JPH0872240A - Ink jet recorder - Google Patents

Abstract

PURPOSE: To provide an ink jet recorder capable of printing an image with gradation of high resolution by low driving voltage by a method wherein an ink drop of an amount corresponding to its gradation can be precisely discharged by simple control according to a binary gradation signal. CONSTITUTION: In an ink jet recorder wherein an electrode opposed at a specific vacant space to a diaphragm 5 which is interconnected to each nozzle hole 4 and provided on one part of a wall face of each independent discharge room 6 is provided, and an ink drop is discharged by deforming the diaphragm 5 by electrostatic force obtained by applying voltage, a plurality of electrodes 31 which are respectively independent are opposed to each other, and an ink drop of an amount corresponding to a gradation signal is discharged by applying pulse voltage to a specific number of the electrodes 31 according to the gradation signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus in which ink droplets are ejected only when recording is required and the ink droplets are adhered to a recording paper surface.

[0002]

2. Description of the Related Art Ink jet recording apparatuses have extremely low noise during recording and are capable of high-speed printing.
It has many advantages such as the ability to use cheap plain paper. Among these, the so-called ink-on-demand method, which ejects ink droplets only when recording is necessary, does not require the collection of droplets of ink that is unnecessary for recording, and is currently in the mainstream.

A conventional ink jet recording apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 55-79171. In this recording apparatus, a plurality of electrostrictive bodies (piezoelectric elements) having different areas facing the ejection chamber are provided, and the electrostrictive body is driven by a binary electric pulse, so that the diameter from the nozzle communicating with the ink chamber is increased. Ink droplets of different colors are ejected to record a gradation image.

[0004]

However, in the structure of such a conventional ink jet recording apparatus, the work of attaching the piezoelectric element to the outside of the ejection chamber is extremely complicated and requires a lot of time. Further, in general, a piezoelectric element has a large thickness variation, and a thickness variation of the adhesive on the diaphragm also occurs, and the size and speed of the ink droplets ejected from the nozzles are different, and the amount of the ink droplet is different according to the gradation signal. It is difficult to eject ink droplets with high precision, that is, to control the amount of ink droplets according to the gradation signal.

Further, the piezoelectric element (especially unimorph type) is
The smaller the size, the larger the driving voltage required to obtain a predetermined strain. Therefore, it is difficult to form the electrostrictive body in a small size, mount it at a high density, and drive at a relatively low driving voltage. Therefore, it is very difficult to form a high-density, multi-nozzle inkjet head using a conventional piezoelectric element and print a high-resolution gradation image with a low driving voltage.

An object of the present invention is to accurately discharge an amount of ink droplets corresponding to a gradation according to a binary gradation signal, and to form a high resolution gradation image with a low driving voltage. An object is to provide an inkjet recording device that can print.

[0007]

The ink jet recording apparatus of the present invention is provided with a plurality of nozzle holes, discharge chambers communicating with each of the nozzle holes, and independent discharge chambers, and a part of the wall surface of the discharge chamber. And an electrostatic head obtained by applying a pulse voltage to the electrostatic actuator, and an inkjet actuator having an electrostatic actuator including an electrode facing the diaphragm with a predetermined gap. In an ink jet recording apparatus having a driving unit that deforms the vibrating plate to eject ink droplets from the nozzle holes, an electrostatic actuator having a plurality of independent electrodes for each vibrating plate, and a gradation Depending on the signal
It is characterized in that it has a driving means for applying a pulse voltage to a predetermined number of the electrodes and ejecting ink droplets of an amount corresponding to the gradation signal from the nozzles. Further, for example, the deflection amount (ink ejection amount) of the diaphragm when a voltage is applied to both of the two electrodes having the same area is that the diaphragm is distorted,
It is difficult to accurately set in advance twice the amount of bending when a voltage is applied to one electrode. In the present invention, by providing the pillar wall that supports the diaphragm between the adjacent electrodes,
Even if a voltage is applied to one of the adjacent electrodes, the deformation of the diaphragm is suppressed, so there is no excessive bending, and the amount of bending is uniquely determined according to the area of the electrode set in advance,
Therefore, it is easy to control the ink ejection amount.

[0008]

The principle of operation of the ink jet recording apparatus of the present invention is that a pulse voltage is applied between the diaphragm and the electrode facing the diaphragm, whereby the electrostatic actuator composed of the diaphragm and the counter electrode is charged. At this time, the vibrating plate is bent by the Coulomb force acting between the vibrating plate and the electrode, and then the electric charge stored in the electrostatic actuator is rapidly discharged. The ink droplets are momentarily raised to eject ink droplets from the nozzles. An electrostatic actuator having a plurality of electrodes independent of each other for one diaphragm, and a pulse voltage is applied to a predetermined number of the electrodes according to a gradation signal, and an ink droplet of an amount corresponding to the gradation signal is applied. By having a driving unit for ejecting the ink from the nozzle, the amount of ink ejected per one nozzle, in other words, 1
Since the size of the dot diameter changes depending on the number of electrodes to which the pulse voltage is applied, by selecting the electrode to which the pulse voltage is applied, the ink ejection amount can be digitally controlled and a gradation image can be displayed. it can.

Further, since the displacement area of the diaphragm can be freely changed by changing the respective electrode areas, a desired discharge amount can be selected by combining the drive electrodes.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an exploded perspective view of an ink jet recording apparatus according to an embodiment of the present invention, which is a partial sectional view. This embodiment shows an example of an edge eject type in which ink droplets are ejected from the nozzle holes 4 at the end of the substrate 2. FIG. 2 is a sectional side view of the assembled inkjet head, and FIG. 3 is a plan view taken along the line AA of FIG. FIG. 4 is a plan view of the electrode portion of the ink jet recording apparatus according to this embodiment of the present invention.

As shown in these figures, the ink jet head 12 which is the main part of the ink jet recording apparatus,
It has a laminated structure in which three substrates 1, 2 and 3 having a structure described in detail below are stacked and joined.

The intermediate substrate 2 is a silicon substrate, and has a plurality of nozzle grooves 21 formed on the surface of the intermediate substrate 2 forming the plurality of nozzle holes 4 in parallel at equal intervals from one end, and each nozzle groove 21. Discharge chamber 6 that communicates with the bottom wall and uses the diaphragm 5 as the bottom wall
, A narrow groove 23 for forming an orifice 7 provided at the rear of the concave portion 22, and a common groove 23 for supplying ink to each ejection chamber 6. Of the ink cavity 8 has a concave portion 24. In addition, a concave portion 25, which constitutes the vibrating chamber 9 for mounting an electrode described later, is provided below the vibrating plate 5. The groove was etched to 0.275 micron. The pitch of the nozzle grooves 21 is 0.508 mm, and the width is 60 μm.

Borosilicate glass was used for the upper substrate 1 bonded to the upper surface of the intermediate substrate 2. By joining the upper substrate 1, the nozzle hole 4, the ejection chamber 6, the orifice 7 and the ink cavity 8 are formed. And the upper substrate 1
An ink supply port 14 communicating with the ink cavity 8 is provided in the. The ink supply port 14 is connected to an ink tank (not shown) via a connection pipe 16 and a tube 17.

Borosilicate glass is used for the lower substrate 3 bonded to the lower surface of the intermediate substrate 2, and the vibration chamber 9 is formed by bonding the lower substrate 3 to the vibration plate 5 of the lower substrate 3. In order to form electrodes, ITO was sputtered at 0.1 μm at the corresponding positions to form three electrodes 31 having the same area as shown in FIG. The electrodes 31 are lead portions 3 respectively
2 and the terminal portion 33. Further, except for the electrode terminals, the borosilicate glass sputtered film was entirely covered with 0.1 μm to form an insulating layer 34 for preventing dielectric breakdown and short circuit during driving.

Next, the upper substrate 1 and the intermediate substrate 2 are 340 degrees Celsius.
Once, 800 V was applied to perform anodic bonding, the intermediate substrate 2 and the lower substrate 3 were bonded under the same conditions, and an inkjet head was assembled as shown in FIG. Further, the drive circuit 26 was connected between the intermediate substrate 2 and the terminal portion 33 of the electrode 31 to form the inkjet recording device 10. The ink 11 is supplied from the ink tank (not shown) to the inside of the intermediate substrate 2 through the ink supply port 14, and fills the ink cavity 8, the ejection chamber 6, and the like. The ink droplets 13 are ejected from the nozzle holes 4 toward the recording paper 15.

FIG. 5 is a circuit diagram showing details of the drive circuit 26. A print data signal including gradation information from a host (not shown) is transmitted and received by the controller 110. In the present embodiment, as shown in FIG. 4, the three electrodes 31a, 31b, 31c per diaphragm face each other, so the controller decodes 3 bits per nozzle based on the print data signal. Is configured to be able to. For example, the electrode 3 of the diaphragm 5
When ink droplets are ejected by bending only the portion corresponding to 1a (the dotted line portion in FIG. 5), the transistor 101a is driven and one portion of the diaphragm 5 is driven by the Coulomb force acting between the diaphragm 5 and the electrode 31a. Bend. Then, the diaphragm 5-electrode 3
The electric charge stored between 1a is transferred to the transistor 101a.
Is turned off and the transistor 102a is driven,
The pressure inside the ejection chamber 6 is instantaneously increased by the restoring force due to the elasticity of the vibrating plate 5 itself by discharging and ink droplets are ejected from the nozzles. The charge / discharge speed of the electrostatic actuator is preset to a desired value by the resistors 103a and 104a. In this embodiment, voltage is applied to all electrodes, voltage is applied to two electrodes, voltage is applied to one electrode, and four types of ink ejection amounts are selected corresponding to the case where no voltage is applied to any electrode. It is possible, and an image with four gradations can be expressed by changing the diameter of dots forming one pixel. As a result of an experiment in which the above-described inkjet head 12 and the drive circuit 26 were incorporated into a printer and a drive voltage of 38 V and a drive frequency of 3.3 kHz, as a result, when a voltage was applied only to the electrode 31a, about 0.04 μcc and the electrodes 31a, 31 were obtained.
When voltage is applied to b, about 0.08 μcc, electrode 31
0.12μ when voltage is applied to a, 31b and 31c
An ink discharge amount of cc was obtained.

FIG. 6 is a plan view of an electrode portion of an ink jet recording apparatus showing another embodiment of the present invention. Similar to the embodiment shown in FIG. 4, three electrodes facing one diaphragm are arranged and the electrode area is electrode 131a: electrode 131b: electrode 13
It was formed so that 1c = 2.5: 5: 10. In this way, if the electrodes having different areas are arranged, it is possible to select the ink ejection amount corresponding to the number of combinations of driven electrodes.
In the present embodiment, an image with 6 gradations can be expressed by changing the diameter of dots forming one pixel.

The ink jet head 12 and the drive circuit 26 of this embodiment were incorporated in a printer, and an experiment was conducted at a drive voltage of 40 V and a drive frequency of 3.3 kHz. When voltage is applied only to 131b, about 0.03μc
c, 0.06 when voltage is applied only to the electrode 131c
μcc, when a voltage is applied to the electrodes 131a, 131b, about 0.05 μcc, for all electrodes, 1131a, 13b
About 0.12μ when voltage is applied to 1b and 131c
The ink discharge amount of cc was measured.

FIG. 7 is an exploded perspective view of a main part of an ink jet recording apparatus according to another embodiment of the present invention.
This embodiment shows an example of a face eject type in which ink droplets are ejected from the nozzle plate hole 4 in the surface portion of the substrate.

As shown in FIG. 7, the ink jet head 42, which is the main part of the ink jet recording apparatus, has a laminated structure in which three substrates 61, 62, 63 having the structure described in detail below are stacked and joined. ing.

The intermediate substrate 62 is a plane-oriented (110) silicon substrate having a thickness of 400 microns, and the discharge chamber 6 of the intermediate substrate 62 has a bottom wall made of silicon of 3 microns as the vibrating plate 5, and the discharge chamber 6 is formed. A recess 22 to be configured,
A narrow groove 23 for an ink inlet that will form an orifice 7 provided at the rear of the recess 22 and a common ink cavity 8 for supplying ink to each ejection chamber 6 will be formed. The recess 24 is formed, and the intermediate substrate 6 is formed.
A thermal oxide film 88 having a thickness of 0.15 μm was formed on the surface 2 to prevent short circuit.

The lower substrate 63 bonded to the lower surface of the intermediate substrate 62 is made of borosilicate glass.
The depth of 0.
A 3 μ recess 40 was formed by etching, and ITO was sputtered in the recess 40 to a thickness of 0.1 μm to form two electrodes 231a, 231b, and lead portions 32 and terminal portions 33 connected to these electrodes. Here, the electrode 231
The electrode area ratio of a and 231b was set to 1: 2. The pitch between the adjacent discharge chambers 6 is 0.14 mm, and the width of the discharge chambers 6 is 100 μm.

As the upper substrate 61 joined to the upper surface of the intermediate substrate 62, a 70-micron-thick nozzle plate having nozzle holes 4 for ejecting SUS ink was used. Further, the upper substrate 61 is provided with the ink supply port 14 communicating with the ink cavity 8. The ink supply port 14 is connected to an ink tank (not shown) via a connection pipe 16 and a tube 17.

Next, as shown in FIG. 2 between the intermediate substrate 62 and the terminal portion 33.
The drive circuit 26 shown in FIG. 2 is connected to form an ink jet recording apparatus, and electrodes 231a, 2 are formed in the same manner as the embodiment shown in FIG.
As a result of an experiment in which a driving voltage of 40 V is applied from the driving circuit 26 to 31b, when a voltage is applied to the electrodes 231a,
Ink discharge amount is 0.04 μcc, both electrodes 231a,
When a voltage was applied to 231b, it was 0.08 μcc.

FIG. 8 is a partial sectional view of an electrode portion showing another embodiment of the present invention.

The lower substrate 3 is a substrate made of borosilicate glass, and is divided by a support wall 202 which constitutes the vibration chambers 9a, 9b and 9c by joining the lower substrate 3 and the intermediate substrate 2 made of silicon. A plurality of recesses are provided. The electrodes 31a, 31b, 31c are connected to the respective vibration chambers 9a, 9b, 9
It is located at the bottom of c. The depth of each vibration chamber is 0.3
Each electrode has the same area and is formed by sputtering ITO to a thickness of 0.1 micron.

The vibrating plate 5 of the intermediate substrate 2 is 1 × boron doped to a depth of 1 micron from the back surface of the substrate by ion implantation.
Implanted at a concentration of 1020 / cm3, after thermal diffusion, the substrate 2
The surface of is patterned by thermal lithographic process, and the exposed portion of silicon is etched with a KOH aqueous solution to form the ink discharge chamber 6, and is formed at the same time. This method uses the property that the high-concentration boron region is difficult to be etched with a KOH aqueous solution.
Using that portion (etch stop layer), the diaphragm 5 having a thickness of about 3 μm can be obtained. After the etching is completed, a thermal oxide film 88 is formed on the surface of the intermediate substrate 2 by 0.1 to prevent short circuit.
The ink jet head is assembled by forming it to a thickness of 5 μm and joining the three substrates by the same process as in Example 1 of FIG.

By dividing and supporting the vibrating chamber under the vibrating plate by the supporting wall as in the present embodiment, the elasticity of the vibrating plate itself can be strengthened even if the vibrating plate is made thin. Is obtained. As a result, since the silicon etch stop technology can be used, a highly accurate diaphragm can be manufactured.

Further, for example, the deflection amount (ink ejection amount) of the diaphragm when a voltage is applied to both electrodes having the same area, the diaphragm is distorted, so that the voltage is applied to one electrode. It is difficult to accurately set in advance twice the amount of flexure when doing. In this embodiment, by providing the pillar wall that supports the vibration plate between the adjacent electrodes, even if a voltage is applied to one of the adjacent electrodes, the deformation of the vibration plate is suppressed. The amount of bending is uniquely determined according to the area of the electrode that is set in advance, and thus the control of the ink ejection amount is easy.

[0031]

As described above, according to the present invention, 2
By simple control according to the gradation signal of the value, it is possible to accurately eject an amount of ink droplets corresponding to the gradation,
An inkjet recording device capable of printing a high-resolution gradation image with a low drive voltage can be provided.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a partially cutaway main part of an inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional side view of the ink jet recording apparatus in one embodiment of the present invention after assembly.

FIG. 3 is a plan view taken along the line AA of the cross-sectional side view after assembly of the inkjet recording apparatus according to the first embodiment of the present invention.

FIG. 4 is a plan view of an electrode portion of an ink jet recording apparatus according to an embodiment of the present invention.

FIG. 5 is a drive circuit diagram of the ink jet recording apparatus in one embodiment of the present invention.

FIG. 6 is a plan view of an electrode portion of an ink jet recording apparatus according to another embodiment of the present invention.

FIG. 7 is an exploded perspective view showing a partially cutaway main part of an inkjet recording apparatus according to another embodiment of the present invention.

FIG. 8 is a cross-sectional view of an electrode portion according to another embodiment of the present invention.

[Explanation of symbols]

 1, 61 Upper substrate 2, 62 Intermediate substrate 3, 63 Lower substrate 4 Nozzle hole 5 Vibration plate 6 Discharge chamber 7 Orifice 8 Ink cavity 9 Vibration chamber 10 Inkjet recording device 11 Ink 12 Inkjet head 13 Ink droplet 14 Ink supply port 15 Paper 16 Connection pipe 17 Tube 21 Nozzle groove 26 Drive circuit 31, 131, 231 Electrode

Claims (5)

[Claims] 1. A plurality of nozzle holes, discharge chambers that communicate with each of the nozzle holes and are independent of each other, a vibration plate provided on a part of a wall surface of the discharge chamber, and a predetermined size for the vibration plate. An ink-jet head having an electrostatic actuator composed of electrodes facing each other with a gap, and the nozzle plate is formed by deforming the diaphragm by an electrostatic force obtained by applying a pulse voltage to the electrostatic actuator. In an ink jet recording apparatus having a driving unit for ejecting ink droplets from the above, an electrostatic actuator having a plurality of independent electrodes for one vibration plate, and a pulse to a predetermined number of the electrodes according to a gradation signal An inkjet recording apparatus comprising: a driving unit that applies a voltage to eject ink droplets of an amount corresponding to the gradation signal from the nozzles. 2. The ink jet recording apparatus according to claim 1, wherein the area of at least one electrode of the plurality of electrodes facing one diaphragm is different from the area of the other electrodes. . 3. The ink jet recording apparatus according to claim 1, further comprising a column that partially restricts the deformation of the vibration plate. 4. The inkjet recording apparatus according to claim 3, wherein the support column is provided between adjacent electrodes facing one diaphragm. 5. A plurality of nozzle holes, discharge chambers communicating with each of the nozzle holes and independent of each other, a vibration plate provided on a part of a wall surface of the discharge chamber, and one vibration plate. An inkjet head having an electrostatic actuator composed of a plurality of independent electrodes facing each other with a predetermined gap, and the diaphragm is deformed by an electrostatic force obtained by applying a pulse voltage to the electrostatic actuator. An ink jet recording apparatus comprising: a driving unit that ejects ink droplets from the nozzle in an amount corresponding to the number of electrodes to which the pulse voltage is applied.