Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-01-04
2002-12-10
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06491378
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet head which ejects ink droplets so as to make the ink droplets adhere onto recording paper only when recording is demanded; an ink jet printer thereof; and a method for driving the ink jet head. In particular, the present invention relates to the prevention of a failure or abnormality in ink ejection.
2. Description of the Related Art
Generally, an ink jet head has pressure build-up chambers for applying pressure to ink so as to eject ink droplets. Then, one end of each pressure build-up chamber communicates with an ink tank through an ink supply channel while the other end of the pressure build-up chamber is provided with an ink nozzle for ejecting an ink droplet. In addition, a bottom portion of the pressure build-up chamber is formed to be deformable and used as a diaphragm. This diaphragm is elastically displaced by electromechanically converting means so as to generate pressure for ejecting an ink droplet from the ink nozzle.
A printer using such an ink jet head has excellent features such as low noise, low power consumption, and so on, and it has come into wide use as an output unit for an information processor. On the other hand, in the ink jet head, menisci in the ink nozzles are pushed out in unstable forms by remaining vibration generated in the pressure build-up chambers. As a result, unnecessary ink droplets constructing no printing may be ejected immediately after necessary ink droplets are ejected. The ejection speed of the unnecessary ink droplets constructing no printing is so low that they adhere to nozzle surfaces and cause a phenomenon such as ink nozzle clogging or dot missing. Thus, the reliability on printing is lowered.
Further, when the printer is left for a long time in the state where the ink jet head is not driven, water, or the like, which is a solvent of ink, evaporates through the ink nozzles. As a result, the viscosity of ink in the ink nozzles increases so that the ink nozzles are clogged. Moreover, with the increase of the ink viscosity, the refil speed of the ink nozzles with ink becomes so low that the refill quantity cannot follow the ink ejection quantity. As a result, bubbles are mixed into ink so that the ink jet head is in a non-ejection state where no ink droplet is ejected. Thus, the reliability on printing is lowered in the same manner as mentioned above.
In the background art, for the former where a failure in ejection is caused by ink adhesion to nozzle surfaces, the nozzle surfaces are rubbed with a wiper (wiped) before the beginning of printing or during a rest period of printing, so that the nozzle surfaces are prevented from wetting due to the adhesion of unnecessary ink droplets to the nozzle surfaces. Further, the publication JP-A-4-369542 discloses a technique in which a second voltage different from a first voltage for ejecting ink droplets is applied to electrostrictive members so as to separate ejected ink droplets and reduce the ejection of unnecessary ink droplets.
On the other hand, for the latter where a failure in ejection is caused by ink nozzle clogging and bubbles in ink, the operation of ejecting several shots of ink droplets, that is, so-called pre-ejection is performed before the beginning of printing or during a rest period of printing. Further, the publication of JP-A-9-30007 proposes a method in which a pulse with electric power at the level at which no-ink droplet is ejected from ink nozzles is applied to electrostrictive members so as to micro-vibrate menisci in order to prevent the ink nozzles from being filmed with ink.
However, the above-mentioned background-art techniques have problems as follows.
1. In the wiping operation, there was a problem that printing time was elongated because the ink jet head had to be moved to shelter at a place other than a print area at any time when wiping was performed. In addition, there was a problem that water-repellant coatings on the nozzle surfaces were deteriorated by the repeated wiping of the nozzle surfaces.
2. In the case where a voltage was applied to the electrostrictive members in order to separate ink droplets, characteristic differences between the electrostrictive members might make it impossible to separate the ink droplet well and might eject even unnecessary ink droplets. Thus, there was a problem that it was difficult to attain stable ejection and separation of ink droplets.
3. In the pre-ejection operation, there was a problem that ink irrelevant to printing was markedly consumed so that the life of the ink tank was shortened. In addition, there was a problem that printing time was elongated because the ink jet head had to be moved to shelter at a place other than a print area at any time when pre-ejection was performed.
4. In regard to the driving method to apply such a low pulse voltage as to eject no ink droplets, if this method was applied to an ink jet head using electrostatic driving actuators, it was difficult to set a driving condition on which menisci were vibrated without ejecting any ink. Accordingly, there was a problem that ink droplets were ejected, or enough vibrations of the menisci to avoid a failure in ink ejection were not obtained. In addition, it was necessary to give driving signals to driving elements for all the ink nozzles respectively. Accordingly, there was a problem that driving control was complicated, etc.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an ink jet head that eliminates or reduces printing trouble caused by a failure or abnormality in ink ejection; an ink jet printer using such an ink jet head; and a method for driving such an ink jet head.
SUMMARY OF THE INVENTION
(1) An ink jet head according to the present invention comprises a plurality of ink nozzles for ejecting ink, a plurality of ink chambers respectively communicating with a corresponding one of the ink nozzles, ink supply channels respectively supplying ink to a corresponding one of the ink chambers, elastically displaceable diaphragms respectively formed in a wall of a corresponding one of the ink chambers, and opposed electrodes oppositely arranged to the diaphragms through a gaps, to eject ink droplets from the ink nozzles by performing electric charge/discharge between the opposed electrodes and the diaphragms; wherein each of the opposed electrodes comprises a main electrode that can perform electric charge/discharge between it and a corresponding one of the diaphragms independently of the other main electrodes, and a sub-electrode that is electrically connected with the sub-electrodes for the other diaphragms.
In the present invention, the electrodes are driven in a desired combination (driving voltages are applied between the opposed electrodes and the corresponding diaphragm so as to perform electric charge/discharge therebetween), so that the quantity of ink ejected from an ink nozzle (density) can be adjusted in multiple stages. In addition, since each sub-electrode is electrically connected with the other sub-electrodes formed for the other diaphragms, a process for vibrating ink in the ink nozzles can be performed in common for the respective ink chambers. Thus, the control of such a process becomes easy.
(2) In the ink jet head according to the present invention as stated in paragraph (1), each main electrode is electrically charged and discharged selectively in accordance with a printing pattern, and a sub-electrode formed on the ink nozzle side is electrically connected with sub-electrodes formed for the other diaphragms. In the present invention, main electrodes are driven selectively in accordance with a printing pattern so that a process of printing is performed. In addition, sub-electrodes are driven appropriately so that ink in the ink nozzles can be vibrated or the effect of separating ejected ink droplets from the ink nozzles can be enhanced. That is, auxiliary electric charge is performed between a sub-electrode and diaphragm so that parts of the diaphragm are bent toward the sub-electrode. Thus, men
Fujii Masahiro
Ishikawa Hiroyuki
Matsuno Yasushi
Gabrik Michael T
Gordon Raquel Yvette
Seiko Epson Corporation
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