Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-30
2002-02-26
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000, C347S009000
Reexamination Certificate
active
06350003
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 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.
7
(
a
) and
7
(
b
), this type of ink droplet ejecting apparatus
600
includes a bottom wall
601
, a top wall
602
and shear mode actuator walls
603
(shown in
FIG. 8
as
603
a-g
) 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, the 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 ink chamber
613
(shown in
FIG. 8
as
613
a-d
) therebetween. The actuator walls
603
that are adjacent to the ink chamber, in a pair, define a space
615
which is narrower than the ink chamber
613
.
A nozzle plate
617
having nozzles
618
(shown in
FIG. 8
as
618
a-d
) 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
(shown in
FIG. 8
as
619
a-d
) 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 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.
7
(
a
) and
7
(
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.
7
(
b
), that communicates with each of the ink chambers
613
, is formed by members
627
and
628
.
Conventionally, in this type of ink droplet ejecting apparatus
600
, when an ink droplet of a small volume is to be ejected for enhancing the printing resolution, a control has been provided to decrease the driving voltage in multiple steps, for example. However, such a method of controlling the voltage in multiple steps leads to an increase in cost of a driver IC, etc., and attempting to reduce the volume of an ink droplet gives rise to the problem that even the speed of the ink droplet decreases. In order to obtain an ink droplet of a small volume without decreasing the ink droplet speed, it has been proposed to use an additional pulse of a low voltage level, after application of a jet pulse and before completion of ink ejection. However, this proposal also leads to an increase in cost of a driver IC, etc. because multiple voltages are needed as driving pulses.
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, after a driving waveform for a primary ejection of ink, only one additional pulse is added, thereby making it possible to obtain an ink droplet of a desired volume and also possible to minimize the decrease of the ink droplet speed.
In order to achieve this object, an ink droplet ejecting method is provided, wherein a jet pulse signal is applied to an actuator, 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. Both the jet pulse signal and an additional pulse signal are applied to the actuator in accordance with a one-dot printing instruction. The jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The additional pulse signal has a pulse width of approximately 0.2T to 0.6T relative to the jet pulse signal, and a time difference between a fall timing of the jet pulse signal and a rise timing of the additional pulse signal is 0.3T to 0.7T.
According to the above method, the ink present in the ink chamber is about to rush out from the nozzle at the leading edge and the trailing edge of the jet pulse signal, and with the additional pulse signal which is subsequently applied halfway at the above timing, a part of the ink droplet which is rushing out from the nozzle is pulled back. Consequently, it is possible to reduce the size of the flying ink droplet after ejection, and hence possible to attain a high printing resolution easily. Further, since it is not necessary to change the driving voltage to reducing the size of the ink droplet, the cost is reduced and the ink droplet speed is only minimally decreased.
In accordance with another aspect of the ink droplet ejecting method, the jet pulse signal and the additional pulse signal have the same peak value. According to this method, a single drive voltage source is sufficient to obtain a small-sized ink droplet, and therefore the cost can be reduced.
An ink droplet ejecting apparatus is also pro
Barlow John
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
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