Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-05-18
2002-12-03
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000
Reexamination Certificate
active
06488349
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink jet head and an ink jet type recording apparatus.
BACKGROUND ART
In recent years, there has been proposed an ink jet type recording apparatus which discharges, during one printing cycle for forming a single dot on recording paper, a plurality of ink droplets from the same nozzle of an ink jet head so as to form a single dot by the plurality of ink droplets, as disclosed in, for example, Japanese Laid-Open Patent Publication No. 10-81012.
An ink jet type recording apparatus of this type includes an ink jet head for discharging ink droplets and relative movement means for relatively moving the ink jet head and the recording paper with respect to each other. The ink jet head includes a head body which is provided with a pressure chamber containing ink and a nozzle, an actuator for discharging the ink in the pressure chamber through the nozzle, and driving signal supply means for supplying driving signals to the actuator.
While the ink jet head and the recording paper are relatively moved with respect to each other by the relative movement means, the driving signal supply means supplies a driving signal including one or more driving pulses during one printing cycle. The actuator is actuated by receiving the driving signal so as to discharge one or more ink droplets through the nozzle. The ink droplets thus discharged strike the recording paper in the order they are discharged so as to form a single ink dot. A predetermined image is formed on the recording paper by a collection of a large number of such ink dots on the recording paper. In this process, the number of ink droplets to be discharged during one printing cycle is adjusted so as to adjust the gradation and the size of the dot, thereby realizing so-called “multiple gray level printing”.
In order to discharge one or more ink droplets during one printing cycle as described above, it is necessary to supply to the actuator a number of driving pulses corresponding to the number of ink droplets to be discharged. However, it is difficult to form a desirable ink dot on the recording paper simply by supplying a number of driving pulses corresponding to the number of ink droplets to be discharged without elaborating the driving signal.
For example, when performing high-speed printing, the speed of the relative movement of the ink jet head and the recording paper is high, whereby it is likely that a plurality of ink droplets discharged from the same nozzle strike the recording paper at positions shifted from each other. As a result, it is likely that the ink dot has an oblong circle shape, thereby deteriorating the printing quality. Therefore, in such a case, it is necessary to successively discharge a plurality of ink droplets so that the ink droplet discharging interval is reduced as much as possible, and to discharge the ink droplets so that each later discharged ink droplet is discharged with a higher discharge velocity than that of the previously discharged ink droplet. Thus, a new technique for precisely discharging ink droplets successively with higher velocities in the order they are discharged has been longed for.
On the other hand, there has also been proposed a method in which two ink droplets discharged from the same nozzle are allowed to merge in flight into a single ink droplet before striking, as disclosed in, for example, U.S. Pat. No. 5,285,215 or Japanese Patent Publication for Opposition No. 7-108568. In such a method, it is necessary to elaborate, particularly, the driving signal. In the apparatus disclosed in Japanese Patent Publication for Opposition No. 7-108568, it is made possible to change the discharge velocity of an ink droplet by changing the inclination angle of the trailing edge portion of a driving pulse.
However, supplying a driving signal including a plurality of driving pulses whose trailing edge portions have different inclination angles to the actuator has complicated the driving signal supply means and increased the cost thereof. In such a background, a new technique for merging a plurality of ink droplets before striking using a driving signal of a simple waveform has been longed for.
Moreover, if the meniscus vibration of ink upon completion of one printing cycle remains in the next printing cycle, the ink discharging performance will be unstable. In view of this, a method for supplying a driving signal which is less susceptible to the adverse influence of the meniscus vibration has been longed for.
The present invention has been made in view of the above, and has an object to improve the ink discharging performance of an ink jet head which discharges one or more ink droplets from the same nozzle during one printing cycle, and the ink discharging performance of an ink jet type recording apparatus incorporating the same.
DISCLOSURE OF THE INVENTION
An ink jet head according to the present invention includes: a head body which is provided with a pressure chamber containing ink and a nozzle communicated to the pressure chamber; an actuator having a piezoelectric element for applying a pressure on the ink in the pressure chamber by a piezoelectric effect of the piezoelectric element; and driving signal supply means for supplying a driving voltage signal including a plurality of driving pulses to the piezoelectric element of the actuator, wherein the driving signal supply means supplies the plurality of driving pulses during one predetermined printing cycle so that a time interval between the driving pulses gradually approaches a natural period of the actuator.
Note that the natural period of the actuator as used herein refers to the natural period of the entire vibration system including an acoustic element (specifically, the ink).
Thus, a plurality of driving pulses are supplied to the piezoelectric element of the actuator during one printing cycle, thereby discharging a plurality of ink droplets from the same nozzle. Now, the time interval of the plurality of driving pulses gradually approaches the natural period of the actuator, whereby the discharge velocity of the plurality of ink droplets discharged from the nozzle gradually increases. Therefore, a later discharged ink droplet has a higher discharge velocity than that of a previously discharged ink droplet. Then, the later discharged ink droplet catches up with the previously discharged ink droplet, and the ink droplets merge before striking the recording medium. As a result, the plurality of ink droplets merge into a single ink droplet and then strike the recording medium, thereby forming a desirable single dot on the recording medium.
It is preferred that the driving signal supply means supplies the plurality of driving pulses so that the time interval between the driving pulses gradually increases.
Thus, the time interval of the driving pulse gradually increases so as to approach the natural period of the actuator, whereby the overall time interval of the driving pulses is shorter than that when the time interval gradually decreases so as to approach the natural period. Therefore, it is possible to reduce the printing cycle, thereby enabling printing at a higher speed.
In the ink jet head described above, the driving voltage signal may include a negative pressure potential for driving the actuator to depressurize the pressure chamber, and a positive pressure potential for driving the actuator to pressurize the pressure chamber; and the plurality of driving pulses may include: an initial driving pulse composed of a potential decreasing waveform which decreases from a predetermined reference potential between a negative pressure potential and a positive pressure potential to the negative pressure potential, a negative pressure potential holding waveform which holds the negative pressure potential, and a potential increasing waveform which increases from the negative pressure potential to the positive pressure potential; and one or more subsequent driving pulses each composed of a positive pressure potential holding waveform which holds a positive pressure potential, a potential decreas
Ikeda Koji
Matsuo Koji
Barlow John
Dudding Alfred E.
Harness & Dickey & Pierce P.L.C.
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