JP2012228843A - Piezoelectric actuator and liquid discharge head and recording device using the piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator having a large displacement amount and a liquid discharge head and a recording device which use the piezoelectric actuator.SOLUTION: In the piezoelectric actuator, an inner electrode 34, a piezoelectric ceramic layer 21b and a surface electrode 35 are laminated on a diaphragm 21a in this order. Total thickness of a first portion 21a-1 of the diaphragm 21a under the surface electrode 35, the inner electrode 34 and a first portion 21b-1 of the piezoelectric ceramic layer 21b is set larger than total thickness of a second portion 21a-2 of the diaphragm 21a around the surface electrode 35, the inner electrode 34 and a second portion 21b-2 of the piezoelectric ceramic layer 21b. Total thickness of the diaphragm 21a under the surface electrode 35 and the inner electrode 34 is set larger than total thickness of the diaphragm 21a around the surface electrode 35 and the inner electrode 34.

Description

  The present invention relates to a piezoelectric actuator that generates displacement using piezoelectricity, and a liquid discharge head and a recording apparatus that discharge droplets using the piezoelectric actuator.

  An ink jet recording apparatus is equipped with a liquid ejection head for ejecting liquid. The liquid discharge head is equipped with a heater as a pressurizing means. The ink is heated and boiled in the flow path filled with ink, and the ink in the flow path is pressurized and discharged by bubbles generated in the flow path. A piezoelectric / electrostatic system that includes a thermal head system that moves and a displacement element as a pressurizing means, and that bends and displaces part of the wall of the flow path filled with ink to mechanically pressurize and eject the ink. Is generally known.

  In addition, in such a liquid discharge head, a serial type that performs recording while moving the liquid discharge head in a direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording medium, and main scanning from the recording medium There is a line type in which recording is performed on a recording medium conveyed in the sub-scanning direction with a liquid discharge head that is long in the direction fixed. The line type has the advantage that high-speed recording is possible because there is no need to move the liquid discharge head as in the serial type.

  In order to print droplets at a high density in any of the serial type and line type liquid discharge heads, the density of the discharge holes for discharging the droplets formed in the liquid discharge head is increased. There is a need.

  Accordingly, the liquid discharge head includes a manifold and a metal flow path member having discharge holes that connect the manifold via the plurality of pressurizing chambers, and a plurality of displacement elements provided so as to cover the pressurizing chambers, respectively. A structure in which a piezoelectric actuator is laminated is known (for example, see Patent Document 1). In this liquid discharge head, the pressurizing chambers connected to the plurality of discharge holes are arranged in a matrix, and the displacement elements of the piezoelectric actuator provided so as to cover them are displaced by the deformation of the piezoelectric body. Ink is ejected from the holes and printing is possible in the main scanning direction at a resolution of 600 dpi. Further, the displacement element has a structure in which the diaphragm, the common electrode, the piezoelectric ceramic layer, and the individual electrode located at the position facing the pressurizing chamber are laminated from the flow path member side.

JP 2003-305852 A

  In the piezoelectric actuator described in Patent Document 1, since the amount of displacement is small, the amount of ejected droplets is less than the desired amount, or the flying speed of the ejected droplets is lower than the desired rate was there.

  Accordingly, an object of the present invention is to provide a piezoelectric actuator having a large displacement, a liquid discharge head using the same, and a recording apparatus.

  The piezoelectric actuator of the present invention is a piezoelectric actuator in which an internal electrode, a piezoelectric ceramic layer, and a surface electrode are laminated in this order on a vibration plate, and the vibration plate, the internal electrode, and the surface electrode under the surface electrode The total thickness of the piezoelectric ceramic layer is thicker than the total thickness of the diaphragm, the internal electrode and the piezoelectric ceramic layer around the surface electrode, and the diaphragm under the surface electrode and The total thickness of the internal electrodes is larger than the total thickness of the diaphragm and the internal electrodes around the surface electrode.

  It is preferable that the thickness of the piezoelectric ceramic layer under the surface electrode is equal to or less than the thickness of the diaphragm under the surface electrode.

  The upper surface of the piezoelectric ceramic layer under the surface electrode is preferably higher than the upper surface of the piezoelectric ceramic layer around the surface electrode, and the upper surface of the piezoelectric ceramic layer is preferably convex.

  It is preferable that the lower surface of the diaphragm under the surface electrode is higher than the lower surface of the diaphragm around the surface electrode, and the lower surface of the piezoelectric ceramic layer is concave.

  In the liquid discharge head of the present invention, the piezoelectric actuator includes a plurality of the surface electrodes, the internal electrodes face the plurality of surface electrodes, and the piezoelectric actuators are connected to the plurality of discharge holes, respectively. The surface electrode and the pressurizing chamber are aligned and laminated on a flow path member in which a plurality of pressurizing chambers are open.

  In a plan view of the piezoelectric actuator, it is preferable that a portion where the total thickness of the diaphragm, the internal electrode, and the piezoelectric ceramic layer is thicker than the surroundings is housed in the pressurizing chamber.

  A recording apparatus comprising: the liquid discharge head; a transport unit that transports a recording medium relative to the liquid discharge head; and a control unit that controls the liquid discharge head.

  According to the present invention, since the displacement force received by the displacement element from the surrounding diaphragm and the piezoelectric ceramic layer is reduced, the amount of displacement is increased.

1 is a schematic configuration diagram of a printer that is a recording apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a liquid discharge head body that constitutes the liquid discharge head of FIG. 1. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. 2, and is a diagram in which some flow paths are omitted for explanation. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. 2, and is a diagram in which a part of the flow path different from FIG. (A) is the longitudinal cross-sectional view along the VV line | wire of FIG. 3, (b) is an enlarged view of the principal part of (a), (c) is expanded the principal part of (a). FIG. (A) is a longitudinal cross-sectional view of the piezoelectric actuator of other embodiment of this invention laminated | stacked on the flow-path member.

FIG. 1 is a schematic configuration diagram of a color ink jet printer which is a recording apparatus including a liquid discharge head according to an embodiment of the present invention. This color inkjet printer 1 (hereinafter referred to as printer 1) has four liquid ejection heads 2. These liquid discharge heads 2
Are arranged along the transport direction of the printing paper P and fixed to the printer 1. The liquid discharge head 2 has an elongated shape in a direction from the front to the back in FIG. This long direction is sometimes called the longitudinal direction.

  In the printer 1, a paper feed unit 114, a transport unit 120, and a paper receiver 116 are sequentially provided along the transport path of the printing paper P. In addition, the printer 1 is provided with a control unit 100 for controlling the operation of each unit of the printer 1 such as the liquid discharge head 2 and the paper feeding unit 114.

  The paper supply unit 114 includes a paper storage case 115 that can store a plurality of printing papers P, and a paper supply roller 145. The paper feed roller 145 can send out the uppermost print paper P among the print papers P stacked and stored in the paper storage case 115 one by one.

  Between the paper feed unit 114 and the transport unit 120, two pairs of feed rollers 118a and 118b and 119a and 119b are arranged along the transport path of the printing paper P. The printing paper P sent out from the paper supply unit 114 is guided by these feed rollers and further sent out to the transport unit 120.

  The transport unit 120 includes an endless transport belt 111 and two belt rollers 106 and 107. The conveyor belt 111 is wound around belt rollers 106 and 107. The conveyor belt 111 is adjusted to such a length that it is stretched with a predetermined tension when it is wound around two belt rollers. Thus, the conveyor belt 111 is stretched without slack along two parallel planes each including a common tangent line of the two belt rollers. Of these two planes, the plane closer to the liquid ejection head 2 is a transport surface 127 that transports the printing paper P.

  As shown in FIG. 1, a conveyance motor 174 is connected to the belt roller 106. The transport motor 174 can rotate the belt roller 106 in the direction of arrow A. The belt roller 107 can rotate in conjunction with the transport belt 111. Therefore, the conveyance belt 111 moves along the direction of arrow A by driving the conveyance motor 174 and rotating the belt roller 106.

  In the vicinity of the belt roller 107, a nip roller 138 and a nip receiving roller 139 are arranged so as to sandwich the conveyance belt 111. The nip roller 138 is urged downward by a spring (not shown). A nip receiving roller 139 below the nip roller 138 receives the nip roller 138 biased downward via the conveying belt 111. The two nip rollers are rotatably installed and rotate in conjunction with the conveyance belt 111.

  The printing paper P sent out from the paper supply unit 114 to the transport unit 120 is sandwiched between the nip roller 138 and the transport belt 111. As a result, the printing paper P is pressed against the transport surface 127 of the transport belt 111 and is fixed on the transport surface 127. The printing paper P is transported in the direction in which the liquid ejection head 2 is installed according to the rotation of the transport belt 111. The outer peripheral surface 113 of the conveyor belt 111 may be treated with adhesive silicon rubber. Thereby, the printing paper P can be securely fixed to the transport surface 127.

The four liquid discharge heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a liquid discharge head main body 13 at the lower end.
A number of ejection holes 8 for ejecting liquid are provided on the lower surface of the liquid ejection head body 13 (see FIGS. 4 and 5).

  Liquid droplets (ink) of the same color are ejected from the ejection holes 8 provided in one liquid ejection head 2. Each liquid discharge head 2 is supplied with liquid from an external liquid tank (not shown). The ejection holes 8 of each liquid ejection head 2 are opened in the ejection hole surface, and are in one direction (a direction parallel to the printing paper P and perpendicular to the conveyance direction of the printing paper P, the longitudinal direction of the liquid ejection head 2). Since they are arranged at equal intervals, printing can be performed without gaps in one direction. The colors of the liquid ejected from each liquid ejection head 2 are magenta (M), yellow (Y), cyan (C), and black (K), respectively. Each liquid discharge head 2 is arranged with a slight gap between the lower surface of the liquid discharge head main body 13 and the transport surface 127 of the transport belt 111.

  The printing paper P transported by the transport belt 111 passes through the gap between the liquid ejection head 2 and the transport belt 111. At that time, droplets are ejected from the liquid ejection head body 13 constituting the liquid ejection head 2 toward the upper surface of the printing paper P. As a result, a color image based on the image data stored by the control unit 100 is formed on the upper surface of the printing paper P.

  A separation plate 140 and two pairs of feed rollers 121a and 121b and 122a and 122b are arranged between the transport unit 120 and the paper receiver 116. The printing paper P on which the color image is printed is conveyed to the peeling plate 140 by the conveying belt 111. At this time, the printing paper P is peeled from the transport surface 127 by the right end of the peeling plate 140. Then, the printing paper P is sent out to the paper receiving unit 116 by the feed rollers 121a to 122b. In this way, the printed printing paper P is sequentially sent to the paper receiving unit 116 and stacked on the paper receiving unit 116.

  Note that a paper surface sensor 133 is installed between the liquid ejection head 2 and the nip roller 138 that are the most upstream in the transport direction of the printing paper P. The paper surface sensor 133 includes a light emitting element and a light receiving element, and can detect the leading end position of the printing paper P on the transport path. The detection result by the paper surface sensor 133 is sent to the control unit 100. The control unit 100 can control the liquid ejection head 2, the conveyance motor 174, and the like so that the conveyance of the printing paper P and the printing of the image are synchronized based on the detection result sent from the paper surface sensor 133.

  Next, the liquid discharge head main body 13 constituting the liquid discharge head of the present invention will be described. FIG. 2 is a plan view of the liquid discharge head main body 13 constituting the liquid discharge head shown in FIG. FIG. 3 is an enlarged view of a region surrounded by a one-dot chain line in FIG. 2, and a part of the flow paths is omitted so that the position of the pressurizing chamber 10 can be easily understood. FIG. 4 is an enlarged view of the same position as FIG. 3, in which some of the flow paths are omitted so that the positions of the discharge holes 8 can be easily understood. In FIGS. 3 and 4, for the sake of easy understanding, the pressurizing chamber 10 (pressurizing chamber group 9), the squeezing chamber 12 and the discharge hole 8 below the piezoelectric actuator 21 and to be drawn by broken lines are shown by solid lines. I'm drawing. 5A is a longitudinal sectional view taken along the line VV in FIG. 3, FIG. 5B is an enlarged view of the main part of FIG. 5A, and FIG. It is the top view to which the principal part of 5 (a) was expanded.

The liquid discharge head body 13 includes a flat plate-like flow path member 4 and a piezoelectric actuator 21 on the flow path member 4. The piezoelectric actuator 21 has a trapezoidal shape, and is disposed on the upper surface of the flow path member 4 so that a pair of parallel opposing sides of the trapezoid is along the longitudinal direction of the flow path member 4. Further, two piezoelectric actuators 21 are arranged along the two virtual straight lines parallel to the longitudinal direction of the flow path member 4, that is, a total of four piezoelectric actuators 21 are arranged on the flow path member 4 as a whole in a staggered manner. . The oblique sides of the piezoelectric actuators 21 adjacent on the flow path member 4 partially overlap in the short direction of the flow path member 4. In the area printed by driving the overlapping piezoelectric actuator unit 21, the droplets discharged by the two piezoelectric actuators 21 are mixed and landed.

  A manifold 5 that is a part of the liquid flow path is formed inside the flow path member 4. The manifold 5 extends along the longitudinal direction of the flow path member 4 and has an elongated shape. An opening 5 b of the manifold 5 is formed on the upper surface of the flow path member 4. A total of ten openings 5 b are formed along each of two straight lines (imaginary lines) parallel to the longitudinal direction of the flow path member 4. The opening 5b is formed at a position that avoids a region where the four piezoelectric actuators 21 are disposed. The manifold 5 is supplied with liquid from a liquid tank (not shown) through the opening 5b.

  The manifold 5 formed in the flow path member 4 is branched into a plurality of branches (the manifold 5 at the branched portion may be referred to as a sub-manifold 5a). The manifold 5 connected to the opening 5 b extends along the oblique side of the piezoelectric actuator 21 and is disposed so as to intersect with the longitudinal direction of the flow path member 4. In a region sandwiched between two piezoelectric actuators 21, one manifold 5 is shared by the adjacent piezoelectric actuators 21, and the sub-manifold 5 a is branched from both sides of the manifold 5. These sub-manifolds 5 a extend in the longitudinal direction of the liquid discharge head main body 13 adjacent to each other in regions facing the piezoelectric actuators 21 inside the flow path member 4.

  The flow path member 4 has four pressure chamber groups 9 in which a plurality of pressure chambers 10 are formed in a matrix (that is, two-dimensionally and regularly). The pressurizing chamber 10 is a hollow region having a substantially rhombic planar shape with rounded corners. The pressurizing chamber 10 is formed so as to open on the upper surface of the flow path member 4. These pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator 21. Accordingly, each pressurizing chamber group 9 formed by these pressurizing chambers 10 occupies a region having substantially the same size and shape as the piezoelectric actuator 21. Further, since the piezoelectric actuators 21 are stacked so as to cover the plurality of pressurizing chambers 10, the opening of each pressurizing chamber 10 is closed by the piezoelectric actuators 21.

  In the present embodiment, as shown in FIG. 3, the manifold 5 branches into four rows of E1-E4 sub-manifolds 5a arranged in parallel with each other in the short direction of the flow path member 4, and each sub-manifold The pressurizing chambers 10 connected to 5a constitute a row of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the four rows are arranged in parallel to each other in the lateral direction. Two rows of the pressure chambers 10 connected to the sub-manifold 5a are arranged on both sides of the sub-manifold 5a.

  As a whole, the pressurizing chambers 10 connected from the manifold 5 constitute rows of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are arranged in 16 rows parallel to each other in the short side direction. ing. The number of pressurizing chambers 10 included in each pressurizing chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape of the displacement element 50 that is an actuator. . The discharge holes 8 are also arranged in the same manner. As a result, it is possible to form an image with a resolution of 600 dpi in the longitudinal direction as a whole.

That is, when the discharge hole 8 is projected so as to be orthogonal to a virtual straight line parallel to the longitudinal direction of the flow path member 4, it is connected to each sub-manifold 5 a within the range of R of the virtual straight line shown in FIG. One discharge hole 8, that is, a total of 16 discharge holes 8, is equally spaced at 600 dpi. Moreover, the individual flow paths 32 are connected to the sub manifolds 5a at intervals corresponding to 150 dpi on average. This is because when the discharge holes 8 for 600 dpi are divided and connected to the four sub-manifolds 5a, the individual flow paths 32 connected to the sub-manifolds 5a are not always connected at equal intervals. 170 in the extension direction, that is, an average of 170 in the main scanning direction
This means that the individual flow paths 32 are formed at intervals of μm (25.4 mm / 150 = 169 μm intervals if 150 dpi).

  Individual electrodes 35 to be described later are formed at positions facing the pressurizing chambers 10 on the upper surface of the piezoelectric actuator 21. That is, the individual electrode 35 is formed on the upper surface of the piezoelectric actuator 21 in a direction different from the first direction and the first direction. The individual electrode 35 includes an individual electrode main body (surface electrode) 35a and an extraction electrode 35b extracted from the individual electrode main body 35a. The individual electrode main body 35 a is slightly smaller than the pressurizing chamber 10, has a shape substantially similar to the pressurizing chamber 10, and is disposed so as to be within a region facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator 21. Has been.

  A large number of discharge holes 8 are formed in the lower surface of the flow path member 4. These discharge holes 8 are arranged at positions avoiding the area facing the sub-manifold 5a arranged on the lower surface side of the flow path member 4. Further, these discharge holes 8 are disposed in a region facing the piezoelectric actuator 21 on the lower surface side of the flow path member 4. These discharge hole groups 7 occupy an area having almost the same size and shape as the piezoelectric actuator 21, and a droplet can be discharged from the discharge hole 8 by displacing the displacement element 50 of the corresponding piezoelectric actuator 21. The arrangement of the discharge holes 8 will be described in detail later. The discharge holes 8 in each region are arranged at equal intervals along a plurality of straight lines parallel to the longitudinal direction of the flow path member 4.

  The flow path member 4 included in the liquid discharge head body 13 has a stacked structure in which a plurality of plates are stacked. These plates are a cavity plate 22, a base plate 23, an aperture (squeezing) plate 24, supply plates 25 and 26, manifold plates 27, 28 and 29, a cover plate 30 and a nozzle plate 31 in order from the upper surface of the flow path member 4. is there. A number of holes are formed in these plates. Each plate is aligned and laminated so that these holes communicate with each other to form the individual flow path 32 and the sub-manifold 5a. As shown in FIG. 5, the liquid discharge head body 13 is configured such that the pressurizing chamber 10 is on the upper surface of the flow path member 4, the sub-manifold 5 a is on the inner lower surface side, and the discharge holes 8 are on the lower surface. Each portion constituting the path 32 is disposed close to each other at different positions, and the sub-manifold 5 a and the discharge hole 8 are connected via the pressurizing chamber 10.

  The holes formed in each plate will be described. These holes include the following. First, the pressurizing chamber 10 formed in the cavity plate 22. Secondly, there is a communication hole that constitutes a flow path that connects from one end of the pressurizing chamber 10 to the sub-manifold 5a. This communication hole is formed in each plate from the base plate 23 (specifically, the inlet of the pressurizing chamber 10) to the supply plate 25 (specifically, the outlet of the sub-manifold 5a). The communication hole includes the aperture 12 formed in the aperture plate 24 and the individual supply flow path 6 formed in the supply plates 25 and 26.

  Third, there is a communication hole constituting a flow path communicating from the other end of the pressurizing chamber 10 to the discharge hole 8, and this communication hole is referred to as a descender (partial flow path) in the following description. The descender is formed on each plate from the base plate 23 (specifically, the outlet of the pressurizing chamber 10) to the nozzle plate 31 (specifically, the discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27 to 29.

Such communication holes are connected to each other to form an individual flow path 32 extending from the liquid inflow port (the outlet of the submanifold 5a) from the submanifold 5a to the discharge hole 8. The liquid supplied to the sub-manifold 5a is discharged from the discharge hole 8 through the following path. First, from the sub-manifold 5a, it passes through the individual supply flow path 6 and reaches one end of the aperture 12. Next, it proceeds horizontally along the extending direction of the aperture 12 and reaches the other end of the aperture 12. From there, it reaches one end of the pressurizing chamber 10 upward. Furthermore, it progresses horizontally along the extending direction of the pressurizing chamber 10 and reaches the other end of the pressurizing chamber 10. While moving little by little in the horizontal direction from there, it proceeds mainly downward and proceeds to the discharge hole 8 opened in the lower surface.

  As shown in FIG. 5, the piezoelectric actuator 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. Each of these piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The thickness of the laminated body of the piezoelectric ceramic layers 21a and 21b of the piezoelectric actuator 21 is about 40 μm, and the displacement can be increased by being 100 μm or less. The piezoelectric actuator 21 is laminated on the planar surface of the flow path member 4 where the pressurizing chamber 10 is open, and the piezoelectric ceramic layers 21 a and 21 b straddle the plurality of pressurizing chambers 10. It extends (see FIG. 3). The piezoelectric ceramic layers 21a and 21b are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity. The 1st site | part 21a-1 which is the diaphragm 21a under the individual electrode 35 is thicker than the 2nd site | part 21a-2 which is the surrounding diaphragm 21a. The first portion 21b-1 that is the piezoelectric ceramic layer 21a under the individual electrode 35 and the second portion 21b-2 that is the surrounding piezoelectric ceramic layer 21b have the same thickness, but the lower portion of the individual electrode 35 Therefore, the upper surface of the piezoelectric ceramic layer 21b has a convex shape. These structures will be described in detail later.

  The piezoelectric actuator 21 includes a common electrode (internal electrode) 34 made of a metal material such as Ag—Pd, an individual electrode 35 made of a metal material such as Au, and an Au-based metal formed on the individual electrode 35. A connection electrode 36 made of a material is provided. As described above, the individual electrode 35 is drawn out from the individual electrode main body 35a disposed at a position facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator 21, and from the individual electrode main body 35a to a position where the pressurizing chamber 10 is not present. And an extraction electrode 35b. A connection electrode 36 is formed at a position of the extraction electrode 35b where the pressurizing chamber 10 is not provided. The thickness of the individual electrode 35 is 0.3 to 1 μm. The connection electrode 36 is made of, for example, gold containing glass frit, has a thickness of about 5 to 15 μm, and is formed on the extraction electrode 35 b. The upper portion of the connection electrode 36 is positioned higher than the individual electrode body having a convex shape. The connection electrode 36 is electrically joined to an electrode provided in an FPC (Flexible Printed Circuit) which is an external wiring (not shown). Although details will be described later, a drive signal (drive voltage) is supplied to the individual electrode 35 from the control unit 100 through the FPC. The drive signal is supplied in a constant cycle in synchronization with the conveyance speed of the print medium P.

  The common electrode 34 is formed over almost the entire surface in the area between the piezoelectric ceramic layer 21a and the piezoelectric ceramic layer 21b. That is, the common electrode 34 extends so as to cover all the pressurizing chambers 10 in the region facing the piezoelectric actuator 21. The thickness of the common electrode 34 is about 1 to 2 μm. The common electrode 34 is grounded in a region not shown, and is held at the ground potential. In the present embodiment, a surface electrode for ground connection (not shown) different from the individual electrode 35 is formed on the piezoelectric ceramic layer 21b so as to avoid the electrode group composed of the individual electrodes 35. The ground connection is electrically connected to the common electrode 34 through a through hole formed inside the piezoelectric ceramic layer 21b, and, like the large number of individual electrodes 35, is connected to another electrode in the external wiring. It is connected.

  The above is a structure in the case where the piezoelectric actuator 21 is a two-layer piezoelectric ceramic layer, but the piezoelectric electrodes are laminated in three or more phases, and the individual electrodes 35 and the common electrodes 34 are arranged alternately. May be.

As shown in FIG. 5, the common electrode 34 and the individual electrode 35 are arranged so as to sandwich the uppermost piezoelectric ceramic layer 21b. A region sandwiched between the individual electrode 35 and the common electrode 34 in the piezoelectric ceramic layer 21b is called an active portion, and the piezoelectric ceramic in that portion is polarized in the thickness direction. In the piezoelectric actuator 21 of the present embodiment, only the uppermost piezoelectric ceramic layer 21b includes an active portion, and the piezoelectric ceramic 21a does not include an active portion and functions as a diaphragm. The piezoelectric actuator 21 has a so-called unimorph type configuration.

  As will be described later, when a predetermined drive signal is selectively supplied to the individual electrode 35, pressure is applied to the liquid in the pressurizing chamber 10 corresponding to the individual electrode 35. As a result, droplets are discharged from the corresponding liquid discharge ports 8 through the individual flow paths 32. That is, the portion of the piezoelectric actuator 21 that faces each pressurizing chamber 10 corresponds to the individual displacement element 50 corresponding to each pressurizing chamber 10 and the liquid discharge port 8. That is, in the laminated body composed of the two piezoelectric ceramic layers 21a and 21b, the displacement element 50 having a unit structure as shown in FIG. The diaphragm 21a, the common electrode 34, the piezoelectric ceramic layer 21b, and the individual electrodes 35 that are positioned immediately above are formed. The piezoelectric actuator 21 includes a plurality of displacement elements 50. In the present embodiment, the amount of liquid ejected from the liquid ejection port 8 by one ejection operation is about 5 to 7 pL (picoliter).

  An example of a driving method at the time of liquid ejection of the piezoelectric actuator 21 in the present embodiment will be described with respect to a driving voltage (drive signal) supplied to the individual electrode 35. When an electric field is applied to the piezoelectric ceramic layer 21b in the polarization direction by setting the individual electrode 35 to a potential different from that of the common electrode 34, the portion to which the electric field is applied functions as an active portion that is distorted by the piezoelectric effect. At this time, the piezoelectric ceramic layer 21b expands or contracts in the thickness direction, that is, the stacking direction, and tends to contract or extend in the direction perpendicular to the stacking direction, that is, the surface direction, due to the piezoelectric lateral effect. On the other hand, since the remaining piezoelectric ceramic layer 21a is an inactive layer that does not have a region sandwiched between the individual electrode 35 and the common electrode 34, it does not spontaneously deform.

  In this configuration, when the individual electrode 35 is set to a predetermined positive or negative potential with respect to the common electrode 34 by the actuator controller so that the electric field and the polarization are in the same direction, a portion sandwiched between the electrodes of the piezoelectric ceramic layer 21b. (Active part) contracts in the surface direction. On the other hand, the piezoelectric ceramic layer 21a, which is an inactive layer, is not affected by an electric field, so that it does not spontaneously shrink and tries to restrict deformation of the active portion. As a result, there is a difference in strain in the polarization direction between the piezoelectric ceramic layer 21b and the piezoelectric ceramic layer 21a, and the piezoelectric ceramic layer 21b is deformed so as to protrude toward the pressurizing chamber 10 (unimorph deformation).

In an actual driving procedure in the present embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34 (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34 every time there is a discharge request. (Hereinafter referred to as a low potential), and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to their original shapes at the timing when the individual electrodes 35 become low potential, and the volume of the pressurizing chamber 10 increases compared to the initial state (the state where the potentials of both electrodes are different). To do. At this time, a negative pressure is applied to the pressurizing chamber 10 and the liquid is sucked into the pressurizing chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a high potential again, the piezoelectric ceramic layers 21a and 21b are deformed so as to protrude toward the pressurizing chamber 10, and the pressure in the pressurizing chamber 10 is reduced due to the volume reduction of the pressurizing chamber 10. The pressure becomes positive and the pressure on the liquid rises, and droplets are ejected. That is, a drive signal including a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. The ideal pulse width is AL (Acoustic Length), which is the length of time that the pressure wave propagates from the orifice 12 to the discharge hole 8. According to this, the pressure chamber 10
When the inside is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplets can be ejected at a stronger pressure.

In the liquid discharge head 2 as described above, in order to increase the displacement of the displacement element 50, the individual electrode 35, more specifically, the portion of the individual electrode 35 that overlaps the pressurizing chamber 10 when viewed in plan view, The size of the individual electrode main body 35 a excluding the extraction electrode 35 drawn from the individual electrode main body 35 a is set to a predetermined size smaller than the pressurizing chamber 10. Some differences may occur depending on the shape of the pressurizing chamber 10 and the structure of the flow path in other parts. However, the displacement of the individual electrode main body 35a is reduced by about 60% of the area of the pressurizing chamber 10. The amount can be maximized, and as a result, the droplet discharge speed can be increased, and the appropriate amount of liquid can be increased.

Furthermore, the amount of displacement can be increased by changing the structure of the piezoelectric actuator 21 below the individual electrode body 35a and the piezoelectric actuator 21 around the individual electrode body 35a. Specifically, the total thickness of the first portion 21a-1 of the diaphragm under the individual electrode main body 35a, the common electrode 34, and the first portion 21b-1 of the piezoelectric ceramic layer is equal to the circumference of the individual electrode main body 35a. By being thicker than the total thickness of the second portion 21a-2 of the diaphragm, the common electrode 34, and the second portion 21b-2 of the piezoelectric ceramic layer, the surrounding constraint on the displacement element 50 is reduced, and the individual electrode main body The thick part at the lower part of 35a is the first part 21a-1 of the diaphragm under the individual electrode body 35a and the total thickness of the common electrode 34 is the first part of the diaphragm around the individual electrode body 35a. Since this is realized by being thicker than the sum of the thicknesses of 21a-2 and the common electrode 34, the position of the first portion 21b-1 of the piezoelectric ceramic layer, which is a portion that undergoes piezoelectric deformation, is shifted upward. Therefore, the expansion and contraction can be efficiently converted into displacement, and the amount of displacement can be increased. As for the thickness of the first portion 21a-1 of the diaphragm and the common electrode 34, either one of them may be thickened or both may be thickened. It may be thicker than the thinned part.

  The individual electrode 35 includes an individual electrode main body 35a and an extraction electrode 35b. However, since the thickness of the entire lower portion of the individual electrode main body 35a is increased, the amount of displacement can be further increased. If the portion where the thickness is thicker is made slightly larger than the individual electrode main body 35a, the variation in the displacement amount with respect to the formation variation of the individual electrode main body 35a can be reduced. The thickness of the lower portion of the extraction electrode 35b is preferably as thin as the other surrounding portions in terms of reducing restraint and increasing displacement, but in order to improve the connectivity with external wiring, The thickness may be the same as that of the individual electrode body 35a.

  Further, the thickened portion, that is, the first portion 21a-1 of the diaphragm under the individual electrode main body 35a, the common electrode 34, and the first portion 21b-1 of the piezoelectric ceramic layer are a plan view of the piezoelectric actuator 21. In this case, since the thickness in the vicinity of the wall surface of the pressurizing chamber 10 that hinders deformation is reduced when the displacement element 50 is displaced, the amount of displacement can be further increased. However, as described above, the lower portion of the extraction electrode 35b may be as thick as the lower portion of the individual electrode main body 35a.

  Further, since the thickness of the first portion 21b-1 of the piezoelectric ceramic layer under the individual electrode body 35a is equal to or less than the thickness of the first portion 21a-1 of the diaphragm under the individual electrode body 35a, the displacement When the element 50 is bent and deformed, the piezoelectric deformation can be prevented from inhibiting the bending. This is because, for example, when the first portion 21b-1 of the piezoelectric ceramic layer is contracted and the displacement element 50 is displaced downward, the lower side of the piezoelectric actuator 21 is located at a position approximately half the thickness of the piezoelectric actuator 21. In this case, if the first portion 21b-1 of the piezoelectric ceramic layer is positioned below the first portion 21b-1, the first portion 21b-1 of the piezoelectric ceramic layer tends to shrink. That is, it is possible to avoid a state in which the piezoelectric deformation of the lower the displacement.

  In addition, since the first portion 21b-1 of the piezoelectric ceramic layer, which is a portion that undergoes piezoelectric deformation, is located at a position closer to the upper portion under the individual electrode main body 35a, the piezoelectric deformation is more effectively used for displacement. Therefore, the displacement can be increased.

Similarly, the upper surface of the first portion 21b-1 of the piezoelectric ceramic layer under the individual electrode body 35a is
The piezoelectric ceramic below the individual electrode main body 35a, which is a portion that undergoes piezoelectric deformation, is located higher than the upper surface of the second portion 21b-2 of the piezoelectric ceramic layer around the individual electrode main body 35a and has a convex shape. The restraint from the periphery of the first portion 21b-1 of the layer can be further reduced, and the position of the portion where the piezoelectric deformation occurs can be further increased, so that the amount of displacement can be increased.

  Next, another embodiment of the liquid discharge head of the present invention will be described with reference to FIG. The basic structure of the liquid discharge head shown in FIG. 6 is the same as that shown in FIGS. 1 to 5, but the structure of the piezoelectric actuator is different. Parts that do not change are given the same reference numerals and description thereof is omitted.

  In the piezoelectric actuator of FIG. 6, the lower surface of the first portion 221a-1 of the diaphragm 221a below the individual electrode body 35a is lower than the lower surface of the second portion 221a-2 of the lower diaphragm 221a around the individual electrode body 35a. Is also in a high position. In other words, a diaphragm recess 221c is provided on the lower surface of the diaphragm 221a below the individual electrode main body 35a, and has a concave shape. Thereby, the quantity of the part which inhibits the expansion-contraction at the time of displacement reduces, and displacement can be enlarged more.

  The piezoelectric actuator 21 as described above can be manufactured by, for example, the following process.

  First, the piezoelectric material used for the piezoelectric ceramic layer 21b and the diaphragm 21a is lead zirconate titanate (PZT), and a slurry is prepared by mixing PZT powder, a binder, and a solvent. From this slurry, a roll coater is formed as a forming method. The green sheet is produced using the method.

  The above-mentioned slurry is screen-printed and dried at a position where the individual electrode main body 35a is formed later on the green sheet that becomes the vibration plate 21a after firing, and the first portion 21a-1 of the vibration plate in that portion becomes thick. Like that. Next, a conductor paste to be the common electrode 34 is applied and dried. At this time, a conductive paste may be patterned at a position where the individual electrode body 35a is formed later, and the common electrode 34 under the individual electrode body 35a may be thickened. A green sheet which becomes the piezoelectric ceramic layer 21b after firing is laminated on this, and pressed to produce a green laminate. Instead of laminating the green sheets, the above slurry may be applied and dried. The slurry is patterned, printed and dried, and the thickness of the first portion 21b-1 of the piezoelectric ceramic layer under the surface electrode body 35a is set to the thickness of the second portion 21b-2 of the surrounding piezoelectric ceramic layer. The thickness may be changed.

  The green laminate is fired at a temperature of 1020 ° C., for example, and then the conductor paste is printed, dried, and baked to form the individual electrodes 35.

  The piezoelectric actuator provided with the diaphragm recess 221c shown in FIG. 6 is a mold having a convex shape on the green sheet of the portion that becomes the first portion 21a-1 of the diaphragm below the individual electrode 35a during pressure lamination. It can be produced by applying pressure and applying pressure with a planar mold and then pressing with a mold having such a shape to cause deformation.

  The amount of displacement when the thickness of each part of the piezoelectric actuator was changed by simulation was confirmed. In the simulation, the displacement amount of a two-dimensional piezoelectric actuator having the shape shown in Table 1 and the following, or in other words, an infinitely long piezoelectric actuator was examined. The simulation was performed with the thicknesses of the individual electrode main body 35a and the common electrode 34 set to zero.

Pressure chamber 10 width: 760 μm
Width of individual electrode body 35a: 560 μm
The amount of displacement when a constant voltage was applied to the actuator having the above basic structure was compared.

  Regarding the height of the upper surface of the piezoelectric ceramic layer 21b, the bottom surface of the piezoelectric actuator is flat except for the sample in which the diaphragm concave portion 221c is formed, and the sample in which the diaphragm concave portion 221c is formed is also the piezoelectric actuator. Since the bottom surface of the plate is flat except for the diaphragm concave portion 221c, it can be understood by adding the thickness of each portion. For example, sample No. 5, the position of the upper surface of the first portion 21b-1 of the piezoelectric ceramic layer under the individual electrode body 35a is 20 + 18 = 38 μm, and the second portion 21b− of the piezoelectric ceramic layer around the individual electrode 35a. Since the position of the upper surface of 2 is 20 + 10 = 30 μm, the upper surface of the second portion 21b-1 of the piezoelectric ceramic layer has a convex shape that is 8 μm higher than the surroundings.

  Sample No. which is a sample within the scope of the present invention. 5 to 13, the total thickness of the first portion 21 b-1 of the piezoelectric ceramic layer under the individual electrode main body 35 a, the common electrode 34, and the first portion 21 a-1 of the diaphragm is around the individual electrode main body 35 a. The thickness of the second portion 21b-2 of the piezoelectric ceramic layer, the common electrode 34, and the thickness of the second portion 21a-2 of the diaphragm is larger than the total thickness of the second portion 21a-2 of the common electrode 34 and the diaphragm. Since the total thickness is larger than the total thickness of the common electrode 34 around the individual electrode main body 35a and the second portion 21a-2 of the diaphragm, the displacement amount is increased.

  Sample No. 1 in which the thickness of the first portion 21b-1 of the piezoelectric ceramic layer under the individual electrode main body 35a is 20 μm. 5 to 10, the thickness of the first portion 21a-1 of the diaphragm is equal to or greater than the thickness of the first portion 21b-1 of the piezoelectric ceramic layer. The displacement amount of 6 to 10 was as large as 354 nm or more.

  Further, the sample No. 1 in which the diaphragm 321a under the individual electrode 35a is concaved. No. 11 has a displacement of 372 nm, which is not a concave shape. The displacement amount of 7 was larger than 364 nm.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 5 ... Manifold 5a ... Sub manifold 5b ... Manifold opening 6 ... Individual supply flow path 8 ... Discharge Hole 9 ... Pressurizing chamber group 10 ... Pressurizing chamber 11a, b, c, d ... Pressurizing chamber row 12 ... Squeezing 13 ... Liquid discharge head body 15a, b, c, d ... Discharge hole array 21 ... Piezoelectric actuator 21a ... Vibration plate (piezoelectric ceramic layer)
21a-1 ... first part of the diaphragm 21a-2 ... second part of the diaphragm 21b, 221b ... piezoelectric ceramic layer 21b-1, 221b-1 ... first part of the piezoelectric ceramic layer 21b-2, 221b-2 ... 2nd part of piezoelectric ceramic layer 221c ... Diaphragm recess 22-31 ... Plate 32 ... Individual flow path 34 ... Common electrode (internal electrode)
35 ... Individual electrode 35a ... Individual electrode body (surface electrode)
35b ... Extraction electrode 36 ... Connection electrode 50 ... Displacement element

Claims (7)

  A piezoelectric actuator in which an internal electrode, a piezoelectric ceramic layer, and a surface electrode are laminated in this order on a vibration plate, and the thickness of the vibration plate, the internal electrode, and the piezoelectric ceramic layer under the surface electrode The total is thicker than the total thickness of the diaphragm, the internal electrode, and the piezoelectric ceramic layer around the surface electrode, and the total thickness of the diaphragm and the internal electrode below the surface electrode The total is thicker than the total thickness of the diaphragm and the internal electrode around the surface electrode.   2. The piezoelectric actuator according to claim 1, wherein a thickness of the piezoelectric ceramic layer under the surface electrode is equal to or less than a thickness of the diaphragm under the surface electrode.   The upper surface of the piezoelectric ceramic layer under the surface electrode is higher than the upper surface of the piezoelectric ceramic layer around the surface electrode, and the upper surface of the piezoelectric ceramic layer has a convex shape. The piezoelectric actuator according to claim 1 or 2.   The lower surface of the diaphragm under the surface electrode is at a position higher than the lower surface of the diaphragm around the surface electrode, and the lower surface of the piezoelectric ceramic layer is concave. Item 4. The piezoelectric actuator according to any one of Items 1 to 3.   The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator according to claim 1 is provided with a plurality of the surface electrodes, and the internal electrodes face the plurality of the surface electrodes. A liquid discharge head, wherein the surface electrode and the pressurizing chamber are laminated in alignment with a flow path member having an open chamber.   When the piezoelectric actuator is viewed in plan, a portion where the total thickness of the diaphragm, the internal electrode, and the piezoelectric ceramic layer is thicker than the surroundings is housed in the pressurizing chamber. The liquid discharge head according to claim 5.   A liquid discharge head according to claim 5, a transport unit that transports a recording medium relative to the liquid discharge head, and a control unit that controls the liquid discharge head. Recording device.

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