Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-10-23
2002-07-02
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S055000
Reexamination Certificate
active
06412895
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an electrostatic ink jet printer and, more particularly, to a head drive unit in an electrostatic ink jet printer, which controls the dot diameter of an ink droplet made of colored particles ejected from pigment ink.
(b) Description of the Related Art
Electrostatic ink jet printers are increasingly used for a personal computer due to its high printing performance as well as small noise. A printing head and a head drive unit in a conventional electrostatic ink jet printer will be described first with reference to
FIGS. 1
to
4
.
FIG. 1
is a perspective view of a printing head
100
in the conventional ink jet printer,
FIG. 2
is a schematic block diagram of the printing head
100
of FIG.
1
and an associated head drive unit
200
,
FIG. 3
is a timing chart of signals applied to an electrophoretic electrode and an ejection electrode in the printing head
100
, and
FIG. 4
is a timing chart of ejecting pulses having an ejecting voltage Vej and supplied to ejection electrodes for recording different dot diameters.
In
FIG. 1
, the printing head
100
includes an ink chamber
102
receiving therein pigment ink
101
and having an ink ejection slit
104
at the front edge thereof, a plurality of ejection electrodes
106
extending in parallel to one another from the rear edge to the front edge of the printing head
100
, an electrophoretic electrode
103
disposed at the rear edge of the ink chamber
102
for driving colored particles in the pigment ink
101
toward the ink ejecting slit
104
for concentration of the colored particles at the ink ejecting slit
104
, and a counter electrode
107
disposed on the back surface of a recording sheet
105
to oppose the front tips of the ejection electrodes
106
.
The ink ejecting slit
104
is partitioned by passage walls
108
corresponding to respective ejection electrodes
106
to generate an ink meniscus of pigment ink on each ejection electrode
106
. The ink chamber
102
is communicated with an ink reservoir (not shown) at an ink inlet port
109
and an ink outlet port
110
through ink tubes. Thus, a back pressure is applied to the pigment ink in the ink chamber
102
, and the pigment ink
101
in the ink chamber
102
is forced to circulate between the ink chamber
102
and the ink reservoir.
The head drive unit
200
, as shown in
FIG. 2
, has an image data control section
205
for receiving gray-scale image data from a processor, a driver control section
203
for generating switching signals for controlling switches in a driver section
202
based on the image data, a pulse width generator
204
for generating pulse width signals based on the image data, and the driver section
202
including a plurality of switches each for receiving the switching signal from the driver control section
203
to apply an ejecting voltage Vej to a corresponding ejection electrode
106
during a time interval based on the pulse width signals.
In operation, the printing head
100
uses an electrophoretic phenomenon wherein colored particles in the pigment ink
101
are driven in a direction specified by an electric field applied to the pigment ink
101
containing electrified colored particles. More specifically, when a constant electrophoretic voltage V
1
shown in
FIG. 3
is applied to the electrophoretic electrode
103
to generate an electric field in the ink chamber
102
filled with the pigment ink
101
, colored particles in the pigment ink
101
move toward the ink ejecting slit
104
at an electrophoretic speed.
After the colored particles move toward the ink ejecting slit
104
, an ink meniscus
206
is form at the tip of each ejection electrode
106
. When a switch in the driver section
202
shown in
FIG. 2
is turned on, an ejecting pulse having a constant voltage Vej and a duty ratio of 50 to 100%, as shown in
FIG. 3
, is applied to a corresponding ejection electrode
106
. Thus, colored particles are driven by the electrostatic field generated between the ejection electrode
106
and the counter electrode
107
, and ejected from the ink ejecting slit
104
against the surface tension of the ink meniscus
206
and the viscous force of the pigment ink
101
. The colored particles are ejected as ink droplets
201
from the tip of the ejection electrode
106
in synchrony with the ejecting pulse P
EJ
to adhere onto the recording sheet
105
as a dot. The colored particles are replenished from the ink reservoir to be iteratively ejected to form an image on the recording sheet
105
.
A conventional technique for forming a desired dot diameter based on the level of the gray-scale data will be now described.
For obtaining a desired dot diameter of the ink droplet
201
, correlation between the dot diameter and the pulse width of the ejecting pulse such as shown in
FIG. 3
is experimentally determined and the list of the pulse widths is stored in combination with the level of the gray-scale image data in a storage device or a memory. The image data control section
205
receives gray-scale image data from the processor, retrieves a pulse width corresponding to the level of the gray-scale image data in the storage device, and transmits the pulse width data to the pulse width generator
204
. The image data control section
205
also transmits the image data for controlling on/off of the switch in the driver section
202
to the driver control unit
203
. The pulse width generator
204
, after receiving the pulse width data, generates a pulse width signal based on each gray-scale level of the ejection electrodes
106
to supply ejecting voltage Vej. Thus, the driver control section
203
closes the switches in the driver section
202
during time intervals based on the respective gray-scale image data to thereby apply the ejecting voltage Vej to the ejection electrodes
106
.
In the example of
FIG. 4
, it is assumed that forty ejection electrodes
106
-
1
to
106
-
40
are provided in the ink jet printer and are applied with the depicted ejecting pulses. If the ejection electrodes
106
-
1
,
106
-
2
,
106
-
3
and
106
-
40
are desired to form dot diameters of 20 &mgr;m, 50 &mgr;m, 75 &mgr;m, and 100 &mgr;m, respectively, ejecting pulses P
EJ
having pulse widths of 50 &mgr;s, 80 &mgr;s, 90 &mgr;s and 100 &mgr;s are applied to the ejection electrodes
106
-
1
,
106
-
2
,
106
-
3
and
106
-
40
, respectively. The respective pulse widths provide desired dot diameters of the ink droplets based on the gray-scale image data, thereby forming desired image data on the recording sheet
105
.
The conventional ink jet recording device as described above has a disadvantage in that the circuit scale of the pulse width generator
204
increases with the increase of the number of ejection electrodes
106
provided and the number of gray-scale levels supplied.
In addition, when a plurality of ejection electrodes
106
have variations of the electric resistance therealong, the dot diameters formed by the respective ejection electrodes
106
depend on the variations of the electric resistance, thereby degrading the printing quality for the gray-scale level.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ink jet printer including a head drive unit having a simpler structure of the pulse width generator even if the number of ejection electrodes and the numbers of gray-scale levels increase.
It is another object of the present invention to provide a uniform dot diameter without depending on variations of the electric resistance of the ejection electrodes.
The present invention provides an ink jet printer comprising a printing head including an ink chamber for receiving therein pigment ink, the ink chamber having an ink jet slit, and an array of ink ejection electrodes, disposed in the ink chamber, for receiving an ejecting voltage to eject the pigment ink from the ink jet slit, and a head drive unit for receiving a set of recording data for the ejection electrodes during each recording clock cycle to generate
Hagiwara Yoshihiro
Minemoto Hitoshi
Mizoguchi Tadashi
Shima Kazuo
Suetsugu Junichi
Huffman Julian D.
NEC Corporation
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