Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-08-28
2001-05-15
Le, N. (Department: 2867)
Incremental printing of symbolic information
Ink jet
Controller
C347S068000, C347S074000
Reexamination Certificate
active
06231151
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to inkjet recording apparatuses, and more particularly, to an inkjet recording apparatus for recording images by expelling ink droplets using a piezoelectric element.
2. Description of the Related Art
Among conventional inkjet printers, some known printers use a piezoelectric element (PZT) for the head. In such a head, a pulse voltage corresponding to image information is applied to the piezoelectric element, and distortion caused by the applied pulse voltage pressurizes ink in a prescribed container (ink channel), which causes ink droplets to be expelled form the nozzle provided at the ink channel toward a recording sheet. A rectangular pulse is conventionally known as the kind of pulse voltage applied to such a piezoelectric element.
FIG. 19
is a waveform chart showing rectangular pulse voltages as conventionally used. In these pulse voltages, the rising time, duration of the pulse amplitude, falling time, size of the pulse amplitude or the like is adjusted to control the speed, size or the like of droplets to be expelled.
The use of such a rectangular pulse voltage however may cause ripples in the pressure applied to ink caused by the vibration of the piezoelectric element for the duration of the pulse amplitude (voltage hold period).
FIG. 20
is an illustration of a narrowed part of an expelled ink produced by the vibration of the piezoelectric element during the voltage hold period.
FIG. 21
is an illustration of ink droplets produced by the expelled ink having a narrowed part.
As shown in
FIG. 20
, an ink pillar
200
having narrow parts
201
,
202
and
203
is produced from a nozzle
150
by applying a pulse voltage having a voltage hold period as shown in FIG.
19
. An ink droplet
251
with satellites
252
and
253
is produced as shown in FIG.
21
. Images formed on a sheet by such droplets are considerably degraded because satellites
252
and
253
stick at unexpected positions or the dot size becomes unstable by change in the volume of ink droplet
251
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of expelling ink in an inkjet recording apparatus capable of forming high definition images.
Another object of the invention is to provide a driver for an inkjet head capable of high speed and high definition printing.
The above objects of the invention are achieved in an inkjet recording apparatus for expelling an ink droplet using a piezoelectric element by a method for expelling the ink droplet. The method includes the following steps of:
(a) outputting a drive pulse voltage from a driver to the piezoelectric element, the drive pulse voltage having a waveform consisting of a plurality of ramps;
(b) applying an energy produced by the piezoelectric element in response to the drive pulse voltage to an ink channel in which ink is filled; and
(c) expelling an ink droplet from the ink channel in response to the applied energy.
According to another aspect of the invention, a driver for driving inkjet head which expels an ink droplet filled in an ink channel in response to an energy produced by a piezoelectric element, the driver outputting a drive pulse voltage to the piezoelectric element to produce the energy, the drive pulse voltage having a waveform consisting of a plurality of ramps.
The waveform of the drive pulse voltage applied to the piezoelectric element is set so as to consist of a plurality of ramps. For example, the drive pulse voltage may have a triangular waveform, a sawtooth waveform, or the like. Thus, the generation of satellites and the associated instability of the dot size as experienced in the conventional art may be prevented, which contributes to improvement in picture quality.
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Hotomi Hideo
Minato Shoichi
Hsieh Shih-Wen
Le N.
Minolta Co. , Ltd.
Sidley & Austin
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