Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-30
2001-07-10
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S011000, C347S015000
Reexamination Certificate
active
06257685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ink droplet ejecting method and apparatus of an ink jet type.
2. Description of Related Art
According to a known ink jet printer of an ink jet type, the volume of an ink flow path is changed by deformation of a piezoelectric ceramic material. When the ink flow path volume decreases, the ink present in the ink flow path is ejected as a droplet from a nozzle. However, when the ink flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of printing head, multiple ink chambers are formed by partition walls of a piezoelectric ceramic material. An ink supply device such as ink cartridges, are connected to one end of each of the multiple ink chambers. The opposite end of each of the ink chambers is provided with an ink ejecting nozzle (hereinafter referred to simply as “nozzles”). The partition walls are deformed in accordance with printing data to make the ink chambers smaller in volume, whereby ink droplets are ejected onto a printing medium from the nozzles to print, for example, a character or a figure.
An example of this type of an ink jet printer is a drop-on-demand type ink jet printer that ejects ink droplets, which is popular because of a high ejection efficiency and a low running cost. An example of a drop-on-demand type ink jet printer is a shear mode type that uses a piezoelectric material, which is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
As shown in FIGS.
12
(
a
) and
12
(
b
), this type of ink droplet ejecting apparatus
600
includes a bottom wall
601
, a top wall
602
and shear mode actuator walls
603
located therebetween. The actuator walls
603
each include a lower wall
607
bonded to the bottom wall
601
and polarized in the direction of arrow
611
, and an upper wall
605
formed of a piezoelectric material, t h e upper wall
605
being bonded to the top wall
602
and polarized in the direction of arrow
609
. Adjacent actuator walls
603
, as a pair, define an ink chamber
613
therebetween. The actuator walls
603
that are adjacent the ink chamber, in a pair, define a space
615
which is narrower than the ink chamber
613
.
A nozzle plate
617
having nozzles
616
is fixed to one end of each of the ink chambers
613
, while the opposite end of each of the ink chambers is connected to an ink supply source (not shown). Electrodes
619
and
621
are respectively formed on both side faces of each actuator wall
603
, as metallized layers. More specifically, electrode
619
is formed on the actuator wall
603
on the side of the ink chamber
613
, while electrode
621
is formed on the actuator wall
603
on the side of the space
615
. The surface of electrode
619
is covered with an insulating layer
630
for insulation from ink. Electrode
621
, which faces the space
615
is connected to a ground
623
, and electrode
619
, which is provided in each ink chamber
613
, is connected to a controller
625
, which provides an actuator drive signal to the electrode.
The controller
625
applies a voltage to the electrode
619
in each ink chamber, whereby the associated actuator walls
603
deform, by virtue of the piezoelectric material, in directions to increase the volume of the ink chamber
613
. For example, as shown in
FIG. 13
, when voltage E(V) is applied to an electrode
619
c
in an ink chamber
613
c
, electric fields are generated in the directions of arrows
631
and
632
respectively in actuator walls
603
e
and
603
f
, so that the actuator walls
603
e
and
603
f
deform in directions to increase the volume of the ink chamber
613
c
. At this time, the internal pressure of the ink chamber
613
c
, including a nozzle
618
c
and the vicinity thereof, decreases. The applied state of the voltage E(V) is maintained for only a one-way propagation time T of a pressure wave in the ink chamber
613
. During this period, ink is supplied from the ink supply source.
Similarly, where voltage is applied to electrodes
619
a
,
619
b
and
619
d
in respective ink chambers
613
a
,
613
b
and
613
d
, electric fields are generated in respective actuator walls
603
a
,
603
b
,
603
c
,
603
d
and
603
g
. Each of the ink chambers
613
a
,
613
b
and
613
d
include corresponding nozzles
618
a
,
618
b
and
618
d.
The one-way propagation time T is a time required for the pressure wave in the ink chamber
613
to propagate longitudinally through the same chamber. Given that the length of the ink chamber
613
is L and the velocity of sound in the ink present in the ink chamber
613
is a, the time T is determined to be T=L/a.
According to the theory of pressure wave propagation, upon lapse of time T, or an odd-multiple time thereof, after the above application of voltage, the internal pressure of the ink chamber
613
reverses into a positive pressure. In conformity with this timing, the voltage being applied to the electrode in the ink chamber
613
c
is returned to 0(V). As a result, the actuator walls
603
e
and
603
f
revert to their original state (FIGS.
12
(
a
) and
12
(
b
)) before the deformation, whereby a pressure is applied to the ink. At this time, the above positive pressure, and the pressure developed by the reverting of the actuator walls
603
e
and
603
f
to their original state before the deformation, are added together to provide a relatively high pressure in the vicinity of the nozzle
618
c
in the ink chamber
613
c
, whereby an ink droplet is ejected from the nozzle
618
c
. An ink supply passage
626
, shown in FIG.
12
(
b
), that communicates with each of the ink chambers
613
, is formed by members
627
and
628
.
In this type of ink droplet ejecting apparatus
600
, it is necessary to eject a small ink droplet in order to attain high print resolution. However, in printing a solid pattern by continuous dot ejection, a drop-out in white may occur, or the print density may become low, because the ink droplet is small. In the case where all of the dots formed during printing are large, the initial writing portion of a figure and fine patterns, are not attractive, or fine lines may become thick to a greater extent than necessary, thus giving rise to the problem that the print quality is deteriorated.
Japanese Published Unexamined Patent Application No. Hei 2-2008 discloses an ink droplet ejecting apparatus wherein, when a printing-free period has been detected, the electric power of a jet pulse for subsequent printing is controlled, to solve the problem of the printed image density being lowered at the initial stage of printing. However, even if such a control is made, the occurrence of a drop-out in white as noted above still remains unsolved when a solid pattern is printed using small ink droplets for effecting high resolution printing.
SUMMARY OF THE INVENTION
The invention solves the above-mentioned problems, and it is an object of the invention to provide an ink droplet ejecting method and apparatus, wherein, when printing is to be performed continuously, the volume of each ink droplet is made small at only the first dot, and is made large at the second and subsequent dots. However, when printing is to be conducted at certain intervals, the volume of each ink droplet is made small, thereby making it possible to effect printing at a high resolution. Further, in printing a solid pattern, for example, a drop-out in white, or the decrease of the print density, no longer occur, and high quality printing can be performed.
In order to achieve the above-mentioned object, an ink droplet ejecting method is provided, wherein a jet pulse signal is applied to an actuator, which is for changing the volume of an ink chamber filled with ink, to generate a pressure wave within the ink chamber, thereby applying pressure to the ink and allowing a droplet of the ink to be ejected from a nozzle. In accordance with a single dot or multiple continuous dots printing instruction, one or multiple jet pulse signals are applied to the actuator at a predetermined
Barlow John
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
Oliff & Berridg,e PLC
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