JPH10128970A - Ink jet recording head and driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently achieve gradation printing and to increase a response speed by reducing the interference of the piezoelectric material layers of a plurality of drive electrodes formed so as to be adjacent to each other to the utmost. SOLUTION: A drive means consists of elastically deformable lower electrodes, piezoelectric material layers formed to the region opposed to pressure generation chambers 2 and upper electrodes supplying a drive signal to the piezoelectric material layers at every pressure generation chambers and the upper electrodes are constituted so as to be divided into a plurality of ones to be made electrically independent. The piezoelectric material layers are also separated by the grooves 13 corresponding to the divided upper electrodes 11, 12. The pressure generation chambers 2 are efficiently contracted and expanded by the drive signals of the voltages corresponding to electrode regions to control the amt. of ink droplets and a signal is applied to other electrodes in the timing optimum to damping to rapidly attenuate residual vibration.

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 head which expands and contracts a part of a pressure generating chamber communicating with a nozzle opening by an actuator which bends and vibrates to discharge ink droplets from the nozzle opening.

[0002]

2. Description of the Related Art An ink jet recording head has a piezoelectric vibration type in which a pressure generating chamber is mechanically deformed to pressurize ink, and a heating element is provided in the pressure generating chamber to generate air bubbles generated by the heat of the heating element. And a bubble jet type in which the ink is pressurized by the pressure of the above. The recording heads of the piezoelectric vibration type are further classified into two types, a first recording head using a piezoelectric vibrator that is displaced in the axial direction, and a second recording head using a piezoelectric vibrator that bends and displaces. . The first recording head is capable of high-speed driving and high-density recording. On the other hand, when the piezoelectric vibrator is processed by a cutting operation, or when the piezoelectric vibrator is fixed to the pressure generating chamber, the first recording head is required to perform three operations. There is a problem that a dimensional assembly operation is required and the number of manufacturing steps is increased.

On the other hand, a second recording head includes a substrate having a pressure generation chamber formed on a silicon single crystal substrate as disclosed in Japanese Patent Application Laid-Open No. 5-504740, and a nozzle communicating with the pressure generation chamber. A plurality of openings are formed, a nozzle plate fixed to one of the substrates is provided, the other surface of the substrate is formed into an elastically deformable film shape, and a piezoelectric material layer is formed on the surface by a film forming method and driven. The drive unit is configured to pressurize the ink in the pressure generating chamber by the flexural vibration of the drive unit to discharge the ink droplet from the nozzle opening.

[0004]

As described above, since the ink pressurizing means can be formed by the film forming technique, it can be formed with high accuracy, but because of the use of flexural vibration, deformation in a form suitable for ink droplet ejection. Is difficult, and inconvenience arises in response speed, resonance characteristics, and the like. In order to solve such problems, as shown in U.S. Pat. No. 4,490,641, U.S. Pat. No. 4,825,227, and U.S. Pat. There has been proposed a recording head in which an upper electrode formed on one piezoelectric diaphragm is substantially equally divided into a plurality of regions, and the timing of a drive signal applied to each electrode can be adjusted.

According to these, the piezoelectric vibrating plate of one pressure generating chamber is deformed in a form suitable for ejecting ink droplets,
Although the response speed and the resonance characteristics can be improved, the width of the pressure generating chamber is increased for high-density printing because a plurality of electrodes are provided on a common piezoelectric vibrator provided in one pressure generating chamber. When the width of the electrode becomes narrow, the displacement of the area where each electrode is provided interferes with each other, and the efficiency of ink droplet ejection is reduced, or the vibration mode of the pressing means itself of the piezoelectric vibrator is changed. There is a problem that it is difficult to control the ink amount of the ink droplet.

Further, since the residual vibration is large, there is a problem that the printing speed is still lower than that of the first recording head. The present invention has been made in view of such a problem, and an object of the present invention is to prevent interference between a plurality of vibration regions, and to discharge ink droplets with a low driving voltage, An object of the present invention is to provide an ink jet recording head capable of rapidly attenuating residual vibration.

Another object of the present invention is to propose a driving method suitable for the recording head.

[0008]

According to the present invention, there is provided a nozzle plate having a plurality of nozzle openings, a reservoir for receiving ink from outside, a reservoir and an ink supply port. And an ink jet recording head comprising a flow path forming substrate having a plurality of pressure generating chambers connected to each of the nozzle openings and connected to the nozzle openings, and a flexibly deformable driving unit that pressurizes ink in the pressure generating chambers. The driving means comprises a lower electrode that is elastically deformable, a piezoelectric material layer formed in a region facing the pressure generating chamber, and an upper electrode that supplies a driving signal to the piezoelectric material layer for each pressure generating chamber. The upper electrode is divided into a plurality of regions so as to be electrically independent, and the piezoelectric material layer is separated by a groove corresponding to the divided upper electrode.

[0009]

When a drive signal is individually applied to a plurality of upper electrodes provided in one pressure generating chamber, the piezoelectric material layers are separated from each other by a groove, so that the rigidity of the piezoelectric material layer in a region not related to vibration is obtained. It is displaced efficiently without being disturbed.

[0010]

1 and 2 show a cross-sectional structure of one embodiment of the present invention in a longitudinal direction of one pressure generating chamber and a width direction of the pressure generating chamber, respectively. Sign 1
Is a flow path forming substrate formed by etching a silicon single crystal substrate. The pressure generating chamber 2, a reservoir 3 for supplying ink to the pressure generating chamber 2, and a constant fluid resistance between the pressure generating chamber 2 and the reservoir 3. And an ink supply port 4 which communicates with the ink supply port.

A nozzle plate 6 having a nozzle opening 5 is fixed in a liquid-tight manner so as to communicate with one end of the pressure generating chamber 2 on the surface where the pressure generating chamber 2 is largely opened, and zirconium oxide is provided on the other surface. An elastic film 7 made of a material having electrical insulation such as is fixed in a liquid-tight manner.

A lower electrode 8 is formed on the surface of the elastic film 7 by forming a platinum (Pt) film having a thickness of about 0.2 μm by sputtering, and a piezoelectric material such as PZT is formed on the surface by sputtering or the like. A piezoelectric material layer 9 having a thickness of 0.0 μm is formed.

An upper electrode 10 having a thickness of about 0.2 μm is formed on the surface of the piezoelectric material layer 9 by sputtering or the like.

As shown in FIG. 3, the upper electrode 10
A plurality of electrically independent patterns, in this embodiment, first and second upper electrodes 11 having different widths W1 and W2 in the width direction of the pressure generating chambers, respectively, are provided in a region opposed to the two pressure generating chambers 2.
12, one end of each is drawn out to the terminal side by the lead patterns 13 and 14, and is configured to be connectable to an external drive circuit (not shown).

Referring back to FIG. 2, the piezoelectric material layer 9 on which the first and second upper electrodes 11 and 12 are formed is at least capable of preventing the displacement of the mutual region from propagating through the piezoelectric material layer 9. Are separated by a groove 13 having a depth d.

As described above, the method of forming the plurality of upper electrodes 11 and 12 in one pressure generating chamber 2 and the method of forming the grooves 13 in the piezoelectric material layer 9 include forming each of them independently by vapor deposition or the like. Further, after forming the pressure generating chamber in a size that covers the entire pressure generating chamber, a method of trimming to a predetermined size can be adopted.

In this embodiment, the pressure generating chamber 2 communicating with the lower electrode 8 and the nozzle opening 5 from which ink droplets are to be ejected.
When a drive signal is applied to the first upper electrode 11 of the piezoelectric material layer 9, only the region of the first upper electrode 11 of the piezoelectric material layer 9 facing the pressure generating chamber 2 bends and vibrates, and corresponds to the amount of deflection displacement of the first upper electrode 11. The ink droplet of the discharged ink amount is ejected.

Since the groove 13 is formed in the piezoelectric material layer 9 on which the first upper electrode 11 and the second upper electrode are formed, the piezoelectric material layer 9a in the region of the first upper electrode 11 2
The first upper electrode 11 can be displaced without being hindered by the upper electrode, and sufficiently displaced at a voltage as low as that when the first upper electrode 11 exists alone.

When a drive signal is applied to the lower electrode 8 and the second upper electrode 12, only the piezoelectric material layer 9a in a region corresponding to the second upper electrode 12 bends and vibrates independently of the region of the first upper electrode 11. I do. Since the area of the second upper electrode 12 is smaller than that of the first upper electrode 11, the amount of deflection is small, and therefore, a smaller amount of ink droplets is ejected than when a drive signal is applied to the first upper electrode 11.

Since the piezoelectric material layer 9b in the area where the second upper electrode is formed is independent of the piezoelectric material layer 9a in the area of the first upper electrode 11 by the groove 13, the first upper electrode 11 is formed. Without being hindered by the piezoelectric material layer 9a in the region where
The second upper electrode 1 can be displaced in response to the drive signal.
2 is sufficiently displaced at a voltage as low as that in the case where the compound 2 exists alone.

Further, when a drive signal is simultaneously applied to the first upper electrode 11 and the second upper electrode 12, the first and second upper electrodes 1
A case where regions corresponding to the total area of 1 and 12 are each independently bent and displaced without being affected by vibration of an adjacent region, and drive signals are applied to the upper electrode 11 and the upper electrode 12 independently. Are ejected in an amount corresponding to the sum of the ink droplets ejected at the same time.

Therefore, by selecting the form of signal application to the two upper electrodes 10 of the first upper electrode 11 and the second upper electrode 12 formed in one pressure generating chamber 2, the ink amount of the ink droplet Can be controlled and gradation printing can be performed.

Further, when the first upper electrode 11 is connected to the first drive circuit and the second upper electrode 12 is connected to the second drive circuit, a drive signal for causing the first upper electrode 11 to discharge ink droplets is provided. Immediately after the ink droplets are ejected to cancel the vibration from the second drive circuit to the second upper electrode 12 at a timing suitable for damping without waiting for the response of the first drive circuit. Therefore, unnecessary residual vibration after ink droplet ejection can be quickly attenuated, and the printing speed can be improved.

That is, when a trapezoidal drive signal as shown in FIG. 4A is applied to the first upper electrode 11 of the pressure generating chamber 2 communicating with the lower electrode 8 and the nozzle opening 5 from which ink droplets are to be ejected. Only the piezoelectric material layer 9a in the region of the first upper electrode 11 facing the pressure generating chamber 2 bends and displaces so that the pressure generating chamber side becomes convex, and pressurizes the ink in the pressure generating chamber 2. As a result, the meniscus of the nozzle opening is largely displaced outward as shown in FIG. 4C, and the ink droplet D is ejected from the nozzle opening 5.

After the ejection of the ink droplets, the meniscus retreats largely toward the pressure generating chamber due to the vibration characteristics determined by the flow path characteristics of the pressure generating chamber and the like, and thereafter has a residual vibration at an attenuation rate (FIG. 4C)
, The displacement indicated by the dotted line).

On the other hand, when the above-described drive signal is applied to the second upper electrode 12 at time t0 when the residual vibration of the meniscus generated after the ink droplet discharge passes through the neutral point (FIG. 4 (b)), the second upper electrode Since the displacement of the pressure generating chamber 12 is small in proportion to its size, the pressure generating chamber 2 contracts by a very small amount.

As a result, the meniscus which is about to move further to the pressure generating chamber side is pushed back to the nozzle opening side, and the residual vibration after ink droplet ejection is rapidly attenuated as shown by the solid line in FIG.

As described above, since the size of the second upper electrode 12 is smaller than that of the first upper electrode 11 for discharging ink droplets, it is the same as the drive signal for discharging ink droplets. By simply applying the above signal with shifted timing, the residual vibration of the meniscus can be suppressed and the printing speed can be improved.

In the above-described embodiment, the first upper electrode and the second upper electrode are arranged in two rows. However, as shown in FIG. When the second upper electrode 16 serving as an auxiliary is formed so as to surround the first upper electrode 15 from three sides, and a groove 17 for preventing propagation of mutual displacement is formed in a "U" shape at the boundary between the two. The relatively bendable central area can be used as a displacement area for ejecting ink droplets, and the relatively hardly bent peripheral part can be used to generate ink drops with a small amount of ink and also to suppress vibration. The level of the drive signal for discharging droplets can be reduced. Note that reference numerals 18 and 19 in the drawing indicate lead patterns.

[0030]

As described above, in the present invention,
The driving means comprises an elastically deformable lower electrode, a piezoelectric material layer formed in a region facing the pressure generating chamber, and an upper electrode for supplying a driving signal to the piezoelectric material layer for each pressure generating chamber. Since the electrode is divided into a plurality of regions so as to be electrically independent, and the piezoelectric material layer is separated by a groove corresponding to the divided upper electrode, the region not related to vibration is restrained by the piezoelectric material layer. Not only can the pressure generation chamber be efficiently contracted and expanded to control the amount of ink to print gradations, but also by applying a drive signal to the other electrode at the optimal timing for vibration suppression. Vibration can be rapidly attenuated.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a recording head of the present invention with a longitudinal cross-sectional structure of one pressure generating chamber.

FIG. 2 is a diagram showing a cross-sectional structure taken along line AA in FIG.

FIG. 3 is a diagram showing an arrangement of upper electrodes of the recording head.

FIGS. 4A to 4C are diagrams showing the relationship between the driving signal applied to the first and second upper electrodes of the recording head of the present invention and the displacement of the meniscus, respectively.

FIGS. 5A and 5B are a top view and a sectional view, respectively, showing another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 flow path forming substrate 2 pressure generating chamber 3 reservoir 4 ink supply port 5 nozzle opening 6 nozzle plate 7 elastic film 8 lower electrode 9 piezoelectric material layer 10 upper electrode 11 first upper electrode 12 second upper electrode

Claims (4)

[Claims] 1. A nozzle plate having a plurality of nozzle openings, a reservoir receiving ink from outside, and a plurality of pressure generating chambers connected to the reservoir via an ink supply port and communicating with each of the nozzle openings. An ink jet recording head comprising: a flow path forming substrate having: and a flexibly deformable driving means for pressurizing the ink in the pressure generating chamber, wherein the driving means faces the elastically deformable lower electrode and the pressure generating chamber. A piezoelectric material layer formed in a region to be formed, and an upper electrode for supplying a drive signal to the piezoelectric material layer for each pressure generating chamber, and divided into a plurality of regions so that the upper electrode is electrically independent. Wherein the piezoelectric material layer is separated by a groove corresponding to the divided upper electrode. 2. The ink jet recording head according to claim 1, wherein the upper electrode formed for each pressure generating chamber is divided so as to have a different width. 3. A nozzle plate having a plurality of nozzle openings formed therein, a reservoir for receiving ink supply from the outside, and a plurality of pressure generating chambers connected to the reservoir via an ink supply port and communicating with each of the nozzle openings. A flow path forming substrate having: and an ink jet recording head comprising a flexibly deformable driving unit that pressurizes the ink in the pressure generating chamber, wherein the driving unit has an elastically deformable lower electrode;
A piezoelectric material layer formed in a region facing the pressure generating chamber,
An upper electrode for supplying a drive signal to the piezoelectric material layer for each pressure generating chamber, wherein the upper electrode is divided into a plurality of parts with different widths, A step of applying a drive signal for discharging ink droplets to the wide electrode among the upper electrodes that have been made, and a step of applying a signal for suppressing vibration of the meniscus to the narrow upper electrode after discharging the ink droplet. A method for driving an ink jet recording head comprising: 4. The method according to claim 3, wherein the signal for suppressing the meniscus has the same waveform as a drive signal for discharging the ink droplet.