Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-07-21
2001-02-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06190004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inkjet recording apparatus which is capable of ejecting particulate matter such as pigment matter and toner matter by making use of an electric field, and more particularly to voltage control for the inkjet recording apparatus.
2. Description of the Related Art
There has recently been a growing interest in non-impact recording methods, because noise while recording is extremely small to such a degree that it can be neglected. Particularly, inkjet recording methods are extremely effective in that they are structurally simple and that they can perform high-speed recording directly onto ordinary medium. As one of the inkjet recording methods, there is an electrostatic inkjet recording method.
The electrostatic inkjet recording apparatus generally has an electrostatic inkjet recording head and a counter electrode which is disposed behind the recording medium to form an electric field between it and the recording head. The electrostatic inkjet recording head has an ink chamber which temporarily stores ink containing toner particles and a plurality of ejection electrodes formed near the end of the ink chamber and directed toward the counter electrode. The ink near the front end of the ejection electrode forms a concave meniscus due to its surface tension, and consequently, the ink is supplied to the front end of the ejection electrode. If positive voltage relative to the counter electrode is supplied to a certain ejection electrode of the head, then the particulate matter in ink will be moved toward the front end of that ejection electrode by the electric field generated between the ejection electrode and the counter electrode. When the coulomb force due to the electric field between the ejection electrode and the counter electrode considerably exceeds the surface tension of the ink liquid, the particulate matter reaching the front end of the ejection electrode is jetted toward the counter electrode as an agglomeration of particulate matter having a small quantity of liquid, and consequently, the jetted agglomeration adheres to the surface of the recording medium. Thus, by applying pulses of positive voltage to a desired ejection electrode, agglomerations of particulate matter are jetted in sequence from the front end of the ejection electrode, and printing is performed.
A first example of such an electrostatic inkjet recording apparatus has been disclosed in Japanese Patent Unexamined Publication No. 62-13379. According to this conventional apparatus, a pulse voltage of one of positive and negative polarities and a predetermined pulse width is applied to the counter electrode to achieve stable inkjet recording regardless of ink resistance.
A second example has been disclosed in Japanese Patent Unexamined Publication No. 1-204750. This conventional apparatus is provided with a bias means and a pressure generating mechanism. The bias means applies a constant bias voltage to a counter electrode. The pressure generating mechanism periodically presses an ink chamber to form constant meniscuses at the ejection nozzle. With the constant bias voltage applied, a recording pulse is further applied to a selected one of the recording electrode in synchronization with the periodical pressing operation of the pressure generating mechanism.
In the first conventional example (Publication NO, 62-13379), however, the pulse voltage is applied to the counter electrode so as to inject charges into ink meniscuses regardless of the recording pulse signal for ejecting ink from the recording electrode. In other words, the pulse voltage applied to the counter electrode is not designed for ink ejection.
On the other hand, the second conventional example (Publication NO. 1-204750) needs the pressure generating mechanism for periodically presses the ink chamber to form constant meniscuses at the ejection nozzle. Therefore, the structure of the inkjet head becomes complicated, resulting in increased cost. Further, the bias voltage is continuously applied to the counter electrode during inkjet recording operation.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an inkjet recording apparatus which can reliably and stably eject ink from an ejection electrode with miniaturization and cost reduction of control circuit.
According to an aspect of the present invention, an inkjet recording apparatus is comprised of an ink chamber containing ink including particulate matter, an electrophoresis electrode placed in a side of the ink chamber, a plurality of ejection electrodes arranged in the ink chamber, and a counter electrode placed at a predetermined distance from the ejection electrodes which are directed to the second electrode. In such a constitution, a controller controls the ejection electrodes and the counter electrode at predetermined intervals such that a first voltage pulse is applied to a selected ejection electrode depending on input data and a second voltage pulse is applied to the counter electrode in synchronization with the first voltage pulse, wherein the first and second voltage pulses produce a voltage difference between the selected ejection electrode and the second electrode, wherein the voltage difference is not smaller than a predetermined threshold voltage which is a minimum value which causes ejection of particulate matter from the selected ejection electrode.
The controller may control the electrophoresis electrode such that a constant voltage is applied to the electrophoresis electrode to produce a voltage difference between the electrophoresis electrode and the counter electrode so as to cause electrophoresis of the particulate matter in the ink chamber.
As described above, since the first and second voltage pulses produce the voltage difference between the selected ejection electrode and the second electrode, the voltage applied to each ejection electrode can be lowered, resulting in enhanced miniaturization and cost reduction.
Further, in the case where a voltage difference is produced between the electrophoresis electrode and the counter electrode so as to cause electrophoresis of the particulate matter, the voltage difference between the electrophoresis electrode and the counter electrode varies according to the second voltage pulse applied to the counter electrode. Therefore, an appropriate amount of meniscus can be formed at the front end of each ejection electrode.
REFERENCES:
patent: 4684957 (1987-08-01), Miura et al.
patent: 4700204 (1987-10-01), Nakayama
patent: 5754200 (1998-05-01), Minemoto et al.
patent: 0774354 (1997-05-01), None
patent: 62-13379 (1987-01-01), None
patent: 1-204750 (1989-08-01), None
patent: 2-198855 (1990-08-01), None
patent: 9-164669 (1997-06-01), None
Japanese Office Action issued Apr. 27, 1999 in a related application.
English-language translation of relevant portions of Apr. 27, 1999 JPO Office Action.
Patent Abstracts of Japan, vol. 013, No. 506 (M-892), Nov. 14, 1989 & JP 01 204750 A (Ricoh Co Ltd), Aug. 17, 1989 *Abstract*.
Hagiwara Yoshihiro
Minemoto Hitoshi
Mizocuchi Tadashi
Shima Kazuo
Suetsugu Junichi
Barlow John
Gordon Raquel Yvette
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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