Abstract:
An inkjet head has a flow path unit having a first surface and a second surface opposite the first surface. The flow path unit ejects ink in an ink ejection direction. The flow path unit has wall plates positioned on the second surface, extending away from the flow path unit. The inkjet head has a cover contacting at least one of the wall plates. The cover covers a portion of the second surface, and the cover has sidewalls. A first portion of at least one of the sidewalls contacts a first portion of corresponding wall plates, and a second portion of at least one of the sidewalls and a second portion of the corresponding wall plates defines a gap between them. The inkjet head has a seal positioned in the gap, and the seal prevents fluid from entering the gap.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Japanese Patent Application No. 2006-268136, filed Sep. 29, 2006, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an inkjet head that ejects ink droplets onto a recording medium for printing. 
     2. Description of Related Art 
     A known inkjet head for ejecting ink droplets onto a recording sheet includes a flow path unit and an actuator. The flow path unit includes individual ink paths connecting common ink chambers, pressure chambers and nozzles. The actuator is configured to apply energy, which is required for ejecting ink droplets from the nozzles, to the pressure chambers. The actuator may be made by interposing a piezoelectric layer made of a lead zirconium titanate (PZT)-based ceramic material having ferroelectric properties between a group of individual electrodes provided in association with the nozzles, and a common electrode to which grand potential is applied. In the actuator, individual electrodes disposed on a surface may be short-circuited due to adhesion of ink mist, thus degrading printing quality and speed. A sealing agent is used to prevent ink mist from entering the inkjet head. However, it is difficult to apply the sealing agent uniformly and fully. Thus, the sealing agent may peel off and ink mist may enter the inkjet head. 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention provides an inkjet head that reliably prevents ink mist from entering the inkjet head. In an embodiment of the invention, parts needed to reliably prevent ink mist from entering the inkjet head may be manufactured without complex manufacturing procedures, thus reducing the cost of manufacturing the inkjet head. 
     According to an embodiment of the invention, an inkjet head inkjet head comprises a flow path unit comprising a first surface and a second surface opposite the first surface, in which the flow path unit is configured to eject ink in an ink ejection direction, an actuator positioned on the second surface, in which the actuator is configured to generate ejection energy for ejecting ink, a plurality of wall plates positioned on the second surface and extending away from the flow path unit in a direction opposite from the ink ejection direction, a covering member contacting at least one of the plurality of wall plates, in which the covering member is configured to cover a portion of the second surface of the flow path unit, and the covering member comprises a plurality of sidewalls, in which a first portion of at least one of the plurality of sidewalls contacts a first portion of a corresponding one of the plurality of wall plates, and a second portion of the at least one of the plurality of sidewalls and a second portion of the corresponding one of the plurality of wall plates defines a gap therebetween, and a seal positioned in the gap, wherein the seal is configured to prevent fluid from entering the gap. 
     Thus, the gap is filled with the sealing agent, so that the sidewall of the covering member and the wall plates adhere to each other tightly and stably. This structure prevents ink mist from entering the ink jet head. In addition, this structure prevents the sealing agent from squeezing out, so that the sides of the ink jet head are resistant to dirt. 
     According to an embodiment of the invention, the gap extends along an entire length of a boundary between each wall plate and the corresponding sidewall. Thus, the sidewall of the covering member and the wall plates adhere to each other more tightly. 
     According to an embodiment of the invention, the seal extends through the entire gap. Thus, the sidewall of the covering member and the wall plates adhere to each other more tightly. 
     According to an embodiment of the invention, the second portion of the at least one of the plurality of sidewalls comprises a recess which defines at least a portion of the gap. Thus, the gap may be formed simply thereby reducing cost of the inkjet head. 
     According to an embodiment of the invention, the second portion of the at least one of the plurality of wall plates comprises a recess which defines at least a portion of the gap. Thus, the gap may be formed simply thereby reducing cost of the inkjet head. 
     According to an embodiment of the invention, the second portion of the at least one of the plurality of wall plates comprises a first recess, and the second portion of the at least one of the plurality of sidewalls comprises a second recess, wherein the first and second recesses define at least a portion of the gap. Thus, the gap may be formed simply thereby reducing cost of the inkjet head. 
     According to an embodiment of the invention, at least one of the plurality of wall plates is a heat sink configured to transfer heat to the outside of the at least one of the plurality of wall plates. Thus, the plurality of wall plates transfer heat to the outside of the at least one of the plurality of wall plates. 
     According to an embodiment of the invention, the heat sink comprises aluminum metal, titanium metal, magnesium metal, stainless steel, or a titanium or magnesium alloy metal. Thus, the heat sink transfers heat to the outside of the heat sink efficiently. 
     According to an embodiment of the invention, the seal is positioned in the gap and held in place by capillary action. Thus, the seal is easily charged into all the way to the gap. 
     According to an embodiment of the invention, the seal comprises a material having a viscosity of 5-20 pascals per second. Thus, the seal is easily charged into all the way to the gap. 
     According to an embodiment of the invention, the first portion of the at least one side wall is larger than the second portion of the at least one sidewall. 
     According to an embodiment of the invention, the first portion of the at least one side wall is smaller than or the same size as the second portion of the at least one sidewall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of embodiments of the present invention, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings. 
         FIG. 1  is a perspective view of an inkjet head, according to an embodiment of the invention. 
         FIG. 2  is a perspective view showing an internal structure of the inkjet head shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the inkjet head taken along a line III-III of  FIG. 1 , according to an embodiment of the invention. 
         FIG. 4  is a perspective view of a head cover shown in  FIG. 1 , according to an embodiment of the invention. 
         FIG. 5  is a side view of a heat sink shown in  FIG. 1 , according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention, and their features and advantages, may be understood by referring to  FIGS. 1-5 , like numerals being used for corresponding parts in the various drawings. 
     An inkjet head  1  according to an embodiment of the invention is shown in  FIG. 1 . Inkjet head  1  may be elongated in one direction, and may be applied to an inkjet-type image recording apparatus such as an inkjet printer. 
     Inkjet head  1  may be disposed in the recording apparatus in a direction facing a recording medium, hereinafter interchangeably referred to as a recording sheet, e.g., a sheet of plain paper or a transparency. The recording sheet may be fed by a feed mechanism. Inkjet head  1  may have a rectangular parallelepiped shaped line head, whose longitudinal direction may be set in a main scanning direction. The feed mechanism may include a conveyor belt and may be configured to feed a recording sheet, fed from a supply mechanism, on the conveyor belt to an area facing inkjet head  1 . Inkjet head  1  may have a printing area extending across substantially the full width of the conveyor belt. A plurality, e.g., four, inkjet heads may be provided in the recording apparatus parallel to a direction in which a recording sheet is fed (hereinafter refereed to as a sheet feeding direction). Each inkjet head  1  may eject ink droplets of a different color, e.g., one each of yellow, cyan, magenta, and black, thereby enabling color printing. Based on externally transmitted image data, the feed mechanism may feed a recording sheet to an opposed position of each inkjet head  1 , and each inkjet head  1  may eject ink droplets onto the recording sheet to form an image. The recording sheet on which the image has been formed further may be fed and stored in a sheet ejection portion. 
     In an embodiment of the invention, the main scanning direction may be defined as a lengthwise, or long, direction of the inkjet head in a plan view, while a sub scanning direction may be defined as a direction perpendicular to the main scanning direction in a horizontal axis, when viewed in a plan view. The direction in which ink droplets may be ejected from the inkjet head  1  may herein be interchangeably referred to as the bottom, downward, or down direction, and the direction opposite the bottom direction may herein be interchangeably referred to as the top, upward, or up direction. 
     As shown in  FIGS. 1 to 3 , inkjet head  1  may include a flow path unit  140 , an ink reservoir  130 , a covering member, e.g., a head cover  110 , side plates, e.g., heat sinks  150 , and a control circuit board  170 . Flow path unit  140  may include nozzles on a bottom surface, e.g., an ejection surface, and ink reservoir  130  may be configured to supply ink to flow path unit  140 . Control circuit board  170 , ink reservoir  130 , and flow path unit  140  may be laminated from top to bottom in this order. 
     Inside flow path unit  140 , ink paths, e.g., a common ink chamber and individual flow paths connecting the common ink chamber and nozzles via pressure chambers, may be formed. A plurality, e.g., four, of actuator units  120  may be mounted on an upper surface e.g., a mounting surface of flow path unit  140 . Each actuator unit  120  may be configured to selectively apply ejection energy to ink in the pressure chambers, so as to eject ink droplets from the nozzles of flow path unit  140  in an ink ejection direction. Actuator unit  120  may be a unimorph-type, that is, a piezoelectric layer may be interposed between a common electrode and a number of individual electrodes may be disposed to face the corresponding pressure chambers. The piezoelectric layer may be made of a lead zirconium titanate (PZT)-based ceramic material having ferroelectric properties. The individual electrodes and the common electrode may be made of, e.g., an Ag—Pd-based metallic material. The individual electrodes may be electrically connected to corresponding wiring patterns  162   a  on Flexible Printed Circuits (FPCs)  162  on an upper surface of actuator unit  120 , via lands which may be made of gold mixed with glass frit. When a predetermined voltage pulse may be applied from a driver IC  160  to an individual electrode via a corresponding wiring pattern  162   a  on FPC  162 , an area on actuator unit  120  corresponding to the individual electrode may be deformed, and a volume of the pressure chamber facing the area may vary. In this manner, ejection energy, e.g., a pressure wave, may be generated in ink in the pressure chamber, and an ink droplet may be ejected from the corresponding nozzle. 
     As shown in  FIGS. 2 and 3 , control circuit board  170  may be configured to control actuator units  120 , and may be fixed in an upper part of ink reservoir  130 . A plurality, e.g., four, of connectors  170   a  may be fixed on an upper surface of control circuit board  170 . Connectors  170   a  may be electrically connected to devices built on control circuit board  170 , e.g., processors and storage devices. 
     One end of each FPC  162  may be electrically connected to a side of each connector  170   a.  FPC  162  may be a flexible sheet on which wiring patterns  162   a  may be formed and driver IC  160  may be mounted. The other end of each FPC  162 , which may be terminals of wiring patterns  162   a,  may be inserted into a recessed portion  133   b  of ink reservoir  130  and may be electrically connected to individual electrodes of actuator unit  120 . 
     Driver IC  160  may be an IC chip configured to drive actuator unit  120 . As shown in  FIG. 3 , each driver IC  160  may be urged against FPC  162  and heat sink  150  by a sponge  161  disposed on a side of ink reservoir  130 . Heat sinks  150  may be metal plates made of metal, e.g., aluminum. A heat dissipation sheet  157  may be affixed to an inner surface of each heat sink  150 , at a position facing driver IC  160 . As driver IC  160  tightly contacts heat sink  150  via heat dissipation sheet  157 , driver IC  160  and heat sink  150  may become thermally coupled. Thus, a heat generated in driver IC  160  may be dissipated via heat sink  150 . 
     Ink reservoir  130  may include an upper reservoir  131 , a reservoir base  132 , and a lower reservoir  133 , which may be disposed in this order in a direction leading toward flow path unit  140 . An ink path  135  may be formed inside upper reservoir  131 . Ink path  135  may be in fluid communication with an ink supply valve  111 . In addition, ink path  135  may be in fluid communication with flow path unit  140  via an ink path (not shown) formed in reservoir base  132 . A part of a lower surface of ink path  135  may be defined by a flexible film  131   d.  A lower surface of flexible film  131   d  faces reservoir base  132  via a gap, and may be movable within the gap. Thus, when film  131   d  vibrates, film  131   d  may absorb the impact generated by a pressure wave in ink filled in ink path  135 . A filter  131   c  having minute holes may be disposed in ink path  135 . 
     As shown in  FIGS. 2 and 3 , lower reservoir  133  may be bonded to flow path unit  140  and recessed portion  133   b  may be partially formed between lower reservoir  133  and flow path unit  140 . Referring to  FIG. 3 , a recessed portion  133   b  may be positioned corresponding to each actuator unit  120 . Each actuator unit  120  may be attached to the surface of flow path unit  140 , in a gap formed by recessed portion  133   b.  Ink supply valve  111  may supply ink to flow path unit  140  through ink path  135  formed in ink reservoir  130 . Before ink reaches flow path unit  140 , ink passes through filter  131   c  positioned in ink path  135 , so that filter  131   c  may filter the impurities from ink. 
     As shown in  FIGS. 1 and 4 , head cover  110  may be substantially box shaped, and may open downward. Head cover  110  may be positioned to cover a space above flow path unit  140 , and also may be positioned above a surface of flow path unit  140  on which actuator units  120  may be mounted. Ink supply valve  111  may be disposed on an upper surface of head cover  110 , and ink may be supplied to ink reservoir  130  via ink supply valve  111 . 
     Head cover  110  may include a plurality of sidewalls  112  facing each other in the sub scanning direction. Sidewalls  112  may have greater length in the main scanning direction than in an up and down direction, i.e., a vertical direction. Each sidewall  112  may be formed with a substantially rectangular-shaped opening  110   a  that may be elongated in the main scanning direction, at a lower edge of sidewall  112 . Opening  110   a  may extend to substantially the midpoint of head cover  110  in a vertical direction. Opening  110   a  may be designed to expose a flat protrusion  150   a  formed in heat sink  150  from head cover  110 . A cutout portion  110   b  may be formed on a portion of an inner wall surface of sidewall  112  along opening  110   a.  Each sidewall  112  may be formed with a recessed portion  112   a  on the inner wall surface so that sidewall  112  may be thin at recessed portion  112   a.  Upper end portion of heat sink  150  may be fitted in recessed portion  112   a.  Thus, heat sink  150  may be supported between sidewall  112  and flow path unit  140 . 
     A heat sink  150  according to an embodiment of the invention may be shown in  FIGS. 3 and 5 . A plurality of heat sinks  150  may have a substantially rectangular shape, and may extend in the longitudinal direction, and also may extend in a direction opposite the ink ejection direction, of flow path unit  140 . Flat protrusion  150   a  may be formed in a central portion of each heat sink  150 . Flat protrusion  150   a  may protrude outward in the sub scanning direction. Flat protrusion  150   a  may be manufactured by deforming, e.g., stamping, a flat metal work piece. Flat protrusion  150   a  thus may be formed in heat sink  150 , and may improve a stiffness of heat sink  150 . 
     Each heat sink  150  may be formed with a plurality, e.g., five, of protrusions  150   b  protruding downward on a lower edge of heat sink  150 . Protrusions  150   b  may be spaced in a longitudinal direction of heat sink  150 . As shown in  FIG. 3 , a plurality of recessed portions  141  may be formed in proximity to both sides, with respect to the sub scanning direction, of the upper surface of flow path unit  140 . As protrusions  150   b  may be engaged in recessed portions  141 , heat sinks  150  may be positioned in proximity to both sides of the upper surface of flow path unit  140 . The lower edge of each heat sink  150 , except for the protrusions  150   b,  may tightly contact the upper surface of flow path unit  140 , to prevent fluids, e.g., ink or ink mist, from entering inkjet head  1  from between heat sink  150  and flow path unit  140 . In an embodiment of the invention, heat sinks  150  may be made of aluminum metal. Heat sinks  150  also may be made of other materials or combinations of materials, e.g., titanium metal, magnesium metal, titanium or magnesium alloy metal, aluminum alloy metal, or stainless steel. 
     Referring again to  FIG. 3 , each heat sink  150  may be positioned so that a perimeter of flat protrusion  150   a  on an outer surface of each heat sink  150  faces at least a portion of an inner surface of corresponding sidewall  112  of head cover  110 . Cutout portion  110   b  may be formed at another portion of an inner surface, e.g., the lower edge of the inner wall surface, of sidewall  112 . A gap may be created between cutout portion  110   b  and the outer surface of heat sink  150 . The gap may be created along a boundary between heat sink  150  and sidewall  112 , and may extend in a main scanning direction. The gap may be created along an entire end surface of sidewall  112 , defining opening  110   a.  A sealing material, e.g., a potting material  156  may be applied along an entire length of the boundary. The applied potting material  156  may fill in the entire gap formed between heat sink  150  and cutout portion  110   b.  Potting material  156  may fill the gap entirely by capillary action. The potting material may have any viscosity which may facilitate capillary action, preferably having a viscosity of 5-20 pascals per second. Gaps between heat sinks  150  and flow path unit  140  are sealed with a potting material  155 . Thus, a space enclosed by head cover  110 , the heat sinks  150 , and flow path unit  140  may be hermetically sealed. 
     According to an embodiment of the invention, the gap between heat sink  150  and cutout portion  110   b  may be filled with potting material  156 , so that sidewall  112  of head cover  110  and corresponding heat sink  150  may adhere to each other tightly and stably. This structure may prevent fluid, e.g., ink or ink mist from entering the inkjet head  1 , and potentially adhering to actuator  120 . In addition, this structure may prevent the potting material  156  from escaping, e.g., being squeezed out, so that the sides of inkjet head  1  may be resistant to foreign objects, e.g., dust, debris, and dirt. 
     In an embodiment of the invention, a plurality, e.g., two, of heat sinks  150  may be positioned in proximity to both sides of flow path unit  140 , with respect to the sub scanning direction. However, the number of heat sinks  150  is not limited to two. In other embodiments of the invention, one or more heat sinks may be positioned in proximity to the flow path unit. 
     In an embodiment of the invention, cutout portion  110   b  may be formed in each sidewall  112  of head cover  110 , and may be configured to form a gap between sidewall  112  and heat sink  150 . However, in another embodiment of the invention, cutout portion  110   b  may not be formed in each sidewall  112 , but a cutout or a recess may be formed in an inner wall of heat sink  150 , to form a gap between heat sink  150  and sidewall  112  of head cover  110 . 
     In an embodiment of the invention, heat sinks  150  may be configured to dissipate heat of driver ICs  160 . In another embodiment of the invention, heat sinks  150  may be side plates which may not function to dissipate heat. Although the embodiment of the present invention has been described in detail herein, the scope of the invention is not limited thereto. It will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the invention. Accordingly, the embodiments disclosed herein are only exemplary. It is to be understood that the scope of the invention is not to be limited thereby, but is to be determined by the claims which follow.