Abstract:
An ink jet head includes an ink supply path, a pressure chamber, an orifice and an oscillator. By bending a portion of the wall surface of the pressure chamber by oscillation of oscillator, ink is emitted. A portion of the wall surface of pressure chamber is formed by an oscillating plate of resin, and a unimorph including an elastic plate and oscillator provided on oscillating plate. Sidewalls separating the inside of pressure chamber are provided, and the dimension between the sidewalls is made shorter than the dimension of the unimorph.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet head used for an ink jet printer or the like, and more specifically, it relates to an ink jet head allowing highly dense arrangement of nozzles. 
     2. Description of the Related Art 
     An ink jet head of interest to the present invention is disclosed, for example, in Japanese Patent Laying-Open No. 6-64163. FIG. 10 is a perspective view of the ink jet head disclosed in this laid-open patent application. Referring to FIG. 10, there are a plurality of nozzle openings  101   a ,  101   b , . . . formed in a nozzle forming member  102 . A pressure chamber forming member  103  is provided adjacent to nozzle forming member  102 . An oscillating plate  104  is adhered to pressure chamber forming member  103 . Electrodes are formed on both sides of oscillator  107 . One electrode is connected to oscillating plate  104  and the other electrode is connected to a driving circuit by means of an anisotropic conductive film  108  or the like. Oscillating plate  104  also serves as a GND electrode. At a portion surrounded by nozzle forming member  102 , pressure chamber forming member  103  and oscillating plate  104 , there are formed a pressure chamber  110  and an ink outlet  111 , filled with ink. When a voltage is applied between electrodes, a unimorph constituted by oscillating plate  104  and oscillator  107  is bent, pressing pressure chamber  110 , so that ink drops are emitted from nozzle openings  101   a ,  101   b , . . . In the figure, the reference character  112  represent a common ink pool, and  117  represents a flexible print circuit (FPC). 
     The conventional ink jet head was structured as described above. However, as the oscillating plate is formed of a metal, it has a problem that reactive force is considerably large. A piezoelectric element is used for the oscillator. When a voltage is applied to the piezoelectric element by a signal from the driving circuit, the oscillating plate is displaced because of unimorph effect with the oscillating plate. That the oscillating plate has high rigidity means there is large reactive force preventing displacement of the oscillating plate. Therefore, displacement of the oscillating plate is suppressed, change in volume of the pressure chamber becomes smaller and the efficiency in emitting ink is degraded. Accordingly, it is necessary to enlarge the area of the oscillator or to apply a high voltage to the oscillator to obtain energy necessary for the emission. However, if the area of the oscillator is enlarged, degree of integration of nozzles becomes lower, the head becomes larger and hence the apparatus as a whole cannot be made compact. Further, if a high voltage is applied to the oscillator to ensure an amount of deformation of the oscillator, power consumed by the head is undesirably increased. 
     FIG. 11 a  is a cross sectional view taken along the XI direction of the ink jet head shown in FIG. 10, and FIG. 11 b  is a side view of FIG. 11 a . Referring to FIGS. 11 a  and  11   b , in the conventional head, the dimensions of an elastic plate  105  and oscillator  107  oscillating the sidewall of the pressure chamber are smaller than the dimension of the corresponding wall surface of the pressure chamber. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an ink jet head which allows higher degree of integration of nozzles. 
     Another object of the present invention is to provide an ink jet head which can be made compact. 
     A still another object of the present invention is to provide an ink jet head allowing reduced power consumption. 
     The above described objects of the present invention can be attained by the ink jet head in accordance with the present invention in which oscillation is caused in a pressure chamber communicated with nozzles so as to partially bent a wall surface of the pressure chamber and to emit ink thereby, including an oscillating plate formed of resin provided at least on a part of the wall surface of the pressure chamber, and a unimorph including an elastic plate and an oscillator provided on the oscillating plate. The dimension of the bending portion provided by the unimorph is larger than the dimension of the wall surface of the pressure chamber corresponding to the unimorph. 
     The dimension of the bending portion provided by the unimorph is made larger than the dimension of the wall surface of the pressure chamber corresponding to the unimorph, whereby the dimension of the oscillator constituting the unimorph is made close to the channel pitch corresponding to the dimension between wall surfaces of the pressure chamber. Accordingly, highly dense arrangement of nozzles becomes possible. 
     More preferably, the ink jet head further includes a conductive film provided on the oscillator. The oscillator is adhered to the elastic plate by means of a first adhesive layer, and adhered to the conductive film by means of a second adhesive layer. The first adhesive layer is thicker than the second adhesive layer. 
     The thickness of the adhesive layer in contact with the oscillator is made thinner than on the side opposite to the oscillating plate, that is, on the side of the conductive film. Therefore, the problem that the adhesive layer on the side opposite to the oscillating plate binds the oscillator and prevents deformation of the oscillating plate, can be prevented. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a  to  1   c  are perspective view and cross sections, respectively, of an ink jet head in accordance with the present invention. 
     FIG. 2 a  is a side view of the ink jet head in accordance with the present invention, and FIG. 2 b  is a partial enlargement of FIG. 2 a.    
     FIG. 3 is a perspective view of another embodiment of the ink jet head in accordance with the present invention. 
     FIG. 4 a  is a side view of the aforementioned another embodiment of the ink jet head in accordance with the present invention, and FIG. 4 b  is a partial enlargement of FIG. 4 a.    
     FIG. 5 shows an oscillating plate and a pattern of electrodes formed on the oscillating plate. 
     FIG. 6 shows an oscillator (PZT) plate in cut state. 
     FIG. 7 shows a pattern of FPC bearing rear electrodes of the oscillator. 
     FIG. 8 a  shows nozzles of the ink jet head in accordance with the present invention, and FIG. 8 b  is a cross section taken along the line  1 — 1 ′ of FIG. 8 a.    
     FIGS. 9 a  to  9   f  are cross sections showing the steps of assembling the ink jet head in accordance with the present invention. 
     FIG. 10 is a perspective view of a conventional ink jet head. 
     FIGS. 11 a  and  11   b  are cross sections of a conventional ink jet head. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Referring to FIGS. 1 a  to  1   c , a plurality of nozzle openings  1   a ,  1   b , . . . are formed in nozzle forming member  2 . Pressure chamber forming member  3  is provided adjacent to nozzle forming member  2 . An oscillating plate  4  formed of resin is provided adjacent to pressure chamber forming member. 
     Referring to FIG. 2 a , an elastic plate  5  which also serves as an electrode, is provided adjacent to oscillating plate  4 . An oscillator  7  formed of a piezoelectric element is provided adjacent to oscillating plate  4 . Electrodes  6   a ,  6   b  are arranged on both surfaces of oscillator  7 . One electrode  6   a  conducts electricity by contacting with the elastic plate  5  which also serves as an electrode, and the other electrode  6   b  conducts electricity by contacting with a connecting terminal  9  with an anisotropic conductive film  8  or the like interposed. 
     In a portion surrounded by nozzle forming member  2 , pressure chamber forming member  3  and oscillating plate  4 , pressure chamber  10  and ink outlet  11  are formed, filled with ink. Ink outlet  11  is further communicated with common ink pool  12 . Head substrate  13  is constituted by nozzle forming member  2  and pressure chamber forming member  3 . 
     When a voltage is applied between electrodes  6   a  and  6   b , a contracting force in the planar direction acts on oscillator  7 , a unimorph constituted by oscillator  7  and elastic plate  5  is bent, pressing oscillating plate  4 , so that volume of pressure chamber  10  is changed and ink drops are emitted from nozzle openings  1 . 
     Nozzle forming member  2  and pressure chamber forming member  3  are formed, for example, of stainless parts, bonded by diffusion bonding, for example, and assembled as head substrate  13 . 
     In the present embodiment, elastic plate  5  electrically in contact with oscillator  7  and oscillating plate  4 , and a signal line connected thereto are formed integrally on an FPC (Flexible Print Circuit)  14 , so as to facilitate assembly. However, it is also possible to fabricate these separately and then assemble the separately provided parts. Referring to FIG.  2 ( a ), oscillating plate  4  is fixed on head substrate  13  by means of an epoxy resin adhesive  15 , for example. 
     Oscillator  7  is formed of a sheet of a piezoelectric element, on both surfaces of which metal films  6   a  and  6   b  as electrodes are formed. The thinner the sheet, the larger strain can be obtained with lower voltage, and hence the smaller becomes the power consumption. 
     Oscillator  7  is in contact with elastic plate  5  on one surface, and in contact with connecting terminal  9  on the other surface. Connecting terminal  9  is integral with FPC, and it is connected to the driving circuit. 
     FIG. 2 b  is an enlarged view of connecting portion between elastic plate  5  and oscillator  7 . Referring to FIG. 2 b , a conductive adhesive or an epoxy resin  16 , for example, Amicon A-316 manufactured by Grace Company, is used for the bonding between oscillator  7  and elastic plate  5 . Though not conductive, epoxy resin layer is sufficiently thin, and therefore it is electrically connected to the electrode (elastic plate  5 ) of FPC  14 , as well as to oscillator  7  at ups and downs of electrode  6   a.    
     Another electrode  6   b  of the PZT is in contact with electrode  9  of FPC  17  by means of anisotropic conductive film  8 , such as 3370C manufactured by Three Bond Company. Anisotropic conductive film  8  is thicker as an adhesive layer as compared with epoxy resin (epoxy resin layer is at most 5 μm, while anisotropic conductive film is about 35 μm in thickness), and therefore it does not strongly bind movement of PZT  7 . Therefore, it does not suppress deformation when PZT  7  and oscillating plate  4  deform toward the pressure chamber. In this case, by fixing only the periphery of electrode  9  by anisotropic conductive film  8 , deformation is less suppressed. 
     FIG. 1 b  is a cross sectional view taken along the direction  1   b  of the ink jet head shown in FIG. 1 a , and FIG. 1 c  is a side view of FIG. 1 b . Referring to FIGS. 1 b  and  1   c , one wall surface of the pressure chamber includes an oscillating plate  4 , an elastic plate  5  formed on oscillating plate  4 , and an oscillator  7  formed on elastic plate  5 , of which dimensions are larger than the dimension of the corresponding wall surface of the pressure chamber. As a result, the size of the oscillator can be selected close to the channel pitch. As a result, highly dense arrangement of nozzles becomes possible. 
     Normal oscillation of the oscillator is ensured even if the channel pitch is made smaller, since oscillation at the sidewall portion of the channel is facilitated by employing a less elastic member as the oscillating plate. 
     In the head as a whole, nozzles are arranged lengthwise and widthwise as shown in FIGS. 8 a  and  8   b.    
     FIG. 6 shows oscillators in the whole head in accordance with the embodiment shown in FIG.  1 . Oscillators corresponding to respective nozzles are arranged like a lattice. The oscillators are cut out by using a dicing saw or the like, from a PZT of a slightly larger size. The method of assembly will be described with reference to FIGS. 9 a ,  9   b ,  9   c ,  9   d  and  9   e . These oscillators are cut out from a large PZT plate  18  and bonded directly. 
     This method of assembly is employed from the following reasons. Namely, rather than adhering a PZT one by one on each corresponding channel, it is preferable that oscillator plate cut out and kept in the cut out state should be adhered as it is are to reduce the number of manufacturing steps and to reduce manufacturing cost. Further, since the size of the oscillator plate is made larger than necessary, the oscillator can be conveniently processed on a jig even when the size and position of the oscillator plate mounted on the jig is unsatisfactory. 
     The oscillator plate is fixed on a jig  22  by means of a double sided adhesive tape  19  which can be separated when heated (FIG. 9 a ), and the oscillator plates are cut to a prescribed size by a dicing saw in accordance with a reference of the jig (FIG. 9 b ). At this time, respective oscillator plates cut out from PZT plate  18  are already located at positions corresponding to the electrode on the side of the oscillating plate. On a sheet having low elasticity, the oscillator plate such as an FPC having a pattern of bodies having high modulus of elasticity is adhered (FIG. 9 c ), and a nozzle body is further adhered (FIG. 9 d ). Here such adhesion is controlled in accordance with reference holes, based on the reference holes of jig  22 . Thus the steps of assembly can be simplified and adhesion with high precision becomes possible. Thereafter, the tape  19  is heated and separated (FIG. 9 e ). Thus oscillating plate  18  can be adhered on electrode  15  of oscillating plate all at once. Thereafter, FPC  17  having rear electrode is mounted with anisotropic conductive film  8  interposed (FIG. 9 f ). 
     The electrodes  5  on the side of the oscillating plate of FPC  14  have rows in the Y direction connected commonly (FIG.  5 ). Electrodes  9  of another FPC  17  have columns in X direction connected in common (FIG.  7 ). By combining these and performing matrix-wise driving, the number of FPC wires and the number of drivers can be reduced, and hence the cost can be reduced. Further, at this time, the electrodes on the side of the oscillating plate are processed to have a pattern common to the oscillators in the longitudinal direction, and the electrodes on the opposite sides are processed to have a pattern common to the oscillating plates in the shorter side direction. By such patterning, the portion of contact between the PZT and the opposite electrodes can be reduced, and binding of the movement of the oscillating plate can be suppressed. 
     Second Embodiment 
     Another embodiment of the present invention will be described with reference to FIGS. 3 and 4. 
     FIG.  3  and FIGS. 4 a  and  4   b  show another embodiment of the present invention. Pressure chamber forming member  3  is formed of a plastic material, such as polyether sulfone. Oscillating plate  4  is also formed of the same material. If the surfaces of these are melted by means of a solvent, such as a methyl ethyl ketone if these are both formed of polyether sulfone, the surfaces are brought into pressure contact. Since adhesive is not used, undesirable influence such as flowing of adhesive into the pressure chamber can be avoided, and highly strong adhesion is realized. 
     An electrode  5  serving also as an elastic plate and a signal line connecting electrode  5  to an electrode  21  on the side of the FPC oscillating plate are formed on oscillating plate  4  by sputtering or vapor deposition. Alternatively, a method may be used in which an electrode material such as copper foil is deposited on the oscillating plate and an electrode pattern is formed by etching. The signal line on oscillating plate  4  is connected to FPC  14  by anisotropic conductive film  20  or the like. On electrode  5  serving also as an elastic plate, electrode  6   a  of oscillator  7  is adhered, and the other electrode  6   b  of the oscillator is connected to FPC  17  by anisotropic conductive film  8 . 
     Here, by forming an electrode by sputtering or vapor deposition on an oscillating plate, it becomes possible to process the oscillating plate and the electrode without using any adhesive, a process for providing each electrode becomes unnecessary, and hence dimensional precision can be improved. When the electrodes are formed collectively by etching, it becomes unnecessary to position each material for providing electrode one by one. Therefore, the manufacturing steps can be simplified and dimension precision can be improved. Further, since the nozzle body and the oscillating plate are bonded by melting the surfaces using a solvent, highly strong bonding becomes possible. Further, since the problem of flowing of the adhesive to the nozzle constituting portion can be avoided, stable dimensional precision can be obtained. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.