Information
-
Patent Grant
-
6309056
-
Patent Number
6,309,056
-
Date Filed
Thursday, April 22, 199925 years ago
-
Date Issued
Tuesday, October 30, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Sidley Austin Brown & Wood
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
An ink jet head for a printer wherein an ink drop is ejected from a nozzle to fly and land on the recording paper to form an image. The ink jet head includes the nozzle for ejecting ink, an ink channel that communicates with the nozzle, a pair of oscillating plates that are opposing to each other on walls of the ink channel, a pair of electrodes disposed in contact with the oscillating plates, an ink chamber for holding the ink, and an inlet for supplying the ink from the ink chamber to the ink channel. A gap between the electrodes is filled with the ink having a relative dielectric constant higher than air. A voltage is applied between the electrodes.
Description
This application is based on Japanese Patent Application Nos. 10-119435 and 10-119436 filed on Apr. 28, 1998, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink jet head, drive method thereof, and ink jet recording apparatus for causing ink to fly across a space with the help of deformation of an oscillating plate by means of electrostatic force.
2. Description of the Related Art
An ink jet type recording apparatus causes an ink drop to be ejected from a nozzle and thrown across a space to land on a recording medium to form an image. A number of ink jet heads have been invented to be used on such a recording apparatus. As an example, Japanese laid-open Patent Publication, JP-A-05-50601, discloses an ink jet head that uses an electrostatic actuator that ejects ink with the help of deformation of an oscillating plate by electrostatic force.
This electrostatic ink jet head has a laminar structure composed of three members joined together, i.e., a channel plate provided with a plurality of recesses, a glass substrate positioned opposite to the bottom surface of the recesses, and a cover plate. The recesses form a nozzle that ejects an ink drop, an ink channel that communicates with the nozzle, an oscillating plate that changes the pressure in the ink channel, a common ink chamber where ink is stored, and an inlet that serves as an ink supply port from the common ink chamber to the ink channel. The bottom wall of the ink channel forms an oscillating plate to generate the pressure for ejecting ink. A plurality of ink channels and nozzles are provided in accordance with the number of dots to be printed at a time. Moreover, a first electrode is provided on the surface of the side which is not facing the ink channel, or on the backside of the oscillating plate. A second electrode is provided on the surface of the glass substrate opposing the first electrode separated by a small gap from the first electrode. The recesses provided on the backside of the oscillating plate and the top surface of the substrate also serves as the members to form these electrodes.
The electrostatic type ink jet ejects ink based on the following operating principle to form an image on the recording medium.
First of all, when a voltage is applied between the first electrode and the second electrode by means of a drive circuit, an electrostatic force is generated between the electrodes. Accordingly, the oscillating plate deforms by being drawn in the direction toward the second electrode, or in the direction of moving itself away from the ink channel, which is communicating with the nozzle. At this time, the volume of the ink channel increases. Therefore, ink is drawn through the inlet into the ink channel to fill it up. Next, the application of the voltage between the first and second electrodes as opposing electrodes is terminated and the charges are discharged. The oscillating plate returns to its original position by the restoring force due to its own rigidity. In the mean time, the oscillating plate sharply compresses the volume of the ink channel to generate a pressure. Consequently, the ink stored in the ink channel is ejected, flies across a space, and lands on the recording medium to form an image.
Such an electrostatic jet head has an advantage of allowing us to realize a higher density constitution and to print using a relatively low voltage in comparison with the method of ejecting ink using the deformation of a piezoelectric device.
However, it is necessary to make the gap between the first and second electrodes extremely small in order to reduce the applied voltage on an electrostatic ink jet head. For example, the electrode gap is set to about 0.3 μm. Consequently, it is necessary to produce and assemble individual components such as the channel plate with extreme accuracy in manufacturing the head.
Moreover, since the electrode gap is only about 0.3 μm, there is a danger of causing a short circuit between the first electrode as an individual electrode and the second electrode as a common electrode when the oscillating plate is oscillated. In order to prevent the short circuit, a protective layer can be provided on top of the electrode. However, a problem with the protective layer is that it is susceptible to chronological changes.
The pressure P generated by the electrostatic ink jet head can be expressed by the following formula:
P=
1/2·{∈
r
·∈
o
·(
V/G
)
2
}
wherein the symbol ∈
r
denotes the relative dielectric constant between the opposing electrodes, the symbol ∈
o
denotes the dielectric constant in vacuum, 8.8×10
−12
[F/m], the symbol V denotes the applied voltage [V], and the symbol G denotes the distance between the electrodes [m].
In case of the conventional electrostatic type ink jet head, air is inserted, whose relative dielectric constant is 1, in the gap between the opposing electrodes. Therefore, it is necessary to set the gap G between the electrodes as small as 0.3 μm as mentioned above in order to generate a sufficient pressure to cause ink to fly using, for example, a drive voltage of 40V. The manufacture of such a head has a problem that it requires high precision machining and assembly practices.
Incidentally, the electrostatic type ink jet head uses a constitution of causing the ink in the ink channel to be ejected and fly by means of deforming the oscillating plate as mentioned above. Therefore, a situation can occur, in which the mechanical constitution can no longer follow the demand when the drive frequency of the ink head, or the frequency of the voltage applied between a pair of electrodes is increased in case of continuous printing. Thus, the ink jet head drive frequency is limited by the natural frequency of the ink in the ink channel and the natural frequency of the oscillating plate.
Therefore, a problem has been noted that there is a limit to the improvement of the head response by means of increasing the drive frequency of the ink jet head.
SUMMARY OF THE INVENTION
An object of the invention is to provide an improved apparatus that is capable of solving the problems described above.
Another object of the invention is to provide an ink jet head that allows the use of a larger gap between the electrodes and to make manufacturing easier thus enhancing its reliability.
Another object of the invention is to increase the restoring force of the oscillating plate so that the drive frequency of the ink jet can be improved.
One aspect of the invention is an ink jet head having an ink channel, a pair of oscillating plates, and a pair of electrodes. The ink channel is filled with ink that communicates with a nozzle that ejects ink. The oscillating plates are disposed opposing to each other on walls of the ink channel. The electrodes are provided in contact with the oscillating plates respectively. In addition, a voltage is applied between the electrodes.
Another aspect of the invention is an ink jet recording apparatus having an ink channel, a pair of oscillating plates, a pair of electrodes, and a controller. The ink channel is filled with ink that communicates with a nozzle that ejects ink. The oscillating plates are disposed opposing to each other on walls of the ink channel. The electrodes are disposed in contact with the oscillating plates, respectively. And, the controller controls a voltage to be applied between the electrodes.
Another aspect of the invention is an ink jet head having an ink channel, an oscillating plate, a first electrode, a second electrode, and a third electrode. The ink channel communicates with a nozzle that ejects ink. The oscillating plate is disposed facing the ink channel. The first electrode is disposed on the oscillating plate and a side where the first electrode is disposed is opposite to a side that faces the ink channel. The second electrode is disposed opposing the first electrode. And, the third electrode is located relative to the first electrode on a side opposite to a side the second electrode is located.
Another aspect of the invention is an ink jet recording apparatus having an ink channel, an oscillating plate, a first electrode, a second electrode, a third electrode, and a controller. The ink channel communicates with a nozzle that ejects ink. The oscillating plate is disposed facing the ink channel. The first electrode is disposed on the oscillating plate and a side where the first electrode is disposed is opposite to a side that faces the ink channel. The second electrode is disposed opposing the first electrode. The third electrode is located relative to the first electrode on a side opposite to a side the second electrode is located. And, the controller controls application of voltages on the electrodes.
Another aspect of the invention is a method for driving an ink jet head, including an oscillating plate, that is disposed facing an ink channel, a first electrode disposed on the oscillating plate, a side where the first electrode is disposed being opposite to a side that faces the ink channel, a second electrode that is disposed opposing the first electrode, and a third electrode located relative to the first electrode on a side opposite to a side the second electrode is located. The method contains the steps of a first voltage application step that applies a voltage between the first and second electrodes, and a second voltage application step that applies a voltage between the first and third electrodes.
The objects, characteristics, and advantages of this invention other than those set forth above will become apparent from the following detailed description of the preferred embodiments, which refers to the annexed drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a perspective view of an ink jet printer using an ink jet head according to the embodiment 1;
FIG. 2
is a perspective view of a carriage that contains the ink jet head for one color of the head unit shown in
FIG. 1
;
FIG. 3
is a sectional view of the ink jet head;
FIG. 4
is an exploded perspective view of a channel plate of the ink jet shown in
FIG. 3
;
FIG.
5
A and
FIG. 5B
are sectional views along the line I—I and the line II—II of
FIG. 3
, respectively;
FIGS. 6A
to
6
H are sectional views for describing the manufacturing method of the ink jet head;
FIG. 7
is a block diagram of a drive circuit;
FIG. 8
is a sectional view of an ink jet head according to the embodiment 2;
FIG. 9
is an exploded perspective view of the ink jet head shown in
FIG. 8
;
FIG. 10
is a sectional view of an ink jet head according to the embodiment 3;
FIG. 11
is an exploded perspective view of an ink jet head according to the embodiment 4;
FIG. 12
is a plan view of the ink jet head seen through the channel plate of
FIG. 11
;
FIG. 13
is a sectional view along the line III—III of
FIG. 12
;
FIG. 14
is a sectional view along the line IV—IV of
FIG. 12
;
FIGS. 15A
to
15
C are sectional views for describing the method of manufacturing the channel plate of
FIG. 13
;
FIG. 16
is a block diagram for describing the constitution of the controller of the ink jet printer; and
FIG.
17
A and
FIG. 17B
are expanded sectional views for describing the motions of the oscillating plate when it ejects an ink drop.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The embodiments of this invention will be described below with reference to the accompanying drawings.
Embodiment 1
The ink jet printer
1
shown in
FIG. 1
is intended for forming or recording an image on a sheet
2
, which is a recording medium such as a sheet of paper or an OHP sheet, and consists of a head scanning system and a sheet feeding system.
The head scanning system includes a head unit
3
having an ink jet type print head, a carriage
4
for holding a head unit
3
, a scan shaft
5
and a guide shaft
6
that guide the carriage
4
for reciprocating in parallel with a surface of the sheet
2
where an image is formed, a pulse motor
7
that drives the carriage
4
to reciprocate along the guide shaft
6
, and a timing belt
9
and an idle pulley
8
for converting the rotation of the pulse motor
7
into a reciprocating motion of the carriage
4
. A single print head or a plurality of print heads are provided depending on the number of colors (3, 4 or 7 colors) used.
On the other hand, the sheet feeding system includes a platen
10
that also serves as a guide plate for guiding the sheet
2
along its transportation passage, a pressure plate
11
that holds down the sheet
2
against the platen
10
to prevent the sheet
2
from floating, a discharge roller
12
and a pressure roller
13
for discharging the sheet
2
, a maintenance device
14
for washing the nozzle surface of the head unit
3
that ejects the ink to correct poor ink ejection condition and to restore the nozzle surface to a better condition, and a knob
15
for manually transporting the sheet
2
.
The sheet
2
is transported by means of a manual feeding or a sheet feeding mechanism (not shown) such as a cut sheet feeder into a recording unit where the head unit
3
and the platen
10
are disposed opposing to each other. The transportation of the sheet to the recording unit is controlled by the number of revolutions of a sheet feeding roller driven by a sheet feed motor. The sheet feeding motor and the sheet feeding roller are not shown here.
An electrostatic type ink jet head
31
, which is an electrostatic actuator and will be described later in detailed, is used as the print head of the head unit
3
. Formation or recording of an image is executed by an ink drop ejected from the ink jet head
31
landing on the sheet
2
.
The carriage
4
is driven laterally (main scanning direction) relative to the sheet
2
by means of the pulse motor
7
, the idle pulley
8
, and the timing belt
9
. Accordingly, the head unit
3
mounted on the carriage
4
forms an image of one line in the lateral or main scanning direction on the sheet
2
. In the mean time, the sheet is fed vertically (secondary scanning direction) when recording of one line is completed. Thus, an image can be formed or recorded on the sheet
2
.
The sheet
2
that has passed the recording unit is discharged with the help of the discharge roller
12
provided on the feed direction side, or on the downstream side and the pressure roller
13
that makes contact with the discharge roller
12
under pressure.
As shown in
FIG. 2
, provided in the vicinity of the carriage
4
are an ink cartridge
43
with an air hole
44
, a casing
41
and a casing lid
45
for containing the ink cartridge
43
, an ink supply tube
42
to which the ink cartridge
43
is detachably connected for supplying ink to the ink jet head
31
, a hook
46
and a lid stop
47
used for affixing the casing lid
45
to the casing
41
when the casing lid
45
is closed, and a pressure spring
48
for urging the ink cartridge
43
in the casing
41
while the casing lid
45
is closed, in the direction opposite to the direction of the arrow D
3
, or to the direction of inserting the ink cartridge
43
.
As the carriage
4
having such a constitution moves laterally, or in the direction of the arrow D
1
, one line of image in the main scanning direction is recorded on the sheet
2
. Also, as the sheet
2
is driven in a vertical direction, or the direction of the arrow D
2
, the motion in the secondary scanning direction is executed for recording the next line of image.
Next, the constitution of the ink jet head
31
will be described in detail referring to
FIGS. 3
,
4
5
A and
5
B.
The electrostatic ink jet head
31
shown in
FIG. 3
is of an edge eject type that ejects an ink drop from an nozzle
54
provided on the head side end shown on the left end of the drawing. The ink jet head
31
includes two channel plates
50
a
and
50
b,
each having several recesses, stacked as one on top of the other as shown in FIG.
4
. The channel plates
50
a
and
50
b
are made of single crystal silicone.
By stacking the channel plates
50
a
and
50
b
in such a way that the recesses provided in the inside are facing to each other, they jointly constitute a plurality of nozzles
54
for ink ejection, a plurality of ink channels
51
that respectively communicate with nozzles
54
to generate pressures for ink ejection, a common ink chamber
52
for storing ink supplied from a tank (not shown), and a plurality of inlets
53
, which serve as an ink supply port from the common ink chamber
52
to each ink channel
51
.
For example, the ink channel
51
is formed by matching a recess
51
a
formed in a channel plate
50
a
shown in the upper portion of
FIG. 4 and a
recess
51
b
formed in a channel plate
50
b
shown in the lower portion thereof. The symbol “
58
” shows the ink supply port for introducing ink to the common ink chamber
52
.
A pair of oscillatory plates
55
a
and
55
b
are formed by the upper and lower walls of the ink channel
51
that are opposing to each other. The volume and inner pressure of the ink channel
51
are variable as the oscillating plates
55
a
and
55
b
make minute displacements.
As shown in FIG.
3
and
FIG. 5A
, a first electrode
56
is provided on the inner surface of the oscillating plate
55
a
that faces the ink channel
51
. A second electrode
72
is provided on the inside of the oscillating plate
55
b
as shown in FIG.
3
and FIG.
5
B. Also, the first electrode
56
is a common electrode as shown in
FIG. 3
, and the second electrode
72
is an individual electrode or a drive electrode, both of which are connected to a drive circuit
20
via wires
81
and
82
.
By applying a voltage from the drive circuit
20
to a pair of electrodes
56
and
72
, the pair of oscillating plates
55
a
and
55
b
are attracted to each other so that the volume of the ink channel
51
contracts sharply. The pressure generated at this time causes an ink drop to be discharged from the nozzle
54
. On the other hand, when the application of the voltage to the electrodes is stopped, causing an electric discharge, the oscillating plates
55
a
and
55
b
are restored to their original shapes due to their own restoring forces resulting from their rigidities and increasing the volume of the ink channel
51
. As a result, ink is supplied from the common ink chamber
52
to the ink channel
51
through the inlet
53
.
The first electrode
56
as the common electrode and the second electrode
72
as an individual electrode are exposed to the ink channel
51
to form a portion of the ink passage. In other words, the ink channel
51
is formed between the common electrode and the individual electrode. Therefore, the space between the pair of electrodes
56
and
72
that cause an electrostatic force contains no air but rather is filled with ink.
The relative dielectric constant ∈
r
of water-based ink is about 60 and is larger than the relative dielectric constant ∈
r
of air, which is 1. Obviously, the electrostatic actuator with the constitution stated above has a better efficiency because of the existence of a material with a relative dielectric constant higher than that of air between the electrodes
56
and
72
. As a result, it is possible to use a larger gap G between the electrodes. For example, while the electrode gap of the conventional head is about 0.3 μm, the gap G between the electrodes in case of the head
31
according to the embodiment 1 is almost ten times of that, or about 3 μm.
Next, the method of manufacturing the ink jet head
31
will be described as an example referring to
FIGS. 6A
to
6
H.
The ink jet head
31
is manufactured using various manufacturing processes including the semiconductor device manufacturing process and the micromachine manufacturing process. It goes without saying that the present invention is applicable to an ink jet head manufactured by a method that is not described here.
As shown in
FIG. 6A
, the backside (topside in the drawing) of a substrate
90
made of a single crystal silicon is sandblasted prior to etching. As a result, through-holes
91
for openings used for taking out electrodes as many as the number of the ink channels
51
are formed. At the same time, a through hole
92
for the ink supply port
58
is formed in the same way. The through holes
91
and
92
become slightly tapered narrowing at the distal ends.
As shown in
FIG. 6B
, recesses for constituting the ink channels
51
, the common ink chamber
52
, the inlets
53
, the nozzles
54
and the oscillating plates
55
a,
55
b
are formed by means of anisotropic etching using KOH solution on the channel plates
50
a,
50
b
More specifically, the silicon substrate
90
has a thickness of 200 μm, and its surface orientation is (1, 1, 0). An orifice flat is formed on the (1, 1, 0) surface. A resist
93
is formed on the bottom surface and the top surface (bottom surface in the drawing) of the silicon substrate
90
. Next, the channel pattern is disposed at an angle of 35.3 degrees from the orifice flat. The desired vertical wall structure is formed when etching is done.
Next, the resist
93
is removed as shown in FIG.
6
C. After that, the area indicated by an arrow in the silicon substrate
90
is cut off using a dicer to form the ink eject port (nozzle
54
) as shown in FIG.
6
D.
Next, as shown in
FIG. 6E
, a CrAu layer is formed inside the tapered through hole
91
by means of sputtering or CVD method from the back side of the silicon substrate
90
, while a 0.1 μm CrAu layer for the electrode
56
is formed on the front side of the silicon substrate
90
by means of sputtering or CVD method. Materials such as ITO, SnO
2
, Pt and other low resistance materials in addition to CrAu are applicable to the electrode
56
.
Next, as shown in
FIG. 6F
, a 0.1 μm SiC layer is formed by means of sputtering as a protection layer
94
of the electrode
56
. Although SiO
2
and MgO in addition to SiC can be as the material for forming the protective layer, SiC is most preferable considering its excellent humidity resistance.
Incidentally, the other channel plate
50
b,
which is in a mirror image relation with the channel plate
50
a,
is to be made using the same procedure.
Next, a low melting point glass film
95
is formed on the junction surface between the channel plates
50
a
and
50
b
as shown in FIG.
6
G. When the channel plates
50
a
and
50
b
are joined together as shown in
FIG. 6H
, the ink jet head
31
is completed. The thickness of the oscillating plates
55
a
and
55
b
is 3 μm and the gap G between the electrodes is 3 μm as well.
The ink jet
31
is a high efficient electrostatic actuator due to the constitution, in which the gap between the electrodes
56
and
72
is filled with ink that has a higher relative dielectric constant than air. Therefore, the gap G between the electrodes can be chosen to be extremely larger than that of a conventional head. Accordingly, manufacturing and assembling of the channel plates
50
a
and
50
b
as components of the ink jet head
31
are substantially easier. This also makes the head manufacturing easier and improves the available percentage.
The electrodes
56
and
72
of the ink jet head
31
manufactured as above are connected to the drive circuit
20
as shown in FIG.
7
.
The drive circuit
20
includes a charging circuit
22
connected to a power circuit
21
, a grounded charging circuit
23
, a switching circuit
24
that selectively connects the electrostatic actuator with the electrodes
56
and
72
to the charging circuit
22
or the discharging circuit
23
by means of a switch, a clock circuit
25
for generating clock pulses as the standard for the work timing, and a timer circuit
26
for controlling the charge timing and the discharge timing.
In order to eject ink, it is necessary to cause the pair of oscillating plates
55
a
and
55
b
to be attracted to each other sharply. The drive circuit
20
generates voltage pulses that cause such motions of the oscillating plates
55
a
and
55
b
to control the application and cut-off of the drive voltage to the electrodes
56
and
72
. Therefore, in order to eject ink, first of all, the switch is connected to the charging circuit
22
to apply the voltage on the electrodes
56
and
72
. Then, the voltage is cut-off. After a predetermined time, the switch is connected to the discharging circuit
23
to clear the remaining charge. The switch timing is controlled by the timer circuit
26
.
When a drive voltage of 35V was applied to the ink jet head
31
, it ejected an ink drop of about 60 picolitter. It was necessary to apply a drive voltage of 40V to eject an ink drop of the same volume in case of a conventional ink jet head using a single oscillating plate. Therefore, the ink jet head
31
can use a lower voltage compared to a conventional head. This is because the ink channel
51
of the ink jet head
31
is sandwiched between the pair of oscillating plates
55
a,
55
b
and it is easier to achieve a larger volume change compared to the conventional case where only one oscillating plate is used.
Moreover, while the conventional type ink jet head with 0.3 μm gap G between the electrodes shorted out at 500 million cycles, the ink jet head
31
using 3 μm gap G between the electrodes according to the embodiment 1 still operated without shorting after two billion cycles. It is understood that the chance of the contact between the electrodes
56
and
72
is eliminated and the ink jet head
31
has less chance of being chronologically affected because the ink jet head
31
has a distance between the electrodes much larger than that of the conventional type. Thus, it is possible to provide an ink jet head with a higher reliability in terms of durability.
Embodiment 2
The ink jet head
131
shown in FIG.
8
and
FIG. 9
is of an electrostatic type where an electrostatic actuator is used, and is different from the embodiment 1 in terms of the position of the oscillating plates. Specifically, while the space between the pair of oscillating plates
55
a
and
55
b
forms a portion of the ink passage in the embodiment 1, a pair of oscillating plates
155
a
and
155
b
is disposed slightly apart from the substantial ink passage from an inlet
153
to a nozzle
154
in case of the ink jet head
131
. Therefore, the ink jet head
131
has an improved high speed printing capability compared to the embodiment 1.
As shown in
FIG. 9
, the ink jet head
131
includes two channel plates
150
a
and
150
b
joined together in the vertical direction in the drawing and a nozzle plate
160
, which is joined on the side thereof. The channel plates
150
a
and
150
b
are made of single crystal silicon having a plurality of recesses and the nozzle plate
160
is provided with nozzles
154
.
An extension
161
of the ink channel
151
is extending toward the backside (right side in
FIG. 8
) relative to the nozzle
154
. The top wall and the bottom wall of this extension
161
constitute the oscillating plates
155
a
and
155
b
. Also, the first electrode
156
used as the common electrode is provided on the inside of the oscillating plate
155
a,
while the second electrode
172
used as the individual electrode is provided on the inside of the oscillating plate
155
b.
The inlet
153
is formed on the top surface of the channel plate
150
a
to supply ink from the ink chamber which is not shown.
The nozzle diameter and the inlet diameter are both chosen to be 23 μm. The nozzle plate
160
is made by Ni electro-casting. The methods of etching from the both sides of the silicon substrates, two stage etching, producing the through hole, forming of the electrodes, joining of the substrates, etc. are the same as in the embodiment 1. The materials for the electrodes and protective layer used in the embodiment 1 may be used here as well. The ejection operation is also the same as in the embodiment 1. Specifically, when a specified voltage from the drive circuit
20
is applied between the electrodes
156
and
172
, the pair of oscillating plates
155
a
and
155
b
are attracted to each other so that the volume of the ink channel
151
contracts sharply. The pressure generated at this time causes an ink drop to be discharged from the nozzle
154
. On the other hand, when the application of the voltage between the electrodes
156
and
172
is stopped causing an electric discharge, the oscillating plates
155
a
and
155
b
are restored to their original shapes due to their own restoring forces resulting from their rigidities, and thus increase the volume of the ink channel
151
.
Same as in the embodiment 1, the ink jet head
131
with the aforementioned constitution uses ink with a large relative dielectric constant ∈
r
of about 60 to fill the space between the electrodes
156
and
172
. As a result, the gap G between the electrodes can be chosen to be as large as 3 μm. Thus, the manufacture of the ink jet head can be made easier and the reliability can be improved at the same time.
Moreover, since the oscillating plates
155
a
and
155
b
are disposed further back of the inlet
153
in relation to the nozzle
154
to be slightly away from the substantial ink passage. Thus, the oscillating plates
155
a
and
155
b
do not interfere with the flow of ink in the ink passage from the inlet
153
to the nozzle
154
. This improves the high speed printing capability compared to the ink jet head
31
of the embodiment 1.
The channel plates used in the embodiment 1 and the embodiment 2 are made from silicon substrates by the wet etching method. However, the dry etching method using HF can be applied for manufacturing the channel plates as well. In that case, a channel pattern matching the mask can be formed on the etching surface irrespective of the surface orientation. As to the substrate material, photosensitive glass, ink resistant plastics such as polyimide or polysulfon can be used in addition to silicon. If a plastic material, such as polyimide and polysulfon, is used, the substrate can be made by a forming method such as molding.
Although the case of using a protection layer on the electrode has been described so far in order to prevent short circuit through ink, the protection layer is not needed if an ink with insulation properties is used.
While edge eject type ink jet heads were described in the embodiment 1 and the embodiment 2, the present invention is not limited to it, but rather it can be applied to an ink jet head of the face eject type as well as shown in the embodiment 3 below.
Embodiment 3
The ink jet head
231
shown in
FIG. 10
is of an electrostatic type using an electrostatic actuator and is different from the embodiment 1 and the embodiment 2 in terms of the nozzle constitution.
Specifically, the ink jet head
231
is of the face ejector type and includes two channels plates
250
a
and
250
b
stacked one on top of the other and has nozzles
254
on the bottom surface of the channel plate
250
b
as shown in the drawing. Members that are common to those of
FIG. 8
are assigned with the same codes and their descriptions are omitted here.
Since a large gap can be selected between the electrodes in this constitution as well, the manufacture of the ink jet head can be made easier and the reliability can be improved also.
Embodiment 4
The ink jet head
331
shown in
FIG. 11
is built into the printer. The general constitution of the ink jet printer and its operation are similar to the contents described in the embodiment 1 so that they are not repeated here. The head response of the ink jet head
331
is improved by means of increasing the drive frequency, or the frequency of applying a voltage between a pair of electrodes in case of continuous printing as described later.
As shown in the drawing, the ink jet head
331
has a multi-layered structure consisting of three elements, i.e., a channel plate
350
, a top plate
360
that covers the top of the channel plate
350
as indicated in the drawing, and a glass substrate
370
. The channel plate
350
includes ink channels
351
, an ink chamber
352
, inlets
353
, nozzles
354
, oscillating plate
355
each provided with a first electrode
356
that serves as a common electrode, and spaces
357
. The glass substrate
370
has second electrodes
372
that serves as individual electrodes formed thereon. The second electrode
372
is disposed facing and separated by spaces
357
from the first electrode
356
that is provided on the oscillating plate
355
of the channel plate
350
.
The nozzles
354
are provided on the side surface of the ink jet head
331
as indicated on the drawing. The oscillating plate
355
serves the purpose of ejecting ink through the nozzle
354
by means of causing the internal pressure change of the ink channel
351
when it deforms. The ink chamber
352
contains the ink to be supplied to the ink channel
351
. The ink stored in the ink chamber
352
is fed into the ink channel
351
through the inlet
353
.
The gap G formed by the space
357
between the first electrode
356
and the second electrode
372
is set to 0.3 μm. The first electrode
356
provided on the oscillating plate
355
consists of an impurity conductive layer formed by diffusing boron as described later.
The first electrode
356
and the second electrode
372
are connected to an ejection control unit
325
, which is the driving means for the oscillating plate, by means of wires
381
and
382
. The wire
381
connected to the first electrode
356
is grounded. The voltage from the ejection control unit
325
is applied to the second electrode
372
via the wire
382
. The oscillating plate
355
is deformed as a result of a predetermined voltage applied between the first and the second electrodes
356
and
372
.
FIG. 13
is a sectional view along the line III-III of
FIG. 12
, and
FIG. 14
is a sectional view along the line IV-IV of FIG.
12
. As shown in
FIG. 11
, FIG.
13
and
FIG. 14
, the ink jet head
331
has third electrodes
361
provided at the top plate
360
. The third electrode
361
is an individual electrode separated by the ink channel
351
and it holds a position opposing the first electrode
356
. In other words, the third electrode
361
is facing the oscillating plate
355
across a space, and is positioned relative to the first electrode
356
on the side opposite to the side the second electrode
372
is located. Therefore, the gap G between the first electrode
356
and the third electrode
361
depends on the depth of the ink channel
351
. The depth of the ink channel
351
is set to 30 μm. The third electrode
361
is connected to the ejection control unit
325
via a wire
383
. Therefore, the third electrode
361
receives a specified voltage from the ejection control unit
325
via the wire
383
.
Next, the method of manufacturing the ink jet head
331
will be described as an example.
The ink jet head
331
is manufactured using various manufacturing processes such as the semiconductor manufacturing process and the micromachine manufacturing process. It goes without saying that the present invention is applicable to an ink jet head manufactured by a method that is not described here.
First, the method of manufacturing the channel plate
350
shown in
FIG. 13
will be described referring to
FIGS. 15A
to
15
C.
A silicon substrate
390
is lapped to about 40 μm as shown in FIG.
15
A. Next, an oxide layer
396
is formed on the entire surface of the silicon substrate
390
by the thermal oxidizing method. The oxide layer
396
on the top surface (as shown in the drawing) of the silicon substrate
390
is then processed with patterning by the known photolithography and the dry etching methods to form the etching mask
396
a
shown in FIG.
15
B. The etching mask
396
a
has openings for defining the shapes of the ink channels
351
, ink chamber
352
, inlets
353
, and nozzles
354
.
Next, the silicon substrate
390
having the etching mask
396
a
formed by patterning the oxide layer
396
is etched anisotropically with KOH solution. The surface orientation of the silicon substrate
390
is (1, 1, 0) or (1, 0, 0). The anisotropic etching performed with the KOH solution stops automatically when the (1, 1, 1) surface of the silicon substrate is exposed. Therefore, by adjusting the size of the openings that become the nozzles
354
and inlets
353
to form the etching mask
396
a,
it is possible to control the etching depths in opening areas to desired values. Also, the sizes of the openings that are to be the ink channels
351
and inlets
353
as well as the etching time are adjusted in order to make the depth of the areas that form oscillating plates
355
be about 6.5 μm. The etching by the KOH solution forms properly tapered surfaces on the side walls of the ink channel
351
and ink chamber
352
by exposing the (1, 1, 1) surface.
Next, the etching mask
396
a
formed by the oxide layer
396
is removed. As a result, the ink channels
351
, ink chamber
352
, inlets
353
, and nozzles
354
are formed on the silicon substrate
390
as shown in FIG.
15
C. The channel plate
350
thus produced has a plurality of ink channels
351
and a plurality of nozzles
354
, so that an ink jet head ejects a plurality of ink drops simultaneously.
Next, the space
357
is formed on the backside of the silicon substrate
390
to produce a 0.3 μm gap G between the electrodes using a method similar to the method described above. Thus, the oscillating plate
355
shown in
FIG. 13
, etc., is formed on the silicon substrate
390
.
A resist pattern is formed on the silicon substrate
390
by the photolithography method. The resist pattern has openings for the oscillating plate
355
and the lead line that electrically connect the first electrode
356
formed on the oscillating plates
355
and the wires
381
that connect to the ejection control unit
325
. Next, boron is implanted into the opening areas for the oscillating plate
355
and the lead lines. As a result, the impurity diffusion layer that becomes the first electrode
356
and the lead lines is formed as shown in FIG.
13
. After that, an oxide layer is formed on the entire surface of the silicon substrate
390
by a thermal oxidation process. Specifically, the insulation layer is formed on the surface of the oscillating plate
355
that is located on the backside of the silicon substrate. This insulation layer is formed to prevent the short circuit between the first electrode
356
and the second electrode
372
.
Next, the formation of the glass substrate
370
where the second electrode
372
is formed will be described.
First, an ITO layer (indium oxide layer containing tin) is formed on the glass substrate
370
. The portion where the ITO layer is formed consists of an area where it faces the oscillating plate
355
of the channel plate
350
and the area adjacent to it when they are joined as shown in FIG.
13
. In addition, a boro-silicated glass substrate is used as the glass substrate
370
. Consequently, the second electrode
372
and the lead line that connect the second electrode
372
and the wire
382
are formed on the glass substrate
370
. In case of an ink jet head that has a plurality of ink channels and a plurality of nozzles, the second electrode and the lead line are formed for each ink channel.
Next, a protection layer such as a SiFH layer or a SiO
2
layer is formed covering the entire surface of the side where the second electrode
372
is formed to a thickness of about 1 μm. This protection layer is to prevent the deterioration of the drive electrode due to the ambient humidity. Therefore, the protection layer is not patterned but rather covers the entire surface of the glass substrate
370
.
The depth of the space
357
is selected in such a way that the gap G, or the distance between the first electrode
356
(insulation layer surface) and the second electrode
372
(SiFH layer surface) to be formed is to be 0.1 to 1 μm, or more preferably 0.1 to 0.5 μm in terms of a lower drive voltage. In case of this embodiment, the gap G between the electrodes is chosen to be 0.3 μm as mentioned before.
The space
357
is formed by digging the area of the oscillating plate
355
of the silicon substrate
390
that constitutes the channel plate
350
from the backside (bottom side in the drawing) by etching. However, the space
357
can be formed in the glass substrate
370
alternatively. Specifically, it is possible to form the space
357
by forming a recess with a specified depth in the area of the glass substrate
370
where it faces the oscillating plate
355
of the channel plate
350
when they are joined together as shown in FIG.
13
.
Next, the formation of the top plate
360
will be described.
The top plate
360
consists of a boro-silicated substrate as in the case of the glass substrate
370
where the second substrate
372
is provided. An ink supply port
362
for introducing ink from the ink cassette disposed above into the ink chamber
352
is formed in the top plate
360
. Next, the ITO layer is formed on the bottom surface of the top plate
360
in the area that faces the oscillating plate
355
of the channel plate
350
and in the specified area adjacent to it. In consequence, the third electrode
361
and the lead line that connects the third electrode
361
and the wire
383
are formed on the bottom side of the glass substrate
360
. In case of an ink jet head that has a plurality of ink channels and a plurality of nozzles as shown in
FIG. 11
, the third electrode and the leads line are formed for each ink channel.
The ink channel plate
350
, the glass substrate
370
and the top plate
360
manufactured as above are joined by the anode joint method as shown in FIG.
11
. The lead line as the impurity diffusion layer formed on the oscillating plate
355
of the channel plate
350
, the lead line formed on the glass substrate
370
and the lead line formed on the top plate
360
are connected to the wires
381
,
382
and
383
respectively to complete the manufacture of the ink jet head.
Next, the inks as used will be described.
As shown in the following Table, four types of ink, i.e., black (K), yellow (Y), magenta (M), and cyan (C) were used. These inks were color adjusted with dyes. However, the inks may be adjusted with pigments instead of dyes.
TABLE
|
|
Color
|
Composition
K
Y
M
C
|
|
Distilled water
82.5
82.5
82.5
82.5
|
Dye
4.6
2.5
2.5
3.0
|
B/BK-SP
B/CA-Y
F/R-
B/CY-BG
|
(Bayer)
(Bayer)
FF3282
(Bayer)
|
(BASF)
|
Diethylene glycol
3.0
3.0
3.0
3.0
|
Glycerin
5.3
6.6
7.4
6.9
|
Triethylene
4.0
4.0
4.0
4.0
|
glycol
|
monobutyl ether
|
Surfactant:
0.2
1.o
0.2
0.2
|
Olefin E1010
|
(Nissin Chemical
|
Ind. Ltd.)
|
pH adjuster:
0.2
0.2
0.2
0.2
|
NaHCO
3
|
Stabilizer:
0.2
0.2
0.2
0.2
|
Triethanol amine
|
|
(Unit: weight %)
|
Next, the controller of the ink jet printer will be described referring to FIG.
16
.
The controller of the ink jet printer includes a CPU
321
, a RAM
322
, a ROM
323
, a data receiving unit
324
, an ejection control unit
325
, a head motion control unit
326
, a feed control unit
327
, a recovery system control unit
328
, and various sensors
329
. The data receiving unit
324
is connected to a machine such as a host computer and receives image data to be recorded.
The CPU
321
that controls the entire system uses the RAM
322
as needed to execute a program recorded in the ROM
323
. The program has a routine for recording the image on the sheet, and a routine for restoring the nozzle surface of the head unit to a good condition. Specifically, the former routine controls the ejection control unit
325
, the head motion control unit
326
, the feed control unit
327
, and various sensors
329
based on the image data inputted via the data receiving unit
324
and the latter routine controls the recovery system control unit
328
as needed by processing the information from various sensors
329
.
The ejection control unit
325
is controlled by the CPU
321
to drive the ink jet head
331
in the head unit. More specifically, the pulse voltage that corresponds to the image data is applied to the second electrode and the third electrode in specified timings by the ejection control unit
325
. Incidentally, the ejection control unit
325
includes a delay circuit, a charge/discharge circuit, a reverse circuit, and a reverse amplifying circuit.
The head motion control unit
326
is controlled by the CPU
321
to drive the motor that moves the carriage that carries the head unit. The feed control unit
327
is controlled by the CPU
321
to drive the sheet feed roller. Moreover, the recovery system control unit
328
is controlled by the CPU
321
to drive the motor and other things that are needed to restore the nozzle surface of the head unit to a good condition.
Next, the action of the ink jet head, or the action of the oscillating plate
355
during the ejection of an ink drop will be described referring to FIG.
17
A and FIG.
17
B.
As the first step in ejecting an ink drop, a drive voltage is applied between the first electrode
356
and the second electrode
372
. The oscillating plate
355
is attracted to the second electrode
372
due to an electrostatic force generated by the drive voltage applied as shown in FIG.
17
A. This causes the oscillating plate
355
to warp toward the second electrode
372
as shown with the two-dot chain lines in the drawing. The ink in the ink chamber
352
flows through the inlet
353
into the ink channel
351
. The first electrode
356
formed on the oscillating plate
355
is grounded. Therefore, the positive voltage, e.g., a 30 V drive voltage is applied to the second electrode (drive electrode)
372
. This drive voltage generates the force F
1
to be applied to the oscillating plate
355
as shown in the drawing.
The drive voltage is held for a predetermined time, e.g., several microseconds to tens microseconds by various circuits in the ejection control unit
325
. Subsequently, the drive voltage is cut off and an auxiliary voltage is applied between the first electrode
356
and the third electrode
361
within a predetermined time. Since the first electrode
356
formed in the oscillating plate
355
is grounded, the positive voltage, e.g., 300V, is applied to the third electrode
361
.
In order to apply a voltage effectively minimizing the waste of energy, the time is preferably 0.1 to 10 microseconds. The reason is as follows: If the predetermined time is chosen to be less than 0.1 microsecond, the predetermined time is shorter than the time required for the oscillating plate
355
to restore back to the restoration position, or the original position, although it depends on the deformation due to the drive voltage. Therefore, the tensile force is developed during the restoration of the oscillating plate
355
, which causes an energy loss. In other words, the loss is less if the tensile force is provided after the restoration. On the other hand, if the predetermined time is chosen to be longer than 10 microseconds, the predetermined time is longer than the time required for the oscillating plate
355
to pass the original position and oscillate one cycle, although it depends on the deformation due to the drive voltage. Therefore, the tensile force is developed at the timing when it returns to the original position after one oscillation. This also causes energy loss and is not desirable.
Thus, the oscillating plate
355
that has been attracted toward the second electrode
372
due to the application of the drive voltage returns to the original position on account of the restoration force of the oscillating plate
355
itself after the drive voltage cut-off. At about the same instant, a force F
2
is applied to the oscillating plate
355
due to the application of the auxiliary voltage as shown in FIG.
17
B. Therefore, the oscillating plate
355
is pulled rapidly away from the second electrode
372
.
The volume of the ink channel
351
contracts sharply and develops a pressure. As a result, the ink which has filled the ink channel
351
flies out as a drop from the nozzle
354
and lands on the sheet
2
to form a specified image.
In the embodiment 4, the third electrode
361
is positioned relative to the first electrode
356
on the side opposite to the side the second electrode
372
is located, the oscillating plate
355
is pulled toward the second electrode
372
when the drive voltage is applied between the first electrode
356
and the second electrode
372
, and the auxiliary voltage is applied between the first electrode
356
and the third electrode
361
when the oscillating plate
355
returns to the original position by its own restoring force.
With this constitution, the restoring force of the oscillating plate
355
is enhanced since the oscillating plate
355
is pulled forcibly away from the second electrode
372
by means of an electrostatic force. This causes the oscillating plate
355
return to its original position quicker than when it depends on the restoring force of the oscillating plate
355
alone. In other words, the tracking capability of the mechanical constitution including the oscillating plate is improved and thus the drive frequency of the ink jet head can be increased. This means that the preparation for the next printing can be done quicker so that the head response can be improved to enable high speed printing.
The ejecting speed of the ink drop ejected from the nozzle
354
was 8 meters per second when the third electrode
361
was not provided. On the contrary, the ejecting speed was increased to 10 meters per second as a result of the enlargement of the restoring force of the oscillating plate
355
when the third electrode
361
was provided. This will prevent the misplacement of the ink drop on its landing on the recording medium, which otherwise may be caused by the time lag between the ejection and the landing on the recording medium. Since the fluctuation of the ink drop flight is reduced, the image distortion is minimized and the better image recording is accomplished.
It is obvious that this invention is not limited to the particular embodiments shown and described above but may be variously changed and modified by any person of ordinary skill in the art without departing from the technical concept of this invention.
In the embodiment 4, as shown in
FIG. 11
, a case of forming the third electrode
361
and the lead line individually for each ink channel
351
was described. However, the present invention is not limited to such a constitution. For example, the lead lines of a plurality of third electrodes
361
can be connected to form a single common electrode so that the auxiliary voltage can be applied to the common electrode. With such a constitution, it is possible to reduce the manufacturing cost because the constitution of each circuit in the ejection control unit
325
is simplified.
Claims
- 1. An electrostatic ink jet head having a set of elements comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of non-piezoelectric oscillating plates that are disposed opposing to each other on walls of said ink channel; and a pair of electrodes provided in contact with said non-piezoelectric oscillating plates, respectively, wherein a voltage is applied between said electrodes.
- 2. An electrostatic ink jet head in accordance with claim 1, wherein said ink is ejected by applying a voltage between said electrodes.
- 3. An electrostatic ink jet head in accordance with claim 1, wherein a plurality of the sets of elements are arranged.
- 4. An electrostatic ink jet head in accordance with claim 4, wherein one of said electrodes is used as a common electrode.
- 5. An ink jet head comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; and a pair of electrodes provided in contact with said oscillating plates, respectively; wherein a voltage is applied between said electrodes; and wherein said electrodes are disposed respectively on an inside of said oscillating plates provided opposing to each other.
- 6. An electrostatic ink jet recording apparatus having a set of elements comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of non-piezoelectric oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said non-piezoelectric oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes.
- 7. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein ink is ejected by applying a voltage between said electrodes.
- 8. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein a plurality of the sets of elements are provided.
- 9. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein one of said electrodes is used as a common electrode.
- 10. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein said controller discharges electric charges of said electrodes.
- 11. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes; wherein a plurality of sets of said composing elements are provided; and wherein said electrodes are disposed respectively on an inside of said oscillating plates provided opposing to each other.
- 12. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes; wherein relative dielectric constant of ink to be filled in said ink channel is larger than 1.
- 13. An ink jet head comprising:an ink channel that communicates with a nozzle that ejects ink; an oscillating plate that is disposed facing said ink channel; a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel; a second electrode that is disposed opposing said first electrode; and a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located.
- 14. An ink jet head in accordance with claim 13, wherein said third electrode is opposing said oscillating plate across said ink channel.
- 15. An ink jet head in accordance with claim 13, wherein said second electrode is separated from said first electrode by a space.
- 16. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; an oscillating plate that is disposed facing said ink channel; a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel; a second electrode that is disposed opposing said first electrode; a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located; and a controller for controlling application of voltages to said electrodes.
- 17. An ink jet recording apparatus in accordance with claim 16, wherein said third electrode is opposing said oscillating plate across said ink channel.
- 18. An ink jet recording apparatus in accordance with claim 16, wherein said controller applies a voltage between said first and third electrodes within a predetermined time after stopping application of a voltage between said first and second electrodes.
- 19. An ink jet recording apparatus in accordance with claim 18, wherein said predetermined time is 0.1 to 10 microseconds.
- 20. An ink jet recording apparatus in accordance with claim 16, wherein said voltage applied between said first and second electrodes is different from said voltage applied between said first and third electrodes.
- 21. A method for driving an ink jet head comprising an oscillating plate that is disposed facing an ink channel, a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel, a second electrode that is disposed opposing said first electrode, and a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located, said method comprising the steps of:a first voltage application step that applies a voltage between said first and second electrodes; and a second voltage application step that applies a voltage between said first and third electrodes.
- 22. A method in accordance with claim 21, wherein said second voltage application step is executed after a predetermined time after said first voltage application step is stopped.
- 23. A method in accordance with claim 22, wherein said predetermined time is 0.1 to 10 microseconds.
- 24. A method in accordance with claim 21, wherein said voltage used in said first voltage application step is different from said voltage used in said second voltage application step.
- 25. An electrostatic ink jet head comprising:an ink channel that is defined by a plurality of surfaces that include a first surface and a second surface opposing to said first surface through said ink channel, said first surface being a main surface of a non-piezoelectric oscillating plate, said ink channel communicating with a nozzle for ejecting ink therefrom; a first electrode provided at a position corresponding to the first surface; and a second electrode provided at a position corresponding to the second surface; wherein an electrical field can be generated between said first and second electrodes by applying an electrical voltage therebetween.
- 26. An electrostatic ink jet head as claimed in claim 25 wherein one of said electrodes is a common electrode.
Priority Claims (2)
Number |
Date |
Country |
Kind |
10-119435 |
Apr 1998 |
JP |
|
10-119436 |
Apr 1998 |
JP |
|
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4228440 |
Horike et al. |
Oct 1980 |
|
Foreign Referenced Citations (1)
Number |
Date |
Country |
5-050601 |
Mar 1993 |
JP |