JP2004322318A - Droplet discharging apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease a voltage level of a drive signal and to suppress discharging unevenness of liquid droplets in a liquid droplet discharging device. <P>SOLUTION: The liquid droplet discharging device discharges a discharge liquid stored in a cavity as liquid droplets from a nozzle by mechanically deforming an actuator by a predetermined drive signal. A waveform of the drive signal is set so that the drive signal vibrates the cavity precedently, and moreover makes the liquid droplets discharged in a state in which the liquid droplets are synchronized with the vibration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a droplet discharge device and method.
[0002]
[Prior art]
As is well known, a droplet discharge device applied to a printer or the like includes a piezoelectric element as an actuator, and a drive signal having a predetermined waveform shape is applied to the piezoelectric element to drop a discharge liquid stored in a cavity into a droplet. There is one that discharges from a nozzle.
[0003]
The waveform shape of the drive signal is generally adjusted so as not to resonate with the natural resonance period in consideration of the variation in the mechanical natural resonance period (for example, the natural resonance period of the cavity or the piezoelectric element) related to the liquid for ejection. Designed. The design concept of such a drive signal is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-09467.
[0004]
[Patent Document 1]
JP-A-2000-094677
[Problems to be solved by the invention]
By the way, as described in the above-mentioned patent document, the drive signal is a kind of pulse signal composed of several parts (waveform parts), and includes a discharge pulse part for discharging droplets, It is formed of a waveform part following this and a vibration suppression pulse part for suppressing the oscillation of the ejection liquid in the cavity. In addition, the discharge pulse section includes a charge waveform section that rises at a predetermined voltage gradient from a predetermined reference voltage, a flat waveform section before discharge that maintains a constant high voltage, and a droplet that falls at a predetermined voltage gradient and discharges droplets. It is formed from a discharge waveform portion (discharge waveform portion). The piezoelectric element is deformed by discharging the charge charged in the charging waveform portion by discharging in the discharge waveform portion, and causes the nozzle to discharge droplets.
[0006]
However, since the conventional drive signal is designed not to resonate with the mechanical natural resonance period related to the liquid for ejection, a part of the vibration given by the piezoelectric element is canceled out, and the desired ejection is performed. In order to obtain energy, it is necessary to increase the voltage change width (that is, the voltage level of the drive signal) in the ejection waveform portion. Therefore, in the conventional droplet driving device, it is necessary to employ a driving circuit having a wide driving voltage range for the driving circuit for driving the piezoelectric element. As a result, there is a problem that the cost of the droplet discharging device is increased. In addition, for example, a high-viscosity material cannot be discharged. If the piezoelectric element is modified so as to increase the maximum amplitude in order to discharge a high viscosity, the oscillation cycle becomes longer, and there is also a problem that minute droplets cannot be ejected.
[0007]
Further, when a drive signal having such a large voltage level is applied to the piezoelectric element, the heat generation naturally increases. There is also a problem that the size of the droplets varies (discharge variation) due to the heat. Such ejection variation occurs particularly when ejecting a high-viscosity ejection liquid as droplets. For example, in the manufacture of an EL (electroluminescence) panel, when a pixel is formed by spraying a liquid luminescent material onto a substrate using a droplet discharge device, the luminescent material has an extremely high viscosity, so that a discharge variation occurs. It easily occurs, and as a result, the amount of the luminescent material forming each pixel varies, and the display performance of the EL panel is reduced.
[0008]
The present invention has been made in view of the above points, and has as its object to reduce the voltage level of a drive signal and to suppress variation in the ejection of droplets in a droplet ejection device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a droplet discharge apparatus and method for discharging a discharge liquid stored in a cavity as a droplet from a nozzle by mechanically deforming an actuator with a predetermined drive signal, Means is adopted in which the drive signal causes the cavity to vibrate in advance, and the waveform is set so that the droplet is ejected in a state synchronized with the vibration.
[0010]
According to such a means, it is possible to discharge a droplet by a drive signal of a smaller level, and thereby it is possible to suppress heat generation of the actuator.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a functional configuration of a droplet discharge device according to the present embodiment. As shown in this figure, the present droplet discharge device includes a control device 1, an XY drive device 2, and a discharge head 3. The control device 1 includes an I / F 1a, a RAM 1b, a ROM 1c, an arithmetic control unit 1d, a drive signal generation unit 1e, an oscillation circuit 1f, and an I / F 1g.
[0012]
The I / F 1a receives image information and various setting information of a drawing target image input from the outside. The RAM 1b temporarily stores the image information, various setting information, and work data of the arithmetic control unit 1d. The ROM 1c stores a control program processed by the arithmetic and control unit 1d, drive waveform data indicating a waveform of a drive signal COM for driving the ejection head 3, various control data necessary for executing the control program, and the like. .
[0013]
The arithmetic control unit 1d executes a control program based on the image information and various setting information to output ejection pattern data indicating a droplet ejection pattern and a motor drive signal for driving the XY drive unit 2. It generates and outputs it to the I / F 1g, acquires drive waveform data from the ROM 1c based on the image information, and outputs it to the drive signal generator 1e.
[0014]
Here, the ejection pattern data specifies dot pattern data corresponding to the image to be drawn, that is, which piezoelectric element 3e is to be applied to the ejection head 3 to which the drive signal COM is applied. The ejection pattern data is serial data in which one word is composed of the number of bits corresponding to the number of piezoelectric elements 3 e provided on the ejection head 3 (= the number of ejection nozzles from which droplets are ejected). For example, when the ejection head 3 has 180 ejection nozzles, the data is 180-bit serial data.
[0015]
The drive signal generation unit 1e is composed of a D / A converter or the like, converts the waveform data (digital signal) into a drive signal COM (analog signal), and outputs the same to the I / F 1g. The oscillation circuit 1f generates a clock having a predetermined frequency. The I / F 1g synchronously outputs the ejection pattern data, the clock, the drive signal COM, and the motor drive signal to the ejection head 3 and the XY drive unit 2 in synchronization with the clock.
[0016]
On the other hand, the XY drive device 2 includes an X-axis motor 2a and a Y-axis motor 2b. The X-axis drive motor 2a is, for example, a stepping motor, and moves the ejection head 3 relative to the stage on which the ejection target is mounted in the X direction (main scanning direction) based on a motor drive signal input from the control device 1. Move to The Y-axis drive motor 2b is, for example, a stepping motor, and moves the stage in the Y direction (sub-scanning direction) based on a motor drive signal input from the control device 1. The stage is, for example, a rectangular flat plate, and an ejection target is fixed on an upper surface thereof. The target object is an object to which droplets ejected from the ejection head 3 are to be attached, such as various types of paper and substrates.
[0017]
The ejection head 3 includes a shift register 3a, a latch circuit 3b, a level shifter 3c, a switch circuit 3d, and a piezoelectric element 3e.
[0018]
The shift register 3a converts the ejection pattern data d (serial data) input from the I / F 1g into parallel data, and outputs the parallel data to the latch circuit 3b. The latch circuit 3b latches the parallel data with a reference clock input from the I / F 1g and outputs the data to the level shifter 3c in synchronization. The level shifter 3c converts the parallel data input from the latch circuit 3b into a voltage and outputs it as a selection signal to the switch circuit 3d.
[0019]
The switch circuit 3d selectively applies the drive signal COM input from the I / F 1g to the piezoelectric element 3e based on the selection signal input from the level shifter 3c. The piezoelectric element 3e is provided corresponding to the ejection hole from which the droplet is ejected, and ejects the droplet from the ejection nozzle by being mechanically deformed in response to the application of the drive signal COM.
[0020]
For example, in the case of the ejection head 3 having 180 ejection nozzles, the ejection nozzles are provided in individual cavities, respectively, and the piezoelectric element 3e is provided in each cavity. That is, the piezoelectric element 3e is provided for each cavity, and applies a pressure to the internal ejection shaking liquid by mechanically deforming a part of the cavity to eject the liquid as droplets from the ejection nozzle.
[0021]
Various liquids are applied to the discharge liquid (that is, droplets) according to the application of the present droplet discharge device. This discharging liquid becomes various printing inks, for example, when the present droplet discharging apparatus is used as a printing apparatus, and becomes a conductive material for forming a wiring pattern when used as a pattern wiring apparatus. When used as an apparatus, it is a transparent resin for forming a microlens, and when used as a color filter manufacturing apparatus, it is a resin for forming a colored layer of a color filter.
[0022]
When used as an organic EL substrate manufacturing apparatus, the liquid for ejection is an electro-optical material (a fluorescent organic compound exhibiting electroluminescence) for forming a luminescent pixel. This electro-optical material has a viscosity of 50 cps, and is the highest viscosity among the above-described various ejection liquids. In order to discharge such a high-viscosity discharge liquid, it is necessary to set the voltage level of the drive signal COM high.
[0023]
Subsequently, the waveform of the drive signal COM will be described with reference to FIG. The drive signal COM shown in FIG. 2 is designed for the ejection head 3 in which the natural resonance period Tc of the cavity is 7 μsec and the natural resonance period Ta of the piezoelectric element 3e is about 3.5 μsec. is there.
[0024]
As shown in this figure, the drive signal COM is formed of a preceding resonance pulse section, an ejection pulse section following the preceding resonance pulse section, and a vibration suppression pulse section following the ejection pulse section. The waveform of the preceding resonance pulse portion is set so as to vibrate the cavity. The waveform of the ejection pulse section is set so as to eject droplets in a state resonating with the vibration of the cavity. The waveform of the vibration damping pulse section is set so that the vibration of the cavity can be damped after discharging the droplet. A general drive signal is formed from a discharge pulse section and a vibration suppression pulse section, and the drive signal COM of the present droplet discharge apparatus is characterized by including a preceding resonance pulse section.
[0025]
More specifically, the leading resonance pulse portion includes a rising portion h1 and a rising portion h1 rising from a reference voltage (bias voltage) of 3.0 V to an intermediate voltage of 23.5 V with a constant gradient in a period of 2.2 μsec. A flat portion h2 for maintaining a period of 2.0 μsec, a falling portion h3 which falls at a constant gradient from 23.5 V to 3.0 V in a period of 2.2 μsec, and a flat portion for maintaining 3.0 V for a period of 2.0 μsec. h4. Note that the voltage level (= 23.5V-3.0V) of the preceding resonance pulse portion is set so as not to discharge the droplet.
[0026]
The total time width t1 to t5 of the preceding resonance pulse portion is theoretically set to the natural resonance period Tc of the cavity, but the fundamental period in the vibration of the cavity is purely unique due to the influence of other mechanical elements related to the cavity. Since the resonance period does not become Tc, the natural resonance period Tc is slightly adjusted from these circumstances. Further, the time widths t1 to t2 and t3 to t4 of the rising portion h1 and the falling portion h3 are theoretically set to Ta / 2 which is half of the natural resonance period Ta of the piezoelectric element 3e. Also, since the fundamental period of the vibration of the piezoelectric element 3e does not become the purely natural resonance period Ta due to the influence of the mechanical element supporting the piezoelectric element 3e, the fundamental period is adjusted with respect to the natural resonance period Ta. In addition, the value is in a range that can be realized by the response speed of the drive signal generation unit used in the present embodiment. Even if the drive waveform slightly deviates from Ta / 2, the effect is reduced, but is not fatal.
[0027]
The discharge pulse portion includes a rising portion h5 that rises at a constant gradient from 3.0 V to a maximum voltage of 30 V during a period of 3.5 μsec, a flat portion h6 that maintains 30 V for a period of 2.5 μsec, and a 2.0 μsec period. The falling portion h7 falls at a constant gradient from 30V to the lowest voltage 0V. The rising part h5 is a charging waveform part for charging the piezoelectric element 3e with electric charge, while the falling part h7 falling from the highest voltage to the lowest voltage is a discharging waveform part for discharging droplets. That is, it is a discharge waveform portion for discharging the electric charge of the piezoelectric element 3e. The voltage level of the ejection pulse portion (= 23.5V-3.0V) is also set so that a droplet is not ejected by itself.
[0028]
The rising portion h5 in such a discharge pulse portion follows the preceding resonance pulse portion having the entire time widths t1 to t5, and therefore has a timing synchronized with the vibration of the cavity caused by the application to the piezoelectric element 3e. Further, a falling portion h7 following the rising portion h5 with a 2.5 μsec flat portion h6 interposed therebetween also has a timing synchronized with the vibration of the cavity.
[0029]
Further, the damping pulse section includes a flat portion h8 for maintaining 0 V for a period of 3.6 μsec, a rising portion h9 for rising from 0 V to 23.5 V with a constant gradient in a period of 2.2 μsec, and a rising portion h9 for 23.5 V for 3.3 μsec. And a falling portion h11 that falls at a constant gradient from 23.5 V to 3.0 V in a period of 3.3 μsec.
[0030]
Next, the operation of the present droplet discharging apparatus thus configured will be described in detail. First, the arithmetic control unit 1d drives the XY driving device 2 and the ejection pattern data indicating the ejection pattern of the droplet by executing a control program based on image information and setting information provided from the outside. And generates waveform data from the ROM 1c based on the image information.
[0031]
The ejection pattern data is supplied from the arithmetic control unit 1d to the I / F 1g, and the motor drive signal is also supplied to the I / F 1g. On the other hand, the waveform data is supplied from the arithmetic control unit 1d to the drive signal generation unit 1e, converted into the drive signal COM, and then supplied to the I / F 1g. These three signals are output to the ejection head 3 or the XY driving device 2 after being synchronized by the I / F 1g.
[0032]
That is, the ejection pattern data is supplied to the shift register 3a, the motor drive signal is supplied to the X-axis motor 2a and the Y-axis motor 2b, and the drive signal COM is supplied to the switch circuit 3d. As a result, the relative position of the discharge head 3 in the X direction and the Y direction with respect to the discharge target sequentially moves in a scanning manner, and is stored in each cavity by driving each piezoelectric element 3e by the drive signal COM. The discharged oscillating liquid is sequentially discharged as droplets from each discharge nozzle, and an image corresponding to the drawn image is drawn (recorded) on the discharge target.
[0033]
In the droplet discharge by the piezoelectric element 3e, in the present droplet discharge device, the drive signal COM is set in the shape as described above. Nevertheless, a high-viscosity ejection liquid can be ejected stably.
[0034]
That is, the cavity (more precisely, the ejection liquid in the cavity) vibrates prior to the preceding resonance pulse portion disposed before the ejection pulse portion. The ejection pulse portions (more precisely, the charging waveform portion h5 and the discharging waveform portion h7) are applied to the piezoelectric element 3e at a timing synchronized with the vibration of the cavity. Drops can be ejected.
[0035]
Moreover, the rising portion h1 and the falling portion h3 of the preceding resonance pulse portion and the rising portion h5 and the falling portion h7 of the ejection pulse portion are set to have waveforms so as to resonate with the piezoelectric element 3e. It can be vibrated well.
[0036]
Therefore, according to such a drive signal COM, even when the voltage level of the ejection pulse portion is small, the piezoelectric element 3e and the cavity are efficiently vibrated, and the ejection liquid in the cavity is ejected as droplets from the ejection nozzle. Can be. As a result, heat generation of the piezoelectric element 3e can be suppressed, so that it is also possible to suppress ejection variations caused by the heat generation.
[0037]
Here, the variation in the natural resonance period Ta is suppressed by selecting the piezoelectric elements used in the present embodiment in the manufacturing process. Further, the variation of the natural resonance period Tc between the nozzles is such that the ejection is not affected. However, a configuration may be adopted in which the drive waveform is adjusted in accordance with each of the natural resonance periods Ta and Tc for each nozzle to suppress variation between nozzles. In this case, one drive signal COM is not selected by a switch circuit, but each piezoelectric element is controlled by an independent signal.
[0038]
Note that the present invention is not limited to the above embodiment, and for example, the following modifications can be considered.
(1) In the above embodiment, one preceding resonance pulse section is arranged before the ejection pulse section, but a plurality of preceding resonance pulse sections may be arranged. By increasing the number of preceding resonance pulse sections, a larger cavity vibration can be obtained, so that the voltage level of the ejection pulse section can be further reduced.
[0039]
(2) In the above embodiment, in addition to the rising part h1 and the falling part h3 of the preceding resonance pulse part, the rising part h5 and the falling part h7 of the ejection pulse part are set so that the piezoelectric element 3e resonates. However, the present invention is characterized by reducing the energy required for droplet ejection by vibrating the cavity by the preceding resonance pulse portion and applying the ejection pulse portion so as to resonate with the vibration. , The rising part h1, the falling part h3, the rising part h5, and the falling part h7 do not necessarily need to be set so that the piezoelectric element 3e resonates. Conversely, with the same piezoelectric element capability, higher viscosity ink can be ejected.
[0040]
【The invention's effect】
As described above, according to the present invention, since the driving signal is set to have a waveform that causes the cavity to vibrate in advance and ejects the liquid droplets in a state synchronized with the vibration, the driving signal having a smaller level This makes it possible to discharge droplets, thereby suppressing heat generation of the actuator. Then, as a result, it is possible to suppress the ejection variation.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a functional configuration of a droplet discharge device according to an embodiment of the present invention.
FIG. 2 is a waveform diagram showing a waveform of a drive signal according to an embodiment of the present invention.
[Explanation of symbols]
1 ... Control device 1a ... I / F
1b RAM
1c ROM
1d ... Calculation control unit 1e ... Drive signal generation unit 1f ... Oscillation circuit 1g ... I / F
2 XY drive device 2a X-axis motor 2b Y-axis motor 3 Discharge head 3
3a shift register 3b latch circuit 3c level shifter 3d switch circuit 3e piezoelectric element

Claims (8)

A droplet discharge device that discharges a discharge liquid stored in a cavity as a droplet from a nozzle by mechanically deforming an actuator with a predetermined drive signal,
The droplet discharge device is characterized in that the drive signal is set to have a waveform so as to vibrate the cavity in advance and discharge droplets in a state synchronized with the vibration. 2. The droplet discharge device according to claim 1, wherein the drive signal is set to have a waveform such that at least one of a charge waveform portion and a discharge waveform portion of the actuator resonates with the actuator. The drive signal is
A pre-resonance pulse section for vibrating the cavity;
3. The droplet discharge device according to claim 1, further comprising: a discharge pulse portion which is a waveform portion following the preceding resonance pulse portion and discharges the droplet in a state synchronized with the vibration of the cavity. The droplet discharge device according to any one of claims 1 to 3, wherein the drive signal includes a vibration suppression pulse unit that suppresses vibration of the cavity after discharging the droplet. A droplet discharge method for discharging a discharge liquid stored in a cavity as a droplet from a nozzle by mechanically deforming an actuator with a predetermined drive signal,
The droplet discharge method is characterized in that the drive signal is set to have a waveform such that the cavity is vibrated in advance and the droplet is discharged in synchronization with the vibration. 6. The droplet discharging method according to claim 5, wherein the drive signal is set to have a waveform such that at least one of a charge waveform portion and a discharge waveform portion of the actuator resonates with the actuator. The drive signal is
A pre-resonance pulse section for vibrating the cavity;
7. The droplet discharging method according to claim 5, further comprising: a discharging pulse portion which is a waveform portion following the preceding resonance pulse portion and discharges the droplet in a state synchronized with the vibration of the cavity. 8. The droplet discharging method according to claim 5, wherein the driving signal includes a vibration damping pulse unit for damping the vibration of the cavity after discharging the droplet.

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