Abstract:
An ink jet head has a first cover member having an ink chamber for storing ink. A piezoelectric body is connected to the first cover member and has channels disposed in communication with the ink chamber of the cover member for receiving ink. A plate member has a first surface connected to the first cover member and the piezoelectric body, a second surface disposed opposite the first surface, an outer peripheral edge, and openings extending through the first and second surfaces and disposed in communication with a respective one of the channels of the piezoelectric body. A second cover member has a first surface, a second surface disposed opposite the first surface, and an opening extending from the first surface to the second surface. The plate member is disposed in the opening so that the second cover member surrounds at least a portion of the outer peripheral edge of the plate member. Electrodes are connected to the piezoelectric body and are driven by a voltage signal to deform a portion of the piezoelectric body to vary a volume of each of the channels to thereby eject ink from the channels through the openings of the plate member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet head mounted on an ink jet recording apparatus applied to, for example, a printer or a facsimile machine. 
     2. Description of the Related Art 
     Conventionally, an ink jet recording apparatus for recording letters or images on a recording medium using a recording head for expelling ink from a plurality of nozzles is known. In such an ink jet recording apparatus, the recording head opposed to the recording medium is provided in a head holder, and the head holder is mounted on a carriage to scan the recording medium in a direction orthogonal to the direction of conveyance of the recording medium. 
     FIG. 6 is an exploded perspective view showing the main part of an example of such conventional recording head. FIG. 7A is a side sectional view and FIG. 7B is a frontal sectional view taken along line  7 B— 7 B in FIG. 7A showing the main part of the conventional recording head. As shown in FIGS. 6 and 7, a plurality of channels  102  are provided side by side in an actuator plate  101  formed of piezoelectric ceramic in its width direction. The channels  102  are separated from one another by side walls  103 . One end portion of the channels  102  in the longitudinal direction extends to one end face of the actuator plate  101 , while the other end portion does not extend to the other end face, with the depth being gradually decreased. An electrode  105  for applying a drive voltage is formed on the surface of the opening side of both side walls  103  and  103  of each channel  102  over the longitudinal direction. 
     A cover plate  107  is joined by an adhesive  109  to the opening side of the channels  102  in the actuator plate  101 . The gap between the shallow portions of the rear end portion of the channels  102  in the actuator plate  101  and the cover plate  107  is sealed with sealant  110 . The cover plate  107  has a common ink chamber  111  which is a concave portion communicating with the shallow, other end portion of the channels  102 , and an ink supply port  112  piercing from the bottom portion of the common ink chamber  111  in the opposite direction from the channels  102 . An ink flow path  114  of a flow path block  113  communicates with and opens to the ink supply port  112 . Further, a filter  116  is attached to an end portion of the ink flow path  114  of the flow path block  113  on the side of the ink supply port  112 . 
     A nozzle plate  115  is affixed and joined by an adhesive to an end face where the channels  102  of the joined body of the actuator plate  101  and the cover plate  107  are open. The width of the nozzle plate  115  is larger than the width of the end face of the joined body and the length of the nozzle plate  115  is larger than the length of the end face of the joined body. Nozzle openings  117  are formed in the nozzle plate  115  at positions opposed to the channels  102 , respectively. Further, as shown in FIGS. 7A,  7 B, a nozzle plate cover  118  is fixed by the adhesive to the rear surface of the nozzle plate  115  so as to cover the outer peripheral surface of an end portion of the joined body of the actuator plate  101  and the cover plate  107  and to cover the rear surface of the nozzle plate  115 . 
     It is to be noted that a wiring board  120  is fixedly attached to a surface of the actuator plate  101  which is opposite to the side of the nozzle plate  115  and opposite to the side of the cover plate  107 . Wirings  122  connected to the electrodes  105 , respectively, using bonding wires  121 , a flexible substrate, or the like are formed on the wiring board  120 , such that drive voltage can be applied to the electrodes  105  via the wirings  122 . 
     In the recording head described above, the channels  102  are filled with ink from the ink flow path  113  via the ink supply port  112  and the common ink chamber  111 . By applying a predetermined drive voltage on side walls  103  on both sides of a predetermined channel  102  via the electrodes  105 , the side walls  103  are deformed to change the volume in the predetermined channel  102 , which leads to expulsion of ink in the channel  102  from the nozzle opening  117 . 
     For example, as shown in FIG. 8 which is a frontal sectional view showing the main part, in the case where ink is expelled from a nozzle opening  117  corresponding to a channel  102   a , positive drive voltage is applied to electrodes  105   a  and  105   b  in the channel  102   a  while electrodes  105   c  and  105   d  opposed to the electrodes  105   a  and  105   b , respectively, are grounded. By this, drive electric field toward the channel  102   a  acts on the side walls  103   a  and  103   b . When this is orthogonal to the direction of polarization of the actuator plate  101  formed of piezoelectric ceramic, due to a piezoelectric thickness sliding effect, the side walls  103   a  and  103   b  are deformed to be warped toward the channel  102 , the volume in the channel  102  is decreased to increase the pressure, and ink is expelled from the nozzle opening  117 . 
     Further, in such a recording head, a water-repellent film having water repellency is provided on the surface of the nozzle plate  115  which is opposed to a printed material for the purpose of preventing a head from getting dirty due to attachment of ink, preventing clogging of the nozzle openings  117 , and the like. Further, the head end face is cleaned at predetermined regular time intervals or at a desired time. The cleaning is typically carried out by wiping out the face of the nozzle plate  115  which is opposed to a printed material with a wiper formed of, for example, rubber which has a relatively high hardness (Hs 40-50) and does not swell. 
     However, in the structure of the recording head described in the above, the whole thickness of the nozzle plate  115  is exposed. Therefore, there is a problem that, when the nozzle plate  115  is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate  115  off the wiper or the printed material acts on the exposed nozzle plate  115 , and thus, the nozzle plate  115  is peeled off the end face of the joined body of the actuator plate  101  and the cover plate  107 . 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of these circumstances, and an object of the present invention is to provide an ink jet head in which a nozzle plate does not peel off the end face of a joined body of an actuator plate and a cover plate and the durability of which is expected to be improved. 
     In order to solve the above problem, according to a first aspect of the present invention, an ink jet head comprises: an actuator plate formed of piezoelectric ceramic with a plurality of channels formed therein, the channels opening to one surface and to one end face; a cover plate with a common ink chamber and an ink supply port formed therein, the common ink chamber being joined to the one surface of the actuator plate to seal a part of openings of the channels and to communicate with the channels, and the ink supply port piercing from the bottom portion of the common ink chamber in a direction opposite to the channels; a flow path block provided with a broad ink flow path, the inlet side thereof communicating with a narrow opening in proximity to an ink inflow port and the outlet side thereof communicating with the ink supply port; and a nozzle plate sealing the one end face of the actuator plate and having nozzle openings corresponding to the channels, respectively, the ink jet head expelling ink filled in the channels from the nozzle openings by applying drive voltage to electrodes provided on side walls of the channels and thereby changing the volume in the channels, and is characterized by comprising a nozzle plate cover joined to an outer side surface of the joined body of the actuator plate and the cover plate for surrounding the nozzle plate to protect the nozzle plate, and is characterized in that a surface of the nozzle plate which is opposed to a printed material is flush with a surface of the nozzle plate cover which is opposed to a printed material or protrudes from the surface of the nozzle plate cover in a predetermined range of height. 
     By structuring the ink jet head in this way, the whole thickness of the nozzle plate is not exposed. Therefore, when the nozzle plate is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material does not greatly act on a greatly exposed edge, and thus, the peeling of the nozzle plate off the end face of the joined body of the actuator plate and the cover plate is prevented and the durability can be expected to be improved. 
     According to a second aspect of the present invention, an ink jet head of the above first aspect of the invention is characterized in that the nozzle plate is formed so as to protrude from the outer edge of a front end of the joined body of the actuator plate and the cover plate, and the nozzle plate cover is shaped so as to surround the outer periphery and the rear surface of the nozzle plate. 
     By structuring the ink jet head in this way, action and effects similar to those of the above first aspect of the invention can be attained. 
     According to a third aspect of the present invention, an ink jet head of the above first or second aspect of the invention is characterized in that the surface of the nozzle plate which is opposed to a printed material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by 0 μm or more and half of the thickness of the nozzle plate or less. 
     When the surface of the nozzle plate which is opposed to a sprinted material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by less than 0 μm (a negative value, that is, when the surface of the nozzle plate which is opposed to a printed material receding with respect to the surface of the nozzle plate cover which is opposed to a printed material, ink remains in, for example, corner portions of the outer edges of the nozzle plate, and the wiping of the nozzle plate with the wiper is not carried out satisfactorily. 
     When the surface of the nozzle plate which is opposed to a printed material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by more than half of the thickness of the nozzle plate, the peripheral surface of the nozzle plate is exposed more greatly than the nozzle plate cover for protection. When the nozzle plate is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material acts on the exposed edges and the side surface of the nozzle plate, and thus, the nozzle plate is liable to peel off the end face of the joined body of the actuator plate and the cover plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more better understanding of the present invention, reference is made of a detailed description to be read in conjunction with the accompanying drawings, in which: 
     FIGS. 1A,  1 B are exploded perspective views of an embodiment of an ink jet head according to the present invention, in which FIG. 1A is an overall view, and FIG. 1B is a partially broken exploded perspective view; 
     FIG. 2 is a perspective view of the embodiment when assembled; 
     FIG. 3 is a longitudinal sectional view taken along the line  3 — 3  of FIG. 2; 
     FIG. 4 is a longitudinal sectional side view of a second embodiment of an ink jet head according to the present invention; 
     FIGS. 5A-5D are sectional views showing a schematic manufacturing process of the second embodiment of an ink jet head according to the present invention; 
     FIG. 6 is an exploded perspective view schematically showing the main part of a conventional recording head; 
     FIGS. 7A,  7 B are sectional views schematically showing the main part of the conventional recording head, in which FIG. 7A is a side sectional view, and FIG. 7B is a frontal sectional view taken along the line  7 B— 7 B in FIG. 7A; and 
     FIG. 8 is frontal sectional view showing the main part of the conventional recording head and of the ink jet head according to the present invention, and illustrating a driving condition thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Though an embodiment of the present invention is described in the following with reference to the attached drawings, the present invention is not limited thereto. 
     FIGS. 1A,  1 B are exploded perspective views of an embodiment of an ink jet head according to the present invention. FIG. 1A is an overall view, FIG. 1B is a partially broken exploded perspective view, FIG. 2 is a perspective view of the embodiment when assembled, and FIG. 3 is a longitudinal sectional view taken along the line  3 — 3  of FIG.  2 . 
     As shown in FIGS. 1A,  1 B, a plurality of channels  12  are provided side by side in a width direction of a piezoelectric body which comprises an actuator plate  11  formed of piezoelectric material such as a ceramic. The channels  12  are separated from one another by side walls  13 . 
     One end portion of the channels  12  in the longitudinal direction is provided to extend to an end face of the actuator plate  11 , while the other end portion is formed so as not to extend to the other end face, with the depth being gradually decreased. An electrode  15  for applying a drive voltage is formed on the surface of the opening side of both side walls  13  and  13  of each channel  12  over the longitudinal direction. 
     A first cover member or plate  17  is joined by an adhesive to the opening side of the channels  12  in the actuator plate  11 . The cover plate  17  has a common ink chamber  21  which is a concave portion communicating with the shallow, other end portion of the channels  12 , and an ink supply port  22  piercing from the bottom portion of the common ink chamber  21  in the opposite direction from the channels  12 . An ink flow path  24  of a block member or flow path block  23  communicates with and opens to the ink supply port  22 . The flow path block  23  has a built-in ink inflow port  29  for receiving ink conveyed from an ink cartridge which is not shown in the figures via a tube which is not shown in the figures, and has the built-in broad ink flow path  24  communicating with a narrow opening  26  on the outlet side of the ink inflow port  29 , with the outlet side of the ink flow path  24  communicating with the ink supply port  22 . Further, a filter  20  for removing a foreign matter in the ink is attached to an end portion of the ink flow path  24  of the flow path block  23  on the side of the ink supply port  22 . 
     It is to be noted that, though the cover plate  17  can be formed of a ceramic plate, a metal plate, or the like, taking into consideration of deformation after joining to the actuator plate  11  formed of piezoelectric ceramic, it is preferable to use a ceramic plate having similar thermal expansion, particularly a piezoelectric ceramic plate. 
     A plate member or nozzle plate  25  is affixed and joined by an adhesive to an end face where the channels  12  of the joined body of the actuator plate  11  and the cover plate  17  are open. Nozzle openings  27  are formed in the nozzle plate  25  at positions corresponding to the channels  12 , respectively. 
     In the present embodiment, the nozzle plate  25  is formed to be a little larger than the area of the end face where the channels  12  of the joined body of the actuator plate  11  and the cover plate  17  are open. The nozzle plate  25  is a polyimide film or the like with the nozzle openings  27  formed therein having the diameter of, for example, 25 μm using, for example, an excimer laser system. Further, though not shown in the figures, a water-repellent film having water repellency is provided on the surface of the nozzle plate  25  which is opposed to a printed material for the purpose of preventing attachment of ink and the like. 
     In the present embodiment, a second cover member or nozzle plate cover  28  having an opening  28   a  which can be fit to the nozzle plate  25  is disposed on an outer side surface of the nozzle plate  25  and on the periphery of the end portion where the channels  12  of the joined body of the actuator plate  11  and the cover plate  17  are open, and is joined by the adhesive to a part of the rear surface and the side surface of the nozzle plate  25  and to the outer side surface of the joined body of the actuator plate  11  and the cover plate  17 . The nozzle plate cover  28  is for protecting the nozzle plate  25  from the situation that, when the nozzle plate  25  is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate  25  off the wiper or the printed material acts and the nozzle plate  25  is peeled off the end face of the joined body of the actuator plate  11  and the cover plate  17 . The nozzle plate cover  28  is attached such that the surface of the nozzle plate  25  which is opposed to a printed material is flush with the surface of the nozzle plate cover  28  which is opposed to a printed material or protrudes from the surface of the nozzle plate cover by a predetermined amount L. 
     The protrusion amount L of the nozzle plate  25  in relation to the nozzle plate cover  28  is preferably 0 μm or larger and is half of the thickness of the nozzle plate or smaller. For example, if the thickness of the nozzle plate is 50 μm, the protrusion amount L is preferably 25 μm or smaller. If the protrusion amount L is a negative value less than 0 μm, the wiping of the nozzle plate  25  with the wiper is not carried out satisfactorily, which is not preferable. Further, when L is larger than half of the thickness of the nozzle plate, the side surface of the nozzle plate  25  is exposed more greatly than the nozzle plate cover  28  for protection. When the nozzle plate  25  is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material acts on the exposed edge  25   c  and the side surface, and thus, the nozzle plate  25  is liable to peel off the end face of the joined body of the actuator plate  11  and the cover plate  17 , which is not preferable. 
     Since the nozzle plate cover  28  and the nozzle plate  25  are positioned with a relatively high accuracy in this way, it is preferable that the nozzle plate cover  28  is formed of a material having a high rigidity, for example, stainless steel, aluminum, hard plastic, or the like. 
     It is to be noted that, though the nozzle plate cover  28  is preferably formed in one piece as shown in the figures, it may be structured with two pieces integrally connected together, for example. 
     In the present embodiment structured as above, the end portion of the nozzle plate  25  on the side opposite to the surface opposed to a printed material is surrounded by the nozzle plate cover  28 . Therefore, a situation is prevented in which, when the nozzle plate  25  is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate  25  off the wiper or the printed material acts and the nozzle plate  25  is peeled off the end face of the joined body of the actuator plate  11  and the cover plate  17 . This improves the durability. 
     An ink jet head  30  (see FIG. 2) structured in this way is formed by, first, joining the actuator plate  11  formed of piezoelectric ceramic and the cover plate  17  using the adhesive, then joining the nozzle plate  25  to the end face of the joined body using the adhesive, and, at the same time, fitting and adhering the nozzle plate cover  28  onto the outer side surface of the nozzle plate  25  and onto the joined body of the actuator plate  11  and the cover plate  17 . 
     FIG. 4 is a longitudinal sectional side showing another embodiment of an ink jet head according to the present invention. 
     In the present embodiment, as shown in FIG. 4, the nozzle plate  25  is formed such that its width is larger than the width of the end face of the joined body of the actuator plate  11  and the cover plate  17 . Also, although not shown in the figures, the nozzle plate  25  is formed such that its length is larger than the length of the end face of the joined body of the actuator plate  11  and the cover plate  17 . The nozzle plate cover  28  is formed so as to surround the peripheral surface of the nozzle plate  25  and so as to surround the outer periphery and the rear surface of the nozzle plate. The base portion of the nozzle plate cover  28  is joined to the outer peripheral surface of the end portion of the joined body of the actuator plate  11  and the cover plate. 17 . 
     The protrusion amount L of the nozzle plate  25  in relation to the nozzle plate cover  28  is preferably 0 μm or larger and half of the thickness of the nozzle plate or smaller, the reason for which is the same as that described in the above embodiment. 
     It is to be noted that, when the nozzle plate cover  28  is fitted and adhered, it is necessary to position both the surface of the nozzle plate  25  and the surface of the nozzle plate cover  28 . Though the method to attain this is not specifically limited, in the present embodiment, the positioning was carried out as described in the following. 
     (1) As shown in FIG. 5A, a heat-resistant tape  34  is affixed onto a glass plate  32 , and then, the nozzle plate  25  is mounted thereon. 
     (2) As shown in FIG. 5B, the end face of the joined body of the actuator plate  11  and the cover plate  17  is positioned and mounted on the nozzle plate  25 . 
     (3) As shown in FIG. 5C, the nozzle plate cover  28  is set such that the space between itself and the nozzle plate  25  and the space between itself and the joined body of the actuator plate  11  and the cover plate  17  are well-balanced. The space between the nozzle plate  25  and the nozzle plate cover  28  and the space between the joined body of the actuator plate  11  and the cover plate  17  and the nozzle plate cover  28  are filled with thermosetting adhesive  36 , which is then heated to be cured. 
     (4) As shown in FIG. 5D, the heat-resistant tape  34  is peeled off the integrally formed ink jet head  30 . According to the method described in the above, the surface of the nozzle plate  25  and the surface of the nozzle plate cover  28  can be positioned to be flush with each other. Further, by using the glass plate, unevenness when the adhesive is filled can be eliminated. 
     It is to be noted that, since the principle of driving and the like of the embodiment of an ink jet head described in the above are the same as those described with respect to prior art, the description thereof is omitted herein. 
     As described in the above, an ink jet head according to the present invention comprises a nozzle plate cover joined to the outer side surface of a joined body of an actuator plate and a cover plate and surrounding a nozzle plate to protect the nozzle plate, and is structured such that it is characterized in that the surface of the nozzle plate which is opposed to a printed material is flush with the surface of the nozzle plate cover which is opposed to a printed material or protrudes from the surface of the nozzle plate cover by half of the thickness of the nozzle plate or less. Therefore, the peripheral surface of the nozzle plate is exposed not much, and thus, when the nozzle plate is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material does not act on a greatly exposed edge and the outer peripheral surface, and thus, the peeling of the nozzle plate off the end face of the joined body of the actuator plate and the cover plate is prevented and the durability can be expected to be improved.