JP6103406B2 - Droplet discharge head driving method, droplet discharge head, and image forming apparatus - Google Patents

Description

  The present invention relates to a method for driving a droplet discharge head, a droplet discharge head that employs this drive method, and an image forming apparatus that employs this droplet discharge head.

  In general, as an image forming apparatus that combines a printer, a fax machine, a copier, a plotter, or a plurality of these functions, for example, there is an ink jet recording apparatus provided with a droplet discharge head that discharges ink droplets. In an ink jet recording apparatus, an image is formed by adhering ink droplets to a sheet by a droplet discharge head while conveying a medium. The medium here is also referred to as “paper”, but the material is not limited, and a recording medium, a recording medium, a transfer material, a recording paper, and the like are also used synonymously. The image forming apparatus means an apparatus for forming an image by ejecting liquid droplets on a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, or ceramic. The image formation is not only giving an image having a meaning such as a character or a figure to the medium but also giving an image having no meaning such as a pattern to the medium (simply ejecting a droplet). Also means. The ink is not limited to so-called ink, and is not particularly limited as long as it becomes a droplet when ejected. For example, a droplet including a DNA sample, a resist, a pattern material, etc. Used generically.

  A droplet discharge head in an ink jet recording apparatus includes a nozzle that discharges ink droplets and a pressurized liquid chamber (also referred to as an ink flow path, a pressure chamber, a pressure chamber, a discharge chamber, and a liquid chamber) that communicates with the nozzle. And pressure generating means for discharging ink in the pressurized liquid chamber. Examples of the pressure generating means include a piezo-type device that uses a piezoelectric element disposed on a vibration plate constituting one wall surface of the pressurized liquid chamber and discharges ink droplets by displacing the vibration plate.

Furthermore, recently, due to advances in semiconductor processes and MEMS (Micro Electro Mechanical Systems), vibration plates and piezoelectric element constituent layers constituting a thin film piezoelectric actuator (hereinafter referred to as thin film piezoelectric) on a Si substrate forming a pressurized liquid chamber. A thin film is directly put into practical use by forming a thin film with high density. The piezoelectric element includes a substrate side electrode, a piezoelectric layer, and a surface electrode. As the thin film of the piezoelectric layer, lead zirconate titanate (PZT) represented by the general formula Pb (Ti _x , Zr _y , M _z ) O ₃ having a perovskite crystal structure is used. However, when the driving waveform is repeatedly applied to drive the thin film piezo, a displacement amount (hereinafter referred to as a displacement characteristic) with respect to the driving waveform is lowered, and there is a problem that the ejection characteristic is deteriorated with time.

In order to recover the displacement characteristics of a thin film piezo by applying the following voltage, it has been proposed.
Patent Document 1 describes a technique in which a DC voltage is applied as a recovery waveform between a drive waveform and a drive waveform, with a decrease in displacement due to a reaction between lead and moisture in the piezoelectric thin film as a problem.
Japanese Patent Application Laid-Open No. 2004-228561 describes a method of applying a recovery waveform obtained by inverting a drive waveform between drive waveforms.
In Patent Document 3, an object is to reduce displacement due to deformation of an inactive region of a piezoelectric thin film, and the driving waveform includes a voltage having a reverse polarity, so that the electric field in the direction opposite to the driving electric field is applied to the thin film piezoelectric. Those that form <U></U>.

As a result of research, the present inventors have found that, in a thin film piezo using a piezoelectric thin film such as PZT having a perovskite crystal structure, when a unidirectional driving electric field is applied to the piezoelectric element, the displacement characteristics due to the following phenomenon are obtained. It has been found that lowering occurs.
The electric field applied to drive the piezoelectric element causes lead defects in the PZT to be drawn toward the negative voltage side electrode. The drawn lead defects are localized at the electrode interface by being trapped at the interface with the negative voltage side electrode. This unevenly distributed lead defect generates an internal electric field, lowers the effective voltage of the driving waveform, and the displacement characteristics of the thin film piezo deteriorate.
Further, the trap of lead defects is a very deep level, and once trapped, it is not easily detrapped, and it becomes an almost irreversible change within the use conditions for ejecting normal droplets. That is, the deterioration of the displacement characteristics of the thin film piezo due to the irreversible change of lead defect trapping cannot be recovered within normal use conditions, and the deterioration of the displacement characteristics proceeds with time.

  The above-mentioned Patent Document 1 applies a DC voltage between a drive waveform and a drive waveform with a problem of a decrease in displacement due to a reaction between lead and moisture in a thin film piezo. If an attempt is made to eliminate the uneven distribution of the lead defects using only a DC voltage, a considerably long application time is required, and it is difficult to establish a sequence for applying the drive waveform.

  In the above-mentioned patent document 3, an electric field in the direction opposite to the driving electric field is formed in the thin film piezo by configuring the driving waveform to include a voltage having a reverse polarity, thereby eliminating the lead defect trap at the interface with the electrode. An effect is obtained. However, since a reverse waveform of a certain condition having a characteristic for suppressing a decrease in displacement of the piezoelectric element is introduced in the drive waveform, the drive waveform is restricted and stable ejection performance cannot be obtained. There is a case.

  In Patent Document 2, a voltage whose polarity is reversed with the same waveform as the driving voltage is applied after the driving voltage is applied. According to this, an electric field in a direction opposite to the driving electric field is formed, and an effect of eliminating the trap of lead defects at the interface with the electrode can be obtained. However, if a new power supply that outputs a voltage having the same waveform as the drive voltage and having the opposite polarity is provided, the drive IC causes a significant increase in cost. In Patent Document 2, the polarity of the drive waveform is inverted using a switch. However, providing a switch also increases the cost of the drive IC. In order to commercialize a droplet discharge head, it is important to suppress the cost increase of the driving IC, to suppress the deterioration of the displacement characteristics over time, and to ensure stable discharging performance. In some cases, it may not be a product.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a droplet ejection head driving method capable of ensuring stable ejection performance at low cost while suppressing deterioration in displacement characteristics of a thin film piezoelectric actuator over time. And a droplet discharge head and an image forming apparatus.

In order to achieve the above object, a first aspect of the present invention is a piezoelectric element in which a piezoelectric film of general formula Pb (Ti _x , Zr _y , M _z ) O ₃ is sandwiched between a first electrode and a second electrode. And configured to pressurize the pressurized liquid chamber communicating with the nozzle, applying a pulse waveform driving voltage and a pulse waveform recovery voltage to the first electrode, and applying a DC voltage to the second electrode. The driving voltage is a first voltage that generates an electric field in the first direction that causes a lead defect trap in the piezoelectric film, and a second direction that is opposite to the first direction. And a second voltage for generating an electric field in the piezoelectric film, and the recovery voltage includes a third voltage for generating an electric field in the first direction in the piezoelectric film and the second direction. And a fourth voltage for generating the electric field in the piezoelectric film, and the waveform of the recovery voltage is the third voltage. From the first voltage to the fourth voltage, and after continuing the fourth voltage for a first time, the fourth voltage is shifted to the third voltage, and the second voltage is The second time continues, and the first time is longer than the second time and is a time other than an integral multiple of the meniscus resonance period in the nozzle, and the fourth voltage to the fourth time At least one of the transition time to the voltage and the transition time from the fourth voltage to the third voltage is longer than the meniscus resonance period .

  According to the present invention, there is an excellent effect that a stable discharge performance can be ensured at a low cost by suppressing a decrease in displacement characteristics of the actuator over time.

FIG. 3 is a cross-sectional view showing a basic configuration of a thin film piezo actuator in the liquid droplet ejection head of this embodiment. Sectional drawing which shows the fundamental layer structure of a thin film piezoelectric actuator. It is sectional drawing of the droplet discharge head of this embodiment, (a) shows the width direction, (b) shows a nozzle row direction. Process sectional drawing which shows the manufacturing process of the droplet discharge head of this embodiment (the 1). Process sectional drawing which shows the manufacturing process of the droplet discharge head of this embodiment (the 2). FIG. 4 is a diagram illustrating an example of a driving waveform for discharging droplets by a droplet discharge head. The graph which shows an example of the relationship between the applied voltage and displacement amount with respect to a piezoelectric element. Explanatory drawing of the measuring method of displacement. Explanatory drawing of an example of the drive waveform which applied the bias voltage. Hysteresis curve of piezoelectric element. Explanatory drawing of the pulse width time in this embodiment, rise time, and fall time. Explanatory drawing of the drive waveform and recovery | restoration waveform of this embodiment. Explanatory drawing of a meniscus resonance period. Explanatory drawing of the recovery waveform which concerns on Example 1. FIG. Explanatory drawing of the recovery waveform which concerns on Example 2. FIG. Explanatory drawing of the recovery waveform which concerns on Example 3. FIG. Explanatory drawing of the recovery waveform which concerns on Example 4. FIG. Explanatory drawing of the recovery waveform which concerns on Example 5. FIG. Explanatory drawing of the recovery waveform which concerns on the comparative example 1. FIG. The graph which shows the evaluation result of the discharge speed of an Example and a comparative example. 1 is a perspective view of an ink jet printer according to an embodiment. The side view of the mechanism part of the inkjet printer of this embodiment.

Hereinafter, a droplet discharge head according to an embodiment of the present invention will be described.
FIG. 1 is a cross-sectional view showing a basic configuration of a thin film piezo actuator in the liquid droplet ejection head of this embodiment. The droplet discharge head 51 includes a nozzle plate 2, a liquid chamber substrate 4, a vibration plate 55, and a piezoelectric element 56 that are stacked. The nozzle plate 2 is formed with nozzles 20 for ejecting ink droplets. The nozzle plate 2, the liquid chamber substrate 4, and the vibration plate 55 form a pressurized liquid chamber 14 (also referred to as an ink flow path, a pressurized chamber, a pressure chamber, a discharge chamber, and a liquid chamber) that communicates with the nozzle 20. Has been. The diaphragm 55 forms one wall surface of the pressurized liquid chamber 14.

  The thin film piezo actuator 200 includes a diaphragm 55 and a piezoelectric element 56. The piezoelectric element 56 includes a lower electrode 151 serving as a substrate side electrode, a piezoelectric thin film 152, and an upper electrode 153 serving as a surface electrode. The piezoelectric element 56 is an element that converts an electrical signal into a mechanical displacement. The piezoelectric element 56 is provided at a position corresponding to the pressurized liquid chamber 14 of the vibration plate 55 formed on one surface of the liquid chamber substrate 4.

  The droplet discharge head 51 is a head that discharges ink droplets from the nozzles 20 by driving the thin film piezoelectric actuator 200. Specifically, the droplet discharge head 51 applies a voltage to the lower electrode 151 or the upper electrode 153 of the piezoelectric element 56 to generate stress in the piezoelectric thin film 152 and vibrate the diaphragm 55. Along with the vibration of the vibration plate 55, the ink in the pressurized liquid chamber 14 is discharged from the nozzle 20 in the form of droplets. Note that illustration and description of ink supply means for supplying ink into the pressurized liquid chamber 14, ink flow paths, fluid resistance, and the like are omitted.

  FIG. 2 is a cross-sectional view showing the basic layer structure of the thin film piezoelectric actuator. As described above, the piezoelectric element 56 is formed by laminating the liquid chamber substrate 4 and the diaphragm 55 and laminating the lower electrode 151, the piezoelectric thin film 152, and the upper electrode 153. In order to form the piezoelectric element 56 in the shape shown in FIG. 1, after the piezoelectric thin film 152 and the upper electrode 153 are formed, the piezoelectric thin film 152 and the upper electrode 153 are formed into desired shapes by an etching technique. Form. Further, a protective layer and an interlayer insulating layer (not shown) (see FIGS. 5 and 6) may be formed only in a desired portion, and are formed by an etching technique so as to have a desired shape.

Hereinafter, description will be added regarding the materials used for each layer and the manufacturing process thereof.
As the liquid chamber substrate 4, it is preferable to use a silicon single crystal substrate, and it is usually preferable to have a thickness of 100 to 600 [μm]. Although there are three types of plane orientations (100), (110), and (111), (100) and (111) are generally widely used in the semiconductor industry. In the present embodiment, a single crystal substrate having a (100) plane orientation is mainly used.

  Further, when the pressurized liquid chamber 14 as shown in FIG. 1 is manufactured, the silicon single crystal substrate is processed using etching. In this case, anisotropic etching is used as an etching method. It is common. Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure.

For example, in anisotropic etching immersed in an alkaline solution such as KOH, the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Therefore, while a structure having an inclination of about 54 ° can be produced in the plane orientation (100), a deep groove can be removed in the plane orientation (110), so that the arrangement density is increased while maintaining rigidity. I know you can. In this embodiment, it is also possible to use a single crystal substrate having a (110) plane orientation. However, in this case, SiO ₂ which is a mask material is also etched, so this area is also used with attention.

As shown in FIG. 1, the vibration plate 55 is deformed and displaced by receiving the force generated by the piezoelectric element 56 and discharges ink droplets in the pressurized liquid chamber 14. In order to have such a function, the diaphragm 55 preferably has a predetermined strength. Examples of the material include Si, SiO ₂ , and Si ₃ N ₄ produced by the CVD method. Furthermore, it is preferable to select a material close to the linear expansion coefficient of the lower electrode 151 and the piezoelectric thin film 152.

As will be described later, PZT is generally used as the piezoelectric thin film 152. Therefore, a material having a linear expansion coefficient of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ that is close to the linear expansion coefficient 8 × 10 ⁻⁶ (1 / K) of the piezoelectric thin film 152 is preferable as the diaphragm 55. Furthermore, a material having a linear expansion coefficient of 7 × 10 ^{−6 to} 9 × 10 ⁻⁶ is more preferable. Specific examples of the material include aluminum oxide, zirconium oxide, iridium oxide, ruthenium oxide, tantalum oxide, hafnium oxide, osmium oxide, rhenium oxide, rhodium oxide, palladium oxide, and compounds thereof. These can be produced by a spin coater using a sputtering method or a Sol-Gel method.

  The film thickness of the diaphragm 55 is preferably 0.1 to 10 [μm], more preferably 0.5 to 3 [μm]. If it is smaller than this range, it becomes difficult to process the pressurized liquid chamber 14 as shown in FIG. 1, and if it is larger than this range, the vibration plate 55 is difficult to be deformed and displaced, and ink droplet ejection becomes unstable.

As the lower electrode 151 and the upper electrode 153, platinum having high heat resistance and low reactivity has been conventionally used as a metal material. However, it may not be said that it has sufficient barrier properties against lead, and examples include platinum group elements such as iridium and platinum-rhodium, and alloy films thereof. In addition, when using platinum, since adhesion with the base (particularly SiO ₂ ) is poor, Ti, TiO ₂ , Ta, Ta ₂ O ₅ , Ta ₃ N _5, etc. should be laminated first as an adhesion layer. Is preferred. As a manufacturing method, vacuum film formation such as sputtering or vacuum deposition is generally used. The film thickness is preferably 0.05 to 1 [μm], more preferably 0.1 to 0.5 [μm].

In addition, due to concerns over the fatigue characteristics of the displacement of the piezoelectric thin film 152 over time, conductivity such as SrRuO ₃ and LaNiO ₃ is provided between the lower electrode 151 and the piezoelectric thin film 152 and between the piezoelectric thin film 152 and the upper electrode 153. It is preferable to stack an oxide as an electrode part.

As the piezoelectric thin film 152, PZT (lead zirconate titanate) is used. PZT is a solid solution of lead zirconate (PbTiO ₃ ) and lead titanate (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, the composition exhibiting excellent piezoelectric properties has a ratio of PbZrO ₃ and PbTiO ₃ of 53:47, and Pb (Zr0.53, Ti0.47) O ₃ in the chemical formula, generally PZT (53 / 47) indicated by 47) can be used.

  The piezoelectric thin film 152 can be manufactured by a spin coater using, for example, a sputtering method or a Sol-Gel method. In that case, since patterning is required, a desired pattern is obtained by etching using photolithography or the like.

  When PZT is produced by the Sol-Gel method, a PZT precursor solution can be produced by using lead acetate, zirconium alkoxide, and titanium alkoxide compounds as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a uniform solution. . Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of acetylacetone, acetic acid, diethanolamine or the like may be added to the precursor solution as a stabilizer.

  When a PZT film is obtained on the entire surface of the diaphragm 55, it is obtained by forming a coating film by a solution coating method such as spin coating, and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since transformation from the coating film to the crystallized film is accompanied by volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a film free from cracks.

  The film thickness of the piezoelectric thin film 152 is preferably 0.5 to 5 [μm], and more preferably 1 to 2 [μm]. If it is smaller than this range, it will not be possible to generate a sufficient displacement, and if it is larger than this range, many layers will be laminated, resulting in an increase in the number of steps and a longer process time.

Next, the droplet discharge head 51 using the actuator will be described.
3A and 3B are cross-sectional views of the droplet discharge head of the present embodiment. FIG. 3A is a cross-sectional view in the width direction, and FIG. 3B is a cross-sectional view in the nozzle row direction. For convenience, (a) shows the right half of the droplet discharge head, and (b) shows only the portion corresponding to the two pressurized liquid chambers 14.

In the liquid chamber substrate 4, groove portions serving as ink flow paths such as the pressurized liquid chamber 14 and the fluid resistance portion 15 are formed.
As the liquid chamber substrate 4, an SOI substrate in which silicon is bonded to a silicon substrate via a silicon oxide film is used. The diaphragm 55 is obtained by applying a pyro-oxidation method to the silicon layer (Si layer) surface of the SOI substrate to form a silicon oxide film. Then, the piezoelectric element 56 is formed on the vibration plate 55 to constitute the thin film piezoelectric actuator 200.

  The piezoelectric element 56 is formed by laminating a multilayer structure of a platinum film serving as the lower electrode 151, a PZT (lead zirconate titanate) film serving as the piezoelectric thin film 152, and a platinum film serving as the upper electrode 153 on the diaphragm 55. It is formed with. The lower electrode 151 is a common electrode, and the upper electrode 153 is an individual electrode. The piezoelectric element 56 is formed in a region facing the pressurized liquid chamber 14 formed by etching a silicon substrate.

  The liquid chamber substrate 4 includes a wiring member 154 that applies a potential to each of the lower electrode 151 and the upper electrode 153. As the wiring member 154, a lower wiring member 154a that electrically connects the lower electrode pad portion 157 to the lower electrode 151, and an upper wiring member 154b that electrically connects the upper electrode pad portion 158 to the upper electrode 153 are provided. ing. Further, the liquid chamber substrate 4 includes an interlayer insulating film 155 disposed between the lower electrode 151 and the upper electrode 153 and the wiring member 154. Further, a passivation film 156 for protecting the wiring member 154 is disposed on the liquid chamber substrate 4 so as to cover the upper surface and the side surface of the thin film piezoelectric actuator 200.

  The nozzle plate 2 is made of a SUS (stainless steel) substrate having a thickness of 30 to 50 [μm], and the nozzle 20 is formed by pressing and polishing. The nozzle 20 is formed so as to face the pressurized liquid chamber 14 of the liquid chamber substrate 4 when the nozzle plate 2 and the liquid chamber substrate 4 are assembled, and to communicate the pressurized liquid chamber 14 and the external space. .

The protective substrate 3 is a substrate that forms the piezoelectric element protection space 22. The protective substrate 3 is formed with a groove portion serving as an ink flow path as the common liquid chamber 18 and a piezoelectric element protection space 22 for preventing the piezoelectric element 56 from being protected and displaced. Further, in order to increase the rigidity of the liquid chamber partition 4 a of the liquid chamber substrate 4, a reinforcing wall 23 that reinforces the liquid chamber partition 4 a through the diaphragm 55 is formed. The reinforcing wall 23 reinforces the liquid chamber partition 4a to support the entire pressurized liquid chamber 14 formed by the liquid chamber partition 4a.
Further, the diaphragm 55 is provided with an individual supply port 60 in a portion that becomes a flow path for supplying ink from the common liquid chamber 18 formed on the protective substrate 3 to the pressurized liquid chamber 14 formed on the liquid chamber substrate 4. It has been. The substrate in which the thin film piezoelectric actuator 200 is formed on the liquid chamber substrate 4 and the protective substrate is bonded is called an actuator substrate 1.

Next, a method for manufacturing the droplet discharge head 51 of the present embodiment will be described with reference to FIGS. 4 and 5 which are process cross-sectional views showing the manufacturing process. In this manufacturing method, the thin film piezo actuator 200 is formed by depositing the material of the diaphragm 55 and the material of the piezoelectric element 56 on the silicon substrate that is the liquid chamber substrate 4.
First, as shown in FIG. 4A, a silicon oxide film having a thickness of 0.2 [μm] and a thickness of 2.0 [μm] are formed on the surface of a <100> silicon layer (silicon substrate) having a thickness of 400 [μm]. An SOI substrate bonded with silicon is used. A silicon oxide film of 0.3 [μm] is formed on the surface of the SOI substrate by a pyro oxidation method, and this is used as a diaphragm 55.

  Thereafter, a lower platinum layer to be the lower electrode 151 of the piezoelectric element 56 is formed by sputtering to a thickness of 0.2 [μm] and is patterned to obtain the state shown in FIG. Further, 2 [μm] of the piezoelectric thin film 152 is formed by a sol-gel method, and an upper platinum layer to be the upper electrode 153 is formed by 0.1 [μm]. Thereafter, the upper electrode 153 and the piezoelectric thin film 152 are patterned by etching using photolithography. As a result, the state shown in FIG.

Next, an insulating layer to be an interlayer insulating film 155 is formed by plasma CVD method to 0.3 [μm], and an opening 155c is formed above the piezoelectric element 56 by lithoetch method. In the interlayer insulating film 155, an upper conductive portion 155b, a lower conductive portion 155a, and a through portion 155d are formed by patterning. As a result, the state shown in FIG.
The upper conductive portion 155b shown in FIG. 4D is a conductive portion between the upper wiring member 154b to be formed next and the upper electrode 153, and the lower conductive portion 155a is the lower wiring member 154a and the lower electrode 151 to be formed next. It is a conduction part. The through portion 155 d is an opening that serves as an ink supply hole from the common liquid chamber 18 to each individual ink supply chamber 24.

  Further, by forming a layer to be the wiring member 154 such as the upper wiring member 154b and the lower wiring member 154a with an aluminum material, the state shown in FIG. The upper wiring member 154 b formed by the wiring member 154 receives stress due to vibration of the diaphragm 55 due to driving of the piezoelectric element 56. For this reason, a soft conductive material (aluminum in this embodiment) is used as the wiring member 154 so that the upper wiring member 154b is not disconnected by the vibration of the diaphragm 55, and the layer thickness is about 1 [μm]. Has been.

  Next, 2 [μm] of a silicon nitride film by plasma CVD is formed as a passivation film 156 for protecting the wiring member 154 and patterned. And the part used as the separate supply port 60 of the diaphragm 55 is etched beforehand. As a result, the state shown in FIG.

Next, gold is laminated by a plating method to form the upper electrode pad portion 158 and the lower electrode pad portion 157 at the same time, so that the state shown in FIG. The upper electrode pad portion 158 is connected to the upper electrode 153 by the upper wiring member 154b. The lower electrode pad portion 157 is connected to the lower electrode 151 by the lower wiring member 154a. Thus, by forming the upper electrode pad portion 158 and the lower electrode pad portion 157 with gold, electrical connection with a driving IC (not shown) can be made by low-temperature wire bonding. Further, gold has a low resistance value, and has a great effect of reducing the resistance values of the upper electrode 153 and the lower electrode 151.
The lower electrode pad portion 157 may be formed separately from the upper electrode pad portion 158 in the formation process. The material of the upper electrode pad portion 158 and the lower electrode pad portion 157 is not limited to gold, and copper, aluminum, or the like can be used. However, when a material other than gold is used, a protective layer that protects against corrosion may be required for the upper electrode pad portion 158 whose surface is not covered with another layer.

Further, separately from the film formation on the liquid chamber substrate 4 described above, the protective substrate 3 in which the pillars are formed on the glass substrate by blasting is created. Then, after the upper electrode pad portion 158 and the lower electrode pad portion 157 are formed, the upper electrode pad portion 158 and the lower electrode pad portion 157 are bonded to the passivation film 156 side with the vibration plate 55 of the portion that becomes the liquid chamber substrate 4 interposed therebetween. As a result, the state shown in FIG.
Further, the surface of the liquid chamber substrate 4 opposite to the side where the protective substrate 3 is bonded is sandwiched between the portions of the vibration plate 55 to be the liquid chamber substrate 4 until the liquid chamber substrate 4 has a desired thickness.
The protective substrate 3 may be a silicon plate-like member obtained by etching a recess by etching using photolithography, and a <100> silicon plate-like member is obtained by wet etching using an alkaline etchant such as TMAH or KOH. It may be processed.
Further, it may be a molded part such as a resin mold or a metal injection mold. In addition, when the drive IC is integrally formed on the actuator substrate, the oxide film formed by the pyro oxidation method is formed by the LOCOS oxidation method, and the drive IC is formed on the same substrate by selecting the oxide film formation region. You can also

  After polishing from the state shown in FIG. 5B until the liquid chamber substrate 4 has a desired thickness, an ICP ((Inductively Coupled Plasma) is applied to the surface of the liquid chamber substrate 4 opposite to the vibration plate 55. By this ICP dry etching, concave portions that become the pressurized liquid chamber 14, the fluid resistance portion 15, and the individual ink supply chamber 24 are formed, whereby the state shown in FIG.

  After the liquid chamber substrate 4 is formed, the separately prepared nozzle plate 2 is bonded to the liquid chamber partition surface of the liquid chamber substrate 4 to obtain the state shown in FIG. Here, the nozzle plate 2 is obtained by forming the nozzle 20 on a SUS substrate having a thickness of 30 to 50 [μm] by pressing and polishing. After the nozzle plate 2 is bonded to the liquid chamber substrate 4, the upper electrode pad portion 158 and the lower electrode pad portion 157 connected to the upper electrode 153 and the lower electrode 151 of the piezoelectric element 56 are connected to a driving IC (not shown). Thereby, the main part of the droplet discharge head 51 is completed.

Next, a driving method that is a characteristic part of the droplet discharge head 51 of the present embodiment will be described.
FIG. 6 is an explanatory diagram of drive waveforms for ejecting droplets by the droplet ejection head. As a drive waveform, a voltage portion (V1) that causes the piezoelectric thin film 152 to generate a first electric field corresponding to a state in which discharge is not performed, and a voltage portion (V2) that generates a second electric field corresponding to the state to be discharged in the piezoelectric thin film 152. ) Is applied in the form of a pulse. Specifically, as shown in FIG. 6, by using a combination of a plurality of pulse waveforms having different potentials of the second electric field corresponding to the state to be ejected, the volume of the ejected droplet can be changed to a large droplet, a medium droplet, It is controlled like a droplet. In FIG. 6, d is a minute vibration waveform for preventing meniscus drying.

  In the present embodiment, when a drive waveform is applied to the piezoelectric element 56 from a drive IC (not shown), the above pulse shape is applied to the upper electrode 153 that is an individual electrode based on the drive signal via the upper electrode pad portion 158. Apply a voltage of. At the same time, a driving method is used in which the DC voltage Vdc is applied as a bias voltage to the lower electrode 151, which is a common electrode, via the lower electrode pad portion 157. Thereby, the displacement efficiency of the piezoelectric element 56 is improved as follows.

  FIG. 7 is a graph showing an example of the relationship between the voltage applied to the piezoelectric element and the amount of displacement. In FIG. 7, the applied voltage is expressed as positive when the potential difference is such that the upper electrode 153> the lower electrode 151. Further, as shown in FIG. 8, the displacement amount is obtained by measuring the displacement amount from the pressurized liquid chamber 14 side with a laser Doppler. In FIG. 7, the displacement indicated by the arrow e uses only the positive voltage as the applied voltage. On the other hand, the displacement indicated by the arrow f in FIG. 7 has the same potential difference as the displacement indicated by the arrow e, but the displacement of the piezoelectric element is better when used from the positive side to the negative side voltage below the coercive electric field. It shows that the amount becomes larger. For this reason, the DC voltage Vdc is applied from the lower electrode 151 to obtain a bias voltage, and the voltage having a pulse shape applied from the upper electrode 153 is used in a range from the positive side to the voltage below the coercive electric field on the negative side. I can do it.

  FIG. 9 is an explanatory diagram of an example of a drive waveform to which a bias voltage is applied. In the present embodiment, the minimum value Vmin of the voltage (V2) that causes the piezoelectric thin film 152 to generate the second electric field with respect to the negative coercive electric field Ec and the bias voltage Vdc have a relationship of Vmin−Vdc> Ec. Just fill it. In this embodiment, the negative coercive electric field (Ec) obtained from the hysteresis curve of the piezoelectric element obtained from FIG. 10 is −4V. For this reason, a pulse-shaped voltage having a minimum value Vmin = 3V is applied from the upper electrode 153, and a DC voltage of Vdc = 6V is applied from the lower electrode 151, so that displacement is performed using a region below the negative coercive electric field. Efficiency can be improved. In this embodiment, the rise time width Tf, the pulse time width Pw, and the fall time Tr are defined by the time based on FIG. In FIG. 9, the rise time width Tf, the pulse time width Pw, and the fall time Tr of the drive waveform use conditions of Tf = 1 μs, Pw = 1.7 μs, and Tr = 1 μs. Note that the interval between the pulse waveforms is appropriately adjusted based on the volume of the droplets to be ejected.

Further, a recovery waveform for recovering the displacement characteristics of the piezoelectric element is applied between the drive waveform and the drive waveform using the drive IC that forms the drive waveform.
FIG. 12 is an explanatory diagram of a drive waveform and a recovery waveform according to the present embodiment. For the driving waveform, a DC voltage Vdc is applied from the lower electrode 151, and the above pulse-shaped voltage is applied from the upper electrode 153. Note that a voltage that generates a first electric field in the piezoelectric thin film in a pulse shape and corresponding to a state in which discharge is not generated is an intermediate potential V1, and a voltage that generates a second electric field that corresponds to a discharge state in the piezoelectric thin film is V2. . Thereby, a desired droplet is discharged.
As a recovery waveform, the DC voltage Vdc is applied as a bias voltage to the lower electrode 151 via the driving IC. At the same time, a voltage having a voltage waveform (V3) that generates a third electric field in the piezoelectric thin film 152 corresponding to a state in which the upper electrode 153 is not discharged, and a voltage having a pulse waveform having a voltage part (V4) smaller than the DC voltage Vdc is applied. To do. In this recovery waveform, a recovery electric field is formed between the lower electrode 151 to which the DC voltage Vdc is applied in the V4 region of the pulse waveform and in the opposite direction to the electric field that causes a lead defect trap formed in the drive waveform. Is done. This reverse electric field can eliminate the trap of lead defects in the PZT piezoelectric thin film 152 at the interface with the lower electrode 151, which is generated by repeatedly forming the drive electric field.

  The minimum value V4 of the pulse waveform applied from the upper electrode 153 as the recovery waveform is the same as the minimum value Vmin of the upper electrode 153 and the pulse waveform V2 applied as the drive waveform with respect to the negative coercive electric field Ec. V4-Vdc> Ec may be satisfied. Note that Vmin, which is the minimum value of V2 of the pulse waveform of the drive waveform, and V4, which is the minimum value of the pulse waveform of the recovery waveform, do not have to be equal.

  However, if a pulse waveform having the same pulse time width Pw as that during driving is simply applied to the upper electrode 153 as a recovery waveform, unnecessary droplets are ejected between the driving waveform. Specifically, when the pulse time width Pw is an integral multiple of the meniscus resonance period or a time of one turn or less, the displacement of the piezoelectric element generated by the recovery waveform excites the meniscus resonance and enters the pressurized liquid chamber 14. Pressure fluctuations for ejecting droplets are caused. In order to prevent unnecessary droplets from being ejected between the drive waveforms, the pulse time width Pw of the recovery waveform is set to a time longer than the meniscus resonance period and other than an integral multiple of the meniscus period. Furthermore, it is preferable to set the pulse time width Pw of the recovery waveform to an anti-integer value multiple that is the antiresonance period of the meniscus resonance period. Thereby, it can be set as the state which does not generate | occur | produce the pressure which discharges a droplet in the pressurized liquid chamber 14 between a drive waveform and a drive waveform.

  Here, the meniscus resonance period is a period unique to the liquid chamber (FIG. 13B) in which the meniscus surface is displaced by vibration in the pressurized liquid chamber 14 as shown in FIG. The waveform of the pulse time width Pw close to the meniscus natural period (time) causes pressure amplification in the pressurized liquid chamber, and pressure fluctuations (rise time Tf, fall time Tr) of a time shorter than the meniscus natural period are also generated. On the other hand, if a pulse voltage having an anti-resonance period of the meniscus resonance period in the pulse time width is applied, the pressure waveform is not generated and the driving waveform is generated. In the state where no pressure is generated between the driving waveform and the driving waveform, the pressure rises when the rise time Tf and the fall time Tr are longer than the meniscus resonance period. There can be no occurrence, a state does not occur the pressure generating such discharges droplets between the drive waveform and the drive waveform.

  In the present embodiment, a recovery waveform that forms an electric field in a direction opposite to the driving electric field is formed using the driving IC for forming a driving waveform that causes the piezoelectric element to eject droplets as described above. The recovery waveform can be realized only by adjusting the minimum value of the pulse waveform applied to the upper electrode 153 and the pulse time width as described above using a drive IC that applies the drive waveform. Further, in the droplet discharge head 51 of the present embodiment, the driving IC outputs a positive voltage, and a pulse waveform voltage is applied to the upper electrode 153 and a DC voltage is applied to the lower electrode 151. I just need it. For this reason, compared with the structure which outputs the pulse waveform of the opposite polarity to a drive waveform, or the structure which reverses the polarity of a drive waveform using a switch, the cost increase of drive IC can be suppressed.

  Next, the recovery waveform formed by using the above driving method will be described in detail based on examples. As a drive waveform, a pulse-shaped voltage having intermediate potentials V1 and V2 is applied to the upper electrode 153 from the drive IC (not shown) via the upper electrode pad portion 158, and the lower electrode is passed through the lower electrode pad portion 157. 151 is applied with a DC voltage Vdc. As a result, a driving waveform having a voltage width of -15 kV / cm that does not exceed the coercive electric field is formed on the positive voltage side and 150 kV / cm that does not exceed the coercive electric field. The description will be made using the electric field strength formed on the piezoelectric thin film 152 below.

<Example 1>
After applying the above drive waveform for 500 ms, a pulse waveform is applied to the upper electrode 153 and a DC voltage Vdc is applied to the lower electrode 151 so that the electric field strength on the positive polarity side is 150 kV / cm, and the electric field strength is -15 kV / cm of reverse polarity. A recovery waveform is applied for 500 ms. A waveform having a combination of the drive waveform and the recovery waveform as one sequence was applied. FIG. 14 is an explanatory diagram of an example of a recovery waveform according to the first embodiment. The rising time Tf, the pulse time width Pw, and the falling time Tr of the recovery waveform pulse waveform are longer than the meniscus resonance period. In the head configuration of the droplet discharge head 51 of this embodiment, since the meniscus resonance period Tc = 3.7 μs, a pulse waveform having a rise time Tf = 25 μs, a pulse width time = 25 μs, and a fall Tr = 25 μs was applied. The voltage V3 of the pulse waveform has an intermediate potential (V3 in FIG. 12) on the positive polarity side, a minimum value (V4 in FIG. 12) is smaller than the DC voltage Vdc, and does not exceed the coercive electric field on the negative polarity side. Vdc> Ec is satisfied. In this example, a pulse waveform that forms a reverse electric field of −15 kV / cm was applied.

<Example 2>
FIG. 15 is an explanatory diagram of a recovery waveform according to the second embodiment. A drive waveform similar to that of Example 1 is applied for 500 ms, and a recovery waveform is obtained by applying a pulse waveform of 200 kV / cm on the positive polarity side and −15 kV / cm on the negative polarity side for 500 ms as one sequence. As in the first embodiment, the recovery waveform has a rising time Tf = 25 μs, a pulse width time = 25 μs, and a falling Tr = 25 μs.

<Example 3>
FIG. 16 is an explanatory diagram of a recovery waveform according to the third embodiment. A drive waveform similar to that of Example 1 is applied for 500 ms, and as a recovery waveform, a pulse waveform of 150 kV / cm on the positive polarity side and −15 kV / cm on the negative polarity side is applied for 100 ms, and then no waveform is applied for 400 ms. One is a sequence. Similar to the first embodiment, the recovery waveform has a rising time Tf = 25 μs, a pulse width time 25 μs, and a falling Tr = 25 μs.

<Example 4>
FIG. 17 is an explanatory diagram of a recovery waveform according to the fourth embodiment. A drive waveform similar to that in Example 1 is applied for 500 ms, no waveform is applied for 400 ms, and then a recovery waveform is applied that is a pulse waveform of 150 kV / cm on the positive polarity side and −15 kV / cm on the negative polarity side for 100 ms. This is a sequence. Similar to the first embodiment, the recovery waveform has a rising time Tf = 25 μs, a pulse width time 25 μs, and a falling Tr = 25 μs.

<Example 5>
FIG. 18 is an explanatory diagram of a recovery waveform according to the fifth embodiment. A drive waveform similar to that of Example 1 is applied for 500 ms, and a recovery waveform having a pulse waveform of 150 kV / cm on the positive polarity side and −15 kV / cm on the negative polarity side is applied for 100 ms, and no waveform is applied for 400 ms. A sequence in which a recovery waveform is applied again for 100 ms is taken as one sequence. Similar to the first embodiment, the recovery waveform has a rising time Tf = 25 μs, a pulse width time 25 μs, and a falling Tr = 25 μs.

<Comparative Example 1>
FIG. 19 is an explanatory diagram of a recovery waveform according to the fifth embodiment. In the same manner as in the first embodiment, the drive waveform is applied for 500 ms, and no waveform is applied for the subsequent 500 ms.

Using the piezoelectric element 56 described above, the waveforms of Examples 1 to 5 and Comparative Example 1 were applied to evaluate the fluctuation of the discharge speed. The change rate of the discharge rate after applying the above waveform was evaluated 10 to ¹⁰ times with the initial discharge rate as a reference. Here, the number of pulses in the recovery waveform is not counted, and only the number of pulses in the drive waveform is counted. FIG. 20 shows the evaluation results of the ejection speed when driven 10 to ¹⁰ times. Table 1 summarizes the rate of change in discharge speed after 10 to ¹⁰ repetitions. Regarding the rate of change, a positive sign indicates that the discharge speed is faster than the initial value, and a negative sign indicates that the discharge speed is slower than the initial discharge speed.

  In all of Examples 1 to 5, the fluctuation range of the discharge speed is within 5%. This shows that the fluctuation of the ejection speed is suppressed because the fluctuation of the displacement of the blocking of the piezoelectric element is suppressed by the recovery waveform by the above driving method. This is because the reverse electric field formed by the recovery waveform eliminates the trap at the interface with the lower electrode 151 of the lead defect in the piezoelectric thin film 152 of PZT, which is generated by repeatedly forming the drive waveform. . Furthermore, since the recovery waveform does not exceed the coercive electric field Ec on the negative polarity side, the polarization state of the piezoelectric thin film 152 does not repeat reversal even if long-term driving is performed. Therefore, the burden on the piezoelectric element 56 is small, and a stable displacement can be obtained, and the problem of an increase in current due to polarization reversal in a coercive electric field can be avoided.

  Since the waveform of the first embodiment has a rise time and a fall time longer than the meniscus natural period, resonance is suppressed, pressure amplification in the liquid chamber is suppressed, and droplet discharge during the recovery operation is suppressed.

  In Example 2, although the electric field strength on the positive side of the recovery waveform is set higher than the electric field strength of the driving waveform, the desired effect is confirmed even when the electric field strength is increased. The electric field strength on the positive side of the recovery waveform is preferably equivalent to the electric field strength formed by the intermediate potential V1 of the drive waveform, and more preferably higher than the intermediate potential. This is to stabilize the deformation of the piezoelectric body within the voltage used in the drive waveform by moving the piezoelectric body with a voltage width equal to or greater than the drive waveform.

  In Examples 3, 4, and 5, the effect can be achieved even when the application time of the recovery waveform is shortened. This is because even if the recovery waveform application time is short, the trapped defects can be eliminated by the drive waveform application time. The application time of the recovery waveform is preferably 100 ms or more. Further, the application timing of the recovery waveform is preferably immediately before or after the drive waveform, and more preferably applied both before and after. This is because the trapped charge associated with the application of the drive waveform is reset, so that the reset effect can be maximized by performing it immediately after or immediately before the drive.

  Further, regarding the shape of the pulse voltage, as in Patent Document 1, the application of only the negative DC voltage did not sufficiently exhibit the effect of the present invention. This is presumably because the application time cannot be sufficiently secured below the coercive electric field, and the charge is excessively accumulated on the electrode surface by direct current alone, and the recovery effect cannot be obtained sufficiently due to the influence. For this reason, it is realized that the electric field is sufficiently applied to the piezoelectric body by making the recovery waveform into a pulse shape.

  In Comparative Example 1, the fluctuation range of the discharge speed is large. This is because, in Comparative Example 1, since no recovery waveform is applied, charges trapped during driving cannot be reset, and the uneven distribution of charges progresses with time.

  Next, an ink jet printer as an image forming apparatus equipped with the droplet discharge head will be described. Inkjet printers have many advantages such as extremely low noise and high-speed printing, and furthermore, low-cost plain paper with a degree of freedom of ink can be used. Therefore, it is widely deployed as an image recording apparatus or an image forming apparatus such as a printer, a facsimile machine, and a copying apparatus.

First, a basic configuration of an ink jet printer (hereinafter referred to as a printer) will be described. 21 is a perspective view of the printer 100, and FIG. 22 is a schematic cross-sectional view including the ink cartridge 102 when viewed from the front side in FIG. 21 in the main scanning direction of the printer 100.
The printer 100 has a printing mechanism 103 that includes a carriage 101, a droplet discharge head 51, and an ink cartridge 102 inside the main body. The carriage 101 is a member that can move in the main scanning direction (the direction of arrow A in FIG. 21 and the direction orthogonal to the paper surface in FIG. 22) that is orthogonal to the transport direction of the paper S within the printer 100 main body. is there. The droplet discharge head 51 is an inkjet head which is an example of a droplet discharge head mounted on the carriage 101, and the ink cartridge 102 supplies ink in the tank unit 102 a to the droplet discharge head 51.

  As illustrated in FIG. 22, the printer 100 includes a paper feed mechanism unit 104 below the print mechanism unit 103. Although details will be described later, the printer 100 takes in the paper S fed from the paper feed tray 230 or the manual feed tray 105 of the paper feed mechanism unit 104 into the apparatus. Then, after a predetermined image is recorded by the printing mechanism unit 103, the image is discharged to a discharge tray 106 mounted on the rear side.

The droplet discharge head 51 is an ink discharge head that discharges yellow (Y), magenta (M), cyan (C), and black (B) ink. The droplet discharge head 51 has a plurality of ink discharge holes (“nozzles 20” described later) arranged in the sub-scanning direction (arrow B direction in the figure) orthogonal to the main scanning direction. The droplet discharge head 51 is mounted on the carriage 101 so that the ink discharge direction is downward.
The carriage 101 of the printing mechanism unit 103 includes four inks containing yellow (Y), magenta (M), cyan (C), and black (B) inks to be supplied to the droplet discharge head 51. Each of the ink cartridges 102 is mounted so as to be replaceable.

Above the tank portion 102a of the ink cartridge 102 (above in FIG. 22), an air port (not shown) communicating with the air is provided. Further, an ink discharge port 102 b that discharges ink in the tank unit 102 a toward the droplet discharge head 51 is provided below the tank unit 102 a. Further, the tank portion 102a has a porous body (not shown) filled with ink, and the ink supplied to the droplet discharge head 51 is slightly negative pressure by the capillary force of the porous body. Is maintained.
As the droplet discharge head 51, the printer 100 is configured to use a plurality of head portions corresponding to each color, but may be a single head portion having nozzles for discharging ink of each color.

  The printing mechanism unit 103 includes a main guide rod 107 and a sub guide rod 108 as guide members horizontally mounted on both side plates (100a and 100b) in the main scanning direction of the main body of the printer 100 as a holding unit that holds the carriage 101. The main guide rod 107 passes through the rear side of the carriage 101 (downstream side in the paper conveyance direction, right side in FIG. 22). The sub guide rod 108 extends in parallel with the main guide rod 107 at a predetermined interval, and the front side of the carriage 101 (upstream side in the sheet conveyance direction, left side in FIG. 22) is placed. The carriage 101 is slidably held by a main guide rod 107 and a sub guide rod 108 so as to be movable in the main scanning direction.

  Further, the printing mechanism unit 103 includes a timing belt 112 as a moving unit for moving and scanning the carriage 101 in the main scanning direction. Further, the printing mechanism 103 includes a driving pulley 110 and a driven pulley 111 that stretch the timing belt 112, and a main scanning motor 109 that rotationally drives the driving pulley 110. As shown in FIG. 21, the driving pulley 110 is arranged on one side plate (100b) side of the printer 100 main body, and the driven pulley 111 is arranged on the other side plate (100a) side of the main body. Extends in parallel with the main scanning direction. A carriage 101 is fixed to the timing belt 112.

  The main scanning motor 109 is a driving source that rotates the driving pulley 110 forward and backward. When the driving pulley 110 rotates, the timing belt 112 moves endlessly in the main scanning direction. Since the carriage 101 is fixed to the timing belt 112, the carriage 101 moves in the main scanning direction together with the timing belt 112. Therefore, the carriage 101 is reciprocated in the main scanning direction by rotating the driving pulley 110 forward and backward by the main scanning motor 109.

The paper feed mechanism unit 104 includes a paper feed tray 230 on which the paper S is stacked, a paper feed roller 113, a friction pad 114, a guide member 115, and a transport roller 116. The sheet feed tray 230 can stack a bundle of a plurality of sheets S from the right side in FIG. 22 and is detachably attached to the printer 100 main body.
The paper feed roller 113 and the friction pad 114 separate and feed the uppermost sheet of the bundle of paper S set in the paper feed tray 230 in order to transport the paper S below the droplet discharge head 51. . The guide member 115 guides the sheet S separated and fed from the sheet feed tray 230 to an area where the sheet is transported by the transport roller 116.

  The paper S fed by the paper feed roller 113 and guided by the guide member 115 is transported to a position facing the lower surface of the droplet discharge head 51 by the transport roller 116 being reversed. A transport roller 117 and a front roller 118 are disposed around the transport roller 116. The conveying roller 117 presses the sheet S against the conveying roller 116 to prevent the sheet S from being separated from the conveying roller 116. The leading end roller 118 feeds the paper S at a predetermined feed angle to a position facing the lower surface of the droplet discharge head 51. The conveyance roller 116 is rotated by a sub-scanning motor 130 via a gear train (not shown), and rotates in the clockwise direction in FIG.

  A printing receiving member 119 is provided at a position facing the lower surface of the droplet discharge head 51. The printing receiving member 119 is a sheet guide member that guides the sheet S fed from the transport roller 116 corresponding to the movement range of the carriage 101 in the main scanning direction on the lower side of the droplet discharge head 51. A post-printing transport roller 120 for sending the paper S in the discharge direction and a post-printing transport spur 121 facing the post-printing transport roller 120 are disposed downstream of the printing receiving member 119 in the paper transport direction. Has been. Further, a paper discharge roller 123 that discharges the paper S sent by the conveying roller 120 after printing to the paper discharge tray 106 and a paper discharge spur 124 that faces the paper discharge roller 123 are provided. In addition, a lower guide member 125 and an upper guide member 126 are disposed between the post-printing conveyance roller 120 and the paper discharge roller 123 as a pair of guide members that form a paper discharge path.

  In addition, the printer 100 is provided with a manual feed tray 105 for manually feeding the paper S. The manual feed tray 105 is attached to the printer 100 main body about the tray opening / closing shaft 105b so that the manual feed tray 105 can be turned over. The paper S placed on the manual feed tray 105 is transported to the transport roller 116 by the manual paper feed roller 105a.

  A recovery device for recovering the ejection failure of the droplet ejection head 51 at a position outside the recording area on the right front side in FIG. 21, which is one end of the movement range of the carriage 101 in the main scanning direction in the printing mechanism unit 103. 127 is arranged. The recovery device 127 includes a capping member, a suction unit, and a cleaning unit. During printing standby, the carriage 101 is moved to the recovery device 127 side (right front side in FIG. 21), and the droplet discharge head 51 is capped by a capping member (not shown). Thereby, the nozzle of the droplet discharge head 51 can be kept in a wet state, and discharge failure due to ink drying can be prevented. Also, by moving the carriage 101 to a position facing the recovery device 127 during recording or the like and discharging ink that is not related to recording, the ink viscosity of all the nozzles is made constant and stable discharge performance is maintained. Can do.

  When a discharge failure occurs, the nozzle on the lower surface of the droplet discharge head 51 is sealed with a capping member, and bubbles and the like are sucked out of the nozzle together with ink through a tube (not shown) provided on the capping member. Further, ink or dust adhering to the head surface (lower surface) where the nozzles are opened is removed by a head surface cleaning means (not shown), and the ejection failure is recovered. The sucked ink is discharged to a waste ink tank (not shown) installed at the lower part of the main body of the printer 100 and absorbed and held by an ink absorber inside the waste ink tank.

Next, the printing operation of the printer 100 will be described.
The printer 100 receives a signal such as image information from an external device such as a personal computer and executes a printing operation. When the printing operation is executed, the paper S is fed from the paper feed tray 230 by the paper feed roller 113 or from the manual feed tray 105 by the manual paper feed roller 105a. The paper S fed from the paper feed tray 230 is guided by the guide member 115 and the transport roller 117, reversed while being transported by the transport roller 116, and transported to a position facing the droplet discharge head 51. On the other hand, the paper S supplied from the manual feed tray 105 is guided to the transport roller 117, transported to the transport roller 116, and transported to a position facing the droplet discharge head 51.

When the sheet S conveyed to a position facing the droplet discharge head 51 reaches a predetermined position, the rotation of the conveyance roller 116 is stopped and the movement of the sheet S is stopped. Then, while the carriage 101 reciprocates in the main scanning direction according to the image signal, a predetermined ink is ejected to a predetermined portion of the stopped paper S, and an image for one line is formed on the paper S. Here, one line means a range in the sub-scanning direction (the moving direction of the sheet S at a position facing the droplet discharging head 51) in which the droplet discharging head 51 can record on the sheet S.
When the image formation for one line in the main scanning direction is completed, the transport roller 116 is rotated for a predetermined time, and the sheet S is moved by one line toward the paper discharge tray 106 and stopped. Then, the carriage 101 forms an image for one line while reciprocating in the main scanning direction according to the image signal.

  Such a process is repeated a predetermined number of times, and a desired image is printed on the paper S. When a recording end signal is received from an external device and a desired image is printed, or when a signal indicating that the trailing edge of the paper S has reached the recording area is received, the paper S is discharged to the paper discharge tray 106. Is done. At this time, the paper S is transported by the post-printing transport roller 120 and post-printing transport spur 121, the paper discharge roller 123 and the paper discharge spur 124, and is discharged to the paper discharge tray 106. When the image formation is completed, the carriage 101 is moved to a position facing the recovery device 127 on the right front side in FIG. 21, and the nozzle of the droplet discharge head 51 is capped with a capping member (not shown).

  As described above, this ink jet printer is equipped with an ink jet head that is driven with a waveform having the drive waveform and the recovery waveform of the first to fifth embodiments. Thereby, stable ink droplet ejection characteristics can be obtained, and the image quality can be improved.

What has been described above is merely an example, and the present invention provides effects specific to each aspect.
(Aspect A)
On a substrate such as the liquid chamber substrate 4 that forms the pressurized liquid chamber 14 that communicates with the nozzle 20, a vibration plate 55 and a perovskite crystal represented by the general formula Pb (Ti _x , Zr _y , M _z ) O _3. A piezoelectric thin film 152 having a structure is laminated with a piezoelectric element 56 sandwiched between a pair of electrodes such as a lower electrode 151 and an upper electrode 153, and an actuator such as a thin film piezo actuator 200 is used. Applying a drive waveform voltage to generate pressure fluctuations for discharging droplets into the pressurized liquid chamber, and suppressing the deterioration of the displacement characteristics of the piezoelectric element between the drive waveform and the next drive waveform This is a method of driving a droplet discharge head that applies a voltage having a recovery waveform. The drive IC outputs a voltage having either positive or negative polarity, applies a pulse-shaped voltage to one of the pair of electrodes, and applies a DC voltage to the other electrode. A voltage portion for generating a first electric field in the piezoelectric thin film corresponding to a state in which the piezoelectric thin film is not discharged; and a voltage portion for generating a second electric field in the piezoelectric thin film corresponding to a state in which discharge is performed; The voltage includes a voltage portion for generating a third electric field in the piezoelectric thin film corresponding to a state in which ejection is not performed, and a DC voltage applied to the other electrode, and the first electric field is a trap for lead defects in the second electric field. And a voltage portion that continues for a predetermined time to generate a recovery electric field in a direction opposite to the electric field that causes the electric field, and the predetermined time is longer than the meniscus resonance period and other than an integral multiple of the meniscus period Is the time.

  In (Aspect A), the driving IC is configured to output a voltage of either positive or negative polarity, and to apply a pulse-shaped voltage to one electrode and a DC voltage to the other electrode. Using this drive IC, a voltage having a recovery waveform that forms an electric field in a direction opposite to the drive electric field is applied between the drive waveform and the drive waveform. Thereby, while suppressing the cost of the driving IC, it is possible to suppress the deterioration of the displacement characteristics with the lapse of time and ensure stable ejection performance.

  At the time of discharging a droplet, a pressure for discharging the droplet into the pressurized liquid chamber by driving the piezoelectric element by applying a voltage having a driving waveform that forms the first electric field and the second electric field to the piezoelectric element. Generate fluctuations. As a recovery waveform, a predetermined electric field that generates a recovery electric field opposite to an electric field that causes a lead defect trap, together with a voltage portion that forms the third electric field on one electrode and a DC voltage applied to the other electrode. A voltage in the form of a pulse having a voltage portion of time duration is applied. An effect of eliminating traps of lead defects that are unevenly distributed at the electrode interface of the piezoelectric thin film can be obtained for a predetermined time in which a recovery electric field opposite to the electric field that causes trapping is formed.

  However, if a voltage having a waveform having a voltage portion that forms the third electric field and a voltage portion that forms the recovery electric field is applied to the piezoelectric element, unnecessary droplets are ejected between the drive waveform and the drive waveform. There is a risk that. This is the case where the duration of the voltage that generates the electric field for recovery is an integral multiple of the meniscus resonance period or a time that is one turn or less. In this case, the displacement of the piezoelectric element generated by the recovery waveform excites the meniscus resonance and causes a pressure fluctuation for discharging the droplet into the pressurized liquid chamber. In order not to cause unnecessary droplet ejection between the drive waveforms, the duration of the voltage for generating the recovery electric field is longer than the meniscus resonance period and a time other than an integral multiple of the meniscus period. To do. As a result, the voltage of the waveform that forms the third electric field and the electric field for recovery is in a state in which no pressure is generated between the driving waveform and the driving waveform such that a droplet is discharged into the pressurized liquid chamber. Can do.

  In the driving method of the present invention, the driving IC outputs a voltage having either positive or negative polarity. By using this drive IC and adjusting the value of the pulse-shaped voltage applied to one electrode and its duration as described above, a recovery electric field can be formed without discharging a droplet. . For this reason, the drive IC is configured to output a positive or negative polarity pulse-shaped voltage in order to form a recovery electric field, or to reverse the polarity of the drive waveform using a switch. Compared to the driving IC, it is greatly suppressed. Thereby, it is possible to secure stable ejection performance at low cost by suppressing the deterioration of the displacement characteristics of the thin film piezoelectric actuator over time.

(Aspect B)
In (Aspect A), the electric field for recovery is less than the coercive electric field of the piezoelectric element. According to this, the polarization state of the piezoelectric thin film does not repeat reversal even if long-term driving is performed. For this reason, the burden placed on the piezoelectric element is small, a stable displacement can be obtained, and the problem of current increase due to polarization reversal in a coercive electric field can be avoided.

(Aspect C)
In (Aspect A) or (Aspect B), a DC voltage is applied to the electrode on the substrate side such as the lower electrode 151 among the pair of electrodes, and the pulse voltage is applied to the opposite electrode such as the upper electrode 153. According to this, it is possible to eliminate the trap of lead defects in the piezoelectric thin film generated at the interface with the electrode on the substrate side by repeatedly forming the drive electric field, and to suppress the deterioration of the displacement characteristics over time.

(Aspect D)
In any one of (Aspect A), (Aspect B), or (Aspect C), the rise time Tf of the voltage of the pulse waveform applied to the other electrode between the drive waveform and the next drive waveform, and the rise The down time Tr is longer than the meniscus resonance period. Pressure fluctuations (rise time Tf, fall time Tr) that are shorter than the meniscus natural period also contribute to the excitation of this vibration and cause pressure amplification. When the rise time Tf and the fall time Tr are shorter than the meniscus natural period, pressure amplification does not occur, and pressure is not generated such that droplets are ejected between the drive waveforms. It can be.

(Aspect E)
In any one of (Aspect A), (Aspect B), (Aspect C), or (Aspect D), the pulse time width Pw of the voltage of the pulse waveform to which a voltage for generating a recovery electric field in the recovery waveform is applied is a The time is a half integer multiple of the meniscus resonance period. According to this, pressure amplification does not occur, and it is possible to achieve a state in which no pressure is generated such that droplets are ejected between the drive waveforms.

(Aspect F)
In any one of (Aspect A), (Aspect B), (Aspect C), (Aspect D) or (Aspect E), a pulse applied to the other electrode between the drive waveform and the next drive waveform. The maximum value V4 of the voltage is not less than the maximum value V1 of the pulse voltage applied to the other electrode as a drive waveform. According to this, by moving the piezoelectric body with a voltage width equal to or greater than the drive waveform, it is possible to stabilize the manner of deformation of the piezoelectric body within the voltage used in the drive waveform.

(Aspect G)
A piezoelectric plate having a perovskite crystal structure represented by a diaphragm 55 and a general formula Pb (Ti _x , Zr _y , M _z ) O ₃ on a liquid chamber substrate 4 forming a pressurized liquid chamber communicating with the nozzle 20. In a droplet discharge head in which a piezoelectric element having a body thin film 152 sandwiched between a pair of electrodes is stacked, the droplet discharge head is driven by the droplet discharge head driving method of any one of (Aspect A) to (Aspect F) Drive IC. According to this, as described in the above-described embodiment, it is possible to ensure stable discharge performance at a low cost by suppressing the deterioration of the displacement characteristics of the thin film piezoelectric actuator over time.

(Aspect H)
In an image forming apparatus that forms an image by adhering droplets ejected by droplet ejecting means to a medium while transporting the medium, a droplet discharge head of (Aspect G) is employed as the droplet ejecting means. According to this, it is possible to provide an image forming apparatus that can obtain a high-quality image at low cost.

DESCRIPTION OF SYMBOLS 1 Actuator board | substrate 2 Nozzle plate 4 Liquid chamber board | substrate 14 Pressurized liquid chamber 18 Common liquid chamber 20 Nozzle 51 Droplet discharge head 55 Vibrating plate 56 Piezoelectric element 151 Lower electrode (electrode on the substrate side)
152 Piezoelectric thin film 153 Upper electrode (surface-side electrode)
154 Wiring member 154a Lower wiring member 154b Upper wiring member 157 Lower electrode pad portion 158 Upper electrode pad portion 100 Printer 200 Thin film piezoelectric actuator

JP 2009-071113 A Japanese Patent No. 4594609 WO2006 / 137528 Japanese Patent No. 3797161

Claims (5)

  General formula Pb (Ti _x , Zr _y , M _z ) O ₃ The piezoelectric film is sandwiched between the first electrode and the second electrode, and is configured to pressurize the pressurized liquid chamber communicating with the nozzle,
  A drive circuit for applying a pulse waveform drive voltage and a pulse waveform recovery voltage to the first electrode, and applying a DC voltage to the second electrode;
  The drive voltage includes a first voltage that generates an electric field in a first direction that causes a trap of lead defects in the piezoelectric film, and an electric field in a second direction that is opposite to the first direction. A second voltage generated in the membrane,
  The recovery voltage includes a third voltage that generates an electric field in the first direction in the piezoelectric film, and a fourth voltage that generates an electric field in the second direction in the piezoelectric film;
  The waveform of the recovery voltage transitions from the third voltage to the fourth voltage, and after the fourth voltage is continued for a first time, from the fourth voltage to the third voltage. Migrate,
  The second voltage lasts for a second time;
  The first time is longer than the second time and is a time other than an integral multiple of the meniscus resonance period in the nozzle,
  At least one of the time for shifting from the third voltage to the fourth voltage and the time for shifting from the fourth voltage to the third voltage is longer than the meniscus resonance period. Liquid discharge head.   The liquid discharge head according to claim 1, wherein an electric field generated by applying the fourth voltage does not exceed a coercive electric field of the piezoelectric element.   3. The liquid ejection head according to claim 1, wherein the first time is an anti-resonance period of a meniscus in the nozzle.   The liquid ejection head according to claim 1, wherein the third voltage is equal to or higher than the first voltage.   The liquid discharge head according to claim 1, 2, 3, or 4,
  An image forming apparatus that discharges liquid from the liquid discharge head while stopping the medium and moving the liquid discharge head.

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