Pressure generating mechanism, manufacturing method thereof, and liquid droplet ejection device including pressure generating mechanism

An actuator unit includes piezoelectric ceramic sheets put in layers. Common and individual electrodes are disposed alternately between the piezoelectric ceramic sheets. Each portion of a piezoelectric ceramic sheet where common and individual electrodes overlap each other is a deformable active portion. Each active portion corresponds to a pressure chamber of an ink passage unit. When a drive electric field is applied selectively between common and individual electrodes in a pair, the corresponding active portion is deformed along the thickness direction of the piezoelectric ceramic sheet to change the volume of the corresponding pressure chamber. Microcrack regions provided on both sides of the deformed active portion prevent the deformation of the active portion from propagating to neighboring active portions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure generating mechanism, for example, used for applying pressure to ink in an ink-chamber in an inkjet printer. The present invention relates also to a manufacturing method of the pressure generating mechanism, and a liquid droplet ejection device including the pressure generating mechanism.

2. Description of Related Art

U.S. patent application publication No. 2002/0024567 and U.S. Pat. No. 6,536,880 disclose a pressure generating mechanism of piezoelectric type used for applying pressure to ink in an ink chamber in an inkjet printer.FIG. 13illustrates a sectional view of an inkjet head including therein an actuator unit as a piezoelectric type pressure generating mechanism.

In the inkjet head101ofFIG. 13, an actuator unit106and a passage unit107are put in layers. The actuator and passage units106and107are bonded to each other with an epoxy-base thermosetting adhesive. Ink passages are formed in the passage unit107. The actuator unit106is driven with a drive pulse signal, which can take selectively one of the ground potential and a predetermined positive potential, generated in a non-illustrated drive circuit. For applying the drive pulse signal from the non-illustrated drive circuit to the actuator unit106, a flexible printed wiring board is bonded to the upper face of the actuator unit106though the flexible printed wiring board is not illustrated inFIG. 13.

The passage unit107is made up of three metal plates, i.e., a cavity plate107a, a spacer plate107b, and a manifold plate107c, and a nozzle plate107dmade of a synthetic resin such as polyimide, which are put in layers. Nozzles109for ejecting ink are formed in the nozzle plate107d. The cavity plate107ain the uppermost layer is in contact with the actuator unit106.

Pressure chambers110are formed in the cavity plate107afor receiving therein ink to be selectively ejected by an action of the actuator unit106. The pressure chambers110are arranged in two rows along the length of the inkjet head101, i.e., in a right-left direction ofFIG. 13. Partitions110aseparate the pressure chambers110from each other. Longitudinal axes of the pressure chambers110are parallel to one another.

In the spacer plate107bformed are connection holes111for connecting one ends of the pressure chambers110to the respective nozzles109, and non-illustrated connection holes for connecting the other ends of the pressure chambers110to manifold channels.

In the manifold plate107cformed are connection holes113for connecting one ends of the pressure chambers110to the respective nozzles109. In the manifold plate107cfurther formed are manifold channels for supplying ink to the pressure chambers110. The manifold channels are formed under the respective rows of the pressure chambers110to extend along the rows. One end of each manifold channel is connected to a non-illustrated ink supply source.

Thus, ink passages are formed each extending from a manifold channel through a non-illustrated connection hole, a pressure chamber110, a connection hole ill, and a connection hole113to a nozzle109.

In the actuator unit106, six piezoelectric ceramic plates106ato106f, each made of a ceramic material of lead zirconate titanate (PZT), are put in layers. Common electrodes121and123are provided between the piezoelectric ceramic plates106band106cand between the piezoelectric ceramic plates106dand106e, respectively. Each of the common electrodes121and123is formed only in an area above the corresponding pressure chamber110of the passage unit107.

Individual electrodes122and124are provided between the piezoelectric ceramic plates106cand106dand between the piezoelectric ceramic plates106eand106f, respectively. Each of the individual electrodes122and124is formed only in an area above the corresponding pressure chamber10of the passage unit107.

The common electrodes121and123are always kept at the ground potential. On the other hand, a drive pulse signal is applied to individual electrodes122and124in a pair. Portions of the piezoelectric ceramic plates106cto106esandwiched by the common electrodes121and123and the individual electrodes122and124are active portions125having been polarized along the thickness of each piezoelectric ceramic plate by an electric field applied in advance through the electrodes. Therefore, when individual electrodes122and124in a pair are set at a predetermined positive potential, the corresponding active portions125of the piezoelectric ceramic plates106cto106eare going to extend in the thickness of each piezoelectric ceramic plate because of the applied electric field. However, this phenomenon does not appear in the piezoelectric ceramic plates106aand106b. As a result, the portion of the actuator unit106corresponding to the active portions125swells up into the corresponding pressure chamber110. Because the volume of the pressure chamber110is thus decreased, ejection pressure is applied to the ink filling the pressure chamber110and thereby ink is ejected through the corresponding nozzle109.

Using the left pressure chamber110,FIG. 13illustrates a state wherein the volume of the pressure chamber110is decreased by the actuator unit106swelled into the pressure chamber110because a predetermined positive potential is applied to the corresponding pair of individual electrodes122and124, and thereby ink is going to be ejected through the nozzle109connected to the pressure chamber110. As for the right pressure chamber110,FIG. 13illustrates a state wherein ink is not ejected through the nozzle109connected to the pressure chamber110because the corresponding pair of individual electrodes122and124are kept at the ground potential like the common electrodes121and123.

In the inkjet head101ofFIG. 13, when a predetermined positive potential is applied to a pair of individual electrodes122and124for ejecting ink through the corresponding nozzle109, crosstalk may occur wherein the mechanical deformation of the corresponding active portions125affects neighboring active portions125. More specifically, as illustrated inFIG. 13, as a reaction to the downward deformation of one unit of active portions125, the neighboring unit of active portions125is deformed upward. Simultaneously with this, both sides of the partition110afacing the respective pressure chambers110are inclined toward the pressure chamber110for which the electric potential has been applied. As a result, the partition110is deformed into a parallelogram in section. Thus, the pressure in the neighboring pressure chamber110has also been changed though any electric potential has not been applied for the pressure chamber110. This may bring about changes in speed and volume of an ink droplet ejected through the nozzle109corresponding to the pressure chamber110in the next ejection action. This causes an error of ink impact position and unevenness in print density, and therefore lowers the print quality.

For this reason, U.S. Pat. No. 5,128,694 discloses a technique for reducing crosstalk by forming slits, each extending along the thickness of the piezoelectric ceramic plates, in the intervals between active portions in the actuator unit with a diamond cutter. In this technique, however, the process itself for forming the slits each extending along the thickness of the piezoelectric ceramic plates, with a diamond cutter, is very troublesome. Further, because a washing process is necessary after the slit formation process, it requires a long-time work. There is a problem that no good manufacture efficiency can be obtained.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pressure generating mechanism in which crosstalk has been reduced and which can be easily manufactured in a short time, a manufacturing method of the pressure generating mechanism, and a liquid droplet ejection device including the pressure generating mechanism.

According to an aspect of the present invention, a pressure generating mechanism comprises a plate member made of a piezoelectric material; first electrodes disposed at the plate member at intervals in a plane direction of the plate member; and second electrodes opposite to the first electrodes in a thickness direction of the plate member substantially perpendicular to the plane direction of the plate member. The plate member comprises active portions formed in the plate member at intervals in the plane direction of the plate member. Each of the active portions are sandwiched by the corresponding first and second electrodes and deformable in the thickness direction of the plate member. The plate member further comprises a microcrack region formed in the plate member between neighboring active portions. The microcrack region includes therein a large number of microcracks.

According to the invention, because the microcrack region is formed in the plate member between the neighboring active portions, crosstalk between the neighboring active portions can be reduced. In addition, because microcracks can be formed without using a diamond cutter unlike the case of forming slits extending along the thickness of the plate member, they can be easily formed in a short time. Further, because crosstalk can be reduced, the number of layers in the plate member can be increased relatively to the prior art. Therefore, even if deformation of one layer is little, large deformation can be obtained as a whole. Thus, the first or second electrode can be driven by a low voltage. This may bring about a decrease in cost of a circuit component for generating a drive signal for the first or second electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First will be described an inkjet head including an actuator unit as a pressure generating mechanism according to a first embodiment of the present invention. As illustrated inFIG. 1, a piezoelectric inkjet head1of this embodiment includes a substantially rectangular parallelepiped passage unit7and an actuator unit6having substantially the same shape as the passage unit7. The actuator unit6is put on the passage unit7. A flexible flat cable or a flexible printed circuit (FPC)5is attached to the upper face of the actuator unit6for connecting the actuator unit6to an external circuit. The inkjet head1ejects ink downward through nozzles9(seeFIGS. 2 and 3) each open in the lower face of the passage unit7.

A large number of surface electrodes3are provided on the upper face of the actuator unit6for electrically connecting the actuator unit6to the FPC5. A large number of pressure chambers (liquid chambers)10each open upward are formed in an upper portion of the passage unit7. A pair of supply holes4aand4bis formed in one end portion of the passage unit7in the length of the passage unit7. As will be described later, each of the supply holes4aand4bis connected to a manifold channel15(seeFIG. 3). The supply holes4aand4bare covered with a filter2for removing dust from ink supplied from a non-illustrated ink cartridge.

Next, a specific structure of the inkjet head1will be described with reference toFIGS. 2 and 3.FIG. 2is a partial sectional view of the inkjet head of FIG.1taken along the length of the inkjet head.FIG. 3is a partial sectional view of the inkjet head ofFIG. 1taken along the width of the inkjet head. InFIGS. 2 and 3omitted is illustration of the FPC5on the actuator unit6.

As illustrated inFIGS. 2 and 3, the actuator unit6and the passage unit7are put in layers. The actuator and passage units6and7are bonded to each other with an epoxy-base thermosetting adhesive. Ink passages are formed in the passage unit7. The actuator unit6is driven through the FPC5with a drive pulse signal, which can take selectively one of the ground potential and a predetermined positive potential, generated in a non-illustrated drive circuit.

The passage unit7is made up of three metal plates, i.e., a cavity plate7a, a spacer plate7b, and a manifold plate7c, and a nozzle plate7dmade of a synthetic resin such as polyimide, which are put in layers. Nozzles9for ejecting ink are formed in the nozzle plate7d. The cavity plate7ain the uppermost layer is in contact with the actuator unit6.

Pressure chambers10are formed in the cavity plate7afor receiving therein ink to be selectively ejected by an action of the actuator unit6. The pressure chambers10are arranged in two rows along the length of the inkjet head1, i.e., in a right-left direction ofFIG. 2. Partitions10aseparate the pressure chambers10from each other. Longitudinal axes of the pressure chambers10are parallel to one another.

In the spacer plate7bformed are connection holes11for connecting one ends of the pressure chambers10to the respective nozzles9, and connection holes12(seeFIG. 3) for connecting the other ends of the pressure chambers10to manifold channels15as will be described later.

In the manifold plate7cformed are connection holes13for connecting one ends of the pressure chambers10to the respective nozzles9. In the manifold plate7cfurther formed are manifold channels15for supplying ink to the pressure chambers10. The manifold channels15are formed under the respective rows of the pressure chambers10to extend along the rows. One end of each manifold channel15is connected to a non-illustrated ink supply source through the corresponding one of the supply holes4aand4bofFIG. 1.

Thus, ink passages are formed each extending from a manifold channel15through a connection hole12, a pressure chamber10, a connection hole11, and a connection hole13to a nozzle9.

In the actuator unit6, six piezoelectric ceramic plates6ato6f, each made of a ceramic material of lead zirconate titanate (PZT), are put in layers. Common electrodes21and23as second electrodes are provided between the piezoelectric ceramic plates6band6cand between the piezoelectric ceramic plates6dand6e, respectively. Each of the common electrodes21and23is formed only in an area above the corresponding pressure chamber10of the passage unit7(seeFIG. 3). In a modification, large-sized common electrodes21and23may be used to cover substantially the whole area of each piezoelectric ceramic plate.

Individual electrodes22and24as first electrodes are provided between the piezoelectric ceramic plates6cand6dand between the piezoelectric ceramic plates6eand6f, respectively. Each of the individual electrodes22and24is formed only in an area above the corresponding pressure chamber10of the passage unit7(seeFIG. 3).

As illustrated inFIG. 2, the common electrodes21and23are always kept at the ground potential. On the other hand, a drive pulse signal is applied to individual electrodes22and24in a pair. Portions of the piezoelectric ceramic plates6cto6esandwiched by the common electrodes21and23and the individual electrodes22and24are active portions25having been polarized along the thickness of each piezoelectric ceramic plate by an electric field applied in advance through the electrodes. In the plan view, each active portion25extends along the corresponding pressure chamber10and has a rectangular shape included in the corresponding pressure chamber10(seeFIG. 5).

When individual electrodes22and24in a pair are set at a predetermined positive potential, the corresponding active portions25of the piezoelectric ceramic plates6cto6eare going to extend in the thickness of each piezoelectric ceramic plate because of the applied electric field. However, this phenomenon does not appear in the piezoelectric ceramic plates6aand6b. As a result, the portion of the actuator unit6corresponding to the active portions25swells up into the corresponding pressure chamber10. Because the volume of the pressure chamber10is thus decreased, ejection pressure is applied to the ink filling the pressure chamber10and thereby ink is ejected through the corresponding nozzle9.

Using the left pressure chamber10,FIG. 2illustrates a state wherein the volume of the pressure chamber10is decreased by the actuator unit6swelled into the pressure chamber10because a predetermined positive potential is applied to the corresponding pair of individual electrodes22and24, and thereby ink is going to be ejected through the nozzle9connected to the pressure chamber10. As for the right pressure chamber10,FIG. 2illustrates a state wherein ink is not ejected through the nozzle9connected to the pressure chamber10because the corresponding pair of individual electrodes22and24is kept at the ground potential like the common electrodes21and23.

To eject ink, a method “fill before fire” may be adopted. In the method “fill before fire”, a voltage is always applied to all individual electrodes22and24to decrease the volumes of all pressure chambers10like the left pressure chamber ofFIG. 2. Only the individual electrodes22and24of a pressure chamber to be used for ink ejection are relieved from the voltage. The volume of the pressure chamber is thereby increased like the right pressure chamber ofFIG. 2to generate a negative pressure wave. Afterward, the voltage is again applied to the individual electrodes22and24to decrease the volume of the pressure chamber10. Thereby, synchronously with the timing when the negative pressure wave is reversed to positive, a positive pressure wave generated by the application of the voltages is superimposed on the negative pressure wave. Thus, using the pressure wave propagating in the pressure chamber10, ejection pressure is efficiently applied to ink.

As described above, in this embodiment, the actuator unit6includes therein the active portions25each deformable substantially perpendicularly to a plane direction of the piezoelectric ceramic plates6ato6f, i.e., in a thickness direction of the piezoelectric ceramic plates6ato6f. In addition, between neighboring active portions25in the plane direction of the actuator unit6, microcrack regions30are provided where a large number of microcracks are formed. This will be described with reference toFIGS. 4 and 5.FIG. 4is an enlarged view of a portion of the inkjet head ofFIG. 2between neighboring active portions25.FIG. 5illustrates a positional relation in the plan view among pressure chambers10, active portions25, and microcrack regions30that are continuously formed with each other.

As illustrated inFIGS. 2 and 4, in the thickness of the piezoelectric ceramic plates6ato6f, microcrack regions30are provided in only three piezoelectric ceramic plates6cto6eof the six piezoelectric ceramic plates6ato6f. As illustrated inFIG. 5, the microcrack regions30are arranged, in the plane direction of the piezoelectric ceramic plates6ato6f, in two rows like the arrangement of the pressure chambers10and formed into a lattice. The microcrack regions30completely isolate neighboring active portions25from each other.

In the three piezoelectric ceramic plates6cto6e, the microcrack regions30are formed only in regions where first microcrack formation electrodes26and28as third electrodes and second microcrack formation electrodes27and29as fourth electrodes, as will be described below, overlap each other. This is because microcracks are formed by applying relatively intense electric fields between the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29to locally damage the piezoelectric ceramic plates6cto6e. The actuator unit6is fixed to the partitions10aof the passage unit7below the microcrack regions30(seeFIG. 2).

In each interval between neighboring active portions25, the first microcrack formation electrodes26and28are provided between the piezoelectric ceramic plates6band6cand between the piezoelectric ceramic plates6dand6e, respectively. In each interval between neighboring active portions25, the second microcrack formation electrodes27and29are provided between the piezoelectric ceramic plates6cand6dand between the piezoelectric ceramic plates6eand6f, respectively. Each of the first and second microcrack formation electrodes26to29has a plurality of electrode segments that are unitarily formed into a lattice in the plan view, similarly to the microcrack region30.

The first microcrack formation electrodes26and28are connected to a common terminal31. The second microcrack formation electrodes27and29are connected to a common terminal32. The terminals31and32are connected to terminals of the FPC5, respectively. As will be described later, in the manufacturing process of the inkjet head1, the terminal31is kept at the ground potential and a relatively high positive potential is temporally applied to the terminal32.

As described above, in the actuator unit6as a pressure generating mechanism according to this embodiment, microcrack regions30are provided in the piezoelectric ceramic plates6cto6ebetween neighboring active portions25. Therefore, upon ink ejection, propagation of deformation of active portions25to the neighboring active portions25is partially interrupted and thereby crosstalk between the neighboring active portions25can be reduced. Thus, printing in high quality is possible.

Particularly in this embodiment, as illustrated inFIG. 5, because the microcrack regions30completely isolate neighboring active portions25from each other in plane, a remarkable effect of reducing crosstalk can be expected. However, in case that neighboring active portions25are thus completely isolated by the microcrack regions30as inFIG. 5, common wiring cannot be used for the common electrodes21and23of the neighboring active portions25. There is a problem that the wiring structure is complicated.

For this reason, in a modification, the continuously formed microcrack regions30may be divided somewhere between neighboring active portions25. Thus, the common electrodes21and23of the neighboring active portions25can be connected to each other through gaps of the microcrack regions30. This can simplify the wiring structure though the effect of reducing crosstalk is somewhat deteriorated. In another modification, as illustrated inFIG. 6, separate microcrack portions30aeach having a rectangular shape may be provided between active portions25neighboring each other along the length of the actuator unit6. In this case, the first and second microcrack formation electrodes26to29are separate electrodes provided corresponding to the separate microcrack region30a. Also in the case of microcrack regions30aofFIG. 6, good effect of reducing crosstalk can be obtained though it is lower than that ofFIG. 5.

As apparent from the manufacturing method as will be described later, microcrack regions30can be formed without using a diamond cutter unlike the case of forming slits extending along the thickness of the piezoelectric ceramic plates6cto6e. They can be easily formed in a short time.

In the actuator unit6of this embodiment, because crosstalk can be reduced, the number of piezoelectric ceramic plates to be put in layers can be increased relatively to the prior art. Therefore, even if deformation of one piezoelectric ceramic plate is little, large deformation can be obtained as a whole. Thus, the individual electrodes22and24can be driven by a low voltage. This may bring about a decrease in cost of a circuit component for generating a drive pulse signal for the individual electrodes22and24.

In the actuator unit6of this embodiment, as apparent from the manufacturing method as will be described later, by setting the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29at different potentials, an electric field can be applied between those electrodes. Therefore, microcracks can be very easily formed in the piezoelectric ceramic plates6cto6e.

In the actuator unit6of this embodiment, the common electrodes21and23and the individual electrodes22and24are provided alternately between the piezoelectric ceramic plates6bto6fin the thickness direction of the piezoelectric ceramic plates6bto6f. In addition, the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29are provided alternately between the piezoelectric ceramic plates6bto6fin the thickness direction of the piezoelectric ceramic plates6bto6f. Thus, the piezoelectric ceramic plates6cto6eare sandwiched by the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29. Therefore, as apparent from the manufacturing method as will be described later, because the distance between electrodes is short, a very high potential need not be applied to the second microcrack formation electrodes27and29for forming microcracks. Further, because microcrack regions30can be formed in the three piezoelectric ceramic plates6cto6e, crosstalk between active portions25can be effectively reduced in comparison with the case wherein microcracks are formed in only one piezoelectric ceramic plate.

In the inkjet head1of this embodiment, the actuator unit6is fixed to the partitions10aof the passage unit7below the microcrack regions30. Therefore, deformation of each active portion25can be effectively used as a change in volume of the corresponding pressure chamber10. This brings about an advantage that good energy efficiency can be obtained.

Next, a manufacturing method of the inkjet head1including the actuator unit of this embodiment will be described with reference to the flowchart ofFIG. 7. To manufacture such an inkjet head1as described with reference toFIGS. 1 to 5, parts such as a passage unit7and an actuator unit6are separately fabricated and then the parts are assembled.

To fabricate a passage unit7, four plates7ato7das illustrated inFIG. 2are made independently of each other. The four plates7ato7dare then put in layers while being positioned to each other. In this state, they are bonded to each other with an adhesive. Pressure chambers10, connection holes11, and so on, are formed in the plates7ato7cby etching. Nozzles9are formed in the plate7dwith a laser beam. These processes are performed in Step S1.

To fabricate an actuator unit6, first, two piezoelectric ceramic green sheets on each of which conductive paste has been deposited into individual electrodes22or24and second microcrack formation electrodes27or29by screen printing, and two piezoelectric ceramic green sheets on each of which conductive paste has been deposited into common electrodes21or23and first microcrack formation electrodes26or28by screen printing, are alternately put in layers. Further, one piezoelectric ceramic green sheet on which no pattern has been printed, and one piezoelectric ceramic green sheet on which conductive paste has been deposited into surface electrodes3by screen printing, are in order put on the above layered structure. These processes are performed in Step S2. Thus, an electrode complex to be an actuator unit6is obtained.

The electrode complex obtained in Step S2is degreased like known ceramics and then sintered at a predetermined temperature (Step S3). Thus, an actuator unit6as described above can be relatively easily fabricated. The actuator unit6is designed by considering in advance shrinkage upon sintering.

Afterward, the passage unit7and the actuator unit6are bonded to each other with a thermosetting adhesive in a state wherein portions to be active portions25of the actuator unit6are positioned to the respective pressure chambers10of the passage unit7. Further, the actuator unit6and an FPC5prepared separately are bonded to each other by soldering so that each surface electrode3is put on the corresponding electrode on the FPC5. These processes are performed in Step S4. In a modification, bonding the FPC5to the actuator unit6may be performed after Step S5as will be described later. In this case, an electric field is applied to the microcrack formation electrodes26to29by a means different from the FPC5.

Afterward, in a state wherein the first microcrack formation electrodes26and28are kept at the ground potential, a high potential is applied to the second microcrack formation electrodes27and29through the FPC5. Thereby, an intense electric field exceeding the breakdown limit of the piezoelectric ceramic plates6cto6e, for example, more than about 6.4 to 24 kV/mm, which is 8 to 30 times the electric field to be applied upon ink ejection operation, is applied to portions of the piezoelectric ceramic plates6cto6esandwiched by the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29. Thus, because of local breakdown, each of the portions of the piezoelectric ceramic plates6cto6eis made into a microcrack region30where a large number of microcracks have been formed (Step S5).

Afterward, in a state wherein the common electrodes21and23are kept at the ground potential, a high potential lower than the potential applied to the second microcrack formation electrodes27and29in Step S5, is applied to the individual electrodes22and24through the FPC5. Thereby, an intense electric field not exceeding the breakdown limit of the piezoelectric ceramic plates6cto6e, for example, about 1.6 to 6.4 kV/mm, which is 2 to 8 times the electric field to be applied upon ink ejection operation, is applied to portions of the piezoelectric ceramic plates6cto6esandwiched by the common electrodes21and23and the individual electrodes22and24. Thus, each portion of the piezoelectric ceramic plates6cto6eis polarized to be an active portion25deformable substantially perpendicularly to the plane direction of the piezoelectric ceramic plates6cto6eupon ink ejection operation (Step S6). An inkjet head1is completed through the above-described processes.

The above-described manufacturing method has an advantage that microcracks can be formed in a very short time by applying an intense electric field to the portions of the piezoelectric ceramic plates6cto6ebetween the first microcrack formation electrodes26and28and the second microcrack formation electrodes27and29. In addition, the method has an advantage that the microcracks can be formed with high positional accuracy. Further, because no washing process is necessary after the microcracks are formed, an actuator unit6in which crosstalk is reduced can be easily fabricated in a short time in comparison with the case wherein slits are formed between active portions25by mechanical processing as described before.

In the above-described manufacturing method, the active portions25and the microcrack regions30are formed after the actuator unit6and the passage unit7are bonded to each other. In a modification, however, the active portions25and the microcrack regions30are formed before the actuator unit6and the passage unit7are bonded to each other. Further, if the order of the microcrack formation step of Step S5and the active portion formation step of Step S6is inverted, it brings about no problem.

Next, an inkjet head including an actuator unit as a pressure generating mechanism according to a second embodiment of the present invention will be described with reference toFIG. 8.FIG. 8is a partial sectional view of an inkjet head taken along the length of the inkjet head, likeFIG. 2. In this embodiment, the same components as in the first embodiment are denoted by the same reference numerals as in the first embodiment, respectively, and thereby description of those components is omitted.

In the inkjet head41ofFIG. 8, a common electrode43, kept at the ground potential, on a piezoelectric ceramic plate6cincluded in an actuator unit46is elongated in one direction to about the midpoint between active portions25neighboring in the plane direction of the actuator unit46. Between two active portions25neighboring each other, one first microcrack formation electrode42as a third electrode is only provided on the lower face of a piezoelectric ceramic plate6f. There is no second microcrack formation electrode to form a pair with the first microcrack formation electrode42, unlike the above-described first embodiment. Only regions of four piezoelectric ceramic plates6cto6fsandwiched by the right extension of the common electrode43inFIG. 8and the first microcrack formation electrode42are made into microcrack regions44. The first microcrack formation electrode42is connected to a terminal47. The inkjet head41has the same structure as the inkjet head1of the first embodiment except the above-described difference.

The manufacturing process of the inkjet head41ofFIG. 8is generally the same as that ofFIG. 7. In this embodiment, however, a high potential is applied to the first microcrack formation electrode42through the terminal47in Step S5. Thus, an intense electric field is applied between the first microcrack formation electrode42and the common electrode43and thereby the portions of the piezoelectric ceramic plates6cto6fsandwiched by the electrodes are made into microcrack regions44.

In the actuator unit46as a pressure generating mechanism of this embodiment, microcrack regions44are formed in four piezoelectric ceramic plates6cto6fbetween neighboring active portions25. Therefore, upon ink ejection, propagation of deformation of active portions25to the neighboring active portions25is partially interrupted and thereby crosstalk between the neighboring active portions25can be reduced, like the first embodiment. Thus, printing in high quality is possible. In addition, the other effects of the first embodiment can be obtained also in this second embodiment.

In the actuator unit46of this embodiment, however, no microcrack formation electrodes are provided between the piezoelectric ceramic plates6cto6fwhere the microcrack regions44are to be formed. Only on the uppermost and lowermost sides of the four piezoelectric ceramic plates6cto6f, the electrodes42and43are provided to sandwich the piezoelectric ceramic plates6cto6f. Therefore, because the distance between the electrodes is large, a potential about several times higher than the potential applied to the second microcrack formation electrodes27and29in the first embodiment must be applied to the first microcrack formation electrode42.

In this embodiment, no second microcrack formation electrode need be provided to form a pair with the first microcrack formation electrode42. Thus, the wiring structure in the actuator unit46is simplified. This makes the manufacture of the actuator unit46easy.

In this embodiment, only one first microcrack formation electrode42is provided and only one of two common electrodes23and43is elongated to about the midpoint between the neighboring active portions25to correspond to the first microcrack formation electrode42. Therefore, the first microcrack formation electrode42and the common electrode43sandwich four piezoelectric ceramic plates6cto6f. Thus, because microcrack regions44are formed in the piezoelectric ceramic plates larger in number than those in the first embodiment, a superior effect of reducing crosstalk can be obtained.

In addition, the structure is simplified in comparison with the case wherein two first microcrack formation electrodes are provided and two common electrodes are elongated to about the midpoint between the neighboring active portions25. This affords a simple structure and an improved yield.

In this embodiment, a common electrode43is elongated to about the midpoint between the neighboring active portions25. In a modification of this embodiment, however, in place of the common electrode43, an individual electrode may be elongated to about the midpoint between the neighboring active portions25. In this case, to form microcrack regions44, a high potential is applied to the elongated individual electrode and the first microcrack formation electrode42is kept at the ground potential.

Next, an inkjet head including an actuator unit as a pressure generating mechanism according to a third embodiment of the present invention will be described with reference toFIG. 9.FIG. 9is a partial sectional view of an inkjet head taken along the length of the inkjet head, likeFIG. 2. In this embodiment, the same components as in the first embodiment are denoted by the same reference numerals as in the first embodiment, respectively, and thereby description of those components is omitted.

In the inkjet head51ofFIG. 9, no microcrack formation electrodes are provided between neighboring active portions in an actuator unit56, unlike the above-described first and second embodiments. In spite of this, microcrack regions54are formed in five piezoelectric ceramic plates6ato6ebetween active portions25neighboring each other in the plane direction of the actuator unit56. This means that the microcrack regions54are formed through a process different from those of the above-described first and second embodiments. The inkjet head51has the same structure as the inkjet head1of the first embodiment except the above-described difference.

In the actuator unit56as a pressure generating mechanism of this embodiment, microcrack regions54are formed in five piezoelectric ceramic plates6ato6ebetween neighboring active portions25. Therefore, upon ink ejection, propagation of deformation of active portions25to the neighboring active portions25is partially interrupted and thereby crosstalk between the neighboring active portions25can be reduced, like the first and second embodiments. Thus, printing in high quality is possible. In addition, the other effects of the first embodiment can be obtained also in this third embodiment.

Next, a manufacturing method of the inkjet head51ofFIG. 9will be described mainly in point of the difference from the first embodiment.

First, in Step S2ofFIG. 7, without printing conductive paste on green sheets to form first and second microcrack formation electrodes, conductive paste is printed on green sheets to form common electrodes21and23and individual electrodes22and24,

Afterward, in Step S4, an actuator unit56obtained through the green sheet sintering process of Step S3and a passage unit7obtained in Step S1are bonded to each other. Thus, a structure58ofFIG. 10to be an inkjet head51is obtained, which is the same as the inkjet head51ofFIG. 9except that microcrack regions54and active portions25have not yet been formed.

Afterward, in Step S5, as illustrated inFIG. 11, a laser beam59is applied through the surface of the piezoelectric ceramic plate6ain each interval between active portions25neighboring each other in the plane direction of the actuator unit56. As a laser source for the laser beam59that can give heat to the target, for example, Yttrium Aluminum Garnet (YAG) is used. As conditions of the laser irradiation, for example, a normal pulse YAG laser of 1.06 micrometer is used, the irradiation energy is 1 to 10 J, and the pulse width is 0.2 to 2 ms. By this laser irradiation, microcrack regions54are formed in the piezoelectric ceramic plates6ato6din each interval between neighboring active portions25.

Afterward, an FPC5is bonded to the actuator unit56. In Step S6, a high potential is applied to the individual electrodes22and24through the FPC5to form active portions25in the piezoelectric ceramic plates6cto6e. Through the above-described processes, such an inkjet head51as illustrated inFIG. 9can be manufactured.

In a modification of the manufacturing method of this embodiment, in place of applying the laser59in Step S5, an indenter60may be used to press down the surface of the piezoelectric ceramic plate6ain each interval between active portions25neighboring each other in the plane direction of the actuator unit56. The indenter60may be provided at its tip end with an artificial diamond. As the pressing condition, for example, the load is 50 to 500 gf in a micro-Vickers indenter. Also by thus pressing with the indenter60, microcrack regions54are formed in the piezoelectric ceramic plates6ato6din each interval between neighboring active portions25.

In the manufacturing method of this embodiment, the microcracks can be formed with high positional accuracy. Further, because no washing process is necessary after the microcracks are formed, an actuator unit56in which crosstalk is reduced can be easily fabricated in a short time in comparison with the case wherein slits are formed between active portions25by mechanical processing as described before.

Among microcracks formed by applying an intense electric field as in the above-described first and second embodiments, microcracks formed by irradiation with the laser59, and microcracks formed by pressing with the indenter60, there are differences in structure such as the lengths of cracks, the intervals between cracks, and the density of cracks. However, the present inventor has confirmed that microcracks formed through any process brings about a sufficient effect of reducing crosstalk.

Microcrack regions may be formed between neighboring active portions by a method other than those of the above-described embodiments.

Microcrack regions need not always be continuously formed to isolate neighboring active portions from each other. Microcrack regions may be discontinuously formed.

In the above-described embodiments, microcrack regions are formed in plural piezoelectric ceramic plates. However, microcrack regions may be formed in only one piezoelectric ceramic plate. Also, active portions may be formed in only one piezoelectric ceramic plate. Further, the actuator unit may include therein not plural piezoelectric ceramic plates in layers but only one piezoelectric ceramic plate.

An apparatus constructed like an inkjet printer according to any of the above-described embodiments may eject droplets of a conductive paste to print a very fine electric circuit pattern. Further, an apparatus constructed like the inkjet printer of any of the above-described embodiments may eject droplets of an organic luminescent material to make a high-resolution display device such as an organic electro luminescence display (OELD). Other than these, in applications wherein small dots are formed on a print medium, apparatus like the ink-jet printer of any of the above-described embodiments can be used very widely.