Incremental printing of symbolic information – Ink jet – Controller
Patent
1996-12-13
2000-08-22
Barlow, John
Incremental printing of symbolic information
Ink jet
Controller
B41J 2938
Patent
active
061060917
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of driving an ink-jet head which selectively deposits ink droplets on an image recording medium, for example, paper.
BACKGROUND TECHNOLOGY
Of non-impact printers which are largely increasing their shares in the market nowadays, ink-jet printers are the simplest in principle, and also suitable for color printing. Of the ink-jet printers, so-called drop-on-demand (DOD) type ink-jet printers, which eject ink droplets only at the time of forming dots, are the most popular.
As a so-called piezoelectric ink-jet head using piezoelectric actuators among ink-jet heads for the DOD type ink-jet printers, there are a Kaiser type one as disclosed in Japanese Patent Publication No. 53-12138, a laminated piezoelectric actuator type one as disclosed in Japanese Patent Laid-Open Publication No. 6-8427, and a share-mode type one as disclosed in Japanese Patent Laid-Open Publication No. 63-252750.
In the piezoelectric ink-jet heads, motions of supplying ink to ink chambers from an ink supply source leading to the ink chambers, and a motion of ejecting ink droplets through nozzle holes formed in the ink chambers are executed by deforming the piezoelectric actuators with a voltage applied thereon, thus changing an inner volume of each of the ink chambers.
Conventional piezoelectric ink-jet heads are driven in a manner described hereafter. The wall faces of ink chambers are partially deformed by applying a voltage varying in a pulse waveform to the piezoelectric actuators, thereby increasing an inner volume of each of the ink chambers. In this step of driving operation, ink is supplied to the ink chambers.
Subsequently, the wall faces of the ink chambers are deformed in a reverse direction by stopping to apply the voltage to the piezoelectric actuators or by applying a voltage varying in a waveform of reverse polarity against the aforesaid waveform to the piezoelectric actuators, thus reducing the inner volume of each of the ink chambers. In this step of driving operation, ink is ejected through nozzle holes. Such a driving method is generally called the "pull-in shot" method.
FIG. 15 shows a pulse waveform of a voltage applied to the piezoelectric actuators and a displacement waveform of the piezoelectric actuators in a conventional method of driving an ink-jet head. In the figure, a waveform (a) indicates the pulse waveform of a voltage applied to the piezoelectric actuators, and a waveform (b) the displacement waveform of the piezoelectric actuators.
As shown in FIG. 15, the piezoelectric actuators which are in an initial condition over an interval of time T0 are charged with electric charge and deformed over an interval of time T1 when a voltage in a pulse waveform is applied thereto. Deformation of the piezoelectric actuators is accompanied by deformation of the walls of the ink chambers, increasing the inner volumes of the ink chambers and supplying ink into the ink chambers. Hereupon, free oscillation of the piezoelectric actuators as well as the ink in the ink chambers continues at a natural oscillation frequency even after deformation stops.
Electric charge that has built up in the piezoelectric actuators is discharged over an interval of time T2, and reverts to its initial condition. Hereupon, the inner volumes of the ink chambers are rapidly reduced, pressurizing the ink chambers and ejecting ink droplets out of the nozzle holes leading to the ink chambers. The free oscillation of the piezoelectric actuators continues at the natural oscillation frequency thereof centered around the initial position even after the ink droplets are ejected.
In the aforesaid conventional method of driving the ink-jet head, rapid supply of ink into the ink chambers is ensured, but on the other hand, the ink droplets are formed before the free oscillation that occurs in the piezoelectric actuators as well as the ink in the ink chambers damps out in case that the piezoelectric actuators are driven at a high frequency in order to increase printing speed. As a result, problems of
REFERENCES:
patent: 5757392 (1998-05-01), Zhang
Mitsuhasi Tadashi
Osawa Seiichi
Segawa Akio
Barlow John
Citizen Watch Co. Ltd.
Dickens C.
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