Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-03-23
2001-01-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06174038
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink jet printer for recording text, symbols, images, and other printing data by ejecting minute ink drops, and relates particularly to a control method for an ink jet printer whereby clogging of nozzles by ink that has become more viscous in the area of the nozzles is prevented.
RELATED TECHNOLOGY
Various methods of driving the nozzles of an ink jet recording device to eject recording ink from the nozzles have been disclosed and are today used on such ink jet recording devices. These methods include using a piezoelectric element as the driving means as taught in Japan Examined Patent Publication (kokoku) 2-51734 (1990-51734); ejecting ink using a heating element for heating the ink as disclosed in Japan Examined Patent Publication (kokoku) 61-59911 (1986-59911); and ejecting ink from the nozzles by using an electrostatic actuator to vibrate a diaphragm by means of electrostatic force as disclosed in Japanese Patent Application (Tokkai) 7-81088.
Generally speaking, such ink jet printers buffer an image signal to RAM or other storage devices, and then selectively drive the appropriate pressure generating means, i.e., piezoelectric element, heating element, or electrostatic actuator, disposed near each nozzle to eject ink and print to a recording medium based on the buffered image signal data.
A problem common to each of these ink jet printer designs is that when ink is not ejected from the nozzles for a certain period of time, ink around the nozzles tends to dry due to evaporation of moisture or other ink solvent. This results in increased viscosity in ink near the nozzles.
When the viscosity of ink near the nozzles thus rises, the nozzles tend to clog, thus completely preventing ink from being ejected during printing, or preventing ink from being ejected at the normal dot size and speed. This increased ink viscosity can also slow the refill rate of ink to the nozzles, thereby preventing the nozzles from being refilled at the same rate ink is ejected. Air can become mixed with the ink when this happens, thus preventing ink drops from being ejected.
To avoid the above problems, many ink jet printers cover the nozzles with a cap when printing (recording) is not in progress. This prevents the nozzles from drying, and prevents an increase in the viscosity of ink around the nozzles.
In addition to such methods of covering the nozzles with a cap, many methods of preventing ink blockage near the nozzles by regularly ejecting microdrops of ink from all nozzles separately from the printing process have also been proposed. These methods also help maintain and recover printing performance.
Exemplary of these methods is the recovery process method disclosed in Japan Examined Patent Publication (kokoku) 6-39163 (1994-39163) for reliably expelling high viscosity ink without introducing air to the nozzles even when the viscosity of ink around the nozzles rises. This is accomplished by setting the ink jet head drive frequency used during the recovery ejection operation lower than the highest drive frequency used when recording text or images.
Methods other than expelling high viscosity ink to recover the nozzles have also been disclosed. Exemplary of these is the method disclosed in Japan Unexamined Patent Publication (kokai) 56-129177 (1981-129177) for preventing nozzle clogging due to dry ink around the nozzles by using an oscillator to vibrate the ink at the resonance frequency of the ink jet head and mobilize the ink when recording is not in progress.
The various methods described above, however, leave the following problems unresolved.
(1) Each of the above methods requires two drive frequencies, a recording frequency for ejecting ink drops during recording, and a nozzle recovery frequency for driving a pressure generating means to prevent clogging, and these two frequencies must be used appropriately. The drive circuit and control thereof are thus complex.
(2) When an ink jet head having high viscosity ink around the nozzles is driven at a frequency lower than a drive frequency used during normal recording as taught in Japan Examined Patent Publication (kokoku) 6-39163 (1994-39163), it can be difficult to expel high viscosity ink in ink jet heads in which the pressure generated by the pressure generating means is itself low. This method therefore cannot be used with all types of ink jet printers.
(3) The viscosity also rises throughout the upstream ink path leading to the nozzles, and not just around the nozzles, after a certain amount of time has passed even if the ink is mobilized by vibrating the ink at the resonance frequency of the ink jet head when recording is not in progress as taught in Japan Unexamined Patent Publication (kokai) 56-129177 (1981-129177). Ink ejecting thus eventually becomes impossible. As a result, this method cannot be used for applications in which normal ink jet recording is not performed for a certain period of time, i.e., a no-ejection condition continues for a certain period of time.
(4) When recording is not in progress the ink viscosity increases around all of the nozzles. During recording, however, fresh ink is constantly supplied to frequently used nozzles and the ink viscosity at those nozzles is therefore low while the ink viscosity around less frequently used nozzles increases. This means that both high viscosity and low viscosity nozzles can be found in the same ink jet head during recording. While the less frequently used nozzles could be maintained by frequent maintenance (recovery) ejecting therefrom, this necessitates analyzing the recording data to determine the no-ejection time for each nozzle. This, however, is difficult to accomplish for each of the more than one-hundred or so nozzles on an ink jet head. A method whereby all nozzles are regularly operated for nozzle recovery is therefore used on the assumption that none of the nozzles has ejected once since the last operation. This method, however, results in the wasteful consumption of ink by frequently used nozzles, nozzles for which such nozzle recovery ejecting is not necessary.
An object of the present invention is therefore to provide an ink jet printer whereby nozzle clogging can be reliably prevented by means of a simple method and construction, thereby resolving the above problems.
A further object of the present invention is to reduce the amount of ink consumed by the recovery process for preventing nozzle clogging.
SUMMARY OF THE INVENTION
To achieve the above objects, a drive method for an ink jet printer comprising a plurality of nozzles for ejecting ink drops, pressure generating means disposed corresponding to said nozzles for pressurizing ink in said nozzles, and a means for transporting said nozzles relative to a printing medium for printing, generates a reference signal of a single frequency, and applies to each pressure generating means of the ink jet printer synchronized to the reference signal one of the following: a first electric pulse of an amplitude enabling ink drop ejecting, and a second electric pulse of an amplitude lower than the amplitude of the first electric pulse for mobilizing ink inside a nozzle.
In addition, an ink jet printer having a plurality of nozzles for ejecting ink drops, pressure generating means disposed corresponding to said nozzles for pressurizing ink in said nozzles, and a means for transporting said nozzles relative to a printing medium for printing, comprises a reference signal generation means for generating a reference signal of a single frequency, and a drive means for applying to each pressure generating means synchronized to the reference signal one of the following: a first electric pulse of an amplitude enabling ink drop ejecting, and a second electric pulse of an amplitude lower than the amplitude of the first electric pulse for mobilizing ink inside a nozzle.
An ink drop is ejected from a nozzle for recording to a recording medium when a first electric pulse is applied to a pressure generating means. Recording to a recording medium can thus be accomplished by selectively
Kobayashi Naoki
Minowa Masahiro
Nakazawa Chiyoshige
Barlow John
Seiko Epson Corporation
Stewart Jr. Charles W.
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