of alignment projections  65   a  are formed. 
         [0031]    The first and second actuator units  12  and  13  and the first and second covers  14  and  15  are combined together to form the base structural portion  10 . During this assembling, the alignment projections  33   a ,  52   a ,  36   a  and  65   a  are inserted to the alignment recess portions  51   a ,  20   a ,  20   b  and  61   a , respectively, as shown in  FIGS. 2 and 5 , how they engage with each other, and thus these members are aligned with each other. 
         [0032]    As shown in  FIGS. 1 ,  5  and  6 , in the base structural portion  10  in the assembled state, as the distal end surface of each of the outer ribs  33 ,  36 ,  52  and  65  and the inner ribs  34  and  66  abuts against the surface of the opposing member, 3 liquid chambers  71  to  73  which are partitioned by a pair of base portions  20  are formed in the upper half portion of the base structural portion  10 . In other words, the plate-like outer ribs  33 ,  36 ,  52  and  65  formed on both of the Y-axial ends form side portions of the liquid chambers  71  to  73 , and the plate-like inner ribs  34  and  66  which extend in the Y direction at the z-axial central portion form bottom portions of the liquid chambers  71  to  73 . 
         [0033]    Further, the guide pipes  32 ,  32  and  64  which respectively extend from the 3 inner ribs  34 ,  34  and  66  from their center portions form the ink channels communicating with the liquid chambers  71  to  73 . The guide pipe  32  formed in the first actuator unit  12  gives rise to an ink outlet  74 , and the guide pipe  32  formed in the second actuator unit  13  gives rise to an ink inlet  75 . The guide pipe  64  formed in the second cover  15  gives rise to an ink outlet  76 . 
         [0034]    The manufacturing process for the ink jet head  1  according to this embodiment will now be described. First, the base portions  20  and the covers  14  and  15  are formed, and these members are assembled together to form the base structural portion  10 . The base portions  20  and the covers  14  and  15  are each formed of a material selected from, for example, a metal, ceramics or resin, into a respective predetermined shape. For example, when the base portions  20  are made of a resin by molding, the outer ribs  33  and  36  and the inner rib  34  as well as the cylindrical guide pipe  32  are formed as an integral unit. Or, when they are formed of a metal, the cylindrical guide pipe  32  may be formed as a separate unit, and then mounted to the inner rib  34 . 
         [0035]    Next, the wirings  42  are formed on the rear surface of each of the base portions  20 , and the driver ICs  41  and the electric connection portions  43  are mounted thereon. 
         [0036]    In order to form a plurality of pressure chambers  23  in the piezoelectric actuator  21 , a piezoelectric material is fixed to the end surface of the base portion  20  by means of the adhesive layer  27 , and then the resultant is subjected to mechanical processing to form grooves in the piezoelectric material. During this process, a load is applied to the base portion  20  in its width direction, but the dimension of the base portion  20  in the width direction is relatively larger, thereby making it possible to prevent the base portion from deforming. 
         [0037]    The first and second actuator units  12  and  13  and the first and second covers  14  and  15  are combined while aligning with each other, and thus the base structural portion  10  is formed. Further, the nozzle plate  11  is attached thereto such as to cover the liquid chambers  71  to  73  opened in the base structural portion  10 . Thus, the assembling of the ink jet head  1  is completed. 
         [0038]    The operation of the ink jet head  1  will now be described. As indicated by arrows in  FIG. 6 , the ink supplied to the liquid chamber  72  from the ink inlet  75  is transferred into the pressure chamber  23 . In the pressure chamber  23 , the ink pressurized by the driver element  22  is discharged as ink drops from the nozzles  11   a . The portion of the ink which was not used as ink drops is discarded to the outside of the liquid chambers  71  and  73  from the ink outlets  74  and  76 . 
         [0039]    In order to discharge ink drops from the nozzles  11   a , a drive voltage is applied to the driver elements via the wirings  42  by the driver circuits. When an electric current flows to the first piezoelectric element  24   a  and the second piezoelectric element  24   b  of the driver element  22 , the first piezoelectric element  24   a  and the second piezoelectric element  24   b  shown in  FIG. 4  are bent in opposite directions from each other. As both of the piezoelectric elements  24   a  and  24   b  are bent, the driver element  22  is bent by deformation into an L-shape, thereby making the adjacent pressure chamber  23  smaller in volume. As the pressure chamber  23  is made smaller in volume, the pressure of the ink in the pressure chamber  23  is made higher, and thus ink drops are discharged vigorously from the nozzles  11   a.    
         [0040]    According to the ink jet head  1  of this embodiment, the following advantages are exhibited. That is, with the structure that the piezoelectric actuator  21  provided on the end surface of the base portion  20 , the base portion  20  is not easily deformed even when a load is applied thereto by the mechanical processing carried out for the formation of the pressure chambers  23 . For this reason, a plurality of pressure chambers  23  can be formed easily at a high precision. Further, the guide rib  31  which stands up on the base portion  20  are formed as an integral unit, and thus the stiffness of the base portion  20  in its thickness direction can be enhanced. 
         [0041]    A plurality of members  12 ,  13 ,  14  and  15  are combined together, and thus the liquid chambers  71  to  73  are formed between the members by means of the outer ribs  33 ,  36  and  65  and the inner ribs  34  and  66  formed to be integrated with the members  12 ,  13 ,  14  and  15 . With this design, the structures of the members are simplified, and the manufacturing process is facilitated. 
         [0042]    Moreover, the piezoelectric actuator  21  is provided on the end surface of the base portion  20 , the ink guide  30  is formed on the front surface and the wirings  42  are formed on the rear surface. With this structure, a plurality of functions can be separated, thereby making it possible to increase the flexibility in designing. For example, in the case where holes for the ink channels are made in the same surface as that of the wirings, the wirings must be set to detour the ink channels. By contrast, with the structure of the above-described embodiment, the formation of the wirings  42  is not so restricted, and therefore it is easy to finely form the pattern of the wirings  42  and adjust the lengths of the wirings  42 . Therefore, the lengths of the wirings  42  connected to the respective pressure chambers  23  can be made even, thereby making it possible to make the resistances of the wirings  42  uniform. 
         [0043]    It should be noted that the present invention, when carried out in practise, is not limited directly to the above-described embodiment, but it can be realized while remodifying the structural elements thereof within the scope where the essence of the invention remains. Further, various types of invention can be achieved by combining or rearranging various structural elements disclosed in the embodiment appropriately. For example, some of the structural elements may be deleted from the entire structure disclosed in the embodiment. Further, structural elements of various versions may be combined together as needed. 
         [0044]    While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.