Layered piezoelectric element realizing stable operating characteristic for high quality image recording

A layered piezoelectric element includes a plurality of driving parts divided by grooves and non-driving parts formed at both ends of the array of the driving parts. The driving parts and the non-driving parts include the alternate layers of piezoelectric layers and internal electrodes. The common electrode of the driving parts is extended from the non-driving parts. The capacitance C (F) of each driving part, the number of the driving parts n, and the resistance R (Ω) between the non-driving parts satisfy R≦8×10−6/n/C.

TECHNICAL FIELD

The present invention generally relates to image recording, and more particularly to a layered piezoelectric element, a method of manufacturing the same, a piezoelectric actuator, a liquid droplet ejecting head, and an ink-jet recording apparatus.

BACKGROUND ART

An ink-jet recording apparatus employed as an image recording apparatus (an imaging apparatus) such as a printer, a facsimile machine, a copier, or a plotter includes an ink-jet head as a liquid droplet ejecting head including nozzles for ejecting ink droplets, liquid chambers (also referred to as ink channels, ejection chambers, pressure chambers, pressure liquid chambers, or channels) communicating with the nozzles, and driving parts (pressure generating parts) for pressurizing ink in the liquid chambers. Liquid droplet ejecting heads include a head ejecting droplets of a liquid resist and a head ejecting droplets of a DNA sample in addition to an ink-jet head, but the following description is given based mainly on the ink-jet head as the liquid droplet ejecting head.

As an ink-jet head, a so-called piezoelectric ink-jet head is well known. The piezoelectric ink-jet head employs a piezoelectric body, particularly a layered piezoelectric body of alternate layers of piezoelectric layers and internal electrodes, as a pressure generation part generating pressure for pressurizing ink in a liquid chamber. An elastically deformable diaphragm forming a wall face of the liquid chamber is deformed by the displacement of the layered piezoelectric element in the d33 direction, so that the volume/pressure inside the liquid chamber is changed, thereby ejecting ink droplets.

Japanese Laid-Open Patent Application No. 10-286951 discloses an ink-jet head using such a layered piezoelectric element. In this ink-jet head, grooves are formed in part of a layered piezoelectric element having an external electrode formed as individual electrodes on one side and a common external electrode formed on the other side, so that a plurality of driving parts (driving channels) are formed between non-driving parts formed on both ends. The common electrode of the layered piezoelectric element extends from the non-driving parts on both ends in the directions in which the driving parts are arranged.

In recent years, the ink-jet recording apparatus has been required to perform image recording with higher quality at higher speeds. In order to increase recording speed, the number of nozzles of a head is increased in the secondary scanning direction so that a single scan of a carriage in the primary scanning direction has a larger width in the secondary scanning direction in printing.

However, in the case of extending the common electrode of the driving parts of the layered piezoelectric element from the non-driving parts on both longitudinal ends thereof as in the above-described ink-jet head, when the layered piezoelectric element is elongated so as to increase the number of driving parts (driving channels) for the purpose of increasing recording speed, the length of conduction from the common electrode extension parts (non-driving parts) to each of the driving channels increases as the number of driving channels increases. As a result, the resistance of the common electrode increases. Particularly, in the case of forming a plurality of driving parts by performing half-cutting on the layered piezoelectric element, the ungrooved remaining part serves as the common external electrode, so that the long narrow part increases the resistance of the common electrode.

The time constant of a driving voltage applied to a driving channel in the case of driving all the driving channels is different from that in the case of driving only one of the driving channels.

The time constant of the driving voltage increases as the number of driving channels increases. Further, the degree of such increase becomes greater as the resistance of the common electrode increases.

When the time constant of the driving voltage thus changes, an ink droplet ejection characteristic, particularly ink droplet velocity, changes to vary the point of impact of an ink droplet. Therefore, when there is a large difference between the time constants of the foregoing two cases, great degradation is caused in image quality especially in the case of printing a high-density image of approximately 600 dpi.

Therefore, in the conventional ink-jet head using a layered piezoelectric element, there is the problem that high image quality cannot be obtained due to the large resistance of the common electrode especially in the case of printing a high-density image of approximately 600 dpi.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to realize image recording in which the above-described disadvantage is eliminated.

A more specific object of the present invention is to provide a layered piezoelectric element reducing the difference between the time constant of a driving voltage in the case of driving all channels and that in the case of driving only one channel, and a method of manufacturing the same.

Another more specific object of the present invention is to provide a piezoelectric actuator having a stable operating characteristic, a liquid droplet ejecting head having a stable ejection characteristic, and an ink-jet recording apparatus capable of high-quality recording.

The above objects of the present invention are achieved by a layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; and non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes, wherein a common electrode of the driving parts is extended from the non-driving parts, and a capacitance C (F) of each of the driving parts, the number of the driving parts n, and a resistance R (Ω) between the non-driving parts satisfy R≦8×10−6/n/C.

The above-described layered piezoelectric element satisfies the expression R≦8×10−6/n/C. Therefore, the difference in its operating characteristic between the case of driving all channels and the case of driving one channel is reduced.

The above objects of the present invention are also achieved by a layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an internal electrode for conduction connected to a common external electrode of the driving parts and undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above-described layered piezoelectric element includes the internal electrode for conduction connected to the common external electrode of the driving parts. Therefore, the common electrode resistance is decreased, so that the difference in its operating characteristic between the case of driving all channels and the case of driving one channel is reduced.

The above objects of the present invention are also achieved by a layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an external electrode for conduction connected to a common external electrode of the driving parts, the external electrode for conduction being formed on a surface of the layered piezoelectric layer which surface is undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above-described layered piezoelectric element includes the external electrode for conduction connected to the common external electrode of the driving parts. Therefore, the common electrode resistance is decreased, so that the difference in its operating characteristic between the case of driving all channels and the case of driving one channel is reduced.

The above objects of the present invention are also achieved by a method of manufacturing a layered piezoelectric element including a plurality of driving parts divided by grooves, non-driving parts formed at both ends of an array of the driving parts, and an internal electrode for conduction connected to a common external electrode of the driving parts and undivided by the grooves, the driving parts and the non-driving parts including alternate layers of piezoelectric layers and internal electrodes, the driving parts having a common electrode extended from the non-driving parts, the method including the steps of (a) fixing a member including a dummy part to a base, the dummy part being formed of a piezoelectric layer to have a shape substantially symmetrical to a shape of a group of the internal electrodes of the alternate layers in a direction in which the alternate layers are formed, and (b) removing the dummy part from the member.

According to the above-described method, the layered piezoelectric element of the present invention can be manufactured suitably with a reduced warp.

The above objects of the present invention are also achieved by a piezoelectric actuator including a movable part and a layered piezoelectric element deforming the movable part, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; and non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes, wherein a common electrode of the driving parts is extended from the non-driving parts, and a capacitance C (F) of each of the driving parts, the number of the driving parts n, and a resistance R (Ω) between the non-driving parts satisfy R≦8×10−6/n/C.

The above objects of the present invention are also achieved by a piezoelectric actuator including a movable part and a layered piezoelectric element deforming the movable part, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an internal electrode for conduction connected to a common external electrode of the driving parts and undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above objects of the present invention are also achieved by a piezoelectric actuator including a movable part and a layered piezoelectric element deforming the movable part, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an external electrode for conduction connected to a common external electrode of the driving parts, the external electrode for conduction being formed on a surface of the layered piezoelectric layer which surface is undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above-described piezoelectric actuators each include the layered piezoelectric element of the present invention deforming the movable part. Therefore, the above-described piezoelectric actuators can obtain a stable operating characteristic with reduced variation.

The above objects of the present invention are also achieved by a liquid droplet ejecting head including a piezoelectric actuator pressurizing a liquid chamber communicating with a nozzle so as to eject a liquid droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; and non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes, wherein a common electrode of the driving parts is extended from the non-driving parts, and a capacitance C (F) of each of the driving parts, the number of the driving parts n, and a resistance R (Ω) between the non-driving parts satisfy R≦8×10−6/n/C.

The above objects of the present invention are also achieved by a liquid droplet ejecting head including a piezoelectric actuator pressurizing a liquid chamber communicating with a nozzle so as to eject a liquid droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts comprising the alternate layers of the piezoelectric layers and the internal electrodes; and an internal electrode for conduction connected to a common external electrode of the driving parts and undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above objects of the present invention are also achieved by a liquid droplet ejecting head including a piezoelectric actuator pressurizing a liquid chamber communicating with a nozzle so as to eject a liquid droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts comprising alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an external electrode for conduction connected to a common external electrode of the driving parts, the external electrode for conduction being formed on a surface of the layered piezoelectric layer which surface is undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above-described liquid droplet ejecting heads each include the piezoelectric actuator of the present invention pressurizing liquid inside the liquid chamber. Therefore, the above-described liquid droplet ejecting heads can obtain a stable operating characteristic with reduced variation so as to be capable of performing image recording with high quality.

The above objects of the present invention are also achieved by an ink-jet recording apparatus including an ink-jet head ejecting an ink droplet, the ink-jet head including a piezoelectric actuator pressurizing a liquid chamber communicating with a nozzle so as to eject the ink droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; and non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes, wherein a common electrode of the driving parts is extended from the non-driving parts, and a capacitance C (F) of each of the driving parts, the number of the driving parts n, and a resistance R (Ω) between the non-driving parts satisfy R≦8×10−6/n/C.

The above objects of the present invention are also achieved by an ink-jet recording apparatus including an ink-jet head ejecting an ink droplet, the ink-jet head including a piezoelectric actuator pressurizing a liquid chamber communicating with a nozzle so as to eject the ink droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an internal electrode for conduction connected to a common external electrode of the driving parts and undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above objects of the present invention are also achieved by an ink-jet recording apparatus including an ink-jet head ejecting an ink droplet, the ink-jet head including a piezoelectric actuator pressurizing an ink chamber communicating with a nozzle so as to eject the ink droplet from the nozzle, the piezoelectric actuator including a layered piezoelectric element, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes; and an external electrode for conduction connected to a common external electrode of the driving parts, the external electrode for conduction being formed on a surface of the layered piezoelectric layer which surface is undivided by the grooves, wherein a common electrode of the driving parts is extended from the non-driving parts.

The above-described ink-jet recording apparatuses each include the liquid (ink) droplet ejecting head of the present invention. Therefore, the above-described ink-jet recording apparatuses can perform stable image recording with high quality.

The above objects of the present invention are further achieved by an ink-jet recording apparatus including an ink-jet head, the ink-jet head including a layered piezoelectric element pressurizing a liquid chamber so as to eject an ink droplet therefrom, the layered piezoelectric element including: a plurality of driving parts divided by grooves, the driving parts including alternate layers of piezoelectric layers and internal electrodes; and non-driving parts formed at both ends of an array of the driving parts, the non-driving parts including the alternate layers of the piezoelectric layers and the internal electrodes, wherein a common electrode of the driving parts is extended from the non-driving parts, and a difference between a time constant of a driving voltage applied to the layered piezoelectric element in a case of driving all of the driving parts and a time constant of a driving voltage applied to the layered piezoelectric element in a case of driving one of the driving parts is smaller than or equal to 2 μsec.

The above-described ink-jet recording apparatus also reduces the difference in its droplet ejection characteristics between the case of driving all channels and the case of driving one channel so as to be capable of performing image recording with high quality.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given, with reference to the accompanying drawings, of embodiments of the present invention.

First Embodiment

First, a description will be given, with reference toFIG. 1, of an ink-jet head as a liquid droplet ejecting head according to a first embodiment of the present invention.FIG. 1is a sectional view of the ink-jet head taken along the directions in which the pressure liquid chamber6thereof extends.

The ink-jet head includes a channel substrate (liquid chamber substrate)1formed of a single-crystal silicon substrate, a diaphragm2joined to the lower face of the channel substrate1, and a nozzle plate3joined to the upper face of the channel substrate1, thereby forming the pressure liquid chambers6and a common liquid chamber8. The pressure liquid chambers6are channels (ink liquid chambers) with which nozzles5ejecting ink droplets communicate through ink communicating channels5a. The common liquid chamber8supplies ink to the pressure liquid chambers6via ink supply channels7serving as fluid resistance parts.

Through holes serving as the ink communicating channels5aand concave parts serving as the pressure liquid chambers6, the ink supply channels7, and the common liquid chamber8are formed in the channel substrate1by performing anisotropic etching on a single-crystal silicon substrate of a (110) crystal plane using an alkaline etchant such as a potassium hydroxide (KOH) aqueous solution.

The diaphragm2is formed of a plate of metal such as nickel. The diaphragm2may also be formed of a resin member or a layered member of resin and metal members.

The nozzles5of 10 through 30 μm are formed in the nozzle plate3so as to correspond to the pressure liquid chambers6. The nozzle plate3is bonded to the channel substrate1with an adhesive agent. The nozzle plate3may be formed of metal such as stainless steel or nickel, a combination of metal and resin such as a polyimide resin film, silicon, or a combination of these materials. A water repellent film is formed on the nozzle surface of the nozzle plate3by a well-known method such as plating or water repellent coating in order to ensure repellence against ink. The nozzle surface refers to a surface of the nozzle plate3in the direction in which ink is ejected. The nozzle surface may also be referred to as an ejection surface.

A layered piezoelectric element12is joined to the external face of the diaphragm2so that individual piezoelectric element parts of the layered piezoelectric element12correspond to the pressure liquid chambers6. The external face refers to a face of the diaphragm2on the opposite side from the pressure liquid chambers6. The diaphragm2and the layered piezoelectric element12form a piezoelectric actuator deforming the diaphragm2that is a movable part.

The layered piezoelectric element12has a first face on one side joined to the diaphragm2and a second face on the opposite side joined and fixed to a base13by an adhesive agent. Further, a side face of the layered piezoelectric element12is connected to an FPC (flexible printed circuit) cable14for supplying driving waveforms to the layered piezoelectric element12.

In this embodiment, the individual layered piezoelectric element parts corresponding to the respective pressure liquid chambers6are formed by forming slits in the long layered piezoelectric element12. In this specification, “the overall length of a piezoelectric element” refers to the length of the original long layered piezoelectric element12from which the individual layered piezoelectric element parts are formed.

In this embodiment, ink inside the pressure liquid chambers6may be pressurized by using the displacement of the layered piezoelectric element12in the d33 direction or in the d31 direction as its piezoelectric direction.

As previously described, the layered piezoelectric element12has the second face joined and fixed to the base13by an adhesive agent. The FPC cable14is joined by an adhesive agent to a face of the base13which face is perpendicular to the face thereof joined to the layered piezoelectric element12. The FPC cable14is further soldered directly to individual external electrodes24of the layered piezoelectric element12.

It is preferable to use metal as material for the base13. By using metal as material for the base13, heat storage resulting from self-heating of the layered piezoelectric element12can be prevented from occurring. The layered piezoelectric element12is joined to the base13by an adhesive agent. As the number of channels increases, however, temperature rises near 100° C. due to self-heating of the layered piezoelectric element12so as to reduce the joining strength significantly. Further, the self-heating of the layered piezoelectric element12increases temperature inside the ink-jet head so as to increase ink temperature. The increase in ink temperature reduces ink viscosity, thus significantly affecting the ink ejection characteristic of the ink-jet head. Accordingly, by preventing the occurrence of heat storage resulting from the self-heating of the layered piezoelectric element12by forming the base13of a metal material, degradation of the ejection characteristic of the ink-jet head due to decrease in the joining strength and the ink viscosity can be prevented.

When the base13has a large liner expansion coefficient, the adhesive agent may peel off at the joining interface between the base13and the layered piezoelectric element12at high or low temperatures. As to the conventional piezoelectric element, there seldom exists the problem of peeling off from the base13due to a difference in temperature caused by environmental variation since the piezoelectric element is shorter in overall length. This problem has been made obvious by using a piezoelectric element that has approximately 40 nozzles at 300 dpi and is approximately 30 through 40 mm in overall length.

Accordingly, it is preferable to use a material having a linear expansion coefficient of 10E-6° C. or lower for the base13. By limiting linear expansion coefficients to this range, the base13is prevented from peeling off from the piezoelectric element12at the joining interface therewith due to a difference in temperature resulting from environmental variation. It has been confirmed that it is very effective in preventing peeling at the joining interface with a piezoelectric element to set the linear expansion coefficient of each component joined thereto to a value lower than or equal to 10E-6° C.

The FPC cable14includes a plurality of driver ICs16for applying driving waveforms (electrical signals) to drive the corresponding channels (corresponding to the pressure liquid chambers6). By providing the driver ICs16to the FPC cable14, electrical signal setting can be performed independently in each of the driver ICs16. This facilitates correction of variations in the displacement characteristics of the driving channels of the layered piezoelectric element12.

As the piezoelectric element becomes greater in length, it has been made obvious that variations in the displacements of the channels become greater. Accordingly, by providing the driver ICs16to the FPC cable14, a variation in the displacement of the layered piezoelectric element12is corrected by voltage in the channel directions (in which the individual layered piezoelectric element parts are arranged), thereby realizing a uniform ejection characteristic.

Further, a frame17is joined to the periphery of the diaphragm2by an adhesive agent. An ink supply channel18for supplying ink from the outside to the common liquid chamber8is formed in the frame17across at least the base13from the driver ICs16. The ink supply channel18communicates with the common liquid chamber8via a through hole2aof the diaphragm2.

The ink supply channel18, the common liquid chamber8, and the fluid resistance parts7are thus arranged on the opposite side from the driver ICs16so that ink can be supplied from the opposite side from the FPC cable14connected to the layered piezoelectric element12, thereby preventing a rise in ink temperature due to heating of the driver ICs16.

As previously described, the heat of the driver ICs16, which may vary depending on the number of channels or driving waveforms, reaches around 100° C. as the layered piezoelectric element12becomes larger in length. When ink temperature rises due to the heating of the driver ICs16, ink viscosity decreases so as to significantly affect the ejection characteristic. Therefore, the decrease in ink viscosity due to the rise in temperature of the driver ICs16should be avoided by any means. The heating of driver ICs is not so significant a problem in the conventional ink-jet head with a small number of channels. As the ink-jet head becomes greater in length, however, the decrease in ink viscosity due to the rise in temperature of driver ICs has become a serious problem. This problem can be solved by employing the above-described configuration.

A detailed description will be given herein, with reference toFIGS. 2 through 7, of the layered piezoelectric element12.FIG. 2is a sectional view of the layered piezoelectric element12of the ink-jet head of this embodiment taken along the directions perpendicular to the directions in which the pressure liquid chamber6extends.FIG. 3is a sectional view of the layered piezoelectric element12of the ink-jet head ofFIG. 2taken along the line A—A.FIG. 4is a sectional view of the layered piezoelectric element12of the ink-jet head ofFIG. 2taken along the line B—B.FIGS. 5A and 5Bare plan views of internal electrode patterns of the layered piezoelectric element12.FIG. 6is a perspective view of the layered piezoelectric element12of the ink-jet head of this embodiment taken from the common electrode side.FIG. 7is a perspective view of the layered piezoelectric element12of the ink-jet head of this embodiment taken from the individual electrode side.

In the layered piezoelectric element12, a plurality of driving parts25(individual piezoelectric element parts) are formed between non-driving parts26on both ends of the array of the driving parts25by performing slitting or grooving processing on alternate layers of piezoelectric layers (piezoelectric material layers)21and internal electrodes22A and22B having pattern shapes as shown inFIGS. 5A and 5B, respectively, with a common external electrode23and the individual external electrodes24formed on the opposing longitudinal sides of the layer structure. The common external electrode23is formed of the external electrodes on the common electrode side of the respective driving parts25.

In this slitting or grooving process, slits are formed in the layered piezoelectric element12so that a bridge part27of a size D in the depth direction remains in the bottom of the layered piezoelectric element12on the base13. Further, a cutout28is formed on the individual external electrode (24) side of the layered piezoelectric element12along the directions in which the driving parts25are arranged.

Accordingly, the internal electrode22A of each driving part25is connected to the common external electrode23, which is prevented from being divided due to the bridge part27, so that the internal electrode22A of each driving part25is connected through the common external electrode23to the internal electrodes22A of the non-driving parts26on both ends. Further, the internal electrodes22A of the non-driving parts26extend to the individual external electrode (24) side of the layered piezoelectric element12as shown inFIG. 4. Therefore, by connecting the FPC cable14to the individual external electrode (24) side, the common electrode and the individual electrodes can be extended from the one side of the layered piezoelectric element12.

In the ink-jet head having the above-described configuration, a driving pulse voltage of 20 to 50 V is applied to a selected one or more of the driving parts25of the layered piezoelectric element12so that the driving parts25to which the driving pulse voltage is applied stretch in the direction in which the layers are formed (that is, in the upward direction inFIGS. 2 through 4) so as to deform the diaphragm2toward the nozzles5. Thereby, the capacity or the volume of each corresponding pressure liquid chamber6changes so as to pressurize ink therein, so that ink droplets are ejected (sprayed) from the corresponding nozzles5.

With the ejection of ink droplets, liquid pressure inside the pressure liquid chambers6decreases, so that a certain negative pressure is generated in the pressure liquid chambers6by the inertia of ink flow at this moment. By suspending application of the voltage to the layered piezoelectric element12in this state, the diaphragm2returns to its original position so as to restore the pressure liquid chambers6to their original shape, thereby generating further negative pressure. At this point, ink flows through the ink supply channel18, the common liquid chamber8, and the ink supply channels (fluid resistance parts)7to be filled into the pressure liquid chambers6. Then, after the vibrations of the ink meniscus surfaces of the nozzles5attenuate to stabilize, another pulse voltage is applied to the layered piezoelectric element12for the next ejection of ink droplets, so that ink droplets are ejected.

FIG. 8is a diagram showing a circuit equivalent to an electrical circuit from a driving waveform generating part to the layered piezoelectric element12. As shown inFIG. 8, each driving part (driving channel)25is formed of a series circuit of a resistor (resistance) Ron(Ω) and a capacitor (capacitance) C (F), and the driving parts25are connected with each other by resistors (resistances) Rc(Ω). The circuit ofFIG. 8is simplified so as to replace the resistors Rcwith common electrode resistors (resistances) Rcom(Ω) each interposed between the driving parts25and each non-driving part26as shown inFIG. 9.

When a pulse driving voltage Pvis applied, as shown inFIG. 10, to the circuit ofFIG. 9, letting the number of driving parts (driving channels)25be n, the time constant τ1(sec) of the driving voltage Pvapplied to the driving part25in the case of driving only one of the n channels is given by the following equation (1):
τ1=C(Ron+Rcom)  (1)

Further, the time constant τall(sec) of the driving pulse Pvapplied to the driving parts25in the case of driving all the n channels is given by the following equation (2):
τall=C(Ron+n·Rcom/2)  (2)

Accordingly, the difference Δτ between the time constant τallin the case of driving all the n channels and the time constant τ1in the case of driving only one of the n channels can be obtained from the following equation (3):

The equation (3) shows that as the number of driving channels n becomes larger or the common electrode resistance Rcombecomes larger, a change in the driving time constant τ becomes greater. That is, a change in the ink droplet ejection characteristic becomes greater.

On the other hand, the ink droplet ejection characteristic most affected by the change in the time constant τ is an ejection velocity Vj. When the ejection velocity Vjchanges, time required for an ink droplet to be ejected from the ink-jet head to be positioned on a paper sheet (a medium onto which ink droplets are ejected) also changes. Since the ink-jet head moves in the primary scanning direction, this change ultimately appears as a deviation of a dot position in the primary scanning direction.

In the case of recording a 600-dpi image, when the deviation of a line (Δdot) exceeds approximately one dot, or 42.3 μm in distance, the deviation is large enough to be visually recognized. Therefore, the deviation is preferably smaller than or equal to 42.3 μm in terms of higher image quality.

Letting the ejection velocity in the case of driving all the n channels, the ejection velocity in the case of driving only one of the n channels, and the nozzle-paper distance be Vjall, Vj1, and L, respectively, the difference ΔT between time required for an ink droplet to travel from nozzle to paper in the case of driving all the n channels and that in the case of driving only one of the n channels is given by the following equation (4):
ΔT=L/Vjall−L/Vj1(4)

Further, letting scanning velocity for the primary scanning direction be Vs, the deviation of a dot (Δdot) is given by the following equation (5):
Δdot=ΔT×Vs=(L/Vjall−L/Vj1)×Vs(5)

Therefore, the ejection velocity Vjallin the case of driving all the n channels is required to satisfy the following equation (6):
Vjall=L/(Δdot/Vs+L/Vj1)  (6)

When the ejection velocity Vj(m/sec) was measured with respect to the rise time (μsec) of the driving voltage Pvwith the primary scanning velocity Vsand the nozzle-paper distance L being set to 0.4 m/s (600 dpi) and 0.001 m, respectively, the characteristic as shown inFIG. 11was obtained.

Here, if the ejection velocity Vj1in the case of driving only one of the n channels is set to 10 m/sec (τ1=approximately 2 μlsec), in order to set Δdot to a value smaller than or equal to 42.3 μm as previously described, the ejection velocity Vjallin the case of driving all the n channels is required to be set to a value larger than or equal to 4.86 m/sec, according to the above-described measurement results. Therefore, the time constant τallin the case of driving all the n channels is set to approximately 4 μsec.

Therefore, it is preferable to set the difference Δτ between the time constant τalland the time constant τ1to a value smaller than or equal to τall−τ1=4−2=2 μsec. Thereby, the degradation of image quality due to the deviation of a dot position can be prevented, particularly in the case of recording an approximately 600-dpi image.

Thus, in the layered piezoelectric element12of the ink-jet head of this embodiment, letting the capacitance of each driving part25, the number of driving parts25, and the resistance between the common electrode extension parts (non-driving parts26) on both ends be C (F), n, and R (Ω), respectively, C (F), n, and R (Ω) satisfy the following condition (7):
R≦8×10−6/n/C (7)

That is, based on the above-described equation (3), the following expression (8) should hold in order to satisfy Δτ ≦2 μsec in the ejection characteristic.
C(n/2−1)·Rcom≦2×10−6(8)

If the actuator is long so that n is sufficiently large, (n/2−1) can be regarded as n/2. Therefore, the above-described expression (8) can be converted to the following expression (9):
Rcom≦4×10−6/n/C(9)

Since the resistance R between the common electrode extension parts of the layered piezoelectric element12is twice the resistance Rcom, the expression (9) can be expressed as the expression (7).

Thereby, the difference between the time constant of the driving voltage Pvapplied in the case of driving one of the channels and the time constant of the driving voltage Pvapplied in the case of driving all the channels can be set to a value smaller than or equal to 2 μsec in the ink-jet head of this embodiment. Thereby, variation in the ejection characteristic of the ink-jet head is reduced so that a stable high-quality image can be obtained.

Second Embodiment

Next, a description will be given, with reference toFIGS. 12 through 14, of an ink-jet head as a liquid droplet ejecting head according to a second embodiment of the present invention. In the second embodiment, the same elements as those described in the first embodiment are referred to by the same numerals.FIG. 12is a sectional view of the layered piezoelectric element12of the ink-jet head taken along the directions in which the pressure liquid chamber thereof extends.FIG. 13is a sectional view of the layered piezoelectric element12of the ink-jet head of this embodiment taken along the directions perpendicular to the directions in which the pressure liquid chamber extends (or the directions in which the driving parts25are arranged).FIG. 14is a plan view of an internal electrode pattern of the layered piezoelectric element12according to this embodiment.

The layered piezoelectric element12of the second embodiment has an internal electrode30for conduction provided in the bridge part27, which is not divided by the grooving processing. The internal electrode30has a pattern whose shape is equal to the planar outline of the layered piezoelectric element12as shown inFIG. 14. In forming the layered piezoelectric element12, the internal electrode30can be formed easily in the bridge part27by forming the internal electrode30between the piezoelectric layers21by printing when the internal electrodes22A and22B are layered, printed on the green sheets serving as the piezoelectric layers21.

The internal electrode30remains connected to the common external electrode23under the driving parts25after the grooving processing. Thereby, the channel of electricity widens greatly on the common electrode side so that the common electrode resistance can be reduced. The internal electrode30may have any shape as long as the internal electrode30is connectable to the common external electrode23of the driving parts25after the grooving processing. The wider the internal electrode30, the greater the desired effect of reduction in the common electrode resistance.

The internal electrode30for conduction that is not divided by the grooving processing is thus provided so as to be connected to the common external electrode23. Thereby, the common electrode resistance is reduced, so that, as previously described, the difference between the time constant of the driving voltage Pvapplied to the layered piezoelectric element12in the case of driving one of the channels and that in the case of driving all the channels can be set to a value smaller than or equal to 2 μsec. Thereby, the difference in the ejection characteristic is reduced, so that a stable high-quality image can be obtained.

Third Embodiment

Next, a description will be given, with reference toFIGS. 15 and 16, of an ink-jet head as a liquid droplet ejecting head according to a third embodiment of the present invention. In the third embodiment, the same elements as those described in the first and second embodiments are referred to by the same numerals.FIG. 15is a sectional view of the layered piezoelectric element12of the ink-jet head taken along the directions in which the pressure liquid chamber thereof extends.FIG. 16is a plan view of an internal electrode pattern of the layered piezoelectric element12according to this embodiment.

The layered piezoelectric element12of the third embodiment has an internal electrode31for conduction provided in the bridge part27, which is not divided by the grooving processing, so as to be connected to the common external electrode23. As shown inFIG. 16, the internal electrode31has a pattern whose shape is equal to that of the internal electrode22A.

Thereby, there is no need to prepare a special print pattern for the internal electrode31for conduction, so that the manufacturing facilities are simplified.

Fourth Embodiment

Next, a description will be given, with reference toFIG. 17, of an ink-jet head as a liquid droplet ejecting head according to a fourth embodiment of the present invention. In the fourth embodiment, the same elements as those described in the first through third embodiments are referred to by the same numerals.FIG. 17is a sectional view of the layered piezoelectric element12of the ink-jet head taken along the directions in which the pressure liquid chamber thereof extends.

The layered piezoelectric element12of the fourth embodiment has the internal electrodes30for conduction of the second embodiment provided in a plurality of layers in the bridge part27, which is not divided by the grooving processing, so as to be connected to the common external electrode23. The internal electrodes30may be replaced by the internal electrodes31of the third embodiment or internal electrodes having another pattern shape.

By thus providing the internal electrodes30in a plurality of layers, the common electrode resistance can be further reduced. Normally, the thickness of the internal electrode is subject to limitation due to a manufacturing method. Therefore, it is not easy to increase the internal electrode in thickness so as to reduce resistance. Further, the internal electrode, which, generally, is formed of a palladium-silver alloy, has a high volume resistivity compared with gold or copper used for the external electrode. Accordingly, a single internal electrode layer for conduction can reduce the common external electrode resistance only to a limited extent. Even when a plurality of internal electrode layers are provided as in this embodiment, the thickness between the internal electrode layers can be as small as approximately 20 μm. Therefore, an adverse effect such as increase in the thickness of a piezoelectric body can be reduced.

Fifth Embodiment

Next, a description will be given, with reference toFIG. 18, of a method of manufacturing the layered piezoelectric element12according to a fifth embodiment of the present invention.FIG. 18is a sectional view of an unprocessed layered piezoelectric element32, which is a member to be processed into the layered piezoelectric element12.

According to the manufacturing method of the fifth embodiment, first, the unprocessed layered piezoelectric element32including a dummy part33is formed. The dummy part33is formed of a piezoelectric layer to be substantially symmetric in shape to the group of the internal electrodes22A and22B (or the structure of the internal electrodes22A and22B with the corresponding piezoelectric layers21) in the direction in which the layers are formed. Then, after fixing the unprocessed layered piezoelectric element32to the base13, the dummy part33is ground to the finishing line C shown inFIG. 18, so that the layered piezoelectric element12ofFIG. 12is formed. The unprocessed layered piezoelectric element32can also be formed into the layered piezoelectric element ofFIG. 15orFIG. 17.

Thereby, the warp of a layered piezoelectric element generated at the time of baking or polarizing the layered piezoelectric element can be reduced, thus preventing problems caused by the warp of the layered piezoelectric element at the time of manufacturing an ink-jet head, such as inability to hold a piezoelectric body by air suction and peeling of an adhesive agent caused by stress in the warp direction at the time of bonding the layered piezoelectric element to a base.

Sixth Embodiment

Next, a description will be given, with reference toFIG. 19, of a method of manufacturing the layered piezoelectric element12according to a sixth embodiment of the present invention.FIG. 19is a sectional view of the unprocessed layered piezoelectric element32according to the manufacturing method of the sixth embodiment.

According to the manufacturing method of the sixth embodiment, a dummy internal electrode35having substantially the same pattern shape as the internal electrode30is formed in the dummy part33of the unprocessed layered piezoelectric element32so that the dummy internal electrode35and the internal electrode30are substantially in symmetrical positions. In the case of forming the layered piezoelectric element12ofFIG. 15, it is preferred that the dummy internal electrode35be formed to have substantially the same pattern shape as the internal electrode31so that the dummy internal electrode35and the internal electrode31are substantially in symmetrical positions. In the case of forming the internal electrodes30in a plurality of layers, it is preferable to form the dummy internal electrodes35in a plurality of layers.

Thereby, the symmetry of the unprocessed layered piezoelectric element32is improved further than by the manufacturing method of the fifth embodiment. Therefore, the warp of a layered piezoelectric element generated at the time of baking or polarizing the layered piezoelectric element can be further reduced, thus further preventing problems caused by the warp of the layered piezoelectric element at the time of manufacturing an ink-jet head, such as inability to hold a piezoelectric body by air suction and peeling of an adhesive agent caused by stress in the warp direction at the time of bonding the layered piezoelectric element to a base.

Seventh Embodiment

Next, a description will be given, with reference toFIG. 20, of a method of manufacturing the layered piezoelectric element12according to a seventh embodiment of the present invention.FIG. 20is a sectional view of the unprocessed layered piezoelectric element32according to the manufacturing method of the seventh embodiment.

According to the manufacturing method of the seventh embodiment, a dummy internal electrode36is formed in the dummy part33of the unprocessed layered piezoelectric element32so as to have the same pattern shape as an internal electrode that alternates with an internal electrode22A that is closest to the surface of the layered piezoelectric element12into which the unprocessed layered piezoelectric element32is processed. That is, in this case, the dummy internal electrode36is formed to have the pattern shape as the internal electrode22B. As previously described, the internal electrode31has the same pattern shape as the internal electrode22A.

By thus forming the dummy internal electrode36, the layering order pattern of internal electrodes can be simplified. Thereby, the number of wasted internal electrodes can be reduced at the time of manufacturing the layered piezoelectric element12.

That is, in the case of forming the dummy internal electrode36and the internal electrode22B into the same shape and forming the internal electrode31and the internal electrode22A into the same shape, the internal electrodes are layered from top to bottom in the order as shown inFIG. 21A. InFIGS. 21A and 21B, “A” refers to an internal electrode having the same pattern shape as the internal electrode22A, and “B” refers to an internal electrode having the same pattern shape as the internal electrode22B. Generally, when internal electrodes are categorized in two types by pattern shape, the two types of internal electrodes alternate with each other in being printed due to their printing method. In this case, each piezoelectric element includes one part of successive “A”s where the internal electrodes “A” are successively layered. Therefore, the internal electrode “B” formed between the successive internal electrodes “A” is wasted.

On the other hand, in the case of forming the dummy internal electrode36as well as the internal electrode31into the same shape as the internal electrode22A, the internal electrodes are layered from top to bottom in the order as shown inFIG. 21B. In this case, two parts of successive “A”s are formed in each piezoelectric element and one part of successive “A”s is formed between each adjacent piezoelectric elements, so that each piezoelectric element includes three successive-“A” parts in total. Therefore, three layers of internal electrodes “B” are wasted per piezoelectric element.

Eighth Embodiment

Next, a description will be given, with reference toFIG. 22, of an ink-jet head as a liquid droplet ejecting head according to an eighth embodiment of the present invention.FIG. 22is a sectional view of the layered piezoelectric element12of the ink-jet head taken along the directions in which the pressure liquid chamber thereof extends according to the eighth embodiment. The layered piezoelectric element12according to this embodiment includes an external electrode40for conduction having the same planar shape as the piezoelectric element12. The external electrode40is formed on a surface of the layered piezoelectric element12which surface is not divided by the grooving processing so as to be connected to the common external electrode23.

The external electrode40is not divided by the grooving processing. Therefore, the channel of electricity widens greatly on the common electrode side so that the common electrode resistance can be reduced. The external electrode40may have any shape as long as the external electrode40is connectable to the common external electrode23of the driving parts25after the grooving processing. The wider the external electrode40, the greater the desired effect of reduction in the common electrode resistance.

By thus providing the external electrode40that is not divided by the grooving processing so that the external electrode40is connected to the common external electrode23, the common electrode resistance is reduced, so that the difference between the time constant of the driving voltage Pvapplied to the layered piezoelectric element12in the case of driving one of the channels and that in the case of driving all the channels can be set to a value smaller than or equal to 2 μm. Thereby, the difference in the ejection characteristic can be reduced, so that a stable high-quality image can be obtained.

Ninth Embodiment

Next, a description will be given, with reference toFIG. 23, of an ink-jet head as a liquid droplet ejecting head according to a ninth embodiment of the present invention.FIG. 23is a sectional view of the ink-jet head taken along the directions in which the pressure liquid chamber6thereof extends according to this embodiment.

The ink-jet head of this embodiment has the nozzles5, the pressure liquid chambers6and the other liquid chambers, and the layered piezoelectric elements12arranged in two lines, respectively. In this embodiment, the layered piezoelectric elements12of the second embodiment are employed, but the layered piezoelectric elements12according to any of the other embodiments may be employed.

Next, a description will be given, with reference toFIGS. 24 and 25, of an ink-jet recording apparatus including the ink-jet head according to the ninth embodiment of the present invention.FIG. 24is a perspective view of the ink-jet recording apparatus, andFIG. 25is a side view of the ink-jet recording apparatus, showing a mechanism part thereof.

The ink-jet recording apparatus includes a print mechanism part112in a recording apparatus main body111. The print mechanism part112is formed of a carriage123movable in the primary scanning direction, a recording head formed of the ink-jet heads of the present invention and mounted in the carriage123, and ink cartridges125supplying ink to the recording head. A paper feed cassette (or a paper feed tray)114capable of containing multiple sheets of paper113can be detachably attached to the lower part of the main body111from the front side or the Y2side inFIGS. 24 and 25. A manual feed tray115for manually feeding the paper sheets113can be turned and opened. The paper sheet113fed from the paper feed cassette114or the manual feed tray115is loaded so that a required image is recorded thereon by the print mechanism part112. Thereafter, the paper sheet113is ejected onto a paper ejection tray116attached to the backside or the Y1side of the main body111.

In the print mechanism part112, the carriage123is held slidably in the primary scanning direction by a primary guide rod121and a secondary guide rod122that are guide members extending between opposing side plates (not shown in the drawings). The primary scanning direction corresponds to the directions in which the primary and secondary guide rods121and122extend. That is, the primary scanning direction corresponds to the X-axis inFIGS. 24 and 25. Heads124formed of the ink-jet heads (liquid droplet ejecting heads) of the present invention ejecting yellow (Y) ink, cyan (C) ink, magenta (M) ink, and black (Bk) ink, respectively, are attached to the carriage123so that a plurality of ink ejection openings thereof are arranged in the directions to cross the primary scanning direction and ink is ejected from the ink ejection openings in the downward direction. The FPC cable14is connected between the heads124and a controller part150so as to apply a driving waveform to each of the heads124. The FPC cable14exchanges signals between the heads124and the controller part150.

The ink cartridges125for supplying the respective color inks to the corresponding heads124are attached replaceably to the carriage123. Each ink cartridge125has a vent formed in its upper part and a supply opening formed in its lower part. The vent communicates with the atmosphere. Ink is supplied from each ink cartridge125through its supply opening to the corresponding head124. Further, each ink cartridge125includes a porous body filled with ink so that the ink supplied to the corresponding head124is maintained at a slightly negative pressure by the capillary force of the porous body.

The heads124for the respective color inks employed as a recording head in this embodiment may be replaced by a single head including nozzles for ejecting ink droplets of the respective color inks.

The primary guide rod121penetrates through the rear (Y1-side) part (part on the downstream side in the direction in which the paper sheet113is conveyed) of the carriage123so that the cartridge123can slide along the primary guide rod121. The front (Y2-side) part (part on the upstream side in the direction in which the paper sheet113is conveyed) of the carriage123is placed on the secondary guide rod122so that the carriage123can slide along the secondary guide rod122. A timing belt130is extended between a drive pulley128rotated by a primary scanning motor127and a driven pulley129. The timing belt130is fixed to the carriage123so that the carriage123is moved back and forth for scanning along the primary scanning direction by the reverse and forward rotations of the primary scanning motor127.

On the other hand, in order to convey each paper sheet113set in the paper feed cassette114to a position below the heads124, the ink-jet recording apparatus includes a paper feed roller131and a friction pad132for separating each paper sheet113from the paper feed cassette114, a guide member133for guiding each paper sheet113, a conveyance roller134conveying each fed paper sheet113upside down, a roller135pressed against the outside surface of the conveyance roller134, and a tip roller136defining an angle at which each paper sheet113is sent from the conveyance roller134. The conveyance roller134is rotated by a secondary scanning motor137via a gear train.

Further, the ink-jet recording apparatus includes a printing reception member139that is a sheet guide member guiding each paper sheet113sent from the conveyance roller134below the heads124. The guide range of the printing reception member139corresponds to the movement range of the carriage123in the primary scanning direction. On the downstream side of the printing reception member139in the direction in which each paper sheet113is conveyed, the ink-jet recording apparatus includes a conveyance roller141and a spur142rotated to send each paper sheet113in a direction to eject each paper sheet113, and further includes an ejection roller143and a spur144for sending out each paper sheet113onto the paper ejection tray116and guide members145and146forming a paper ejection path through which each paper sheet113is conveyed to be ejected.

At the time of recording, the heads124are driven in accordance with an image signal with the carriage123being moved. Thereby, ink is ejected onto the stationary paper sheet113so that recording is performed for one line. Then, after the paper sheet113is conveyed a predetermined distance, recording is performed for the next line. When a recording end signal or a signal indicating that the trailing edge of the paper sheet113has reached the recording region is received, the recording operation is terminated so that the paper sheet113is ejected. In this case, since each of the ink-jet heads of the present invention forming the heads124has improved controllability of ink droplet ejection, thereby suppressing variation in its characteristic, the ink-jet recording apparatus can record a stable high-quality image.

Further, the ink-jet recording apparatus includes a recovery part147for recovering from ejection failure in the heads124. The recovery part147is provided on the X1side in the moving directions of the carriage123in a position outside the recording region as shown inFIG. 24. The recovery part147includes a capping part, a suction part, and a cleaning part. While waiting for printing, the carriage123is moved to the recovery part (147) side so as to have the heads124capped by the capping part. Thereby, the ink ejection openings of the heads124are maintained in a moist state, so that ejection failure due to drying is prevented. Further, during a recording operation, ink irrelevant to the recording is ejected so that all the ink ejection openings have the same ink viscosity, thereby maintaining a stable ejection characteristic.

In the case of the occurrence of ejection failure, the ink ejection openings (nozzles5) of the heads124are hermetically sealed by the capping part, and air bubbles as well as ink are evacuated from the ink ejection openings through a tube by the suction part. Ink or dust adhering to the ink ejection surface of each head124is removed by the cleaning part. Thereby, the heads124recover from ejection failure. The evacuated ink is ejected to a waste ink reservoir (not shown in the drawings) provided in a lower part of the main body111. In the waste ink reservoir, the waste ink is absorbed and kept in an ink absorbing body.

Thus, the ink-jet recording apparatus of this embodiment includes the ink-jet heads of the present invention. Therefore, the difference between the time constant of the case of driving one channel and the time constant of the case of driving all channels can be reduced, so that a stable high-quality image can be recorded.

In the above-described embodiments, the present invention is applied to an ink-jet head as a liquid droplet ejecting head. However, the present invention is also applicable to liquid droplet ejecting heads other than the ink-jet head, such as a liquid droplet ejecting head ejecting droplets of a liquid resist and a liquid droplet ejecting head ejecting droplets of a DNA sample.

Further, in the above-described embodiments, the present invention is applied to the actuator part (pressure generating part), as a piezoelectric actuator, of a liquid droplet ejecting head such as an ink-jet head. However, the present invention is also applicable to a microswitch (a micro relay), an actuator for a multi-optical lens (an optical switch), a micro flow meter, and a pressure sensor as well as a micropump and an optical device (an optical modulator).

Further, in the above-described embodiments, the present invention is applied to a side-shooter head in which the direction in which a diaphragm is displaced is equal to the direction in which an ink droplet is ejected. However, the present invention is also applicable to an edge-shooter head in which the direction in which a diaphragm is displaced is perpendicular to the direction in which an ink droplet is ejected.

The present invention is not limited to the specifically disclosed embodiments, but variations and modifications may be made without departing from the scope of the present invention.

The present application is based on Japanese priority application No. 2002-047371 filed on Feb. 25, 2002, the entire contents of which are hereby incorporated by reference.