Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-04-14
2002-04-09
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06367914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic ink-jet head which ejects an ink drop from a pressurizing chamber onto recording paper through a nozzle opening by pressurizing the ink in the pressurizing chamber with an oscillation plate that is electrostatically actuated by an electrode opposite to the oscillation plate. Further, the present invention relates to a method of production of an electrostatic ink-jet head having an electrostatic actuator.
2. Description of the Related Art
Ink-jet heads are provided for ink-jet recording systems, which are included in various image forming systems such as printers, facsimiles, copiers, plotters, and other such image forming devices. In a typical, ink-jet head, an ink drop is ejected from a pressurizing chamber onto recording paper through a nozzle by pressurizing the ink in the pressurizing chamber. The pressurizing chamber communicates with the nozzle. An energy generating device is provided to generate energy used to pressurize the ink in the pressurizing chamber. When a driving voltage is applied to the energy generating device, the energy generating device generates the energy so that the ink-jet head ejects an ink drop from the nozzle onto the recording paper by pressurizing the ink in the pressurizing chamber. Currently, the on-demand ink-jet head is dominant in the related art. In ink-jet heads of this type, the head ejects ink drops onto the recording paper only when recording is required.
For example, as disclosed in Japanese Published Patent Application No. 2-51734, a conventional ink-jet head includes a plurality of nozzle openings arranged parallel to each other so as to eject ink drops therefrom, a plurality of pressurizing chambers respectively attached to the nozzle openings, each pressurizing chamber having walls one of which is arranged to function as a diaphragm, a plurality of piezoelectric elements respectively attached to the corresponding diaphragms, and a common ink cavity for supplying ink to each of the pressurizing chambers.
When a driving voltage is applied to any one of the piezoelectric elements in the above-mentioned ink-jet print head, the diaphragm corresponding to the one of the piezoelectric elements is mechanically deflected so that the volume of the pressurizing chamber corresponding to the diaphragm is instantaneously reduced and the ink in the pressurizing chamber is pressurized. As a result, an ink drop is ejected from the corresponding nozzle opening onto the recording paper.
However, the above piezoelectric type ink-jet print head requires much time and labor for mounting the piezoelectric elements on the pressurizing chambers because the piezoelectric elements must be attached to the outside of the pressurizing chambers through glass or resin plates forming the diaphragms or must be arranged in the inside of the pressurizing chambers. Further, it is very difficult for the piezoelectric ink-jet head to achieve high-speed, high-quality printing because the piezoelectric ink-jet head must be equipped with a larger number of nozzle openings for ejecting ink drops.
Further, as disclosed in Japanese Published Patent Application No.61-59911, another conventional ink-jet head is also known. In this ink-jet head, the ink in the pressurizing chamber is heated by a heater, so that the pressure in the pressurizing chamber is increased by the bubbles generated by evaporation of the ink. As a result, the ink-jet head ejects ink drops from the pressurizing chambers.
However, the above-mentioned heating system has a problem in that the operational life of the head is comparatively short because the heating resistors are damaged by the repetition of heating/cooling and by the shock at the time of the breaking of bubbles in the ink.
In order to eliminate the problems of the above conventional heads, an electrostatic ink-jet head has been proposed. As disclosed in Japanese Laid-Open Patent Application No. 6-71882, the electrostatic ink-jet head includes a plurality of nozzle openings, a plurality of pressurizing chambers respectively attached to the nozzle openings, diaphragms respectively disposed in the corresponding pressurizing chambers, a plurality of driving electrodes for respectively driving the corresponding diaphragms, and a common ink cavity for supplying ink to the plurality of pressurizing chambers. Each of the diaphragms defines a bottom of one of the pressurizing chambers. The diaphragms and the pressurizing chamber walls are arranged parallel to each other, and a parallel gap is provided between each diaphragm and the corresponding pressurizing chamber.
In the above-mentioned ink-jet print head, when driving pulses are applied to the driving electrodes, the driving electrodes respectively actuate the diaphragms via an electrostatic force in a direction to increase the pressures in the respective pressurizing chambers to eject ink drops from the nozzle openings onto recording paper.
In the electrostatic ink-jet head of the above type, the amount of displacement of the diaphragm and the electrostatic attraction pressure on the diaphragm, when the diaphragm is driven, are calculated as follows.
Suppose that the diaphragm has a rectangular shape including a short-side length “2
a
” and long-side length “
b
”. The amount of displacement &dgr; (m) of the thin plate (the diaphragm) is represented by
&dgr;=
k·{
12(1−&ngr;
2
)/
Eh
2
}·Pa
4
(1)
where “k” is a constant, “&ngr;” is Poisson's ratio, “E” is Young's modulus (N/m
2
), “h” is a thickness (m) of the diaphragm, and “P” is an electrostatic attraction pressure (N/m
2
) between the diaphragm and the electrode.
Further, in the electrostatic inkjet head of the above type, the electrostatic attraction pressure P (N/m
2
) between the diaphragm and the electrode is represented by:
P
=(1/2)·∈·(V/t)
2
(2)
where “∈” is a dielectric constant (F/m), “V” is the applied voltage (V), and “t” is a distance (m) between the diaphragm and the electrode.
In order to mount a larger number of nozzle openings on the electrostatic ink-jet head of the above type for achieving high-speed, high-quality printing, it is necessary to reduce the short-side length “a” of each of the diaphragms. However, as is apparent from the above equation (1), if the length “a” is reduced, the amount of displacement of the diaphragm is greatly decreased. Hence, the short-side length “a” of the diaphragm must be maintained at a certain level.
In order to allow adequate amount of displacement of the diaphragm for ejecting a proper amount of ink while maintaining the short-side length “a” of the diaphragm at a certain level, it is necessary to meet any of the following requirements in accordance with the equations (1) and (2): (i) the diaphragm thickness “h” must be reduced; (ii) the distance “t” between the diaphragm and the electrode must be reduced; and (iii) the driving voltage “V” must be increased.
Regarding the requirement (i) above, if the thickness “h” of the diaphragm is reduced, the rigidity of the diaphragm is greatly decreased, which will significantly lower the ink ejecting pressure of the diaphragm. Regarding the requirement (ii) above, if the distance “t” is reduced, the maximum amount of displacement of the diaphragm is decreased, which will considerably reduce the amount of ink drops ejected by the head and will cause defective printing on the recording paper. Regarding the requirement (iii) above, if the driving voltage “V” is increased the cost is considerably increased.
Accordingly, it is desired to provide an electrostatic ink-jet head which has a construction that overcomes the problems described above and achieves adequate amount of displacement of the diaphragm for ejecting a proper amount of ink while maintaining the short-side length of the diaphragm at a certain level.
Japanese Laid-Open Patent Application No. 9-39235 discloses an electrostatic ink-jet head in which a pressurizing chamber is provided and a bottom wall of the pressu
Ebi Yutaka
Hashimoto Kenichiro
Irinoda Mitsugu
Miyaguchi Yohichiro
Ohta Eiichi
Gordon Raquel Yvette
Greenberg & Traurig, LLP
Ricoh & Company, Ltd.
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