Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-08-30
2002-10-29
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S071000
Reexamination Certificate
active
06471342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head used in an ink jet printer.
2. Description of Prior Art
Japanese Patent Laid-Open Publication No. H9-234864 discloses an example of an ink jet head. This ink jet head has a plurality of pressure chambers to which ink is supplied. The pressure chambers have one faces made of a common diaphragm. Provision is made such that a piezoelectric element bents the diaphragm to reduce the corresponding pressure chamber in volume, causing the nozzle connected to this pressure chamber to discharge the ink. Put on the common diaphragm is a common reinforcing plate, on which the piezoelectric elements are placed. Each individual electrode (upper electrode) is formed on the obverse surface of each piezoelectric element, while a common electrode (lower electrode) is formed on the reverse surfaces of the piezoelectric elements.
Each of the pressure chambers has a slender rectangular section in a plan elevation. In this ink jet head, such slender rectangular pressure chambers are transversely arranged. In this ink jet head, a block forming the pressure chambers is connected to a block forming an ink reservoir and ink discharge nozzles.
In this ink jet head of prior art, when it is intended to increase each maximum ink discharge amount such that the ink discharge can be controlled with good gradation, this introduces the problems that each pressure chamber is accordingly increased in size, a high dot density cannot be achieved and the entire head is increased in size. It is to increase the dot density as high as possible that each pressure chambers is formed in a slender rectangular shape. When each pressure chamber is formed in a slender rectangular shape, however, there is required high positioning precision for connecting the block forming the pressure chambers, the block forming the ink passages and the block forming the ink discharge nozzles to one another. This results in lowered yield.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink jet head which is advantageous in ink discharge control with good gradation, high dot density and compact head design.
The present invention achieves this object by improving an ink jet head in various points such as the diaphragm thickness, the deformation amount, the diaphragm shape (the shape of each of the openings of pressure chambers covered by the diaphragm), the arrangement of the pressure chambers and the like.
In an ink jet head comprising: a head main body in which formed are a plurality of pressure-chamber concave portions having supply ports for supplying ink and discharge ports for discharging ink; and a plate-like actuator which covers the pressure-chamber concave portions of the head main body, which forms a plurality of pressure chambers together with the pressure-chamber concave portions, and portions covering the pressure-chamber concave portions of which is deformable by field induction distortion serving as a drive source, causing ink in at least one pressure chamber to be discharged,
the ink jet head of the present invention is characterized in that the deformation amount of each deformable portion of the actuator is set such that the ratio A/V between the maximum discharge amount V (p
1
) of each pressure chamber and that area A (&mgr;m
2
) of each deformable portion of the actuator which corresponds to the opening area of each pressure-chamber concave portion, is not greater than 10000.
The maximum discharge amount V refers to the maximum amount of ink to be discharged from each pressure chamber when each deformable portion of the actuator is bent and deformed one time toward the inside of each pressure chamber.
The ratio A/V≦10000 means that a large amount of ink can be discharged even though each deformable portion of the actuator is small in area. This is advantageous in ink discharge control with good gradation. Further, the smaller area of each deformable portion is more advantageous in both high dot density and compact head design.
Preferably, the ratio A/V is in the range of 6000 to 10000.
To obtain a deformation amount such that the ratio A/V is not greater than 10000, it is preferable that each deformable portion of the actuator has a thickness of not greater than 8 &mgr;m and is made in the form of an oval in which the ratio L/S of the shorter diameter S to the larger diameter L is in the range of 1 to 3. According to such an arrangement, a large deformation amount can be obtained even though each deformable portion of the actuator is reduced in area. This is more advantageous in ink discharge control with good gradation, high dot density and compact head design.
Preferably, each deformable portion of the actuator has a maximum thickness in the range of 2 to 8 &mgr;m.
Preferably, the actuator comprises: a diaphragm which covers the pressure-chamber concave portions of the head main body and which forms the pressure chambers together with the pressure-chamber concave portions; piezoelectric elements, each in the form of a thin film, respectively disposed for the pressure chambers and bonded to the diaphragm at the deformable portions thereof which form the pressure chambers, each piezoelectric elements being arranged to deform each deformable portion to discharge ink in each pressure chamber; and individual electrodes respectively disposed for the piezoelectric elements for applying a voltage thereto, each deformable portion of the diaphragm having a thickness of 1 to 5 &mgr;m.
A field induction distortion of a piezoelectric element bends and deforms that deformable portion of the diaphragm to which this piezoelectric element is bonded. This changes the corresponding pressure chamber in volume to cause ink therein to be discharged. Since each deformable portion of the diaphragm has a thickness of 1~5 &mgr;m, each deformable portion can be bent and deformed in a large amount as compared with its area.
In a ink jet head in which the pressure chambers are arranged in not less than three columns,
it is preferable that a group of electric contacts for individual electrodes, of the actuator, respectively disposed for the pressure chambers, is disposed outside of the outermost pressure-chamber column out of the pressure-chamber columns, and that a plurality of conductors for connecting, to the corresponding contacts of the group of electric contacts, the individual electrodes for the pressure chambers in the columns inside of the outermost pressure-chamber column, pass between adjacent pressure chambers in the outermost pressure-chamber column, the conductors above-mentioned passing at the head surface side.
More specifically, when the pressure chambers are arranged in not less than three columns, the dot density can be increased. However, if the electric contacts of the individual electrodes are disposed in the vicinity of the pressure chambers, it is required to provide contact spaces around the pressure chambers. This prevents the pressure chambers from being densely arranged. As a result, a number of ink discharge holes are extensively dispersedly disposed, contributing to the increase of the ink jet head in size. Thus, according to the present invention, there are utilized, as the wiring spaces, the spaces opposite to the top end faces of partition walls which partition adjacent pressure chambers (the spaces at the head surface side). Accordingly, the electric contacts can be gathered outside of the outermost pressure-chamber column, thus facilitating the wiring of the electric contacts. Further, the pressure chambers can densely be disposed. This is advantageous in both high dot density and compact head design.
When the ink jet head is arranged such that the plurality of pressure chambers are arranged in a plurality of columns, and that the actuator comprises: a diaphragm which covers the pressure-chamber concave portions of the head main body and which forms the pressure chambers together with the pressure-chamber concave portions; piezoelectric elements, each in the form of a thin film,
Fukano Akira
Horio Hideaki
Ikeda Koji
Miyazono Yutaka
Matsushita Electric - Industrial Co., Ltd.
Pham Hai
Studebaker Donald R.
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