JP2016041485A - Liquid injection apparatus and electrode position determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid injection apparatus capable of ensuring that crosstalk is suppressed while making the distortion of a piezoelectric actuator as large as possible.SOLUTION: A first individual electrode 44 overlapping a central portion of a pressure chamber 10 in a transport direction, and a second individual electrode having two overlap portions 45a overlapping two end portions of the pressure chamber 10 in the transport direction, respectively are disposed on an upper surface of a piezoelectric layer 42. The piezoelectric layer 42 is held between the first individual electrode 44 and the overlap portions 45a and a common electrode 43. A center 46a of a clearance 46 between the first individual electrode 44 and each overlap portion 45a is located in a predetermined region Ra overlapping a central region of the pressure chamber 10. The predetermined region Ra is a region where the distortion of a piezoelectric actuator 22 toward the pressure chamber 10 becomes a maximum level when an electric field in a thickness direction is generated in the entire predetermined region Ra.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a liquid ejecting apparatus that ejects liquid from a nozzle, and an electrode position determining method that determines the position of an electrode in the liquid ejecting apparatus.

  As a liquid ejecting apparatus that ejects liquid from a nozzle, Patent Document 1 describes an inkjet head that ejects ink from a nozzle. The ink jet head described in Patent Document 1 includes a cavity unit and a piezoelectric actuator. The cavity unit has a plurality of pressure chambers arranged in the arrangement direction of the recording paper. The piezoelectric actuator is provided with three piezoelectric material layers arranged on top of each other on the upper surface of the cavity unit, a first constant potential electrode to which a first constant potential is always applied, and a second constant potential at all times. A second constant potential electrode and an individual electrode are provided. The first constant potential electrode is disposed in a portion of the three piezoelectric material layers that overlaps the central portion of the pressure chamber between the central piezoelectric material layer and the upper piezoelectric material layer. The second constant potential electrode is arranged in a portion overlapping the both ends of the pressure chamber in the recording paper conveyance direction between the lower piezoelectric material layer and the central piezoelectric material layer among the three piezoelectric material layers. Yes. The individual electrode overlaps both the first constant potential electrode and the second constant potential electrode in a portion overlapping the pressure chamber on the upper surface of the upper piezoelectric material layer among the three piezoelectric material layers. In addition, the portion of the upper piezoelectric material layer sandwiched between the first constant potential electrode and the individual electrode is polarized upward in the thickness direction. Further, the portions of the upper and central piezoelectric material layers sandwiched between the second constant potential electrode and the individual electrodes are polarized downward in the thickness direction.

  When the first constant potential is applied to the individual electrode, a downward electric field in the thickness direction parallel to the polarization direction is generated in a portion sandwiched between the individual electrode and the second constant potential electrode of the piezoelectric material layer. As a result, this portion of the piezoelectric material layer contracts in the plane direction, and the portion overlapping the pressure chamber of the piezoelectric actuator bends to the opposite side of the pressure chamber. On the other hand, when the second constant potential is applied to the individual electrode, an upward electric field in the thickness direction parallel to the polarization direction is generated in a portion sandwiched between the individual electrode and the first constant potential electrode of the piezoelectric material layer. Thereby, this portion of the piezoelectric material layer is contracted in the surface direction, and the portion overlapping the pressure chamber of the piezoelectric actuator is bent toward the pressure chamber.

  When the piezoelectric actuator is driven by switching the potential applied to the individual electrode between the first constant potential and the second constant potential, the portion sandwiched between the individual electrode and the first constant potential electrode of the piezoelectric layer is When contracting in the surface direction, a portion of the piezoelectric layer sandwiched between the individual electrode and the second constant potential electrode extends in the surface direction to a state before contraction. Further, when the portion sandwiched between the individual electrode and the second constant potential electrode of the piezoelectric layer contracts in the plane direction, the portion sandwiched between the individual electrode and the first constant potential electrode of the piezoelectric layer is in a state before contraction. Elongate in the surface direction. At this time, one of the portion of the piezoelectric layer sandwiched between the individual electrode and the first constant potential electrode and the portion of the piezoelectric layer sandwiched between the individual electrode and the second constant potential electrode in the surface direction. Shrinkage is offset by the planar extension of the other part. Accordingly, it is possible to suppress so-called crosstalk in which the deformation of the portion overlapping the pressure chamber with the piezoelectric layer affects the deformation of the portion overlapping the adjacent pressure chamber of the piezoelectric layer.

JP 2011-51121 A

  Here, in the ink jet head described in Patent Document 1, usually, when the individual electrode is set to the first constant potential, the deflection of the piezoelectric actuator to the side opposite to the pressure chamber causes the second electrode to move to the second electrode. This is smaller than the deflection of the piezoelectric actuator toward the pressure chamber when the constant potential is set to. At this time, if the difference between the deflection of the piezoelectric actuator on the pressure chamber side and the deflection on the side opposite to the pressure chamber is too large, the effect of suppressing the crosstalk may not be sufficiently obtained.

  On the other hand, in Patent Document 1, the end portion of the first constant potential electrode and the end portion of the second constant potential electrode overlap each other in the conveyance direction of the recording paper. However, the deformation of the lower piezoelectric layer due to the potential difference between the first constant potential electrode and the second constant potential electrode is suppressed, the insulation between the first constant potential electrode and the second constant potential electrode is ensured, etc. From this point of view, it is preferable that the first constant potential electrode and the second constant potential electrode are arranged with a gap in the recording sheet conveyance direction. However, in this case, at least one of the first constant potential electrode and the second constant potential electrode and the individual electrode are compared with the case where the first constant potential electrode and the second constant potential electrode overlap each other. There is a possibility that the area of the piezoelectric actuator will be small, and the deflection of the piezoelectric actuator will be small when the individual electrode is switched between the first constant potential and the second constant potential.

  An object of the present invention is to provide a liquid ejecting apparatus and a method for determining an electrode position in the liquid ejecting apparatus that can reliably suppress crosstalk while suppressing a decrease in the bending of a piezoelectric actuator as much as possible.

  A liquid ejecting apparatus according to the present invention communicates with a nozzle for ejecting liquid, and has a flow path unit having a plurality of pressure chambers arranged in one direction, and applies pressure to the liquid in the plurality of pressure chambers. The piezoelectric actuator comprises: a piezoelectric layer continuously extending across the plurality of pressure chambers; and a first electrode disposed on a portion of the piezoelectric layer overlapping a central portion of the pressure chamber. And a second electrode disposed on a portion of the piezoelectric layer that overlaps the pressure chamber and outside the first electrode in the one direction, and the first electrode and the second electrode, Is disposed with a gap in the one direction, and the center of the gap is located in a predetermined area that is an area overlapping the central area of the pressure chamber of the piezoelectric layer in the one direction, and the predetermined area is The entire predetermined area When an electric field is generated in the viewing direction, deflection to the pressure chamber side of the piezoelectric actuator is the region of maximum.

  An electrode position determination method according to the present invention is a flow path unit having a plurality of pressure chambers arranged in one direction and communicating with a nozzle for ejecting liquid, and applies pressure to the liquid in the plurality of pressure chambers. A piezoelectric actuator, and the piezoelectric actuator is disposed in a portion overlapping the piezoelectric layer continuously extending over the plurality of pressure chambers and a central portion of the pressure chamber of the piezoelectric layer. In the liquid ejecting apparatus, comprising: an electrode; and a second electrode disposed in a portion of the piezoelectric layer that overlaps the pressure chamber in an outer side of the first electrode in the one direction. And an electrode position determining method for determining the position of the second electrode, wherein the first electrode and the second electrode are arranged with a gap in the one direction, and the center of the gap is In one direction, front The positions of the first electrode and the second electrode are determined so as to be located in a predetermined area that is an area overlapping with a central area of the pressure chamber of the piezoelectric layer, and the predetermined area extends in the thickness direction over the entire predetermined area. When the electric field is generated, the piezoelectric actuator is the region where the deflection of the piezoelectric actuator toward the pressure chamber is maximized.

  When the first electrode and the second electrode are disposed on the same surface of the piezoelectric layer, it is necessary to provide a gap between the first electrode and the second electrode. Even when the first electrode and the second electrode are arranged on different surfaces of the piezoelectric layer, there is a gap between the first electrode and the second electrode from the viewpoint of ensuring insulation reliability between the electrodes. Preferably there is.

  On the other hand, when a plurality of pressure chambers are arranged in one direction and the piezoelectric layer continuously extends across the plurality of pressure chambers, the deformation of the portion overlapping the pressure chamber with the piezoelectric layer is changed. There is a possibility that so-called crosstalk, which affects the deflection of the portion overlapping the adjacent pressure chambers, may occur. In the present invention, an electric field is generated in the piezoelectric layer using the first electrode and the piezoelectric actuator is bent toward the pressure chamber side, and an electric field is generated in the piezoelectric layer using the second electrode and the piezoelectric actuator is moved to the pressure chamber. When switching between the state bent to the opposite side, one of the portions overlapping the first electrode and the second electrode of the piezoelectric layer contracts and the other portion expands to the state before contraction. To do. As a result, the contraction of the one part and the extension of the other part are offset, and crosstalk can be suppressed. However, in a piezoelectric actuator in which the first electrode overlaps with the central portion of the pressure chamber and the second electrode overlaps with a portion outside the portion overlapping the first electrode of the pressure chamber, the deflection toward the pressure chamber is And greater than the deflection to the opposite side. At this time, if the difference between the deflection toward the pressure chamber and the deflection toward the opposite side of the pressure chamber is large, the effect of suppressing the crosstalk is reduced.

  Therefore, in the present invention, the first electrode and the second electrode are positioned so that the center of the gap between the first electrode and the second electrode is located in a predetermined region that overlaps the central region of the pressure chamber of the piezoelectric layer in one direction. Is arranged. Here, the predetermined region is a region where the deflection of the piezoelectric actuator toward the pressure chamber side is greatest when an electric field in the thickness direction is generated in the entire predetermined region. As a result, the difference between the deflection of the piezoelectric actuator toward the pressure chamber side and the deflection toward the opposite side of the pressure chamber is compared with the case where the center of the gap is located outside the predetermined region in one direction. Can be small. Thereby, crosstalk can be reliably suppressed.

  Further, in the present invention, the deflection of the piezoelectric actuator toward the pressure chamber is reduced as compared with the case where the center of the gap is located outside a predetermined region in one direction. However, as described above, in the piezoelectric actuator, the deflection toward the pressure chamber side is larger than the deflection toward the side opposite to the pressure chamber. Therefore, when the center of the gap is located in a predetermined area in one direction, the gap is larger than the case where the center of the gap is located outside the predetermined area in one direction. The influence on the deflection of the piezoelectric actuator due to the formation of can be reduced.

1 is a schematic configuration diagram of a printer according to a first embodiment. It is a top view of the inkjet head of FIG. It is the III-III sectional view taken on the line of FIG. It is the VI-IV sectional view taken on the line of FIG. (A) is a figure equivalent to FIG. 4 which shows the comparative example with 1st Embodiment, (b) is a figure equivalent to FIG. 4 which shows the comparative example different from (a). (A) is a table | surface which shows the relationship between the length of the pressure chamber in 1st Embodiment, and the length of a predetermined area | region, (b) is the relationship of (a), the horizontal axis shows the length of a pressure chamber, and the vertical axis | shaft. It is the figure shown on the plane which makes the length of a predetermined area | region. It is a top view of the ink jet head concerning a 2nd embodiment. (A) is a top view of the lower piezoelectric layer, (b) is a top view of the intermediate piezoelectric layer, and (c) is a top view of the upper piezoelectric layer. It is the IX-IX sectional view taken on the line of FIG. FIG. 3 is a sectional view taken along line XX in FIG. 2. (A) is a figure equivalent to FIG. 10 which shows the comparative example with 2nd Embodiment, (b) is a figure equivalent to FIG. 10 which shows the comparative example different from (a). (A) is a table | surface which shows the relationship between the length of the pressure chamber in 2nd Embodiment, and the length of a predetermined area | region, (b) is the relationship of (a), the horizontal axis shows the length of a pressure chamber, and the vertical axis | shaft. It is the figure shown on the plane which makes the length of a predetermined area | region. (A) is a figure equivalent to FIG. 10 of the modification 1, (b) is a figure equivalent to FIG. 10 of the modification 2. (A) is a figure equivalent to FIG. 10 of the modification 3, and (b) is a figure equivalent to FIG. 10 of the modification 4.

[First Embodiment]
Hereinafter, a preferred first embodiment of the present invention will be described.

(Printer)
As shown in FIG. 1, the printer 1 according to the first embodiment includes a carriage 2, an inkjet head 3, a conveyance roller 4, and the like. The carriage 2 is supported by two guide rails 5 extending in the scanning direction, and reciprocates along the guide rail 5 in the scanning direction. In the following description, the right and left sides in the scanning direction are defined as shown in FIG.

  The inkjet head 3 is mounted on the carriage 2 and ejects ink from a plurality of nozzles 15 formed on the lower surface thereof. The conveyance rollers 4 are arranged on both sides of the carriage 2 in the conveyance direction orthogonal to the scanning direction, and convey the recording paper P in the conveyance direction.

  In the printer 1, printing is performed on the recording paper P by ejecting ink from the inkjet head 3 that reciprocates in the scanning direction together with the carriage 2 while transporting the recording paper P in the transport direction by the transport roller 4.

(Inkjet head)
As shown in FIGS. 2 to 4, the inkjet head 3 includes a plurality of nozzles 15, a flow path unit 21 having an ink flow path such as a plurality of pressure chambers 10 communicating with the plurality of nozzles 15, and the pressure chamber 10. And a piezoelectric actuator 22 for applying pressure to the ink.

<Flow path unit>
The flow path unit 21 is formed by stacking four plates 31 to 34. Of the four plates 31 to 34, the upper three plates 31 to 33 are made of a metal material such as stainless steel. The plate 34 is made of a synthetic resin material such as polyimide. Or the plate 34 may also be comprised with the metal material similar to the plates 31-33.

  A plurality of pressure chambers 10 are formed in the plate 31. The pressure chamber 10 has a substantially elliptical shape with the scanning direction as the longitudinal direction, and the length X in the transport direction is about 250 to 400 [μm]. The plurality of pressure chambers 10 are arranged in the transport direction to form a pressure chamber row 9. On the plate 31, four pressure chamber rows 9 are arranged in the scanning direction. In the plate 32, a plurality of substantially circular through holes 12 are formed in portions overlapping the left end portions of the plurality of pressure chambers 10. Further, a plurality of substantially circular through holes 13 are formed in the plate 32 at portions overlapping the right end portions of the plurality of pressure chambers 10.

  Four manifold channels 11 are formed in the plate 33. The four manifold channels 11 are provided for the four pressure chamber rows 9, extend in the transport direction, and overlap the portions excluding the right end portion of the corresponding pressure chamber rows 9. The four manifold channels 11 are supplied with black, yellow, cyan, and magenta inks from the ink supply port 8 provided at the downstream end in the transport direction in order from the one arranged on the right side. In addition, a plurality of substantially circular through holes 14 are formed in the plate 33 so as to overlap the plurality of through holes 13. In the plate 34, a plurality of nozzles 15 are formed in portions overlapping with the plurality of through holes 14.

<Piezoelectric actuator>
The piezoelectric actuator 22 includes an ink separation layer 40, piezoelectric layers 41 and 42, a common electrode 43, a plurality of first drive electrodes 44, a plurality of second drive electrodes 45, and the like. The ink separation layer 40 is made of a metal material such as stainless steel, and is disposed on the upper surface of the flow path unit 21 so as to cover the plurality of pressure chambers 10. The ink separation layer 40 is for preventing the ink in the pressure chamber 10 from coming into contact with the piezoelectric layer 41. The thickness of the ink separation layer 40 is, for example, about 10 [μm].

  The piezoelectric layer 41 is made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate, and is disposed on the upper surface of the ink separation layer 40 and spans the plurality of pressure chambers 10. It extends continuously. The thickness of the piezoelectric layer 41 is, for example, about 15 [μm]. Here, the piezoelectric layer 41 is for insulating a common electrode 43 and an ink separation layer 40 described later. The piezoelectric layer 42 is made of the same piezoelectric material as the piezoelectric layer 41 and is disposed on the upper surface of the piezoelectric layer 41. The thickness of the piezoelectric layer 42 is, for example, about 18 [μm].

  The common electrode 43 extends over almost the entire area between the piezoelectric layer 41 and the piezoelectric layer 42. The common electrode 43 is always held at the ground potential. The plurality of first individual electrodes 44 are individually provided for the plurality of pressure chambers 10. The first individual electrode 44 is disposed so as to overlap the central portion of the pressure chamber 10 in the transport direction. Further, the first individual electrode 44 extends to the left side so as not to overlap the pressure chamber 10, and the tip thereof serves as a connection terminal 44 a. A driver IC (not shown) is connected to the connection terminal 44a via a wiring member (not shown). Thereby, one of the ground potential and the drive potential of, for example, about 20V is selectively applied to the plurality of first individual electrodes 44 individually by the driver IC.

  The plurality of second individual electrodes 45 are individually provided for the plurality of pressure chambers 10. The second individual electrode 45 includes two overlapping portions 45a and a connecting portion 45b. The two overlapping portions 45a overlap the upstream end portion and the downstream end portion of the pressure chamber 10 in the transport direction. Further, the first individual electrode 44 and each overlapping portion 45a are disposed with a gap 46 in the transport direction. The position of the gap 46 will be described in detail later. The connecting portion 45b extends in the transport direction and connects the right end portions of the two overlapping portions 45a. The connecting portion 45b is connected to a driver IC (not shown) via a wiring member (not shown). The plurality of second individual electrodes 45 are selectively given a ground potential and any one of the drive potentials individually by the driver IC.

  Corresponding to the arrangement of the common electrode 43, the plurality of first individual electrodes 44, and the plurality of second individual electrodes 45 as described above, the common electrode 43 and each first individual electrode of the piezoelectric layer 42 are provided. The first active part T1 sandwiched between 44 and the second active part T2 sandwiched between the common electrode 43 and each second individual electrode 45 is polarized downward in the thickness direction.

(Piezoelectric actuator drive method)
Here, a driving method of the piezoelectric actuator 22 will be described. In the piezoelectric actuator 22, a plurality of first individual electrodes 44 are previously held at a driving potential, and a plurality of second individual electrodes 45 are held at a ground potential. In this state, due to the potential difference between the first individual electrode 44 and the common electrode 43, a downward electric field in the thickness direction parallel to the polarization direction is generated in the first active portion T1, and the surface where the first active portion T1 is orthogonal to the polarization direction. Shrink in the direction. Thereby, the part which overlaps with the pressure chamber 10 of the piezoelectric layers 41 and 42 and the ink separation layer 40 is bent to the pressure chamber 10 side as a whole.

  When ejecting ink from a certain nozzle 15, first, the potential of the first individual electrode 44 corresponding to this nozzle 15 is switched to the ground potential, and the potential of the second individual electrode 45 corresponding to this nozzle 15 is switched to the drive potential. . Then, the first individual electrode 44 and the common electrode 43 have the same potential, so that the first active portion T1 extends to a state before contraction. Further, due to the potential difference between the second individual electrode 45 and the common electrode 43, a downward electric field in the thickness direction parallel to the polarization direction is generated in the second active portion T2, and the second active portion T2 contracts in the plane direction due to this electric field. . For these reasons, the portions of the piezoelectric layers 41 and 42 and the ink separation layer 40 that overlap with the pressure chamber 10 are bent to the opposite side of the pressure chamber 10 as a whole. As a result, the volume of the pressure chamber 10 increases, the pressure of the ink in the pressure chamber 10 decreases, and the ink flows from the manifold channel 11 into the pressure chamber 10. However, the bending to the opposite side to the pressure chamber 10 at this time is due to the pressure chamber 10 side when the first individual electrode 44 is held at the driving potential and the second driving electrode 45 is held at the ground potential. It is smaller than the deflection.

  At this time, the extension of the first active portion T1 and the contraction of the second active portion T2 are offset, so that the deformation of the portion of the piezoelectric layer 42 overlapping the pressure chamber 10 is adjacent to the conveyance direction of the piezoelectric layer 42. It is possible to suppress so-called crosstalk that affects the deformation of the portion overlapping the pressure chamber 10 to be performed.

  Then, after a predetermined time has elapsed, the first individual electrode 44 is returned to the drive potential, and the second individual electrode 45 is returned to the ground potential. Then, the first active portion T1 contracts and the second active portion T2 expands to the state before contraction, so that the portions of the piezoelectric layers 41 and 42 and the ink separation layer 40 that overlap with the pressure chamber 10 as a whole. Bend to the side. As a result, the volume of the pressure chamber 10 decreases, the pressure of the ink in the pressure chamber 10 increases, and ink is ejected from the nozzle 15 communicating with the pressure chamber 10. At this time, the contraction of the first active part T1 and the extension of the second active part T2 are offset. Thereby, crosstalk can be suppressed.

(Gap position)
Next, the position of the gap 46 between the first individual electrode 44 and the second individual electrode 45 will be described. The position of the gap 46 is determined according to the position of the predetermined region Ra of the piezoelectric layer 42. Here, the predetermined region Ra overlaps the central region of the pressure chamber 10 of the piezoelectric layer 42, and when the electric field in the thickness direction is generated in the entire predetermined region Ra, the piezoelectric actuator 22 is flexed to the pressure chamber 10 side. It is an area that becomes. That is, the predetermined region Ra is a region that contributes to bending the piezoelectric actuator 22 toward the pressure chamber 10 when an electric field in the thickness direction of the piezoelectric layer 42 is generated. On the other hand, of the portion of the piezoelectric layer 42 that overlaps the pressure chamber 10, the region outside the predetermined region Ra bends the piezoelectric actuator 22 to the side opposite to the pressure chamber 10 when an electric field in the thickness direction is generated. This is a region that contributes to The position of the predetermined region Ra of the piezoelectric layer 42 is determined to be one if the structure of the inkjet head 3 is determined, such as the length of the pressure chamber 10 in the transport direction and the thickness and material of the ink separation layer 40 and the piezoelectric layers 41 and 42. It is. In FIG. 4, hatching where straight lines intersect is given to the predetermined region Ra.

  In the first embodiment, the end of the first individual electrode 44 in the transport direction is located inside the end of the predetermined region Ra in the transport direction. Further, the end of the overlapping portion 45a in the transport direction on the first individual electrode 44 side overlaps the end of the predetermined region Ra in the transport direction. As a result, the entire gap 46 including the center 46a in the transport direction is located in the predetermined region Ra.

  In the piezoelectric actuator 22, the first individual electrode 44 and the second individual electrode 45 are disposed on the upper surface of the piezoelectric layer 42. Therefore, it is necessary to provide a gap 46 between the overlapping portion 45a of the first individual electrode 44 and the second individual electrode 45 in the transport direction. At this time, unlike the present invention, the center 46a of the gap 46 can be positioned outside the predetermined region Ra in the transport direction. For example, as shown in FIG. 5A, the entire gap 46 including the center 46a can be positioned outside the predetermined region Ra in the transport direction. Alternatively, as shown in FIG. 5B, the center 46a can be positioned outside the predetermined region Ra by partially positioning the gap 46 outside the predetermined region Ra in the transport direction.

  However, in these cases, compared with the case of the first embodiment, the area where the first individual electrode 44 and the common electrode 43 face each other is large, and the second individual electrode 45 and the common electrode 43 face each other. The area becomes smaller. Therefore, as compared with the case of the first embodiment, the deflection of the piezoelectric actuator 22 toward the pressure chamber 10 is increased, and the deflection toward the side opposite to the pressure chamber 10 is decreased. As described above, the piezoelectric actuator 22 originally has a larger deflection toward the pressure chamber 10 than a deflection toward the opposite side of the pressure chamber 10. Therefore, in these cases, the difference between the deflection of the piezoelectric actuator 22 toward the pressure chamber 10 and the deflection toward the opposite side of the pressure chamber 10 becomes large. If the difference between the deflection of the piezoelectric actuator 22 toward the pressure chamber 10 and the deflection toward the opposite side of the pressure chamber 10 becomes too large, the first active portion T1 and the second active portion T2 are not driven when the piezoelectric actuator 22 is driven. Of these, the contraction of one active part and the extension of the other active part are not sufficiently offset, and crosstalk may not be sufficiently suppressed.

  On the other hand, in the first embodiment, the entire gap 46 including the center 46a is located in the predetermined area Ra. Therefore, the center 46a of the gap 46 is located outside the predetermined area Ra in the transport direction. Compared to the case, the deflection of the piezoelectric actuator 22 toward the pressure chamber 10 is reduced, and the deflection toward the opposite side of the pressure chamber 10 is increased. Therefore, in the first embodiment, compared to the case where the center 46a of the gap 46 is located outside the predetermined region Ra in the transport direction, the bending of the piezoelectric actuator 22 toward the pressure chamber 10 side, The difference from the deflection to the opposite side can be reduced. Accordingly, when the piezoelectric actuator 22 is driven, the contraction of one active part and the extension of the other active part of the first active part T1 and the second active part T2 are sufficiently offset, and crosstalk is reliably suppressed. can do.

  Further, when the entire gap 46 is located in the predetermined region Ra, the pressure chamber 10 of the piezoelectric actuator 22 is compared with the case where the center 46a of the gap 46 is located outside the predetermined region Ra in the transport direction. The deflection to the side is reduced. However, the piezoelectric actuator 22 originally has a larger deflection toward the pressure chamber 10 than the deflection toward the opposite side of the pressure chamber 10. Therefore, the reduction of the deflection of the piezoelectric actuator 22 toward the pressure chamber 10 has a smaller influence on the deflection of the piezoelectric actuator 22 than the reduction of the deflection of the piezoelectric actuator 22 toward the opposite side of the pressure chamber 10. On the other hand, when the end of the overlapping portion 45a in the transport direction is arranged so as to overlap the end of the predetermined region Ra in the transport direction, it is common with the second individual electrode 45 in the region outside the predetermined region Ra of the piezoelectric layer 42. The area where the electrode 43 overlaps is maximized, and the second individual electrode 45 does not overlap the predetermined region Ra. Therefore, the deflection of the piezoelectric actuator 22 to the side opposite to the pressure chamber 10 can be maximized.

(Method for specifying the position of the predetermined area)
Next, a method for specifying the position of the predetermined region Ra will be described. In the piezoelectric actuator 22 of the first embodiment, when the length X of the pressure chamber 10 in the transport direction is 250 [μm] or more and 400 [μm] or less, the length Ya [μm] is set to Ya = ( 0.72 · X + 11) / 2, which overlaps with the central region of the pressure chamber 10 in the transport direction, and positions of both ends in the transport direction are Ya from the center 10a of the pressure chamber 10 in the transport direction. An area separated by [μm] in the transport direction is specified as the predetermined area Ra.

  Here, FIG. 6A is a diagram illustrating a relationship between the length X [μm] of the pressure chamber 10 in the transport direction and the length Za (= 2 · Ya) [μm] of the predetermined region Ra. In FIG. 6A, the thickness of the ink separation layer 40 is 10 [μm], the thickness of the piezoelectric layer 41 is 15 [μm], the thickness of the piezoelectric layer 42 is 18 [μm], and the predetermined region Ra is conveyed. The relationship between the length X of the pressure chamber 10 in the transport direction and the length Za [μm] of the predetermined region Ra when the direction is symmetrical to the center 10a of the pressure chamber 10 is shown.

  Then, when the relationship of FIG. 6A is illustrated on a plane in which the horizontal axis is length X [μm] and the vertical axis is length Za [μm], it is as shown in FIG. 6B. From the result of FIG. 6B, when the length X [μm] of the pressure chamber 10 is in the range of 250 [μm] to 400 [μm], the length X [μm] and the length Za [μm] are It can be seen that it is almost linearly proportional. A straight line La obtained by linear approximation of the result of FIG. 6A by the least square method or the like is a straight line that satisfies the relationship of Za = 0.72 · X + 11. Therefore, as described above, if the length Ya (= Za / 2) [μm] is calculated and the position of the predetermined area Ra is specified based on the calculation result, the position of the predetermined area Ra can be specified accurately. Can do. In addition, if the position of the predetermined area Ra is specified in this way, the position of the predetermined area Ra can be easily specified.

  In the first embodiment, the piezoelectric layer 42 corresponds to the piezoelectric layer of the present invention. The first individual electrode 44 corresponds to the first electrode of the present invention, and the second individual electrode 45 corresponds to the second electrode of the present invention. In the first embodiment, the transport direction corresponds to one direction of the present invention.

[Second Embodiment]
Next, a preferred second embodiment of the present invention will be described. However, in the second embodiment, since the piezoelectric actuator 22 of the first embodiment is replaced with a piezoelectric actuator 122 described below, the configuration of the piezoelectric actuator 122 will be mainly described below.

(Piezoelectric actuator)
As shown in FIGS. 7 to 10, the piezoelectric actuator 122 of the second embodiment includes an ink separation layer 140, a lower piezoelectric layer 141, an intermediate piezoelectric layer 142, an upper piezoelectric layer 143, a first constant potential electrode 144, and a second constant voltage. A potential electrode 145, a plurality of individual electrodes 146, and the like are provided.

  Like the ink separation layer 40 (see FIG. 3), the ink separation layer 140 is made of a metal material such as stainless steel, is disposed on the upper surface of the flow path unit 21, and covers the plurality of pressure chambers 10. The thickness of the ink separation layer 140 is, for example, about 10 [μm]. The piezoelectric layers 141 to 143 are made of the same piezoelectric material as the piezoelectric layers 41 and 42 (see FIG. 3). The lower piezoelectric layer 141 continuously extends over the plurality of pressure chambers 10 on the upper surface of the ink separation layer 140. The thickness of the piezoelectric layer 141 is, for example, about 14 [μm]. Here, the piezoelectric layer 141 is for insulating a second constant potential electrode 145 and an ink separation layer 40 described later. The intermediate piezoelectric layer 142 is disposed on the upper surface of the lower piezoelectric layer 141. The thickness of the intermediate piezoelectric layer 142 is, for example, about 18 [μm]. The upper piezoelectric layer 143 is disposed on the upper surface of the intermediate piezoelectric layer 142. The thickness of the upper piezoelectric layer 143 is, for example, about 18 [μm].

  The first constant potential electrode 144 is disposed between the intermediate piezoelectric layer 142 and the upper piezoelectric layer 143. The first constant potential electrode 144 has a plurality of overlapping portions 144a, four connecting portions 144b, a connecting portion 144c, and a lead-out portion 144d. The overlapping portion 144a is individually provided for the plurality of pressure chambers 10, and overlaps the central portion of the pressure chamber 10 in the transport direction. The four connecting portions 144b are provided corresponding to the four pressure chamber rows 9, and extend in the transport direction to connect the right end portions of the plurality of overlapping portions 144a corresponding to the pressure chamber rows 9. Yes. The connecting portion 144c extends in the scanning direction and connects the ends of the four connecting portions 144b on the downstream side in the transport direction. The lead-out portion 144d is connected to the left end portion of the connecting portion 144c and extends in the transport direction from the connecting portion with the connecting portion 144c. The lead portion 144d is drawn to the upper surface of the upper piezoelectric layer 143 through a through hole 139a formed in the upper piezoelectric layer 143, and is connected to the surface electrode 148 formed on the upper surface of the upper piezoelectric layer 143. The surface electrode 148 is connected to a driver IC (not shown) via a wiring member (not shown). The first constant potential electrode 144 is always held at a predetermined driving potential such as 20 V by the driver IC.

  The second constant potential electrode 145 is disposed between the lower piezoelectric layer 141 and the intermediate piezoelectric layer 142. The second constant potential electrode 145 includes a plurality of overlapping portions 145a, four connecting portions 145b, a connecting portion 145c, and a leading portion 145d. The plurality of overlapping portions 145a are disposed so as to overlap both end portions of the plurality of pressure chambers 10 in the transport direction. Further, the overlapping portion 145a of the second constant potential electrode 145 is arranged with a gap 147 in the transport direction from the overlapping portion 144a of the first constant potential electrode 144. The position of the gap 147 will be described in detail later. The four connecting portions 145 b are provided corresponding to the four pressure chamber rows 9, extend in the transport direction, and connect the left ends of the plurality of overlapping portions 145 a corresponding to the pressure chamber rows 9. Yes. The connecting portion 145c extends in the scanning direction and connects the upstream ends of the four connecting portions 145b in the transport direction. The lead portion 145d extends from the left end portion of the connecting portion 145c to the downstream side in the transport direction. The lead portion 145 d is drawn to the upper surface of the upper piezoelectric layer 143 through a through hole 139 b extending across the intermediate piezoelectric layer 142 and the upper piezoelectric layer 143, and is connected to the surface electrode 149 disposed on the upper surface of the upper piezoelectric layer 143. Has been. The surface electrode 149 is connected to a power source (not shown) via a wiring member (not shown). The second constant potential electrode 145 is always held at the ground potential by a power source (not shown).

  The plurality of individual electrodes 146 are individually provided for the plurality of pressure chambers 10. The individual electrode 146 overlaps substantially the entire pressure chamber 10 and overlaps both the overlapping portion 144a of the first constant potential electrode 144 and the overlapping portion 145a of the second constant potential electrode 145. A connection terminal 146 a extending to a position that does not overlap with the pressure chamber 10 is provided at the left end of the individual electrode 146. The connection terminal 146a is connected to a driver IC (not shown) via a wiring member (not shown). A plurality of individual electrodes 146 are selectively given a ground potential and any one of the drive potentials by a driver IC.

  Corresponding to the arrangement of the first constant potential electrode 144, the second constant potential electrode 145, and the plurality of individual electrodes 146, the individual electrode 146 and the first constant potential electrode 144 of the upper piezoelectric layer 143 are arranged. The first active portion S1 sandwiched between the overlapping portions 144a is polarized upward in the thickness direction. Further, the second active portion S2 sandwiched between the individual electrode 146 and the overlapping portion 145a of the second constant potential electrode 145 of the intermediate piezoelectric layer 142 and the upper piezoelectric layer 143 is polarized downward in the thickness direction.

(Piezoelectric actuator drive method)
Next, a method for driving the piezoelectric actuator 122 will be described. In the piezoelectric actuator 122, all the individual electrodes 146 are previously held at the ground potential. In this state, due to the potential difference between the individual electrode 146 and the first constant potential electrode 144, an electric field upward in the thickness direction parallel to the polarization direction is generated in the first active portion S1. As a result, the portion of the upper piezoelectric layer 143 contracts in the surface direction, and the portions of the piezoelectric layers 141 to 143 and the ink separation layer 140 that overlap with the pressure chamber 10 are bent toward the pressure chamber 10 as a whole.

  When ejecting ink from a certain nozzle 15, first, the potential of the individual electrode 146 corresponding to the nozzle 15 is switched to the driving potential. Then, the individual electrode 146 becomes the same potential as the first constant potential electrode 144, and the first active part S1 expands to a state before contraction. On the other hand, due to the potential difference between the individual electrode 146 and the second constant potential electrode 145, a downward electric field in the thickness direction parallel to the polarization direction is generated in the second active portion S2, and the second active portion S2 contracts in the plane direction. As a result, the portions of the piezoelectric layers 141 to 143 and the ink separation layer 140 that overlap with the pressure chamber 10 are bent to the opposite side of the pressure chamber 10 as a whole. As a result, the volume of the pressure chamber 10 increases, the pressure of the ink in the pressure chamber 10 decreases, and ink is supplied to the pressure chamber 10 from the manifold channel 11 side. However, the deflection toward the side opposite to the pressure chamber 10 at this time is smaller than the deflection toward the pressure chamber 10 when the individual electrode 146 is held at the drive potential. At this time, the crosstalk can be suppressed by canceling out the expansion of the first active part S1 and the contraction of the second active part S2.

  Then, after a predetermined time has elapsed, the potential of the individual electrode 146 is returned to the ground potential. Then, as described above, the first active portion S1 contracts in the surface direction, and the second active portion S2 expands to a state before contraction. Thereby, the part which overlaps with the pressure chamber 10 of the piezoelectric layers 141-143 and the ink separation layer 140 bends to the pressure chamber 10 side as a whole. As a result, the volume of the pressure chamber 10 decreases, the pressure of the ink in the pressure chamber 10 increases, and ink is ejected from the nozzle 15 communicating with the pressure chamber 10. At this time, the contraction of the first active part S1 and the extension of the second active part S2 are offset, and crosstalk can be suppressed.

(Gap position)
Next, the position of the gap 147 between the overlapping portion 144a of the first constant potential electrode 144 and the overlapping portion 145a of the second constant potential electrode 145 will be described. The position of the gap 147 is determined according to the position of the predetermined region Rb of the piezoelectric layers 142 and 143. Here, the predetermined region Rb overlaps the central region of the pressure chamber 10 of the upper piezoelectric layer 142, 143, and when the electric field in the thickness direction is generated over the entire predetermined region Rb, the piezoelectric actuator 122 side of the pressure actuator 10 This is a region where the deflection to the maximum is maximized. The position of the predetermined region Rb is determined to be one if the structure of the inkjet head 3 is determined, such as the length of the pressure chamber 10 in the transport direction, the thickness and material of the ink separation layer 140 and the piezoelectric layers 141 to 143.

  The first constant potential electrode 144 is arranged such that the end of the overlapping portion 144a in the transport direction is located inside the end of the predetermined region Rb in the transport direction. In the second constant potential electrode 145, the end of the overlapping portion 145a in the transport direction on the overlapping portion 144a side overlaps the end of the predetermined region Rb in the transport direction. As a result, the entire gap 147 including the center 147a in the transport direction is located in the predetermined region Rb.

(Gap position)
Next, the position of the gap 147 between the first constant potential electrode 144 and the second constant potential electrode 145 will be described. In the second embodiment, the first constant potential electrode 144 is disposed between the intermediate piezoelectric layer 142 and the upper piezoelectric layer 143, whereas the second constant potential electrode 145 is disposed between the lower piezoelectric layer 141 and the intermediate piezoelectric layer. 142. Therefore, unlike the first embodiment, it is possible to arrange the first constant potential electrode 144 and the second constant potential electrode 145 so that the overlapping portion 144a and the overlapping portion 145a overlap each other. Or it is also possible to arrange | position so that both the edge of the overlap part 144a in a conveyance direction and the edge of the overlap part 145a may be located in the edge of the predetermined area | region Rb in a conveyance direction. That is, it is possible not to provide the gap 147 between the overlapping portion 144a and the overlapping portion 145a.

  However, if the overlapping portion 144a and the overlapping portion 145a overlap, the portion of the intermediate piezoelectric layer 142 sandwiched between the overlapping portion 144a and the overlapping portion 145a is always contracted by the electric field generated by these potential differences, There is a possibility that the bending of the piezoelectric actuator 122 is hindered. In addition, if there is no gap 147 between the overlapping portion 144a and the overlapping portion 145a, there is a possibility that sufficient insulation between the overlapping portion 144a and the overlapping portion 145a cannot be ensured.

  For these reasons, the overlapping portion 144a and the overlapping portion 145a are preferably arranged with a gap 147 therebetween. However, unlike the present invention, the center 147a of the gap 147 can be positioned outside the predetermined region Rb in the transport direction. For example, as shown in FIG. 11A, the entire gap 147 including the center 147a can be positioned outside the predetermined region Rb in the transport direction. Alternatively, as shown in FIG. 11B, by positioning a part of the gap 147 outside the predetermined area Rb in the transport direction, the center 147a of the gap 147 can be positioned outside the predetermined area Rb. .

  However, in these cases, compared to the second embodiment, the area where the overlapping portion 144a and the individual electrode 146 face each other is large, and the area where the overlapping portion 145a and the individual electrode 146 face each other is small. . Therefore, compared with the case of 2nd Embodiment, the bending to the pressure chamber 10 side of the piezoelectric actuator 122 becomes large, and the bending to the opposite side to the pressure chamber 10 becomes small. As described above, the piezoelectric actuator 122 originally has a larger deflection toward the pressure chamber 10 than a deflection toward the opposite side of the pressure chamber 10. Therefore, in these cases, the difference between the deflection of the piezoelectric actuator 122 toward the pressure chamber 10 and the deflection toward the opposite side of the pressure chamber 10 becomes large. If the difference between the deflection of the piezoelectric actuator 122 toward the pressure chamber 10 and the deflection toward the opposite side of the pressure chamber 10 becomes too large, there is a possibility that the crosstalk cannot be sufficiently suppressed as described above.

  In contrast, in the second embodiment, as described above, the entire gap 147 including the center 147a is located in the predetermined region Rb. Therefore, compared to the case where the center 147a of the gap 147 is located outside the predetermined region Rb in the transport direction, the bending of the piezoelectric actuator 122 toward the pressure chamber 10 is reduced, and the pressure chamber 10 is moved to the opposite side. Deflection increases. Therefore, compared to the case where the center 147a of the gap 147 is located outside the predetermined region Rb in the transport direction, the deflection of the piezoelectric actuator 122 toward the pressure chamber 10 and the deflection toward the opposite side of the pressure chamber 10 Can be reduced. Thereby, when the piezoelectric actuator 122 is driven, the contraction of one active part and the extension of the other active part of the first active part S1 and the second active part S2 are sufficiently offset, and crosstalk is reliably suppressed. can do.

  Further, when the entire gap 147 is located in the predetermined region Rb, the pressure chamber 10 of the piezoelectric actuator 122 is compared with the case where the center 147a of the gap 147 is located outside the predetermined region Rb in the transport direction. The deflection to the side is reduced. However, the piezoelectric actuator 122 originally has a larger deflection toward the pressure chamber 10 than the deflection toward the opposite side of the pressure chamber 10. Therefore, a reduction in the deflection of the piezoelectric actuator 122 toward the pressure chamber 10 has less influence on the deflection of the piezoelectric actuator 122 than a reduction in the deflection of the piezoelectric actuator 122 toward the opposite side of the pressure chamber 10. . On the other hand, when the end of the overlapping portion 145a in the transport direction is arranged so as to overlap the end of the predetermined region Rb in the transport direction, the second constant potential electrode is formed in a region outside the predetermined region Rb of the piezoelectric layers 142 and 143. The area where 145 and the individual electrode 146 overlap is maximized, and the second constant potential electrode 145 does not overlap the predetermined region Rb. Therefore, the bending of the piezoelectric actuator 122 to the side opposite to the pressure chamber 10 can be maximized.

(Method for determining the position of the predetermined area)
Next, a method for specifying the position of the predetermined region Rb will be described. In the piezoelectric actuator 122 of the second embodiment, when the length X of the pressure chamber 10 in the transport direction is 250 [μm] or more and 400 [μm] or less, the length Yb [μm] is set to Yb = ( 0.7 · X + 28.333) / 2, which overlaps the central region of the pressure chamber 10 in the transport direction, and the positions of both ends in the transport direction are the center 10a of the pressure chamber 10 in the transport direction. A region that is separated in the transport direction by Yb [μm] is specified as the predetermined region Rb.

  Here, FIG. 12A is a diagram illustrating a relationship between the length X [μm] of the pressure chamber 10 in the transport direction and the length Zb [μm] of the predetermined region Rb in the second embodiment. In FIG. 12A, the thickness of the ink separation layer 140 is 10 [μm], the thickness of the lower piezoelectric layer 141 is 14 [μm], the thickness of the intermediate piezoelectric layer 142 is 18 [μm], and the thickness of the upper piezoelectric layer 143 is When the thickness is 18 [μm] and the predetermined region Rb is symmetrical to the center 10a of the pressure chamber 10 in the transport direction, the length X [μm] of the pressure chamber 10 in the transport direction and the predetermined region Rb The relationship with the length Zb [μm] is shown.

  Then, when the relationship of FIG. 12A is illustrated on a plane in which the horizontal axis is length X [μm] and the vertical axis is length Zb [μm], it is as shown in FIG. From the result of FIG. 12B, it can be seen that the length X [μm] and the length Zb [μm] are approximately linearly proportional. A straight line Lb obtained by linear approximation of the result of FIG. 12A by the least square method or the like is a straight line that satisfies the relationship of Zb = 0.7 · X + 28.333. Therefore, as described above, if the length Yb (= Zb / 2) [μm] is calculated and the position of the predetermined region Rb is specified based on the calculation result, the position of the predetermined region Rb can be specified accurately. Can do. Further, if the position of the predetermined region Rb is specified in this way, the position of the predetermined region Rb can be easily specified.

  In the second embodiment, the piezoelectric layers 142 and 143 correspond to the piezoelectric layers of the present invention. The overlapping portion 144a of the first constant potential electrode 144 corresponds to the first electrode of the present invention, and the overlapping portion 145a of the second constant potential electrode 145 corresponds to the second electrode of the present invention.

  Next, modified examples in which various changes are made to the first and second embodiments will be described.

  In the first embodiment, the position of the predetermined region Ra in the piezoelectric actuator 22 is specified based on the length Ya [μm] calculated by Ya = (0.72 · X + 11) / 2. In the second embodiment, Although the position of the predetermined region Rb in the piezoelectric actuator 122 is specified based on the length Yb [μm] calculated by Yb = (0.7 · X + 28.333) / 2, the present invention is not limited to this.

  In the second embodiment, as in the first embodiment, the position of the predetermined region Rb in the piezoelectric actuator 122 is specified based on the length Ya [μm] calculated by Ya = (0.72 · X + 11) / 2. To do. In this case, the same relational expression is used regardless of the configuration of the piezoelectric actuator, such as whether the piezoelectric actuator is the piezoelectric actuator 22 of the first embodiment or the piezoelectric actuator 122 of the second embodiment. The position of the predetermined area can be specified.

  Here, in the second embodiment, as described above, when the relationship between the length X of the pressure chamber 10 in the transport direction and the length Y of the predetermined region Ra is first-order approximated, Yb = 0.7 · X + 28.333 become that way. On the other hand, when comparing the length Ya [μm] and the length Yb [μm], when the length X [μm] of the pressure chamber 10 is 250 [μm] or more and 400 [μm] or less, the length Ya And the length Yb satisfy the relationship Ya <Yb. Therefore, in the second embodiment, the predetermined area specified based on the length Ya [μm] is a part of the predetermined area Rb specified based on the length Yb [μm]. Therefore, if the first constant potential electrode 144 and the second constant potential electrode 145 are arranged so that the entire gap 147 is located in the predetermined region Rc, the entire gap 147 is always located in the predetermined region Rb.

  Further, when the length X [μm] of the pressure chamber 10 is 250 [μm] or more and 400 [μm] or less, the length Za (= 2 · Ya) [μm] and the length Zb (= 2 · Yb) ) [Μm] difference (Zb−Za) [μm] is 9.333 [μm] at the minimum (when X = 400), and 12.333 [μm] (when X = 250) at the maximum. Become. Therefore, the difference between the length Zc [μm] of the predetermined region Rc and the length Zb [μm] of the predetermined region Rb is sufficiently smaller than the length X [μm] of the pressure chamber 10.

  Moreover, the thickness of each layer of the piezoelectric actuators 22 and 122 is not limited to that of the first and second embodiments. In the piezoelectric actuators 22 and 122, the difference in the length of the predetermined regions Ra and Rb in the transport direction due to the difference in the thickness of each layer is the difference between the predetermined regions Ra and Rb in the transport direction due to the difference in the length X [μm] of the pressure chamber 10. It is small compared to the difference in length. Therefore, even if the thicknesses of the layers of the piezoelectric actuators 22 and 122 are slightly different from those in the first and second embodiments, the positions of the predetermined regions Ra and Rb can be specified in the same manner as in the first and second embodiments. For example, the positions of the predetermined regions Ra and Rb can be specified accurately.

  In the first and second embodiments, the length X [μm] of the pressure chamber 10 in the transport direction is 250 [μm] or more and 400 [μm] or less, but is not limited thereto. The length X [μm] of the pressure chamber 10 in the transport direction may be less than 250 [μm] or may be greater than 400 [μm].

  In these cases, FIG. 6A and FIG. 12A when the length of the pressure chamber 10 is changed in a range including the actual length X [μm] of the pressure chamber 10 by analysis or the like. ) And the length of the predetermined area in the transport direction are obtained, and the lengths corresponding to the lengths Ya and Yb are calculated using an approximate expression obtained from the obtained relation. May be.

  In the first and second embodiments, the positions of the predetermined regions Ra and Rb are determined based on the calculated lengths Ya [μm] and Yb [μm]. However, the present invention is not limited to this. For example, when a plurality of types of inkjet heads 3 including the piezoelectric actuators 22 are manufactured with the positions of the gaps 46 being different, and a drive potential is applied to the first individual electrode 44 among the plurality of types of inkjet heads 3, In the piezoelectric actuator in which the deflection of the piezoelectric actuator toward the pressure chamber 10 is the largest, the region where the first individual electrode 44 is disposed may be set as the predetermined region Ra. Also, a plurality of types of inkjet heads 3 including the piezoelectric actuators 122 are manufactured with different lengths of the overlapping portions 144a of the first constant potential electrodes 144 in the transport direction. In the piezoelectric actuator in which the bending of the piezoelectric actuator toward the pressure chamber 10 when the drive potential is applied to 146 is the largest, the region where the overlapping portion 144a is disposed may be set as the predetermined region Rb. In these cases, for example, the larger the size of the ink droplet ejected from the nozzle 15 when the drive potential is applied to the first individual electrode 44 and the individual electrode 146, the larger the pressure chamber 10 of the piezoelectric actuators 22 and 122. What is necessary is just to judge that the deflection to the side is large.

  In the first embodiment, the end of the first individual electrode 44 in the transport direction is located inside the end of the predetermined region Ra in the transport direction, and the first individual electrode 44 of the overlapping portion 45a of the second individual electrode 45 is located. Although the first individual electrode 44 and the second individual electrode 45 are arranged so that the end on the side overlaps the end of the predetermined region Ra in the transport direction, the present invention is not limited to this.

  In the first modification, as shown in FIG. 13A, the end of the overlapping portion 45a on the first individual electrode 44 side in the transport direction is located inside the end of the predetermined region Ra in the transport direction. In the second modification, as shown in FIG. 13B, the center 46a of the gap 46 in the transport direction is located in the predetermined region Ra, but the first individual electrode 44 side of the overlapping portion 45a in the transport direction. Is located outside the predetermined region Ra.

  Also in the first and second modifications, since the center 46a of the gap 46 is located in the predetermined region Ra, the center 46a of the gap 46 is predetermined in the transport direction as in FIGS. 5 (a) and 5 (b). Compared to the case where the region is located outside the region Ra, the effect of suppressing the crosstalk is high, and the influence on the bending of the piezoelectric actuator 22 due to the provision of the gap 46 is small.

  In the second embodiment, the end of the overlapping portion 144a in the transport direction is located inside the end of the predetermined region Rb in the transport direction, and the end of the overlap portion 145a in the transport direction on the overlapping portion 144a side is the transport direction. Although the first constant potential electrode 144 and the second constant potential electrode 145 are disposed so as to overlap with the end of the predetermined region Rb in FIG.

  In Modification 3, as shown in FIG. 14A, the end of the overlapping portion 145a in the transport direction on the side of the overlapping portion 144a is located inside the end of the predetermined region Rb in the transport direction. Further, in Modification 4, as shown in FIG. 14B, the center 147a of the gap 147 in the transport direction is located in the predetermined region Rb, but the end of the overlapping portion 145a in the transport direction on the overlapping portion 144a side. Is located outside the predetermined region Rb.

  Also in the modified examples 3 and 4, since the center 147a of the gap 147 is located in the predetermined region Rb, the center 147a of the gap 147 is predetermined in the transport direction as in FIGS. 11A and 11B. Compared to the case of being located outside the region Rb, the effect of suppressing the crosstalk is high, and the influence on the bending of the piezoelectric actuator 122 due to the provision of the gap 147 is small.

  The configuration of the piezoelectric actuator is not limited to the configuration of the piezoelectric actuator 22 of the first embodiment and the piezoelectric actuator 122 of the second embodiment. The piezoelectric actuator includes a first electrode that overlaps the central portion of the pressure chamber 10 in the transport direction of the piezoelectric layer, and a second portion that overlaps a portion of the piezoelectric layer that overlaps the pressure chamber of the piezoelectric layer and outside the first electrode in the transport direction. It may have another configuration including an electrode.

  Moreover, although the example which applied this invention to the inkjet head which ejects an ink from a nozzle was demonstrated above, it is not restricted to this. The present invention can also be applied to a liquid ejecting apparatus other than an ink jet head that ejects liquid other than ink from a nozzle.

DESCRIPTION OF SYMBOLS 10 Pressure chamber 15 Nozzle 21 Flow path unit 22 Piezoelectric actuator 41, 42 Piezoelectric layer 43 Common electrode 44 1st separate electrode 45 2nd separate electrode 46 Gap 122 Piezoelectric actuator 141, 142, 143 Piezoelectric layer 144 1st constant potential electrode 145 1st 2 Constant potential electrode 146 Individual electrode 147 Gap

Claims (6)

A flow path unit having a plurality of pressure chambers arranged in one direction in communication with a nozzle for ejecting liquid;
A piezoelectric actuator for applying pressure to the liquid in the plurality of pressure chambers,
The piezoelectric actuator is
A piezoelectric layer extending continuously across the plurality of pressure chambers;
A first electrode disposed on a portion of the piezoelectric layer overlapping a central portion of the pressure chamber;
Of the portion of the piezoelectric layer that overlaps the pressure chamber, the second electrode disposed in a portion outside the first electrode in the one direction,
The first electrode and the second electrode are arranged with a gap in the one direction,
The center of the gap is located in a predetermined region which is a region overlapping the central region of the pressure chamber of the piezoelectric layer in the one direction,
The liquid ejecting apparatus according to claim 1, wherein the predetermined region is a region where the deflection of the piezoelectric actuator toward the pressure chamber is maximized when an electric field in the thickness direction is generated in the entire predetermined region. The length X [μm] of the pressure chamber in the one direction is 250 [μm] or more and 400 [μm] or less,
The predetermined region overlaps the central region of the pressure chamber of the piezoelectric layer, and the positions of both ends in the one direction are Y = (0.72X + 11) / 2 from the center of the pressure chamber in the one direction. The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting apparatus is a region that is separated in the one direction by a length Y [μm] calculated by the formula (1). The first electrode and the second electrode are disposed on the same surface of the piezoelectric layer;
The piezoelectric actuator may further include a third electrode that overlaps both the first electrode and the second electrode on a surface of the piezoelectric layer opposite to the first electrode and the second electrode. The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting apparatus is provided. The piezoelectric layer has a first piezoelectric layer and a second piezoelectric layer laminated on the opposite side of the first piezoelectric layer from the flow path unit,
The first electrode is disposed between the first piezoelectric layer and the second piezoelectric layer,
The second electrode is disposed on a surface of the first piezoelectric layer opposite to the second piezoelectric layer;
The piezoelectric actuator further includes a fourth electrode that overlaps both the first electrode and the second electrode on a surface of the second piezoelectric layer opposite to the first piezoelectric layer. Item 3. The liquid ejecting apparatus according to Item 1 or 2. A flow path unit having a plurality of pressure chambers arranged in one direction in communication with a nozzle for ejecting liquid;
A piezoelectric actuator for applying pressure to the liquid in the plurality of pressure chambers,
The piezoelectric actuator is
A piezoelectric layer extending continuously across the plurality of pressure chambers;
A first electrode disposed on a portion of the piezoelectric layer overlapping a central portion of the pressure chamber;
A liquid ejecting apparatus comprising: a second electrode disposed on a portion of the piezoelectric layer that overlaps the pressure chamber, the second electrode being disposed outside the first electrode in the one direction. An electrode position determination method for determining the position of two electrodes,
The first electrode and the second electrode are arranged with a gap in the one direction, and the center of the gap overlaps with the central region of the pressure chamber of the piezoelectric layer in the one direction. Determining the position of the first electrode and the second electrode so as to be located in a predetermined region,
The electrode position determining method, wherein the predetermined region is a region where the deflection of the piezoelectric actuator toward the pressure chamber is maximized when an electric field is generated in the thickness direction over the predetermined region. When the length X [μm] of the pressure chamber in the one direction is 250 [μm] or more and 400 [μm] or less,
The predetermined region overlaps the central region of the pressure chamber of the piezoelectric layer, and the positions of both ends in the one direction are Y = (0.72X + 11) / 2 from the center of the pressure chamber in the one direction. 6. The electrode position according to claim 5, wherein the positions of the first electrode and the second electrode are determined on the assumption that the region is separated in the one direction by a length Y [μm] calculated by the following equation. Decision method.

Images