JP2007237746A - Inkjet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head which can reduce a structural cross talk in order to raise quality of an inkjet printer. <P>SOLUTION: A discrete electrode 35 of an approximate parallelogram is arranged on a piezoelectric sheet 41 in an actuator unit 21. A land part 36 is electrically connected to one acute angle section of a discrete electrode 35. A land part 36 is arranged between other two adjoining discrete electrodes 35. In a perimeter of a land part 36, a grooved part 61 of a C character shape piercing a piezoelectric sheet 41 is formed along an outline of a land part 36. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet head that performs printing by ejecting ink onto a recording medium.

  In an ink jet printer or the like, an ink jet head distributes ink supplied from an ink tank to a plurality of pressure chambers, and ejects ink from nozzles by selectively applying a pulsed pressure to each pressure chamber. As one means for selectively applying pressure to the pressure chamber, an actuator unit in which a plurality of piezoelectric sheets made of piezoelectric ceramic are laminated may be used.

  As an example of such an ink jet head, a plurality of continuous flat plate-like piezoelectric sheets straddling a plurality of pressure chambers are laminated, and at least one piezoelectric sheet is common to a number of pressure chambers and held at a ground potential. One having one actuator unit sandwiched between a common electrode and a large number of individual electrodes, that is, drive electrodes arranged at positions facing each pressure chamber is known (see Patent Document 1). The portion of the piezoelectric sheet sandwiched between the individual electrode and the common electrode and polarized in the laminating direction is external in the polarization direction of the piezoelectric sheet when the individual electrodes on both sides of the sandwiched portion are set to a different potential from the common electrode. When an electric field is applied, it expands and contracts in the stacking direction by a so-called piezoelectric longitudinal effect. In this case, the portion of the piezoelectric sheet sandwiched between the individual electrode and the common electrode functions as an active layer that is deformed by the piezoelectric effect when an external electric field is applied. As a result, the volume in the pressure chamber fluctuates, and ink can be ejected from the nozzle communicating with the pressure chamber toward the recording medium.

Japanese Patent Laid-Open No. 4-341852 (FIG. 1)

  In recent years, in the ink jet head as described above, as the pressure chambers are arranged with high density in order to meet the demand for higher resolution of images and high-speed printing, the active layer facing the pressure chamber is deformed. As a result, even the piezoelectric sheet facing the adjacent pressure chamber is deformed, and ink is ejected from an ink ejection port that should not eject ink, or the ink ejection amount is increased or decreased from the original amount. So-called structural crosstalk has become a problem. In particular, a land that extends from an individual electrode and serves as an input portion for a voltage applied to the individual electrode does not directly drive the pressure chamber. However, the inventor of the present invention has found that the land portion can deform the surrounding piezoelectric sheet and cause crosstalk. Furthermore, the inventor has also found that the influence of the land portion is so large that it cannot be ignored because the land portion is disposed closer to the adjacent pressure chamber than the individual electrode. When such structural crosstalk occurs, the image quality of the printed image is deteriorated. Therefore, in order to improve the quality of the ink jet printer, reduction of the structural crosstalk is a very important problem.

  The main object of the present invention is to provide an inkjet head capable of reducing structural crosstalk.

Means and effects for solving the problems

The inkjet head of the present invention has a flow path unit in which a plurality of pressure chambers communicating with nozzles are arranged adjacent to each other in a matrix along a plane, and is fixed to one surface of the flow path unit to change the volume of the pressure chamber. A plurality of electrode regions arranged at positions facing each of the plurality of pressure chambers, and a terminal region connected to the electrode region and connected to the signal line. A plurality of individual electrodes configured to include a common electrode provided across a plurality of pressure chambers, a piezoelectric sheet sandwiched between the common electrode and the individual electrodes, and a recess formed only around the terminal region Is included.

According to the present invention, since the concave portion is formed around the terminal region, the distortion of the piezoelectric sheet facing the terminal region is less likely to propagate to the piezoelectric sheet facing the other pressure chamber, thereby reducing structural crosstalk. can do. Thereby, the volume and speed of the ink droplets to be ejected can be made uniform. In addition, since the recess is present only around the terminal region, the distance at which the recess is formed is shortened, so that the structural crosstalk is reduced and the recess is formed while suppressing a decrease in the rigidity of the actuator unit. Cost can be reduced.

In the present invention, it is more preferable that the piezoelectric sheet is a continuous flat plate layer provided across the plurality of pressure chambers.

  In the present invention, the planar shape of the pressure chamber is a parallelogram having two acute corners or a parallelogram with rounded corners, and the terminal region is near one acute corner of the pressure chamber. And may be located between the electrode regions of the other two adjacent individual electrodes. According to this, even when the pressure chambers are arranged at high density, structural crosstalk can be reduced.

  In the present invention, the recess may be formed through at least one piezoelectric sheet sandwiched between the common electrode and the individual electrode. According to this, since the region of the piezoelectric sheet corresponding to the terminal region that operates as the active layer is not directly continuous between the adjacent individual electrodes and pressure chambers, structural crosstalk can be effectively reduced. .

  In the present invention, the recess may be formed along the outer shape of the terminal region. According to this, since the distance at which the concave portion is formed becomes shorter, it is possible to further suppress the reduction in the rigidity of the actuator unit and further reduce the cost of forming the concave portion.

  In the present invention, the individual electrode may include a connection region that connects the electrode region and the terminal region, and the concave portion may be continuously formed over substantially the entire circumference of the terminal region excluding a portion facing the connection region. . According to this, structural crosstalk can be reduced in almost all directions around the terminal region.

  In the present invention, a plurality of recesses may be formed around the terminal region. According to this, structural crosstalk can be efficiently reduced by forming a plurality of recesses according to the shape of the pressure chamber and the arrangement position of the terminal region.

  In the present invention, two recesses are formed around the terminal region, and these two recesses may be formed symmetrically with respect to a straight line connecting the electrode region and the terminal region. According to this, when the structural crosstalk in the direction connecting the electrode region and the terminal region is relatively small, it is possible to reduce the cost of forming the recess while reducing the structural crosstalk in the direction other than the direction. .

  In the present invention, the concave portion may be formed at a position crossing an imaginary line connecting the shortest distance between the terminal region and the electrode region of the adjacent individual electrode. According to this, a portion where vibration is most easily transmitted to the adjacent individual electrodes can be suppressed, and structural crosstalk can be effectively reduced.

In this invention, it is preferable that a terminal area | region opposes the partition which divides the said adjacent pressure chamber. According to this, since the terminal area is not disposed in the drive portion of the actuator unit, it is possible to make it difficult to inhibit the drive of the actuator unit. In the present invention, the concave portion may face a partition wall that partitions the adjacent pressure chambers. Further, in the present invention, the planar shape of the pressure chamber is a parallelogram having two acute angles or a parallelogram with rounded corners, and the terminal region is one acute angle of the pressure chamber. It may be located between the electrode regions of the other two individual electrodes adjacent to the portion. In addition, in the present invention, the actuator unit is a laminated body in which a plurality of piezoelectric sheets are laminated, and the piezoelectric sheet that is the most separated from the flow path unit among the plurality of piezoelectric sheets is the common. It is sandwiched between the electrode and the individual electrode, and the recess may reach the inside of another piezoelectric sheet adjacent to the flow path unit side of the piezoelectric sheet. Further, in the present invention, the individual electrode is configured to further include a connection region that connects the electrode region and the terminal region and is disposed at a position that does not face the pressure chamber. The terminal region may be formed to a position facing the connection region. Furthermore, in the present invention, the terminal region may be located between the electrode region connected to the terminal region and another electrode region.

  A first embodiment according to the present invention will be described below with reference to the drawings.

  FIG. 1 is an external perspective view of the ink jet head according to the first embodiment. 2 is a cross-sectional view taken along line II-II in FIG. The inkjet head 1 includes a head main body 70 having a rectangular planar shape extending in the main scanning direction for ejecting ink onto a sheet, and an ink that is disposed above the head main body 70 and supplied to the head main body 70. And a base block 71 on which two ink reservoirs 3 are formed.

  The head body 70 includes a flow path unit 4 in which an ink flow path is formed, and a plurality of actuator units 21 bonded to the upper surface of the flow path unit 4. Both the flow path unit 4 and the actuator unit 21 are configured by laminating a plurality of thin plates and bonding them together. Further, a flexible printed circuit (FPC) 50, which is a power supply member, is bonded to the upper surface of the actuator unit 21 and pulled out to the left and right. The base block 71 is made of a metal material such as stainless steel. The ink reservoir 3 in the base block 71 is a substantially rectangular parallelepiped hollow region formed along the longitudinal direction of the base block 71.

  The lower surface 73 of the base block 71 protrudes downward from the periphery in the vicinity of the opening 3b. The base block 71 is in contact with the flow path unit 4 only in the portion 73a near the opening 3b of the lower surface 73. Therefore, a region other than the portion 73a near the opening 3b on the lower surface 73 of the base block 71 is separated from the head main body 70, and the actuator unit 21 is disposed in this separated portion.

  The base block 71 is bonded and fixed in a recess formed on the lower surface of the grip portion 72 a of the holder 72. The holder 72 includes a gripping portion 72a and a pair of flat projections 72b extending from the upper surface of the gripping portion 72a at a predetermined interval in a direction orthogonal thereto. The FPC 50 bonded to the actuator unit 21 is disposed along the surface of the protruding portion 72b of the holder 72 via an elastic member 83 such as a sponge. And driver IC80 is installed on FPC50 arrange | positioned on the protrusion part 72b surface of the holder 72. FIG. The FPC 50 is electrically joined to both by soldering so as to transmit the drive signal output from the driver IC 80 to the actuator unit 21 (described later in detail) of the head body 70.

  Since the heat sink 82 having a substantially rectangular parallelepiped shape is closely disposed on the outer surface of the driver IC 80, the heat generated in the driver IC 80 can be efficiently dissipated. A substrate 81 is disposed above the driver IC 80 and the heat sink 82 and outside the FPC 50. The upper surface of the heat sink 82 and the substrate 81 and the lower surface of the heat sink 82 and the FPC 50 are bonded by a seal member 84, respectively.

  FIG. 3 is a plan view of the head main body 70 shown in FIG. In FIG. 3, the ink reservoir 3 formed in the base block 71 is virtually drawn with a broken line. The two ink reservoirs 3 extend in parallel with each other at a predetermined interval along the longitudinal direction of the head body 70. The two ink reservoirs 3 each have an opening 3a at one end, and are always filled with ink by communicating with an ink tank (not shown) through the opening 3a. A large number of openings 3b are provided in each ink reservoir 3 along the longitudinal direction of the head main body 70, and connect each ink reservoir 3 and the flow path unit 4 as described above. A large number of the openings 3 b are arranged close to each other along the longitudinal direction of the head body 70. A pair of openings 3b communicating with one ink reservoir 3 and a pair of openings 3b communicating with the other ink reservoir 3 are arranged in a staggered manner.

  In the area where the openings 3b are not arranged, a plurality of actuator units 21 having a trapezoidal planar shape are arranged in a staggered pattern in a pattern opposite to the pair of the openings 3b. The parallel opposing sides (upper side and lower side) of each actuator unit 21 are parallel to the longitudinal direction of the head body 70. Further, a part of the oblique sides of the adjacent actuator units 21 overlap in the width direction of the head main body 70.

  FIG. 4 is an enlarged view of a region surrounded by a one-dot chain line drawn in FIG. As shown in FIG. 4, an opening 3b provided in each ink reservoir 3 communicates with a manifold 5 that is a common ink chamber, and the tip of each manifold 5 branches into two to form a sub-manifold 5a. Yes. Further, in plan view, two sub-manifolds 5a branched from the adjacent openings 3b extend from the two oblique sides of the actuator unit 21, respectively. That is, below the actuator unit 21, a total of four sub-manifolds 5 a that are separated from each other extend along the parallel opposing sides of the actuator unit 21.

  The lower surface of the flow path unit 4 facing the adhesion area of the actuator unit 21 is an ink ejection area. A large number of nozzles 8 are arranged in a matrix on the surface of the ink discharge area, as will be described later. In order to simplify the drawing, only a few of the nozzles 8 are depicted in FIG. 4, but they are actually arranged over the entire ink discharge region.

  FIG. 5 is an enlarged view of a region surrounded by a dashed line drawn in FIG. 4 and 5 show a state where a plurality of pressure chambers 10 in the flow path unit 4 are arranged in a matrix when viewed from a direction perpendicular to the ink ejection surface. Each pressure chamber 10 has a substantially rhombic planar shape with rounded corners, and the longer diagonal line is parallel to the width direction of the flow path unit 4. One end of each pressure chamber 10 communicates with the nozzle 8, and the other end communicates with the sub-manifold 5a serving as a common ink flow path via an aperture 12 (see FIG. 6). An individual electrode 35 similar to the pressure chamber 10 and having a slightly smaller planar shape than the pressure chamber 10 is formed on the actuator unit 21 at a position overlapping each pressure chamber 10 in plan view. FIG. 5 shows only some of the large number of individual electrodes 35 in order to simplify the drawing. 4 and 5, the pressure chambers 10 and the apertures 12 that are to be drawn with broken lines in the actuator unit 21 or the flow path unit 4 are drawn with solid lines for easy understanding of the drawings.

  In FIG. 5, the plurality of virtual rhombus regions 10x each accommodating the pressure chambers 10x share the sides without overlapping each other, and the arrangement direction A (first direction) and the arrangement direction B (second Are arranged adjacently in a matrix in two directions. The arrangement direction A is the longitudinal direction of the inkjet head 1, that is, the extending direction of the sub-manifold 5a, and is parallel to the shorter diagonal line of the rhombic region 10x. The arrangement direction B is an oblique side direction of the rhombus region 10x that forms an obtuse angle θ with the arrangement direction A. The pressure chamber 10 has a common center position with the opposing rhombus region 10x, and the contour lines of both are separated from each other in plan view.

  The pressure chambers 10 adjacently arranged in a matrix in two directions of the arrangement direction A and the arrangement direction B are separated along the arrangement direction A by a distance corresponding to 37.5 dpi. Further, 18 pressure chambers 10 are arranged in the arrangement direction B in one ink ejection region. However, the pressure chambers at both ends in the arrangement direction B are dummy and do not contribute to ink ejection.

  The plurality of pressure chambers 10 arranged in a matrix form a plurality of pressure chamber rows along the arrangement direction A shown in FIG. The pressure chamber rows are the first pressure chamber row 11a and the second pressure chamber row according to the relative position with respect to the sub-manifold 5a when viewed from the direction (third direction) perpendicular to the paper surface of FIG. 11b, a third pressure chamber row 11c, and a fourth pressure chamber row 11d. Each of the first to fourth pressure chamber rows 11a to 11d is periodically arranged in the order of 11c → 11d → 11a → 11b → 11c → 11d → ... → 11b from the upper side to the lower side of the actuator unit 21. Has been placed.

  In the pressure chambers 10a constituting the first pressure chamber row 11a and the pressure chambers 10b constituting the second pressure chamber row 11b, a direction (fourth direction) orthogonal to the arrangement direction A when viewed from the third direction. ), The nozzle 8 is unevenly distributed on the lower side of the drawing sheet of FIG. And the nozzle 8 is located in the lower end part of the rhombus area | region 10x which each opposes. On the other hand, in the pressure chambers 10c constituting the third pressure chamber row 11c and the pressure chambers 10d constituting the fourth pressure chamber row 11d, the nozzle 8 is unevenly distributed on the upper side in FIG. 5 in the fourth direction. Yes. And the nozzle 8 is located in the upper end part of the rhombus area | region 10x which each opposes. In the first and fourth pressure chamber rows 11a and 11d, when viewed from the third direction, more than half of the pressure chambers 10a and 10d overlap the sub-manifold 5a. In the second and third pressure chamber rows 11b and 11c, the entire region of the pressure chambers 10b and 10c does not overlap the sub-manifold 5a when viewed from the third direction. Therefore, for the pressure chambers 10 belonging to any pressure chamber row, the width of the sub-manifold 5a is made as wide as possible while the nozzle 8 communicating therewith does not overlap the sub-manifold 5a, and ink is supplied to each pressure chamber 10. It can be supplied smoothly.

  Next, the cross-sectional structure of the head body 70 will be further described with reference to FIGS. FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5, in which the pressure chambers 10a belonging to the first pressure chamber row 11a are depicted. FIG. 7 is a partially exploded perspective view of the head body. As can be seen from FIG. 6, the nozzle 8 communicates with the sub-manifold 5 a through the pressure chamber 10 (10 a) and the aperture 12. In this manner, the individual ink flow paths 32 extending from the outlet of the sub-manifold 5 a to the nozzle 8 through the aperture 12 and the pressure chamber 10 are formed in the head main body 70 for each pressure chamber 10.

  As can be seen from FIG. 7, the head body 70 includes the actuator unit 21, the cavity plate 22, the base plate 23, the aperture plate 24, the supply plate 25, the manifold plates 26, 27, 28, the cover plate 29, and the nozzle plate 30. A total of 10 sheet materials are laminated. Among these, the flow path unit 4 is composed of nine metal plates excluding the actuator unit 21.

  As will be described later in detail, the actuator unit 21 is formed by stacking four piezoelectric sheets 41 to 44 (see FIG. 9) and arranging electrodes so that only the uppermost layer becomes an active layer when an electric field is applied. A layer having a portion (hereinafter simply referred to as “a layer having an active layer”), and the remaining three layers are inactive layers. The cavity plate 22 is a metal plate provided with a number of substantially rhombic openings facing the pressure chamber 10. The base plate 23 is a metal plate provided with a communication hole between the pressure chamber 10 and the aperture 12 and a communication hole from the pressure chamber 10 to the ink nozzle 8 with respect to one pressure chamber 10 of the cavity plate 22. The aperture plate 24 is provided with a communication hole from the pressure chamber 10 to the ink nozzle 8 in addition to the aperture 12 formed by two etching holes and a half-etching region connecting the two holes with respect to one pressure chamber 10 of the cavity plate 22. Metal plate. The supply plate 25 is a metal plate provided with a communication hole between the aperture 12 and the sub-manifold 5 a and a communication hole from the pressure chamber 10 to the ink nozzle 8 with respect to one pressure chamber 10 of the cavity plate 22. The manifold plates 26, 27, and 28 are connected to each other when stacked, and in addition to the holes constituting the sub-manifold 5 a, each pressure chamber 10 of the cavity plate 22 has a communication hole from the pressure chamber 10 to the ink nozzle 8. It is a provided metal plate. The cover plate 29 is a metal plate in which a communication hole from the pressure chamber 10 to the ink nozzle 8 is provided for one pressure chamber 10 of the cavity plate 22. The nozzle plate 30 is a metal plate in which the nozzles 8 are provided for one pressure chamber 10 of the cavity plate 22.

  These nine metal plates are stacked in alignment with each other so that individual ink flow paths 32 as shown in FIG. 6 are formed. The individual ink flow path 32 first extends upward from the sub-manifold 5a, extends horizontally at the aperture 12, then further upwards, extends horizontally again at the pressure chamber 10, and then moves away from the aperture 12 for a while. Toward the nozzle 8 in a vertically downward direction.

  Next, a detailed structure of the actuator unit 21 stacked on the uppermost cavity plate 22 in the flow path unit 4 will be described. FIG. 8 is an enlarged plan view of the upper surface side of the actuator unit 21. 9 is a partial cross-sectional view of the actuator unit 21, FIG. 9 (a) is a partial cross-sectional view along the line IXA-IXA in FIG. 8, and FIG. 9 (b) is along the line IXB-IXB in FIG. FIG.

  As shown in FIG. 9A, the actuator unit 21 includes four piezoelectric sheets 41 to 44 formed to be the same with a thickness of about 15 μm. These piezoelectric sheets 41 to 44 are continuous layered flat plates (continuous flat plate layers) so as to be disposed across a number of pressure chambers 10 formed in one ink discharge region in the head main body 70. . Since the piezoelectric sheets 41 to 44 are arranged as a continuous flat plate layer across a large number of pressure chambers 10, the individual electrodes 35 can be arranged on the piezoelectric sheet 41 with high density by using, for example, a screen printing technique. It has become. Therefore, the pressure chambers 10 formed at positions facing the individual electrodes 35 can also be arranged with high density, and high-resolution images can be printed. The piezoelectric sheets 41 to 44 are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  On the uppermost piezoelectric sheet 41, individual electrodes 35 are formed. Between the uppermost piezoelectric sheet 41 and the lower piezoelectric sheet 42, a common electrode 34 having a thickness of about 2 μm formed on the entire surface of the sheet is interposed. Both the individual electrode 35 and the common electrode 34 are made of, for example, a metal material such as Ag—Pd.

As shown in FIG. 8, the individual electrode 35 has a thickness of about 1 μm and a substantially rhombic (parallelogram) planar shape (electrode region) that is substantially similar to the pressure chamber 10 and is arranged in a matrix. (See FIG. 5). One of the acute angle portions of the substantially rhomboid individual electrode 35 is extended in the same direction (lower side in the drawing), and a circular land having a diameter of approximately 160 μm is electrically connected to the individual electrode 35 at the tip region. A portion 36 (terminal region) is provided. The land portion 36 is made of, for example, gold containing glass frit, and is adhered on the surface of the extended portion of the individual electrode 35. Further, the land portion 36 is electrically joined to a contact provided on the FPC 50, and does not face the pressure chamber 10 as shown in FIGS. 9 (a) and 9 (b). It is disposed so as to face the partition walls 2 2 for partitioning the pressure chamber 10. In addition, the connection area | region 35a is arrange | positioned at the individual electrode 35 as an area | region which does not oppose the pressure chamber 10 which connects between an electrode area | region and a terminal area | region.

  The common electrode 34 is grounded in a region not shown. As a result, the common electrode 34 is kept at the same ground potential in the region facing all the pressure chambers 10. In addition, the individual electrode 35 is a driver via the FPC 50 and the land portion 36 including separate lead wires for each individual electrode 35 so that the potential can be controlled for each of the pressure chambers 10 facing each pressure chamber 10. It is electrically connected to the IC 80 (see FIGS. 1 and 2).

  On the outer periphery of the land portion 36, an imaginary line 62 connecting the shortest distance between the land portion 36 and the adjacent individual electrode 35 so as to follow the outer shape of the land portion 36 except for the connection region 35 a of the individual electrode 35 in plan view. A C-shaped groove (concave portion) 61 is formed so as to cross the line. As a result, the land portion 36 that causes structural crosstalk is completely covered by the C-shaped groove portion 61. As shown in FIG. 9, the groove 61 has a U-shaped cross-sectional shape with a width of about 30 μm and a depth of about 15 μm, and penetrates the piezoelectric sheet 41, and its bottom reaches the position of the common electrode 34. Has reached. The groove 61 is formed by laser processing using a YAG laser or the like.

  Next, a method for driving the actuator unit 21 will be described. The polarization direction of the piezoelectric sheet 41 in the actuator unit 21 is the thickness direction. In other words, the actuator unit 21 has one piezoelectric sheet 41 on the upper side (that is, apart from the pressure chamber 10) as a layer in which the active layer is present and three piezoelectric sheets on the lower side (that is, close to the pressure chamber 10). It has a so-called unimorph type structure in which 42 to 44 are inactive layers. Therefore, when the individual electrode 35 is set to a predetermined positive or negative potential, for example, if the electric field and the polarization are in the same direction, the electric field application portion sandwiched between the electrodes in the piezoelectric sheet 41 acts as an active layer and is polarized by the piezoelectric lateral effect. Shrink in the direction perpendicular to the direction. On the other hand, since the piezoelectric sheets 42 to 44 are not affected by the electric field and do not spontaneously shrink, the piezoelectric sheets 42 to 44 are not contracted in a direction perpendicular to the polarization direction between the upper piezoelectric sheet 41 and the lower piezoelectric sheets 42 to 44. A difference is caused in the distortion, and the entire piezoelectric sheets 41 to 44 try to be deformed so as to protrude toward the non-active side (unimorph deformation). At this time, as shown in FIG. 9, the lower surfaces of the piezoelectric sheets 41 to 44 are fixed to the upper surface of the cavity plate 22 that partitions the pressure chambers. As a result, the piezoelectric sheets 41 to 44 protrude toward the pressure chamber side. It transforms to become. For this reason, the volume of the pressure chamber 10 is reduced, the pressure of the ink is increased, and the ink is ejected from the nozzle 8. Thereafter, when the individual electrode 35 is returned to the same potential as that of the common electrode 34, the piezoelectric sheets 41 to 44 return to the original shape and the volume of the pressure chamber 10 returns to the original volume, so that ink is sucked from the manifold 5 side.

  As another driving method, the individual electrode 35 is set to a potential different from that of the common electrode 34 in advance, and the individual electrode 35 is once set to the same potential as the common electrode 34 every time there is an ejection request, and then again individually at a predetermined timing. The electrode 35 can be at a different potential from the common electrode 34. In this case, when the individual electrodes 35 and the common electrode 34 are at the same potential, the piezoelectric sheets 41 to 44 return to their original shapes, so that the volume of the pressure chamber 10 is in an initial state (the potentials of the two electrodes are different). ) And the ink is sucked into the pressure chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a potential different from that of the common electrode 34 again, the piezoelectric sheets 41 to 44 are deformed so as to protrude toward the pressure chamber 10, and the pressure on the ink increases due to the volume reduction of the pressure chamber 10. Ink is ejected.

  If the direction of the electric field applied to the piezoelectric sheet 41 and the polarization direction thereof are opposite, the active layer in the piezoelectric sheet 41 sandwiched between the individual electrode 35 and the common electrode 34 has a polarization direction due to the piezoelectric lateral effect. Attempts to stretch in a perpendicular direction. Accordingly, the piezoelectric sheets 41 to 44 are deformed so as to be concave toward the pressure chamber 10 side. For this reason, the volume of the pressure chamber 10 increases and ink is sucked from the manifold 5 side. Thereafter, when the potential of the individual electrode 35 is restored, the piezoelectric sheets 41 to 44 have the original flat plate shape, and the volume of the pressure chamber 10 is restored to the original volume, and thus ink is ejected from the nozzle 8.

  As described above, in the inkjet head 1 according to the first embodiment, the non-active layer side of the actuator unit 21 facing the position where the land portion 36 is arranged is fixed to the upper surface of the partition wall 22 defining the pressure chamber, and the uppermost layer. Only the piezoelectric sheet 41 is configured to include an active layer that generates spontaneous displacement due to the piezoelectric effect. When a voltage is applied to the land portion 36, as in the case where a voltage is applied to the individual electrode 35, if the direction of the electric field and the polarization are the same, the active layer directly below the land portion 36 is also based on the piezoelectric lateral effect. Shrink in the direction perpendicular to the polarization direction. Here, among the piezoelectric sheets directly under the land portion 36, the piezoelectric sheet 44, which is an inactive layer, is fixed to the upper surface of the partition wall 22 defining the pressure chamber 10, so that it corresponds to the deformation of the active layer directly under the land portion 36. Therefore, it becomes almost impossible to displace as it approaches the piezoelectric sheet 44 that is an inactive layer from the piezoelectric sheet 41 that functions as an active layer. On the contrary, the displacement of the active layer that can be freely deformed mainly extends the region adjacent to the land portion 36 of the piezoelectric sheet 41 including the active layer, corresponding to the amount of displacement. At this time, if the pressure chamber 10 exists corresponding to the stretched region, it is not spontaneous deformation, but the piezoelectric sheet 41 of the uppermost layer among the piezoelectric sheets provided corresponding to the pressure chamber 10. Takes the same state as extending in the plane direction. On the other hand, the piezoelectric sheet 44 positioned directly above the pressure chamber 10 is originally an inactive layer, and displacement in the land portion 36 adjacent to the structure hardly propagates. Therefore, the piezoelectric sheets 41 to 44 corresponding to the pressure chamber 10 cause a unimorph type deformation that is concave with respect to the pressure chamber 10 as a whole. That is, the displacement of the active layer accompanying the application of voltage to the land portion 36 tends to propagate directly to the adjacent region. However, since the groove portion 61 is formed along the outer shape of the land portion 36, even if the active layer in the portion facing the land portion 36 is deformed, the piezoelectric sheet in the portion facing another adjacent pressure chamber 10. The amount of deformation of 41 is reduced. That is, even if the pressure chambers 10 are arranged at high density, a so-called structural cross in which ink is ejected from nozzles that should not eject ink or the ink ejection amount is increased or decreased from the original amount. The occurrence of talk can be reduced.

  Moreover, since the groove part 61 is formed so that the external shape of the land part 36 may be followed, the distance of the groove part 61 formed becomes short and the fall of the rigidity of the actuator unit 21 can be suppressed. Furthermore, since the use time of the laser for forming the groove portion 61 is shortened, the cost for forming the groove portion 61 can be reduced.

  Further, since the groove 61 operates as an active layer and is formed by penetrating the piezoelectric sheet 41 that causes the largest displacement compared to other piezoelectric sheets, structural crosstalk can be effectively reduced. .

  In addition, since the groove portion 61 is continuously formed over substantially the entire circumference of the land portion 36 excluding the connection region between the individual electrode 35 and the land portion 36, the groove portion 61 is structurally extended in almost the direction of the land portion 36. Crosstalk can be reduced.

  Next, an ink jet head according to a second embodiment of the present invention will be described. The ink jet head according to the second embodiment differs from the first embodiment only in the position and shape of the groove formed in the actuator unit. Therefore, in the drawings according to the second embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 10 is an enlarged plan view of the actuator unit 21A in the ink jet head according to the second embodiment of the present invention.

  As shown in FIG. 10, the individual electrode 35 has a thickness of approximately 1 μm and a substantially rhombic (parallelogram) planar shape (electrode region) that is substantially similar to the pressure chamber 10 and is arranged in a matrix. (See FIG. 5). One of the acute angle portions of the substantially rhomboid individual electrode 35 is extended in the same direction (the lower side in the drawing), and a circular land portion having a diameter of approximately 160 μm is electrically connected to the individual electrode 35 at the tip thereof. A (terminal region) 36 is provided. In the individual electrode 35, a connection region 35a is disposed as a region that does not face the pressure chamber 10 between the electrode region and the terminal region. On the outer periphery of the land portion 36, the land portion 36 is sandwiched in plan view and along the outer shape of the land portion 36 from both sides of the connection region of the individual electrode 35 to the vicinity of the opposite side of the connection region in the terminal region. Two C-shaped groove portions (recess portions) 61Aa and 61Ab are formed. The groove portions 61Aa and 61Ab are formed at positions crossing an imaginary line 62 that connects the shortest distance between the land portion 36 and the adjacent individual electrode 35, and are symmetrical with respect to a straight line passing through two acute angle portions of the individual electrode 35. It has the shape which becomes. Further, in the cross section of the actuator unit 21A, the groove portions 61Aa and 61Ab have a U-shaped cross-sectional shape with a width of about 30 μm and a depth of about 15 μm, and penetrate the piezoelectric sheet 41, and the bottom of the groove 61 Has reached to.

  As described above, according to the second embodiment, the groove portions 61Aa and 61Ab are formed for each virtual line 62 in which the structural crosstalk generated from the land portion 36 propagates most strongly to the adjacent pressure chamber 10. Therefore, structural crosstalk can be efficiently reduced. Further, since the distance between the groove portions 61Aa and 61Ab can be shortened, a decrease in the rigidity of the actuator unit 21A can be suppressed. Furthermore, since the use time of the laser for forming the groove portions 61Aa and 61Ab is shortened, the cost for forming the groove portions 61Aa and 61Ab can be reduced.

  Next, an ink jet head according to a third embodiment of the present invention will be described. The ink jet head according to the third embodiment is different from the first embodiment only in the position and shape of the groove formed in the actuator unit. Therefore, in the drawings according to the third embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 11 is an enlarged plan view of the actuator unit 21B in the ink jet head according to the third embodiment of the present invention.

  As shown in FIG. 11, the individual electrodes 35 have a thickness of about 1 μm and a substantially rhombic (parallelogram) planar shape (electrode region) that is substantially similar to the pressure chamber 10 and are arranged in a matrix. (See FIG. 5). One of the acute angle portions of the substantially rhomboid individual electrode 35 is extended in the same direction (the lower side in the drawing), and a circular land portion having a diameter of approximately 160 μm is electrically connected to the individual electrode 35 at the tip thereof. A (terminal region) 36 is provided. In the individual electrode 35, a connection region 35a is disposed as a region that does not face the pressure chamber 10 between the electrode region and the terminal region. Two linear grooves (concave portions) 61Ba and 61Bb are formed on the outer periphery of the land portion 36 so as to sandwich the land portion 36 in a plan view. The groove portions 61Ba and 61Bb are formed so as to be orthogonal to a virtual line 62 that connects the shortest distances between the land portion 36 and the adjacent individual electrode 35, and are formed with respect to a straight line passing through two acute angle portions of the individual electrode 35. It has a line-symmetric shape. Further, in the cross section of the actuator unit 21B, the groove portions 61Ba and 61Bb have a U-shaped cross-sectional shape with a width of about 30 μm and a depth of about 15 μm, and penetrate the piezoelectric sheet 41, and the bottom portion is the position of the common electrode 34. Has reached to.

  As described above, according to the third embodiment, the groove portions 61Ba and 61Bb are formed for each virtual line 62 in which the structural crosstalk generated from the land portion 36 propagates most strongly to the adjacent pressure chamber 10. Therefore, structural crosstalk can be efficiently reduced. Further, since the distance between the groove portions 61Ba and 61Bb can be shortened, a decrease in the rigidity of the actuator unit 21A can be suppressed. Furthermore, since the use time of the laser for forming the groove portions 61Ba and 61Bb is shortened, the cost for forming the groove portions 61Ba and 61Bb can be reduced.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims. For example, in the first to third embodiments, the materials of the piezoelectric sheet and the electrodes are not limited to those described above, and may be changed to other known materials. Further, the planar shape and cross-sectional shape of the pressure chamber, the arrangement form, the number of piezoelectric sheets including the active layer, the number of inactive layers, and the like may be appropriately changed. For example, only one elongated actuator unit may be bonded to the flow path unit. Further, the piezoelectric sheet including the active layer and the non-active layer may have different thicknesses.

  According to the first to third embodiments, the groove portions 61, 61Aa, 61Ab, 61Ba, 61Bb are formed only on the outer periphery of the land portion 36, but may be formed beyond the periphery of the land portion 36. Good.

  Further, according to the first to third embodiments, the grooves 61, 61Aa, 61Ab, 61Ba, 61Bb are formed by penetrating only the piezoelectric sheet 41, but at least a part of the piezoelectric sheet 41 is missing. It may be formed by penetrating not only the piezoelectric sheet 41 but also any position of the common electrode 34 and the piezoelectric sheets 42 to 44. Further, when a plurality of active layers are formed in the actuator, the groove portion may be formed by penetrating the active layer at an arbitrary position, or may be formed by penetrating the plurality of active layers.

  Furthermore, according to the second and third embodiments, the two groove portions 61Aa, 61Ab, 61Ba, 61Bb are formed around the land portion 36, but even if three or more groove portions are formed. Good.

  Further, according to the first to third embodiments, the grooves 61, 61Aa, 61Ab, 61Ba, 61Bb are formed at positions crossing the virtual line 62 that connects the shortest distance between the land portion 36 and the adjacent individual electrode 35. However, it may be formed at a position that does not cross the virtual line 62.

  Furthermore, according to the first and second embodiments, the groove portions 61, 61Aa, 61Ab are not formed at the position facing the connection region 35a of the individual electrode 35, but the position facing the connection region 35a is reached. A groove portion may be formed.

1 is a perspective view of an ink jet head according to a first embodiment of the present invention. It is sectional drawing along the II-II line of FIG. FIG. 3 is a plan view of a head body included in the inkjet head depicted in FIG. 2. FIG. 4 is an enlarged view of a region surrounded by an alternate long and short dash line drawn in FIG. 3. It is an enlarged view of the area | region enclosed with the dashed-dotted line drawn in FIG. It is sectional drawing along the VI-VI line of FIG. FIG. 5 is a partially exploded perspective view of the head body depicted in FIG. 4. FIG. 6 is an enlarged plan view of the actuator unit depicted in FIG. 5. FIG. 9 is a partial cross-sectional view of the actuator unit depicted in FIG. 8. It is an enlarged plan view of an actuator unit according to a second embodiment of the present invention. It is an enlarged plan view of an actuator unit according to a third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 4 Flow path unit 5 Manifold 5a Sub manifold 10 Pressure chamber 12 Aperture 21 Actuator unit 32 Ink flow path 34 Common electrode 35 Individual electrode 36 Land part (terminal area)
41 Piezoelectric sheet (layer including active layer)
42, 43, 44 Piezoelectric sheet (inactive layer)
61 Groove (recess)
70 head body

Claims (10)

A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged adjacent to each other in a matrix along a plane;
An actuator unit fixed to one surface of the flow path unit and changing a volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes configured to include a plurality of electrode regions disposed at positions facing each of the plurality of pressure chambers, and a terminal region connected to the electrode region and connected to a signal line;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrodes;
An ink jet head comprising a recess formed around the terminal region. The inkjet head according to claim 1, wherein the concave portion exists only around the terminal region. The planar shape of the pressure chamber is a parallelogram having two acute angles or a parallelogram with rounded corners, and the terminal region is near one acute angle of the pressure chamber, and The inkjet head according to claim 1, wherein the inkjet head is located between the electrode regions of the other two adjacent individual electrodes. 4. The inkjet head according to claim 1, wherein the concave portion is formed through at least one of the piezoelectric sheets sandwiched between the common electrode and the individual electrode. 5. The inkjet head according to claim 1, wherein the recess is formed along an outer shape of the terminal region. The individual electrode includes a connection region that connects the electrode region and the terminal region,
The inkjet head according to claim 5, wherein the concave portion is formed continuously over substantially the entire circumference of the terminal region except for a portion facing the connection region. The inkjet head according to claim 5, wherein a plurality of the recesses are formed around the terminal region. The two concave portions are formed around the terminal region, and the two concave portions are formed symmetrically with respect to a straight line connecting the electrode region and the terminal region. Item 8. The ink jet head according to Item 7. The said recessed part is formed in the position which cross | intersects the virtual line | wire which connects the shortest distance with the electrode area | region of the said individual electrode adjacent to the said terminal area | region, The Claim 1 characterized by the above-mentioned. Inkjet head. 10. The inkjet head according to claim 1, wherein the terminal region faces a girder that partitions the adjacent pressure chambers.

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