JPH10119259A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high density ink jet head which is good in productivity having a strong structure. SOLUTION: In the ink jet head, a head unit 10 composed of a piezoelectric element unit 25 wherein a plurality of laminated piezoelectric elements 23 are bonded onto an insulating substrate 21, a hammer body 34, a base plate 35, a fixing component holding the piezoelectric element unit 25, the hammer body 34 and the base plate 25, a diaphragm bonded to a free end of the hammer body 34 and onto its fixing component, and a channel substrate on which a pressure chamber bonded onto the diaphragm and an ink feed opening are formed, is fixed frame body 11, and a nozzle plate 13 is bonded to an end face of the head unit 10 and a face of the frame body 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of an ink-on-demand type ink jet head using a piezoelectric element.

[0002]

2. Description of the Related Art Using a displacement of a piezoelectric strain coefficient d33 in the same direction as the polarization of a laminated piezoelectric element, a diaphragm forming one of the walls of a pressure chamber is displaced to pressurize the ink filled in the pressure chamber and pressurize the ink. An ink jet head for ejecting ink from a nozzle communicating with a pressure chamber is disclosed in Japanese Patent Publication No. 7-57545. The outline of the structure is as shown in FIG.
A plurality of laminated piezoelectric elements 107 that can be independently driven are formed by bonding a laminated piezoelectric material thereon and forming a groove in the laminated piezoelectric material 104, and a pressure chamber 102 formed on a substrate 101.
The pressure is applied to the ink filled in the pressure chamber 102 by displacing the vibration plate 103 forming one wall, and the ink droplet is ejected from a nozzle 111 communicating with the pressure chamber 102.
Independently drivable laminated piezoelectric element 107 has electrodes 105 and 106 at both ends thereof connected to electrodes 110 and 108 connected to an external drive circuit, respectively, and applied between electrodes 110 and 108 by an external drive circuit. Driven by the applied voltage. This configuration is intended to increase the amount of displacement in the thickness direction by laminating the piezoelectric bodies, and as a result, to arrange the pressure chambers with high density.

In the above conventional example, the pressure chambers can be arranged at a higher density without reducing the amount of displacement as compared with the one utilizing the deformation caused by the piezoelectric strain coefficient d31 perpendicular to the polarization direction. However, as a result of the increase in density, the piezoelectric elements corresponding to one pressurized chamber are multilayered in the thickness direction and have a small cross-sectional area, resulting in a weak structure. There has been a problem that the electrical connection between the piezoelectric element and the FPC may be broken or, in extreme cases, even broken. In addition, when "pulling", which is an effective driving method for improving frequency characteristics and gradation controllability, is employed, it is necessary to apply a high voltage to keep the piezoelectric element in an extended state during standby. At this time, a malfunction due to a leak current is likely to occur. In order to prevent this, it is necessary to maintain a high insulation resistance at various places so that the charges charged in the piezoelectric element do not leak. In other words, it is necessary to make the processing conditions extremely strict so as not to cause the adhesion (smearing) of the cutout of the electrode layer to the contact cross-section which occurs at the time of the groove processing of the piezoelectric element, which causes a decrease in insulation resistance. There was a problem with mass production.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-density multi-nozzle head having a small and rigid structure and having no problem in mass production with respect to insulation of a piezoelectric element. To provide.

[0005]

According to the present invention, there is provided a laminated piezoelectric element unit comprising a plurality of laminated piezoelectric elements adhered on an insulating substrate, a hammer, a laminated piezoelectric element unit, and the like. Consists of a base plate and a fixing member for holding the hammer body, a diaphragm joined to the free end plane of the hammer body and the fixing member, and a flow path substrate formed with a pressure chamber and an ink supply port adhered to the diaphragm. The head unit to be fixed is fixed to a frame, and a nozzle plate is joined to the end surface of the head unit and the surface of the frame.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG.
A laminated piezoelectric body 20 is formed by sequentially laminating a paste-like electrode layer 31 containing silver as a main component on a thin paste-like piezoelectric material plate 30 of about 0 μm and then firing. The electrode layers 31 are formed on both sides of each piezoelectric material plate, one of which is exposed to the end face collector 22a and the other is exposed to the opposite end face collector 22b. Collector electrodes 22a, 22b
Is formed by sequentially applying chromium, nickel, and gold to the laminated piezoelectric body 20 by a thin film forming means such as vacuum evaporation. When a voltage is applied between the collecting electrode 22a and the collecting electrode 22b of the laminated piezoelectric body 20, an electric field is generated in each of the piezoelectric material plates 30, and each of the piezoelectric material plates extends by a minute dimension in the thickness direction. As integration, the laminated piezoelectric body 20 is displaced by a required amount in the thickness direction.

As shown in FIG. 3, the laminated piezoelectric body 20 is bonded on an insulating substrate 21 made of an insulating material such as ceramic. Further, a groove is formed from the upper surface of the laminated piezoelectric body 20 by a mechanical processing means such as a wire saw so that the laminated piezoelectric body 2 is formed.
The piezoelectric element unit 25 is formed by dividing 0 into the independently operable laminated piezoelectric elements 23. External drive voltage is FP
C (flexible printed cable) 24,
The ends 24a and 24b of the FPC 24 are
a, It is electrically connected to the collecting electrode 22b by a method such as soldering.

As shown in the cross-sectional view of FIG. 4, the insulating substrate 21, the piezoelectric element unit 25 composed of the laminated piezoelectric body 20 and the FPC 24, and the hammer body 34 are adhered on the upper surface of the hammer body fixed end 34a. The hammer body 34 and the hammer body fixed end 34a
Is adhered to the base plate 35 at the lower surface of. As shown in FIG. 2, the hammer bodies 34 are provided one by one for each of the laminated piezoelectric elements 23 that can be driven independently.

The integrated piezoelectric element unit 25, hammer body 34 and base plate 35 are inserted into a fixing member 26 made of a resin material having windows formed at the center and rear. Upper surface of hammer body free end 34b and fixing member 26
After the upper surface of the base plate 34 becomes flat,
And the insulating substrate 21 are bonded and fixed to the fixing member 26.

The upper surface of the fixing member 26 and the free end 3 of the hammer body
The thin diaphragm 27 is laminated on a plane formed by the upper surface of the diaphragm 4b. The vibration plate 27 is bonded to the upper surface of the free end 34b of the hammer body and the upper surface of the fixing member 26. Here, the diaphragm 27 is a nickel plate of about several μm formed by an electroforming method. Further, the flow path substrate 28 provided with the pressure chamber 32 and the ink supply port 33 corresponding to each of the hammer bodies 34 and formed of a resin material is bonded. The unit manufactured in this manner is hereinafter referred to as a head unit 10.

Here, the hammer body 34 is a member made of a lightweight and highly rigid material such as aluminum and the like.
a, free end 34b, cutout 34c and joint 34
has d. This hammer body 34 is a hammer body joint 34
With d as a fulcrum, the lower part of the laminated piezoelectric body 20 is set as a point of force, and acts as a lever with the upper surface of the free end 34b of the hammer as a point of action. The joint 34d acts as a leaf spring, and the natural frequency of the vibration system centered on the spring is about 50 kHz or higher, which is sufficiently higher than the printing cycle frequency of 7.2 kHz. In addition, the cut portion 34c is provided to adjust the spring constant and, consequently, the natural frequency by changing the thickness of the joint portion 34d.

A voltage is applied to one laminated piezoelectric element 23 to extend the same, and the upper surface of the free end 34b of the hammer body is lowered downward. By displacing the diaphragm 27 by displacing｝ times downward and deforming the diaphragm 27, the volume of the pressure chamber 32 is increased and ink is sucked. Thereafter, if the applied voltage of the laminated piezoelectric element 23 is reduced to zero and the amount of extension is reduced to zero, the upper surface of the free end 34b returns to the original position by the leaf spring action of the hammer body 34, thereby reducing the volume of the pressure chamber 32. Ejects ink.

As can be seen from the above, the laminated piezoelectric element 23
Is amplified by the lever action of the hammer body, the number of layers is reduced by ｛(the distance between the operating point and the fulcrum) / (the power point-) as compared with the case where the volume of the pressure chamber 32 is directly increased or decreased by the laminated piezoelectric element 23. (Distance between fulcrum points) can be reduced to about 1 /｝, and the structure of the laminated piezoelectric element 23 can be made robust. The applied voltage of the laminated piezoelectric element 23 is zero in the standby state in which the discharging operation is not performed, and the maximum voltage is applied only for a very short time during the discharging operation. Therefore, a malfunction due to a leak current that occurs when a high voltage is applied for a long time as in the related art does not occur without taking special measures.

FIG. 2 is an exploded perspective view of the head unit 10. As shown in FIG.

FIG. 1 is an exploded perspective view of the entire ink jet head constituted by using the head unit 10 formed as described above. The head unit 10 is inserted into the window of the frame 11 made of a resin material, and the head unit end surface 10a and the end surface 11a of the frame 11 are positioned so as to be flush with each other. An adhesive is filled in the gap with the unit 10 and fixed. Thereafter, the nozzle plate 13 having the nozzles 12 formed thereon is bonded to the head unit end face 10a and the end face 11a of the frame body 11 to form an ink jet head.

FIG. 5 is a sectional view of a head unit of an ink jet head for explaining a second embodiment of the present invention.

As in the first embodiment, an electrode layer 61 is sequentially laminated on a piezoelectric material plate 60 and then fired to form a laminated piezoelectric body 50 on an insulating substrate 51 made of an insulating material such as ceramic. Glue. Further, a groove is formed from the upper surface of the laminated piezoelectric body 50 by a mechanical processing means such as a wire saw to divide the laminated piezoelectric body 50 into laminated piezoelectric elements that can be independently driven to form a piezoelectric element unit 55. An external drive voltage is supplied by an FPC (flexible print cable) 54.

The insulating substrate 51, the laminated piezoelectric body 50 and the F
The piezoelectric element unit 55 constituted by the PC 54 and the hammer body 64 are bonded to the base plate 65 such that the upper surface of the laminated piezoelectric body 50 is in contact with the upper side surface of the joining portion 64d of the hammer body 64 as shown in FIG. The integrated piezoelectric element unit 55, hammer body 64, and base plate 65 are inserted into a fixing member 56 made of a resin material having windows formed at the center and rear. After the upper surface of the hammer body free end 64b and the upper surface of the fixing member 56 are made flat, the base plate 64 and the insulating substrate 51 are bonded and fixed to the fixing member 56.

That is, in the first embodiment, the piezoelectric element pushes the hammer body directly below, whereas in the second embodiment, the piezoelectric element pushes in the lateral direction. As can be seen from FIG.
As compared with the embodiment, there is no portion where the piezoelectric body overlaps the hammer body in the vertical direction, so that there is an advantage that the head unit can be made thinner.

[0020]

According to the present invention, since the displacement of the laminated piezoelectric element is amplified by the lever action of the hammer, the number of laminated piezoelectric elements is reduced as compared with the case where the volume of the pressure chamber is directly increased or decreased by the laminated piezoelectric element. The structure of the portion of the laminated piezoelectric element can be made firm. Further, since the constituent members other than the laminated piezoelectric element are not brittle and have high strength as compared with the laminated piezoelectric element, a robust small-sized and high-density inkjet head can be configured.

The applied voltage of the laminated piezoelectric element is zero in a standby state in which the discharging operation is not performed, and the maximum voltage is applied only for a very short time during the discharging operation. Therefore, a malfunction due to a leak current does not occur even if no special measures are taken.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an inkjet head according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a head unit according to the embodiment of the present invention.

FIG. 3 is a perspective view of a piezoelectric element unit according to the embodiment of the present invention.

FIG. 4 is a sectional view of a head unit according to the embodiment of the present invention.

FIG. 5 is a sectional view of a head unit according to a second embodiment of the present invention.

FIG. 6 is an exploded perspective view showing a conventional technique.

[Explanation of symbols]

 Reference Signs List 10 head unit 11 frame 13 nozzle plate 21, 51 insulating substrate 22a, 22b, 52a, 52b collector electrode 23 laminated piezoelectric element 24, 54 FPC 25, 55 piezoelectric element unit 26, 56 fixing member 27, 57 diaphragm 28, 58 Flow path substrate

Claims (2)

[Claims] 1. A method according to claim 1, wherein a vibration plate forming one pressure wall of the pressure chamber is deformed by using a displacement of the piezoelectric element to pressurize ink filled in the pressure chamber and eject ink droplets from a nozzle communicating with the pressure chamber. In an inkjet head, a piezoelectric element unit in which a plurality of laminated piezoelectric elements are bonded on an insulating substrate, a hammer, a base plate, a fixing member that holds the piezoelectric element unit, the hammer, and the base plate, and a free end of the hammer A head unit composed of a diaphragm adhered on a fixing member and a flow path substrate formed with a pressure chamber and an ink supply port adhered on the diaphragm is fixed to a frame, and a nozzle plate is provided on an end surface of the head unit and a frame surface. An ink-jet head, characterized by adhering. 2. The ink jet head according to claim 1, further comprising a piezoelectric element having a polarization direction in the same direction as the electric field direction and having the same piezoelectric strain constant d33 as the polarization direction.