Abstract:
An ink jet recording apparatus includes an ink jet head, a body frame, and a cover plate. The ink jet head has a plurality of nozzles that eject ink onto a recording medium, a plurality of pressure chambers provided in association with the nozzles, and a plurality of pressure generating portions that apply pressure to the pressure chambers so as to allow the ink to be ejected from the nozzles. The body frame communicates with an ink supply source and the ink jet head so as to supply the ink to the ink jet head. The cover plate has at least one window in a shape so as to enclose the nozzles. The cover plate is fixed to cover the ink jet head and fixed to the body frame. The ink jet recording apparatus further includes an inlet that communicates with an internal space formed between the body frame and the cover plate and an at least one outlet that communicates with the internal space. A filling material is supplied from the inlet and ejected to the at least one outlet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to an ink jet recording apparatus and a method for producing the same, and more particularly to an ink jet head unit and a method of producing the same.  
           [0003]    2. Description of Related Art  
           [0004]    An ink jet head recording apparatus performs printing by ejecting ink onto a sheet from nozzles provided in an ink jet head. The ink jet head includes a cavity plate having the nozzles, pressure chambers formed for the nozzles, and ink chambers, an actuator (a pressure generating portion) having driving elements associated with the pressure chambers, and a flexible flat cable sending an electrical signal to the actuator. The flexible flat cable, the actuator and the cavity plate are laminated one above the other.  
           [0005]    The ink jet head communicates with an ink cartridge via ink supply passages formed in a body frame, and is adhesively secured to the body frame.  
           [0006]    The ink jet head is covered with a cover plate so as to be protected against collision with recording sheets and to keep a connection between the actuator and the flexible flat cable free of foreign materials, such as ink and paper dust, to prevent an electrical short circuit from occurring. The cover plate is hermetically sealed around the ink jet head by the use of a sealer made of silicon. The cover plate has a window from which the nozzles protrude. The sealer is applied to the periphery of the window to prevent ink from spreading.  
           [0007]    For example, U.S. Pat. No. 5,874,971 discloses an ink jet head that includes a nozzle case in which an ink jet head component having a nozzle is housed. The nozzle is connected to a cover head case. A groove is provided for forming a space between the ink jet head component and the cover head case. The nozzle case is provided with an adhesive injection opening to inject an adhesive from the injection opening into the groove. The area around the ink jet head is sealed by the adhesive and fastened to the case.  
           [0008]    U.S. Pat. No. 4,994,825 discloses an ink jet head that includes an unevenly shaped groove or island at the bonding surface between the orifice plate and the head main body. The unevenly shaped groove or island buffers the stress generated due to curing shrinkage of the bonding agent or a difference in the thermal expansion coefficients between the respective constituent materials through the recessed portion constituting the space formed between the orifice plate and the head main body by the above uneven portion.  
           [0009]    U.S. Pat. No. 6,079,810 discloses an ink jet head in which spaced circular holes, formed transversely through an orifice plate, and corresponding circular openings extending rearwardly into a body through its front end surface, are positioned in such that they are aligned with one another when the orifice plate is operatively secured to the front end of the body with adhesive, so that the holes and corresponding openings are filled with the adhesive.  
           [0010]    It is desirable to increase a strength of bond in the above-described ink jet heads.  
         SUMMARY OF THE INVENTION  
         [0011]    The invention provides an improved ink jet recording apparatus that comprises an ink jet head, a body frame, and a cover plate. The ink jet head has a plurality of nozzles that eject ink onto a recording medium, a plurality of pressure chambers provided in association with the nozzles, and a plurality of pressure generating portions that apply pressure to the pressure chambers so as to allow the ink to be ejected from the nozzles. The body frame communicates with an ink supply source and the ink jet head so as to supply the ink to the ink jet head. The cover plate has at least one window in a shape so as to enclose the nozzles. The cover plate is fixed to cover the ink jet head and fixed to the body frame. The ink jet recording apparatus further comprises an inlet that communicates with an internal space formed between the body frame and the cover plate and at least one outlet that communicates with the internal space. A filling material is supplied from the inlet and ejected to at least one outlet. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be described in greater detail with reference to preferred embodiments thereof and the accompanying drawings wherein,  
         [0013]    [0013]FIG. 1 is a perspective view of a color ink jet printer and an ink jet recording apparatus according to a first and second embodiments of the invention;  
         [0014]    [0014]FIG. 2 is a perspective view of a head unit according to a first embodiment;  
         [0015]    [0015]FIG. 3 is a perspective view of the head unit disassembled into structural parts according to the first embodiment;  
         [0016]    [0016]FIG. 4 is a perspective view of the head unit disassembled into structural parts according to the first embodiment;  
         [0017]    [0017]FIG. 5 is a top view of a body frame according to the first embodiment;  
         [0018]    [0018]FIG. 6 is an exploded perspective view of a piezoelectric ink jet head according to the first embodiment;  
         [0019]    [0019]FIG. 7 is an exploded perspective view of a cavity plate according to the first embodiment;  
         [0020]    [0020]FIG. 8 is an enlarged exploded perspective view of a part of the cavity plate according to the first embodiment;  
         [0021]    [0021]FIG. 9 is a bottom view of the body frame according to the first embodiment;  
         [0022]    [0022]FIG. 10 is a sectional view taken along line X-X of FIG. 9 according to the first embodiment;  
         [0023]    [0023]FIG. 11 is a sectional view taken along line XI-XI of FIG. 5 according to the first embodiment;  
         [0024]    [0024]FIG. 12 is a sectional view taken along line XII-XII of FIG. 5 according to the first embodiment;  
         [0025]    [0025]FIG. 13 is a perspective view of a head unit according to a second embodiment of the invention according to the second embodiment;  
         [0026]    [0026]FIG. 14 is a perspective view of the head unit disassembled into structural parts according to the second embodiment;  
         [0027]    [0027]FIG. 15 is a perspective view of the head unit disassembled into structural parts according to the second embodiment;  
         [0028]    [0028]FIG. 16 is a top view of a body frame according to the second embodiment;  
         [0029]    [0029]FIG. 17 is a partially enlarged cutaway view of a bonding area on a rear side surface of the piezoelectric ink jet head according to the second embodiment;  
         [0030]    [0030]FIG. 18 is an enlarged sectional view of a bonding process among the body frame, the piezoelectric ink jet heads, and a cover plate according to the second embodiment;  
         [0031]    [0031]FIG. 19 is an enlarged sectional view of a bonding portion among the body frame, the piezoelectric ink jet heads, and the cover plate, taken along the arrowed line VII-VII of FIG. 16, according to the second embodiment;  
         [0032]    [0032]FIG. 20 is an enlarged sectional view taken along the arrowed line VIII-VIII of FIG. 16 according to the second embodiment;  
         [0033]    [0033]FIG. 21 is an enlarged sectional view taken along the arrowed line IX-IX of FIG. 16 according to the second embodiment;  
         [0034]    [0034]FIG. 22 is an exploded perspective view of the piezoelectric ink jet head according to the second embodiment;  
         [0035]    [0035]FIG. 23 is an exploded perspective view of parts of a cavity plate according to the second embodiment;  
         [0036]    [0036]FIG. 24 is a partially enlarged perspective view of the cavity plate according to the second embodiment;  
         [0037]    [0037]FIG. 25A is an enlarged sectional view of a bonding portion between the cavity plate and the nozzle plate according to the second embodiment;  
         [0038]    [0038]FIG. 25B is an enlarged sectional view of an agent-receiving portion according to the second embodiment;  
         [0039]    [0039]FIG. 26 is an enlarged sectional side view of the piezoelectric ink jet head according to the second embodiment;  
         [0040]    [0040]FIG. 27A is an enlarged sectional view of a bonding portion between the cavity plate and the nozzle plate according to a third embodiment;  
         [0041]    [0041]FIG. 27B is an enlarged sectional view of an agent-receiving portion according to the third embodiment; and  
         [0042]    [0042]FIG. 27C is an enlarged sectional view of an agent-receiving portion according to a fourth embodiment. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0043]    A first embodiment of the invention will be described in detail with reference to the accompanying drawings.  
         [0044]    As shown in FIG. 1, a color ink jet printer  100  includes an ink cartridge  61 , a head unit  63 , a carriage  64 , a driving unit  65 , a platen roller  66 , and a purging device  67 . The ink cartridge  61  includes four different color inks, for example, cyan, magenta, yellow, and black. The head unit  63  has a piezoelectric ink jet head  6  for printing on a sheet  62 . The ink cartridge  61  and the head unit  63  are loaded on the carriage  64 , which is straightly reciprocated by the driving unit  65 . The platen roller  66  is disposed in face-to-face relation with the piezoelectric ink jet head  6 .  
         [0045]    The driving unit  65  includes a carriage shaft  71 , a guide plate  72 , two pulleys  73  and  74 , and an endless belt  75 . The carriage shaft  71  is disposed at a lower end portion of the carriage  64  and extends in parallel with the platen roller  66 . The guide plate  72  is disposed at an upper end portion of the carriage  64  and extends in parallel with the carriage shaft  71 . The endless belt  75  is looped between the pulleys  73  and  74 , which are disposed at both ends of the carriage shaft  71  between the carriage shaft  71  and the guide plate  72 .  
         [0046]    When a motor drives and one pulley  73  is rotated in a normal or opposite direction, the carriage  64  connected to the endless belt  75  is straightly reciprocated along the carriage shaft  71  and the guide plate  72 .  
         [0047]    The sheet  62  is supplied into the color ink jet printer  100  from a paper cassette (not shown) provided at a side of the ink jet printer  100 , and fed between the piezoelectric ink jet head  6  and the platen roller  66 , where printing is performed on the sheet  62  by the ink ejected from the piezoelectric ink jet head  6 , and then ejected from the printer  100 . In FIG. 1, a sheet feed mechanism and sheet eject mechanism are not shown.  
         [0048]    The purging device  67  is provided on a side of the platen roller  66  and disposed so as to face the piezoelectric ink jet head  6  when the head unit  63  is in a reset position. The purging device  67  includes a purge cap  81  that is in contact with nozzle surface so as to cover nozzles of the piezoelectric ink jet head  6 , a pump  82 , a cam  83 , and an ink restoring portion  84 . When the head unit  63  is in the reset position, the nozzles of the piezoelectric ink jet head  6  are covered with the purge cap  81 , deteriorated ink containing air bubbles accumulated inside the piezoelectric ink jet head  6  is sucked in by the pump  82 , which is driven by the cam  83 . By doing so, the piezoelectric ink jet head  6  is recovered. The sucked deteriorated ink is stored in the ink reservoir portion  84 .  
         [0049]    The cap  85  is used to cover the nozzles  22  of the piezoelectric ink jet head  6  mounted on the carriage  64  which returns to the reset position after printing is finished, so as to prevent the ink from being dried.  
         [0050]    [0050]FIGS. 2, 3, and  4  are perspective views of the head unit  63 . FIG. 5 is a top view of a body frame  1  of the head unit  63 . FIG. 9 is a bottom view of the body frame  1  of the head unit  63 . FIGS.  2  to  5 , and  9  show the head unit  63  when the ink cartridge  61  is not attached. FIGS. 3 and 4 show the head unit  63  in an exploded view for easy understanding.  
         [0051]    The body frame  1  mounted on the carriage  64  (FIG. 1) is an injection molded article and made of a synthetic resin such as polyethylene and polypropylene. The body frame  1  has a substantially box shape and an upper open structure (FIG. 4). The upper open structure is provided with an installation portion  3  to detachably attach the ink cartridge  61 . Ink supply passages  4   a,    4   b,    4   c,  and  4   d,  which are connected to an ink discharging portion (not shown) of the ink cartridge  61  to be installed in the installation portion  3 , are drilled through a side  3   a  of the installation portion  3 . Each of the ink supply passages  4   a,    4   b,    4   c,  and  4   d  extends through to an undersurface of the body frame  1  where a bottom plate  5  (FIG. 3) is formed. Rubber packings (not shown) are disposed around each of the ink supply passages  4   a,    4   b,    4   c,  and  4   d  so as to fit with the ink discharging portion of the ink cartridge  61 .  
         [0052]    The bottom plate  5  is used to position the ink jet heads  6  and is formed horizontally so as to protrude from the body frame  1  (refer to FIG. 3). The bottom plate  5  has two supporting portions  8 , where two piezoelectric ink jet heads  6  are arranged in parallel. The supporting portions  8  have holes  9   a,    9   b,  where a UV adhesive  7  (FIG. 12) is supplied to secure the piezoelectric ink jet heads  6 . The holes  9   a,    9   b  continuing to the installation portion  3  are located so that one piezoelectric ink jet head  6  can be secured at four corners. In this embodiment, the holes  9   a  are widely formed in such a manner that each of the holes  9   a  spreads astride the two piezoelectric ink jet heads  6  arranged in parallel.  
         [0053]    Connecting portions  10   a  to  10   d  that communicate with the ink cartridge  61  via the ink supply passages  4   a  to  4   d  are provided on one end of each of the supporting portions  8 . Engagement grooves  11  formed in the shape of the numeral “8”, in a plan view, are recessed around the connecting portions  10   a  to  10   d  (FIG. 9). Rubber ring-shape packings  47  are inserted into the engagement grooves  11 . When the piezoelectric ink jet heads  6  are adhesively fixed to the body frame  1 , the packings  47  are pressed so as to enclose ink supply ports  21  (FIG. 6) of the piezoelectric ink jet heads  6  at ends thereof, so that connections between the packings  47  and the ink supply ports  21  are hermetically sealed.  
         [0054]    [0054]FIG. 6 is an exploded perspective view of one piezoelectric ink jet head  6 . The piezoelectric ink jet head  6  includes a multi-layered cavity plate  20 , a plate-type piezoelectric actuator  30 , and a flexible flat cable  40 . The piezoelectric actuator  30  is adhered to the cavity plate  20  via an adhesive or an adhesive sheet (not shown), and the flexible flat cable  40  is bonded to the top of the piezoelectric actuator  30  for electrical connection with external equipment. Via the ink supply ports  21  provided at an upper surface of the cavity plate  20  (in FIG. 6), ink supplied from the ink cartridge  61  is downwardly discharged from the nozzles  22 , opened toward a lower surface of the cavity plate  20 .  
         [0055]    [0055]FIG. 7 is an exploded perspective view of the cavity plate  20 . FIG. 8 is an exploded enlarged perspective view of the cavity plate  20 . FIG. 8 shows the cavity plate  20  in a cross section cut in a direction orthogonal to a longitudinal direction of the cavity plate  20 . As shown in FIG. 7, the cavity plate  20  includes five thin metal plates of substantially rectangular shape: a nozzle plate  23 , two manifold plates  24 ,  25 , a spacer plate  26 , and a base plate  27 , which are adhesively bonded to each other. In this embodiment, each plate  23  to  27  is made of steel alloyed with 42% nickel and has a thickness of 50 μm-150 μm. Each plate  23  to  27  is not limited to metal and may be made of other material such as resin.  
         [0056]    As shown in FIG. 8, the base plate  27  is drilled to define two rows of staggered narrow pressure chambers  28  each of which extends in a direction orthogonal to a longitudinal direction of the base plate  27 . Aperture portions  28   d  that are connected to the pressure chambers  28  and ink supply holes  28   b  that are connected to the aperture portions  28   d  are recessed in the base plate  27  at a side facing the spacer plate  26 . The ink supply holes  28   b  communicate with the ink chambers  33  in the manifold plate  25  via corresponding ink supply holes  29  opened at opposite sides of the spacer plate  26 . Narrow end portions  28   a  of the pressure chambers  28  communicate with nozzles  22  staggered in the nozzle plate  23  via through holes  32  having an extremely small diameter similarly staggered in the spacer plate  26  and the two manifold plates  24 ,  25 .  
         [0057]    As shown in FIG. 7, the base plate  27  and the spacer plate  26  have two ink supply ports  21 ,  21   a  respectively that supply ink from the ink cartridge  61  to the two ink chambers  31 ,  33  in the manifold plates  24 ,  25 . The manifold plates  24 ,  25  are formed with ink chambers  31 ,  33  extending in parallel astride the rows of the nozzles  22  in the nozzle plate  23 . End portions of the ink chambers  31 ,  33  are bent inward so as to communicate with the ink supply ports  21 ,  21   a.  The ink chambers  33  are opened in the manifold plate  25 , and hermetically sealed as the spacer plate  26  is laminated onto the manifold plate  25 . The ink chambers  31  are recessed in the manifold plate  24 .  
         [0058]    The nozzle plate  23  is formed with the nozzles  22  having an extremely small diameter (approximately 25 μm in this embodiment), from which ink is ejected. The nozzles  22  are disposed in a staggered arrangement along the longitudinal direction of the nozzle plate  23 .  
         [0059]    The piezoelectric actuator  30  is structured wherein electrodes associated with the pressure chambers  28  are formed on a piezoelectric sheet, as in the case disclosed in Japanese Laid-Open Patent Publication No. 4-341851. The piezoelectric actuator  30  selectively drives pressure generating portions corresponding to each of the pressure chambers  28  to cause ink to be ejected from the nozzles  22 .  
         [0060]    A cover plate  44 , which is an elastic thin metal plate, is fixed on the face side of the piezoelectric ink jet heads  6  so as to cover the piezoelectric ink jet heads  6  (FIG. 2). The cover plate  44  is of a substantially box shape defined by a bottom wall  44   b  and side walls  44   c  standing around the bottom wall  44   b.  The bottom wall  44   b  is formed with windows  44   a  where the nozzle plates  23  are accommodated in such a manner to face the nozzles  22  outward. A flange  44   d,  protruding externally, is formed around edges of the side walls  44   c  of the cover plate  44  (FIG. 3).  
         [0061]    The body frame  1  has channels  50 ,  51  where the side walls  44   c  and the flange  44   d  of the cover plate  44  are inserted (FIG. 9). Ribs  52  are formed on the body frame  1  with a distance from both ends of the bottom plate  5 . The channels  50  are defined between ribs  52  and the bottom plate  5 , and the channel  51  is formed on a side of the bottom plate  5  and connected to the channels  50 . The channels  50 ,  51  are arranged in a substantially U shape along the three sides of the bottom plate  5 . End portions of the channels  50  along the ribs  52  are connected to the side portion  5   a  of the bottom plate  5 .  
         [0062]    Filler inlets  12 , from which a filler  46  of silicon resin is supplied, are formed at a bottom of the channel  51  associated with end portions of the supporting portions  8 . The filler inlets  12  are located between a pair of the connecting portions  10   a,    10   b  and between a pair of the connecting portions  10   c,    10   d.  Each of the filler inlets  12  is open through the body frame  1  toward the installation portion  3  where the ink cartridge  61  is mounted, which is the opposite side where the cover plate  44  is overlaid. The side portion  5   a  of the bottom plate  5  has vents  13   a  (FIGS. 3 and 10). Each of the vents  13   a  is open through the body frame  1  toward the installation portion  3 . The engagement grooves  11  are closed at places associated with the filler inlets  12  by walls  11   a,  and have openings  11   b  which contact with the channels  51  at places associated with the pair of the connecting portions  10   a,    10   b,  and the pair of the connecting portions  10   c,  and  10   d.    
         [0063]    Channels  53  extending in parallel with the channels  50  are formed in the center of each of the supporting portions  8 . The channels  53  communicate with the engagement grooves  11  between connecting portions  10   a,    10   b  and between the connecting portions  10   c,    10   d  at one end, and connect to the side portion  5   a  of the bottom plate  5  at the other end. Each of the supporting portions  8  is formed with a plurality of vents  13   b  which pass through the body frame  1  to the installation portion  3 .  
         [0064]    A lid plate  54  (FIG. 2) is secured to a surface of the body frame  1  continuing to the side portion  5   a  of the bottom plate  5  so as to cover the flexible flat cable  40  extending along the surface. The flexible flat cable  40  has a chip  55  (FIG. 10) to drive the piezoelectric actuator  30 , and is pressed by an elastic member  56  of rubber or sponge, so that the chip  55  is in contact with the lid plate  54 . By doing so, the chip  55  discharges a heat, incident to driving, to the lid plate  54  functioning as a heat sink.  
         [0065]    A method of producing the head unit  63  will be described. FIG. 10 is a sectional view taken along line X-X of FIG. 9. FIGS. 11 and 12 are sectional views taken along line XI-XI and line XII-XII of FIG. 5, respectively. FIG. 10 shows a state that the filler  46  is to be supplied into an internal space  15  where the piezoelectric ink jet head  6  is accommodated. FIGS. 11 and 12 show a state that the filler  46  has been supplied.  
         [0066]    To produce the head unit  63 , the two piezoelectric ink jet heads  6  are placed in position and secured to the cover plate  44 . In detail, as shown in FIG. 4, the cover plate  44  is placed facedown on a jig (not shown). The piezoelectric ink jet heads  6  are overlaid on the cover plate  44 , so that the nozzle plates  23  of the two piezoelectric ink jet heads  6  are aligned with the windows  44   a  of the cover plate  44 , and the rows of the nozzles  22  are arranged in parallel with each other at established intervals. The piezoelectric ink jet heads  6  and the cover plate  44  are connected by the use of a sealer  45  doubling as an adhesive therebetween.  
         [0067]    The body frame  1  is placed on the piezoelectric ink jet heads  6  from above. The piezoelectric ink jet heads  6  are set in agreement with the supporting portions  8 . The UV adhesive  7 , which is a fast setting and viscous denatured acrylic resin-base adhesive, is applied at the holes  9   a  and  9   b  in a direction of X of FIG. 12 from the topside of the body frame  1 . An ultraviolet light is radiated to the holes  9   a,    9   b  from the topside of the body frame  1 . The UV adhesive  7  sets in a short time (within several tens of seconds).  
         [0068]    When the piezoelectric ink jet heads  6  are set on the supporting portions  8 , the ink supply ports  21  in the piezoelectric ink jet heads  6  are arranged in agreement with the connecting portions  10   a  to  10   d  via the packings  47 . At this time, crevices  14  are formed among the supporting portions  8 , the flexible flat cable  40 , the piezoelectric actuator  30 , and further the cavity plate  20 . However, because the UV adhesive  7  gets in such crevices  14  and solidifies instantly, the piezoelectric ink jet heads  6  can be secured to the main body  1  without excess external forces exerted on the piezoelectric ink jet heads  6  by the main body  1 . The cover plate  44  does not have a rigidity as much as it can immovably hold the two piezoelectric ink jet heads  6 . Therefore, as the cavity plates  20  of the piezoelectric ink jet heads  6  are maintained in parallel with the jig, the rows of nozzles  22  in the cavity plates  20  are precisely in place.  
         [0069]    The holes  9   a,    9   b  are arranged in such a manner to face the four corners of each of the piezoelectric ink jet heads  6  substantially rectangular in a plan view. This can minimize the misalignment of the piezoelectric ink jet heads  6 , which results from curing shrinkage of the UV adhesive  7 . Each of the piezoelectric ink jet heads  6  is fixed at the four corners thereof. By doing so, there is an advantage that the nozzle plates  23  do not become deformed when they are pressed in tight contact with the rubber cap  85  (FIG. 1) to prevent the nozzles  22  from drying while the printer  100  is not used.  
         [0070]    Further, as shown in FIG. 12, the holes  9   a  are widely formed in such a manner that each of the holes  9   a  spreads astride the two piezoelectric ink jet heads  6  arranged in parallel. Thus, the two piezoelectric ink jet heads  6  can be fixed at one hole  9   a  by supplying the UV adhesive  7  to the hole  9   a  and radiating the ultraviolet light to cure the UV adhesive  7 . This greatly contributes to reduced operating speed and improved manufacturing efficiencies. The piezoelectric ink jet heads  6  are secured to the cover plate  44  by the use of the adhesive, and then secured to the body frame  1 . However, the piezoelectric ink jet heads  6  can be first secured to the body frame  1  and then the cover plate  44  can be secured to the piezoelectric ink jet heads  6 .  
         [0071]    The body frame  1 , the piezoelectric ink jet heads  6 , and the cover plate  44 , which are bonded to each other, are placed in such a manner that the nozzles  22  can face upward as shown in FIG. 2, and the periphery of the cover plate  44  is sealed. When the piezoelectric ink jet heads  6  are attached to the body frame  1 , the side walls  44   c  and the flange  44   d  on the three sides of the cover plate  44  are inserted into the channels  50 ,  51  of the bottom plate  5 . The sealer  45  is applied to the flange  44   d  to be supplied between the side walls  44   c  and the channels  50 ,  51 , as shown in FIGS.  10  to  12 .  
         [0072]    The lid plate  54  is secured to the surface of the body frame  1  so as to cover the flexible flat cable  40 . A juncture between the lid plate  54  and the body frame  1  is similarly sealed with the sealer  45 . A juncture between a remaining side of the cover plate  44  and the lid plate  54  is also sealed with the sealer  45 .  
         [0073]    After the juncture between the body frame  1  and the cover plate  44  is sealed, an operation is shifted to a filling process. The filler  46  is supplied into the internal space  15  formed between the body frame  1  and the cover plate  44 . As shown in FIG. 10, the filler  46  is inserted into the filler inlet  12  from the installation portion  3  side (in a direction of Y). The filler  46  inserted into the filler inlet  12  flows inside the internal space  15  while releasing air remaining inside to the vents  13   a,    13   b.  The filler  46  flows in passages from the channel  51  to the channels  50  and in passages from the channel  51  to the channels  53 . In the former passages from the channel  51  to the channels  50 , the filler  46  is charged between sides of the bottom plate  5  and the inner surfaces of the side walls  44   c  of the cover plate  44  associated with the channels  51 ,  50 . In the latter passages from the channel  51  to the channels  53 , the filler  46  is charged in the engagement grooves  11 , so that the ink supply ports  21  in the cavity plates  20  and connecting portions  10   a  to  10   d  are sealed along with the packings  47 . The filler  46  then flows in the channels  53  along the upper surfaces of the piezoelectric ink jet heads  6 .  
         [0074]    The filler  46  flowing along the channels  50 ,  53  moves sideways into narrow gaps between the piezoelectric ink jet heads  6  and the supporting portions  8 . Further, the filler  46  is charged between the side portion  5   a  of the bottom plate  5  and the inner surface of the side wall  44   c  of the cover plate  44  from ends of the channels  50 ,  53 . By doing so, the surrounding area of the piezoelectric ink jet heads  6  is sealed with the filler  46 . As a result, ink does not enter the internal space  15  and erode the UV adhesive  7 , so that a short circuit at an electrical connecting point between the piezoelectric actuator  30  and the flexible flat cable  40  can be prevented.  
         [0075]    As described above, while the filler  46  flows, the air remaining inside the internal space  15  is released from the vents  13   a  located farthest from the filler inlets  12 , and the vents  13   b  located corresponding to the narrow gaps between the piezoelectric ink jet heads  6  and the supporting portions  8  away from the channels  50 ,  53 . When the filler  46  is charged, it is ejected from the vents  13   b  near the filler inlets  12  one after another. As a result, it can be seen how far in the internal space  15  the filler  46  is charged. When the filler  46  is ejected from the vents  13   a  located at the ends of the internal space  15 , which is the farthest from the filler inlets  12 , it can be seen that charging of the filler  46  is completed. Therefore, if there are variations of sizes of elemental parts, such as the body frame  1  and the piezoelectric ink jet heads  6 , variations of charging conditions such as a temperature when the filler  46  is charged, or variations of charging characteristics of a charging device, the charging status can be seen from the filler  46  ejected from the vents  13   a,    13   b.  In this way it is easy to detect poor charging of the filler  46 .  
         [0076]    The vents  13   a,    13   b  have different internal diameters. In the embodiment, the farther the vent is located from the filler inlets  12 , the greater the internal diameter of the vent. That is, of the vents  13   b,  a vent  13   b  located nearest to the filler inlets  12  has the smallest internal diameter. A vent  13  a located the farthest from the filler inlets  12  has the greatest internal diameter. The filler  46  continues to be discharged from the vents  13   b  scattered on the way to the ends of the internal space  15  which are located the farthest from the filler inlets  12 . To save the filler  46 , the internal diameter of the vents from which the filler  46  is discharged for a long time (nearer the filler inlets  12 ) is set smaller. Thus, the amount of the discharged filler  46  can be saved, and as a result, total quantity consumed of the filler  46  can be reduced.  
         [0077]    The internal diameter of each of the vents  13   a,    13   b  is set according to the distance from the filler inlets  12 . However, it is preferred to change the internal diameter according to the shape of the internal space  15 . When the shape of the internal space  15  is complicated, the filler  46  is reluctant to flow to a blind spot viewed from the filler inlets  12  even if it is near the filler inlets  12 , so that air is easily trapped in such a place. Such air can be released by providing a vent having a small internal diameter in such a place.  
         [0078]    The filler inlets  12  and the vents  13   a,    13   b  may be provided on the cover plate  44 , however, they are preferably provided on the body frame  1  rather than the cover plate  44  because product appearance may be impaired or the adhered filler  46  should be removed.  
         [0079]    As shown in FIGS. 3 and 9, the connecting portions  10   a  to  10   d  in the body frame  1  and corresponding ink supply ports  21  of the piezoelectric ink jet heads  6  are sealed with the packings  47  inserted into the engagement grooves  11  recessed around the connecting portions  10   a  to  10   d.  However, it is preferred that the engagement grooves  11  are previously filled with the filler  46  as soon as the packings  47  are inserted thereinto. By doing so, while the piezoelectric ink jet heads  6  and the body frame  1  are adhesively fixed to each other, the ends of the packings  47  are pressed so as to enclose the ink supply ports  21  of the piezoelectric ink jet heads  6 , at the same time, the sealer  45  makes contact with the piezoelectric ink jet heads  6 , so that the ink supply ports  21  and the packings  47  are hermetically sealed. The filler  46  supplied in the charging process is further overlaid on a portion hermetically sealed, thereby improving the reliability of the sealed fit.  
         [0080]    According to the first embodiment, the vents  13   a,    13   b  are drilled into the body frame  1 . At least one vent may be provided at an end of the internal space  15  which is substantially the farthest from the filler inlets  12 . Alternatively, a number of vents may be drilled at the end of the internal space  15 . The vents have different internal diameters in the embodiment, however, the vents may have the same internal diameter.  
         [0081]    According to the first embodiment, two piezoelectric ink jet heads  6  are provided in parallel with each other. However, in the example, the number of piezoelectric ink jet heads  6  is arbitrary. One to four piezoelectric ink jet heads may be provided.  
         [0082]    A second embodiment of the invention will be described. FIGS. 13, 14, and  15  are perspective views of piezoelectric ink jet heads according to the second embodiment of the invention. FIG. 17 is a rear side surface of one piezoelectric ink jet head. FIG. 19 is a sectional view showing that a bottom plate, the piezoelectric ink jet heads and a cover plate are adhered. FIG. 23 is a perspective view of elemental parts of a cavity plate. FIG. 25A is an enlarged sectional view showing a nozzle plate adhered to the cavity plate. FIG. 25B is an enlarged sectional view of a recess.  
         [0083]    As shown in FIGS.  13  to  19 , a head unit of the second embodiment includes a body frame  101 , two piezoelectric ink jet heads  106 , and a cover plate  144 . The body frame  101  is an injection molded article and made of a synthetic resin such as polyethylene and polypropylene. The two piezoelectric ink jet heads  106  are arranged in parallel on a lower surface of a bottom plate  105  of the body frame  101 . The cover plate  144  is fixed over the piezoelectric ink jet heads  106  and the body frame  101 . The cover plate  144  has two windows  144   a  from which nozzles  122  on the piezoelectric ink jet heads  106  are exposed.  
         [0084]    The body frame  101  has a substantially box shape and an upper open structure (FIG. 15). The upper open structure is provided with an installation portion  103  to detachably attach an ink cartridge  102  (FIG. 21) having four inks as ink supply sources. Ink supply passages  104   a,    104   b,    104   c,  and  104   d,  which are connected to an ink discharging portion (not shown) of the ink cartridge  102  to be installed in the installation portion  103 , are drilled in a stepped portion  103   a  of the installation portion  103 . Each of the ink supply passages  104   a,    104   b,    104   c,  and  104   d  is in communication with an undersurface of the bottom plate  105  of the body frame  101 .  
         [0085]    The bottom plate  105  is formed horizontally so as to protrude from the installation portion  103 . The bottom plate  105  has two stepped supporting portions  108 , where two piezoelectric ink jet heads  106  are arranged in parallel. Connecting portions  110  associated with the ink supply passages  104   a  to  104   d  are provided on one end of the supporting portions  108 , as shown in FIGS. 16 and 21. Engagement grooves  111  substantially ring-shaped in a plan view are recessed around the connecting portions  110 . Ring-shape packings  147  of soft rubber, which have a good sealing fit, are inserted into the engagement grooves  111 . (Refer to FIGS. 14 and 21.)  
         [0086]    The supporting portions  108  in the bottom plate  105  have through holes  109   a,    109   b,  where a fast-setting UV adhesive  107 , as a first adhesive, is supplied so as to fix the piezoelectric ink jet heads  106 . The piezoelectric ink jet heads  106  and the cover plate  144  that covers the piezoelectric ink jet heads  106 , except for nozzle plates  123  at the front side surfaces of the piezoelectric ink jet heads  106 , are fixed to each other via the UV adhesive  107  supplied from the through holes  109   a,    109   b.    
         [0087]    When the piezoelectric ink jet heads  106  are fixed to the stepped supporting portions  108 , a gap between the supporting portions  108  and flexible flat cables  140  on the back of each of the piezoelectric ink jet heads  106  is formed.  
         [0088]    As shown in FIGS. 14, 18, and  19 , the through holes  109   a,    109   b  are drilled in such a manner to face the four corners of each of the piezoelectric ink jet heads  106 . The through holes  109   a  are widely formed between the two supporting portions  108  so as to spread across the two piezoelectric ink jet heads  106  arranged in parallel.  
         [0089]    Rubber packings (not shown) are disposed around each of the ink supply passages  104   a  to  104   d  on the stepped portion  103   a  of the installation portion  103  so as to fit with the ink discharging portion.  
         [0090]    The structure of the front side surface of the piezoelectric ink jet head  106  will be described. As shown in FIGS. 14, 17,  23 ,  24 , and  25 A, a nozzle plate  123  is adhesively fixed to the middle of the front side surface (lower surface) of the cavity plate  120  by the use of an adhesive  155  (FIG. 25A). The nozzle plate  123  is a thin plate made of synthetic resin, which has two rows of staggered nozzles  122 . There are  75  nozzles  122  in one row. (Refer to FIGS. 23 and 24.) Ink is ejected from the nozzles  122  (FIG. 26). A known water-repellent film is formed on the front side surface of the nozzle plate  123 .  
         [0091]    The cover plate  144  that protects the front side surface of each of the piezoelectric ink jet heads  106  is a thin metal plate, in which the two windows  144   a  are drilled by stamping work. The two windows  144   a  are arranged with a clearance (FIGS. 14, 15) to enclose the nozzle plates  123  of the piezoelectric ink jet heads  106 . The cover plate  144  is fixed to the front side surface (lower surface) of each of the piezoelectric ink jet heads  106 , by the use of a second adhesive  156  (FIGS. 18 and 19) made of silicone having ink repellency, which is applied to the periphery of each of the two windows  144   a.  It is desirable that the cover plate  144  is slightly thicker than the nozzle plate  123 .  
         [0092]    The front side surface (a manifold plate  124 ) of the piezoelectric ink jet head  106  has two recessed blocking grooves  60  on both sides. The blocking grooves  60  are located outwardly from the peripheral edges of the windows  144   a  of the cover plate  144  and inwardly from the through holes  109   a,    109   b,  in order to prevent the second adhesive  156  from mixing with the UV adhesive  107 . That is, as shown in FIG. 17, the blocking grooves  60  are disposed outside an area  123   a  where the nozzle plate  123  is adhered. The blocking grooves  60  are formed along the rows of the nozzles  122  and through holes  132  in the manifold plate  124 .  
         [0093]    As shown in FIGS. 17 and 25A, there are many agent-receiving portions  58 ,  59  recessed in the area  123   a  in a plan view and scattered in the area  123   a  on the manifold plate  124 . The agent-receiving portions  58  are located in a first area near the rows of the nozzles  122 . The diameter of each of the agent-receiving portions  58  is approximately 0.15 mm in this embodiment, and set slightly greater than that of the nozzles  122  (approximately 0.025 mm). The agent-receiving portions  58  are densely arranged with a pitch of approximately 0.25 mm. The nozzles  122  are arranged with a pitch of approximately 0.34 mm.  
         [0094]    The agent-receiving portions  59  are located in a second area outside the first area. The diameter of each of the agent-receiving portions  59  is approximately 0.2 mm in this embodiment, and set slightly greater than that of the agent-receiving portions  58 . The agent-receiving portions  59  are non-densely arranged with a pitch of approximately 0.5 mm.  
         [0095]    When the adhesive  155  is applied to the area  123   a  including the first area and the second area (FIG. 25A), and is spread by a force exerted when the nozzle plate  123  is adhered to the manifold plate  124 , the agent-receiving portions  58 ,  59  receive a surplus of the adhesive  155  (FIG. 25B).  
         [0096]    In addition, the adhesive  155  moistens peripheral walls of the agent-receiving portions  58 ,  59  and then solidifies. Therefore, a total space where the adhesive  155  is applied becomes larger than that of a planer face of the area  123   a,  and a strength of bond between the nozzle plate  123  and the manifold plate  124  is also increased because the adhesive  155  solidifies on the peripheral walls of the agent-receiving portions  58 ,  59  and the planar face of the area  123   a  where they intersect each other.  
         [0097]    Because the first area where the agent-receiving portions  58  are densely arranged is set near the nozzles  122 , it is sufficiently sealed by the adhesive  155 . In addition, ink ejected from the nozzles  122  can be prevented from entering the inside of the cavity plate  120  from the clearance between the nozzle plate  123  and the manifold plate  124 .  
         [0098]    In the embodiment the agent-receiving portions  58 ,  59  are formed on the manifold plate  124 , however, they may be formed on another plate to be adhered to the manifold plate  124 .  
         [0099]    Positioning holes  61   a,    62   a  are drilled at a front and rear of the through holes  132  in the area  123   a.  When the nozzle plate  123  is adhered to the front side surface of the manifold plate  124  and the piezoelectric ink jet heads  106  are adhered to the bottom of the body frame  101  in parallel, the positioning holes  61   a,    62   a  are used. The positioning holes  61   a,    62   a  are located so as to align with the positioning holes  61 ,  62  in the nozzle plate  123  shown in FIG. 23.  
         [0100]    A method of fixing the piezoelectric ink jet head  106  and the cover plate  144  to the body frame  101  will be described. The cover plate  144  having the two windows  144   a  is placed on a positioning jig  163  (shown by a dot dash line in FIG. 19). The second adhesive  156  is applied to the outer regions around the windows  144   a  from the reverse side surface of the cover plate  144  (FIG. 18).  
         [0101]    The positioning holes  61 ,  62  in the nozzle plates  123  are fit into the positioning pins  164  of the jig  163  (only one shown in FIG. 19). The two nozzle plates  123  are placed so as to expose from the windows  144   a,  and the rows of the nozzles  122  are spaced on the piezoelectric ink jet heads  106  evenly and in parallel with each other. The front side surfaces of the piezoelectric ink jet heads  106  and the reverse side surface of the cover plate  144  are fixedly adhered to each other by the use of the second adhesive  156 . The body frame  101  is overlaid thereon, and the piezoelectric ink jet heads  106  are positioned in alignment with the supporting portions  108 . The UV adhesive  107  is supplied from the through holes  109   a,    109   b,  and solidified by the ultraviolet radiation to fix the piezoelectric ink jet heads  106 .  
         [0102]    By doing so, as shown in FIG. 19, the second adhesive  156  is spread into a thin layer between the front side surface of the manifold plate  124  and the reverse side surface of the cover plate  144  by a pressing force. However, as the second adhesive  156  is blocked at the blocking grooves  60 , it is resistant to leaks outwardly therefrom. On the other hand, the UV adhesive  107  tends to flow along the edges of each piezoelectric ink jet head  106  from its reverse side surface, pass through the gaps formed between the piezoelectric ink jet head  106  and the reverse side surface of the cover plate  144 , and flow into the windows  144   a.  However, the UV adhesive  107  is also resistant to leaks because of its instantaneous solidification. If the UV adhesive  107  flows into the windows  144   a,  the blocking grooves  60  can prevent the UV adhesive  107  and the second adhesive  156  from mixing.  
         [0103]    When different kinds of adhesives are mixed, solidification is difficult, so that a part where it is not solidified occurs. As a result, an electrical short circuit may occur due to leakage of ink. Such a short circuit can be prevented from occurring by the methods and systems as described.  
         [0104]    The through holes  109   a,    109   b  are arranged so as to face the four corners of each of the piezoelectric ink jet heads  106 . Thereby, the piezoelectric ink jet heads  106  can be prevented from becoming misaligned due to curing shrinkage of the UV adhesive  107 . As shown in FIGS. 16 and 17, the through holes  109   a  are widely formed in such a manner that each of the holes  109   a  spreads astride the two piezoelectric ink jet heads  106  arranged in parallel. Thus, the two piezoelectric ink jet heads  106  can be fixed at one hole  109   a  by supplying the UV adhesive  107  to the hole  109   a  and radiating the ultraviolet light to solidify the UV adhesive  107 . This greatly contributes to reduced operating speed and improved manufacturing efficiencies.  
         [0105]    Further, an advantage is gained because the nozzle plates  123  do not become deformed when they are pressed in tight contact with a rubber cap that prevents the nozzles  122  from being dried while the printer is not used.  
         [0106]    As shown in FIGS. 20 and 21, a sealer  145  is applied between the periphery of the cover plate  144  and the body frame  101 . Before the body frame  101  is overlaid on the piezoelectric ink jet heads  106 , the sealer  145  should be applied between the flexible flat cable  140  and the body frame  101 , between the flexible flat cable  140  and the cover plate  144 , and between a bending portion  144   b  of the cover plate  144  and the body frame  101 . By doing so, piezoelectric actuators  130  and electrical connecting portions in the piezoelectric ink jet heads  106  can be completely sealed, thereby preventing foreign matter such as ink and dust from intruding from outside.  
         [0107]    The piezoelectric ink jet heads  106  and the parts that makeup the heads  106  will be described. As shown in FIGS.  22  to  24 , each piezoelectric ink jet head  106  includes a multi-layered cavity plate  120 , a plate-type piezoelectric actuator  130 , and a flexible flat cable  140 . The piezoelectric actuator  130  is adhered to the cavity plate  120  via an adhesive sheet  41  (FIG. 26), and the flexible flat cable  140  is bonded to the top of the piezoelectric actuator  130  for electrical connection with external equipment.  
         [0108]    A filter  29  (FIGS. 22, 23) for eliminating dust in the ink supplied from the ink cartridge  102  is adhesively fixed over ink supply ports  19   a  drilled on one side of the base plate  127 , which is on the reverse side surface of the piezoelectric ink jet head  106 . When the cavity plate  120  is attached to the body frame  101 , the ink supply ports  19   a  make contact with the packings  147  and communicate with the ink supply passage  104   a.    
         [0109]    As shown in FIGS. 23 and 24, the cavity plate  120  includes five thin metal plates: a nozzle plate  123 , two manifold plates  124 ,  125 , a spacer plate  126 , and a base plate  127 , which are adhesively bonded to each other. In this embodiment, each plate is made of steel alloyed with 42% nickel and has a thickness of 50 μm-150 μm. Each plate is not limited to be constructed of metal and may be made of other material such as resin or ceramics.  
         [0110]    The manifold plate  124  is adhered to the nozzle plate  123 . The through holes  132  communicating with the nozzles  122  are longitudinally staggered in two rows, with a fixed pitch, on the manifold plates  124 ,  125  and the spacer plate  126 . The manifold plates  124 ,  125  are formed with ink chambers  131 ,  133  extending along the rows of the through holes  132 . The ink chambers  131  are recessed in the manifold plate  124  (FIG. 24). The ink chambers  131 ,  133  in the manifold plates  124 ,  125  are hermetically sealed as the spacer plate  126  is laminated onto the manifold plate  125 .  
         [0111]    The base plate  127  has two rows of staggered narrow pressure chambers  128  each of which extends in a direction orthogonal to a centerline along a longitudinal direction of the base plate  127 . Reference lines  127   a,    127   b,  which are parallel to each other, are set at both sides of the centerline. Narrow end portions  128   a  of the pressure chambers  128  on the left of the centerline are disposed on the reference line  127   a,  and the narrow end portions  128   a  of the pressure chambers  128  on the right of the centerline are disposed on the reference line  127   b.  The narrow end portions  128   a  of the pressure chambers on the right and left sides of the centerline are alternately positioned. That is, alternate pressure chambers  128  extend from the narrow end portions  128   a  in direction opposite to each other.  
         [0112]    The narrow end portions  128   a  of the pressure chambers  128  communicate with the staggered through holes  132  drilled in the spacer plate  126  and the manifold plates  124 ,  125 . Other end portions  128   b  of the pressure chambers  128  communicate with the ink passages  131 ,  133  in the manifold plates  124 ,  125  via ink supply holes  129  drilled on opposite sides of the spacer plate  126 . As shown in FIGS. 24 and 26, the other end portions  128   b  of the pressure chambers  128  are recessed on the lower surface of the base plate  127 .  
         [0113]    By doing so, ink flows in the ink passages  131 ,  133  from ink supply ports  19   a,    19   b  drilled at an end portion of the base plate  127  and the spacer plate  126 , passes from the ink passage  133  to the ink supply holes  129 , and is distributed into each of the pressure chambers  128 . The ink passes from the pressure chambers  128  to the nozzles  122  via the through holes  132 . (Refer to FIG. 26.)  
         [0114]    As shown in FIG. 26, the piezoelectric actuator  130  is structured wherein a plurality of piezoelectric sheets  136  are laminated one above the other. As in the case disclosed in Japanese Laid-Open Patent Publication No. 4-341851, narrow electrodes (not shown) are formed with respect each of the pressure chambers  128  on upper surfaces of the lowest piezoelectric sheet  136  and the odd piezoelectric sheets  136  counted upward from the lowest one. On upper surfaces of the even piezoelectric sheets  136  counted from the lowest one, common electrodes (not shown) are formed with respect to some pressure chambers  128 . Surface electrodes  134 ,  135  are provided on the top surface of the piezoelectric actuator  130  along the edges of the long sides. The surface electrodes  134  are electrically connected to the each of the narrow electrodes and the surface electrodes  135  are electrically connected to the common electrodes. (Refer to FIG. 22.)  
         [0115]    The piezoelectric actuator  130  is laminated to the cavity plate  120  in such a manner that each of the narrow electrodes in the piezoelectric actuator  130  is associated with each of the pressure chambers  128  in the cavity plate  120 . As the flexible flat cable  140  is overlaid on an upper surface of the piezoelectric actuator  130 , various wiring patterns (not shown) in the flexible flat cable  140  are electrically connected to the surface electrodes  134 ,  135 .  
         [0116]    With this structure, when voltage is applied between one of the narrow electrodes and one of the common electrodes in the piezoelectric actuator  130 , the piezoelectric sheet  136  sandwiched between the narrow electrode and the common electrode deforms by piezoelectric effect in a direction where the sheets are laminated. By this deformation, the volume of the pressure chamber  128  corresponding to the narrow electrode is reduced, causing ink stored in the pressure chamber  128  to be ejected in a droplet from the associated nozzle  122  (FIG. 26), thereby performing printing.  
         [0117]    The number of the piezoelectric ink jet heads  106  can be one to four. The cavity plate  120  may be made of ceramics in addition to metal. Further, the ink jet printer of the invention is driven by the piezoelectric actuator  130  in the shape of a plate, however, the ink jet printer of the invention may be driven by a piezoelectric actuator in any form. In addition, the ink jet printer may be structured wherein ink is ejected from the nozzles  122  by vibrating a plate covering the reverse side surface of the pressure chambers by static electricity.  
         [0118]    In a third embodiment, the agent-receiving portions  58 ,  59  are formed on the back of the nozzle plate  123  (FIGS. 27 and 27B).  
         [0119]    In a forth embodiment, as shown in FIG. 27C, the agent-receiving portions  58 ,  59  are drilled through the nozzle plate  123 .  
         [0120]    In any case, the area where the adhesive  155  is applied is increased, thereby improving strength of adhesion between plates. The agent-receiving portions  58 ,  59  may be shaped in not only a circle but also other shapes such as a rectangle and an oval.  
         [0121]    While the invention has been described with reference to the embodiments, it is to be understood that the invention is not restricted to the particular forms shown in the foregoing embodiments. Various modifications and alternations can be made thereto without departing from the scope of the invention.