Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-10-16
2003-02-25
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S010000
Reexamination Certificate
active
06523923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to an ink ejection apparatus that ejects ink droplets from a nozzle by driving an actuator to generate a pressure wave in an ink chamber, particularly to an ink ejection apparatus capable of ejecting three or more ink droplets for one printing command.
2. Description of Related Art
Non-impact type printing devices have recently taken the place of conventional impact type printing devices and are holding an ever-growing share of the market. Of these non-impact type printing devices, ink jet type printing devices have the simplest operation principle, but are still capable of effectively and easily performing multi-gradation and color printing. Of these devices, a drop-on demand type that ejects ink droplets only used for printing has rapidly gained popularity because of its excellent ejection efficiency and low running cost.
A conventional ink ejection apparatus used in a drop-on demand type printing device includes a nozzle from which ink is ejected, an ink chamber that is provided on the back of the nozzle and stores ink, an actuator that changes the volume of the ink chamber, and a driving device that drives the actuator to generate pressure wave vibrations in the ink chamber causing ink to be ejected from the nozzle. This kind of ink ejection apparatus is of a design wherein the driving device drives the actuator to generate the pressure wave vibrations in the ink chamber in response to a change in the volume of the ink chamber, thereby ejecting ink from the nozzle.
The actuator may be made of a piezoelectric element that deforms through the application of a drive voltage. In this case, ink is ejected by applying a pulse voltage (hereinafter referred to as a drive pulse) to the piezoelectric elements from a drive circuit. In this kind of ink ejection apparatus, it is conceivable that the drive pulse is repeatedly applied to the actuator in response to one print command, to eject multiple ink droplets from one nozzle, so that one dot is formed. As one dot is produced from large quantity of ink in this case, an image can be formed having a deep color.
There is a shear mode type of piezoelectric element in an ink ejection apparatus using the piezoelectric element as the actuator, for example. An exemplary ink ejection apparatus of this kind, which also is the apparatus to which the invention is applied, is shown in
FIGS. 10A and 10B
.
FIG. 10A
is a sectional view taken along line
10
—
10
of FIG.
10
B.
FIG. 10B
is a sectional view taken along line
11
—
11
of FIG.
10
A.
As shown in
FIG. 10A
, an ink ejection apparatus
600
includes a bottom wall
601
, a top wall
602
, and elongated shear mode actuator walls
603
sandwiched therebetween. Each actuator wall
603
includes an upper wall
605
of piezoelectric material, which is adhesively attached to the top wall
602
and polarized in a direction indicated by an arrow
609
, and a lower wall
607
of piezoelectric material, which is adhesively attached to the bottom wall
601
and polarized in a direction indicated by an arrow
611
. Alternating pairs of actuator walls
603
form in alternation between ink chambers
613
and spaces
615
, the spaces
615
narrower than the ink chambers
613
.
As shown in
FIG. 10B
, a nozzle plate
617
having nozzles
618
is fixedly secured to one end of each ink chamber
613
and an ink supply source (not shown) is connected to the other end of each ink chamber
613
via a manifold
626
. The manifold
626
includes a front wall
627
formed with openings in positions corresponding to the ink chambers
613
, a rear wall
628
for sealing the space between the bottom wall
601
and the top wall
602
. The manifold
626
is structured to distribute the ink supplied from the ink supply source to the front wall
627
and the rear wall
628
into each of the ink chambers
613
.
Electrodes
619
,
621
are provided on both sides of each of the actuator walls
603
. Specifically, the electrode
619
is provided on the actuator wall
603
in the ink chamber
613
and the electrode
621
is provided on the actuator wall
603
in the space
615
. The electrode
621
is also provided on the outer side surface of each of the two outermost actuator walls
603
. The electrode
619
is covered by an insulating layer (not shown) to insulate it from the ink. Each electrode
621
is connected to a ground
623
. Each electrode
619
provided in the ink chamber
613
is connected to a control unit
625
and carries a voltage (drive signal) described later.
When the control unit
625
applies the voltage to the electrodes
619
in the ink chambers
613
, pairs of the actuator walls
603
deform in the shear mode such that the volume of each ink chamber
613
increases. An example of this operation is shown in FIG.
11
. When a voltage of E volts, which is the crest value, is applied to an electrode
619
c
of the ink chamber
613
c,
an electric field develops in each of the actuator walls
603
e
and
603
f
in the directions indicated by the arrows
631
and
632
, respectively. The actuator walls
603
e
and
603
f
deform in the shear mode to increase the volume of the ink chamber
613
c.
At this time, the pressure in the ink chamber
613
c
including the nozzle
618
c
decreases.
The voltage of E volts is applied to the electrode
619
only for a one-way propagation time T. While the voltage is applied, ink is supplied from the ink supply source. The one-way propagation time T is a time required for a pressure wave in the ink chamber
613
to propagate once in the lengthwise direction of the ink chamber
613
. The one-way propagation time T is calculated by the following expression:
T=L/a,
wherein L is the length of the ink chamber
613
and a is the speed of sound in the ink in the ink chamber
613
.
According to the theory of pressure wave propagation, the pressure in the ink chamber
613
reverses into a positive pressure when the one-way propagation time T passes after the application of the voltage. When the pressure becomes positive, the control unit
625
returns the voltage applied to the electrode
619
of the ink chamber
613
to zero volts, so that the deformed actuator walls
603
e
and
603
f
revert to their initial shape, as shown in
FIG. 10A
, and pressure is applied to the ink. The pressure reverted to positive and the pressure generated when the deformed actuator walls
603
e
and
613
f
return to their initial shape are combined into a relatively high pressure that develops near the nozzle
618
c
in the ink chamber
613
c,
ejecting ink from the nozzle
618
c.
However, when three or more ink droplets are ejected for one printing command in a drive waveform, as shown in
FIG. 8E
, the drive pulses are set as follows:
T
1
=
T
2
=
T
3
=
T,
W
1
=
W
2
=2
T,
wherein T is the one-way propagation time, T
1
is a pulse width of a drive pulse P
1
for ejecting a first ink droplet, T
2
is a pulse width of a drive pulse P
2
for ejecting a second ink droplet, T
3
is a pulse width of a drive pulse P
3
for ejecting a third ink droplet, W
1
is an interval between the drive pulses P
1
and P
2
, and W
2
is an interval between the drive pulses P
2
and P
3
.
In this case, the application of the pressure to the ink chamber and the cancellation of the pressure application are performed in synchronization with the one-way propagation time T. In other words, the pressure is applied in accordance with a rising point of the ink pressure wave and the application of the pressure is cancelled in accordance with a falling point of the ink pressure wave. Therefore, the pressure wave is gradually amplified to perform efficient ink ejection. However, the pressure applied to the ink becomes greater whenever the ink droplet is ejected, and ejecting speed becomes faster for a later ink droplet. As a result of the influence of the pressure wave, the ink may be ejected from an adjacent nozzle, ink ejection may become unstable and the interval to eject ink droplets may become short when t
Barlow John
Brother Kogyo Kabushiki Kaisha
Nguyen Lam
Oliff & Berridg,e PLC
LandOfFree
Wavefrom prevents ink droplets from coalescing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wavefrom prevents ink droplets from coalescing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wavefrom prevents ink droplets from coalescing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3134863