JP2003080698A - Apparatus for driving ink-jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for driving an ink-jet type recording head by which fluctuation of displacement of a piezoelectric element can be rapidly suppressed. SOLUTION: The apparatus for driving the ink-jet type recording head in which a pressure room is contracted by loading an electric voltage on the piezoelectric body to discharge an ink is provided. When printing operation is performed, a driving wave shape exhibiting an electric field strength exceeding resistance to the electric field strength of the piezoelectric body is loaded on the piezoelectric body (A). When the printing operation is not performed, a continuous pulse wave shape being an opposite polarity to the driving wave shape during printing operation is loaded on the piezoelectric body (B). It is possible to rapidly suppress fluctuation of the displacement of the piezoelectric element and to obtain a stable discharging characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for an ink jet recording head which ejects ink by controlling a voltage applied to a piezoelectric element, and more particularly, adjusts remanent polarization of each piezoelectric element at times other than printing operation. However, the present invention relates to a drive device that prevents variations between elements. Further, the present invention relates to a printer provided with such a driving device and a method for driving an inkjet recording head.

[0002]

2. Description of the Related Art An on-demand type ink jet recording head has a pressure chamber for generating ink pressure by a piezoelectric element or a heating element, an ink chamber for supplying ink to the pressure chamber, and an ink discharge from the pressure chamber. And a nozzle. Then, a drive signal is applied to the element corresponding to the print signal to generate a pressure, and the ink droplet is ejected from the nozzle to the recording medium. In particular, the ink jet recording head using the piezoelectric element has advantages that the ink is not easily deteriorated because it does not use heat, and clogging is less likely to occur.

In an ink jet recording head using this piezoelectric element, it is known that the piezoelectric film is subjected to a polarization treatment in advance in order to improve the ink ejection characteristics of the piezoelectric film.

FIG. 6 shows characteristics of strain (S) with respect to electric field strength (E) of the piezoelectric film in order to explain the concept of polarization treatment. When the polarization process is not performed, the electric field strength E =
When 0, the distortion S = 0. When the piezoelectric element is driven in this state, the strain S increases along the thick line L in the figure as the electric field strength E increases. On the other hand, when the polarization process has been performed in advance, the strain S has already exceeded 0 due to polarization when the electric field strength E = 0. When the piezoelectric element is driven in this state, the strain S increases along the thick line H in the figure as the electric field strength E increases. As described above, even when the same electric field strength is applied from the electric field strength E = 0, a higher strain can be obtained when the polarization processing is performed in advance than when the polarization processing is not performed.

The polarization generated by this polarization process is gradually lost over time. JP-A-9-141866
The publication discloses re-polarizing the piezoelectric element member with a voltage having the same polarity as the polarization direction at the time of ink ejection, in order to eject the ink at a desired ejection amount even after long-term use.

[0006]

However, the above-mentioned polarization treatment is effective in the case of driving in a range smaller than the coercive electric field, but when the piezoelectric thin film is used, the electric field strength of the driving is sufficiently larger than the coercive electric field. The polarization treatment does not show its effect sufficiently. On the other hand, since the residual polarization of the piezoelectric thin film tends to be reduced relatively quickly, a difference in polarization occurs between an element having a driving history and an element having no driving history, which in turn causes variations among the elements.

In order to solve such a problem, it can be considered to add a waveform having a polarity opposite to that of the drive waveform to erase the polarization and suppress the variation between the elements.

However, when the polarization is accompanied by the rotation of the domain, there is a further problem that it takes time to eliminate the polarization because the rotation of the domain is slow.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a driving device for an ink jet type recording head which can quickly suppress variations in displacement of piezoelectric elements.

[0010]

A drive device according to the present invention is a drive device for an ink jet recording head that contracts a pressure chamber to eject ink by applying a voltage to a piezoelectric body. A drive waveform showing an electric field strength exceeding the coercive electric field strength of the body is applied to the piezoelectric body,
At other times than the printing operation, a continuous pulse waveform having a polarity opposite to that of the driving waveform during the printing operation is applied to the piezoelectric body. As a result, it is possible to quickly eliminate the variation in polarization between the elements and obtain stable ejection characteristics.

In the above driving device, it is preferable that the waveform applied during a time other than the printing operation is a waveform showing an electric field strength equal to or higher than a coercive electric field strength of the piezoelectric body. This makes it possible to effectively eliminate variations in polarization.

In the above driving device, it is preferable that the waveform applied during a time other than the printing operation is a waveform that does not eject ink.

In the above driving device, it is preferable that the waveform applied at a time other than the printing operation is a waveform showing an electric field strength of an absolute value equal to or less than the maximum electric field strength shown by the driving waveform during the printing operation. . This makes it possible to suppress ink ejection.

In the above driving device, it is desirable that the frequency of the waveform applied during a time other than the printing operation is 1 [Hz] or more and 50 [kHz] or less. As a result, it is possible to quickly eliminate the variation in polarization.

In the above driving device, the application time of the waveform applied at a time other than the printing operation is 0.1 [se].
c] or more is desirable. This makes it possible to effectively eliminate the variation in polarization.

In the above driving device, the waveform applied at a time other than the printing operation is
It is desirable to apply the voltage before or after cleaning the head surface, at the time of exchanging the ink cartridge, or after the paper is discharged.

It is desirable that the driving device applies a voltage to the piezoelectric thin film. Since the thin film piezoelectric body is driven by a coercive electric field or more, the effect of the present invention is exerted highly.

The ink jet recording apparatus of the present invention is provided with the above driving device, and the ink jet recording head is driven by the driving device to perform recording.

The printer of the present invention is for recording by ejecting ink by the above-mentioned ink jet recording apparatus.

A method of driving an ink jet recording head of the present invention is a method of driving an ink jet recording head in which a pressure chamber is contracted by applying a voltage to a piezoelectric material to eject ink, and the piezoelectric material is used during a printing operation. A drive waveform showing an electric field strength exceeding the coercive electric field strength of is applied to the piezoelectric body, and a continuous pulse waveform having a polarity opposite to that of the drive waveform during the print operation is applied to the piezoelectric body during a printing operation other than the printing operation. To do.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Overall Structure of Inkjet Printer) FIG. 1 is a perspective view for explaining the structure of a printer in which the driving device of this embodiment is used. This printer has a main unit 2
The tray 3, the outlet 4, and the operation button 9 are provided in the. Further, inside the main body 2, an inkjet recording head 1, a supply mechanism 6, and a control circuit 8 are provided. The control circuit 8 comprises the drive device according to the invention.

The ink jet recording head 1 has a piezoelectric element described later. The inkjet recording head 1 responds to the ejection signal supplied from the control circuit 8,
Ink can be ejected from the nozzle.

The main body 2 is the housing of the printer, and the supply mechanism 6 is arranged at a position where the paper 5 can be supplied from the tray 3, and the ink jet recording head 1 is arranged so that the paper 5 can be printed. There is. The tray 3 is configured to be able to supply the paper 5 before printing to the supply mechanism 6, and the discharge port 4 is an outlet for discharging the paper 5 after printing.

The supply mechanism 6 includes a motor 600 and a roller 60.
1, 602, and other mechanical structures (not shown). The motor 600 is rotatable in response to the drive signal supplied from the control circuit 8. The mechanical structure is configured to be able to transmit the rotational force of the motor 600 to the rollers 601, 602. The rollers 601 and 602 are configured to rotate when the rotational force of the motor 600 is transmitted, and the rotation causes the sheet 5 placed on the tray 3 to be drawn and supplied by the head 1 in a printable manner. There is.

The control circuit 8 includes a CPU, RO (not shown).
M, a RAM, an interface circuit, etc. are provided, and a drive signal is supplied to the supply mechanism 6 or an ejection signal is supplied to the ink jet recording head 1 in accordance with print information supplied from a computer through a connector (not shown). You can do it. Further, the control circuit 8 can perform operation mode setting, reset processing and the like in response to an operation signal from the operation panel 9.

(Structure of Inkjet Recording Head) FIG. 2 is an explanatory view of the structure of an inkjet recording head driven by the driving device. As shown in the figure, the ink jet recording head 1 includes a nozzle plate 10, a pressure chamber substrate 20, and a vibration plate 30. This head constitutes an on-demand type piezo jet head.

The pressure chamber substrate 20 is a pressure chamber (cavity).
21, side wall (partition wall) 22, reservoir 23 and supply port 2
It is equipped with 4. The pressure chamber 21 serves as a space for storing ink or the like formed by etching a substrate made of silicon or the like. The side wall 22 is formed so as to partition the pressure chambers 21. The reservoir 23 is
It is a flow path for commonly filling the pressure chambers 21 with ink. The supply port 24 extends from the reservoir 23 to each pressure chamber 2.
1 is formed so that ink can be introduced.

The nozzle plate 10 is provided with nozzle holes 1 at positions corresponding to the respective pressure chambers 21 provided in the pressure chamber substrate 20.
1 is attached to one surface of the pressure chamber substrate 20. The pressure chamber substrate 20 to which the nozzle plate 10 is attached is further housed in the housing 25 to form the ink jet recording head 1.

The vibration plate 30 is attached to the other surface of the pressure chamber substrate 20. The vibration plate 30 is provided with a piezoelectric element (not shown). The vibrating plate 30 is provided with an ink tank port (not shown) so that ink stored in an ink tank (not shown) can be supplied into the pressure chamber substrate 20.

(Layer Structure) FIG. 3 is a sectional view for explaining a more specific structure of the ink jet recording head. This sectional view is an enlarged sectional view of one pressure chamber and a piezoelectric element. As shown in the figure, the diaphragm 30
Is formed by laminating an insulating film 31 and a lower electrode 32, and the piezoelectric element 40 has a piezoelectric thin film layer 4 on the lower electrode 32.
1 and the upper electrode 42 are laminated. The ink jet recording head 1 is composed of a piezoelectric element 40, a pressure chamber 21 and a nozzle hole 11 which are continuously arranged at a constant pitch. The pitch between the nozzles can be changed in design according to the printing accuracy. For example, 400 dpi
It is arranged to be (dot per inch).

The insulating film 31 is made of a material which is not conductive, for example, silicon dioxide (SiO ₂ ) and has a thickness of about 1 μm. The insulating film 31 is deformed by the deformation of the piezoelectric thin film layer, and the pressure inside the pressure chamber 21 is instantaneously changed. It is configured to be able to increase.

The lower electrode 32 is one electrode for applying a voltage to the piezoelectric thin film layer, and is made of a conductive material,
For example, platinum (Pt) or the like is formed to have a thickness of about 0.2 μm. The lower electrode 32 is formed in the same region as the insulating film 31 so as to function as an electrode common to the plurality of piezoelectric elements formed on the pressure chamber substrate 20. However,
It is also possible to form the piezoelectric thin film layer 41 in the same size, that is, in the same shape as the upper electrode.

The upper electrode 42 becomes the other electrode for applying a voltage to the piezoelectric thin film layer, and is made of a conductive material.
For example, platinum (Pt) or iridium (Ir) having a thickness of 0.
The thickness is about 1 μm.

The piezoelectric thin film layer 41 is, for example, a crystal of piezoelectric ceramics such as lead zirconate titanate (PZT) having a perovskite structure, and is formed on the diaphragm 30 in a predetermined shape. The thickness of the piezoelectric thin film layer 41 is 2 μm
The following is preferable, and the thickness is, for example, about 1 μm. The coercive electric field of this piezoelectric thin film is, for example, about 2 × 10 ⁶ [V / m].

(Printing Operation) The printing operation of the ink jet recording head 1 will be described. When the drive signal is output from the control circuit 8, the feeding mechanism 6 operates and the sheet 5 is conveyed by the head 1 to a printable position. No ejection signal is supplied from the control circuit 8 to the piezoelectric element 4.
When no voltage is applied to 0, the piezoelectric thin film layer 41 is not deformed. No pressure change occurs in the pressure chamber 21 provided with the piezoelectric element 40 to which the ejection signal is not supplied, and no ink droplet is ejected from the nozzle hole 11.

On the other hand, when a discharge signal is supplied from the control circuit 8 and a constant voltage is applied to the piezoelectric element 40, the piezoelectric thin film layer 41 is deformed. In the pressure chamber 21 in which the piezoelectric element 40 to which the ejection signal is supplied is provided, the vibration plate 3 is
0 flexes greatly. Therefore, the pressure in the pressure chamber 21 is instantaneously increased, and ink droplets are ejected from the nozzle hole 11.
Arbitrary characters and figures can be printed by individually supplying the ejection signals to the piezoelectric element at the position where printing is desired in the head.

(Drive Device) FIG. 4 is a circuit diagram of the drive device according to the present embodiment. As shown in the drawing, the piezoelectric thin film element 40 provided for each nozzle (each pressure chamber) of the inkjet head is expressed as a capacitor on an electric circuit, and one electrode of each capacitor is made common and the common electrode Is grounded.

The driving device drives from the waveform generating circuit 81 and the waveform generating circuit 81 that generate a driving waveform for driving the piezoelectric thin film element 40 and a waveform for eliminating polarization remaining in the piezoelectric thin film element 40. Waveforms for each piezoelectric thin film element 40
A nozzle selection circuit 82 for selectively transmitting to the nozzle.

(Drive Signal) FIG. 5 is a waveform diagram showing an example of a voltage waveform applied to the piezoelectric element by the drive device according to the present embodiment. Particularly, FIG. 5A shows a waveform at the time of ink ejection, and FIG. 5B shows a waveform for polarization elimination.

The waveform at the time of ink ejection shown in FIG.
Here, the potential rise period a1, the potential maintenance period a2, and the potential fall period a3 are provided. Potential rising period a1 and potential maintaining period a2
Then, by applying a voltage to the piezoelectric body to contract the pressure chamber, ink is ejected from the nozzle. In the potential lowering period, by expanding the pressure chamber, the ink that has not been ejected is drawn into the nozzle and the ink is newly drawn from the ink tank (not shown). The maximum voltage V ₁ in the waveform during ink ejection is applied during the potential maintenance period a2 and is, for example, 20 to 30 [V]. In this case, assuming that the thickness of the piezoelectric thin film is 1 μm, the electric field strength of the piezoelectric in the potential maintaining period a2 is 2 × 10 ^{7 to} 3 × 10 ⁷ [V /
m], and the coercive electric field 2 × 1 of the piezoelectric body in the present embodiment.
0 ⁶ [V / m] which is about 10 times higher of.

The waveform for polarization elimination shown in FIG. 5B is a pulse waveform having a polarity opposite to that of the drive waveform. Potential with the maximum absolute value in the waveform for polarization elimination -V
The electric field strength (absolute value) of the piezoelectric thin film when ₂ is applied is preferably equal to or higher than the coercive electric field. Then, it is desirable that the electric field strength is equal to or less than the maximum electric field strength in the drive waveform at the time of ink ejection. Further, it is desirable that the waveform for erasing polarization is a waveform that does not eject ink. Whether or not the ink is ejected is not determined only by the electric field strength at the maximum potential −V _2, but also depends on the slope of the waveform. The electric field strength of the piezoelectric film when the maximum potential −V ₂ is applied is −5 × 10 5 in a preferable example.
⁶ [V / m] to -1 × 10 ⁷ [V / m].

The polarization erasing waveform shown in FIG. 5B is a waveform in which only a voltage having a polarity opposite to that of the drive waveform is applied, but the waveform is not limited to this. For example, a voltage having the same polarity as the drive waveform is applied. After that, a waveform having a polarity opposite to that of the drive waveform and having a field strength equal to or higher than the coercive electric field may be applied.

By continuously applying the waveform for polarization elimination as described above at times other than the printing operation, even a piezoelectric thin film whose polarization is accompanied by domain rotation,
Polarization can be erased quickly. Especially 1 [H
It is preferable to continuously apply at a frequency of z] or more and 50 [kHz] or less, and more preferably 50 [Hz] or more and 25 [kHz] or less. The application time is 0.1 [sec]
It is preferably 60 [min] or less and more preferably 1 [sec] or more and 30 [min] or less.

The above-mentioned waveform is preferably applied at a time other than when the ink is ejected from the ink jet head, particularly before the ink ejection, such as immediately after the power supply to the printer is turned on, before and after the cleaning of the head surface, when the ink cartridge is replaced, and after the paper is ejected.

(Example) Thickness 1 μm, coercive electric field strength 2 × 1
0 ⁶ [V / m], displacement amount when applying 30 [V] is 44
An ink jet type recording head provided with a piezoelectric thin film of 0 nm has a driving waveform as shown in FIG. 5A and has a maximum potential V ₁ = 30 [V] and a frequency of 20.5 [kHz] 30.
After continuously driving for 30 minutes, the displacement amount at the time of applying 30 [V] was measured and was 402 nm.

For this ink jet recording head,
A waveform for polarization elimination as shown in FIG. 5B has a maximum potential of −V ₂ = −10 [V] and a frequency of 20.5 [kHz].
After 30 minutes of continuous application, the displacement amount when 30 [V] was applied was measured, and it was recovered to 435 nm.

[0048]

According to the ink jet recording head driving device and the driving method of the present invention, it is possible to provide the ink jet recording head driving device which can quickly suppress the variation in the displacement of the piezoelectric element.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a structure of a printer in which a driving device according to an exemplary embodiment is used.

FIG. 2 is an explanatory diagram of a structure of an ink jet recording head driven by the driving device.

FIG. 3 is a cross-sectional view illustrating a more specific structure of the inkjet recording head.

FIG. 4 is a circuit diagram of the driving device according to the present embodiment.

FIG. 5 is a waveform diagram showing an example of a voltage waveform applied to the piezoelectric element by the driving device according to the present embodiment.

FIG. 6 is a strain (S) with respect to the electric field strength (E) of the piezoelectric film.
It is a graph which shows the characteristic of.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Nozzle plate, 20 ... Pressure chamber substrate, 30 ... Vibration plate, 31 ... Insulating film, 32 ... Lower electrode, 40 ... Piezoelectric element, 41 ... Piezoelectric thin film layer, 42 ... Upper electrode, 2
1 ... Pressure chamber

Claims (11)

[Claims] 1. A drive device for an ink jet recording head that contracts a pressure chamber by applying a voltage to a piezoelectric body to eject ink, wherein an electric field strength exceeding a coercive electric field strength of the piezoelectric body is generated during a printing operation. A drive device which applies the drive waveform shown to the piezoelectric body, and applies a continuous pulse waveform having a polarity opposite to that of the drive waveform during the printing operation to the piezoelectric body, except during the printing operation. 2. The drive device according to claim 1, wherein the waveform applied during a time other than the printing operation is a waveform indicating an electric field strength equal to or higher than a coercive electric field strength of the piezoelectric body. 3. The drive device according to claim 1, wherein the waveform applied during a time other than the printing operation is a waveform that does not eject ink. 4. The waveform according to claim 1 or 2, wherein the waveform applied during a time other than the printing operation indicates an electric field strength of an absolute value equal to or less than a maximum electric field strength indicated by a drive waveform during the printing operation. Drive, which is corrugated. 5. The driving device according to claim 1, wherein a frequency of the waveform applied during a time other than the printing operation is 1 [Hz] or more and 50 [kHz] or less. 6. The drive device according to claim 1, wherein an application time of the waveform applied during a time other than the printing operation is 0.1 [sec] or more. 7. The waveform according to any one of claims 1 to 6, wherein the waveform applied at a time other than the printing operation is immediately after the printer power is turned on, before and after cleaning the head surface, when the ink cartridge is replaced, and when the paper is discharged. Drive device to apply at some later time. 8. The drive device according to claim 1, wherein a voltage is applied to the piezoelectric thin film. 9. An ink jet recording apparatus comprising the drive device according to claim 1, wherein the drive device drives an ink jet recording head to perform recording. 10. A printer for performing recording by ejecting ink by the ink jet recording apparatus according to claim 9. 11. A method for driving an ink jet recording head, wherein a pressure chamber is contracted and ink is ejected by applying a voltage to a piezoelectric body, the electric field strength exceeding a coercive electric field strength of the piezoelectric body during a printing operation. A driving method in which the driving waveform shown in the table is applied to the piezoelectric body, and a continuous pulse waveform having a polarity opposite to that of the driving waveform at the time of the printing operation is applied to the piezoelectric body at the time other than the printing operation.