JPH0557893A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To realize a small-sized high density highly reliable ink jet printing head having a simple structure and enabling gradation expression by vibrating the part held between the selected segment electrode and common electrode of a piezoelectric vibration plate by applying AC voltage across both selected electrodes and atomizing the ink received in a slit by the vibrated part to emit the same. CONSTITUTION:A piezoelectric vibration plate 1, an opposed plate 17, the slit 2 formed to one end part of the piezoelectric vibration plate 1 by superposing both plates 1, 17 one upon another, the common electrode 3 formed to the end part of the surface on the slit side of the piezoelectric vibration plate 1, a plurality of the segment electrodes 4 formed to the end part of the other surface of the piezoelectric vibration plate 1 and a drive means 6 selectively applying AC voltage across the segment electrodes and the common electrode are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head mainly used in an ink jet printer.

[0002]

2. Description of the Related Art A so-called ink jet printer which ejects ink droplets to write a character graphic according to input information on a recording medium is excellent in that it can print directly on plain paper quietly. On the other hand, however, this type of printer is provided with ink chambers for the number of elements on the head, ink pressurizing means or bubble generating means for each of them, and a large number of nozzles connected to these parts with high density. Because it must be placed, extremely precise molding technology is required,
In addition to having problems in lowering the price, nozzle clogging easily occurs due to ink drying or adhesion of dust, etc., and head reliability is impaired unless adequate measures are taken. I have a problem such as.

To address such a problem, Japanese Patent Laid-Open No. 2-17
5157 and Japanese Patent Application Laid-Open No. 63-166545, it has been proposed in recent years to realize a nozzleless inkjet print head by a method of ejecting ink by applying ultrasonic vibration to the ink. These proposals are to make the ink mist form to give gradation to the printed image, or to propose a nozzleless structure, but all of them are quite complicated in practice, and multiple elements are arranged in a line array. It is difficult to achieve high density, and therefore, it is not suitable for realizing a small and inexpensive printing apparatus.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of various types of ink jet print heads, and an object thereof is to provide a compact structure capable of gradation expression with a simple structure, a high density, It is about to realize a highly reliable inkjet printhead.

[0005]

That is, in order to solve the above problems, the present invention provides a piezoelectric vibrating plate, a counter plate, and a piezoelectric vibrating plate by stacking the piezoelectric vibrating plate and the counter plate with a gap therebetween. A slit formed at one end, a common electrode formed at the end of the slit-side surface of the piezoelectric diaphragm, a plurality of segment electrodes formed at the end of the other surface of the piezoelectric diaphragm, and held by the slit It is provided with ink and drive means for selectively applying an AC voltage between the segment electrode and the common electrode.

[0006]

With the nozzleless ink jet head having the above structure, an alternating voltage is applied between the common electrode and the segment electrode formed on the front and back surfaces of the piezoelectric vibrating plate so that the piezoelectric electrode is sandwiched between the common electrode and the segment electrode. The piezoelectric vibrating plate in the separated portion is vibrated, and the ink in the vicinity thereof is ejected in a mist state from the slit by the action of acoustic pressure due to acoustic streaming and the surface tension wave generated on the ink surface. Since the ink is in the form of mist, gradation can be expressed by modulating the amount of ejected ink. Also, since the ink flow path is slit-shaped and there is no nozzle for each element, the conventional inkjet printer It is possible to realize a highly reliable inkjet printhead without nozzle clogging, which was a drawback. Also, a common electrode is formed on one surface of one piezoelectric vibrating plate and segment electrodes of the required number of elements are formed on the opposite surface. Since this is a very simple structure in which the and the opposing plate are arranged so as to overlap with each other, a small size and high density ink jet print head can be easily realized.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A print head manufactured as an embodiment according to the present invention will be described with reference to FIGS. 1, 2, 3, 4, and 5.

FIGS. 1, 2 and 3 show a 96-element print head manufactured as an embodiment of the present invention.
FIG. 1 is a perspective view of a part of the embodiment, and a part thereof is shown in section for explaining the structure. FIG. 2 is a sectional view of the embodiment. FIG. 3 is an overall view showing the appearance of the embodiment shown in FIGS. In FIG. 3, the ink supplied through the ink supply pipe 101 is slit 2 according to the drive signal.
5a to 5a, the ink is atomized and discharged.

The structure of the embodiment of the present invention will be described with reference to FIGS. The piezoelectric vibrating plate 1 and the piezoelectric vibrating plate 1 ′ are arranged so as to form the slit 2 and the ink chamber 8 by sandwiching the spacer 7. In this embodiment, two piezoelectric vibrating plates are used and the segment electrodes are shifted by a half pitch and face each other, thereby realizing an ink jet print head having an element density twice as high as the element density that can be realized by one piezoelectric vibrating plate. .. If a flat plate is used in place of one of the piezoelectric vibrating plates 1 of this embodiment and a piezoelectric vibrating plate and an opposing plate are used, the element density is half that of this embodiment, but the same function can be realized. In this embodiment, the piezoelectric vibrating plate 1 and the piezoelectric vibrating plate 1'also have the function of opposing plates to each other.
The piezoelectric vibrating plate 1 ′ also functions as a facing plate of the piezoelectric vibrating plate 1, and the piezoelectric vibrating plate 1 also functions as a facing plate of the piezoelectric vibrating plate 1 ′. Therefore, in this embodiment, the piezoelectric diaphragm 1 and the piezoelectric diaphragm 1 '
The relationship between the two is contrasting, and for the sake of simplicity, the piezoelectric diaphragm 1
The description will be centered on the case where the piezoelectric vibrating plate 1 ′ is vibrated and used as the opposing plate.

In FIG. 1 and FIG. 2, the ink 5 is supplied to the ink chamber 8 through the ink supply path 10 formed in the base plate 9 in a groove shape, and the slit 2 is always filled with the ink. At the end of the piezoelectric vibrating plate 1, a common electrode 3 is formed on the surface on which the slit is formed, and a plurality of segment electrodes orthogonal to the common electrode are formed on the surface opposite to the surface on which the slit is formed. The piezoelectric vibrating plate 1 has a comb blade shape in which the thickness of the segment electrode 4 is different from that of the segment electrode. Printed wiring is provided on the base plate 9 and the driver IC 6 is mounted thereon. The common electrode of the piezoelectric vibrating plate is grounded, and the segment electrodes of the piezoelectric vibrating plate are connected to the drive driver by wire bonding, printed wiring of the base plate, etc., and an AC voltage is applied between the common electrode and a specific segment electrode. Can be applied.

FIG. 4 shows a configuration diagram of a common electrode, a segment electrode, and a drive circuit of the piezoelectric diaphragm. Piezoelectric diaphragm 1, 1 '
Common electrodes 3, 3'and segment electrodes 4,
An AC voltage generation source P is connected via a switch S to the vibrating portion W sandwiched by 4 '.
The sixth portion can be vibrated by applying an AC voltage P6 by opening and closing the switch S6. Note that this circuit configuration is the simplest example, and may be any circuit that can selectively apply an AC voltage to the common electrode and the specific segment electrode.

Here, the principle of ink ejection will be described with reference to the most simplified example of the present invention shown in FIG. FIG. 5 shows the piezoelectric vibration plate 2.
01 and the counter plate 206 form a slit 202 therebetween, and the common electrode 203 is formed at the slit side end of the piezoelectric vibrating plate.
However, a segment electrode 204 is formed on the opposite side. By filling the slits 202 with the ink 205 and connecting the AC voltage generation source P between the common electrode and the segment electrode, an AC electric field is applied to the portion 201a of the piezoelectric diaphragm 201 to vibrate the piezoelectric diaphragm 201. The vibration of the piezoelectric vibrating plate acts on the ink 205 filled in the slit 202 to generate a strong acoustic pressure, a surface tension wave is generated on the ink surface at the opening of the slit, and the ink is ejected only from a portion near 201a where the vibration is strongest. It atomizes and ejects in the opening direction of the slit. Since ink is ejected only from the portion directly under the segment electrode to which an AC voltage is applied, it is not necessary to form a wall between adjacent elements as in the conventional inkjet printer, and a multi-element inkjet print head can be connected continuously. It can be realized with one slit. According to experiments, it was confirmed that the atomized and ejected ink 205a flew in a certain direction without spreading, and the component thereof was a group of extremely fine particles flying at a high density. Further, since the ink ejection is performed only while the AC voltage is being applied, it is possible to control the ink ejection simply by opening and closing the switch S. In a conventional inkjet printer, it is necessary to apply a pulsed pressure to ink by applying a voltage in a fixed sequence to a piezoelectric element or a heating element in order to eject one dot.
A certain amount of time is required for firing a dot due to a time constant determined by the piezoelectric element or the heating element and the capacity of the ink chamber, and the ink amount of one dot could hardly be modulated. According to this, since ink is continuously ejected only while the AC voltage is applied, electrical control is simple, and at the same time, by modulating the time during which the AC voltage is applied, one ink The ejection amount can be easily modulated. The frequency of the alternating voltage applied to the piezoelectric diaphragm is preferably matched with the natural frequency of the piezoelectric diaphragm, and the vibration mode of the piezoelectric diaphragm is the thickness vibration or the end portion of the piezoelectric diaphragm as in this embodiment. When an electrode is formed on and vibrated, it is preferable to use thickness edge mode vibration. In the embodiment shown in FIG. 1, the piezoelectric vibrating plate is made of lead zirconate titanate having a thickness of about 0.5 mm, the segment electrodes have a width of about 0.15 mm and a pitch of about 0.28 m.
m, and the frequency of the AC voltage applied between the common electrode and the segment electrode was about 2.6 MHz, but the piezoelectric diaphragm is a piezoelectric material with a large electromechanical coupling coefficient and its thickness is 0.2
mm to several mm, the frequency to vibrate is several 10 kHz
It is advisable to select an appropriate value in the range of about several MHz. Also,
In this embodiment, the slit spacing is about 5 μm, but it is several μm.
It is advisable to select an interval that maximizes the ink ejection efficiency in the range from 1 to several tens of μm.

In the flat plate type piezoelectric vibrating plate as shown in FIG. 5, vibration is easily transmitted from the vibrating portion 201a to the peripheral portion of the piezoelectric vibrating plate. Particularly, in the thickness vibration mode, the vibration portion spreads widely, and when a multi-element head is realized by arranging a large number of segment electrodes, crosstalk with adjacent elements may occur. In this embodiment, the thickness edge mode is used as the vibration mode, and the thickness of the segment electrode portion and the segment electrode-free portion of the piezoelectric vibrating plate is changed by providing a groove between adjacent segment electrodes,
By preventing the leakage of vibration to adjacent elements, high-density lines of multiple elements have been realized. If you can change the resonance frequency of the vibration of the segment electrode part and the part without segment electrode, not only can you change the thickness,
The same effect can be obtained by changing the shape and material.

As described above, according to the present invention, the number of elements can be increased by forming the segment electrodes corresponding to the number of elements on one piezoelectric vibrating plate, so that the line can be remarkably simpler than the conventional ink jet print head. -Shaped inkjet print head can be realized. Further, even if the number of elements is increased, the number of parts is almost unchanged, and even if the element density is increased, it is not necessary to downsize each part as in the conventional ink jet printer, and a small size and high density head can be easily manufactured. Can be manufactured.

Regarding the constitution of the piezoelectric vibrating plate and the counter plate, the operation is possible even if the piezoelectric vibrating plate and the counter plate are opposed to each other on the segment electrode side to form a slit, but according to the present invention, the common electrode side is formed. By forming the slits, the problems that the segment electrodes are electrically shorted by the ink filled in the slits and the ink is electrolyzed by the electric field applied between the segment electrodes are eliminated in principle, and the reliability of the head is improved. Can be obtained. Further, in the embodiment of the present invention, the segment electrodes are exposed, but actually the segment electrodes are molded with a resin or the like leaving a slit portion for prevention of short circuit of the segment electrodes due to ink scattering, protection from dust, etc. Is also good.

According to the present invention, since an AC voltage having a relatively high frequency is used to drive the piezoelectric diaphragm, if the head portion and the driving circuit are separated from each other by a cable like a conventional print head, electrical loss will occur. Since it is large and electromagnetic induction is likely to occur in the wiring adjacent to the cable and the surrounding electric circuit, it is preferable to connect the segment electrode of the piezoelectric diaphragm to the driving means directly or through the adjacent printed wiring. good. As in the embodiment shown in FIG. 1, the segment electrode 4 is connected to the drive driver IC 6 which generates an AC voltage via the printed wiring 11 on the adjacent base plate.
It is effective to prevent electrical crosstalk by making the high frequency wiring as short as possible. In this embodiment, a drive control signal coded from the outside is supplied to the drive signal wiring 12 as a power source.
Thus, since the drive control signal is applied to the driver IC, the drive control signal is decoded in the driver IC, and the AC voltage is supplied to each segment electrode, the number of wirings for electrical connection with the main body can be significantly reduced.

Recording by the ink jet print head manufactured in this example was quick-drying and had no bleeding. Compared to the conventional method of recording one dot with one ink drop, which gives an excessive amount of ink to the recording medium, the present invention records one dot with a very fine and large set of ink drops. It is considered that this makes it possible to apply an appropriate amount of ink to the recording medium. It was also confirmed that the density expression of 100 gradations or more can be performed in 1-dot units by modulating the ejection time once.

The shape and size of the piezoelectric vibrating plate according to the present invention, and the material of each part are variously determined depending on the element density, driving frequency, applied voltage, ink material, etc. of the ink jet print head to be manufactured. It goes without saying that it is not the same as the one adopted in the example.

In addition to the purpose of recording information such as characters and pictures on a recording medium such as paper with ink, the ink jet print head according to the present invention selects various liquids such as various coatings using liquids and dropping liquids such as trace liquids. It can also be used for the purpose of ejecting ink.

[0020]

According to the present invention, by forming a slit on the common electrode side, the ink filled in the slit electrically short-circuits the segment electrodes, or the electric field applied between the segment electrodes causes the ink to be electrolyzed. It was possible to improve the reliability of the head by eliminating problems such as wear.

[Brief description of drawings]

FIG. 1 is a perspective view showing a partial cross section of a structure of an embodiment according to the present invention.

FIG. 2 is a sectional view showing the structure of an embodiment according to the present invention.

FIG. 3 is a perspective view showing an entire embodiment according to the present invention.

FIG. 4 is a diagram showing a drive circuit configuration of an embodiment according to the present invention.

FIG. 5 is a diagram illustrating a basic configuration of an embodiment according to the present invention.

[Explanation of symbols]

 1 --- Piezoelectric diaphragm (opposing plate) 2 --- Slit 3 --- Common electrode 4 --- Segment electrode 5 ---・ ・ Ink 5a ・ ・ Ejected ink 6 ・ ・ ・ ・ Driver IC 7 ・ ・ ・ ・ Spacer 8 ・ ・ ・ ・ Ink chamber 9 ・ ・ ・ ・ Base Plate 10: Ink supply path 11: Driving voltage wiring 12: Driving signal wiring 13: Wire bonding wiring 101: Ink supply pipe 102-Drive signal connector 103-Drive signal cable P --- AC voltage source S --- Switch W --- Piezoelectric diaphragm Vibrating part 201 ... Piezoelectric diaphragm 201a ... Piezoelectric diaphragm vibrating part 202 ... Slit 03 ..... common electrode 204 ----- segment electrode 205 ----- ink 205a · · · · ejecting ink 206 ..... opposing plate

Claims (5)

[Claims] 1. A piezoelectric vibrating plate, an opposing plate, a slit formed at one end of the piezoelectric vibrating plate by stacking the piezoelectric vibrating plate and the opposing plate with a gap therebetween, and the piezoelectric vibrating plate. A common electrode formed at the end of the surface on the slit side, a plurality of segment electrodes formed at the end of the other surface of the piezoelectric vibrating plate, ink held in the slit, the segment electrode and the common An ink jet print head comprising: a driving unit that selectively applies an alternating voltage between the electrodes. 2. The ink jet print head according to claim 1, wherein the thickness of the end portion of the piezoelectric vibrating plate is different between the segment electrode portion and the portion sandwiched by the segment electrodes. 3. The ink jet printhead according to claim 1, wherein the piezoelectric print plate is composed of two piezoelectric vibrating plates, and the opposing plate of each piezoelectric vibrating plate also serves as the other piezoelectric vibrating plate. 4. The ink jet print according to claim 3, wherein the relative positions of the segment electrode groups on the two piezoelectric vibrating plates are shifted in the array direction of the segment electrode groups by half the array pitch of the segment electrodes. head. 5. The ink jet print head according to claim 1, wherein the segment electrode group of the piezoelectric vibrating plate is connected to a driving means directly or via an adjacent printed wiring.