JP4580201B2 - Piezoelectric element regeneration method and liquid ejection device - Google Patents

Description

  The present invention relates to a reproducing method for regenerating a piezoelectric element having a lowered displacement performance and restoring the original displacement performance, and a liquid ejection apparatus having a function of regenerating a piezoelectric element by this reproducing method. .

In recent years, recording apparatuses using an inkjet recording method, such as inkjet printers and inkjet plotters, are not only small printers for consumers, but also, for example, formation of electronic circuits, manufacture of color filters for liquid crystal displays, organic EL display It is also widely used for industrial applications such as manufacturing.
In an ink jet recording system recording apparatus, an ink jet head is moved in a main scanning direction, and a recording paper, a substrate, or the like is moved in a sub scanning direction intersecting the main scanning direction, and the ink jet head is moved according to recording information. Recording is performed by driving and ejecting ink droplets intermittently from the nozzle openings of the inkjet head. For example, in the case of a small printer, characters and images are recorded on the surface of a recording paper or the like, and in the case of an industrial recording apparatus, an electronic circuit, a color filter of a liquid crystal display, a light emitting cell of an organic EL display, etc. It is formed.

  In order to eject ink droplets from the opening of a nozzle, the volume of a pressurizing chamber that communicates with the nozzle and is filled with ink is increased or decreased at a predetermined timing. The surface meniscus (the free surface of the ink exposed at the nozzle) is vibrated to generate ink droplets, and is ejected from the nozzle openings by the kinetic energy of the ink when the ink droplets are generated. The means for increasing / decreasing the volume of the pressurizing chamber includes a piezoelectric element and a diaphragm, and a piezoelectric actuator for increasing / decreasing the volume of the pressurizing chamber when the piezoelectric element is deformed and the diaphragm is bent. Generally, a heater or the like that reduces the volume by generating bubbles in the pressurizing chamber by heating and vaporizing the ink is generally used. However, in industrial applications, not only water-based inks but also inks using organic solvents are used. Therefore, there are few restrictions on the types of inks that can be ejected as the above means, and the piezoelectrics have excellent durability. The use of actuators has attracted attention.

In an inkjet head using a piezoelectric actuator, in order to improve the displacement performance of the piezoelectric element and improve the ink ejection characteristics, the piezoelectric element is generally polarized. However, the polarization of the piezoelectric element is gradually lost over time, and the displacement performance tends to gradually decrease.
Therefore, in order to maintain the displacement performance of the piezoelectric element so that the ink can be ejected with desired ejection characteristics even after aged use, the piezoelectric element is not less than the ambient temperature at any time when the inkjet head is used. In addition, a method of repolarization by applying a voltage having the same polarity as the drive voltage waveform applied when ejecting ink droplets while heating below the Curie temperature has been proposed (see Patent Document 1).

  However, when the piezoelectric element is driven by performing control such as charge control or injection energy control, an internal electric field is formed in a direction opposite to the direction of the applied electric field, so that the piezoelectric element works effectively in the domain. The electric field decreases. Further, even in a low electric field region (electric field is zero or weak reverse electric field), a reverse electric field more than necessary acts on the domain. Therefore, simply applying a voltage having the same polarity as the drive voltage waveform increases the contribution of the 90 ° domain inversion to the displacement of the piezoelectric element, and in some cases also causes a 180 ° domain inversion that is unrelated to the displacement. As a result, there is a problem in that loss energy during one cycle increases and sufficient displacement performance cannot be expected.

Applying a voltage to the piezoelectric element that has a polarity opposite to that of the drive voltage waveform and an absolute value of the voltage value equal to or greater than the coercive electric field voltage of the piezoelectric element at any time during use, A regenerating method for recovering the displacement performance of the piezoelectric element by solving the problem has been proposed (see Patent Document 2).
According to this reproducing method, as described above, the internal electric field of the piezoelectric element can be eliminated at an arbitrary time point during use. Subsequently, for example, a driving voltage waveform is applied to drive the piezoelectric element. In some cases, the displacement performance can be sufficiently recovered by repolarizing the piezoelectric element more efficiently than in the case where the reproduction process is performed without eliminating the internal electric field.

However, in a plurality of piezoelectric elements arranged on the inkjet head, there is a possibility that variations in the state of elimination of internal polarization may occur due to the difference in driving history. Therefore, a voltage having the same polarity as the drive voltage waveform is first applied to the plurality of piezoelectric elements, and subsequently, the polarity is opposite to that of the drive voltage waveform, and the absolute value of the voltage value is equal to the coercive electric field of the piezoelectric element. It has also been proposed to eliminate the internal electric field by applying a voltage equal to or higher than the voltage value (see, for example, Patent Document 3).
JP-A-9-141866 (Claim 1, columns 0006 to 0007, column 0028, FIG. 5) JP-A-6-342946 (Claim 1, columns 0006 to 0007, columns 0009 to 0010, columns 0015 to 0021) JP 2002-355967 (Claim 1, Claim 2, Columns 0007 to 0011, Columns 0036 to 0041)

According to the reproduction method described in Patent Document 3, a plurality of piezoelectric elements arranged on an ink-jet head are uniformly eliminated regardless of their driving history, and then the driving is continued. When a voltage waveform is applied, the piezoelectric element can be repolarized more efficiently and uniformly, and the displacement performance can be recovered sufficiently and uniformly.
However, during reproduction, a voltage having the same polarity as the drive voltage waveform is applied first, and then a reverse polarity voltage is applied. Since it is necessary to apply them simultaneously, the value of the current flowing through the drive circuit of the ink jet head increases with the charging and discharging of the piezoelectric element. Therefore, in particular, there is a problem that as the number of piezoelectric elements mounted on one inkjet head increases, the burden on the drive circuit increases.

  In addition, the piezoelectric element suddenly changes from a deformed state in which a voltage having the same polarity as the driving voltage waveform is applied to a deformed state in the opposite direction to the above in which a charge of reverse polarity is applied. Therefore, the burden on the piezoelectric element is increased. In addition, the piezoelectric element immediately after such rapid deformation may vibrate due to inertial force, which may cause unnecessary ink droplet ejection, thereby increasing the ink consumption.

  The object of the present invention is to reduce the burden on the drive circuit and the piezoelectric element and prevent the ejection of unnecessary ink droplets, while the displacement performance of a plurality of piezoelectric elements arranged on an inkjet head, for example, It is an object of the present invention to provide a reproducing method that can be recovered uniformly and sufficiently regardless of the difference between the above and a liquid ejecting apparatus having a function of regenerating a piezoelectric element by this reproducing method.

According to the first aspect of the present invention, after the voltage V ₁ having the same polarity as the drive voltage waveform is applied to the piezoelectric element, the polarity is opposite to that of the voltage V ₁ , and the absolute value of the voltage value is the coercive electric field of the piezoelectric element. a method of reproducing a piezoelectric element including a step of applying a voltage V ₃ is equal to or higher than the voltage value of the voltage applied to the piezoelectric element during the step of changing from voltages V ₁ to the voltage V _3, the piezoelectric element, A method for regenerating a piezoelectric element, wherein a voltage V ₂ having the same polarity as the voltage V ₃ and an absolute value of the voltage value V ₂ <V ₃ is applied for a predetermined time.

According to a second aspect of the invention, the voltage V _2, a method for regenerating a piezoelectric element according to claim 1, wherein the set to a voltage value which the polarization direction of the re-inversion of the piezoelectric element does not occur.
The invention described in claim 3
(1) a pressurized chamber filled with liquid;
(2) a nozzle communicating with the pressurizing chamber;
(3) a piezoelectric actuator that includes a piezoelectric element and flexes it by deformation of the piezoelectric element to increase or decrease the volume of the pressurizing chamber, thereby discharging the liquid in the pressurizing chamber as droplets through the nozzle;
The method for regenerating a piezoelectric element according to claim 1, wherein a piezoelectric element incorporated in the piezoelectric actuator of a liquid ejection apparatus comprising:

Fourth aspect of the present invention, the time t ₁ required to change the voltage applied to the piezoelectric element from the voltages V ₁ to the voltage V _2, the sum T _{1 =} t ₁ and the time t ₂ for applying the voltage V ₂ + T ₂ , the ratio T ₁ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator in a state where the pressurized chamber is filled with the liquid is:
0.15 ≦ T ₁ / T ₀ ≦ 0.3
The method for regenerating a piezoelectric element according to claim 3, wherein the piezoelectric element is set in a range satisfying the above.

According to a fifth aspect of the invention, the time _{t 3} when required to change the voltage applied to the piezoelectric element from the voltage _{V 2} to the voltage _{V 3,} the sum _T 2 _{= T} 1 + _{t 3} between the time _{T 1,} the piezoelectric The ratio T ₂ / T ₀ to the natural vibration period T ₀ of the actuator is
0.2 ≦ T ₂ / T ₀ ≦ 0.6
The method for regenerating a piezoelectric element according to claim 4, wherein the piezoelectric element is set in a range satisfying the above.

According to the sixth aspect of the present invention, the ratio T ₃ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator in the state where the pressure chamber ₃ is filled with the liquid is set as the time T ₃ for applying the voltage V ₃ .
0.7 ≦ T ₃ / T ₀
The method for regenerating a piezoelectric element according to claim 3, wherein the piezoelectric element is set in a range satisfying the above.
The invention of claim 7, wherein the time constant voltage V _3, after the application, with the same polarity or opposite polarity to the voltage V _1, and the absolute value of constant voltage V ₄ is V _{4 <V 5} of the voltage value time, applied, and then a method for regenerating a piezoelectric element according to claim 3, wherein applying a voltage V ₅ is the same polarity as the voltage V _1.

The invention according to claim 8 is the method for regenerating a piezoelectric element according to claim 7, wherein the voltage V ₄ is set to a voltage value that has the same polarity as the voltage V ₁ and does not cause re-inversion of the polarization direction of the piezoelectric element. is there.
The invention of claim 9, wherein the absolute value of the voltage value of the voltage V _5, a method for regenerating a piezoelectric element according to claim 7 wherein the set voltage V _{5 =} voltage V _1.
The invention of claim 10 wherein is provided with a time _{t 4} when required the voltage applied to the piezoelectric element to change from the voltage _{V 3} to the voltage _{V 4,} the sum _T 4 = _{t 4} and the time _{t 5} for applying a voltage _{V 4} + T ₅ is a ratio T ₄ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator in a state where the pressurized chamber is filled with liquid,
0.15 ≦ T ₄ / T ₀ ≦ 0.3
The method for regenerating a piezoelectric element according to claim 7, wherein the piezoelectric element is set in a range satisfying the above.

According to the eleventh aspect of the present invention, the sum T ₅ = T ₄ + t ₆ of the time t ₆ required to change the voltage applied to the piezoelectric element from the voltage V ₄ to the voltage V ₅ and the time T ₄ is expressed as piezoelectric The ratio T ₅ / T ₀ to the natural vibration period T ₀ of the actuator is
0.2 ≦ T ₂ / T ₀ ≦ 0.6
The method for regenerating a piezoelectric element according to claim 10, wherein the piezoelectric element is set in a range satisfying the above.

According to a twelfth aspect of the present invention, the liquid ejecting apparatus is a piezoelectric ink jet head incorporated in a recording apparatus of an ink jet recording method, immediately after turning on the recording apparatus, at the time of nozzle cleaning, at the time of discharging the recording paper, and immediately before the start of recording. The method for regenerating a piezoelectric element according to claim 3, wherein a regeneration process for the piezoelectric element is performed.
The invention according to claim 13
(1) a pressurized chamber filled with liquid;
(2) a nozzle communicating with the pressurizing chamber;
(3) a piezoelectric actuator that includes a piezoelectric element and flexes it by deformation of the piezoelectric element to increase or decrease the volume of the pressurizing chamber, thereby discharging the liquid in the pressurizing chamber as droplets through the nozzle;
A driving power source for applying a driving voltage to the piezoelectric element, and a control means for controlling the driving power source to apply the driving voltage to the piezoelectric element. A liquid ejecting apparatus having an element regeneration function of controlling a driving power source so as to cause the element to regenerate the piezoelectric element by performing the piezoelectric element regeneration method according to claim 1. .

  According to a fourteenth aspect of the present invention, there is provided a piezoelectric ink jet head incorporated in an ink jet recording type recording apparatus, wherein the control means is immediately after turning on the recording apparatus, at the time of nozzle cleaning, at the time of discharging the recording paper, and immediately before the start of recording. The liquid ejection apparatus according to claim 13, wherein the piezoelectric element is regenerated.

According to the first aspect of the present invention, in the middle of changing the voltage applied to the piezoelectric element from the voltage V ₁ to the voltage V ₃ , the piezoelectric element has the same polarity as the voltage V ₃ and the voltage value absolute value a predetermined time the voltage V ₂ is V _{2 <V 3} is, since the applied, as in the prior art, after the application of the voltage V _1, as compared with the case of applying immediately a voltage V _3, V ₁ The potential difference between −V ₂ and V ₂ −V ₃ can be reduced. Therefore, it is possible to reduce the load on the drive circuit by reducing the value of the current flowing through the drive circuit of the inkjet head as the piezoelectric element is charged and discharged. Moreover, since the rapid deformation of the piezoelectric element can be alleviated, the burden on the piezoelectric element can be reduced. Furthermore, since the deformation speed of the piezoelectric element can be reduced, the piezoelectric element immediately after the deformation vibrates due to inertial force, which causes unnecessary ink droplet ejection and increases the ink consumption. Can also be suppressed.

Moreover, according to the first aspect of the invention, as in the method described in Patent Document 3, first, the voltage V ₁ having the same polarity as the drive voltage waveform is applied to the piezoelectric element, and then, as described above. through the voltage V _2, a plurality in the opposite polarity and, arranged from the absolute value of the voltage value is applied a voltage V ₃ is equal to or higher than the voltage value of the coercive field of the piezoelectric element, for example, on an ink jet head This piezoelectric element can be repolarized more efficiently and evenly when the internal electric field is eliminated and the drive voltage waveform is subsequently applied, regardless of the difference in drive history. The displacement performance can be recovered sufficiently and uniformly.

According to the second aspect of the present invention, the voltage V ₂ has the same polarity as the voltage V ₃ as described above, that is, a voltage that is opposite to the voltage V ₁ and does not cause re-inversion of the polarization direction of the piezoelectric element. set to a value, is applied while preventing the polarization direction of the re-inversion, time constant state of being deformed into a state opposite to the direction of applying the voltages V _1, by maintaining, in the piezoelectric element, the voltages V ₁ and to impart mechanical stress of the deformed allowed state opposite direction, generated in the piezoelectric element in a state of being deformed by applying a voltage V _1, the orientation of the domain that occurs in the direction of lowering the residual polarization, It can be returned to the original direction. Therefore, the internal electric field of the piezoelectric element can be eliminated more effectively.

According to the invention described in claim 3, the piezoelectric element incorporated in the piezoelectric actuator of the liquid ejection apparatus such as an ink jet head can be reproduced by the reproducing method of the invention described in claim 1.
In the above liquid ejecting apparatus, the piezoelectric element incorporated in the piezoelectric actuator and applied with the voltage V ₁ is subjected to both tensile stress generated in the plane direction due to the piezoelectric effect and compressive stress due to mechanical deformation. Is in a state. When the voltage applied to the piezoelectric element is gradually changed from the voltage V ₁ toward the voltage V ₂ , the piezoelectric actuator including the piezoelectric element is accompanied by a volume change of the pressurizing chamber filled with the liquid. Free vibration is started at the natural vibration period T ₀ . With this free vibration, the mechanically acting stress on the piezoelectric element is attenuated while acting periodically on the compression side and then on the tension side.

Here, as described in claim 4, the sum of the voltage applied to the piezoelectric element from the voltages V ₁ and the time t ₁ required to change to a voltage V _2, and the time t ₂ for applying the voltage V ₂ T the ₁ = _{t 1} + _{t 2,} the ratio _T 1 / _{T 0} for the natural vibration period _{T 0,}
0.15 ≦ T ₁ / T ₀ ≦ 0.3
Is set to a range that satisfies the above, the applied voltage can be changed to the voltage V ₂ within a time period during which the stress acting on the piezoelectric element is still on the compression side. Then, it is possible a certain time the voltage V ₂ to the piezoelectric element, while applying, to continue to act a compressive stress to the piezoelectric element. Therefore, the internal electric field of the piezoelectric element can be eliminated more effectively.

According to the invention of claim 5, wherein the time _{t 3} when required to change the voltage applied to the piezoelectric element from the voltage _{V 2} to the voltage _{V 3,} the sum _T 2 _{= T} 1 + _{t 3} between the time _{T 1} , the ratio _T 2 / _{T 0} for the natural vibration period _{T 0} is,
0.2 ≦ T ₂ / T ₀ ≦ 0.6
Therefore, the vibration of the piezoelectric element accompanying the change of the voltage and the vibration of the piezoelectric actuator are caused by the change of the voltage from the voltage V ₁ to the voltage V _3. By canceling out vibration due to the deformation of the element, it is possible to further suppress the ejection of unnecessary ink droplets and the accompanying increase in ink consumption.

According to the sixth aspect of the present invention, the time T ₃ for applying the voltage V ₃ is determined by the ratio T ₃ / T ₀ to the natural vibration period T ₀ .
0.7 ≦ T ₃ / T ₀
Due to the set in a range satisfying the, the piezoelectric element of the piezoelectric actuator after the time T _3, can be driven by applying a driving voltage waveform of the free oscillation phase opposite to previously mentioned, piezoelectric By preventing the resonance of the actuator, it is possible to further suppress unnecessary ink droplet ejection and the accompanying increase in ink consumption. In addition, when the internal electric field of the piezoelectric element is more reliably eliminated and then a drive voltage waveform is subsequently applied, the displacement performance can be sufficiently restored by repolarizing more efficiently.

According to the seventh aspect of the invention, after the voltage V ₃ is applied for a certain time to eliminate the internal electric field of the piezoelectric element, the voltage applied to the piezoelectric element is temporarily changed to the voltage V ₅ via the voltage V _4. As described above, the piezoelectric element can be repolarized more efficiently and its displacement performance can be sufficiently restored while reducing the burden on the drive circuit and the piezoelectric element as in the case of the first aspect. Can do. In addition, since the deformation speed of the piezoelectric element can be reduced, the piezoelectric element immediately after deformation vibrates due to the inertial force, and as a result, unnecessary ink droplet ejection occurs, resulting in an increase in ink consumption. Can also be suppressed.

According to the eighth aspect of the present invention, the voltage V ₄ is set to a voltage value that has the same polarity as the voltage V ₁ , that is, a polarity that is opposite to the voltage V ₃ and that does not cause re-inversion of the polarization direction of the piezoelectric element. while preventing the polarization direction of the re-inversion, time constant state of deforming the voltage V ₃ to the applied status and reverse, by maintaining, in the piezoelectric element, it is deformed by applying the voltage V ₃ Applying mechanical stress in the opposite direction to the state, and applying the voltage V ₃ to deform the piezoelectric element, the domain orientation generated in the direction of reducing the remanent polarization is returned to the original direction. be able to. Therefore, the internal electric field of the piezoelectric element can be eliminated more effectively.

State voltage V ₃ piezoelectric element is applied, which as if the voltages V ₁ is applied, the tensile stress occurring in the planar direction by the piezoelectric effect, both compressive stress due to mechanical deformation acting When the voltage applied to the piezoelectric element is gradually changed from the voltage V ₃ toward the voltage V ₄ , the piezoelectric actuator starts free vibration at the natural vibration period T ₀ . With this free vibration, the mechanically acting stress on the piezoelectric element is attenuated while acting periodically on the compression side and then on the tension side.

Therefore, as described in claim 9, and the time t ₄ when required the voltage applied to the piezoelectric element to change from the voltage V ₃ to the voltage V _4, the sum T ₄ and the time t ₅ for applying a voltage V ₄ = T ₄ + t ₅ , the ratio T ₄ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator is
0.15 ≦ T ₄ / T ₀ ≦ 0.3
Is set in a range that satisfies the above, as in the case of claim 4 above, the applied voltage can be changed to the voltage V ₂ within the time when the stress acting on the piezoelectric element is still on the compression side. Then, a certain period of time the voltage V ₂ to the piezoelectric element, while the application of, since it is possible to continue to act a compressive stress to the piezoelectric element, the internal electric field of the piezoelectric element, more effectively, can be eliminated.

According to the tenth aspect of the present invention, the sum T ₅ = T ₄ + t ₆ of the time t ₆ required to change the voltage applied to the piezoelectric element from the voltage V ₄ to the voltage V ₅ and the time T ₄ is obtained. , the ratio _T 5 / _{T 0} for the natural vibration period _{T 0} is,
0.2 ≦ T ₂ / T ₀ ≦ 0.6
Therefore, the vibration of the piezoelectric element accompanying the change of the voltage and the vibration of the piezoelectric actuator are caused by the change of the voltage from the voltage V ₁ to the voltage V _3. By canceling out vibration due to the deformation of the element, it is possible to further suppress the ejection of unnecessary ink droplets and the accompanying increase in ink consumption.

  When the liquid ejecting apparatus is a piezoelectric ink jet head incorporated in an ink jet recording type recording apparatus, the above-described piezoelectric element regeneration processing is performed immediately after the recording apparatus is turned on. If it is performed during the waiting time required for recording, such as at the time of cleaning, when the recording paper is discharged, and immediately before the start of recording, the operation rate of the piezoelectric element is reduced without reducing the operating rate of the piezoelectric inkjet head. The displacement performance can always be maintained in a good state. Therefore, for example, in a recording apparatus for industrial use, an electronic circuit, a color filter for a liquid crystal display, a light emitting cell for an organic EL display, etc., can be accurately formed in a desired shape without reducing productivity. it can. In addition, in a small printer for consumer use, it is possible to continue recording characters and images without increasing the standby time and reducing the operation speed other than the normal standby time.

Hereinafter, a case where the present invention is applied to an inkjet head incorporated in a recording apparatus such as an inkjet printer or an inkjet plotter will be described as an example.
<Inkjet head>
FIG. 1 is an enlarged cross-sectional view of a part of the ink jet head of this example. 2A to 2C are cross-sectional views further enlarging the nozzle portion of the ink jet head, showing the process of carrying out the driving method of the present invention using the ink jet head of the above example.

  Referring to FIG. 1, the ink jet head of this example has a flow path member in which a plurality of pressurizing chambers 11 for filling ink are arranged at a predetermined dot pitch on the upper surface side in the drawing. As a substrate 1, a piezoelectric actuator 2 laminated on the upper surface of the substrate 1 so as to close the pressurizing chamber 11, a drive circuit 3 for operating the piezoelectric actuator 2, and a piezoelectric circuit by controlling the drive circuit 3. And a control means 4 for operating the actuator 2.

In addition, the piezoelectric actuator 2 is laminated on the substrate 1 in this order, each having a vibration plate 21 having a size covering the plurality of pressurizing chambers 11, a common electrode 22, and a plate-like piezoelectric ceramic layer 23. (Piezoelectric element) and a plurality of individual electrodes 24 formed separately corresponding to the respective pressurizing chambers 11.
Each pressurizing chamber 11 communicates with a nozzle 12 for ejecting ink droplets that reaches the lower surface of the substrate 1 on the side opposite to the side on which the piezoelectric actuator 2 is laminated, in the drawing. Although not shown, each pressurizing chamber 11 is connected to a common supply path for supplying ink from an ink replenishing section of the ink jet printer through a supply port.

  And the nozzle which discharges an ink drop among the common electrode 22 and the several individual electrode 24 in the state which filled each pressurization chamber 11 from the ink supply part via the common supply path and the supply port. When a drive voltage having a predetermined pulse waveform is applied from the drive circuit 3 to the individual electrodes 24 corresponding to 12, the region of the piezoelectric ceramic layer 23 to which the drive voltage is applied is deformed accordingly. Thus, the same region of the piezoelectric actuator 2 operates, and the volume of the pressurizing chamber 11 is increased or decreased at a predetermined timing. Along with this, the meniscus of the ink surface formed in the nozzle 12 vibrates, and ink droplets are ejected from the nozzle 12 to perform recording.

  Of the above, the substrate 1 is formed using a metal plate, a ceramic plate, or the like. For example, the metal substrate 1 is manufactured by forming a pressurizing chamber 11 and a nozzle 12 by etching a plate material formed to have a predetermined thickness by a rolling method or the like. Examples of the metal material forming the substrate 1 include an Fe—Cr alloy, an Fe—Ni alloy, a WC—TiC meter alloy, and the like. Ni-based alloys are preferred.

  In the piezoelectric actuator 2, the piezoelectric ceramic layer 23 is formed, for example, by firing a piezoelectric green sheet or polishing a sintered body of a piezoelectric material into a thin plate shape. As the piezoelectric ceramic constituting the piezoelectric ceramic layer 23, for example, lead zirconate titanate (PZT) or one or more oxides of lanthanum, barium, niobium, zinc, nickel, manganese, etc. are added to the PZT. Examples thereof include PZT-based piezoelectric materials such as those added, for example, PLZT. In addition, lead magnesium niobate (PMN), lead nickel niobate (PNN), lead zinc niobate, lead manganese niobate, lead antimony stannate, lead titanate, barium titanate, etc. You can also. The piezoelectric green sheet contains a compound that becomes one of the above piezoelectric materials by firing.

The diaphragm 21 can be formed of a single metal such as molybdenum, tungsten, tantalum, titanium, platinum, iron, nickel, an alloy of these metals, or a metal material such as stainless steel. Preferably, the piezoelectric ceramic layer 23 described above is formed of the same piezoelectric ceramic.
Further, the diaphragm 21, the common electrode 22, and the piezoelectric ceramic layer 23 include a ceramic green sheet that is the basis of the diaphragm 21 and the piezoelectric ceramic layer 23, and a layer of conductive paste that is the basis of the common electrode. It is preferable that the laminate is formed by sintering at the same time. Thereby, the warp deformation of the piezoelectric ceramic layer 23 can be corrected.

  Examples of the metal forming the common electrode 22 include simple metals such as Ag, Pd, Pt, Rh, Au, Ni, and alloys containing these metals, and Ag—Pd alloys are particularly preferable. As described above, the common electrode 22 is formed by sintering a conductive paste containing the above metal or alloy powder together with the ceramic green sheet that is the basis of the diaphragm 21 and the piezoelectric ceramic layer 23. The thickness is preferably 0.5 to 8 μm, more preferably 1 to 3 μm as a range that does not hinder the deformation of the piezoelectric actuator 2 while ensuring sufficient conductivity.

  Examples of the metal forming the individual electrode 24 include the same metals and alloys as described above, and Au is preferable in consideration of electrical resistance, corrosion resistance, and the like. The thickness of the individual electrode is preferably 0.5 to 5 μm, and more preferably 0.5 to 2 μm. The individual electrode 24 is formed, for example, by printing a conductive paste containing a metal powder having excellent conductivity such as Au on the surface of the piezoelectric ceramic layer 23 in a predetermined shape by a printing method such as a screen printing method. Or a thin plate made of the above metal is integrated on the surface of the piezoelectric ceramic layer 23 by using, for example, an adhesive, and then formed into a predetermined shape by etching using a photolithographic method, or Using a photolithographic method or the like on the surface of the piezoelectric ceramic layer 23, a plating resist layer having an opening of a predetermined shape is formed. After plating the metal, the resist layer is removed to form a predetermined shape. Can be.

  The total thickness of the piezoelectric actuator 2 is 100 μm or less, preferably 80 μm or less, more preferably 65 μm or less, particularly 50 μm or less, considering that the piezoelectric actuator 2 is well deformed when a drive voltage is applied from the drive circuit 3. good. In consideration of giving sufficient mechanical strength and preventing breakage during handling and operation, the thickness should be 3 μm or more, preferably 5 μm or more, more preferably 20 μm or more.

  The substrate 1 and the piezoelectric actuator 2 can be integrated by bonding through, for example, an adhesive layer (not shown). Examples of the adhesive include various conventionally known adhesives. In consideration of improving the heat resistance of the ink jet head and the resistance to ink, an epoxy resin system having a thermosetting temperature of 100 to 250 ° C., phenol It is preferable to use a thermosetting adhesive such as a resin or polyphenylene ether resin. An ink jet head is manufactured by laminating the substrate 1 and the piezoelectric actuator 2 through these adhesive layers and heating them to the thermosetting temperature of the adhesive.

Of the piezoelectric actuator 2 of the ink jet head, the common electrode 22 and the individual electrode 23 are each connected to the drive circuit 3, and the drive circuit 3 is connected to the control means 4.
At the time of recording, for example, the control unit 4 controls the driving circuit 3 based on recording information such as characters and images transmitted from the host computer, and the driving circuit 3 controls the common electrode 22 and any individual electrode. 23, a drive voltage having a predetermined pulse waveform is applied. Then, the region of the piezoelectric actuator 2 to which the driving voltage is applied operates, and ink droplets are ejected from the nozzle 12 communicating with the pressurizing chamber 11 corresponding to the region, and recording is performed.

  Specifically, the piezoelectric actuator 2 is operated in a state where the ink surface meniscus is formed in the nozzle 12 to increase or decrease the volume of the pressurizing chamber 11 at a predetermined timing. If it does so, the ink in a supply port, the pressurization room 11, and the nozzle 12 will vibrate, and a meniscus will vibrate in connection with it. As a result, the meniscus is pushed out to the outside in a columnar shape as a result of the vibration speed going outward from the nozzle 12. This extruded ink is called an ink column because of its shape.

  The speed of vibration eventually goes inward of the nozzle 12, but the ink column continues to move outward as it is, and is thus separated from the meniscus. Then, the separated ink columns are collected into about 1 to 2 ink droplets, which fly in the direction of the recording paper or the like to form dots on the surface of the recording paper or the like. Characters, images, and the like are recorded on the surface of recording paper or the like by the collection of dots.

  As a driving method for operating the piezoelectric actuator 2 to eject ink droplets, there are a so-called strike-type drive method and a push-type drive method. As shown in FIG. 4 (a), the drive voltage is continuously applied to the region corresponding to all the pressurizing chambers 11 of the piezoelectric ceramic layer 23 of the piezoelectric actuator 2, and the charged deformation state is maintained for all. Thus, the state in which the volume of the pressurizing chamber 11 is reduced is maintained.

In the pressurizing chamber 11 for ejecting ink droplets from the nozzles 12 during recording,
(1) First, at S1 in FIG. 4 (a), the corresponding region of the piezoelectric ceramic layer 23 is discharged to release the deformation, and the volume of the pressurizing chamber 11 is increased, so that the meniscus in the nozzle 12 is reduced. After drawing into the pressure chamber 11 side,
(2) At the time of S2 in FIG. 4 (a), the corresponding region of the piezoelectric ceramic layer 23 is charged again to be in a deformed state, thereby reducing the volume of the pressurizing chamber 11,
The meniscus in the nozzle 12 is vibrated to generate ink droplets by the above mechanism and to eject from the nozzle 12. Further, during this time, in the pressurizing chamber 11 in which the ink enemy is not ejected, the charged deformation state of the corresponding region of the piezoelectric ceramic layer 23 is continuously maintained.

Then, it is possible to perform recording by selectively ejecting ink droplets only from the nozzles 12 corresponding to the pressurizing chamber 11 in which the operations (1) and (2) are performed.
On the other hand, in the push-type driving method, at the time of standby, as shown in FIG. 4B, a driving voltage is applied to the area corresponding to all the pressure chambers 11 of the piezoelectric ceramic layer 23 of the piezoelectric actuator 2. Without maintaining the discharged deformation release state, the volume of the pressurizing chamber 11 is maintained in a normal state.

In the pressurizing chamber 11 in which ink droplets are ejected from the nozzle 12 when recording is performed, the corresponding region of the piezoelectric ceramic layer 23 is charged and deformed at the time S1 in FIG. Ink drops are generated by reducing the volume of 11.
Further, during this time, in the pressurizing chamber 11 in which the ink enemy is not ejected, the discharged deformation release state of the corresponding region of the piezoelectric ceramic layer 23 is continuously maintained. Then, it is possible to perform recording by selectively ejecting ink droplets only from the nozzles 12 corresponding to the pressurizing chamber 11 on which the above operation is performed. After the formation of the dots, at the time of S2 in FIG. 4B, the corresponding region of the piezoelectric ceramic layer 23 is discharged to be in the deformation release state, thereby returning to the standby state.

<Piezoelectric element regeneration method>
Although the control unit 4 does not perform the recording operation by ejecting ink droplets as described above, during the standby time required for performing the recording, in detail, immediately after turning on the power of the recording apparatus, the nozzle cleaning is performed. At the time of discharging the recording paper and immediately before starting recording, a voltage having a predetermined voltage waveform is applied to the piezoelectric ceramic layer 23 of the piezoelectric actuator 2 to eliminate the internal electric field generated in the piezoelectric ceramic layer 23. Thus, it has an element reproducing function for reproducing the piezoelectric ceramic layer 2.

Specifically, the control means 4 controls the drive circuit 3 during the standby time described above, and first applies the voltage V ₁ to the piezoelectric ceramic layer 23 as shown in FIG. The piezoelectric actuator 2, when the driven by pulling out type drive method as is with a driving voltage that is continuously applied at the time of standby, may be substituted for the voltage V _1. On the other hand, in the case of push and eject type drive method, so that the newly applies the voltage V _1.

Next, the control unit 4 controls the drive circuit 3, a voltage applied to the piezoelectric ceramic layer 23, the voltage V _1, over time t _1, the reverse polarity to the voltage V _1, and, absolute value is varied to a voltage V ₂ which is set to V _{2 <V 3} of the voltage value, while the voltage V ₂ of the time t _2, was maintained and further over time t _3, the voltage, the voltage V _2, the reverse polarity to the voltage V _1, and the absolute value of the voltage value is changed to a voltage V ₃ which is set to or higher than the voltage value of the coercive field of the piezoelectric element, and, T ₃ the voltage V ₃ times Maintain during.

When the above operation is performed, the mechanism described above reduces the burden on the drive circuit and the piezoelectric ceramic layer 23, and prevents the discharge of unnecessary ink droplets, while preventing the internal discharge generated in the piezoelectric ceramic layer 23 from occurring. The electric field can be eliminated efficiently. Therefore, for example, in the case of push and eject type drive method, as shown in FIG, after the time T _3, so as to return to the recordable standby state, the piezoelectric ceramic layer 23, the same polarity as voltages V ₁ In the case of the example shown in the figure, the piezoelectric ceramic layer 23 can be favorably repolarized by applying the voltage V ₅ having the same absolute value of the voltage value. In the case of push and eject type drive method, the time constant voltage V _5, applied to, after well repolarization piezoelectric ceramic layer 23, by stopping the application, be returned to the standby state Can do.

Of the above, the voltage V ₂ is preferably set to a voltage value that does not cause re-inversion of the polarization direction of the piezoelectric element. Further, the sum T ₁ = t ₁ + t ₂ of the times t ₁ and t ₂ is a ratio T ₁ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator in a state where the pressurizing chamber is filled with liquid.
0.15 ≦ T ₁ / T ₀ ≦ 0.3
Is preferably set in a range that satisfies the above. Further, the sum T ₂ = T ₁ + t ₃ of the time t ₃ and the time T ₁ has a ratio T ₂ / T ₀ to the natural vibration period T ₀ .
0.2 ≦ T ₂ / T ₀ ≦ 0.6
Is preferably set in a range that satisfies the above. Furthermore, the time T ₃ is a ratio T ₃ / T ₀ to the natural vibration period T ₀ ,
0.7 ≦ T ₃ / T ₀
Is preferably set in a range that satisfies the above.

By performing these settings, as described above, the internal electric field of the piezoelectric ceramic layer 23 can be further reduced while further reliably preventing ink drops from being ejected from the nozzles 12 and increasing ink consumption. This can be solved more efficiently.
FIG. 3 is a graph showing another example of the element regeneration function by the control means 4. In the example shown, the control unit 4 controls the drive circuit 3, a voltage applied to the piezoelectric ceramic layer 23, the voltage V _1, over time t _1, the reverse polarity to the voltage V _1, And, after changing the absolute value of the voltage value to the voltage V ₂ set to V ₂ <V ₃ and maintaining this voltage V ₂ for the time t ₂ , the voltage is changed over the time t ₃ from the voltage V _2, at opposite polarity to the voltage V _1, and the absolute value of the voltage value is changed to a voltage V ₃ which is set to or higher than the voltage value of the coercive field of the piezoelectric element, and the voltage V ₃ times between T _3, to maintain. The steps so far are the same as in the example of FIG. The preferred range of each voltage value and the preferred range of time are the same as in the example of FIG.

After the time T ₃ has elapsed, the control means 4 controls the drive circuit 3 so that the voltage applied to the piezoelectric ceramic layer 23 is changed from the voltage V ₃ to the time t ₄ in the example shown in the figure. and the same polarity as the voltage _{V 1,} can alter the absolute value of the voltage value to a voltage _{V 4} is _V 4 _{<V 5,} while the voltage _{V 4} time _{t 5,} after maintaining, more time _{t 6} over, the voltage from the voltage V _4, with the voltages V ₁ the same polarity, and the case of the example of FIG vary from the voltage V ₅ absolute value is equal to the voltage value.

When this operation is performed, the internal mechanism generated in the piezoelectric ceramic layer 23 while reducing the burden on the drive circuit and the piezoelectric ceramic layer 23 and preventing unnecessary ejection of ink droplets by the mechanism described above. The electric field can be efficiently eliminated and the piezoelectric ceramic layer 23 can be favorably repolarized.
Thereafter, the pull-push driving method, by maintaining the voltage V _5, can be returned to the standby state. In the case of push and eject type drive method, the time constant voltage V _5, applied to, after well repolarization piezoelectric ceramic layer 23, by stopping the application, be returned to the standby state Can do.

Of the above, the voltage V ₄ may have a polarity opposite to that of the voltage V ₁ . The sum T ₄ = t ₄ + t ₅ of the times t ₄ and t ₅ is a ratio T ₄ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator in a state where the pressurizing chamber is filled with liquid.
0.15 ≦ T ₄ / T ₀ ≦ 0.3
Is preferably set in a range that satisfies the above. Further, the sum T ₅ = T ₄ + t ₆ of the time t ₆ and the time T ₄ has a ratio T ₅ / T ₀ to the natural vibration period T ₀ of the piezoelectric actuator.
0.2 ≦ T ₂ / T ₀ ≦ 0.6
Is preferably set in a range that satisfies the above.

By performing these settings, as described above, the internal electric field of the piezoelectric ceramic layer 23 can be further reduced while further reliably preventing ink drops from being ejected from the nozzles 12 and increasing ink consumption. This can be solved more efficiently.
The application of the present invention is not limited to the ink jet head described above, and can be applied to, for example, a micro pump.

It is sectional drawing to which some inkjet heads were expanded as a liquid discharge apparatus with which the reproduction | regenerating method of the piezoelectric element of this invention is applied. 2 is a graph showing an example of a waveform of a voltage applied to a piezoelectric element in order to reproduce the piezoelectric element of the ink jet head of FIG. 1 by the reproducing method of the present invention. 6 is a graph showing another example of a waveform of a voltage applied to a piezoelectric element in order to reproduce the piezoelectric element of the ink jet head of FIG. 1 by the reproducing method of the present invention. FIGS. 7A and 7B are graphs showing examples of drive voltage waveforms applied to the piezoelectric elements when the inkjet head of FIG. 1 is driven.

Explanation of symbols

11 Pressurizing chamber 12 Nozzle 2 Piezoelectric actuator 23 Piezoelectric ceramic layer (piezoelectric element)
3 the drive power 4 control means V ₁ ~V ₅ Voltage

Claims (13)

After the voltage V ₁ having the same polarity as the drive voltage waveform is applied to the piezoelectric element, the voltage V has the opposite polarity to the voltage V ₁ and the absolute value of the voltage value is equal to or greater than the voltage value of the coercive electric field of the piezoelectric element. ₃ a method of reproducing a piezoelectric element including a step of applying a, a voltage applied to the piezoelectric element during the step of changing from voltages V ₁ to the voltage V _3, the piezoelectric element, the same polarity as the voltage V _3, A method for regenerating a piezoelectric element, wherein a voltage V ₂ having an absolute value of V ₂ <V ₃ is applied for a certain period of time. The voltage V _2, the method of reproducing the piezoelectric element according to claim 1, wherein the set to a voltage value which the polarization direction of the re-inversion of the piezoelectric element does not occur. (1) a pressurized chamber filled with liquid;
(2) a nozzle communicating with the pressurizing chamber;
(3) a piezoelectric actuator that includes a piezoelectric element and flexes it by deformation of the piezoelectric element to increase or decrease the volume of the pressurizing chamber, thereby discharging the liquid in the pressurizing chamber as droplets through the nozzle;
The method for regenerating a piezoelectric element according to claim 1, wherein a piezoelectric element incorporated in the piezoelectric actuator of a liquid ejection apparatus comprising: The voltage applied to the piezoelectric element and the time _{t 1} required to change from voltages _{V 1} to the voltage _{V 2,} the sum _T 1 ₌ t 1 + _{t 2} and the time _{t 2} for applying the voltage _{V 2,} the pressure chamber The ratio T ₁ / T ₀ with respect to the natural vibration period T ₀ of the piezoelectric actuator in the state filled with the liquid is
0.15 ≦ T ₁ / T ₀ ≦ 0.3
The method for regenerating a piezoelectric element according to claim 3, wherein the piezoelectric element is set in a range satisfying the above. The sum T ₂ = T ₁ + t ₃ of the time t ₃ required to change the voltage applied to the piezoelectric element from the voltage V ₂ to the voltage V ₃ and the time T ₁ with respect to the natural vibration period T ₀ of the piezoelectric actuator. The ratio T ₂ / T ₀ is
0.2 ≦ T ₂ / T ₀ ≦ 0.6
The method for regenerating a piezoelectric element according to claim 4, wherein the value is set in a range satisfying the above. The ratio T ₃ / T ₀ with respect to the natural vibration period T ₀ of the piezoelectric actuator in the state where the pressure chamber ₃ is filled with the liquid is set as the time T ₃ for applying the voltage V ₃ .
0.7 ≦ T ₃ / T ₀
The method for regenerating a piezoelectric element according to claim 3, wherein the piezoelectric element is set in a range satisfying the above. Time constant voltage V _3, after the application, with the same polarity or opposite polarity to the voltage V _1, and the absolute value predetermined time voltage V ₄ is V _{4 <V 5} is the voltage value, is applied, then the voltage V _The method for regenerating a piezoelectric element according to claim 3, wherein a voltage V ₅ having the same polarity as ₁ is applied. The voltage V _4, the same polarity as the voltage V _1, and a method of reproducing a piezoelectric element according to claim 7, wherein the set to a voltage value which the polarization direction of the re-inversion of the piezoelectric element does not occur. The sum of the time t ₄ required to change the voltage applied to the piezoelectric element from the voltage V ₃ to the voltage V ₄ and the time t ₅ to apply the voltage V ₄ is T ₄ = t ₄ + t _5. The ratio T ₄ / T ₀ with respect to the natural vibration period T ₀ of the piezoelectric actuator in the state filled with the liquid is
0.15 ≦ T ₄ / T ₀ ≦ 0.3
The method for regenerating a piezoelectric element according to claim 7, wherein the range is set in a range satisfying the above. The sum T ₅ = T ₄ + t ₆ of the time t ₆ required to change the voltage applied to the piezoelectric element from the voltage V ₄ to the voltage V ₅ and the time T ₄ is relative to the natural vibration period T ₀ of the piezoelectric actuator. The ratio T ₅ / T ₀ is
0.2 ≦ T ₂ / T ₀ ≦ 0.6
The method for regenerating a piezoelectric element according to claim 9, wherein the piezoelectric element is set in a range satisfying the above.   The liquid ejection device is a piezoelectric ink jet head incorporated in a recording device of an ink jet recording method, and the piezoelectric element is regenerated immediately after turning on the power of the recording device, at the time of nozzle cleaning, at the time of discharging the recording paper, and immediately before the start of recording. The method for regenerating a piezoelectric element according to claim 3. (1) a pressurized chamber filled with liquid;
(2) a nozzle communicating with the pressurizing chamber;
(3) a piezoelectric actuator that includes a piezoelectric element and flexes it by deformation of the piezoelectric element to increase or decrease the volume of the pressurizing chamber, thereby discharging the liquid in the pressurizing chamber as droplets through the nozzle;
A driving power source for applying a driving voltage to the piezoelectric element, and a control means for controlling the driving power source to apply the driving voltage to the piezoelectric element. A liquid ejecting apparatus having an element regeneration function of controlling a drive power source so that the element can be regenerated by performing the piezoelectric element regeneration method according to claim 1.   A piezoelectric ink jet head incorporated in a recording apparatus of an ink jet recording system, and the control means performs a reproduction process of the piezoelectric element immediately after turning on the power of the recording apparatus, at the time of nozzle cleaning, at the time of discharging the recording paper, and immediately before the start of recording. The liquid ejection device according to claim 12.

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