Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-10-25
2003-07-29
Pham, Hai (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000
Reexamination Certificate
active
06598950
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording apparatus capable of ejecting extremely small ink droplets and a method of driving an ink jet recording head incorporated in the apparatus.
An ink jet recording apparatus includes a recording head having a multiplicity of nozzle orifices arranged in a sub-scanning direction (a recording paper feeding direction) and is arranged to attain desired printing result by moving the recording head in a main-scanning direction (a width direction of the recording sheet) by a carriage mechanism to thereby perform predetermined paper feeding. Ink droplets are respectively ejected at predetermined timings from the respective nozzle orifices of the recording head based on dot pattern data which is obtained by converting print data inputted from a host computer. These ink droplets reach and attach to a print recording medium such as a recording sheet to thereby form dot images and complete the printing operation.
The recording head is configured in a manner that the deformation of a piezoelectric vibrator is transmitted to a vibration plate and a pressure chamber is contracted to increase the inner pressure thereof to thereby eject an ink droplet from the nozzle orifice. The piezoelectric vibrator is deformed by changing driving voltage inputted to the piezoelectric vibrator. In general, the piezoelectric vibrator is arranged so as to have larger deformation when higher driving voltage is inputted thereto. Thus, an ink droplet is ejected by applying a drive signal for changing the voltage level of the driving voltage to the piezoelectric vibrator to thereby expand and contract the pressure chamber.
As described above, the ink jet recording apparatus constitutes an image depending on whether ink droplets are ejected or not, that is, depending on the presence or non-presence of dot images. Thus, the ink jet recording apparatus can not print and output half-tone such as a gray image, if the apparatus is as it is.
Thus, there has been employed a method in which half-tone is realized by forming a single pixel with plural dots such as 4×4, 8×8 matrix. Although it is possible to perform finer tone reproduction when the pixel resolution is made higher, the substantial resolution rather degrades if the pixel resolution is made higher without changing the diameter of each recording dot. On the other hand, if each dot diameter is large, the graininess in a highlight image becomes remarkable. Thus, in order to perform tone reproduction with a high resolution, it is required to make the volume of an ink droplet as small as possible to thereby make the diameter of a recording dot small.
FIG. 7
shows a related drive signal for ejecting a fine ink droplet. This example of the signal is employed in such a type of recording head that a piezoelectric vibrator changes in a direction for expanding a pressure chamber when a driving voltage rises, while the piezoelectric vibrator changes in a direction for contracting the pressure chamber when the driving voltage lowers.
In a standby state P
0
of the aforesaid drive signal, as shown in FIG.
8
A, a meniscus
50
stops at a nozzle orifice
28
. When a signal (P
1
) for rising the voltage from the minimum driving voltage VL in the standby state P
0
to a maximum driving voltage VH
1
, the pressure chamber expands so that the meniscus
50
is pulled toward the pressure chamber from the nozzle orifice
28
as shown in FIG.
8
B. Then, after holding the maximum driving voltage VH
1
for a predetermined time period (P
2
), a signal (P
3
) for rapidly lowering the voltage to a voltage VH
2
which is almost the middle between VL and VH
1
is inputted, and the voltage VH
2
is held for a predetermined time period (P
4
). At this time, the pressure chamber in the expanded state contracts to increase the pressure therein, whereby ink in the vicinity of the center of the meniscus
50
thus pulled is ejected and jetted as an ink droplet as shown in FIG.
8
C. Thereafter, a signal (P
5
) for lowering the voltage to the minimum driving voltage VL same as that of the standby state at a relatively slow speed not ejecting an ink droplet is inputted, whereby the meniscus
50
is returned to the position of the nozzle orifice
28
as shown in
FIG. 8D
while the residual vibration thereof is damped.
In the recording apparatus using the drive signal, the pressure within the pressure chamber is increased in the state where the meniscus
50
is once pulled to a large extent within the chamber thereby to eject the ink in the vicinity of the center of the meniscus
50
thus pulled as an ink droplet. Thus, an ink droplet relatively small as compared with the diameter of the nozzle orifice
28
can be ejected.
Recently, in order to further improve the resolution, there has been desired a recording apparatus capable of ejecting a further fine ink droplet. However, in the aforesaid related recording apparatus, the reduction of the diameter of an ink droplet to be ejected is limited. It is considered to make an ink droplet to be ejected fine by reducing the diameter of the nozzle orifice
28
. However, if the diameter of the nozzle orifice
28
is reduced, it becomes difficult to process the nozzle orifice
28
, so that the cost of the apparatus rises and the accuracy of the apparatus likely degrades. Further, there arises a problem that the clogging may be severe that is caused when the ink in the vicinity of the nozzle orifice
28
dries during the suspension or the like of the apparatus and the recovery from the clogging is difficult. Thus, such a proposal can not be actually realized.
SUMMARY OF THE INVENTION
The invention has been made in view of the aforesaid circumstance of the prior art, and an object of the invention is to provide an ink jet recording apparatus and a method of driving an ink jet recording head incorporated in the apparatus, capable of ejecting extremely small ink droplets without reducing the diameter of a nozzle.
In order to achieve the above object, according to the present invention, there is provided an ink jet recording apparatus, comprising:
a recording head, provided with a pressure chamber communicated with a nozzle orifice from which an ink droplet is ejected, and a vibration plate which constitutes a part of the pressure chamber;
a pressure generating element, which deforms the vibration plate to vary a volume of the pressure chamber, and
a drive signal generator, which generates a drive signal for driving the pressure generating element, the drive signal including;
a first waveform component, which drives the pressure generating element so as to contract the pressure chamber, to push out a meniscus of ink from the nozzle orifice such an extent that an ink drop is not ejected therefrom;
a second waveform component, which follows the first waveform component and drives the pressure generating element so as to expand the pressure chamber to a first volume, to pull the meniscus toward the pressure chamber;
a third waveform component, which follows the second waveform component and drives the pressure generating element so as to contract the pressure chamber from the first volume to a second volume which is larger than an initial volume of the pressure chamber, and hold the contracted state to eject an ink droplet from the nozzle orifice; and
a fourth waveform component which follows the third waveform component and drives the pressure generating element so as to contract the pressure chamber such an extent that an ink droplet is not ejected from the nozzle orifice.
In this configuration, since the meniscus is once pushed out and then pulled toward the pressure chamber, a portion in the vicinity of the center of the meniscus is locally pulled by the second waveform component. Since the third waveform component is inputted in this state thereby to contract the pressure chamber, the ink at an extremely small area in the substantial center of the meniscus moves to the nozzle orifice and is ejected therefrom as an ink droplet. Thus, an extremely small ink droplet can be e
Hosono Satoru
Otokita Kenji
Dudding Alfred E
Pham Hai
Seiko Epson Corporation
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