Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-12-22
2002-09-17
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S068000
Reexamination Certificate
active
06450626
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet head which uses a piezoelectric actuator to discharge ink from a pressure chamber to the outside, a method for producing the same, and an ink jet type recording apparatus incorporating the same.
Ink jet heads which use a piezoelectric actuator to discharge ink from a pressure chamber to the outside are known in the prior art. A conventional ink jet head of this type is disclosed, for example, in Japanese Laid-Open Patent Publication No. 9-232644. As illustrated in
FIG. 11
, the conventional ink jet head includes a pressure chamber structure member b having a plurality of pressure chambers a which are filled with ink. A common electrode d is provided substantially entirely across one surface (the upper surface in the illustrated example) of the pressure chamber structure member b along which openings c are provided respectively for the pressure chambers a. Piezoelectric layers e and separate electrodes f, which form a piezoelectric actuator together with the common electrode d, are provided at respective positions on the common electrode d corresponding to the openings c of the pressure chambers a. Upon application of a voltage between the common electrode d and one of the separate electrodes f, a corresponding one of the piezoelectric layers e expands/contracts in the planar direction (the horizontal direction in the figure). Since the expansion/contraction of a portion (i.e., the lower portion in the figure) of the piezoelectric layer e on the side of the pressure chamber a is restricted by the common electrode d, the expansion/contraction of the piezoelectric layer e in the planar direction is converted to a displacement in the thickness direction (the vertical direction in the figure). As a result of this conversion, the piezoelectric layer e is displaced in the thickness direction entailing the common electrode d and the separate electrode f, thereby changing the volume of the pressure chamber a so as to discharge the ink from the pressure chamber a to the outside.
Another type of conventional ink jet head uses a restriction plate, in addition to the common electrode d, provided on one of the surfaces of each piezoelectric layer e which are perpendicular to the thickness direction thereof for restricting the expansion/contraction of the piezoelectric layer e in the planar direction on that surface. The expansion/contraction of the piezoelectric layer e in the planar direction is converted by the restriction plate into a displacement in the thickness direction.
In recent years, the popularity of personal computers has rapidly increased. Accordingly, there is an increasing demand for improving the printed image quality as much as possible. For the above-described type of ink jet heads, it is important to improve the performance of the piezoelectric actuator in order to meet the demand.
The present invention has been made in view of such circumstances in the prior art, and has an objective of improving the deformation characteristic of a piezoelectric actuator as much as possible so as to improve the ink discharging capability and thus the printed image quality.
SUMMARY OF THE INVENTION
In order to achieve the object described above, according to the first aspect of the present invention, there is provided an ink jet head, including: a pressure chamber structure member including a plurality of pressure chambers which are filled with ink, and a plurality of openings respectively for the pressure chambers which are provided along a predetermined surface of the pressure chamber structure member; and a piezoelectric actuator provided on one surface of the pressure chamber structure member along which the openings of the pressure chambers are provided, wherein: the piezoelectric actuator includes a piezoelectric layer which is provided substantially entirely across one surface of the pressure chamber structure member along which the openings of the pressure chambers are provided and which expands/contracts in a planar direction perpendicular to a thickness direction according to a direction of an electric field applied in the thickness direction; each portion of the piezoelectric actuator which corresponds to the opening of one of the pressure chambers and which generally corresponds to a center of the opening is defined as a displacement section, wherein when an electric field for expanding/contracting the piezoelectric layer in the planar direction is applied across a portion of the piezoelectric layer corresponding to the displacement section, the expansion/contraction of the piezoelectric layer in the planar direction is converted to a displacement in the thickness direction, whereby the displacement section is displaced in the thickness direction as a result of the conversion; each portion of the piezoelectric actuator which corresponds to the opening of one of the pressure chambers and which is in a vicinity of the displacement section is defined as an expansion/contraction section, wherein when an electric field for expanding/contracting the piezoelectric layer in the planar direction is applied across a portion of the piezoelectric layer corresponding to the expansion/contraction section, the expansion/contraction section expands/contracts in the planar direction by the expansion/contraction of the piezoelectric layer in the planar direction; and the displacement of the displacement section in the thickness direction is controlled by the expansion/contraction of the expansion/contraction section in the planar direction, so that the displacement of the displacement section in the thickness direction changes a volume of the corresponding pressure chamber, thereby discharging ink from the pressure chamber to the outside.
With such a structure, upon application of an electric field in the thickness direction of the piezoelectric layer of the piezoelectric actuator, the piezoelectric layer expands/contracts according to the direction of the electric field. Specifically, when the direction of the electric field is the same as the polarization direction of the piezoelectric layer (i.e., from the negative side to the positive side), the piezoelectric layer contracts in the planar direction. When the direction of the electric field is opposite to the polarization direction of the piezoelectric layer, the piezoelectric layer expands in the planar direction.
In either case, in the displacement section (which is defined as a portion of the piezoelectric actuator which corresponds to the opening of one of the pressure chambers and which generally corresponds to the center of the opening), an electric field is applied across the piezoelectric layer in the displacement section, whereby the piezoelectric layer expands/contracts in the planar direction, and the expansion/contraction of the piezoelectric layer in the planar direction is converted into a displacement in the thickness direction, whereby the displacement section is displaced in the thickness direction. The displacement of each displacement section of the piezoelectric actuator in the thickness direction changes the volume of the corresponding pressure chamber, thereby discharging ink from the pressure chamber to the outside.
At this time, in the expansion/contraction section of the piezoelectric actuator provided in the vicinity of each displacement section, an electric field is applied across the piezoelectric layer in the expansion/contraction section, whereby the piezoelectric layer expands/contracts in the planar direction, and the expansion/contraction section is expanded/contracted in the planar direction by the expansion/contraction of the piezoelectric layer in the planar direction. By the expansion/contraction of each expansion/contraction section in the planar direction, the displacement of the corresponding displacement section in the thickness direction is controlled. For example, if the expansion/contraction section expands when the displacement section is displaced from the flat shape into a convex or concave shape, the amount of displaceme
Ikeda Koji
Matsuo Koji
Matsushita Electric - Industrial Co., Ltd.
Nguyen Thinh
LandOfFree
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