Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-09
2002-11-19
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S069000
Reexamination Certificate
active
06481833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Our invention relates to a driving method for an electrostatic inkjet head whereby ink drops are ejected from ink nozzles communicating with an ink pressure chamber by flexibly displacing the diaphragm of the ink pressure chamber by means of electrostatic force. More particularly, our invention relates to a method and/or a device for driving an electrostatic inkjet head so that ink pressure crosstalk between adjacent ink pressure chambers is prevented even when the ink pressure chambers are formed in a high density arrangement. Our invention also relates to an inkjet printer having such a driving device or employing such method.
2. Description of the Related Art
As taught in Japanese Unexamined Patent Application (kokai) 2-289351, for example, an electrostatic inkjet head has a diaphragm, which is a resonance electrode formed on the bottom of each ink pressure chamber part of the ink path, and an electrode plate, which is an individual electrode disposed opposite the diaphragm with a specific small gap therebetween. The internal volume of the ink pressure chamber is changed by applying a specific drive voltage between these opposing electrodes of a desired ink nozzle to produce the electrostatic force causing the diaphragm to bend. The resulting change in ink pressure is used to eject an ink drop from the ink nozzle communicating with the driven ink pressure chamber, thereby recording on an opposing recording medium.
A large number of ink nozzles must be disposed in a high density arrangement in order to achieve high quality output from this type of electrostatic inkjet head. This requires a similarly high density arrangement of the ink paths communicating with the ink nozzles, and more specifically the ink pressure chambers associated with the ink nozzles. The walls partitioning the ink pressure chambers by necessity must therefore be extremely thin.
A problem that arises when the walls dividing the ink pressure chambers are very thin is that a change in pressure in the ink pressure chamber can cause the partitioning wall to bend. That is, as shown in
FIG. 13A
, when diaphragm
23
(
3
) of ink pressure chamber
22
(
3
), in communication with driven ink nozzle
21
(
3
) from which an ink drop is to be discharged, is attracted to individual electrode
25
(
3
), partitioning walls
24
(
2
) and
24
(
3
) might bend as a result of the internal pressure change in the ink pressure chamber
22
(
3
).
As shown in
FIG. 13B
, when diaphragm
23
(
3
) separates from individual electrode
25
(
3
) when an ink drop is discharged, partitioning walls
24
(
2
) and
24
(
3
) can likewise bend as a result of the internal pressure change in the ink pressure chamber
22
(
3
).
When the partitioning walls bend during ink discharge, pressure loss occurs in ink pressure chamber
22
(
3
), and an ink drop of the desired volume or diameter may not be discharged from the driven ink nozzle
21
(
3
).
Furthermore, when partitioning walls
24
(
2
) and
24
(
3
) between the driven ink nozzle
21
(
3
) and adjacent non-driven ink nozzles
21
(
2
) and
21
(
4
) bend, pressure change also occurs in the ink pressure chambers
22
(
2
) and
22
(
4
) of the non-driven ink nozzles. This pressure change can produce a further undesired discharge of a very small ink drop from a non-driven ink nozzle.
Moreover, as a result of a pressure change leaking to an adjacent ink pressure chamber through intervening partitioning walls
24
(
2
) and
24
(
3
), or in other words due to the resulting ink pressure crosstalk, the internal pressure change occurring in the ink pressure chamber of the driven ink nozzle will differ according to whether an adjacent ink nozzle is simultaneously driven or not driven. As a result, the ink discharge characteristics (ink discharge speed and volume) of the driven ink nozzle vary according to the drive status of an adjacent ink nozzle, leading possibly to a drop in print quality.
A method for avoiding these problems is taught, for example, in Japanese Unexamined Patent Application (kokai) 5-69544 and 7-17039. The methods taught address these problems in an inkjet head in which the ink nozzles are arranged in line by using a delay circuit to offset the ink drop eject timing when adjacent even and odd numbered ink nozzles are driven to print on the same line.
This method, however, complicates the inkjet head driver circuit, and thus introduces new problems, specifically increased cost and slower printing because more time is required to print from adjacent ink nozzles.
In addition to the above problems, ink discharge characteristics can deteriorate due to pressure crosstalk between the ink pressure chambers of non-adjacent ink nozzles. That is, the ink pressure chambers of the individual ink nozzles generally communicate with a common ink chamber. Ink pressure crosstalk can thus be relayed between non-adjacent ink pressure chambers by way of this common ink chamber, thus degrading ink discharge characteristics and preventing normal, stable ink drop discharge.
OBJECTS OF THE INVENTION
With consideration for the aforementioned problems, an object of our invention is to provide a method and a device for driving an electrostatic inkjet head so that ink discharge operations can be accomplished without bending partitioning walls between ink pressure chambers, thereby preventing pressure crosstalk between ink pressure chambers even in high density arrangements, and assuring high resolution, precise print quality.
A further object of our invention is to provide a method and a device for driving an electrostatic inkjet head so that ink discharge operations can be accomplished without bending partitioning walls between ink pressure chambers and without inviting complication of the inkjet head driver circuit or a drop in printing speed. Our invention can thus prevent pressure crosstalk between ink pressure chambers even in high density arrangements, and easily assure high resolution, precise print quality.
A yet further object of our invention is to provide a method and a device for driving an electrostatic inkjet head for preventing pressure crosstalk between ink pressure chambers communicating with the ink nozzles, and easily assuring high resolution, precise print quality, even when a large number of ink nozzles is arranged in line.
A yet further object of our invention is to provide a printer employing our novel electrostatic inkjet head driver device.
SUMMARY OF THE INVENTION
To achieve these objects, the drive method of our invention applies to an electrostatic inkjet head having at least first and second ink pressure chambers separated by a partitioning wall, first and second ink nozzles communicating respectively with the ink pressure chambers, first and second diaphragms that are flexibly displaceable and form part of a wall of the first and second ink pressure chambers, and first and second individual electrodes opposing the diaphragms. An ink drop is discharged from the first ink nozzle by applying a drive voltage between the first diaphragm and first individual electrode to flexibly displace the first diaphragm. Our drive method has a second diaphragm attracting step for attracting the second diaphragm to the second individual electrode and maintaining contact therebetween; and a discharge step for flexibly displacing (releasing) the first diaphragm to discharge an ink drop from the first ink nozzle.
To discharge an ink drop from a first ink nozzle, that is, a driven ink nozzle, the electrostatic inkjet head drive method of our invention holds the diaphragm of the second ink pressure chamber communicating with the second ink nozzle, which is non-driven and does not discharge, attracted to and in contact with the corresponding second individual electrode. Elastic displacement of the second diaphragm is thus restricted and the rigidity of the second ink pressure chamber walls is high so that compliance of the second ink pressure chamber is low. As a result, movement and bending of the partitioning wall separating the second non-dischar
Fujii Masahiro
Ishikawa Hiroyuki
Matsuno Yasushi
Nguyen Thinh
Seiko Epson Corporation
Watson Mark P.
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