Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-30
2003-03-18
Williams, Hezron (Department: 2855)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06533378
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of 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, 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, while when the flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of a printing head, a plurality of ink chambers are formed by partition walls of a piezoelectric ceramic material, and an ink supply device, such as ink cartridges are connected to one end of each of the multiple ink chambers, while at the opposite end of each of the ink chambers are provided ink ejecting nozzles (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.
As this type of an 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 using a piezoelectric material, as is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
As shown in
FIGS. 7A-8
, this type of an ink droplet ejecting apparatus
600
comprises a bottom wall
601
, a top wall
602
and shear mode actuator walls
603
located therebetween. The actuator walls
603
each comprise 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
which is narrower than the ink chamber
613
.
A nozzle plate
617
having nozzles
618
is fixed to one end of each of the ink chambers
613
, while to the opposite end of each of the ink chambers is connected an ink supply source (not shown). 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
which 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
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
undergo a piezoelectric thickness slip deformation in directions to increase the volume of the ink chamber
613
. For example, as shown in
FIG. 8
, when 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 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 the theory of pressure wave propagation, upon the 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
621
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. 7A
) 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
.
Heretofore, when this kind of ink droplet jet apparatus
600
prints while the resolution varies, it is necessary to obtain dot diameters matched with respective resolutions by changing the volume of each droplet of ink. As a method of changing the volume of a droplet of ink, there is a known method of changing the volume of droplet of ink by changing the voltage value of a jet pulse. In that case, a plurality of voltage sources are required which makes the ink droplet jet apparatus unavoidably expensive.
Also, as shown in Japanese Published Unexamined Application No. Hei 6-84073, there is a known method 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 the natural vibration period of a nozzle portion, considering an influence of meniscus vibration resulting from ink-jetting. However, according to this method, for the purpose of effectively utilizing the energy required when the pulse voltage rises, the vibration of the next ink-jetting period is overlapped on the vibration generated when a piezoelectric element returns after the ink-jetting vibration was stopped. Thus, this method does not provide a countermeasure executed in the continuous vibration periods at a high printing frequency.
Moreover, as shown in Japanese Published Unexamined Patent Application No. Sho 61-120764, there is a known method 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 becomes constant regardless of the dot interval. However, this known method is also not able to change resolutions of continuous dots.
SUMMARY OF THE INVENTION
The invention provides an ink droplet ejecting method and apparatus in which volumes of droplets of ink may be controlled arbitrarily with ease without changing the voltage value of a jet pulse and allowing a desired resolution to be printed.
According to an aspect of the invention, there is provided an ink droplet ejecting method in which a pressure wave is generated within an ink chamber by applying a jet pulse signal to an actuator which changes the capacity of the ink chamber by applying pressure to the ink thereby jetting droplets of ink from a nozzle. The ink droplet ejecting method includes jetting droplets of ink by applying a single jet pulse or a plurality of jet pulses to the actuator at a predetermined timing period in accordance with a printing command for a single dot or a plurality of continuous dots, and changing the predetermined timing period in response to a desired volume of ink droplets. In this method, by setting a timing period of a jet pulse signal, that is, setting the printing frequency to a predetermined value corresponding to a multiple o
Brother Kogyo Kabushiki Kaisha
Dickens C
Oliff & Berridg,e PLC
Williams Hezron
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