Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-08-09
2001-09-18
Tran, Huan (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S011000, C347S068000
Reexamination Certificate
active
06290315
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of driving an ink jet recording head used for a recording apparatus, such as a printer and a plotter, and more particularly to an ink jet recording head capable of plural kinds of ink drops of different volumes through the same nozzle orifice.
In the ink jet recording head used for the printing device, a called “pull and shoot” control method is used in which a pressure generating chamber is expanded, and then is contracted to eject an ink drop through a nozzle orifice. In this control method controls an expansion of the pressure generating chamber to thereby control the volume of an ink drop to be ejected.
To eject a relatively large ink drop, the pressure generating chamber is controlled so that the meniscus (free surface) of ink in the nozzle orifice stays at a position near the front edge of the nozzle orifice, and then the pressure generating chamber is contracted. As a result, a large amount of ink is ejected through the nozzle orifice, to form an ink drop for forming a large dot.
To eject a relatively small ink drop, the pressure generating chamber is expanded so as to pull the meniscus toward the pressure generating chamber, and in this state, the pressure generating chamber is contracted. In this case, an ink drop of a small volume is ejected through the nozzle orifice. That is, the ink drop is for forming a small dot.
To perform a gradation print by use of ink drops of different volumes, small and large dots are printed on the same line on a recording medium or paper.
To print a pattern containing small dots X
1
and large dots X
2
as shown in FIG.
11
(
a
), in a first scan (first path), the recording head is moved in the main scanning direction to print the small dots X
1
(FIG.
11
(
b
)). In a second scan (second path), the recording head is moved in the main scanning direction to print the large dots X
2
(FIG.
11
(
c
)).
Thus, a plurality of printing operations are repeated along one printing line. This is because a driving signal (driving pulse) for large dots and another driving signal for small dots are separately generated. The large-dot driving signal and the small-dot driving signal are separately generated, and those signals are selectively applied to the recording head every printing operation (printing path). Therefore, a plurality of the printing operations is repeated along one printing line inevitably.
As described above, the small dots Xl and the large dots X
2
are printed on the same printing line. This results in reduction of the printing speed.
There is possibility that the scanning speeds for the printing operations of the small dots X
1
and the large dots X
2
lose their uniformity. If the scanning speeds lose their uniformity, the landing positions of the ink drops, viz., the landing center positions of the small and large dots X
1
and X
2
, are deviated from the correct positions every size (diameter) of ink drop. The result is degradation of the print quality.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of driving an ink jet recording head wherein the printing speed can be increased and the print quality can be improved.
In order to achieve the above object, there is provided a method of driving an ink jet recording head capable of ejecting plural kinds of ink drops having different volumes, comprising the steps of: generating a driving signal successively including: an expansion wave element for expanding a pressure generating chamber of the recording head, the expansion wave element composed of a first expanding element and a second expanding element which are successively arranged in order; an contraction wave element for contracting the pressure generating chamber expanded by the expansion wave element; generating selectively either a first driving pulse or a second driving pulse from the driving signal in accordance with the volume of the ink drop to be ejected, the first driving pulse including the first and second expanding elements and the contracting wave element, the second driving pulse including the second expanding element and the contracting wave element; and applying the either driving pulse to the pressure generating chamber in order to control the expansion and contraction thereof.
Accordingly, two expanding elements can be contained in the print period for forming one dot. The first and second driving pulses are selectively generated by properly selecting the expanding elements. Thus, two types of dots of different diameters can be printed on one print line by applying the first and second driving pulses. In other words, two types of dots can be printed through one printing operation (one main scanning), so that the printing speed is increased.
The two types of ink drops of different diameters may be ejected by use of the same contraction wave element. The result is to lessen a deviation of the landing center position of the ink drop irrespective of the size of the ink drop, and to improve the print quality.
In the method, the gradient of voltage variation of the first expanding element is smaller than those of the second expanding element and the contraction wave element.
Accordingly, the gradient of voltage variations of the second expansion wave element contained in both the first and second driving pulses serve as a major factor to determine a jetting velocity of an ink drop. Thus, a jetting velocity of an ink drop caused by the first drive pulse signal may be made to approach to that of an ink drop caused by the second drive pulse signal. Therefore, both the ink drops can be made to land at the correct landing center positions.
In the method, the expansion wave element further includes a connecting element for connecting the end point of the first expanding element and the start point of the second expanding element. A potential difference between the start point of the first expanding element and the connecting element defines a volume difference between the ink drops ejected by the first driving pulse and the second driving pulse.
Accordingly, the size difference between the different dots can be increased. As a result, the print quality cab be improved while the printing speed is increased.
In the method, a potential difference between the end point of the second expanding element and the contraction wave element defines driving voltage of the driving signal.
Accordingly, the driving voltage is determined based on the voltage for ejecting an ink drop for large dot. Therefore, the image quality for shadow area can be improved.
The method is applicable to an ink jet recording head in which a flexural vibration mode piezoelectric vibrator is used.
The method is applicable to an ink jet recording head in which a longitudinal vibration mode piezoelectric vibrator is used.
The method is applicable to an ink jet recording head of bubble-jet type.
REFERENCES:
patent: 4523200 (1985-06-01), Howkins
patent: 5980015 (1999-11-01), Saruta
patent: 6079806 (2000-06-01), Wen et al.
patent: 6092886 (2000-07-01), Hosono
patent: A2 0 721 840 (1996-07-01), None
patent: A1 0 810 097 (1996-12-01), None
patent: A2 0 827 838 (1998-03-01), None
patent: 09242203 (1999-03-01), None
Dudding Alfred E
Seiko Epson Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tran Huan
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