Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-10-05
2003-04-01
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S009000, C347S011000, C347S057000
Reexamination Certificate
active
06540338
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a driving method for an ink jet recording head enabled to eject an ink droplet, and to an ink jet recording apparatus for recording images and characters on recording paper by using such an ink jet recording head. More particularly, the invention relates to a driving method for an ink jet recording head adapted to eject an extremely small amount of ink in an ink droplet, which can form a microdot, and to an ink jet recording apparatus for recording images and characters on recording paper by using such an ink jet recording head.
Some printers and plotters are well known as typical ink jet recording apparatus (hereunder referred to simply as recording apparatus). In these recording apparatus, the diameter of a dot recorded on recording paper, that is, the resolution of the apparatus is determined according to the quantity of ink of ink droplets ejected from an ink jet recording head. Therefore, the ink quantity of the ejected ink droplets is important. Thus, there has been proposed a recording apparatus having a recording head adapted to eject ink droplets, the respective ones of which have different amounts of ink, from the same nozzle orifice. This recording head has a pressure generating element adapted to cause variation in pressure in ink contained in a pressure chamber. The recording head is caused to eject ink droplets, the respective ones of which have different amounts of ink, by supplying a plurality of kinds of drive pulses, which differ in electric potential change pattern from one another, to the pressure generating element.
Further, a related microdot drive pulse, that is, a drive pulse for ejecting an extremely small amount of ink of an ink droplet has a decompressing component for largely decompressing the pressure chamber, a decompressed state holding component for holding a decompressed state of the pressure chamber, and a compressing component for compressing the pressure chamber so as to eject ink droplets from the nozzle orifice. Supply of the decompressing component and the decompressed state holding component of this microdot drive pulse causes a central portion of the meniscus of ink (that is, a free surface of ink, which is exposed to the nozzle orifice) to protrude in such a manner as to have a columnar shape. Further, supply of the discharging component causes the recording head to eject the columnar portion of the ink as an ink droplet.
When the recording head is driven by such a microdot drive pulse, an ink droplet is divided into a main ink droplet, which is separated from an end portion of an ink column and jetted, and a satellite ink droplet that is jetted in such a way as to accompany the main ink droplet. The jetting speed of this satellite ink droplet is lower than that of the main ink droplet. Moreover, the amount of ink of the satellite ink droplet is less than that of ink of the main ink droplet. For example, when the jetting speed of the main ink droplet is about 7 m/s, that of the satellite ink droplet is approximately 4 m/s. Furthermore, the amount of ink of the satellite ink droplet is two thirds of that of the main ink droplet.
In recent years, it is demanded a recording apparatus capable of recording image with further improved quality. It is necessary for meeting this demand to more reduce an ink amount of each ink droplet. However, when an ink droplet is ejected in response to a related microdot drive pulse, the amount of ink of the satellite ink droplet is extremely small. For instance, when about 1.5 pL of ink of an ink droplet is ejected, the amount of ink of the satellite ink droplet is about 0.5 pL.
Thus, the satellite ink droplet is largely affected by the viscous resistance of air. Consequently, the jetting speed of the satellite ink droplet is largely reduced until the satellite ink droplet impacts on recording paper. On the other hand, generally, the amount of ink of the main ink droplet is more than that of ink of the satellite ink droplet. Thus, the degree of reduction in the speed of the main ink droplet is lower than that of reduction in the speed of the satellite ink droplet. Consequently, when the droplet impacts on the recording paper, the difference in the jetting speed between the main ink droplet and the satellite ink droplet increases still more. Further, the ejection of the ink droplets is performed by simultaneously moving the recording head. This raises the problems that the impact positions of the main ink droplet and the satellite ink droplet deviate from each other owing to the difference in the jetting speeds, and that the image quality is degraded contrary to the demand.
Moreover, there is a probability that the satellite ink droplets cannot reach the recording paper due to the air resistance. In such a case, the satellite ink droplets float as ink mists. When such ink mists adhere to a casing and a nozzle plate of the recording head, the deflection of flight path of the ink droplet and the contamination of the inside of the apparatus are caused, so that the reliability of the apparatus is degraded.
SUMMARY OF THE INVENTION
Accordingly, a first object of the invention is to provide a driving method for an ink jet recording head enabled to increase the jetting speed of an ink droplet even when an ink amount of the ink droplet is extremely small, and to provide an ink jet recording apparatus incorporating such a recording head.
A second object of the invention is to make the impact positions of a main ink droplet and a satellite ink droplet coincide with each other, while preventing the satellite ink droplets from becoming ink mists, thereby to improve the image quality.
In order to achieve the above objects, according to the present invention, there is provided a method of driving an ink jet recording head provided with a pressure chamber communicated with a nozzle orifice from which a main ink droplet and a satellite ink droplet accompanied with the main ink droplet are ejected to form an ink dot on a recording medium, comprising the steps of:
generating pressure fluctuation in the pressure chamber;
ejecting ink contained therein from the nozzle orifice as the main ink droplet having a first volume, due to the pressure fluctuation; and
ejecting ink contained therein from the nozzle orifice as the satellite ink droplet having a second volume which is larger than the first volume, due to the pressure fluctuation.
In this configuration, the satellite ink droplet becomes more resistible to the influence of the viscous resistance of air, as compared with the main ink droplet. Moreover, the rate of reduction in the ratio of the speed to the flight distance of the satellite ink droplet becomes smaller than that corresponding to the main ink droplet. This enables reduction in the difference in the speed at the impact position between the main ink droplet and the satellite ink droplet. Thus, the deviation of the impact position of the satellite ink droplet from that of the main ink droplet is decreased. Consequently, even when an extremely small ink droplet is ejected, the impact position of the main ink droplet is made to coincide with that of the satellite ink droplet, so that the image quality of the recorded image is improved. Furthermore, the amount of ink of the satellite ink droplet, the jetting speed of which is liable to be low, is more than that of the main ink droplet. Thus, the ink droplets are enabled to reliably land onto the recording medium. Consequently, the ink droplets are prevented from becoming ink mists.
There may be accompanied plural satellite ink droplets. In this case, the amount (second volume) of at last one of these satellite ink droplets is more than the amount of ink of a main ink droplet.
Preferably, the pressure fluctuation generating step includes the steps of:
decompressing the pressure chamber such that a central portion of a meniscus of ink in the nozzle orifice is locally pulled toward the pressure chamber; and
compressing the pressure chamber when the pulled meniscus reactionally moves in a direction in w
Takahashi Tomoaki
Teramae Hirofumi
Do An H.
Gordon Raquel Yvette
Seiko Epson Corporation
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