Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-30
2001-07-03
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S069000
Reexamination Certificate
active
06254213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet ink droplet ejecting method and apparatus.
2. Description of Related Art
In a known ink jet printer, the volume of an ink flow path is changed by deformation of a piezoelectric ceramic material, and when the flow path volume decreases, the ink present in the ink flow path is ejected as a droplet from a nozzle. However, when the flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of printing head, a plurality of ink chambers is formed by partition walls made of a piezoelectric ceramic material. Ink supply means, such as ink cartridges, are connected to first ends of the ink chambers, while at the opposite, second ends, ink ejecting nozzles (hereinafter referred to as “nozzles”) are provided. 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.
For example, as this type of ink jet printer, a drop-on-demand type ink jet printer, which ejects ink droplets, is popular because of a high ejection efficiency and a low running cost. As an example of the drop-on-demand type there is known a shear-mode type that uses a piezoelectric material, as is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
FIGS. 8A and 8B
illustrate this shear-mode type of ink droplet ejecting apparatus
600
comprising a bottom wall
601
, a top wall
602
and shear mode actuator walls
603
located therebetween. Each actuator wall
603
comprises 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
, in a pair, define an ink chamber
613
therebetween, and next adjacent actuator walls
603
, in a pair, define a space
615
that is narrower than the ink chamber
613
.
A nozzle plate
617
having nozzles
618
is fixed to first ends of the ink chambers
613
. An ink supply source (not shown) is connected to the opposite ends of the ink chambers. As illustrated in
FIG. 8B
, on both side faces of each actuator wall
603
are formed electrodes
619
and
621
respectively as metallized layers. More specifically, the electrode
619
is formed on the actuator wall
603
on the side of the ink chamber
613
, while the electrode
621
is formed on the actuator wall
603
on the side of the space
615
. The surface of the electrode
619
is covered with an insulating layer
630
for insulation from ink. The electrode
621
that faces the space
615
is connected to a ground
623
, and the electrode
619
provided in each ink chamber
613
is connected to a controller
625
that 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
undergo a piezoelectric thickness slip deformation in different directions to increase the volume of the ink chamber
613
. For example, as shown in
FIG. 9
, when a voltage E(v) is applied to an electrode
619
c
in an ink chamber
613
c
, electric fields are generated in 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
undergo a piezoelectric thickness slip deformation in different 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.
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 pressure wave propagation theory, 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
619
c
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 (
FIG. 8A
) before the deformation, whereby a pressure is applied to the ink. At this time, the above positive pressure and the pressure developed by reverting of the actuator walls
603
e
and
603
f
to their original state before the deformation are added together to afford 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
communicating with the ink chamber
613
is formed by members
627
and
628
.
Conventionally, in this kind of apparatus
600
for jetting droplets of ink, when a printing frequency requires an increase of when droplets of ink of consecutive dots are jetted then, within a certain frequency range, the ink-jet tends to become unstable due to a meniscus vibration of ink within the nozzle. As a consequence, during continuous ink-jetting, jet speeds of second and third ink droplets and volumes of ink droplets are fluctuated and become uneven, thereby resulting in decreased printing quality.
Conventionally, as shown in Japanese Published Unexamined Patent Application No. Hei 6-84073, to compensate for the influence of the meniscus vibration of ink-jetting and to effectively use energy required when a pulse voltage rises, there is a method known in which a time period ranging from the trailing edge of a pulse voltage to the leading edge of the next pulse voltage is set to ½ of a natural vibration period of a nozzle portion. However, according to this method, vibration of the next ink-jetting is overlapped with vibration generated when a piezoelectric element returns to a stable position after a vibration of ink-jetting is stopped. This method does not provide a counter-measure executed during the continuous vibration at a high printing frequency.
Additionally, as shown in Japanese Published Unexamined Patent Application No. Sho 61-120764, a method is known in which a drive signal for a piezoelectric element is controlled with reference to a dot interval in such a manner that the volume of droplets of ink remains constant regardless of the dot interval. However, this method is not able to prevent fluctuation of the volume of ink droplets of a second and subsequent continuous dots.
SUMMARY OF THE INVENTION
The present invention solves the above-mentioned problems, and provides an ink ejecting method and apparatus in which a printing frequency, used when continuous dots are printed, is set to a predetermined value so that stable ink-jetting is possible during continuous vibration, fluctuation of jetting speeds and volumes of ink droplets of a second dot, and subsequent dots are prevented and excellent ink-jet printing quality is provided.
In order to attain the above-described objects, according to a first aspect of the present invention, there is provided an ink ejecting method in which a pressure wave is generated within an ink chamber by applying a jet pulse signal to an actuator which changes a capacity of the ink chamber containing a quantity of ink to apply a pressure to the ink thereby jetting droplets of ink from a nozzle. This ink ejecting method uses a printing frequency such that volumes of ink droplets of a second dot and subsequent dots become substantially equal to a volume of the ink droplet of the first dot when the jet pulse signa
Barlow John
Brother Kogyo Kabushiki Kaisha
Dudding Alfred E
Oliff & Berridg,e PLC
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