JP3885808B2 - Inkjet head - Google Patents

Description

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

  In Patent Document 1, a plurality of pressure chambers are arranged adjacent to each other in a matrix shape in a flow path unit, and a piezoelectric element and one electrode (common electrode) are formed in a sheet shape across a plurality of pressure chambers. An ink jet head is disclosed in which the other electrode (individual electrode) that sandwiches the piezoelectric element therebetween is disposed at a position facing each pressure chamber. In this ink jet head, ink is ejected from nozzles communicating with the corresponding pressure chambers by making the potential of the individual electrodes different from that of the common electrode.

JP 2002-292860 (FIG. 1)

  In the ink jet head of the type described in Patent Document 1, the present inventor has an ink ejection speed from a nozzle communicating with a pressure chamber corresponding to the vicinity of the central portion of the piezoelectric sheet corresponding to the vicinity of the outer edge portion of the piezoelectric sheet. It has been found that since the ink discharge speed from the nozzle communicating with the pressure chamber is faster, the image quality is greatly affected.

  Accordingly, an object of the present invention is to provide an ink jet head in which the ink discharge speed from the nozzles can be made substantially uniform in an ink jet head in which a piezoelectric sheet and a common electrode straddle a plurality of pressure chambers.

Means and effects for solving the problems

An inkjet head according to the present invention includes a flow path unit in which a plurality of pressure chambers communicating with nozzles are arranged along a plane, an actuator unit that is fixed to a surface of the flow path unit and changes the volume of the pressure chamber. It has. The actuator unit includes a plurality of individual electrodes arranged at positions facing each pressure chamber, a common electrode provided across the plurality of pressure chambers, and a piezoelectric material sandwiched between the common electrode and the individual electrodes. And a seat. And, the thermal expansion coefficient of the flow path unit is larger than the thermal expansion coefficient of the actuator unit, and the facing area between the individual electrode and the common electrode in the central portion of the actuator unit is the outer edge of the actuator unit. It is smaller than the facing area between the individual electrode and the common electrode.

  According to this configuration, the facing area between the individual electrode and the common electrode is adjusted according to the location in the actuator unit so that the difference in ink discharge speed is eliminated. Therefore, the ink discharge speed from the nozzle can be made substantially uniform. In addition, there is almost no need to change dimensional parameters or control parameters other than the electrode planar shape, which is advantageous in design.

  In this invention, it is preferable that the area of the said individual electrode arrange | positioned at the center part of the said actuator unit is smaller than the area of the said individual electrode arrange | positioned at the outer edge part of the said actuator unit. According to this, the opposing area of an individual electrode and a common electrode can be adjusted easily.

  In the present invention, from the viewpoint of enabling high integration of the nozzles, the plurality of individual electrodes may be arranged in a matrix. In this case, in particular, if the ink discharge speed tends to change along one direction in the actuator unit, in order to eliminate the difference in ink discharge speed, the facing area in the actuator unit is unidirectional. It is preferable to change along.

  In the present invention, the actuator unit may have a plurality of blocks. And at this time, it is preferable that the facing area in one block is the same, and the facing area in the block at the center is smaller than the facing area in another block at the outer edge. . According to this configuration, it is only necessary to change the planar shape of the electrode in units of blocks, so that it is easy to manufacture.

  In this invention, the thickness of the said individual electrode in the center part of the said actuator unit may be larger than the thickness of the said individual electrode in the outer edge part of the said actuator unit. With this configuration, the difference in ink ejection speed can be resolved not only by the opposing area of both electrodes but also by the thickness of the individual electrodes, so even if there is a large difference in the original ink ejection speed, it can be made uniform Is possible.

In another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and is fixed to a surface of the flow path unit, so that the volume of the pressure chamber is reduced. And an actuator unit to be changed. The actuator unit includes a plurality of individual electrodes arranged at positions facing each pressure chamber, a common electrode common to the plurality of pressure chambers, and a piezoelectric sheet sandwiched between the common electrode and the individual electrodes. I have. The thermal expansion coefficient of the flow path unit is larger than the thermal expansion coefficient of the actuator unit, and the thickness of the individual electrode at the center of the actuator unit is larger than the thickness of the individual electrode at the outer edge of the actuator unit. large.

In another aspect, the inkjet head according to the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and is fixed to a surface of the flow path unit. And an actuator unit for changing the volume. The actuator unit includes a plurality of individual electrodes arranged at positions facing each pressure chamber, a common electrode common to the plurality of pressure chambers, and a plurality of stacked layers sandwiched between the common electrode and the individual electrodes. The piezoelectric sheet is provided. The thermal expansion coefficient of the flow path unit is larger than the thermal expansion coefficient of the actuator unit, and the overlapping number of the individual electrodes in the piezoelectric sheet in the piezoelectric sheet stacking direction is an outer edge portion than the central portion of the actuator unit. Many.

  According to this configuration, since the thickness or the number of overlapping of the individual electrodes is adjusted according to the location in the actuator unit so that the difference in ink discharge speed is eliminated, regardless of the position of the pressure chamber with respect to the actuator unit, The ink discharge speed from the nozzle can be made substantially uniform.

In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes disposed at positions facing each pressure chamber, a common electrode provided across the plurality of pressure chambers, and the common And a piezoelectric sheet sandwiched between the electrodes and the individual electrodes . And, the thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the facing area between the individual electrode and the common electrode in the central part of the actuator unit is the outer edge part of the actuator unit. It is larger than the opposing area of the individual electrode and the common electrode.

  According to this configuration, the facing area between the individual electrode and the common electrode is adjusted according to the location in the actuator unit so that the difference in ink discharge speed is eliminated. Therefore, the ink discharge speed from the nozzle can be made substantially uniform. In addition, there is almost no need to change dimensional parameters or control parameters other than the electrode planar shape, which is advantageous in design.

In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes arranged at positions facing each pressure chamber, a common electrode common to the plurality of pressure chambers, the common electrode, and the And a piezoelectric sheet sandwiched between the individual electrodes. And, the thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the thickness of the individual electrode in the central part of the actuator unit is larger than the thickness of the individual electrode in the outer edge part of the actuator unit. small.
In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes arranged at positions facing each pressure chamber, a common electrode common to the plurality of pressure chambers, the common electrode, and the And a plurality of stacked piezoelectric sheets sandwiched between individual electrodes. Further, the thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the number of overlapping of the individual electrodes in the piezoelectric sheet in the piezoelectric sheet stacking direction is an outer edge portion than the central portion of the actuator unit. And few.
In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes disposed at positions facing each pressure chamber, a common electrode provided across the plurality of pressure chambers, and the common And a piezoelectric sheet sandwiched between the electrodes and the individual electrodes. When the opposing area of the individual electrode and the common electrode is the same, when the ink discharge speed is faster at the center than the outer edge of the actuator unit, the individual electrode at the center of the actuator unit and the The facing area with the common electrode is smaller than the facing area between the individual electrode and the common electrode at the outer edge of the actuator unit.
In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes disposed at positions facing each pressure chamber, a common electrode provided across the plurality of pressure chambers, and the common And a piezoelectric sheet sandwiched between the electrodes and the individual electrodes. When the thickness of the individual electrode is the same and the ink discharge speed is faster at the center than the outer edge of the actuator unit, the thickness of the individual electrode at the center of the actuator unit is It is larger than the thickness of the said individual electrode in an outer edge part.
In still another aspect, the inkjet head of the present invention includes a flow path unit in which a plurality of pressure chambers communicating with a nozzle are arranged along a plane, and a volume of the pressure chamber fixed to the surface of the flow path unit. And a plurality of individual electrodes disposed at positions facing each pressure chamber, a common electrode provided across the plurality of pressure chambers, and the common And a piezoelectric sheet sandwiched between the electrodes and the individual electrodes. When the number of overlapping of the individual electrodes in the piezoelectric sheet stacking direction is the same and the ink discharge speed is faster at the center than the outer edge of the actuator unit, the piezoelectric sheet stack of the individual electrodes in the piezoelectric sheet The number of overlapping directions is greater at the outer edge than at the center of the actuator unit.

When in this configuration, it can be made substantially uniform ink discharge speed from Bruno nozzle.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an external perspective view of the ink jet head according to the first embodiment of the present invention. 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 corresponding to 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 corresponding 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 row has four different positions relative to the sub-manifold 5a, that is, the position relative to the sub-manifold 5a, as viewed from the direction perpendicular to the paper surface of FIG. 5 (third direction). The first pressure chamber row 11a, the second pressure chamber row 11b, the third pressure chamber row 11c, and the fourth pressure chamber row 11d are divided according to their relative positions. 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 corresponding rhombus area | region 10x. 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 corresponding rhombus area | region 10x, respectively. 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 formed as wide as possible while preventing the nozzle 8 communicating therewith from overlapping the sub-manifold 5a. Ink 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, and the pressure chambers 10 a belonging to the first pressure chamber row 11 a are depicted in FIG. 6. As can be seen from FIG. 6, each nozzle 8 communicates with the sub-manifold 5 a via the pressure chamber 10 a and the aperture 12. In this way, the head main body 70 is formed with the individual ink flow path 32 from the outlet of the sub-manifold 5a to the nozzle 8 through the aperture 12 and the pressure chamber 10a for each pressure chamber 10.

  As is clear from FIG. 6, the pressure chamber 10 and the aperture 12 are provided at different height levels in the stacking direction of the plurality of thin plates. As a result, as shown in FIG. 5, in the flow path unit 4 corresponding to the ink discharge area below the actuator unit 21, the aperture 12 communicating with one pressure chamber 10 is moved to a pressure chamber adjacent to the pressure chamber. 10 and can be arranged at the same position in plan view. As a result, the pressure chambers 10 are in close contact with each other and are arranged in a matrix with high density, so that high-resolution image printing is realized by the inkjet head 1 having a relatively small occupied area.

  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 22 to 30 excluding the actuator unit 21 made of a ceramic material. When the actuator unit 21 and the flow path unit 4 are fixed, both are fixed using an adhesive in a heated state. In the present embodiment, the metal plates 22 to 30 constituting the flow path unit 4 are made of stainless steel and have a higher thermal expansion coefficient than the ceramic actuator unit 21.

  As will be described in detail later, the actuator unit 21 is formed by stacking four piezoelectric sheets 41 to 44 (see FIGS. 10A and 10B) and arranging the electrodes, thereby forming the uppermost layer. Only a layer having a portion that becomes an active layer when an electric field is applied (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 diamond-shaped openings corresponding to the pressure chambers 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 nozzle 8 for 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 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. It is a 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 nozzle 8 for one pressure chamber 10 of the cavity plate 22. The manifold plates 26, 27, and 28 are metal plates each provided with a communication hole from the pressure chamber 10 to the nozzle 8 for one pressure chamber 10 of the cavity plate 22 in addition to the sub-manifold 5 a. The cover plate 29 is a metal plate provided with a communication hole from the pressure chamber 10 to the nozzle 8 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 ten sheets 21 to 30 are stacked in alignment with each other so that the 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, the configuration of the actuator unit 21 will be described. FIG. 8 is a plan view of the actuator unit 21. A large number of individual electrodes 35 are arranged in a matrix on the actuator unit 21 in the same pattern as the pressure chamber 10. In this case, according to the knowledge of the present inventor, variations in the ink discharge speed in the actuator unit 21 often occur along the longitudinal direction of the actuator unit 21, that is, the arrangement direction A. This is considered to be caused by a difference in thermal expansion coefficient between the actuator unit 21 and the flow path unit 4 to which the actuator unit 21 is bonded. Below, this point is demonstrated concretely.

  When the inkjet head 1 is manufactured, the flow path unit 4 and the actuator unit 21 are pressure-bonded in a heated state using an adhesive, and then cooled for several minutes to cure the adhesive, The path unit 4 and the actuator unit 21 are joined. At this time, due to the influence of the difference in thermal expansion coefficient between the flow path unit 4 and the actuator unit 21, the inkjet head 1 is in a state where stress is applied in the in-plane direction of the actuator unit 21. Which of the central part and the outer edge part of the actuator unit 21 is applied with a large stress depends on which of the flow path unit 4 and the actuator unit 21 has a larger thermal expansion coefficient. It has been found by the inventors to be determined.

  More specifically, when the flow path unit 4 has a higher thermal expansion coefficient than the actuator unit 21, the outer edge portion of the actuator unit 21 is in a state in which a larger stress than the central portion is applied, When the flow path unit 4 has a lower thermal expansion coefficient than the actuator unit 21, a stress is applied to the central portion of the actuator unit 21 that is greater than that of the outer edge portion. Further, it has been found that the phenomenon in which stress is applied becomes significant in the longitudinal direction of the actuator unit 21.

  In addition, the inventor of the pressure chamber 10 when the voltage applied to a drive element (described later) in the actuator unit 21 is constant according to the magnitude of the stress applied in the in-plane direction of the actuator unit 21. It has been found that the volume change amount becomes small, that is, the ink ejection speed becomes slow.

  In the present embodiment, since the flow path unit 4 is made of stainless steel and the actuator unit 21 is made of ceramic, the thermal expansion coefficient of the flow path unit 4 is larger than that of the actuator unit 21. Therefore, the ink ejection speed at both ends of the actuator unit 21 along the arrangement direction A is slower than that at the center.

  Therefore, in the present embodiment, even when the voltage applied to the drive element is constant, the ink discharge speed is equalized in all the drive elements in the actuator unit 21 and will be described below. It is structured.

  That is, in the inkjet head 1 according to the present embodiment, two types of individual electrodes 35 having similar shapes and different plane sizes (the larger one is represented by reference numeral 35a and the smaller one is represented by reference numeral 35b) are prepared. In addition, a parallelogram block 51 having a width corresponding to ten individual electrodes on the left side (the left side of the actuator unit 21 in FIG. 8) along the arrangement direction A, and the right side (in FIG. 8) along the arrangement direction A. In the actuator unit 21, the individual electrode 35 a is formed in the parallelogram block 52 having a width corresponding to 10 individual electrodes on the right side of the actuator unit 21, and is sandwiched between the two parallelogram blocks 51, 52. An individual electrode 35b is formed on the trapezoidal block 53 at the center of each. That is, the individual electrode 35 b belonging to the trapezoidal block 53 is arranged in the central portion when the actuator unit 21 is viewed along the arrangement direction A. In addition, the individual electrodes 35a belonging to the parallelogram blocks 51 and 52 are arranged on the outer edge portion when the actuator unit 21 is viewed along the arrangement direction A, that is, the portion close to the oblique side of the trapezoid of the actuator unit 21. ing.

  In the present embodiment, a plurality of regions including parallelogram blocks 51 and 52 (second region) and trapezoidal block 53 (first region) are set in the actuator unit 21, and the first and second One of the two types of individual electrodes 35a and 35b is arranged in each region. As shown in FIG. 8, the actuator unit 21 is divided into three regions (parallelogram blocks 51) by two virtual dividing lines parallel to the left and right edges (corresponding to the outer edges of the actuator unit 21). , 52 and trapezoidal block 53). As is clear from FIG. 8, the occupied area of the first region (trapezoidal block 53) set in the center portion of the actuator unit 21 is the second region (set in the outer edge portion of the actuator unit 21). The occupied area of the parallelogram blocks 51 and 52) is larger.

  FIG. 9A is a plan view of the individual electrode 35a, and FIG. 9B is a plan view of the individual electrode 35b. Fig.10 (a) is sectional drawing along the XA-XA line | wire of Fig.9 (a). FIG.10 (b) is sectional drawing along the XB-XB line | wire of FIG.9 (b).

  As shown in FIG. 10A and FIG. 10B, the actuator unit 21 includes four piezoelectric sheets 41, 42, 43, and 44 formed to have the same thickness of about 15 μm. Yes. 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 35a and 35b can be arranged on the piezoelectric sheet 41 at a high density by using, for example, a screen printing technique. It is possible. For this reason, the pressure chambers 10 formed at positions corresponding to the individual electrodes 35a and 35b can 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 35a and 35b 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 actuator unit 21 is interposed. Both the individual electrodes 35a and 35b and the common electrode 34 are made of, for example, a metal material such as Ag—Pd.

  In the inkjet head 1, a pressure chamber in which individual electrodes 35 arranged in the actuator unit 21, a common electrode 34, and a portion where the piezoelectric sheets 41, 42, 43, 44 are stacked are formed at corresponding positions. It will function as a driving element that deforms each of the 10 volumes.

  As shown in FIG. 9A and FIG. 9B, the individual electrodes 35 a and 35 b both have a rhombus or substantially rhombus planar shape that is substantially similar to the pressure chamber 10. The lower acute angle portions of the rhombic or substantially rhombic individual electrodes 35a and 35b are extended, and a circular land portion 36 electrically connected to the individual electrodes 35a and 35b is provided at the tip thereof. The land portion 36 is made of, for example, gold including glass frit, and is bonded onto the surface of the extended portion of the individual electrodes 35a and 35b as shown in FIGS. 9 (a) and 9 (b). Although the illustration of the FPC 50 is omitted in FIGS. 10A and 10B, the land portion 36 is electrically joined to a contact provided on the FPC 50.

  The individual electrode 35a has a length L1 and a width W1, and the individual electrode 35b has a length L2 and a width W2. The length L1 and the width W1 of the individual electrode 35a are sized so that the planar shape of the individual electrode 35a can be accommodated in the pressure chamber 10. In the present embodiment, the length L1 is 10% longer than the length L2, and the width W1 is 10% larger than the width W2. In principle, if the individual electrode 35 is within the size range that can be accommodated in the pressure chamber 10, the larger the area of the individual electrode 35, the greater the displacement of the actuator unit 21, and the higher the ink ejection speed. Therefore, the lengths and widths of the two types of individual electrodes 35a and 35b eliminate the unevenness of the ink discharge speed along the arrangement direction A in the actuator unit 21, and the nozzles 8 in the parallelogram blocks 51 and 52 are eliminated. And the average ink discharge speed from the nozzles 8 in the trapezoidal block 53 are determined so as to be almost eliminated.

  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 regions corresponding to all the pressure chambers 10. In addition, the individual electrode 35 is connected via the FPC 50 and the land portion 36 including separate lead wires for each individual electrode 35a, 35b so that the potential can be controlled for each corresponding to each pressure chamber 10. Are connected to the driver IC 80 (see FIGS. 1 and 2).

  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. Accordingly, when the individual electrodes 35a and 35b are 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 serves as an active layer (pressure generating portion). Works and contracts in a direction perpendicular to the polarization direction due to the piezoelectric transverse effect. 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. 9A, the lower surfaces of the piezoelectric sheets 41 to 44 are fixed to the upper surfaces of the partition walls (cavity plates) 22 that partition the pressure chambers. Is deformed to be convex toward the pressure chamber. 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 electrodes 35a and 35b are returned to the same potential as 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 electrodes 35a and 35b are set to a potential different from that of the common electrode 34 in advance, and the individual electrodes 35a and 35b are once set to the same potential as the common electrode 34 every time there is a discharge request, and then the predetermined timing is reached. The individual electrodes 35a and 35b can be set to a potential different from that of the common electrode 34. In this case, when the individual electrodes 35a and 35b and the common electrode 34 become 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 both electrodes are The ink is sucked into the pressure chamber 10 from the manifold 5 side. After that, at the timing when the individual electrodes 35a and 35b are set to a potential different from that of the common electrode 34, the piezoelectric sheets 41 to 44 are deformed so as to protrude toward the pressure chamber 10, and the pressure on the ink is reduced due to the decrease in the volume of the pressure chamber 10. The ink rises and ink is ejected.

  Returning to FIG. 5, consider a strip region R having a width (678.0 μm) corresponding to 37.5 dpi in the arrangement direction A and extending in the arrangement direction B. In the strip-shaped region R, there is only one nozzle 8 in any of the 16 pressure chamber rows 11a to 11d. That is, when such a belt-like region R is partitioned at an arbitrary position in the ink discharge region corresponding to one actuator unit 21, 16 nozzles 8 are always distributed in the belt-like region R. . The positions of the points where the 16 nozzles 8 are projected on a straight line extending in the arrangement direction A are separated by an interval corresponding to 600 dpi which is the resolution at the time of printing.

  The sixteen nozzles 8 belonging to one band-shaped region R are written as (1) to (16) in order from the left of the projected position of the sixteen nozzles 8 on the straight line extending in the arrangement direction A. These 16 nozzles 8 are (1), (9), (5), (13), (2), (10), (6), (14), (3) from the bottom. , (11), (7), (15), (4), (12), (8), (16). In the inkjet head 1 configured as described above, when the actuator unit 21 is appropriately driven in accordance with the conveyance of the printing medium, characters, figures, and the like having a resolution of 600 dpi can be drawn.

  For example, a case where a straight line extending in the arrangement direction A is printed with a resolution of 600 dpi will be described. First, the case of an embodiment in which the nozzle 8 communicates with the acute angle portion on the same side of the pressure chamber 10 will be briefly described. In this case, in response to the printing butterfly being conveyed, ink discharge is started from the nozzle 8 in the pressure chamber row located at the bottom in FIG. The nozzle 8 to which it belongs is selected and ink is ejected. As a result, ink dots are formed while being adjacent to each other in the arrangement direction A at an interval of 600 dpi. Eventually, a straight line extending in the arrangement direction A is drawn with a resolution of 600 dpi as a whole.

  On the other hand, in the present embodiment, ink discharge is started from the nozzle 8 in the pressure chamber row 11b located at the bottom in FIG. 5, and the pressure chambers are sequentially adjacent to the upper side as the print medium is conveyed. The communicating nozzle 8 is selected and ink is ejected. At this time, since the displacement in the arrangement direction A of the positions of the nozzles 8 is not the same every time one pressure chamber rises from the lower side to the upper side, the nozzles are sequentially formed along the arrangement direction A as the print medium is conveyed. Ink dots are not evenly spaced at 600 dpi.

  That is, as shown in FIG. 5, in response to the printing medium being transported, first, ink is ejected from the nozzle (1) communicating with the lowermost pressure chamber row 11b in the figure, and onto the printing medium. Dot rows are formed at intervals corresponding to 37.5 dpi. Thereafter, when the straight line formation position reaches the position of the nozzle (9) communicating with the second pressure chamber row 11a from the bottom along with the conveyance of the printing medium, ink is ejected from the nozzle (9). As a result, a second ink dot is formed at a position displaced in the arrangement direction A by 8 times the interval corresponding to 600 dpi from the initially formed dot position.

Next, when the straight line formation position reaches the position of the nozzle (5) communicating with the third pressure chamber row 11d from the bottom along with the conveyance of the printing medium, ink is ejected from the nozzle (5). As a result, a third ink dot is formed at a position displaced in the arrangement direction A by four times the interval corresponding to 600 dpi from the initially formed dot position. Further, when the printing medium is conveyed and the straight line formation position reaches the position of the nozzle (13) communicating with the fourth pressure chamber row 11c from the bottom, ink is ejected from the nozzle (13). As a result, a fourth ink dot is formed at a position displaced in the arrangement direction A by 12 times the interval corresponding to 600 dpi from the position of the dot formed first. Further, when the straight line formation position reaches the position of the nozzle (2) communicating with the fifth pressure chamber row 11b from the bottom along with the conveyance of the printing medium, ink is ejected from the nozzle (2). As a result, a fifth ink dot is formed at a position displaced in the arrangement direction A by an interval corresponding to 600 dpi from the initially formed dot position.
In the same manner, ink dots are sequentially formed while selecting the nozzles 8 communicating with the pressure chambers 10 positioned from the lower side to the upper side in the drawing. At this time, if the number of the nozzle 8 shown in FIG. 5 is N, the arrangement direction from the dot position formed first is equivalent to (magnification n = N−1) × (interval corresponding to 600 dpi). Ink dots are formed at positions displaced to A. When 16 nozzles 8 have been finally selected, the distance between the ink dots formed by the nozzle (1) in the lowermost pressure chamber row 11b in the drawing at an interval corresponding to 37.5 dpi is 600 dpi. It is possible to draw a straight line extending in the arrangement direction A with a resolution of 600 dpi as a whole, which is connected by 15 dots formed at intervals corresponding to each other.

  Note that, in the vicinity of both end portions (the oblique sides of the actuator unit 21) in the arrangement direction A of each ink discharge region, both ends in the arrangement direction A of the ink discharge region corresponding to another actuator unit 21 facing the width direction of the head body 70. By being in a complementary relationship with the vicinity of the image, printing at a resolution of 600 dpi is possible.

  As can be seen from the above description, in the inkjet head 1 of the present embodiment, the plane size of the individual electrode 35 a formed in the parallelogram blocks 51 and 52 is the same as that of the individual electrode 35 b formed in the trapezoid block 53. Since the common electrode 34 is provided over the entire area of the actuator unit 21, the opposed area of the individual electrode 35 and the common electrode 34 in the parallelogram blocks 51 and 52 rather than the trapezoid block 53. Is getting bigger. The electrode facing area in each block 51, 52, 53 is equal to the area of the individual electrode in each block 51, 52, 53. When the electrode facing areas in the three blocks 51, 52 and 53 are not adjusted, the variation in the ink ejection speed particularly in the arrangement direction A becomes large and the image quality deteriorates. However, in the present embodiment, since the electrode facing area is adjusted, the average ink discharge speeds in the three blocks 51, 52, and 53 are substantially the same. Therefore, the image quality of the printed image is greatly improved. In addition, the uniform ink discharge speed by adjusting the electrode facing area as in the present embodiment is designed in that there is almost no need to change dimensional parameters and control parameters other than the electrode planar shape in accordance with such adjustment. This is advantageous.

  In the present embodiment, the planar size of the individual electrode 35 is changed according to the block in the actuator unit 21 in order to adjust the electrode facing area. Therefore, it is not necessary to change the shape of the common electrode 34, and the facing area between the individual electrode 35 and the common electrode 34 can be easily adjusted.

  Further, in the present embodiment, the actuator unit 21 is divided into three blocks 51, 52, and 53, and the planar size of the individual electrode 35 in each block is the same. For this reason, although the effect of adjusting the variation in the ink ejection speed is slightly inferior to the case where the plane size of each individual electrode 35 is adjusted without a block, the plane size of the individual electrode 35 may be changed in units of blocks. So it becomes easier to manufacture.

  As a modification of the present embodiment, in addition to adjusting the planar size of the individual electrode 35, the thickness of the individual electrode 35 is increased, so that the rigidity of the individual electrode 35 itself is increased and is difficult to be deformed. The principle of slowing may be used. That is, by making the thickness of the individual electrode 35b larger than the thickness of the individual electrode 35a, variations in ink discharge speed can be reduced. In this case, since the difference in ink discharge speed can be compensated not only by the electrode facing area but also by the thickness of the individual electrode 35, even if there is a large difference in the original ink discharge speed, it can be made uniform. It becomes.

  As another modification, the plane size of the individual electrode 35 is made common in the blocks 51, 52, 53 and the shape of the common electrode 34 is adjusted so that the electrode facing area in the blocks 51, 52 is in the block 53. It may be made larger than the electrode facing area. Alternatively, the electrode facing area may be controlled by adjusting both the individual electrode 35 and the common electrode 34.

  Next, a second embodiment of the present invention will be described. In the ink jet head according to the present embodiment, the shape of the individual electrode 35 is partially different from that of the first embodiment. That is, regarding the structure depicted in FIGS. 1 to 7, the ink jet head of the present embodiment is the same as that of the first embodiment, and FIGS. 8, 9, 10 (a), and FIG. The two are different with respect to the depicted structure. Therefore, hereinafter, the difference will be mainly described, and the same members as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 11A is a cross-sectional view corresponding to FIG. 10A of the head body in the present embodiment. FIG. 11B is a cross-sectional view corresponding to FIG. 10B of the head body in the present embodiment. In the present embodiment, among the three blocks 51, 52 and 53 shown in FIG. 8, the individual electrodes 35c are formed in the blocks 51 and 52, and the individual electrodes 35d are formed in the block 53. Both the individual electrode 35c and the individual electrode 35d have the same planar size as the individual electrode 35a shown in FIG. As can be seen from FIGS. 11A and 11B, the individual electrode 35d is thicker than the individual electrode 35c. This is because if the individual electrode 35 becomes thicker, the rigidity of the individual electrode 35 itself becomes higher, and even if the same drive voltage is applied to the electrode, the electrode is thick, so that the displacement of the active layer of the actuator unit 21 is hindered. This is because the average ink discharge speed in the three blocks 51, 52, and 53 is adjusted using the above-described principle that the ink discharge speed is reduced as a result.

  In the present embodiment, the thickness of the individual electrode 35c and the individual electrode 35d is adjusted to such a thickness that the average ink discharge speeds in the three blocks 51, 52, and 53 are substantially the same. When such adjustment is not performed, the variation in the ink ejection speed particularly along the arrangement direction A becomes large, and the image quality of the printed image deteriorates. However, in the present embodiment, the electrode thickness is adjusted so that the average ink ejection speeds in the three blocks 51, 52, and 53 are substantially the same, so that the image quality of the printed image is greatly improved. In addition, according to the present embodiment, the same benefits as in the first embodiment can be obtained.

  Next, a third embodiment of the present invention will be described. The inkjet head according to the present embodiment is partially different from the first embodiment in the number of individual electrodes 35 superimposed. That is, regarding the structure depicted in FIGS. 1 to 7, the ink jet head of the present embodiment is the same as that of the first embodiment, and FIGS. 8, 9, 10 (a), and FIG. The two are different with respect to the depicted structure. Therefore, hereinafter, the difference will be mainly described, and the same members as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 12A is a cross-sectional view corresponding to FIG. 10A of the head body in the present embodiment. FIG. 12B is a cross-sectional view corresponding to FIG. 10B of the head body in the present embodiment. In the present embodiment, among the three blocks 51, 52, 53 shown in FIG. 8, the individual electrodes 35e are formed on the piezoelectric sheet 41 in the blocks 51, 52, and the piezoelectric sheet 42 and the piezoelectric sheet 43 are formed. An individual electrode 35f is formed at a position facing the individual electrode 35e between the two electrodes. On the other hand, individual electrodes 35g are formed in the block 53. The individual electrodes 35e, 35f, and 35g all have the same planar size and thickness as the individual electrode 35a shown in FIG.

  Under the land portions 36 in the blocks 51 and 52, through holes are formed in the piezoelectric sheets 41 and 42, and the through holes are filled with a conductive material (silver palladium or the like). Therefore, the two individual electrodes 35e and 35f in the blocks 51 and 52 are electrically connected via a conductive material, and the individual electrode 35f is controlled to the same potential as the individual electrode 35e. In the blocks 51 and 52, in addition to the region sandwiched between the individual electrode 35e and the common electrode 34 in the piezoelectric sheet 41, the region sandwiched between the individual electrode 35f and the common electrode 34 functions as an active layer in the piezoelectric sheet 42. That is, the blocks 51 and 52 of the actuator unit 21 have a unimorph type structure in which the upper two piezoelectric sheets 41 and 42 are active layers and the lower two piezoelectric sheets 43 and 44 are inactive layers. It has become. On the other hand, the block 53 has a unimorph type configuration in which the upper one piezoelectric sheet 41 is an active layer and the lower three piezoelectric sheets 42, 43, and 44 are inactive layers.

  In principle, if the number of superimposed individual electrodes 35 increases, the number of active layers that cause displacement increases even when the same drive voltage is applied, and the actuator unit 21 causes a large displacement. Increases speed. In the present embodiment, by setting the number of overlapping of the individual electrodes 35 in the blocks 51 and 52 to 2 and setting the number of overlapping of the individual electrodes 35 in the block 53 to 1, the average ink discharge speed in the three blocks 51, 52 and 53 Are almost the same. When the number of overlapping of the individual electrodes 35 in the three blocks 51, 52, and 53 is the same, the variation in the ink ejection speed particularly in the arrangement direction A becomes large, and the image quality of the printed image deteriorates. However, in the present embodiment, the number of overlapping of the individual electrodes 35 is adjusted so that the average ink discharge speeds in the three blocks 51, 52, and 53 are substantially the same. improves. In addition, according to the present embodiment, the same benefits as in the first embodiment can be obtained.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the contents described in the claims. Is. For example, the pressure chambers and the individual electrodes may be arranged along one direction instead of the matrix arrangement. In this case, the electrode facing area, the thickness of the individual electrodes, and the number of overlapping are adjusted along the one direction. It only has to be.

  In the above-described embodiment, the electrode facing area and the thickness of the individual electrode are adjusted in the actuator unit so as to change along the longitudinal direction of the actuator unit. However, the ink from the nozzle corresponding to the actuator unit is adjusted. Depending on the state of variation in the discharge speed, the electrode facing area may be adjusted so as to change along two directions of the longitudinal direction of the actuator unit and the direction intersecting with the longitudinal direction. In addition, when the variation in the ink discharge speed from the nozzle is larger in the direction intersecting the actuator unit than in the longitudinal direction, the electrode facing area is adjusted so that it changes only along the direction intersecting the actuator unit longitudinal direction. May be.

  Furthermore, as an example of adjusting the ink discharge speed, the example in which the electrode facing area, the thickness of the individual electrode, or the number of overlapping individual electrodes is changed in the above-described embodiment has been described, but any two or more of these methods are combined. The ink discharge speed may be adjusted accordingly.

  In the above-described embodiment, the electrode facing area and the like are made equal for every three blocks provided in the actuator unit, but the number of blocks may be changed to an arbitrary number. In addition, the electrode facing area may be adjusted for each individual electrode without providing such a block in the actuator unit. Furthermore, in the above-described embodiment, the size and thickness of the individual electrodes are adjusted as appropriate so that the ink discharge speeds of the plurality of nozzles in the actuator unit are uniform. It is not limited to what makes it uniform. That is, in contrast to the case where all the individual electrodes have the same size and the like, it is sufficient that the difference in the ink discharge speed of the nozzles is reduced to a level that can be practically tolerated.

  Furthermore, the arrangement of the pressure chamber and the common ink chamber is not limited to the above-described embodiment, and various design changes can be made.

  In the above-described embodiment, since the flow path unit 4 is made of stainless steel and the actuator unit 21 is made of ceramic, the thermal expansion coefficient of the flow path unit 4 is greater than that of the actuator unit 21. large. However, for example, when the flow path unit 4 is made of a so-called 4-2 alloy and the thermal expansion coefficient of the flow path unit 4 is smaller than that of the actuator unit 21, the individual electrode 35 and the common electrode 34 The opposite area, the thickness of the individual electrodes 35, or the number of the individual electrodes 35 superimposed are designed to be opposite to those of the above-described embodiment at the central portion and the outer edge portion of the actuator unit 21, thereby Adjustment may be made so that the ink discharge speed is uniform.

  As described above, in the above-described embodiment, the ink discharge speed at the center of the actuator unit generated when the ceramic actuator unit and the metal channel unit are bonded and fixed in a heated state is the outer edge portion. This is to cope with a phenomenon that the ink discharge speed is higher than the vicinity. In the case of the above-described embodiment, since the thermal expansion coefficient of the metal flow path unit is higher than that of the ceramic actuator unit, the present inventor has determined that the ink discharge speed at the center is higher than the ink discharge speed at the outer edge. Is estimated to be related to the coefficient of thermal expansion. However, it cannot be determined that there is no case where the ink discharge speed near the outer edge of the actuator unit is faster than the ink discharge speed at the center due to other factors. When such a case occurs, the opposing area of the individual electrode and the common electrode at the outer edge of the actuator unit is made smaller than that at the center, or the thickness of the individual electrode at the outer edge is made smaller than that at the center. The ink ejection speed can be adjusted by increasing the thickness or by reducing the number of active layers at the outer edge portion as compared with the central portion. Of course, the ink ejection speed may be adjusted by combining any two or more of these methods.

1 is a perspective view of an inkjet 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 depicted in FIG. 3. It is an enlarged view of the area | region enclosed with the dashed-dotted line drawn by FIG. It is sectional drawing along the VI-VI line of FIG. FIG. 7 is a partial exploded perspective view of the head main body depicted in FIG. 6. FIG. 7 is a plan view of the actuator unit depicted in FIG. 6. FIG. 9A is a plan view of individual electrodes formed on the left and right block surfaces of the actuator unit. FIG. 9B is a plan view of the individual electrodes formed on the surface of the central block of the actuator unit. FIG. 10A is a cross-sectional view taken along line XA-XA in FIG. FIG. 10B is a cross-sectional view taken along line XB-XB in FIG. FIG. 11A is a cross-sectional view of the head main body of the ink jet head according to the second embodiment of the present invention, corresponding to FIG. FIG. 11B is a cross-sectional view corresponding to FIG. FIG. 12A is a cross-sectional view of the head main body of the ink jet head according to the third embodiment of the present invention, corresponding to FIG. FIG. 12B is a cross-sectional view corresponding to FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 4 Flow path unit 5 Manifold 5a Submanifold 8 Nozzle 10 Pressure chamber 21 Actuator unit 34 Common electrode 35a, 35b Individual electrode 41, 42, 43, 44 Piezoelectric sheet 51, 52, 53 Block 70 Head body

Claims (14)

A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
The thermal expansion coefficient of the flow path unit is larger than the thermal expansion coefficient of the actuator unit, and the opposed area of the individual electrode and the common electrode in the central part of the actuator unit is the individual electrode in the outer edge part of the actuator unit. And an ink jet head characterized in that it is smaller than the facing area of the common electrode.   2. The inkjet head according to claim 1, wherein an area of the individual electrode disposed at a central portion of the actuator unit is smaller than an area of the individual electrode disposed at an outer edge portion of the actuator unit.   The inkjet head according to claim 1, wherein the plurality of individual electrodes are arranged in a matrix.   The inkjet head according to claim 3, wherein the facing area is changed along one direction in the actuator unit. The actuator unit has a plurality of blocks,
2. The opposed area in one block is the same, and the opposed area in the block at the center is smaller than the opposed area in another block at the outer edge. The inkjet head of any one of -4.   6. The inkjet head according to claim 1, wherein a thickness of the individual electrode in a central portion of the actuator unit is larger than a thickness of the individual electrode in an outer edge portion of the actuator unit. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode common to the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
Greater than the thermal expansion coefficient of the channel unit is the thermal expansion coefficient of the actuator unit, the thickness of the individual electrodes in the central portion of the actuator unit is larger than the thickness of the individual electrodes in the outer edge of the actuator unit An inkjet head characterized by the above. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode common to the plurality of pressure chambers;
A plurality of stacked piezoelectric sheets sandwiched between the common electrode and the individual electrodes,
The thermal expansion coefficient of the flow path unit is larger than the thermal expansion coefficient of the actuator unit, and the number of overlapping of the individual electrodes in the piezoelectric sheet in the piezoelectric sheet stacking direction in the piezoelectric sheet is larger at the outer edge than at the center of the actuator unit. An inkjet head characterized by that. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
The thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the opposing area of the individual electrode and the common electrode in the central part of the actuator unit is the individual electrode in the outer edge part of the actuator unit. And an ink jet head characterized in that it is larger than the area facing the common electrode . A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode common to the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
The thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the thickness of the individual electrode at the center of the actuator unit is smaller than the thickness of the individual electrode at the outer edge of the actuator unit. An inkjet head characterized by the above. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
An actuator unit that is fixed to the surface of the flow path unit and changes the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode common to the plurality of pressure chambers;
A plurality of stacked piezoelectric sheets sandwiched between the common electrode and the individual electrodes,
The thermal expansion coefficient of the flow path unit is smaller than the thermal expansion coefficient of the actuator unit, and the number of overlapping of the individual electrodes in the piezoelectric sheet in the piezoelectric sheet stacking direction is smaller at the outer edge portion than the central portion of the actuator unit. An inkjet head characterized by that. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
  An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
When the opposing area of the individual electrode and the common electrode is the same, when the ink discharge speed is faster at the center than the outer edge of the actuator unit, the individual electrode and the common electrode at the center of the actuator unit The ink jet head is characterized in that a facing area of the actuator unit is smaller than a facing area of the individual electrode and the common electrode at an outer edge portion of the actuator unit. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
  An actuator unit fixed to the surface of the flow path unit and changing the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
When the thickness of the individual electrode is the same and the ink discharge speed is faster at the center than the outer edge of the actuator unit, the thickness of the individual electrode at the center of the actuator unit is the outer edge of the actuator unit. An ink jet head, wherein the thickness is larger than the thickness of the individual electrode. A flow path unit in which a plurality of pressure chambers communicating with the nozzle are arranged along a plane;
  An actuator unit that is fixed to the surface of the flow path unit and changes the volume of the pressure chamber;
The actuator unit is
A plurality of individual electrodes arranged at positions facing each pressure chamber;
A common electrode provided across the plurality of pressure chambers;
A piezoelectric sheet sandwiched between the common electrode and the individual electrode;
When the number of overlapping of the individual electrodes in the piezoelectric sheet stacking direction is the same, and the ink discharge speed is faster at the center than the outer edge of the actuator unit, An inkjet head characterized in that the number of superpositions is greater at the outer edge than at the center of the actuator unit.

Images