JPH0664162A - Liquid drop discharging device, and driving method therefor - Google Patents

Abstract

PURPOSE:To make high density printing possible in a simple structure while improving durability without being affected by crosstalk, and to decrease the level of operating sound. CONSTITUTION:Perpendicular partition walls 1a-1g are provided to a passage substrate 3, and passages 2a-2f divided by the partition walls 1a-1g are provided. A piezoelectric element covering plate 4 is attached to the ends of the partition walls. Surface electrodes 6a-6f and undersurface electrodes 7a-7f are provided, corresponding to the passages 2a-2f, to the covering plate 4. The surface electrodes 6a, 6c, and 6e are made conductive respectively with the undersurface electrodes 7b, 7d and 7f, each positioned to the right of each of the surface electrodes 6a, 6c and 6e. The surface electrodes 6b, 6d and 6f are made conductive respectively with the undersurface electrodes 7a, 7c and 7e, each positioned to the left of each of the surface electrodes 6b, 6d and 6f. In the case where ink is discharged through the passage 2d, the capacity of the passage is reduced with electric field E in the direction the same as polarization direction P applied between the electrodes 6d and 7d, while the capacity of the passage 2c is increased with the electric field E' in the opposite direction applied between the electrodes 6c and 7c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge apparatus, and more particularly to an on-demand type multi-nozzle ink jet recording apparatus having a plurality of nozzles and ejecting ink droplets from each nozzle as needed.

[0002]

2. Description of the Related Art Presently, as an on-demand multi-nozzle ink jet device, a method of converting an electric signal into a mechanical displacement by using a piezoelectric element to apply pressure to ink in a flow path to eject an ink droplet, There is a so-called bubble jet method in which ink droplets are ejected by the pressure of steam generated by applying heat to ink. A conventional inkjet recording device using a piezoelectric element has the advantages of high energy efficiency and the ability to use any ink, but is not suitable for high density printing with a large number of nozzles for high quality printing. Further, the bubble jet method has problems such as low energy efficiency, large restrictions on ink, and poor durability.

Therefore, in order to provide a large quantity and a low cost of an ink jet printer having a novel principle and structure which has a large number of nozzles arranged in high density and is energy efficient and durable, And a flow path substrate having a plurality of partition walls provided in a direction substantially perpendicular to the direction and a flow path partitioned by the partition walls, and a piezoelectric element plate polarized in the thickness direction and fixed on the partition wall end face. Patent application No. 4-1.
Proposed by No. 30419.

FIG. 7 is a perspective view of a droplet discharge device proposed by the present inventor, and FIG. 8 is a sectional view thereof. A plurality of flow path partition walls 1 are formed on the flow path substrate 3 substantially at right angles to the surface direction, and the partition walls 1 partition the ink flow paths 2. The cross section of each flow path 2 and flow path partition 1 is substantially rectangular. Each flow path 2 is independent on the nozzle plate 5 side and communicates with a common ink chamber 11 for supplying ink on the opposite side. Each flow channel 2 and flow channel partition wall 1 extend in parallel from the nozzle portion to the common ink chamber portion and the nozzle 5a.
Equal to the pitch of. For this reason, it is not necessary to take a fan-shaped flow path arrangement as seen in a conventional inkjet head using a piezoelectric element, and it is possible to create a multi-nozzle inkjet head having an arbitrary number of nozzles. ,
It has the advantage of being applicable to both serial printers and line printers.

A piezoelectric element plate 4 having a ground electrode 9 on the lower surface and a drive electrode 10 corresponding to each flow path on the upper surface is mounted on the flow path substrate 3. This piezoelectric element plate serves as an actuator that deforms the flow path partition wall 1 and also has a function as a flow path cover. Each drive electrode 10 has an electrode terminal 12 for supplying a signal from a flexible cable or the like. Nozzle 5 corresponding to each flow path on the front of the head
The nozzle plate 5 having a formed therein is mounted.

Next, a method of driving the above-mentioned droplet discharge device will be described with reference to FIG. Here, the operation of ejecting ink droplets from the flow path 2b will be described. In the following description, the flow paths for ejecting ink droplets are shown by black circles, and the flow paths that are not ejected are shown by white circles. Of the three drive electrodes 10a to 10c shown, the drive electrode 10 corresponding to the flow path 2b
The voltage V is applied only to b in the direction in which the piezoelectric element 4 contracts in the plane (direction in which the electric field E is generated in the same direction as the polarization direction P).
Since only the upper portion of the flow path 2b of the piezoelectric element plate 4 contracts, the flow path partition walls 1b and 1c on both sides of the flow path 2b are attracted, and the volume of the flow path 2b decreases. Therefore, pressure is applied to the ink in the flow path 2b, and ink droplets are ejected from the nozzle. In addition, the non-selected channel 2a will be described. Since the piezoelectric element plate above the adjacent channel 2b contracts, the piezoelectric element portion above the channel 2a and the channel partition walls 1a and 1b are also attracted toward the channel 2b. Deform. However, in this case, since the flow path partition walls on both sides are deformed in the same direction, the volume of the flow path 2a does not change, and no pressure is applied to the ink in the flow path 2a. In this way, it is possible to select only a specific flow path using the structurally integrated piezoelectric element plate 4 and eject ink droplets.

[0007]

FIG. 10 is a diagram showing an example in which all the flow paths are simultaneously driven by the above-mentioned conventional driving method. When driving a very small number of channels as shown in FIG. 9, it does not matter, but when all channels or a large number of channels are driven simultaneously,
The piezoelectric element cover plate 4 is entirely contracted in the plane direction. Therefore, the piezoelectric element cover plate 4 and the flow path substrate 3
Has a bimorph structure and is bent and deformed as shown in FIG.

This phenomenon will be described using a specific example. X
When a print density of [dpi (dots per inch)] is realized in n rows of channels, the adjacent channel pitch DN is DN = 0.0254 × n / X (1) When the thickness of the piezoelectric element plate is T0, the width of the drive electrode is 0.8 times the channel pitch (0.8 × DN), the applied voltage is V, and the lateral piezoelectric constant is d, the piezoelectric element plate per channel The contraction amount ω of is as follows. ω = d × V × 0.8 × DN / T0 (2) Here, when a print density of 300 [dpi] is realized with a single row of flow passages, the flow passage pitch DN is expressed by the equation (1) as DN. = 8.5 · 10 ^-5 [m]. The lateral piezoelectric strain constant d is 198 × 10 ⁻¹² [m /
V], the driving voltage V is 200 [V], the thickness T of the piezoelectric element plate
When 0 is set to 1 × 10 ⁻⁴ [m], the contraction amount ω1 of the piezoelectric element plate per flow path is given by the formula (2), and ω1 = 2.7 × 10 ⁻⁸ [m], which is a sufficiently small value. The influence on other channels and the entire recording apparatus can be ignored. However, when many flow paths are simultaneously driven by the multi-nozzle head, for example, when the flow paths of a recording apparatus having 100 nozzles are simultaneously driven, the shrinkage amount ω2 is ω2 = 2.7 × 10 ⁻⁶ [ m] becomes a large value. Therefore, there are problems that the entire recording head is largely curved and noise is generated, stress is generated in the base portion of the flow path substrate 3 and the recording head supporting portion, and the durability of the recording apparatus is deteriorated.

Further, in the conventional method, when the flow path volume is reduced and pressure is applied to the ink to eject an ink droplet, backflow and pressure propagation of the ink to the common ink chamber 11 side opposite to the nozzle occur. However, the state of the inside of the common ink chamber 11 has changed depending on the number of channels that are simultaneously driven. Therefore, when most of the flow paths are driven at the same time, a large pressure is also generated in the ink in the common ink chamber, and ink droplets are ejected from the non-selected flow paths, and are ejected depending on the number of flow paths that are driven at the same time. There was a phenomenon called so-called crosstalk, such as changes in characteristics such as velocity volume of ink droplets.

As described above, the droplet discharge device previously disclosed by the present inventor has a simple structure in which the piezoelectric element cover plate is used as an actuator, and has a large number of nozzles and channels arranged at high density. Although the device is an apparatus, it has drawbacks such that durability is deteriorated by internal stress, noise is generated, and crosstalk occurs when multiple channels are simultaneously driven.

SUMMARY OF THE INVENTION It is an object of the present invention to realize a quiet droplet discharge device which has a simple structure and is capable of high-density printing, has excellent durability, is free from crosstalk, and is capable of high-quality printing.

[0012]

In order to achieve the above-mentioned object, the droplet discharge device of the present invention comprises a plurality of partition walls provided in a direction substantially perpendicular to the surface direction and partition walls formed by the partition walls. A cover made of a flow path substrate having a plurality of flow paths and a piezoelectric element plate that is polarized in the thickness direction and has a plurality of drive electrodes corresponding to the flow paths provided on both sides, and fixed to the end face of the partition wall. It includes a plate and
The drive electrode provided on one surface of the cover plate corresponding to the flow path is at least one of the drive electrodes provided on the other surface of the cover plate corresponding to the flow path adjacent to the flow path. It is conducted.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the preferred embodiments shown in the accompanying drawings. FIG. 1 is a diagram showing an ink jet recording apparatus which is an embodiment of the droplet discharge apparatus of the present invention. The droplet discharge device of the present invention includes a plurality of partition walls 1a, 1b, 1c, 1d, 1e, 1f, which are substantially perpendicular to the surface direction.
1 g is formed, and the ink flow paths 2a, 2b,
A flow path substrate 3 in which 2c, 2d, 2e, and 2f are defined and formed, a piezoelectric element cover plate 4 fixed to the flow path surface, and a structure similar to that shown in FIG. And a nozzle plate 5 to be used. In this embodiment, the piezoelectric element cover plate 4 is polarized in the direction perpendicular to the plate surface and toward the flow path substrate 3 from the surface (arrow P).
). Drive electrodes (front surface electrodes 6a to 6f and back surface electrodes 7a to 7f) separated according to the shape of the flow path are formed on both surfaces of the piezoelectric element cover plate 4, and the front surface electrode corresponding to a certain flow path is , One of the back surface electrodes corresponding to the adjacent channel is electrically connected. Ie 2
The surface electrodes 6b, 6d, 6f corresponding to the n-th (n is a natural number) flow paths 2b, 2d, 2f are the 2n-1th flow path 2
Conductive with the back surface electrodes 7a, 7c, 7e corresponding to a, 2c, 2e, and the 2n-1th flow paths 2a, 2c, 2e.
The front surface electrodes 6a, 6c, 6e corresponding to the back surface electrodes 7b, 7d, 7 corresponding to the 2nth flow paths 2b, 2d, 2f.
It is electrically connected to f.

As a method of connecting the electrodes as described above,
An electrode pattern corresponding to the electrode pattern on the back surface of the piezoelectric element cover plate 4 is formed on the flow path substrate 3, and solder,
Connect the back electrode once to the electrode on the flow path substrate with anisotropic conductive rubber, conductive adhesive, etc., then use the flexible cable,
There is a method of connecting the electrode on the flow path substrate and the electrode on the piezoelectric element cover plate 4 by using wire bonding or the like.
However, these methods complicate the manufacturing process. Therefore, as a method of realizing the connection of the electrodes by only the piezoelectric element cover plate 4 as a single component, as shown in FIG. 2, the contact holes 8 are formed in the piezoelectric element cover plate 4 to form the electrode front surfaces 6a to 6f and the back surface electrodes 7a to. 7f can be connected. By using the contact hole 8, the electrode terminal 9 for receiving the drive signal can be formed only on the surface of the piezoelectric element cover plate 4 with a simple structure.

Next, the operation of ejecting ink droplets from only one flow path will be described with reference to FIG. In order to eject ink droplets from the flow channel 2d, it is necessary to reduce the volume of the flow channel 2d by a predetermined amount and apply pressure to the ink in the flow channel. The piezoelectric element cover plate 4 of the present embodiment is perpendicular to the plate surface and includes front surface electrodes 6a to 6f to back surface electrodes 7a to 7f.
Since it is polarized in the direction toward f (direction of arrow P),
By setting the back electrode 7d to the ground level and applying a positive voltage to the front electrode 6d, an electric field E in the same direction as the polarization direction P is applied, and the portion of the piezoelectric element cover plate 4 corresponding to the front electrode 6d is in the plate in-plane direction. Shrink.

At this time, the front surface electrode 6c is electrically connected to the electrode 7d, so that the voltage is 0V, and the back surface electrode 7c is electrically connected to the electrode 6d, so that the voltage becomes a positive voltage. An electric field E ′ in the direction opposite to the polarization direction P is applied and extends in the plate in-plane direction. Since the amount of this expansion is substantially the same as the amount of contraction of the surface electrode 6d portion, these strains only deform the flow channel partition wall 1d between the flow channel 2c and the flow channel 2d, and other flow channel substrate portions and No deformation or stress is applied to the entire recording head. Therefore, only the flow channel partition wall 1d between the flow channel 2c and the flow channel 2d adhered to the piezoelectric element cover plate 4 is deformed in the flow channel 2d direction,
The volume of the flow path 2d decreases, the ink inside is pressurized, and ink droplets are ejected. On the contrary, in order to eject the ink droplets from the flow path 2c, the surface electrode 6d may be electrically connected to the ground level and a positive voltage may be applied to the surface electrode 6c.

The operation when simultaneously driving a plurality of flow paths is shown in FIG. As with the one-pass injection described above, 2
Since the n-th electrode group and the 2n−1-th electrode group are alternately conducted to the ground level and driven in a time-division manner, expansion and contraction portions are alternately formed in the piezoelectric element cover plate 4, so that the piezoelectric element cover plate 4 and the piezoelectric element cover plate 4 It is possible to drive a plurality of flow paths at the same time without causing deformation or stress to the entire road substrate 3, and there is no problem such as deterioration of durability and noise.

FIG. 4 shows an example of an actual drive voltage waveform when ejecting ink droplets from the flow path. When ejecting an ink droplet from an even (2n) channel, a surface electrode on an odd (2n-1) channel (hereinafter referred to as "2n-1 electrode") is electrically connected to the ground level and a surface electrode on a 2n channel ( Hereinafter, “2n electrode”) is changed from 0 [V] to a predetermined positive drive voltage + v [V] in a short rise time. Therefore, the channel 2c and the channel 2
The flow path partition wall 1d between d is suddenly deformed to the flow path 2d side, a large pressure is applied to the ink in the flow path 2d, and an ink droplet is ejected. After maintaining the voltage value for a predetermined time, the 2n electrode voltage value is returned to 0 (V) with a long fall time. At this time, since the flow path wall slowly returns to the 2n-1 flow path side, a large pressure is not generated in the 2n-1 flow path, and ink droplets are ejected from the 2n-1 flow path in this process. There is no such thing.

In order to eject an ink droplet from the 2n-1 channel, the 2n channel is electrically connected to the ground level at a different timing from the ejection of the ink droplet from the 2n channel, and the 2n-1 channel is predetermined. It is sufficient to apply the voltage waveform of.

Another driving example to which the present invention is applied is shown in FIG. When the ink droplets are ejected from the 2n flow path, the drive waveform of FIG. 5 temporarily deforms the flow path partition between the 2n flow path and the 2n-1 flow path to the 2n-1 flow path side to reduce the volume of the 2n flow path. The voltage is increased and then the return flow path partition is rapidly returned to its original state with a short fall time to 0 V.
A pressure is generated in the n-channel to eject ink droplets from the 2n-channel. In this driving method, extremely efficient driving can be performed by deforming the flow path wall in accordance with the pressure vibration of the ink generated in the flow path when the flow path wall is slowly deformed first.

In the driving method shown in FIG. 6, the surface electrode (2n-1 electrode) on the odd-numbered flow path is always electrically connected to the ground level.
The drive waveform is applied only to the n-electrode, and the rising time and the falling time of the waveform are adjusted to selectively eject each flow path. As described above, when the 2n-1 electrode is connected to the ground level and a positive voltage is applied to the 2n electrode, the channel partition between the 2n channel and the 2n-1 channel is deformed to the 2n channel side. Therefore, when the potential of the 2n electrode is changed from 0 V to a predetermined positive voltage with a short rise time, an ink droplet is ejected from the 2n flow path. Next, when the voltage is changed to 0V after a predetermined time with a short fall time, the flow path partition is rapidly returned from the 2n flow path side to the initial position on the 2n-1 flow path side 2n-1.
Ink droplets are ejected from the flow path.

When the rising time of the 2n electrode potential is lengthened as shown by the dotted line in the figure, the movement of the flow path partition wall becomes slow, so that no ink droplet is ejected from the 2n flow path and the falling time is delayed. In that case, ink drops will not be ejected from the 2n-1 flow path. In this driving method, since it is sufficient to supply the driving waveform to the electrodes that are half the number of flow paths, the driving circuit can be cut in half and the connection cable from the circuit section to the print head section can be saved, thus reducing the cost of the printing apparatus. it can.

In the printing apparatus according to the present invention, since even-numbered channels and odd-numbered channels are driven in a time-division manner, there is a concern that the maximum ejection frequency of the entire printing apparatus may be lowered. However, for example, when ejecting the even-numbered channels after ejecting the odd-numbered channels, it is not necessary to wait until the ink pressure oscillation in the odd-numbered channels is dampened or the ink refilling is completely completed. Frequency is 1
It is only slightly lower than the maximum ejection frequency of the flow path.

Next, crosstalk will be described. In the recording apparatus of the present invention, the volume of the adjacent flow channel increases by about the same as the volume reduction amount of the flow channel selected for injection. Therefore, the ink flows from the common ink chamber to the adjacent flow channel by substantially the same amount as the amount of the ink that flows back to the common ink chamber side from the flow channel selected for ejection. Further, the pressure wave having a substantially reverse waveform propagates from the adjacent flow path to the common ink chamber, so that the pressure waves cancel each other out, and the state of the common ink chamber hardly changes. This can be said even if the number of flow paths that are driven at the same time increases, so that so-called crosstalk in which the ejection characteristics such as the droplet speed and the volume change depending on the ejection pattern does not occur.

Further, P is used as the piezoelectric element cover plate material.
When piezoelectric ceramics such as ZT are used, it is known that when a large electric field called a coercive electric field above a certain threshold value is applied to these materials, the polarization direction changes to the electric field direction. As described above, since the electric field E having the same direction as the polarization direction P and the electric field E ′ having the opposite direction are alternately applied to the piezoelectric element cover plate 4, the application is performed so that the polarization direction does not change. The electric field must be below the coercive field.

Although the piezoelectric element cover plate 4 is polarized in the direction of the front surface electrode from the front surface electrode side in the present embodiment, the electric field to be applied even when it is polarized in the direction of the front surface electrode from the rear surface electrode side. It goes without saying that they can be driven in exactly the same way by applying drive waveforms so that they are in opposite directions.

In the printing apparatus of the present invention, the flow path partition is deformed and pressure is applied to the liquid in the flow path to eject droplets from the nozzle. Can also be used with ink. Therefore, the present invention is not limited to a printing device as a computer terminal, and can be applied to a wide range of applications such as ejecting any liquid, for example, an industrial printing device, a small amount of reagent ejection, and a facsimile.

In the above embodiment, one front surface electrode is electrically connected to only one of the adjacent back surface electrodes, but it is also possible to make it electrically connected to both adjacent back surface electrodes.

[0029]

As described above, according to the present invention, it is possible to provide a quiet recording apparatus having high energy efficiency, excellent durability, no crosstalk, and high print quality.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a plan view of a main part of one embodiment.

FIG. 3 is a sectional view illustrating the operation of the embodiment.

FIG. 4 is a voltage waveform diagram showing a first example of a driving method of the present invention.

FIG. 5 is a voltage waveform diagram showing a second example of the driving method.

FIG. 6 is a voltage waveform diagram showing a third example of a driving method.

FIG. 7 is a perspective view of a conventional example.

FIG. 8 is a sectional view of a conventional example.

FIG. 9 is a cross-sectional view illustrating the operation of a conventional example.

FIG. 10 is a cross-sectional view showing another operating state of the conventional example 1a to 1g ... Flow path partition walls 2a to 2f ... Flow path 3 ... Flow path substrate 4 ... Piezoelectric element cover plate 5 ... -Nozzle plate 5a ... Nozzles 6a-6f ... Front surface electrode 7a-7f ... Back surface electrode

Claims (5)

[Claims] 1. A flow channel substrate having a plurality of partition walls provided in a direction substantially perpendicular to a plane direction and a plurality of flow channels partitioned by the partition walls, and polarized in the thickness direction. A plurality of drive electrodes corresponding to the flow path, which are formed of piezoelectric element plates on both sides, and a cover plate fixed on the partition wall end surface, one of the cover plates corresponding to the flow path. The drive electrode provided on the surface of the cover plate is electrically connected to at least one of the drive electrodes provided on the other surface of the cover plate corresponding to the flow path adjacent to the flow path. Characteristic droplet discharge device. 2. The droplet discharge according to claim 1, wherein a nozzle communicating with the flow path is formed, and the nozzle includes a nozzle plate fixed to an end surface of the flow path substrate and the cover plate. apparatus. 3. The droplet discharge device according to claim 1, wherein the drive electrodes that are electrically connected to each other are electrically connected to each other through contact holes. 4. The 2n-th electrode group and 2 on one surface of the cover plate according to claim 1.
A driving method of a droplet discharge device, characterized in that the even-numbered flow channel group and the odd-numbered flow channel group are time-divisionally driven by alternately connecting the (n-1) th electrode group to the ground level. 5. The 2n-th electrode group or 2n on the surface of the cover plate according to claim 1.
-By setting either voltage of the first electrode group to the ground level at all times and changing the rising time constant and the falling time constant of the voltage waveform applied to the drive electrode in the opposite electrode group, And a method for driving a droplet discharge device, characterized in that the odd-numbered channels are driven in a time division manner.