JP6548098B2 - Method of driving liquid ejection head, liquid ejection head and image forming apparatus - Google Patents

Description

  The present invention relates to a method of driving a droplet discharge head, a droplet discharge head adopting this driving method, and an image forming apparatus adopting this droplet discharge head.

  Generally, as an image forming apparatus combining a printer, a fax machine, a copier, a plotter, or a plurality of functions among them, there is, for example, an ink jet recording apparatus provided with a droplet discharge head for discharging ink droplets. In the ink jet recording apparatus, while the medium is being conveyed, ink droplets are adhered to the sheet by the droplet discharge head to perform image formation. 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. Further, the image forming apparatus means an apparatus for forming an image by discharging droplets to a medium such as paper, yarn, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic. And, the image formation is not only applying an image having meaning such as characters and figures to the medium, but also applying an image having no meaning such as a pattern to the medium (simply discharge droplets). Also mean. Further, the ink is not limited to so-called ink, and is not particularly limited as long as it becomes a droplet when discharged, for example, a droplet including DNA sample, resist, pattern material, etc. Used as a generic term.

  A droplet discharge head in an inkjet recording apparatus is a nozzle that discharges ink droplets, and a pressurized liquid chamber in which the nozzle communicates (also referred to as an ink flow path, a pressure chamber, a pressure chamber, a discharge chamber, a liquid chamber, etc.) And pressure generating means for discharging the ink in the pressure liquid chamber. As a pressure generating means, there is a piezo type that discharges ink droplets by displacing a diaphragm using a piezoelectric element disposed on a diaphragm that constitutes one wall surface of a pressurized liquid chamber.

Furthermore, recently, with advances in semiconductor processes and MEMS (Micro Electro Mechanical Systems), a diaphragm forming a thin film piezoelectric actuator (hereinafter referred to as thin film piezo) and a constituent layer of a piezoelectric element on a Si substrate forming a pressurized liquid chamber. It is put to practical use to form thin films directly at high density. The piezoelectric element is composed of a substrate side electrode, a piezoelectric layer, and a surface electrode. As the thin film of the piezoelectric layer, lead zirconate titanate (PZT) or the like represented by a general formula Pb (Ti _x , Zr _y , M _z ) O ₃ having a perovskite crystal structure is used. However, when the drive waveform is repeatedly applied to drive the thin film piezo, the displacement amount with respect to the drive waveform (hereinafter, referred to as displacement characteristic) is lowered, and the discharge characteristic is deteriorated with time.

It has been proposed that the following voltage is applied to recover the displacement characteristic of the thin film piezo in order to recover it.
Patent Document 1 describes that a DC voltage is applied as a recovery waveform between a drive waveform and a drive waveform with a problem of displacement reduction due to the reaction between lead and moisture in a piezoelectric thin film.
Patent Document 2 describes application of a recovery waveform obtained by inverting a drive waveform between a drive waveform and a drive waveform.
Patent Document 3 deals with the problem of displacement reduction due to deformation of the non-active region of the piezoelectric thin film, and by configuring the drive waveform to include a voltage of reverse polarity, the electric field in the reverse direction to the drive electric field for the thin film piezo. What forms is described.

As a result of the research, in the thin film piezo using a piezoelectric thin film such as PZT having a perovskite crystal structure, when the piezoelectric element is continuously applied with a driving electric field in one direction, displacement characteristics due to the following phenomena are It was found that a decline occurred.
The electric field applied to drive the piezoelectric element pulls the lead defect in the PZT toward the electrode on the negative voltage side. The drawn lead defects are localized at the electrode interface by being trapped at the interface with the negative voltage side electrode. The unevenly distributed lead defects generate an internal electric field to lower the effective voltage of the drive waveform, and the displacement characteristics of the thin film piezo are degraded.
Furthermore, the lead defect trap is at a very deep level, and once trapped, it is not easily detrapped, resulting in a nearly irreversible change under normal operating conditions for discharging droplets. That is, the deterioration of the displacement characteristics of the thin film piezo due to the irreversible change of the lead defect trap can not be recovered within the normal use condition, and the deterioration of the displacement characteristics progresses with time.

  The above-mentioned patent document 1 applies a DC voltage between the drive waveform and the drive waveform, with the problem of displacement reduction due to the reaction of lead and moisture of the thin film piezo. In order to eliminate the uneven distribution of the lead defects only by the DC voltage, a considerably long application time is required, and it is difficult to establish as a sequence to be applied between the drive waveform and the drive waveform.

  In Patent Document 3 described above, by including a voltage of reverse polarity in the drive waveform, an electric field in the reverse direction to the drive electric field is formed in the thin film piezo, and the lead defect trap at the interface with the electrode is eliminated. An effect is obtained. However, since a waveform of the opposite polarity to a certain condition having characteristics for suppressing the displacement decrease of the piezoelectric element is introduced in the drive waveform, the drive waveform can be restricted, and stable discharge performance can not be obtained. There is a case.

  In Patent Document 2 described above, after application of a drive voltage, a voltage whose polarity is reversed with the same waveform as the drive voltage is applied. According to this, an electric field in the opposite direction to the drive electric field is formed, and an effect of eliminating the trap of the lead defect at the interface with the electrode can be obtained. However, providing a new power supply that outputs a voltage of the same polarity as the drive voltage and having the opposite polarity results in a significant increase in cost of the drive IC. Further, in Patent Document 2, although the polarity of the drive waveform is inverted using a switch, the cost of the drive IC is also increased by providing the switch. In order to commercialize the droplet discharge head, it is important to suppress the cost increase of the drive IC and to suppress the decrease of the displacement characteristic with time to secure the stable discharge performance, and the cost of the drive IC becomes high. In some cases, it does not hold as a product.

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

In order to achieve the above object, the invention according to claim 1 comprises a piezoelectric element configured to sandwich a piezoelectric body between a first electrode and a second electrode and apply pressure to a liquid chamber communicating with a nozzle. A method of driving a liquid discharge head, comprising: applying a pulse-like discharge waveform voltage and a pulse-like non-discharge waveform voltage to the first electrode; applying a DC voltage to the second electrode; The ejection waveform voltage includes a first voltage higher than the DC voltage and a second voltage lower than the DC voltage and continuing for a first time, and the non-ejection waveform voltage is higher than the DC voltage. And the fourth voltage lower than the DC voltage, the non-ejection waveform voltage is shifted from the third voltage to the fourth voltage, and the fourth voltage is used as a second time. After continuing from the fourth voltage to the third voltage, the second The time is longer than the first time, and at least one of the time of transition from the third voltage to the fourth voltage and the time of transition from the fourth voltage to the third voltage , the rather long than meniscus resonance period in the nozzle, at least one before and immediately after application of the discharge waveform voltage, is characterized in applying the non-discharge waveform voltage.

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

FIG. 2 is a cross-sectional view showing the basic configuration of a thin film piezoelectric actuator in the droplet discharge head of the present embodiment. FIG. 2 is a cross-sectional view showing a basic layer configuration of a thin film piezoelectric actuator. It is a sectional view of a droplet discharge head of this embodiment, and (a) shows a cross direction and (b) shows a nozzle line 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. 6 is a view showing an example of a drive waveform for causing a droplet discharge head to discharge droplets. The graph which shows an example of the relationship between the applied voltage with respect to a piezoelectric element, and a displacement amount. Explanatory drawing of the measuring method of displacement amount. 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, rising time, and falling time. Explanatory drawing of the drive waveform of this embodiment, and a recovery waveform. Explanatory drawing of a meniscus resonance period. FIG. 7 is an explanatory diagram of a recovery waveform according to the first embodiment. FIG. 8 is an explanatory diagram of a recovery waveform according to a second embodiment. 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. FIG. 1 is a perspective view of an inkjet printer of the present embodiment. FIG. 2 is a side view of a mechanical unit of the ink jet printer according to the 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 the basic configuration of a thin film piezoelectric actuator in the droplet discharge head of the present embodiment. The droplet discharge head 51 is formed by laminating the nozzle plate 2, the liquid chamber substrate 4, the diaphragm 55, and the piezoelectric element 56. The nozzle plate 2 is formed with a nozzle 20 for discharging an ink droplet. A pressurized liquid chamber 14 (also referred to as an ink flow path, a pressure chamber, a pressure chamber, a discharge chamber, a liquid chamber, etc.) communicating with the nozzle 20 is formed by the nozzle plate 2, the liquid chamber substrate 4 and the diaphragm 55. It is done. The diaphragm 55 forms one wall surface of the pressure liquid chamber 14.

  The thin film piezo actuator 200 comprises a diaphragm 55 and a piezoelectric element 56. The piezoelectric element 56 has a lower electrode 151 to be a substrate side electrode, a piezoelectric thin film 152, and an upper electrode 153 to be 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 of the diaphragm 55 formed on one surface of the liquid chamber substrate 4 corresponding to the pressurized liquid chamber 14.

  The droplet discharge head 51 is a head that discharges ink droplets from the nozzles 20 by driving the thin film piezo 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 to vibrate the diaphragm 55. It has a function of discharging the ink in the pressurized liquid chamber 14 in the form of droplets from the nozzle 20 in accordance with the vibration of the vibrating plate 55. The illustration and description of the ink supply means for supplying the ink into the pressurizing liquid chamber 14, the flow path of the ink, the fluid resistance and the like are omitted.

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

The following will describe 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 usually, it is preferable to have a thickness of 100 to 600 μm. There are three kinds of plane orientations such as (100), (110) and (111), but (100) and (111) are widely used in the semiconductor industry in general. In the present embodiment, a single crystal substrate mainly having a (100) plane orientation is mainly used.

  In the case of producing the pressurized liquid chamber 14 as shown in FIG. 1, the silicon single crystal substrate is processed using etching. In this case, anisotropic etching is used as the etching method. Is common. Anisotropic etching utilizes the property that etching rates differ 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 as 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 the arrangement density is high while maintaining rigidity. I know that I can do it. In the present embodiment, it is also possible to use a single crystal substrate having a plane orientation of (110). However, in this case, SiO ₂ which is a mask material is also etched, so this area is also used with care.

As shown in FIG. 1, the diaphragm 55 receives a force generated by the piezoelectric element 56 and is deformed and displaced to discharge ink droplets in the pressurized liquid chamber 14. In order to have such a function, the diaphragm 55 preferably has a predetermined strength. The _material, Si, those prepared by SiO _2, Si 3 _{N 4} by CVD and the like. 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 described later, PZT is generally used as the piezoelectric thin film 152. Therefore, as the diaphragm 55, a material having a linear expansion coefficient of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ which is close to the linear expansion coefficient 8 × 10 ⁻⁶ (1 / K) of the piezoelectric thin film 152 is preferable, 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 sputtering method or a spin coater using a Sol-Gel method.

  The film thickness of the diaphragm 55 is preferably 0.1 to 10 μm, and more preferably 0.5 to 3 μm. If it is smaller than this range, processing of the pressurized liquid chamber 14 as shown in FIG. 1 becomes difficult, and if it is larger than this range, the diaphragm 55 becomes difficult to deform and displace, and the discharge of the ink droplet becomes unstable.

Conventionally, platinum having high heat resistance and low reactivity has been used as the metal material for the lower electrode 151 and the upper electrode 153. However, it may not be said that it has sufficient barrier properties to lead, and platinum group elements such as iridium and platinum-rhodium, and alloy films of these metals may also be mentioned. When using platinum, it is necessary to laminate Ti, TiO ₂ , Ta, Ta ₂ O ₅ , Ta ₃ N ₅ or the like as the adhesion layer first because the adhesion to the base (especially SiO ₂ ) is poor. Is preferred. As a manufacturing method, vacuum deposition such as sputtering or vacuum deposition is generally used. The film thickness is preferably 0.05 to 1 μm, and more preferably 0.1 to 0.5 μm.

In addition, the conductivity of the lower electrode 151 and the piezoelectric thin film 152, and between the piezoelectric thin film 152 and the upper electrode 153, such as SrRuO ₃ , LaNiO ₃ or the like, from the concern over the time-dependent fatigue characteristics of the displacement of the piezoelectric thin film 152 It is preferable to stack an oxide as an electrode portion.

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 its characteristics differ depending on the ratio. The composition showing generally excellent piezoelectric properties is a ratio of PbZrO ₃ to PbTiO ₃ of 53:47, and the chemical formula shows Pb (Zr 0.53, Ti 0.47) O ₃ , generally PZT (53/47). PZT etc. indicated as 47) can be used.

  The piezoelectric thin film 152 can be produced by, for example, a spin coater using 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 prepared by the Sol-Gel method, a PZT precursor solution can be prepared by using lead acetate, zirconium alkoxide, titanium alkoxide compound as a starting material and dissolving in methoxyethanol as a common solvent to obtain a uniform solution . Since metal alkoxide compounds are easily hydrolyzed by moisture in the air, an appropriate amount of acetylacetone, acetic acid, diethanolamine or the like may be added as a stabilizer to the precursor solution.

  When a PZT film is obtained on the entire surface of the diaphragm 55, a coating film is formed by a solution coating method such as spin coating, and obtained by performing each heat treatment of solvent drying, thermal decomposition, and crystallization. Since transformation from a coating film to a crystallized film is accompanied by volume contraction, adjustment of the precursor concentration is required to obtain a film thickness of 100 nm or less in one process in order to obtain a film free from cracks.

  The 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, sufficient displacement can not be generated, and if it is larger than this range, many layers are stacked, so the number of steps increases and the process time becomes long.

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

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

  The piezoelectric element 56 has a multilayer structure of a platinum film to be the lower electrode 151, a PZT (lead zirconate titanate) film to be the piezoelectric thin film 152, and a platinum film to be the upper electrode 153 laminated on the diaphragm 55. It is made of 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 the silicon substrate.

  The liquid chamber substrate 4 is provided with a wiring member 154 for applying a potential to each of the lower electrode 151 and the upper electrode 153. As the wiring member 154, a lower wiring member 154a electrically connecting the lower electrode pad portion 157 to the lower electrode 151 and an upper wiring member 154b electrically connecting the upper electrode pad portion 158 to the upper electrode 153 are provided. ing. The liquid chamber substrate 4 further includes an interlayer insulating film 155 disposed between the lower electrode 151 and the upper electrode 153 and the wiring member 154. Furthermore, 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 an 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 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 with the external space. .

The protective substrate 3 is a substrate for forming the piezoelectric element protective 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 protection and displacement of the piezoelectric element 56. Further, in order to increase the rigidity of the liquid chamber partition 4 a of the liquid chamber substrate 4, a reinforcing wall 23 is formed which reinforces the liquid chamber partition 4 a via the diaphragm 55. The reinforcing wall 23 supports the entire pressurized liquid chamber 14 formed by the liquid chamber partition 4 a by reinforcing the liquid chamber partition 4 a.
Further, the diaphragm 55 is provided with an individual supply port 60 at a portion serving as a flow path for supplying the ink from the common liquid chamber 18 formed in the protective substrate 3 to the pressurized liquid chamber 14 formed in the liquid chamber substrate 4. It is done. The thin film piezo actuator 200 is formed on the liquid chamber substrate 4, and the substrate bonded with the protective substrate is called an actuator substrate 1.

Next, a method of manufacturing the droplet discharge head 51 of the present embodiment will be described with reference to FIGS. 4 and 5 which are process sectional views showing manufacturing steps. In this manufacturing method, the thin film piezoelectric actuator 200 is formed by depositing the material of the diaphragm 55 and the material of the piezoelectric element 56 on the silicon substrate which is the liquid chamber substrate 4.
First, as shown in FIG. 4A, a silicon oxide film with 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) with a thickness of 400 μm. A silicon-on-insulator substrate is used. A silicon oxide film is formed to a thickness of 0.3 μm on the surface of the SOI substrate by a wet 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 to a film thickness of 0.2 μm by sputtering, and is patterned to be in the state shown in FIG. 4B. Further, a piezoelectric thin film 152 is formed to a thickness of 2 μm by a sol-gel method, and an upper platinum layer to be an upper electrode 153 is further formed to a thickness of 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. 4 (c) is obtained.

Next, an insulator layer to be the interlayer insulating film 155 is formed to a thickness of 0.3 μm by plasma CVD, and an opening 155c is formed in the upper part of the piezoelectric element 56 by lithography. Further, in the interlayer insulating film 155, the upper conduction portion 155b, the lower conduction portion 155a and the through portion 155d are formed by patterning. As a result, the state shown in FIG. 4 (d) is obtained.
The upper conductive portion 155b shown in FIG. 4D is a conductive portion between the upper wiring member 154b and the upper electrode 153 to be formed next, and the lower conductive portion 155a is a lower wiring member 154a and a lower electrode 151 to be formed next. It is a conduction part of The penetrating portion 155 d is an opening serving as an ink supply hole from the common liquid chamber 18 to each of the individual ink supply chambers 24.

  Further, by forming a layer to be the wiring member 154 such as the upper wiring member 154 b and the lower wiring member 154 a by an aluminum material, the state shown in FIG. 4E is obtained. The upper wiring member 154 b formed by the wiring member 154 receives stress due to the vibration of the diaphragm 55 by the drive of the piezoelectric element 56. Therefore, a soft conductive material (aluminum in the present embodiment) is used as the wiring member 154 so that the upper wiring member 154b is not broken by the vibration of the diaphragm 55, and the wiring layer 154 is formed with a thick layer thickness of about 1 μm. It is done.

  Next, as a passivation film 156 for protecting the wiring member 154, a silicon nitride film is formed to a thickness of 2 μm by plasma CVD and patterned. Then, the portion to be the individual supply port 60 of the diaphragm 55 is etched in advance. As a result, the state shown in FIG. 4 (f) is obtained.

Next, gold is laminated by a plating method to simultaneously form the upper electrode pad portion 158 and the lower electrode pad portion 157, whereby the state shown in FIG. 5A is obtained. The upper electrode pad portion 158 is connected to the upper electrode 153 by the upper wiring member 154 b. The lower electrode pad portion 157 is connected to the lower electrode 151 by the lower wiring member 154a. By thus forming the upper electrode pad portion 158 and the lower electrode pad portion 157 with gold, electrical connection with a drive IC (not shown) can be connected by low temperature wire bonding. Further, gold has a low resistance value, and the effect of lowering the resistance values of the upper electrode 153 and the lower electrode 151 is large.
The lower electrode pad portion 157 may be formed separately from the upper electrode pad portion 158. Moreover, as a material of the upper electrode pad part 158 and the lower electrode pad part 157, not only gold but copper, aluminum, etc. can also be used. However, when a material other than gold is used, a protective layer may be required to protect against corrosion for the upper electrode pad portion 158 whose surface is not covered with another layer.

Further, separately from the film formation and the like on the liquid chamber substrate 4 described above, a protective substrate 3 in which a pillar is formed on a glass substrate by blast processing is created. Then, after the upper electrode pad portion 158 and the lower electrode pad portion 157 are formed, bonding is made to the passivation film 156 side with the diaphragm 55 of the portion to be the liquid chamber substrate 4 interposed therebetween. As a result, the state shown in FIG. 5 (b) is obtained.
Further, the surface of the liquid chamber substrate 4 on the opposite side to the side where the protective substrate 3 is joined with the diaphragm 55 in the portion to be the liquid chamber substrate 4 is polished until the liquid chamber substrate 4 has a desired thickness.
The protective substrate 3 may be a plate member made of silicon and a recessed portion processed by etching using photolithography, and a plate member made of <100> silicon is wet etched using an alkaline etching solution such as TMAH or KOH. It may be processed.
In addition, molded parts such as resin molds and metal injection molds may be used. Further, when integrally forming the drive IC on the actuator substrate, the oxide film formed by the pyro oxidation method is formed by the LOCOS oxidation method, and the formation region of the oxide film is selected to form the drive IC on the same substrate. You can also

  After the liquid chamber substrate 4 is polished to a desired thickness from the state shown in FIG. 5B, ICP (Inductively Coupled Plasma) dry is applied to the surface of the liquid chamber substrate 4 opposite to the diaphragm 55. Do the etching. By ICP dry etching, concave portions to be the pressure liquid chamber 14, the fluid resistance portion 15, and the individual ink supply chamber 24 are formed. As a result, the state shown in FIG. 5 (c) is obtained.

  After the liquid chamber substrate 4 is formed, the separately formed nozzle plate 2 is adhered to the liquid chamber partition wall forming surface of the liquid chamber substrate 4 to obtain the state of 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 bonding the nozzle plate 2 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 drive IC (not shown). Thus, the main part of the droplet discharge head 51 is completed.

Next, a driving method which is a feature of the droplet discharge head 51 of the present embodiment will be described.
FIG. 6 is an explanatory view of a drive waveform for discharging a droplet by the droplet discharge head. As a drive waveform, a voltage portion (V1) causing the piezoelectric thin film 152 to generate a first electric field corresponding to a non-ejection state, and a voltage portion (V2) generating a second electric field corresponding to the ejection state to the piezoelectric thin film 152 And applying a pulse-shaped voltage having Specifically, as shown in FIG. 6, by combining and using a plurality of pulse waveforms different in the potential of the second electric field corresponding to the state to be discharged, the volume of the droplet to be discharged can be large drop, middle drop, Control like a drop. In FIG. 6, d represents a minute vibration waveform for preventing the drying of the meniscus.

  Further, in the present embodiment, when applying a drive waveform to the piezoelectric element 56 from a drive IC (not shown), the pulse shape is generated based on the drive signal via the upper electrode pad portion 158 to the upper electrode 153 which is an individual electrode. Apply a voltage of At the same time, a driving method is used in which a 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. Thus, 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. Note that, in FIG. 7, the applied voltage is represented as positive when the relationship of the potential difference is the upper electrode 153> the lower electrode 151. In addition, as the displacement amount, as shown in FIG. 8, the result of measuring the displacement amount from the pressurized liquid chamber 14 side by laser Doppler is used. In the displacement shown by the arrow e in FIG. 7, only the positive voltage is used as the applied voltage. On the other hand, the displacement indicated by the arrow f in FIG. 7 provides the same potential difference as the displacement indicated by the arrow e, but the displacement from the positive side to the negative side equal to or less than the coercive electric field causes displacement of the piezoelectric element. It shows that the amount will increase. Therefore, by applying a DC voltage Vdc from the lower electrode 151 to make it a bias voltage, a voltage having a pulse shape applied from the upper electrode 153 can be used in a range from positive to negative coercive electric field. I am able to 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 generates the second electric field in the piezoelectric thin film 152 with respect to the coercive electric field Ec on the negative side and the bias voltage Vdc have a relationship of Vmin-Vdc> Ec. It should be satisfied. In the present embodiment, the coercive electric field (Ec) on the negative side obtained from the hysteresis curve of the piezoelectric element obtained from FIG. 10 is −4V. Therefore, by applying a pulse-shaped voltage of minimum value Vmin = 3 V from the upper electrode 153 and applying a DC voltage of Vdc = 6 V from the lower electrode 151, displacement is performed using a region lower than the coercive electric field on the negative side. Efficiency can be improved. The rise time width Tf, the pulse time width Pw, and the fall time Tr in the present embodiment are defined by the time based on FIG. In FIG. 9, for the rise time width Tf, the pulse time width Pw, and the fall time Tr of the drive waveform, the conditions of Tf = 1 μs, Pw = 1.7 μs, and Tr = 1 μs are used. The interval between the pulse waveform and the pulse waveform is appropriately adjusted based on the volume and the like of the droplet to be ejected.

Furthermore, a recovery waveform for recovering the displacement characteristic of the piezoelectric element is applied between the drive waveform and the drive waveform using a drive IC that forms this drive waveform.
FIG. 12 is an explanatory diagram of drive waveforms and recovery waveforms according to the present embodiment. The driving waveform applies a DC voltage Vdc from the lower electrode 151 and applies the above-described pulse shape voltage from the upper electrode 153. In the pulse shape, the voltage causing the piezoelectric thin film to generate the first electric field corresponding to the non-ejection state is the intermediate potential V1, and the voltage causing the piezoelectric thin film to generate the second electric field corresponding to the ejection state is V2. . Thereby, desired droplets are discharged.
Further, as the recovery waveform, the DC voltage Vdc is applied as a bias voltage to the lower electrode 151 via the drive IC. At the same time, a voltage having a pulse waveform having a voltage portion (V3) for causing the piezoelectric thin film 152 to generate a third electric field corresponding to a state not discharged from the upper electrode 153 and a voltage portion (V4) smaller than the DC voltage Vdc is applied. 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 a recovery electric field opposite to the electric field causing traps of lead defects formed in the drive waveform. Be done. With this reverse electric field, it is possible to eliminate the trap of the lead defect 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 pulse waveform V2 applied as the drive waveform with respect to the negative coercive electric field Ec. , V4-Vdc> Ec. The minimum value Vmin of V2 of the pulse waveform of the drive waveform and the minimum value V4 of the pulse waveform of the recovery waveform do not have to be equal.

  However, when a pulse waveform having the same pulse time width Pw as that for driving is simply applied to the upper electrode 153 as a recovery waveform, unnecessary droplets are ejected between the driving waveform and the driving waveform. Specifically, when the pulse time width Pw is a time equal to or less than an integral multiple of the meniscus resonance period, the displacement of the piezoelectric element generated by the recovery waveform excites the meniscus resonance to enter the pressurized liquid chamber 14. It causes pressure fluctuation for discharging the droplets. In order to prevent unnecessary droplet ejection between the drive waveform and the drive waveform, 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 antiinteger multiple that is the anti-resonance period of the meniscus resonance period. As a result, it is possible to prevent pressure generation such as discharging droplets into the pressurized liquid chamber 14 between the drive waveform and the drive waveform.

  Here, as shown in FIG. 13A, the meniscus resonance period is a period unique to the liquid chamber (FIG. 13B) in which the meniscus surface is displaced by the vibration in the pressurized liquid chamber. The waveform having a pulse duration Pw close to the meniscus intrinsic period (time) generates pressure amplification in the pressurized liquid chamber. In addition, pressure fluctuation (rise time Tf, fall time Tr) in a time shorter than the meniscus inherent period also contributes to the excitation of this vibration, which causes pressure amplification. On the other hand, when a pulse voltage having an anti-resonance period of the meniscus resonance period as a pulse time width is applied, pressure amplification does not occur, and pressure generation does not occur such as discharging a droplet between drive waveforms. It can be in the state. Furthermore, if the rise time Tf and the fall time Tr are made longer than the meniscus resonance period, pressure amplification does not occur, and pressure generation does not occur such as discharging a droplet between the drive waveform and the drive waveform. can do.

  In the present embodiment, using the drive IC for forming the drive waveform for causing the piezoelectric element to discharge droplets as described above, a recovery waveform for forming an electric field in the reverse direction to the drive electric field is formed. 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 for applying a drive waveform. Further, in the droplet discharge head 51 of the present embodiment, the drive IC outputs a positive voltage, and applies a pulse waveform voltage to the upper electrode 153 and applies a DC voltage to the lower electrode 151. It is good if it is. Therefore, the cost increase of the drive IC can be suppressed as compared with a configuration in which a pulse waveform of the opposite polarity to the drive waveform is output or a configuration in which the polarity of the drive waveform is inverted using a switch.

  Next, a recovery waveform formed by using the above driving method will be described in detail based on the embodiment. 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) through the upper electrode pad portion 158, and the lower electrode is formed via the lower electrode pad portion 157. A direct current voltage Vdc is applied to 151. As a result, a drive waveform having a voltage width of 150 kV / cm in which the positive voltage side exceeds the coercive electric field and a voltage width of -15 kV / cm in which the negative polarity side does not exceed the coercive electric field is formed. The description will be made using the electric field strength formed in the following piezoelectric thin film 152.

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 of reverse polarity -15 kV / cm. Apply 500 ms of recovery waveform. A waveform was applied in which the combination of the drive waveform and the recovery waveform was one sequence. FIG. 14 is an explanatory diagram of an example of a recovery waveform according to the first embodiment. The rise time Tf, the pulse time width Pw, and the fall time Tr of the pulse waveform of the recovery waveform are longer than the meniscus resonance period. In the head configuration of the droplet discharge head 51 of the present embodiment, since the meniscus resonance period Tc = 3.7 μs, a pulse waveform with a rise time Tf = 25 μs, a pulse width time = 25 μs, and a fall Tr = 25 μs is applied. The voltage V3 of the pulse waveform is V4- so that the positive polarity side is an intermediate potential (V3 in FIG. 12) and the 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. It satisfies Vdc> Ec. In the present embodiment, a pulse waveform forming 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 the first embodiment is applied for 500 ms, and a recovery waveform of a pulse waveform of 200 kV / cm on the positive side and -15 kV / cm on the negative side is applied for one cycle. The pulse waveform of the recovery waveform is the rise time Tf = 25 μs, the pulse width time = 25 μs, and the fall Tr = 25 μs, as in the first embodiment.

Example 3
FIG. 16 is an explanatory diagram of a recovery waveform according to the third embodiment. Apply the same drive waveform as in Example 1 for 500 ms, apply 100 ms as a recovery waveform, and apply a pulse waveform of 150 kV / cm on the positive side and -15 kV / cm on the negative side, then do not apply the waveform for 400 ms. Let things be one sequence. The pulse waveform of the recovery waveform is the rise time Tf = 25 μs, the pulse width time 25 μs, and the fall Tr = 25 μs, as in the first embodiment.

Example 4
FIG. 17 is an explanatory diagram of a recovery waveform according to the fourth embodiment. The same drive waveform as in Example 1 is applied for 500 ms, no waveform is applied for 400 ms, and then a recovery waveform is applied for 100 ms with a pulse waveform of 150 kV / cm on the positive side and -15 kV / cm on the negative side. The one that has been made into one sequence. The pulse waveform of the recovery waveform is the rise time Tf = 25 μs, the pulse width time 25 μs, and the fall Tr = 25 μs, as in the first embodiment.

Example 5
FIG. 18 is an explanatory diagram of a recovery waveform according to the fifth embodiment. Apply the same drive waveform as in Example 1 for 500 ms, apply 100 ms as the recovery waveform for 150 kV / cm on the positive side and -15 kV / cm for the negative side, and apply no waveform for 400 ms. The application of the recovery waveform for 100 ms again is regarded as one sequence. The pulse waveform of the recovery waveform is the rise time Tf = 25 μs, the pulse width time 25 μs, and the fall Tr = 25 μs, as in the first embodiment.

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.

The waveforms of Examples 1 to 5 and Comparative Example 1 were applied using the piezoelectric element 56 described above, and the fluctuation of the ejection speed was evaluated. The rate of change of the discharge speed after applying the above waveform was evaluated 10 ¹⁰ times, based on the initial discharge speed as a reference. Here, the number of pulses of the recovery waveform is not counted, and only the number of pulses of the drive waveform is counted. FIG. 20 shows the evaluation results of the ejection speed after 10 ¹⁰ times of driving. In addition, Table 1 summarizes the change rate of the discharge speed after repeating 10 ¹⁰ times. The change rate has a positive sign when the discharge speed is higher than that at the initial stage, and a negative sign is a state where the discharge speed is slower than the initial discharge speed.

  In Examples 1 to 5, the fluctuation range of the discharge speed is all within 5%. It can be understood 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 driving method. This is because the reverse electric field formed by the recovery waveform removes the trap at the interface between the lower electrode 151 and the lead defect in the PZT piezoelectric thin film 152 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 inversion even if long-term driving is performed. Therefore, the load applied to the piezoelectric element 56 is small, and a stable displacement can be obtained, and the problem such as an increase in current accompanying polarization inversion in the coercive electric field can also be avoided.

  In the waveform of the first embodiment, since the rise time and the fall time are longer than the meniscus intrinsic period, the resonance is suppressed, the pressure amplification in the liquid chamber is suppressed, and the discharge of the droplet during the recovery operation is suppressed.

  In Example 2, although the electric field strength on the positive side of the recovery waveform is made higher than the electric field strength of the drive waveform, it is confirmed that the required effect is obtained even if 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 move the piezoelectric body with a voltage width equal to or greater than the drive waveform, thereby stabilizing the deformation of the piezoelectric body within the voltage used for the drive waveform.

  In Examples 3, 4 and 5, the effect is achieved even if the application time of the recovery waveform is shortened. This is because even if the application time of the recovery waveform is short, the defect trapped by the application time of the drive waveform can be eliminated. 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 immediately after the drive waveform, and more preferably both before and after. This is because, since the trapped charges accompanying the application of the drive waveform are reset, the effect of the reset can be maximized by performing immediately after or immediately before the drive.

  Further, with regard to the shape of the pulse voltage, in the case where only the negative DC voltage is applied as in Patent Document 1, the effect as in the present invention is not sufficiently exhibited. This is considered to be because the application time can not be sufficiently secured below the coercive electric field, and the electric charge is accumulated excessively on the electrode surface only by direct current, and the recovery effect can not be sufficiently obtained due to the effect. Therefore, by applying a pulse shape to the recovery waveform, it is realized that the electric field is sufficiently applied to the piezoelectric body.

  In Comparative Example 1, the fluctuation range of the discharge speed is large. In Comparative Example 1, since the recovery waveform is not applied, the charge trapped during driving can not be reset, and therefore, uneven distribution of charge progresses with time.

  Next, an ink jet printer as an image forming apparatus having the droplet discharge head mounted thereon will be described. The ink jet printer has many advantages such as extremely low noise and high speed printing, as well as the ability to use inexpensive plain paper with freedom of ink. Therefore, it is widely developed as an image recording apparatus or an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

First, the 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 in a cross section including the ink cartridge 102 as viewed from the front side in FIG. 21 in the main scanning direction of the printer 100.
The printer 100 has a printing mechanism unit 103 including a carriage 101, a droplet discharge head 51, and an ink cartridge 102 inside the main body. The carriage 101 is a member movable in the main scanning direction (direction of arrow A in FIG. 21, a direction orthogonal to the paper surface in FIG. 22) which is a direction orthogonal to the conveyance direction of the sheet S inside the printer 100 main body. is there. The droplet discharge head 51 is an inkjet head which is an example of the droplet discharge head mounted on the carriage 101, and the ink cartridge 102 supplies the ink in the tank portion 102 a to the droplet discharge head 51.

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

The droplet discharge head 51 is an ink discharge head that discharges ink of each color of yellow (Y), magenta (M), cyan (C), and black (B). The droplet discharge head 51 has a plurality of ink discharge holes ("nozzles 20" described later) arrayed 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 discharge direction of the ink is downward.
The carriage 101 of the printing mechanism unit 103 contains four inks for each color of yellow (Y), magenta (M), cyan (C), and black (B) to be supplied to the droplet discharge head 51. The ink cartridges 102 are mounted replaceably.

An atmosphere port (not shown) communicating with the atmosphere is provided above the tank portion 102 a of the ink cartridge 102 (the upper side in FIG. 22). Further, below the tank portion 102a, an ink discharge port 102b for discharging the ink in the tank portion 102a toward the droplet discharge head 51 is provided. Furthermore, the inside of the tank portion 102a has a porous body (not shown) filled with ink, and the ink supplied to the droplet discharge head 51 by the capillary force of the porous body is reduced to a slight negative pressure. I keep it.
Although the printer 100 is configured to use a plurality of head units corresponding to each color as the droplet discharge head 51, it may be a single head unit having nozzles for discharging ink of each color.

  The printing mechanism section 103 has a main guide rod 107 and a secondary guide rod 108 as a guide member which is laid across the side plates (100a and 100b) in the main scanning direction of the printer 100 as holding means for holding the carriage 101. The main guide rod 107 penetrates the rear side of the carriage 101 (downstream side in the sheet conveyance direction, right side in FIG. 22). Further, the secondary guide rod 108 extends in parallel with the main guide rod 107 at a constant distance, and the front side of the carriage 101 (upstream side in the sheet conveyance direction, the left side in FIG. 22) is placed. The carriage 101 is slidably held movably in the main scanning direction by the main guide rod 107 and the sub guide rod 108.

  The printing mechanism unit 103 also has a timing belt 112 as a moving unit for moving and scanning the carriage 101 in the main scanning direction. Further, the printing mechanism section 103 has a drive pulley 110 and a driven pulley 111 for stretching the timing belt 112, and a main scanning motor 109 for rotating the drive pulley 110. As shown in FIG. 21, the driving pulley 110 is disposed on one side plate (100b) side of the main body of the printer 100, and the driven pulley 111 is disposed on the other side plate (100a) side of the main body. Extends parallel to the main scanning direction. Further, a carriage 101 is fixed to the timing belt 112.

  The main scanning motor 109 is a drive source for rotating the driving pulley 110 forward and reverse. When the driving pulley 110 rotates, the timing belt 112 endlessly moves along the main scanning direction. Since the carriage 101 is fixed to the timing belt 112, it moves in the main scanning direction together with the timing belt 112. For this reason, the carriage 101 is reciprocated in the main scanning direction by rotating the drive pulley 110 in the forward and reverse directions by the main scanning motor 109.

The sheet feeding mechanism unit 104 includes a sheet feeding tray 230 on which sheets S are stacked, a sheet feeding roller 113, a friction pad 114, a guide member 115, and a conveying roller 116. The sheet feeding tray 230 can load a bundle of a plurality of sheets S from the right side in FIG. 22 and is detachably mounted to the printer 100 main body.
The sheet feed roller 113 and the friction pad 114 separate and feed one of the uppermost sheets of the bundle of sheets S set in the sheet feed tray 230 in order to convey the sheet S to the lower side of the droplet discharge head 51. . The guide member 115 guides the sheet S separated and fed from the sheet feeding tray 230 to an area conveyed by the conveyance roller 116.

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

  A printing receiving member 119 is provided at a position facing the lower surface of the droplet discharge head 51. The print receiving member 119 is a sheet guide member for guiding the sheet S delivered from the transport roller 116 corresponding to the movement range of the carriage 101 in the main scanning direction below the droplet discharge head 51. On the downstream side of the print receiving member 119 in the sheet conveyance direction, a post-printing transport roller 120 for delivering the sheet S in the discharge direction and a post-printing transport spur 121 facing the post-printing transport roller 120 are disposed. It is done. Furthermore, the sheet ejection roller 123 for ejecting the sheet S fed by the conveyance roller 120 after printing onto the sheet ejection tray 106 and the sheet ejection spur 124 opposed to the sheet ejection roller 123 are provided. 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 forming a paper discharge path.

  Further, the printer 100 is provided with a manual feed tray 105 for manually feeding the sheet S. The manual feed tray 105 is attached to the main body of the printer 100 so as to be able to open and fold around the tray opening and closing shaft 105b. The sheet S placed on the manual feed tray 105 is conveyed to the conveyance roller 116 by the manual feed roller 105 a.

  A recovery device for recovering a discharge failure of the droplet discharge head 51 at a position outside the recording area on the right front side in FIG. 21, which is one end of the moving range of the carriage 101 in the main scanning direction in the printing mechanism unit 103 I have placed 127. The recovery device 127 has a capping member, suction means and cleaning means. 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). As a result, the nozzles of the droplet discharge head 51 can be kept wet, and discharge failure due to ink drying can be prevented. In addition, by moving the carriage 101 to a position facing the recovery device 127 during recording, etc., and discharging ink not related to recording, the ink viscosity of all the nozzles is made constant, and stable discharge performance is maintained. Can.

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

Next, the print 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 performed, the sheet S is fed from the sheet feeding tray 230 by the sheet feeding roller 113 or from the manual feeding tray 105 by the manual sheet feeding roller 105 a. The sheet S fed from the sheet feed tray 230 is guided by the guide member 115 and the conveyance roller 117, is conveyed to the conveyance roller 116 while being inverted, and is conveyed to a position facing the droplet discharge head 51. On the other hand, the sheet S supplied from the manual feed tray 105 is guided by the conveyance roller 117, conveyed by the conveyance roller 116, and conveyed to a position facing the droplet discharge head 51.

When the sheet S conveyed to the 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 discharged to a predetermined position of the stopped sheet S, and an image of one line is formed on the sheet 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 discharge head 51) in which the droplet discharge head 51 can record on the sheet S.
When the image formation for one line in the main scanning direction is completed, the conveyance roller 116 is rotated for a predetermined time to move the sheet S by one line toward the discharge tray 106 and to stop. Then, the carriage 101 reciprocates in the main scanning direction according to the image signal to form an image of one line.

  Such a process is repeated a predetermined number of times, and a desired image is printed on the sheet S. When a desired image is printed by receiving a recording end signal from an external device, or when receiving a signal that the trailing edge of the sheet S has reached the recording area, the sheet S is discharged to the discharge tray 106. Be done. At this time, the sheet S is conveyed by the conveyance roller 120 after printing, the conveyance spur 121 after printing, the discharge roller 123 and the discharge spur 124, and is discharged to the 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 by a capping member (not shown).

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

What has been described above is an example, and the present invention has the following specific effects.
(Aspect A)
A perovskite-type crystal represented by a diaphragm 55 and a general formula Pb (Ti _x , Zr _y , M _z ) O ₃ on a substrate such as a liquid chamber substrate 4 forming a pressurized liquid chamber 14 communicated with the nozzle 20 An actuator such as a thin film piezoelectric actuator 200 formed by laminating a piezoelectric element 56 in which a piezoelectric thin film 152 having a structure is sandwiched between a pair of electrodes such as a lower electrode 151 and an upper electrode 153 is used. A voltage of a drive waveform for generating pressure fluctuation for discharging a droplet into the pressurized liquid chamber is applied, and a decrease in displacement characteristics of the piezoelectric element between the drive waveform and the next drive waveform is suppressed. This is a method of driving a droplet discharge head which applies a voltage of a recovery waveform. The driving 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, and the driving waveform is A voltage portion for generating a first electric field corresponding to the non-ejection state to the piezoelectric thin film and a voltage portion for generating a second electric field corresponding to the ejection state to the piezoelectric thin film The voltage generates a third electric field in the piezoelectric thin film corresponding to the non-ejecting state, and the DC voltage applied to the other electrode, and the first electric field is a trap of a lead defect in the second electric field. And a voltage portion for a predetermined time duration for generating in the piezoelectric thin film a recovery electric field reverse to the electric field for generating 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 drive IC outputs a voltage of either positive or negative polarity, and applies a pulse-shaped voltage to one electrode and a DC voltage to the other electrode. Using this drive IC, a voltage of a recovery waveform that forms an electric field reverse to the drive electric field is applied between the drive waveform and the drive waveform. As a result, while suppressing the cost of the drive IC, a decrease in displacement characteristics over time is suppressed, and stable discharge performance is ensured.

  At the time of droplet discharge, a voltage for driving the piezoelectric element is driven by applying a voltage of a drive waveform that forms the first electric field and the second electric field to the piezoelectric element, and a pressure for discharging the liquid droplet into the pressurized liquid chamber Generate fluctuations. As a recovery waveform, a voltage portion for forming the third electric field and a DC voltage applied to the other electrode are generated in one of the electrodes to generate a recovery electric field reverse to the electric field causing the lead defect trap. Applying a pulse-shaped voltage having a time-continuous voltage portion. In the predetermined time in which the recovery electric field reverse to the electric field causing the trap is formed, the effect of eliminating the lead defect localized in the electrode interface of the piezoelectric thin film is obtained.

  However, when a voltage having a waveform having a voltage portion forming the third electric field and a voltage portion forming 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 of This is the case where the duration of the voltage for generating the recovery electric field is a time equal to or less than an integral multiple of one cycle of the meniscus resonance cycle. In this case, displacement of the piezoelectric element generated by the recovery waveform excites meniscus resonance to cause pressure fluctuation for discharging a droplet into the pressurized liquid chamber. In order to prevent unnecessary droplet discharge between the drive waveform and the drive waveform, the duration of the voltage for generating the recovery electric field is longer than the meniscus resonance cycle and a time other than an integral multiple of the meniscus cycle. Do. By this, the voltage of the waveform that forms the third electric field and the recovery electric field is set in a state where there is no pressure generation that discharges a droplet into the pressurized liquid chamber between the drive waveform and the drive waveform. Can.

  In the driving method of the present invention, the driving IC outputs a voltage of either positive or negative polarity. By adjusting the value of the pulse-shaped voltage applied to one of the electrodes and the duration thereof as described above using this drive IC, it is possible to form a recovery electric field without discharging droplets. . Therefore, the cost increase of the drive IC is such that the drive IC is configured to output a pulse-shaped voltage of positive and negative polarity to form a recovery electric field, or the polarity of the drive waveform is inverted using a switch. It can be greatly reduced compared to drive ICs. As a result, it is possible to suppress the decrease in displacement characteristics of the thin film piezoelectric actuator over time and to ensure stable discharge performance at low cost.

(Aspect B)
In (Aspect A), the recovery electric field 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 inversion even if long-term driving is performed. Therefore, the load applied to the piezoelectric element is small, and a stable displacement can be obtained, and the problem such as an increase in current accompanying polarization inversion in the 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 other electrode such as the upper electrode 153. According to this, by repeatedly forming the driving electric field, it is possible to eliminate the trap of the lead defect in the piezoelectric thin film generated at the interface with the electrode on the substrate side, and to suppress the deterioration of the displacement characteristic over time.

(Aspect D)
In any 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 down time Tr is longer than the meniscus resonance period. Pressure fluctuations (rise time Tf, fall time Tr) in a time shorter than the meniscus inherent period also contribute to the excitation of this vibration, and pressure amplification occurs. If the rise time Tf and the fall time Tr are shorter than the meniscus intrinsic period, pressure amplification does not occur, and pressure generation does not occur such as discharging a droplet between the drive waveform and the drive waveform. It can be done.

(Aspect E)
In any of (Aspect A), (Aspect B), (Aspect C) or (Aspect D), the pulse time width Pw of the voltage of the pulse waveform for applying the voltage for generating the recovery electric field in the recovery waveform is a The time is a half integral multiple of the meniscus resonance period. According to this, it is possible to prevent pressure generation from occurring such as discharging a droplet between the drive waveform and the drive waveform without generating pressure amplification.

(Aspect F)
In any 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 V 3 of the voltage is the maximum value V1 or more 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 deformation of the piezoelectric body in the voltage used for the drive waveform.

(Aspect G)
A piezoelectric substrate having a diaphragm 55 and a perovskite crystal structure represented by the 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 the droplet discharge head in which the piezoelectric thin film 152 is sandwiched between the pair of electrodes and the piezoelectric element is stacked, the droplet discharge head is driven by the method for driving the droplet discharge head according to any one of (Aspect A) to (Aspect F) Drive IC. According to this, as described in the above-described embodiment, it is possible to suppress the decrease in the displacement characteristic of the thin film piezoelectric actuator with time and to ensure stable discharge performance at low cost.

(Aspect H)
In an image forming apparatus that forms an image by causing droplets discharged by droplet discharge means to adhere to the medium while transporting the medium, the droplet body discharge head of (Mode G) is adopted as the droplet discharge means. According to this, it is possible to provide an image forming apparatus capable of obtaining a high quality image at low cost.

1 actuator substrate 2 nozzle plate 4 liquid chamber substrate 14 pressurized liquid chamber 18 common liquid chamber 20 nozzle 51 droplet discharge head 55 diaphragm 56 piezoelectric element 151 lower electrode (electrode on substrate side)
152 Piezoelectric thin film 153 Upper electrode (electrode on front side)
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 piezo actuator

JP, 2009-071113, A Patent No. 4594069 WO 2006/137528 Patent 3797161 gazette

Claims (9)

A driving method of a liquid discharge head comprising a piezoelectric element configured to sandwich a piezoelectric body between a first electrode and a second electrode and apply pressure to a liquid chamber communicating with a nozzle,
Applying a pulsed discharge waveform voltage and a pulsed non-discharge waveform voltage to the first electrode;
Applying a DC voltage to the second electrode;
The ejection waveform voltage includes a first voltage higher than the DC voltage, and a second voltage lower than the DC voltage and continuing for a first time.
The non-ejection waveform voltage includes a third voltage higher than the DC voltage and a fourth voltage lower than the DC voltage.
The non-ejection waveform voltage shifts from the third voltage to the fourth voltage and continues from the fourth voltage for a second time, and then from the fourth voltage to the third voltage. Migrate
The second time is longer than the first time,
Said third voltage and the third voltage at least one of time of time to shift to from the time and the fourth voltage transitions to the fourth voltage from, rather long than meniscus resonance period in the nozzle ,
A method of driving a liquid discharge head , comprising applying the non-discharge waveform voltage at least one of immediately before and after application of the discharge waveform voltage . In the method of driving a liquid discharge head according to claim 1,
A method of driving a liquid discharge head, wherein an electric field generated by applying the fourth voltage does not exceed a coercive electric field of the piezoelectric element. In the method of driving a liquid discharge head according to claim 1 or 2,
A method of driving a liquid discharge head, wherein the second time is an anti-resonance period of a meniscus. In the method of driving a liquid discharge head according to claim 1, 2 or 3.
A method of driving a liquid discharge head, wherein the third voltage is equal to or higher than the first voltage. A piezoelectric element configured to sandwich a piezoelectric body between a first electrode and a second electrode and apply pressure to a liquid chamber communicating with a nozzle;
A driving circuit for applying a pulse-like ejection waveform voltage and a pulse-like non-ejection waveform voltage to the first electrode and applying a DC voltage to the second electrode;
The drive circuit applies the discharge waveform voltage including the first voltage higher than the DC voltage and the second voltage lower than the DC voltage and continuing for a first time to the first electrode.
The drive circuit applies the non-ejection waveform voltage including a third voltage higher than the DC voltage and a fourth voltage lower than the DC voltage to the first electrode.
The non-ejection waveform voltage output by the drive circuit is shifted from the third voltage to the fourth voltage, and after the fourth voltage is continued for a second time, the fourth voltage is output from the fourth voltage. Transition to the third voltage,
The second time is longer than the first time,
Said third voltage and the third voltage at least one of time of time to shift to from the time and the fourth voltage transitions to the fourth voltage from, rather long than meniscus resonance period in the nozzle ,
A liquid discharge head characterized in that the non-discharge waveform voltage is applied at least one immediately before and / or immediately after the application of the discharge waveform voltage . In the liquid discharge head according to claim 5,
A liquid discharge head, wherein an electric field generated by applying the fourth voltage does not exceed a coercive electric field of the piezoelectric element. In the liquid discharge head according to claim 5 or 6,
A liquid discharge head characterized in that the second time is an anti-resonance period of a meniscus. The liquid discharge head according to claim 5, 6 or 7.
The liquid discharge head, wherein the third voltage is equal to or higher than the first voltage.   A liquid discharge head according to claim 5, 6, 7, or 8.
  An image forming apparatus which discharges a liquid from the liquid discharge head while stopping a medium and moving the liquid discharge head.

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