Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-01-06
2002-03-12
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S010000, C347S068000
Reexamination Certificate
active
06354685
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a driving device and a driving method of an on-demand ink jet printer head, and in particular, to a driving device and a driving method of an on-demand ink jet printer head by which discharge of minute ink drops from orifices of the printer head can be executed correctly and stably according to image data, and thereby high quality printed output can be obtained with high stability.
DESCRIPTION OF THE PRIOR ART
Ink jet printers are generally classified into two types according to their ink drop discharging method: continuous ink jet printers and on-demand ink jet printers. In a continuous ink jet printer, the printer head constantly discharges ink drops continuously and only ink drops necessary for generating images are allowed to reach an object such as paper. In an on-demand ink jet printer, the printer head selectively discharges ink drops which are necessary for generating images.
The on-demand ink jet printer head is generally provided with orifices (nozzles) for discharging ink drops and a mechanism for controlling the discharging operation of the printer head from the orifices according to image data. In the on-demand ink jet printer head, a pressure generation means is generally provided to each ink chamber corresponding to an orifice, and ink drops are discharged from each orifice onto the object such as paper due to acoustic waves which are generated by the pressure generation means corresponding to the orifice. In the ink drop discharging method using the pressure generation means, at least a part of walls of the ink chamber is deformed by an electric-mechanic transducer (actuator) so as to generate acoustic waves, and ink drops are discharged by the acoustic energy of the acoustic waves.
In another ink drop discharging method, an electric-thermal transducer is provided to each ink chamber corresponding to an orifice. The ink is heated and vaporized into bubbles by the electric-thermal transducer so as to generate acoustic waves, and ink drops are discharged by acoustic energy of the acoustic waves.
In printers employing such ink drop discharging methods, a printer head unit having a plurality of orifices for discharging ink drops is mounted on a carrier with an ink cartridge. The carrier which is driven by a motor moves above the object such as paper in scanning movement. Along with the scanning movement of the carrier, ink drops are discharged from the orifices according to timing based on image data, and thereby an image according to the image data is generated on the object by the applied ink dots.
Some measures have been taken to realize high speed printing. The number of orifices has been increased so as to increase the number of simultaneously printed ink dots, and the ink discharge frequency (printing frequency) of each orifice (i.e. the driving frequency of the printer head) has been raised by optimizing the total configuration of the ink channel from the ink cartridge to the edge of the orifice.
The ink used for the ink jet printer is roughly divided into water-base ink and non-water-base ink. The water-base ink has the following advantages:
(1) The tolerances of physical properties (surface tension, viscosity, etc.) of the ink are wide and thus the stability of ink drop discharge properties can be made high.
(2) The main solvent is water and thus the change of physical properties due to volatilization does not occur much.
(3) Safe, stable, and easily handled.
(4) Good color development on paper.
On the other hand, the non-water-base ink has the following advantages:
(1) The materials for the printed object can be selected widely (iron, ceramic, etc.).
(2) Superior fixation on the printed object, little blur of ink.
(3) High water-resistance of prints.
The water-base ink is mainly used today for general and personal use, from the viewpoint of print quality, reliability of the printer head, etc.
In the water-base ink, coloring agents (dyes, pigments, etc.) and a variety of agents such as ink property control agents (surface-active agents, pH control agents, high-boiling-point agents) are mixed together. The agents are mixed together in a proper mixture ratio, in consideration of synergistic effects of the agents, physical properties of the ink, structure design of the printer head, etc.
The solubility in the main solvent varies depending on dyes, that is, depending on the color of ink, and thus agents such as die-solubility accelerator becomes necessary for some colors. Therefore, the type and the amount of additives vary depending on ink colors and thus the properties and stability of ink are necessitated to vary depending on colors. In order to raise the color density on the object and obtain vivid print, the amount of the coloring agent in ink has been increased.
The ink in the orifice of the ink jet printer head has a meniscus, that is, the interface of the ink to air. The meniscus has a concave curve which is caused by surface tension of the ink and a negative pressure of the ink cartridge. Evaporation of volatile ingredients of the ink easily occurs around the meniscus and thereby the properties of the ink tend to change around the meniscus. Especially, the viscosity of the ink tends to increase near the meniscus.
Due to the change of ink properties, the statuses of discharged ink drops are easily deteriorated when the ink is discharged after a long pause. Especially, change in the size of an ink drop, decrease of ink drop speed, variations in flying direction of ink drops, etc. occur, and thereby the quality of print is necessitated to be deteriorated. If the statuses of the ink around the meniscus gets worse, the orifice is stopped up with ink and ink discharge becomes difficult or impossible, causing fatal flaws in the printed output.
Some printer head maintenance methods have been proposed for avoiding the change of ink properties in the orifices (especially, the ink coagulation due to evaporation of volatile ingredients). In the following, a few conventional techniques for avoiding the ink coagulation due to change of ink properties will be explained.
In a conventional “ink jet printing method” disclosed in Japanese Patent Application Laid-Open No.SHO57-61576, each piezoelectric element which is used for discharging ink drops is driven also in pause periods with a voltage that is lower than a threshold voltage necessary for discharging the ink drops. In the conventional technique, an electric-mechanic transducer (i.e. the piezoelectric element) which is used for discharging ink drops is driven by the lower voltage (by which ink drops are not discharged) so as to give subtle vibration to the meniscus, and thereby the ink coagulation is prevented.
A conventional ink jet printing device is provided with an energy increase means which increases initial ink discharge energy in the case where ink drop discharge is restarted after a discharge pause period that is longer than a predetermined period. In the conventional technique, the ink discharge energy when the ink drop discharge is restarted is increased so that the properties of discharged ink drops such as speed, size, etc. will be close to those in continuous ink drop discharge operation.
The above conventional techniques could be employed for discharging ink drops stably in the case where the size of an ink drop is larger than the size of the orifice, since the ink drop discharge properties could have enough margins, that is, since a little environmental change did not exert effects on the ink drop discharge properties. However, the conventional techniques can not be employed for discharging ink drops stably and uniformly in the case where ink drops smaller than the diameter of the orifice are discharged by means of meniscus position control and acoustic wave control. In such cases, if the pause continues longer than a certain period, the ink drop discharge properties deteriorate considerably (decrease in speed and size of the ink drop, unstable flying statuses of the ink drops, etc.) causing shift of ink dot positions, uneven diameter o
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