Information
-
Patent Grant
-
6172693
-
Patent Number
6,172,693
-
Date Filed
Tuesday, November 25, 199726 years ago
-
Date Issued
Tuesday, January 9, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Barlow; John
- Gordon; Raquel Yvette
Agents
-
CPC
-
US Classifications
Field of Search
US
- 347 55
- 347 120
- 347 123
- 347 111
- 347 159
- 347 141
- 347 151
- 347 122
- 347 128
- 347 17
- 347 103
- 347 154
-
International Classifications
-
Abstract
An ink jet recording head comprises a plurality of electrophoretic electrodes corresponding to a plurality of ejecting electrodes, and a pair of stirring electrodes disposed at both ends of the row of the ejecting electrodes. The stirring of the colored particles by the stirring electrodes prevents block of an ink jet slit by the concentrated colored particles, whereas individual control of the electrophoretic electrodes prevents undesirable ink ejection from non-specified ejecting electrode.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an ink jet recording head and, more particularly, to an ink jet recording head capable of controlling the movement of colored particles in a pigmented ink by an electrophoretic force.
Non-impact recording methods attract a large attention in a-printing technology for their low noise during a recording operation. Among other non-impact recording methods, an ink jet recording method has several advantages of direct and high-speed printing onto a recording medium such as a plain paper. A variety of proposals are presented heretofore for improving the ink jet recording head.
A conventional ink jet recording head, such as described in JP-A-60(1985)-228162, comprises a plurality of ejecting electrodes and a counter electrode disposed behind a recording paper. A driving voltage is applied between a specified ejecting electrode and the counter electrode to generate an electric field, which applies an electrostatic force for ejecting colored particles in a pigmented ink from the ejecting electrode.
FIG. 1
shows a conventional ink jet recording head of the type as described above. The ink jet recording head comprises an ink chamber
301
having an ink jet slit
302
for ejecting therefrom colored particles in pigmented ink
310
, an electrophoretic electrode
303
disposed at a rear wall of the ink chamber
301
for concentrating colored particles in the pigmented ink in the vicinity of the ink jet slit
302
, a plurality of elongate, ejecting electrodes
305
arranged in a row along the ink jet slit
302
for ejecting ink droplets
311
of the colored particles from a specified ejecting electrode
305
, and a counter electrode
309
disposed behind a recording medium or paper
304
for generating an electric field between the specified ejecting electrode
305
and the counter electrode
309
.
Ink jet slit
302
is separated by separating walls
308
into a plurality of short channels each corresponding to one of the ejecting electrodes
305
, thereby forming a meniscus of the pigmented ink
310
at each ejecting electrode
305
. The ink chamber
301
is communicated to an ink reservoir not shown in the drawing by tubes connected to the ink inlet port
306
and an ink outlet port
307
for circulating the pigmented ink
310
by a back pressure applied to the pigmented ink in the ink chamber
301
.
FIG. 2
shows voltage waveforms applied to the electrophoretic electrode and the ejecting electrodes of FIG.
1
. The ink jet recording head utilizes an electrophoretic force by which the charged or electrified colored particles in the pigmented ink are moved in a specified direction.
Specifically, an electric field is generated in the ink chamber
301
, which is filled with the pigmented ink, by applying a constant electrophoretic voltage V
1
, as shown in
FIG. 2
, to the electrophoretic electrode
303
. The colored particles in the pigmented ink are moved by the electric field toward the ink jet slit
302
at a constant electrophoretic mobility and concentrated therein, thereby forming an ink meniscus at the front tip of each ejecting electrode
305
. After the ejecting electrode
305
specified for ink ejection receives a voltage pulse having an amplitude of V
2
and a duration of T
2
, the colored particles are further moved toward and concentrated at the tip of the specified ejecting electrode
305
.
The colored particles overcomes the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force and are ejected from the tip of the specified ejecting electrode
305
, forming minute ink droplets
311
, in accordance with the timing in synchrony with the voltage pulse, to adhere to the recording medium
304
. The operation described above is repeated until a desired image is formed on the recording medium
304
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink jet recording head capable of preventing the colored particles from being ejected from the tip of an ejecting electrode other than the specified ejecting electrode, thereby obtaining a stable operation of the ink jet recording head and an excellent image quality.
The present invention provides, in one aspect thereof, an ink jet recording head comprising an ink jet recording head comprising a housing defining an ink chamber having an ink jet slit at a front side thereof for ejecting colored particles in pigmented ink, at least one electrophoretic electrode disposed at a rear side of the ink chamber for receiving an electrophoretic voltage for moving the colored particles by an electrophoretic force, a plurality of ejecting electrodes having respective tips arranged in a row along the ink jet slit, each of the ejecting electrodes receiving an ejecting voltage, a counter electrode opposed to the row of tips of the ejecting electrodes and maintained at a potential, and a pair of stirring electrodes disposed at both ends of rows of tips of the ejecting electrodes for receiving a stirring voltage therebetween, the stirring voltage reversing its polarity at least once.
The present invention also provides, in another aspect thereof, an ink jet recording head comprising a housing defining an ink chamber having an ink jet slit at a front side thereof for ejecting colored particles in pigmented ink, a plurality of electrophoretic electrodes arranged at a rear side of the ink chamber, each of the electrophoretic electrodes receiving an electrophoretic voltage for moving the colored particles by an electrophoretic force, a plurality of ejecting electrodes disposed corresponding to the electrophoretic electrodes and having respective tips arranged in a row along the ink jet slit, each of the ejecting electrodes receiving an ejecting voltage, and a counter electrode opposed to the row of tips of ejecting electrodes and maintained at a potential.
In accordance with the ink jet recording head of the present invention, colored particles are prevented from being ejected by an ejecting electrode other than the specified ejecting electrode for obtaining a stable operation of the ink jet recording head and an excellent image quality.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a perspective view of a conventional ink jet recording head;
FIG. 2
is a timing chart of the signals in the ink jet recording head of
FIG. 1
;
FIG. 3
is a schematic cross-sectional view of an ink jet recording head according to a first embodiment as well as a fourth embodiment of the present invention;
FIG. 4
is a timing chart of the signals in the ink jet recording head of
FIG. 3
;
FIG. 5
is a schematic cross-sectional view of an ink jet recording head according to a second embodiment of the present invention;
FIG. 6
is a timing chart of the signals in the ink jet recording head of
FIG. 5
;
FIG. 7
is a schematic cross-sectional view of an ink jet recording head according to a third embodiment of the present invention;
FIG. 8
is a timing chart of the signals in the ink jet recording head of
FIG. 7
;
FIG. 9
is flowchart of the operation of the ink jet recording head according to a fourth embodiment of the present invention;
FIG. 10
is a timing chart of the signals in the ink jet recording head of
FIG. 9
;
FIG. 11
is another flowchart of the operation of the ink jet recording head of
FIG. 9
;
FIG. 12
is detailed flowchart in the step of
FIG. 11
;
FIG. 13
is another timing chart of the signals in the ink jet recording head of
FIG. 9
;
FIG. 14
is a schematic cross-sectional view of an ink jet recording head according to a fifth embodiment of the present invention; and
FIG. 15
is a timing chart of the signals in the ink jet recording head of FIG.
14
.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention is more specifically described with reference to the accompanying drawings, wherein similar constituent elements are designated by the same or similar reference numerals in some embodiments.
Referring to
FIG. 3
, an ink jet recording head according to a first embodiment of the present invention comprises an ink chamber
101
defined by a dielectric housing
116
for receiving therein pigmented ink, an electrophoretic electrode
110
disposed at the rear wall of the housing
116
for moving colored particles
115
in the pigmented ink by an electrophoretic force and concentrating the colored particles
115
in the vicinity of an ejecting slit
102
of the ink chamber
101
, a plurality of elongate, ejecting electrodes
112
,
117
,
118
etc. disposed in a row along the ink jet slit
102
for ejecting colored particles
115
concentrated in the vicinity of the ejecting slit
102
toward a counter electrode
109
disposed behind a recording medium
104
, all of which are similar to those in the conventional ink jet recording head of FIG.
1
.
The ink jet recording head further comprises a pair of stirring electrodes
105
and
106
disposed at the both ends of the row of the ejecting electrodes
112
,
117
,
118
etc. and a set of control sections including a control unit
114
for receiving input data and control signals from a computer not shown in the figure via an interface
113
to control other control sections, an electrophoretic electrode control section
108
for applying an electrophoretic voltage to the electrophoretic electrode
110
, a stirring electrode control section
107
for applying a stirring voltage to the stirring electrodes
105
and
106
, and an ejecting electrode control section
103
for applying an ejecting voltage pulse to a specified one or group of the ejecting electrodes
112
,
117
,
118
etc.
Referring to
FIG. 3
, in general operation of the ink jet recording head of the present embodiment, a constant electrophoretic voltage V
1
is applied to the electrophoretic electrode
110
for a set period of time to concentrate the colored particles at the tip of the ejecting electrodes
112
,
117
,
118
etc., followed by application of an alternate stirring voltage to the stirring electrodes
105
and
106
to stir the colored particles concentrated at the tips of the ejecting electrodes
112
,
117
,
118
etc. Then, an ejecting voltage pulse is applied to specified ejecting electrodes for ejecting colored particles from the specified ejecting electrodes. The alternating stirring voltage moves reciprocally the colored particles
115
concentrated in the vicinity of the ink jet slit
102
for stirring of the colored particles
115
for avoiding blocking of the ink jet slit
102
.
Now a specific operation will be described for the case in that the print data and external control signals supplied from the computer via the interface
113
control the specified ejecting electrodes
112
and
118
to eject ink droplets
115
, and control the ejecting electrode
117
not to eject an ink droplet.
The control unit
114
receives the print data and external control signal supplied from the computer via the interface
113
at the beginning of an interval “a” to generate a first control signal to the electrophoretic electrode control section
108
, which responds to the first control signal to supply an electrophoretic voltage V
1
to the electrophoretic electrode
110
during interval “a” for the time length of T
1
.
The ink chamber
101
receiving therein pigmented ink is applied with an electric field by the electrophoretic electrode
110
. As a result, the colored particles
115
in the pigmented ink are moved toward the ink jet slit
102
at a constant electrophoretic mobility, whereby colored particles are concentrated at the tips of the ejecting electrodes
112
,
117
,
118
etc.
During the next interval “b”, the control unit
114
delivers a second control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
. As a result, the electrophoretic electrode control section
108
cancels the electrophoretic voltage V
1
, whereas the stirring electrode control section
107
applies an alternating stirring voltage pulse, which alternates at a period of Tab between voltage levels Vab and −Vab for a time length of 3·Tab/2, to each of the pair of stirring electrodes
105
and
106
during the second interval “b”. The polarities of the stirring electrodes
105
and
106
are opposite to each other, thereby applying charged colored particles with an alternating voltage.
After the electrophoretic voltage V
1
is turned off at the end of interval “a”, the movement of the colored particles toward the ink jet slit
102
stops. The colored particles
115
are then moved alternately in the opposite directions between the pair of stirring electrodes
105
and
106
at the period of Tab to be stirred in the pigmented ink, whereby the colored particles are moved in the vicinity of the tips of the ejecting electrodes
112
,
117
,
118
etc. during an interval “b
1
” for distribution of the colored particles.
At the end of interval “b
1
”, the control unit
114
delivers a third control signal to the stirring electrode control section
107
and the ejecting electrode control section
103
. The stirring electrode control section
107
cancels the alternating stirring voltage to stop the movement of the colored particles, whereby the colored particles are distributed uniformly in the vicinity of the tips of the ejecting electrodes
112
,
117
,
118
etc.
During a next interval “c”, the ejecting electrode control section
103
responds to the control signal supplied from the control unit
114
to apply an ejecting voltage pulse having an amplitude of V
2
and a duration of T
2
to the specified ejecting electrodes
112
and
118
, which drive the colored particles in the vicinities of the specified ejecting electrodes
112
and
118
from the tips of the electrodes
112
and
118
by an electrostatic force generated between the specified electrodes
112
and
118
and the counter electrode
109
.
The colored particles
115
overcome the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force, and are ejected as ink droplets
111
from the specified ejecting electrodes
112
and
118
at the timing in synchrony with the ejecting pulse, thereby forming an image on the recording medium
104
. The colored particles
115
are not concentrated in the vicinity of the tip of the ejecting electrode
117
, which is not specified for the ink ejection, thereby preventing the colored particles from being ejected from the non-specified ejecting electrode
117
irrespective of the influence by the driving pulses applied to the adjacent electrodes
112
and
118
.
After a subsequent ink ejection from the ejecting electrodes
112
and
118
is requested, the control unit
114
again delivers during interval “c” a third control signal to the electrophoretic electrode control section
108
, which responds thereto to supply an electrophoretic voltage V
1
to the electrophoretic electrode
110
for the time length of T
1
, thereby generating an electric filed in the ink chamber
101
filled with the pigmented ink. The colored particles
115
in the pigmented ink are moved toward the ink jet slit
102
at the electrophoretic mobility during interval “c”, thereby again causing concentration of colored particles in the vicinities of the ejecting electrodes
112
,
117
,
118
etc.
Subsequently, the control unit
114
delivers another second control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
during a next interval “b
2
”. The electrophoretic electrode control section
108
responds to the another second control signal to cancel the electrophoretic voltage V
1
supplied to the electrophoretic electrode
110
. The stirring electrode control section
107
also responds to the another second control signal to supply an alternating stirring voltage to the stirring electrodes
105
and
106
during interval “b
2
”, similarly to the case of interval “b
1
”.
After the electrophoretic voltage V
1
is turned off at the end of interval “c”, the colored particles
115
stop the movement toward the ink jet slit
102
. The colored particles are then reciprocally moved in the opposite directions by the electrostatic force generated between the pair of stirring electrodes
105
and
106
, whereby the colored particles are stirred and uniformly distributed in the vicinities of the tips of the ejecting electrodes
112
,
117
,
118
etc.
At the end of interval “b
2
”, the control unit
114
delivers a fourth control signal to the stirring electrode control section
107
and the ejecting electrode control section
103
. The stirring electrode control section
107
responds to the fourth control signal to cancel the stirring voltage supplied to the stirring electrodes
105
and
106
to thereby stop stirring of the colored particles, which are distributed uniformly in the vicinities of the ejecting electrodes
112
,
117
,
118
etc.
The ejecting electrode control section
103
also responds to the fourth control signal supplied from the control unit
114
, thereby supplying an ejecting pulse to each of the ejecting electrodes
112
and
118
, similarly to the case of interval “c”. The colored particles disposed in the vicinities of the ejecting electrodes
112
and
118
are urged from the tips of the ejecting electrodes
112
and
118
and concentrated therein. The colored particles then overcome the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force, to be ejected from the tips of the ejecting electrodes
112
and
118
onto the recording medium
104
while forming ink droplets
111
. The colored particles disposed in the vicinity of the ejecting electrode
117
are not ejected therefrom because the colored particles are not concentrated in the vicinity of the ejecting electrode
117
irrespective of the influence by the voltage pulse applied to the adjacent ejecting electrodes
112
and
118
.
In the above operation, if there is no request for ejection from either of the ejecting electrodes
112
,
117
,
118
etc., the control unit
14
delivers a control signal to the electrophoretic electrode control section
108
, which responds thereto to cancel the electrophoretic voltage.
Referring to
FIG. 5
, an ink jet recording head according to a second embodiment of the present invention is similar to the ink jet recording head of
FIG. 3
except that a plurality of electrophoretic electrodes
119
,
120
,
121
etc. are disposed corresponding to the ejecting electrodes
112
,
117
,
118
etc. in the second embodiment. Similar constituent elements are designated by the same reference numerals in both the drawings, and detailed description thereof is omitted herein for avoidance of a duplication.
Referring to
FIG. 6
showing a signal timing chart of the second embodiment, similarly to
FIG. 4
, it is shown that each of the electrophoretic electrodes
119
,
120
,
121
etc. is applied with a constant electrophoretic voltage V
1
for concentration of the colored particles for the time length T
1
before a corresponding ejecting electrode is applied with an ejecting voltage pulse for ejection of the colored particles.
The stirring electrodes
105
and
106
are applied with an alternating stirring voltage pulse having a period of Tab for stirring the colored particles between the activation of the electrophoretic electrode and the activation of the corresponding ejecting electrode. The stirring voltage pulse is applied for the time length of 3·Tab/2.
In the second embodiment, since colored particles
115
are not concentrated in the vicinity of the tips of the ejecting electrodes not specified for the ink ejection, it is more assured that the colored particles are not ejected by the activation of the adjacent ejecting electrode compared to the first embodiment.
In the first and second embodiments, the pair of stirring electrodes
105
and
106
disposed at both edges of the ejecting slit function for stirring colored particles in the vicinities of the tips of the ejecting electrodes not specified for ink ejection, thereby preventing concentration of the colored particles in the vicinities. As a result, an undesirable ejection of colored particles due to the activation of the adjacent ejecting electrodes are prevented to obtain a stable image quality.
Referring to
FIG. 7
, an ink jet recording head according to a third embodiment of the present invention is similar to the ink jet recording head shown in
FIG. 5
except that a pair of stirring electrodes are disposed at both sides of each ejecting electrode
112
,
117
,
118
, . . . in the present embodiment. Similar constituent elements are designated by the same reference numerals in both the drawings, and detailed description thereof is avoided herein for avoiding a duplication.
Referring to
FIG. 8
showing a timing chart of the ink jet recording head of
FIG. 7
, the control unit
114
receives printing data and external control signals from a computer via the interface
113
for ejecting colored particles
115
from, for example, ejecting electrodes
112
,
117
and
118
. By this print data and control signals, the ejecting electrode
117
repeats ejection of the colored particles at a short time interval, whereas both the ejecting electrodes
112
and
118
disposed at both sides of the ejecting electrode
117
repeat the ejection at a larger time interval.
The control unit
114
delivers a first control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
at the beginning of interval “a”. The electrophoretic electrode control section
108
responds to the first control signal to supply constant electrophoretic voltages V
1
to the specified electrophoretic electrodes
119
,
120
and
121
for generation of electric field in the ink chamber
101
in the vicinity of the specified electrophoretic electrodes. As a result, the colored particles in the pigment ink are moved toward the ink jet slit
102
at the constant electrophoretic mobility, to be concentrated in the vicinities of the specified ejecting electrodes
112
,
117
and
118
. On the other hand, the stirring electrode control section
107
respond to the first control signal to supply a constant stirring voltage V
1
to each of the stirring electrodes
105
,
106
,
110
, and
122
disposed adjacent to the specified ejection electrodes.
The control unit
14
also delivers the first control signal to the ejecting electrode control section
103
, which responds thereto to supply an ejecting voltage pulse having an amplitude of V
2
and a duration of T
2
to each of the specified ejecting electrodes
112
,
117
and
118
. The colored particles
115
in the vicinity of the ejecting slit
102
are urged from the tips of the ejecting electrodes
112
,
117
and
118
. The colored particles
115
overcome the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force applied thereto, to be ejected from the tips of the respective ejecting electrodes
112
,
117
and
118
at the timing in synchrony with the ejecting voltage pulse and adhered onto the recording medium
104
.
At the end of interval “a”, the control unit
114
receives print data and external control signals for ejecting colored particles
115
only from the ejecting electrode
117
, and delivers a second control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
. The electrophoretic electrode control section
108
responds thereto to cancel the electrophoretic voltage V
1
supplied to the ejecting electrodes
112
and
118
which are not specified for ink ejection.
The stirring electrode control section
107
responds to the second control signal to reciprocally change the stirring voltages supplied to the stirring electrodes
105
and
122
between voltage levels V
4
and V
3
wherein V
3
<V
1
<V
4
at a period of Ts for a time length of 3·Ts/2, with the stirring voltages V
1
supplied to the remaining stirring electrodes
106
and
110
which sandwich the specified ejecting electrode
117
being unchanged.
After the electrophoretic voltages supplied to the electrophoretic electrodes
119
and
121
are turned off at the end of interval “a”, colored particles
15
stop themovement toward the inkjet slit
102
. In addition, the direction of the electric field between the stirring electrodes
105
and
106
and between the stirring electrodes
110
and
122
changes at a period of Ts/2 because the stirring voltages supplied to the stirring electrodes
105
and
122
sandwiching the stirring electrodes
106
and
110
change at a period of Ts from the constant stirring voltage V
1
. As a result, the colored particles
115
in the vicinities of the tips of the ejecting electrodes
102
and
108
are moved in the opposite directions at the period of Ts/2 between the ejecting electrodes
105
and
106
and between ejecting electrodes
110
and
122
, and stirred.
In this operation, the colored particles
115
are moved uniformly in the vicinities of the tips of the ejecting electrodes
112
and
118
. Since the constant stirring voltage V
1
is applied to the stirring electrodes
106
and
110
, the change in the electric field as described above does not influence the electric field between the stirring electrodes
106
and
110
sandwiching the specified ejecting electrode
117
.
The control unit
114
also delivers the second control signal during interval “b” to the ejecting electrode control section
103
, which responds thereto to supply an ejecting voltage pulse having an amplitude of V
2
and a duration of T
2
to the ejecting electrode
117
. As a result, the colored particles
115
in the vicinity of the tip of the ejecting electrode
117
are moved to the tip of the ejecting electrode
117
by the electrostatic force generated therein and are concentrated at the tip. The colored particles
115
then overcome the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force at a timing in synchrony with the ejecting voltage pulse, to be ejected as ink droplets
111
onto the recording medium
104
.
At the beginning of interval “c”, the control unit
114
receives printing data and external control signals for ejection from the ejecting electrode
112
,
117
and
118
. The control unit
114
delivers a third control signal to the stirring electrode control section
107
and the electrophoretic electrode control section
108
. The stirring electrode control section
107
responds to the third control signal to supply a constant stirring voltage V
1
to the stirring electrodes
105
and
122
. As a result, the colored particles
115
in the vicinities of the tips of the ejecting electrodes
112
and
118
stops the movement, whereby the colored particles
115
are distributed uniformly in the vicinities of the ejecting electrodes
112
and
118
.
On the other hand, the electrophoretic electrode control section
108
responds to the third control voltage to again supply an electrophoretic voltage V
1
during interval “c” to each of the electrophoretic electrodes
119
,
120
and
121
, thereby generating an electric field in the ink chamber
101
filled with the pigmented ink. The colored particles
115
in the pigmented ink are moved at the electrophoretic mobility toward the ink jet slit
102
, whereby the colored particles
115
are concentrated in the vicinities of the tips of the ejecting electrodes
112
,
117
and
118
.
The control unit
114
also delivers the third control signal to the ejecting electrode control section
103
, which responds thereto to supply an ejecting voltage having an amplitude of V
2
and a duration of T
2
to the ejecting electrodes
112
,
117
and
118
. The colored particles
115
distributed in the vicinities of the tips of the ejecting electrodes
112
,
117
and
118
are urged from tips of the ejecting electrodes
112
,
117
and
118
by the electrostatic force thus generated, and are concentrated therein.
The colored particles
115
in the vicinities of the tips of the ejecting electrodes
112
,
117
and
118
overcome the meniscus force, surface tension and viscosity of the pigmented ink by virtue of the electrostatic force, to be ejected from the ejecting electrodes
112
,
117
and
118
as ink droplets onto the recording medium during interval “c”.
At the end of interval “c”, the control unit
114
receives print data and external control signals for non-ejection from any of the ejecting electrodes
112
,
117
,
118
etc. The control unit
114
delivers a fourth control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
. The electrophoretic electrode control section
108
responds thereto to cancel the electrophoretic voltage supplied to the electrophoretic electrode
119
,
120
and
121
. The stirring electrode control section
107
also responds to the fourth control signal to supply alternating stirring voltages to the stirring electrodes
105
,
106
,
110
and
122
. The alternating stirring voltages change their level between V
4
and V
3
wherein V
3
<V
1
<V
4
, and has opposite polarities between the stirring electrodes
105
and
106
and between the stirring electrodes
110
and
122
at a period of Ts and for a time length of 3·Ts/2.
The colored particles
115
stop movement toward the ink jet slit
102
after the electrophoretic voltage is turned off at the electrophoretic electrodes
119
,
120
and
121
at the end of interval “c”. Instead, the alternating stirring voltage reciprocally moves the colored particles in the vicinity of the ink jet slit
102
in the opposite directions for stirring. The colored particles
115
are distributed substantially uniformly in the vicinities of the ejecting electrodes
112
,
117
,
118
etc. for preparing a next ejection. Thereafter, the alternating stirring voltage is turned off for stopping the recording.
The ink jet recording head of the present embodiment has an advantage in preventing the colored particles which are not ejected and remain in the vicinity of the ink jet slit from being concentrated and ejected from the non-specified ejecting electrode as well as in preventing the block of the ink jet slit by the colored particles not ejected, thereby obtaining a stable recording and an excellent image quality.
An ink jet recording head according to a fourth embodiment of the present invention is similar to the first embodiment of
FIG. 3
except for the program stored in the ROM
130
. In the present embodiment, the recording head can be shifted in a standby mode canceling the stirring voltage after a specified time length elapsed since the start of the application of the stirring voltage by.
FIG. 9
is a flowchart of the program stored in the ROM
130
. The control unit
114
monitors the time length that elapsed since the time instant at which an ejecting voltage pulse having an amplitude of V
2
and a duration of T
2
is applied to the ejecting electrode
112
at step
41
, and also the time length that elapsed since the ejecting voltage is cancelled at step
42
.
If it is detected that a time length of S
1
elapsed since the turn-off of the ejecting electrode at step
43
, as shown in
FIG. 10
, the control unit
114
delivers a first control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
. The electrophoretic electrode control section
108
responds to the first control signal to cancel the electrophoretic voltage V
1
supplied to the electrophoretic electrode
110
at step
45
. At step
46
, the stirring electrode control section
107
responds to the first control signal to change the stirring voltages supplied to the stirring electrodes
105
and
106
between the voltage levels Vab and −Vab at a period of Tab, with the polarities of the stirring voltages being opposite to each other. The colored particles
115
stop the movement toward the ink jet slit
102
after the electrophoretic voltage is turned off, and the colored particles in the vicinity of the ejecting electrodes are moved reciprocally in the opposite directions along the ink jet slit
102
by the alternating stirring voltage applied between the stirring electrodes
105
and
106
.
If there is no request for ink ejection at steps
48
and
49
from the computer for the next time interval S
2
, the colored particles
115
are reciprocally moved along the ink jet slit
102
by the alternating stirring pulse at the period Tab for stirring the colored particles
115
. The colored particles
115
are distributed uniformly in the vicinity of the ink jet slit
102
by the stirring to enter a standby mode for preparing a next ink ejection beginning at step
41
.
Referring to
FIG. 11
, the electrophoretic electrode control section
108
responds to the first control signal from the control unit
114
at step
45
to cancel the electrophoretic voltage V
1
supplied to the electrophoretic electrode
110
. The stirring electrode control section
107
also responds to the first control signal to supply an alternating stirring voltage pulse at step
46
to the pair of stirring electrodes
105
and
106
. If the control unit
114
detects a request for the ink ejection at step
48
from the computer before the time length S
2
elapses, the control unit
14
delivers a second control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
. The electrophoretic electrode control section
108
again supplies an electrophoretic voltage V
1
to the electrophoretic electrode
110
by responding to the second control signal.
On the other hand, the stirring electrode control section
107
cancels the alternating stirring voltage supplied to the stirring electrodes
105
and
106
. After the electrophoretic voltage V
1
is supplied to the electrophoretic electrode
110
, the colored particles
115
in the pigmented ink are moved toward the ink jet slit
102
, and are concentrated in the vicinity of the ink jet slit
102
. When an ejecting voltage pulse is applied to a specified ejecting electrode
112
, the colored particles are ejected therefrom as ink droplets, to be adhered onto the recording medium.
FIG. 12
shows a flow-chart of another case wherein the control unit
114
detects a request for a power-off at step
47
in
FIG. 9
before the time length SI elapses since the end of the ejecting voltage applied to the specified ejecting electrode
112
. After the control unit detects the request for the power-off at step
47
in
FIG. 9
, the control unit
114
delivers a control signal to the electrophoretic electrode control section
108
and the stirring electrode control section
107
.
The electrophoretic electrode control section
108
responds to the control signal at step
51
to cancel the electrophoretic voltage supplied to the electrophoretic electrode
110
, thereby stopping the movement of the colored particles
115
toward the ink jet slit. The stirring electrode control section
107
also responds to the control signal to supply an alternating stirring voltage to the stirring electrodes
105
and
106
at step
52
, thereby reciprocally moving the colored particles in the vicinities of the ink jet slit between the ejecting electrodes
105
and
106
in opposite directions.
After the control unit
114
detects a time length of S
2
elapsed at step
53
, the control unit
14
delivers another control signal to control the stirring electrode control section
107
to cancel the stirring voltage at step
54
. Thereafter, the power supply for the recording head is turned off.
Referring to
FIG. 13
, there is shown a timing chart of the ink jet recording head of the present embodiment, wherein ejecting voltage is repeatedly applied without an interval of S
1
. The stirring electrode control section supplies a constant voltage to the stirring electrodes.
In the operation of the fourth embodiment of the present invention, since the stirring electrodes
105
and
106
are controlled depending on the next state of the ink jet recording head, the colored particles are uniformly distributed along the ink jet slit during an inoperative state of the ink jet recording head, thereby preventing the ink jet slit
102
from being blocked by the colored particles
115
not ejected for a long time.
Referring to
FIG. 14
, an ink jet recording head according to a fifth embodiment of the present invention comprises an ink chamber
201
defined by a dielectric housing
216
, a plurality of electrophoretic electrodes
210
,
208
,
203
etc., a plurality of ejecting electrodes
205
,
206
,
207
etc. each corresponding to one of the electrophoretic electrodes, a counter electrodes
209
disposed behind a recording medium
204
, which receives ink droplets
216
ejected by the ejecting electrode, an interface
213
, a control unit
214
having a ROM
230
, and an electrode control section
215
including a plurality of controllers
216
,
217
,
218
etc. each for controlling voltages for a pair of electrophoretic electrode and ejecting electrode. Those elements in the present embodiment have respective functions similar to those described in connection with the first through fourth embodiment.
Referring to
FIG. 15
showing a timing chart of the present embodiment, there is shown a case wherein ejecting electrodes
205
,
207
and
206
are consecutively activated for ejection of ink droplets
211
of the colored particles from the ink jet slit
202
.
In operation, the control unit
214
receives printing data and external control signals to determine which pair of electrophoretic electrode and ejecting electrode should be applied with driving voltages as well as which driving voltage should be provided to each of the pair thus determined. The control unit
214
then supplies a first control signal to the first controller
216
for driving the first pair of electrophoretic electrode
210
and ejecting electrode
205
.
The first controller
216
supplies a constant electrophoretic voltage V
1
to the electrophoretic electrode
210
for the first interval, and supplies an ejecting voltage pulse having an amplitude of V
2
and a duration of Tp to an ejecting electrode
205
at the end of the first interval for ejection of colored particles. Other pairs of electrophoretic electrode and ejecting electrode are not applied with driving voltages and maintained at zero potential.
After the driving voltages for the first pair of electrophoretic electrode
210
and ejecting electrode
205
are cancelled, the second pair of electrophoretic electrode
203
and ejecting electrode
207
are applied with driving voltages similarly to the first pair by the second controller
218
. The third pair of electrophoretic electrode
208
and ejecting electrode
206
are then driven similarly by the third controller
217
.
In the present embodiment, the pair of electrophoretic electrode and ejecting electrode are driven within a single interval so that colored particles are concentrated only in the vicinity of the specified ejecting electrode just before ejection, thereby avoiding undesirable ejection of the colored particles from non-specified ejecting electrodes.
Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alterations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention.
Claims
- 1. An ink jet recording head comprising a housing defining an ink chamber having an ink jet slit at a front side thereof for ejecting colored particles in pigmented ink, at least one electrophoretic electrode disposed at a rear side of said ink chamber receiving an electrophoretic voltage for moving said colored particles by an electrophoretic force, a plurality of ejecting electrodes having respective tips arranged in a row along said ink jet slit, each of said ejecting electrodes receiving an ejecting voltage, a counter electrode opposed to said row of tips of said ejecting electrodes and maintained at a potential, and a pair of stirring electrodes, one of said stirring electrodes being disposed at each end of the row of the tips of said ejecting electrodes, said stirring electrodes receiving a stirring voltage therebetween that reverses polarity at least once to move the particles perpendicular to an ink election direction.
- 2. An ink jet recording head as defined in claim 1, wherein said stirring electrodes receive the stirring voltage in the absence of said electrophoretic voltage and said ejecting voltage.
- 3. An ink jet recording head as defined in claim 1 further comprising additional stirring electrodes that are each disposed between a different pair of adjacent tips of said ejecting electrodes.
- 4. An ink jet recording head as defined in claim 3, wherein said at least one electrophoretic electrode includes a plurality of electrophoretic electrodes disposed corresponding to said ejecting electrodes.
- 5. An ink jet recording head as defined in claim 1, further comprising a timer for measuring a time length elapsed since an end of said ejecting voltage to output a timing signal, and a control unit for responding to said timing signal to generate a stirring signal for application of said stirring voltage.
- 6. An ink jet recording head as defined in claim 5, wherein said control unit generates said stirring signal when said electrophoretic voltage is off.
- 7. An ink jet recording head as defined in claim 6, wherein said control unit stops said stirring signal after a time length elapses since the generation of said stirring signal before a standby mode of said ink jet recording head.
Priority Claims (4)
Number |
Date |
Country |
Kind |
8-315130 |
Nov 1996 |
JP |
|
8-318306 |
Nov 1996 |
JP |
|
8-318307 |
Nov 1996 |
JP |
|
8-318308 |
Nov 1996 |
JP |
|
Foreign Referenced Citations (7)
Number |
Date |
Country |
0703080 |
Mar 1996 |
EP |
405208499 |
Aug 1993 |
JP |
406234219 |
Aug 1994 |
JP |
8-90825 |
Apr 1996 |
JP |
8-207307 |
Aug 1996 |
JP |
8-309993 |
Nov 1996 |
JP |
WO 9311866 |
Jun 1993 |
WO |