JP7615417B1 - Droplet ejection head and recording device - Google Patents

Abstract

A droplet ejection head according to the present disclosure has a nozzle, a pressure chamber, and a piezoelectric element. The nozzle ejects droplets. The pressure chamber is connected to the nozzle. The piezoelectric element deforms when a voltage is applied to it, thereby deforming the pressure chamber. The piezoelectric element has a surface electrode and a first groove portion. The surface electrode faces the pressure chamber. The first groove portion is located around the surface electrode and extends in a shape corresponding to the outer shape of the surface electrode. When the maximum value of the distance between the outer edge of the pressure chamber and the outer edge of the first groove portion in a planar perspective view is A1 and the minimum value is A2, and when the maximum value of the distance between the outer edge of the surface electrode and the outer edge of the first groove portion in a planar view is B1 and the minimum value is B2, the following formula (1) is satisfied.
A1-A2<B1-B2...(1)

Description

The present disclosure relates to a droplet ejection head and a recording device.

Inkjet printers and inkjet plotters that use the inkjet recording method are known as printing devices. Such inkjet printing devices are equipped with a droplet ejection head for ejecting liquid.

The droplet ejection head ejects the liquid in the pressure chamber from the nozzle by driving a piezoelectric element located at the top of the pressure chamber to change the pressure in the pressure chamber. The piezoelectric element has a piezoelectric body, an internal electrode located inside the piezoelectric body, and a surface electrode located on the surface of the piezoelectric body.

Patent document 1 discloses an inkjet head having a piezoelectric element in which a groove is formed around the surface electrode to surround the surface electrode in order to suppress the occurrence of crosstalk between the piezoelectric elements.

JP 2003-311954 A

A droplet ejection head according to one aspect of the present disclosure has a nozzle, a pressure chamber, and a piezoelectric element. The nozzle ejects droplets. The pressure chamber is connected to the nozzle. The piezoelectric element deforms when a voltage is applied to it, thereby deforming the pressure chamber. The piezoelectric element has a surface electrode and a first groove portion. The surface electrode faces the pressure chamber. The first groove portion is located around the surface electrode and extends in a shape according to the outer shape of the surface electrode. When the maximum value of the distance between the outer edge of the pressure chamber and the outer edge of the first groove portion in a planar perspective view is A1 and the minimum value is A2, and when the maximum value of the distance between the outer edge of the surface electrode and the outer edge of the first groove portion in a planar view is B1 and the minimum value is B2, the following formula (1) is satisfied.
A1-A2<B1-B2...(1)

FIG. 1 is a schematic side view of a printer according to the first embodiment. FIG. 2 is a schematic plan view of the printer according to the first embodiment. FIG. 3 is a schematic exploded perspective view of the droplet ejection head according to the first embodiment. FIG. 4 is a schematic plan view showing a main part of the head main body according to the first embodiment. FIG. 5 is a schematic enlarged view of a region V shown in FIG. FIG. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. FIG. 7 is a schematic plan view of the piezoelectric element according to the first embodiment. FIG. 8 is a schematic plan view of the piezoelectric element according to the first embodiment. FIG. 9 is a schematic plan view of the piezoelectric element according to the first embodiment. FIG. 10 is a schematic plan view of the piezoelectric element according to the first embodiment. FIG. 11 is a schematic plan view of the piezoelectric element according to the first embodiment. FIG. 12 is a schematic cross-sectional view of the reinforcing plate and the flow path member according to the first embodiment. FIG. 13 is a schematic cross-sectional view showing a main part of the head main body according to the first embodiment. FIG. 14 is a schematic plan view showing a main part of the head main body according to the first embodiment. FIG. 15 is a plan view showing the configuration of the reinforcing plate according to the first embodiment. FIG. 16 is a schematic plan view showing the configuration of a piezoelectric element according to the second embodiment.

Below, a detailed description will be given of a form for implementing the droplet ejection head and recording device according to the present disclosure (hereinafter, referred to as an "embodiment") with reference to the drawings. Note that the present disclosure is not limited to this embodiment. Furthermore, each embodiment can be appropriately combined as long as the processing content is not contradictory. Furthermore, the same parts in each of the following embodiments are given the same reference numerals, and duplicate explanations will be omitted.

In addition, in the embodiments described below, expressions such as "constant," "orthogonal," "vertical," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "vertical," or "parallel" strictly. In other words, each of the above expressions allows for deviations due to, for example, manufacturing precision or installation precision.

In addition, in the drawings referred to below, for ease of understanding, an orthogonal coordinate system may be shown in which the X-axis, Y-axis, and Z-axis directions are defined as being orthogonal to each other, with the positive Z-axis direction being the vertically upward direction. The direction of rotation about the vertical axis may be referred to as the θ direction.

The grooves in the inkjet head described in Patent Document 1 are formed by bonding a flow path unit including multiple pressure chambers to an actuator unit having a piezoelectric element, and then performing laser processing based on the position of the surface electrode.

In order to increase the driving displacement of the piezoelectric element, it is preferable that a groove portion is formed along the edge of the pressure chamber in a plan view perspective. However, when the actuator unit is bonded to the flow path unit, the actuator unit may be bonded in a state where it is shifted from the desired position relative to the flow path unit. In other words, the position of the surface electrode relative to the pressure chamber may be shifted from the desired position. In the conventional technology described above, the groove portion is formed based on the position of the surface electrode. Therefore, if the position of the surface electrode is shifted from the desired position, the groove portion will not be positioned along the edge of the pressure chamber, and as a result, there is a risk that the driving displacement of the piezoelectric element will be smaller than the desired value.

Therefore, it is hoped that an inkjet head can be provided in which the driving displacement of the piezoelectric element is less likely to decrease even if a positional misalignment occurs between the pressure chamber and the surface electrode.

First Embodiment
<Printer configuration>
First, an overview of a printer 1, which is an example of a recording apparatus according to the first embodiment, will be described with reference to Figures 1 and 2. Figure 1 is a schematic side view of the printer 1 according to the first embodiment, and Figure 2 is a schematic plan view of the printer 1 according to the first embodiment. The printer 1 according to the first embodiment is, for example, a color inkjet printer.

As shown in FIG. 1, the printer 1 comprises a paper feed roller 2, a guide roller 3, an applicator 4, a head case 5, a plurality of transport rollers 6, a plurality of frames 7, a plurality of droplet ejection heads 8, a transport roller 9, a dryer 10, a transport roller 11, a sensor unit 12, and a recovery roller 13.

Furthermore, the printer 1 has a control unit 14 that controls the paper feed roller 2, guide roller 3, coater 4, head case 5, multiple conveying rollers 6, multiple frames 7, multiple droplet ejection heads 8, conveying roller 9, dryer 10, conveying roller 11, sensor unit 12 and recovery roller 13.

The printer 1 records images or characters on the printing paper P by landing droplets on the printing paper P. The printing paper P is an example of a recording medium. Before use, the printing paper P is wound around the paper feed roller 2. The printer 1 then transports the printing paper P from the paper feed roller 2 through the guide roller 3 and the coater 4 into the inside of the head case 5.

The coater 4 applies the coating agent evenly to the printing paper P. This allows the printing paper P to be surface-treated, thereby improving the printing quality of the printer 1.

The head case 5 houses a plurality of transport rollers 6, a plurality of frames 7, and a plurality of droplet ejection heads 8. Inside the head case 5, a space is formed that is isolated from the outside, except for a portion connected to the outside, such as a portion where the printing paper P enters and exits.

At least one of the control factors such as temperature, humidity, and air pressure of the internal space of the head case 5 is controlled by the control unit 14 as necessary. The transport rollers 6 transport the printing paper P inside the head case 5 to the vicinity of the droplet ejection head 8.

The frame 7 is a rectangular flat plate, and is positioned close to and above the print paper P being transported by the transport rollers 6. As shown in FIG. 2, the frame 7 is positioned so that its longitudinal direction is perpendicular to the transport direction of the print paper P. Inside the head case 5, multiple (e.g., four) frames 7 are positioned along the transport direction of the print paper P.

The droplet ejection head 8 is supplied with liquid, such as ink, from a liquid tank (not shown). The droplet ejection head 8 ejects the droplets supplied from the liquid tank.

The control unit 14 controls the droplet ejection head 8 based on data such as images or characters to eject droplets toward the printing paper P. The distance between the droplet ejection head 8 and the printing paper P is, for example, about 0.5 to 20 mm.

The droplet ejection head 8 is fixed to the frame 7. The droplet ejection head 8 is fixed to the frame 7, for example, at both ends in the longitudinal direction. The droplet ejection head 8 is positioned so that its longitudinal direction is perpendicular to the transport direction of the printing paper P.

That is, the printer 1 according to the first embodiment is a so-called line printer in which the droplet ejection head 8 is fixed inside the printer 1. Note that the printer 1 according to the first embodiment is not limited to a line printer, and may be a so-called serial printer. A serial printer is a printer that alternates between recording while moving the droplet ejection head 8 back and forth in a direction intersecting the transport direction of the printing paper P, for example, in a direction approximately perpendicular to the direction, and transporting the printing paper P.

As shown in Figure 2, multiple (e.g., five) droplet ejection heads 8 are fixed to one frame 7. Figure 2 shows an example in which three droplet ejection heads 8 are positioned in front and two in the rear in the transport direction of the printing paper P, and the droplet ejection heads 8 are positioned in the transport direction of the printing paper P such that the centers of each droplet ejection head 8 do not overlap.

A head group 8A is made up of multiple droplet ejection heads 8 positioned on one frame 7. The four head groups 8A are positioned along the transport direction of the print paper P. The same color ink is supplied to droplet ejection heads 8 belonging to the same head group 8A. This allows the printer 1 to print with four colors of ink using the four head groups 8A.

The colors of ink ejected from each head group 8A are, for example, magenta (M), yellow (Y), cyan (C) and black (K). The control unit 14 controls each head group 8A to eject multiple colors of ink onto the printing paper P, thereby printing a color image on the printing paper P.

In addition, in order to treat the surface of the printing paper P, a coating agent may be ejected onto the printing paper P from the droplet ejection head 8.

In addition, the number of droplet ejection heads 8 included in one head group 8A, or the number of head groups 8A mounted on the printer 1, can be changed as appropriate depending on the object to be printed or the printing conditions. For example, if the color to be printed on the printing paper P is a single color and the area printable by one droplet ejection head 8 is to be printed, the number of droplet ejection heads 8 mounted on the printer 1 may be one.

The printing paper P that has been printed inside the head case 5 is transported to the outside of the head case 5 by the transport rollers 9 and passes through the inside of the dryer 10. The dryer 10 dries the printing paper P that has been printed. The printing paper P that has been dried in the dryer 10 is transported by the transport rollers 11 and collected by the collection rollers 13.

In the printer 1, by drying the printing paper P in the dryer 10, it is possible to reduce adhesion between overlapping sheets of printing paper P wound up on the recovery roller 13 and rubbing of undried liquid.

The sensor unit 12 is composed of a position sensor, a speed sensor, a temperature sensor, etc. Based on information from the sensor unit 12, the control unit 14 can determine the state of each part of the printer 1 and control each part of the printer 1.

In the printer 1 described so far, we have shown a case where printing paper P is used as the printing target (i.e., recording medium), but the printing target in the printer 1 is not limited to printing paper P. For example, the printing target may be a roll of cloth, etc.

The printer 1 may also transport the print paper P on a conveyor belt instead of directly. By using a conveyor belt, the printer 1 can print on sheets of paper, cut pieces of cloth, wood, tiles, etc.

The printer 1 may also print wiring patterns for electronic devices by ejecting droplets containing conductive particles from the droplet ejection head 8. The printer 1 may also produce chemicals by ejecting a predetermined amount of liquid chemicals or droplets containing chemicals from the droplet ejection head 8 toward a reaction vessel or the like.

<Configuration of Droplet Ejection Head>
Next, the configuration of the droplet ejection head 8 according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic exploded perspective view of the droplet ejection head 8 according to the first embodiment.

The droplet ejection head 8 has a head body 20, a wiring section 30, a housing 40, and a pair of heat sinks 45. The head body 20 has a flow path member 21, a reinforcing plate 172 (see FIG. 4), a piezoelectric actuator 22 (see FIG. 4), and a reservoir 23.

In the following description, for convenience, the direction in which the head body 20 is provided in the droplet ejection head 8 may be referred to as "down" and the direction in which the housing 40 is provided relative to the head body 20 may be referred to as "up."

The flow path member 21 of the head body 20 is generally flat and has a first surface 21a, which is one main surface, and a second surface 21b (see FIG. 6) located on the opposite side of the first surface 21a. The first surface 21a has an opening (not shown), and liquid is supplied from the reservoir 23 to the inside of the flow path member 21 through the opening.

The second surface 21b has a plurality of ejection holes 163 (see FIG. 6) that eject droplets onto the printing paper P. The flow path member 21 has an internal flow path that allows liquid to flow from the first surface 21a to the second surface 21b.

The reinforcing plate 172 is located on the first surface 21a of the flow path member 21. The reinforcing plate 172 has a first surface 172a that faces the first surface 21a of the flow path member 21, and a second surface 172b (see FIG. 6) that is located on the opposite side of the first surface 172a.

The piezoelectric actuator 22 is located on the first surface 172a of the reinforcing plate 172. The piezoelectric actuator 22 has a plurality of piezoelectric elements 170 (see FIG. 6). The piezoelectric actuator 22 is electrically connected to the flexible substrate 31 of the wiring section 30.

A reservoir 23 is positioned on the piezoelectric actuator 22. The reservoir 23 has openings 23a at both ends in the main scanning direction, which is perpendicular to the transport direction of the print paper P and parallel to the print paper P. The reservoir 23 has a flow path inside, and liquid is supplied from the outside through the openings 23a. The reservoir 23 supplies liquid to the flow path member 21. The reservoir 23 also stores the liquid supplied to the flow path member 21.

The wiring section 30 has a flexible substrate 31, a wiring substrate 32, a plurality of driver ICs 33, a pressing member 34, and an elastic member 35. The flexible substrate 31 transmits a predetermined signal sent from the outside to the head body 20. As shown in FIG. 3, the droplet ejection head 8 according to the first embodiment may have two flexible substrates 31.

One end of the flexible substrate 31 is electrically connected to the piezoelectric actuator 22 of the head body 20. The other end of the flexible substrate 31 is pulled upward so as to pass through the slit portion 23b of the reservoir 23, and is electrically connected to the wiring substrate 32. This allows the piezoelectric actuator 22 of the head body 20 to be electrically connected to the outside.

The wiring board 32 is located above the head body 20. The wiring board 32 distributes signals to multiple driver ICs 33.

The multiple driver ICs 33 are located on one of the main surfaces of the flexible substrate 31. As shown in Figure 3, in the droplet ejection head 8 according to the first embodiment, two driver ICs 33 are provided on each flexible substrate 31, but the number of driver ICs 33 provided on each flexible substrate 31 is not limited to two.

The driver IC 33 drives the piezoelectric actuator 22 of the head body 20 based on a drive signal sent from the control unit 14 (see FIG. 1). In this way, the driver IC 33 drives the droplet ejection head 8.

The pressing member 34 has a generally U-shape in cross section and presses the driver IC 33 on the flexible substrate 31 from the inside toward the heat sink 45. As a result, in the first embodiment, heat generated when the driver IC 33 is driven can be efficiently dissipated to the outer heat sink 45.

The elastic member 35 is provided so as to contact the outer wall of the pressing portion (not shown) of the pressing member 34. By providing such an elastic member 35, it is possible to reduce the possibility that the pressing member 34 will damage the flexible substrate 31 when the pressing member 34 presses the driver IC 33.

The elastic member 35 is made of, for example, a double-sided foam tape. In addition, by using, for example, a non-silicon heat conductive sheet as the elastic member 35, the heat dissipation of the driver IC 33 can be improved. Note that the elastic member 35 is not necessarily required.

The housing 40 is disposed on the head body 20 so as to cover the wiring section 30. This allows the housing 40 to seal the wiring section 30. The housing 40 is made of, for example, resin or metal.

The housing 40 is a box shape that extends long in the main scanning direction, and has a first opening 40a and a second opening 40b on a pair of side surfaces that face each other along the main scanning direction. The housing 40 also has a third opening 40c on the bottom surface and a fourth opening 40d on the top surface.

One side of the heat sink 45 is arranged at the first opening 40a so as to cover the first opening 40a, and the other side of the heat sink 45 is arranged at the second opening 40b so as to cover the second opening 40b.

The heat sink 45 is arranged to extend in the main scanning direction and is made of a metal or alloy with high heat dissipation properties. The heat sink 45 is arranged in contact with the driver IC 33 and dissipates heat generated by the driver IC 33.

The pair of heat sinks 45 are each fixed to the housing 40 by screws (not shown). Therefore, the housing 40 to which the heat sinks 45 are fixed has a box shape in which the first opening 40a and the second opening 40b are closed and the third opening 40c and the fourth opening 40d are open.

The third opening 40c is positioned to face the reservoir 23. The flexible substrate 31 and the pressing member 34 are inserted into the third opening 40c.

The fourth opening 40d is provided for inserting a connector (not shown) provided on the wiring board 32. If the space between the connector and the fourth opening 40d is sealed with resin or the like, it becomes difficult for liquid or dust to enter the inside of the housing 40.

The housing 40 also has a heat insulating section 40e. The heat insulating section 40e is disposed adjacent to the first opening 40a and the second opening 40b, and is provided so as to protrude outward from the side surface of the housing 40 along the main scanning direction.

The heat insulating section 40e is formed to extend in the main scanning direction. That is, the heat insulating section 40e is located between the heat sink 45 and the head body 20. By providing the heat insulating section 40e in the housing 40 in this way, heat generated by the driver IC 33 is less likely to be transmitted to the head body 20 via the heat sink 45.

Note that Figure 3 shows an example of the configuration of the droplet ejection head 8, and may further include components other than those shown in Figure 3.

<Configuration of Head Body>
Next, a description will be given of the configuration of the head body 20 according to the first embodiment. Fig. 4 is a schematic plan view showing a main part of the head body 20 according to the first embodiment.

As described above, the head body 20 has a flow path member 21, a reinforcing plate 172, and a piezoelectric actuator 22. The flow path member 21, the reinforcing plate 172, and the piezoelectric actuator 22 have a flat plate shape, and are positioned from the bottom side of the head body 20 in the order of the flow path member 21, the reinforcing plate 172, and the piezoelectric actuator 22 (see FIG. 6).

4, the flow path member 21 and the reinforcing plate 172 are larger than the piezoelectric actuator 22. Specifically, the widths of the flow path member 21 and the reinforcing plate 172 in the longitudinal direction are larger than the width of the piezoelectric actuator 22 in the longitudinal direction. In addition, the widths of the flow path member 21 and the reinforcing plate 172 in the lateral direction are larger than the width of the piezoelectric actuator 22 in the lateral direction.

The flow path member 21 has a first through hole 21c in a region located outside the piezoelectric actuator 22. The first through hole 21c is formed, for example, at both ends of the flow path member 21 in the longitudinal direction.

The reinforcing plate 172 has a second through hole 172g at a position corresponding to the first through hole 21c. Specifically, the second through hole 172g is disposed above the first through hole 21c at a position overlapping the first through hole 21c in a plan view. The first through hole 21c and the second through hole 172g will be described later with reference to FIG. 13.

The piezoelectric actuator 22 is located approximately in the center of the reinforcing plate 172. The piezoelectric actuator 22 has an ejection area 24. A plurality of piezoelectric elements 170 are located in the ejection area 24.

Figure 5 is a schematic enlarged view of region V shown in Figure 4. Note that Figure 5 is a plan view of the piezoelectric element 170 viewed from a direction perpendicular to the surface of the piezoelectric ceramic body 171. Note that in Figure 5, the first groove portion 100 described below is omitted.

5, the plurality of piezoelectric elements 170 are arranged at positions corresponding to the plurality of pressure chambers 162 of the flow path member 21. Specifically, the plurality of piezoelectric elements 170 are arranged such that the electrode body 174a of the surface electrode 174 described later is located above the pressure chambers 162.

Here, the configuration of the flow path member 21 having the pressure chamber 162 will be described. Figure 6 is a schematic cross-sectional view taken along the line VI-VI shown in Figure 5. Note that line VI-VI shown in Figure 5 is a straight line passing through the center point P1 of the electrode body 174a of the surface electrode 174, which will be described later, and the center point P2 of the connection electrode 175, which will be described later.

6, the flow path member 21 has a layered structure in which multiple plates are stacked. Specifically, the flow path member 21 has a cavity plate 21A, a base plate 21B, an aperture (restriction) plate 21C, a supply plate 21D, manifold plates 21E, 21F, 21G, a cover plate 21H, and a nozzle plate 21I. These plates are positioned in this order from the first surface 21a side of the flow path member 21. These plates are formed of a metal such as stainless steel (SUS).

The plates that make up the flow path member 21 have a large number of holes formed in them. The thickness of each plate is approximately 10 μm to 300 μm. This allows for high precision in the hole formation. The plates are aligned and stacked so that these holes communicate with each other to form the individual flow paths 164 and the supply manifold 161.

In the flow path member 21, the supply manifold 161 and the discharge hole 163 are connected by an individual flow path 164. The supply manifold 161 is located on the second surface 21b side inside the flow path member 21, and the discharge hole 163 is located on the second surface 21b of the flow path member 21.

The individual flow path 164 has a pressure chamber 162 and an individual supply flow path 165. The pressure chamber 162 is located on the first surface 21a of the flow path member 21, and the individual supply flow path 165 is a flow path that connects the supply manifold 161 and the pressure chamber 162.

In addition, the individual supply flow path 165 includes a restriction 166 that is narrower than the other portions. The restriction 166 has a high flow path resistance because it is narrower than the other portions of the individual supply flow path 165. In this way, when the flow path resistance of the restriction 166 is high, the pressure generated in the pressure chamber 162 is less likely to escape to the supply manifold 161.

Next, the configuration of the piezoelectric element 170 and the reinforcing plate 172 will be described with reference to Figures 5 and 6. As shown in Figures 5 and 6, the piezoelectric element 170 has a piezoelectric ceramic body 171, a reinforcing plate 172, an internal electrode 173, a surface electrode 174, and a connection electrode 175.

The piezoelectric ceramic body 171 has a flat plate shape. The piezoelectric ceramic body 171 is located on the first surface 21a of the flow path member 21 via a reinforcing plate 172.

The piezoelectric ceramic body 171 includes, for example, a plurality of piezoelectric ceramic layers 171a and 171b. The piezoelectric ceramic layers 171a and 171b each have a thickness of, for example, about 20 μm. Each of the piezoelectric ceramic layers 171a and 171b extends across the plurality of pressure chambers 162. The plurality of piezoelectric elements 170 share one piezoelectric ceramic body 171.

Ferroelectric lead zirconate titanate (PZT) based ceramic material can be used for the piezoelectric ceramic layers 171a and 171b.

Here, an example is shown in which the piezoelectric ceramic body 171 includes two piezoelectric ceramic layers 171a, 171b, but the piezoelectric ceramic body 171 may include three or more piezoelectric ceramic layers.

The piezoelectric ceramic layer 171b is an example of a vibration plate. Note that the vibration plate does not necessarily have to be a piezoelectric ceramic body such as PZT.

The internal electrode 173 is located inside the piezoelectric ceramic body 171. Specifically, the internal electrode 173 is located between the two piezoelectric ceramic layers 171a, 171b. The internal electrode 173 is formed over substantially the entire surface in the region between the piezoelectric ceramic layers 171a and 171b. In other words, the internal electrode 173 overlaps with all pressure chambers 162 in the region facing the piezoelectric actuator 22. Such internal electrode 173 functions as a common electrode shared by multiple piezoelectric elements 170.

The internal electrode 173 may be made of a metal material such as Ag-Pd. The thickness of the internal electrode 173 is, for example, about 2 μm.

The internal electrode 173 is electrically connected to a connection electrode (not shown) located on the surface of the piezoelectric ceramic body 171 through a via hole formed in the piezoelectric ceramic layer 171a. The connection electrode for the internal electrode 173 is grounded and held at ground potential.

The surface electrode 174 has an electrode body 174a and an extraction electrode 174b. The electrode body 174a is located in an area facing the pressure chamber 162. The electrode body 174a is slightly smaller than the pressure chamber 162 and has a shape roughly similar to that of the pressure chamber 162.

As shown in Figure 5, the first embodiment shows, as an example, a case in which the pressure chamber 162 and the electrode body 174a are circular in plan view. However, the shapes of the pressure chamber 162 and the electrode body 174a are not limited to this example. This point will be described later with reference to Figure 16.

The extraction electrode 174b is extracted from the electrode body 174a. The extraction electrode 174b extends linearly toward the connection electrode 175, which will be described later. That is, the connection electrode 175 is located at the portion of the extraction electrode 174b that is extracted outside the region facing the pressure chamber 162 at one end of the extraction electrode 174b.

The electrode body 174a and the extraction electrode 174b of the surface electrode 174 may be made of a metal material such as an Au-based material.

The connection electrode 175 has a convex shape with a thickness of, for example, about 15 μm. The connection electrode 175 is located on the surface of the piezoelectric ceramic body 171 and is connected to the surface electrode 174. Specifically, the connection electrode 175 is located on the extraction electrode 174b and is electrically connected to the electrode body 174a via the extraction electrode 174b. The connection electrode 175 is electrically joined to an electrode provided on the flexible substrate 31 (see FIG. 3).

The connection electrode 175 contains a metal that is more likely to cause ion migration than the metal (e.g., Au) contained in the surface electrode 174. For example, the connection electrode 175 contains Ag, Cu, Sn, Pb, and Ni. Specifically, silver-palladium containing glass frit is used as the connection electrode 175. The connection electrode 175 is an example of a bump.

In addition, the piezoelectric actuator 22 has a dummy connection electrode 25 in addition to the connection electrode 175 required for electrical connection between the surface electrode 174 and the flexible substrate 31. The dummy connection electrode 25 has, for example, a convex shape and is located on the surface of the piezoelectric ceramic body 171. The dummy connection electrode 25 is an example of a bump.

In order to individually control the potential of the multiple surface electrodes 174, each is electrically connected to the control unit 14 (see FIG. 1) via the connection electrode 175, the flexible substrate 31, and wiring. When the surface electrodes 174 and the internal electrodes 173 are set to different potentials and an electric field is applied in the polarization direction of the piezoelectric ceramic layer 171a, the portion of the piezoelectric ceramic layer 171a to which the electric field is applied operates as an active portion that deforms due to the piezoelectric effect.

The reinforcing plate 172 has a flat plate shape. The reinforcing plate 172 is located between the flow path member 21 and the piezoelectric element 170. Specifically, the reinforcing plate 172 is located between the first surface 21a of the flow path member 21 and the back surface of the piezoelectric ceramic body 171 opposite to the front surface on which the surface electrode 174 is located. The reinforcing plate 172 extends across the multiple pressure chambers 162 and forms the ceiling portion of the multiple pressure chambers 162. The multiple piezoelectric elements 170 share one reinforcing plate 172.

It should be noted that the head body 20 does not necessarily have to have a reinforcing plate 172. In this case, the piezoelectric ceramic body 171 forms the ceiling portion of the multiple pressure chambers 162.

That is, the piezoelectric element 170 is formed by the surface electrode 174 of the piezoelectric actuator 22, the piezoelectric ceramic layer 171a, the reinforcing plate 172, and the portion of the internal electrode 173 that faces the pressure chamber 162. When the piezoelectric element 170 undergoes unimorph deformation, the pressure chamber 162 is pressed, and liquid is ejected from the ejection hole 163. The ejection hole 163 is an example of a nozzle that penetrates the nozzle plate 21I.

<Configuration of First Groove Portion>
7 to 9 are schematic plan views of the piezoelectric element 170 according to the first embodiment. Note that in Fig. 7 to Fig. 9, the size of the first groove portion 100 is exaggerated for ease of understanding.

7, the piezoelectric element 170 has a first groove portion 100. The first groove portion 100 is located around (outside) the electrode body 174a of the surface electrode 174 in a plan view, and extends in a shape corresponding to the outer shape of the electrode body 174a. In other words, the first groove portion 100 has a shape that is approximately similar to the outer shape of the electrode body 174a in a plan view.

7, the first groove 100 extends in an arc shape along the outer shape of the electrode body 174a so as to surround the circular electrode body 174a. Both ends of the first groove 100 in the longitudinal direction are located outside the extraction electrode 174b so as to sandwich the extraction electrode 174b. Specifically, one end of the first groove 100 in the longitudinal direction faces one side of the extraction electrode 174b, and the other end faces the other side of the extraction electrode 174b.

In this way, by providing the first groove portion 100 around the electrode body 174a, the rigidity of the piezoelectric ceramic body 171 can be reduced, and the driving displacement of the piezoelectric element 170 can be increased compared to when the first groove portion 100 is not provided.

Here, as shown in FIG. 7, when the outer edge of the first groove portion 100 is formed so as to follow the outer edge of the pressure chamber 162 in a planar perspective view, the driving displacement of the piezoelectric element 170 can be made larger than when the outer edge of the first groove portion 100 is formed so as not to follow the outer edge of the pressure chamber 162.

However, when the piezoelectric actuator 22 is bonded to the flow path member 21, the piezoelectric actuator 22 may be bonded in a state where it is shifted from the desired position relative to the flow path member 21. In other words, the position of the surface electrode 174 relative to the pressure chamber 162 may be shifted from the desired position. Figures 8 and 9 show the piezoelectric element 170 when the position of the surface electrode 174 is shifted from the desired position (for example, the position shown in Figure 7) relative to the pressure chamber 162. For example, when the first groove portion 100 is formed based on the position of the surface electrode 174, there is a problem that the position of the surface electrode 174 is shifted from the desired position. As a result, the outer edge of the first groove portion 100 is not arranged along the outer edge of the pressure chamber 162, and as a result, the driving displacement of the piezoelectric element 170 may be smaller than the desired value.

Therefore, the first groove portion 100 is formed at a position along the outer edge of the pressure chamber 162. Specifically, the configuration of the pressure chamber 162, the surface electrode 174, and the first groove portion 100 may satisfy the following formula (1) when the maximum value of the distance between the outer edge of the pressure chamber 162 and the outer edge of the first groove portion 100 is A1 and the minimum value is A2, and the maximum value of the distance between the outer edge of the surface electrode 174 and the outer edge of the first groove portion 100 is B1 and the minimum value is B2, as shown in FIG.
A1-A2<B1-B2...(1)

According to this configuration, the positional deviation between the outer edge of the pressure chamber 162 and the outer edge of the first groove portion 100 is smaller than the positional deviation between the outer edge of the electrode body 174a and the outer edge of the first groove portion 100. In other words, the first groove portion 100 is disposed closer to the outer edge of the pressure chamber 162 than to the outer edge of the surface electrode 174, and even if a positional deviation occurs between the pressure chamber 162 and the surface electrode 174, the driving displacement of the piezoelectric element 170 is less likely to decrease.

Furthermore, the configuration of the pressure chamber 162, surface electrode 174 and first groove portion 100 may satisfy the following formula (2) as shown in FIG. 9, when the maximum value of the distance between the center point P3 of the pressure chamber 162 and the outer edge of the first groove portion 100 is C1 and the minimum value is C2, and the maximum value of the distance between the center point P1 of the surface electrode 174 and the outer edge of the first groove portion 100 is D1 and the minimum value is D2.
C1-C2<D1-D2...(2)

According to this configuration, the misalignment between the center of the pressure chamber 162 and the outer edge of the first groove portion 100 is smaller than the misalignment between the center of the electrode body 174a and the outer edge of the first groove portion 100. In other words, the first groove portion 100 is disposed so as to correspond more closely to the center point P3 of the pressure chamber 162 than to the center point P1 of the surface electrode 174, so that even if misalignment occurs between the pressure chamber 162 and the surface electrode 174, the driving displacement of the piezoelectric element 170 is less likely to decrease.

In addition, the first groove portion 100 penetrates the piezoelectric actuator 22 in the thickness direction (see FIG. 10). With this configuration, the rigidity of the piezoelectric ceramic body 171 can be made lower than when the first groove portion 100 does not penetrate the piezoelectric actuator 22, and the driving displacement of the piezoelectric element 170 can be made even larger.

In addition, the first groove portion 100 does not necessarily have to penetrate the piezoelectric actuator 22.

<Positional Relationship Between First Groove Portion, Pressure Chamber, and Surface Electrode>
Next, a description will be given of the positional relationship between the first groove portion 100 according to the first embodiment and the pressure chamber 162 and the surface electrode 174. Fig. 10 is a schematic plan view of the piezoelectric element 170 according to the first embodiment.

10, the extraction electrode 174b extends from the electrode body 174a in the positive X-axis direction (an example of a first direction). In this case, when a part of the outer edge of the first groove portion 100 is located outside the outer edge of the pressure chamber 162 in a planar perspective view, the outer edge of the first groove portion 100 may be furthest from the outer edge of the pressure chamber in the positive X-axis direction among the positive X-axis direction, the negative X-axis direction (an example of a second direction), the positive Y-axis direction (an example of a third direction), and the negative Y-axis direction (an example of a fourth direction).

The positional relationship between the first groove portion 100 and the electrode body 174a may also be similar. That is, the outer edge of the first groove portion 100 may be farthest from the outer edge of the electrode body 174a in the positive X-axis direction among the positive X-axis direction, the negative X-axis direction, the positive Y-axis direction, and the negative Y-axis direction.

10, the extraction electrode 174b is located on the positive X-axis direction side of the electrode body 174a, and therefore the first groove portion 100 is not provided around the extraction electrode 174b so as not to overlap with the extraction electrode 174b. Therefore, the area of the first groove portion 100 in the positive X-axis direction of the four directions is smaller than the area of the first groove portion 100 in the other three directions. Therefore, when the outer edge of the first groove portion 100 is farthest from the outer edge of the pressure chamber 162 in the positive X-axis direction of the four directions, the driving displacement of the piezoelectric element 170 is less likely to decrease compared to the other directions.

The same is true for the positional relationship between the first groove portion 100 and the electrode body 174a. When the outer edge of the first groove portion 100 and the center of the electrode body 174a are furthest apart in the positive X-axis direction among the four directions, the driving displacement of the piezoelectric element 170 is less likely to decrease compared to the other directions.

<Positional Relationship Between First Groove Portion and Surface Electrode>
Next, a description will be given of the positional relationship between the first groove portion 100 and the surface electrode 174 according to the first embodiment. Fig. 11 is a schematic plan view of the piezoelectric element 170 according to the first embodiment.

As described above using Figure 8, in the first embodiment, in order to prevent a decrease in the driving displacement of the piezoelectric element 170 even if the position of the surface electrode 174 deviates from the desired position relative to the pressure chamber 162, the first groove portion 100 is formed at a position along the outer edge of the pressure chamber 162.

Here, if the pressure chamber 162 and the surface electrode 174 are misaligned in the left-right direction (Y-axis direction) by more than a threshold value, when the first groove portion 100 is formed in a position along the outer edge of the pressure chamber 162, there is a risk that the first groove portion 100 will overlap the surface electrode 174. This will result in a portion of the surface electrode 174 being scraped off. In particular, if the extraction electrode 174b of the surface electrode 174 is scraped off, the wiring will be cut off, and there is a risk that the ejection function will be reduced (lost).

Therefore, the first groove 100 is formed so as to secure a certain distance or more between the lead electrode 174b. Specifically, the configuration of the first groove 100 and the surface electrode 174 may satisfy the following formula (3) as shown in Fig. 11, where E1 is the distance between one end and the other end of the first groove 100, E2 is the width of the lead electrode 174b, and E3 is the average distance between the outer edge of the surface electrode 174 and the inner edge of the first groove 100.
(E1-E2)/2>E3...(3)

With this configuration, even if misalignment occurs in the left-right direction (Y-axis direction) between the surface electrode 174 and the first groove portion 100, the extraction electrode 174b is less likely to be scraped off. As a result, compared to a case in which the extraction electrode 174b of the surface electrode 174 is scraped off, a processing defect can be identified more quickly by a capacitance test, and the effect on the ejection function can be reduced.

<Size Relationship Between First Through Hole and Second Through Hole>
Next, a description will be given of the size relationship between the first through hole 21c and the second through hole 172g according to the first embodiment. Fig. 12 is a schematic cross-sectional view of the reinforcing plate 172 and the flow path member 21 according to the first embodiment.

As described above with reference to FIG. 4, the flow path member 21 has a first through hole 21c in a region located outside the piezoelectric actuator 22. The reinforcing plate 172 has a second through hole 172g at a position corresponding to the first through hole 21c. In this case, as shown in FIG. 12, the second through hole 172g may be larger than the first through hole 21c in a planar perspective. With this configuration, the position of the first through hole 21c of the flow path member 21 is clear in a planar view, so that it is easy to grasp the position of the outer edge of the pressure chamber 162 of the flow path member 21 using the position of the first through hole 21c as a marker. Therefore, when forming the first groove portion 100 in the piezoelectric actuator 22 after bonding the piezoelectric actuator 22, the reinforcing plate 172, and the piezoelectric actuator 22, the first groove portion 100 can be easily formed at a position along the outer edge of the pressure chamber 162 using the first through hole 21c as a reference.

Although an example in which the first through hole 21c and the second through hole 172g are both circular in plan view has been described here, the shapes of the first through hole 21c and the second through hole 172g are not limited to this example. For example, the shapes of the first through hole 21c and the second through hole 172g may be rectangular or elongated.

<Configuration of reinforcing plate>
Next, the configuration of the reinforcing plate 172 according to the first embodiment will be described with reference to Fig. 13 to Fig. 15. Fig. 13 is a schematic cross-sectional view showing a main portion of the head body 20 according to the first embodiment. Fig. 14 is a schematic plan view showing a main portion of the head body 20 according to the first embodiment. Fig. 15 is a plan view showing the configuration of the reinforcing plate 172 according to the first embodiment.

13, the reinforcing plate 172 may have a second groove portion 172c on the second surface 172b, which is the adhesive surface with the piezoelectric actuator 22. As shown in FIG. 14, the second groove portion 172c is formed at a position that does not overlap with the first groove portion 100 and the pressure chamber 162 in a planar perspective. Specifically, the second groove portion 172c is located outside the first groove portion 100 and the pressure chamber 162 in a planar perspective. Note that the dashed line shown in FIG. 14 indicates the side wall portion of the second groove portion 172c.

In this way, by forming the second groove portion 172c on the adhesive surface of the reinforcing plate 172 with the piezoelectric actuator 22, when the piezoelectric actuator 22 and the reinforcing plate 172 are adhered, excess adhesive or air bubbles can be allowed to escape (flow) into the second groove portion 172c. Therefore, it is possible to make it difficult for uneven transfer or air bubbles to occur, and as a result, it is possible to reduce variations in the ejection characteristics. In addition, by forming the second groove portion 172c at a position that does not overlap with the first groove portion 100 and the pressure chamber 162, it is possible to reduce the possibility that the first groove portion 100 and the pressure chamber 162 will communicate with each other when the first groove portion 100 is formed, compared to when the second groove portion 172c is formed at a position that overlaps with the first groove portion 100 and the pressure chamber 162.

15, the second groove portion 172c has a plurality of individual groove portions 172e and a collective groove portion 172f. The plurality of individual groove portions 172e extend along the periphery of two or more of the pressure chambers 162 in a planar perspective view. The collective groove portion 172f communicates with the plurality of individual groove portions 172e.

The flow path member 21 has a communication hole 21d that communicates with the collecting groove portion 172f. The communication hole 21d opens to the second surface 21b (see FIG. 6), which is the surface of the flow path member 21 opposite to the joint surface with the reinforcing plate 172.

That is, the communication hole 21d of the flow path member 21 and the individual groove portion 172e of the second groove portion 172c are connected via the collective groove portion 172f. Therefore, when the piezoelectric actuator 22 and the reinforcing plate 172 are bonded, outgas or bubbles that flow into the second groove portion 172c are released to the outside of the droplet ejection head 8 through the individual groove portion 172e, the collective groove portion 172f, and the communication hole 21d. Therefore, the internal pressure of the second groove portion 172c is unlikely to become high, and as a result, the variation in the ejection characteristics can be reduced.

13, the reinforcing plate 172 has a pillar portion 172d inside the second groove portion 172c. One end of the pillar portion 172d is located in the piezoelectric actuator 22, and the other end is located in the reinforcing plate 172.

In a plan view, the pillar portion 172d is disposed at a position overlapping the connection electrode 175 or the dummy connection electrode 25 located on the surface of the piezoelectric actuator 22. In other words, no groove is formed in the reinforcing plate 172 vertically below the connection electrode 175 or the dummy connection electrode 25.

When electrically connecting the flexible substrate 31 and the piezoelectric actuator 22, a certain amount of pressure is applied to the connection electrode 175 and the dummy connection electrode 25. For this reason, if a groove is formed vertically below the connection electrode 175 or the dummy connection electrode 25, the head body 20 may not be able to withstand the pressure and may crack. Therefore, as described above, if a pillar 172d is formed inside the second groove 172c at a position that overlaps with the connection electrode 175 or the dummy connection electrode 25 in a plan view, the pillar 172d can withstand the pressure, making it difficult for cracks to occur in the head body 20.

Thus, according to the droplet ejection head 8 of the first embodiment, the driving displacement of the piezoelectric element 170 is less likely to decrease even if a positional misalignment occurs between the pressure chamber 162 and the surface electrode 174.

Second Embodiment
<Piezoelectric element shape>
Fig. 16 is a schematic plan view showing the configuration of a piezoelectric element 170 according to the second embodiment. The shape of the piezoelectric element 170 is not limited to the shape shown in Fig. 5. For example, as shown in Fig. 16, the shape of the piezoelectric element 170 may be a bowling pin shape.

Specifically, the pressure chamber 162 may have a diamond shape with rounded corners in a plan view. In this case, the electrode body 174a of the surface electrode 174 also has a diamond shape with rounded corners in a plan view to match the shape of the pressure chamber 162. The extraction electrode 174b extends linearly from an acute corner of the multiple corners of the electrode body 174a toward the connection electrode 175. The connection electrode 175 is circular in a plan view.

In this case as well, the piezoelectric element 170 may have a first groove portion 100 (not shown here) located around the electrode body 174a of the surface electrode 174 and extending in a shape corresponding to the outer shape of the electrode body 174a. Also in this case as well, the first groove portion 100 may be formed in a position along the outer edge of the pressure chamber 162.

In one embodiment, (1) a droplet ejection head (for example, the droplet ejection head 8) has a nozzle (for example, an ejection hole 163), a pressure chamber (for example, the pressure chamber 162), and a piezoelectric element (for example, the piezoelectric element 170). The nozzle ejects droplets. The pressure chamber is connected to the nozzle. The piezoelectric element deforms when a voltage is applied to deform the pressure chamber. The piezoelectric element has a surface electrode (for example, the surface electrode 174) and a first groove portion (for example, the first groove portion 100). The surface electrode faces the pressure chamber. The first groove portion is located around the surface electrode and extends in a shape according to the outer shape of the surface electrode. When the maximum value of the distance between the outer edge of the pressure chamber and the outer edge of the first groove portion in a planar perspective view is A1 and the minimum value is A2, and when the maximum value of the distance between the outer edge of the surface electrode and the outer edge of the first groove portion in a planar view is B1 and the minimum value is B2, the following formula (1) is satisfied.
A1-A2<B1-B2...(1)

(2) The droplet ejection head has a nozzle, a pressure chamber, and a piezoelectric element. The nozzle ejects droplets. The pressure chamber is connected to the nozzle. The piezoelectric element deforms when a voltage is applied to deform the pressure chamber. The piezoelectric element has a surface electrode and a first groove. The surface electrode faces the pressure chamber. The first groove is located around the surface electrode and extends in a shape according to the outer shape of the surface electrode. The pressure chamber and the surface electrode are circular in planar perspective, and may satisfy the following formula (2) when the maximum value of the distance between the center of the pressure chamber and the outer edge of the first groove in planar perspective is C1 and the minimum value is C2, and the maximum value of the distance between the center of the surface electrode and the outer edge of the first groove in planar perspective is D1 and the minimum value is D2.
C1-C2<D1-D2...(2)

(3) In the droplet ejection head of (1) or (2) above, the surface electrode has an electrode body (for example, electrode body 174a) located in an area facing the pressure chamber and an extraction electrode (for example, extraction electrode 174b) extending in a first direction from the electrode body, and when a portion of the outer edge of the first groove portion is located outside the outer edge of the pressure chamber in a planar perspective view, the outer edge of the first groove portion may be farthest from the outer edge of the pressure chamber in the first direction among the first direction, the second direction that is the opposite direction to the first direction, the third direction that is perpendicular to the first direction and the second direction, and the fourth direction that is the opposite direction to the third direction.

(4) In the droplet ejection head of (1) or (2) above, the surface electrode has an electrode body located in an area facing the pressure chamber and an extraction electrode extending from the electrode body in a first direction, and in a planar view, the outer edge of the first groove portion may be farthest from the outer edge of the electrode body in a first direction among the first direction, a second direction that is the opposite direction to the first direction, a third direction perpendicular to the first and second directions, and a fourth direction that is the opposite direction to the third direction.

(5) In a droplet ejection head according to any one of (1) to (4) above, the pressure chamber is circular in plan view, the surface electrode has an electrode body having a circular shape in plan view located in a region facing the pressure chamber, and an extraction electrode extending in a first direction from the electrode body, the first groove portion has an arc shape surrounding the electrode body and located outside the extraction electrode so that both ends sandwich the extraction electrode, and when, in plan view, the distance between one end and the other end of the first groove portion is E1, the width of the extraction electrode is E2, and the average distance between the outer edge of the surface electrode and the inner edge of the first groove portion is E3, the following formula (3) may be satisfied.
(E1-E2)/2>E3...(3)

(6) Any one of the droplet ejection heads (1) to (5) above has a flat-plate-shaped piezoelectric actuator (for example, piezoelectric actuator 22) having multiple piezoelectric elements, a flat-plate-shaped flow path member (for example, flow path member 21) having multiple pressure chambers, and a reinforcing plate (for example, reinforcing plate 172) located between the flow path member and the piezoelectric elements, in which the flow path member and the reinforcing plate are larger than the piezoelectric actuator in a planar perspective, the flow path member has a first through hole (for example, first through hole 21c) in an area located outside the piezoelectric actuator, and the reinforcing plate has a second through hole (for example, second through hole 172g) in a position corresponding to the first through hole, and the second through hole may be larger than the first through hole in a planar perspective.

(7) In the droplet ejection head of (6) above, the first groove portion penetrates the piezoelectric actuator in the thickness direction, and the reinforcing plate may have a second groove portion (for example, second groove portion 172c) on the adhesive surface with the piezoelectric actuator, outside the first groove portion and the pressure chamber when viewed from above.

(8) In the droplet ejection head of (7) above, the second groove portion has a plurality of individual groove portions (for example, individual groove portion 172e) extending along the periphery of two or more of the plurality of pressure chambers in a planar perspective view, and a collective groove portion (for example, collective groove portion 172f) communicating with the plurality of individual groove portions, and the flow path member has a communication hole (for example, communication hole 21d) communicating with the collective groove portion, and the communication hole may open on the surface opposite to the joint surface with the reinforcing plate.

(9) In the droplet ejection head of (7) or (8) above, the reinforcing plate has a pillar portion (for example, pillar portion 172d) inside the second groove portion that contacts the piezoelectric actuator, and in a planar perspective, the piezoelectric actuator may have a bump (for example, connection electrode 175, dummy connection electrode 25) at a position overlapping with the pillar portion.

(10) A recording device (for example, printer 1) may have a droplet ejection head described in any one of (1) to (9) above, and a control unit (for example, control unit 14) that controls the droplet ejection head.

(11) The recording device may have a droplet ejection head described in any one of (1) to (9) above, and an arm that holds the droplet ejection head.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims.

For example, the present disclosure may be applied to a recording device (painting robot) that includes a droplet ejection head and an arm that holds the droplet ejection head. The painting robot can be used for painting vehicle bodies. The droplet ejection heads used in painting robots may eject highly viscous paint, have short paint ejection intervals, and eject large amounts of paint. Therefore, a decrease in ejection performance due to a decrease in the driving displacement of the piezoelectric element, and non-ejection due to a broken wire, may significantly affect the painting quality.

However, by applying the present disclosure, the reduction in the driving displacement of the piezoelectric element can be suppressed, the displacement variation between pressure chambers can also be suppressed, and the probability of non-ejection due to disconnection can be reduced, thereby improving painting quality even when used in a painting robot.

REFERENCE SIGNS LIST 1 printer 8 droplet ejection head 14 control unit 20 head body 21 flow path member 21c first through hole 21d communication hole 22 piezoelectric actuator 25 dummy connection electrode 100 first groove portion 162 pressure chamber 163 ejection hole 170 piezoelectric element 171 piezoelectric ceramic body 172 reinforcing plate 172c second groove portion 172d pillar portion 172e individual groove portion 172f collective groove portion 172g second through hole 173 internal electrode 174 surface electrode 174a electrode body 174b extraction electrode 175 connection electrode

Claims (10)

A nozzle for ejecting droplets;
A pressure chamber connected to the nozzle;
a piezoelectric element that deforms when a voltage is applied to the piezoelectric element to deform the pressure chamber;
The piezoelectric element is
a surface electrode facing the pressure chamber;
a first groove portion located around the surface electrode and extending in a shape corresponding to an outer shape of the surface electrode;
The pressure chamber has a circular shape in a plan view,
The surface electrode is
an electrode body having a circular shape in a plan view and located in an area facing the pressure chamber;
an extraction electrode extending in a first direction from the electrode body;
having
the first groove portion has an arc shape surrounding the electrode body and positioned outside the extraction electrode such that both ends of the first groove portion sandwich the extraction electrode therebetween,
When the maximum value of the distance between the outer edge of the pressure chamber and the outer edge of the first groove portion in a planar perspective view is A1 and the minimum value is A2, and when the maximum value of the distance between the outer edge of the surface electrode and the outer edge of the first groove portion in a planar perspective view is B1 and the minimum value is B2, the following formula (1) is satisfied:
A droplet ejection head that satisfies the following formula (3), when, in a plan view, the distance between one end and the other end of the first groove portion is E1, the width of the extraction electrode is E2, and the average value of the distance between the outer edge of the surface electrode and the inner edge of the first groove portion is E3 .
A1-A2<B1-B2...(1)
(E1-E2)/2>E3...(3) A nozzle for ejecting droplets;
A pressure chamber connected to the nozzle;
a piezoelectric element that deforms when a voltage is applied to the piezoelectric element to deform the pressure chamber;
The piezoelectric element is
a surface electrode facing the pressure chamber;
a first groove portion located around the surface electrode and extending in a shape corresponding to an outer shape of the surface electrode;
The pressure chamber has a circular shape in a plan view,
The surface electrode is
an electrode body having a circular shape in a plan view and located in an area facing the pressure chamber;
an extraction electrode extending in a first direction from the electrode body;
having
the first groove portion has an arc shape surrounding the electrode body and positioned outside the extraction electrode such that both ends of the first groove portion sandwich the extraction electrode therebetween,
the pressure chamber and the surface electrode are circular in plan view,
When the maximum value of the distance between the center of the pressure chamber and the outer edge of the first groove portion in a planar perspective view is C1 and the minimum value is C2, and the maximum value of the distance between the center of the surface electrode and the outer edge of the first groove portion in a planar perspective view is D1 and the minimum value is D2, the following formula (2) is satisfied,
A droplet ejection head that satisfies the following formula (3), when, in a plan view, the distance between one end and the other end of the first groove portion is E1, the width of the extraction electrode is E2, and the average value of the distance between the outer edge of the surface electrode and the inner edge of the first groove portion is E3 .
C1-C2<D1-D2...(2)
(E1-E2)/2>E3...(3) The surface electrode is
an electrode body located in an area facing the pressure chamber;
and an extraction electrode extending in a first direction from the electrode body,
2. The droplet ejection head of claim 1, wherein when a portion of an outer edge of the first groove portion is located outside the outer edge of the pressure chamber in a planar perspective view, the outer edge of the first groove portion is farthest from the outer edge of the pressure chamber in the first direction among the first direction, a second direction that is the opposite direction to the first direction, a third direction perpendicular to the first direction and the second direction, and a fourth direction that is the opposite direction to the third direction. The surface electrode is
an electrode body located in an area facing the pressure chamber;
and an extraction electrode extending in a first direction from the electrode body,
The droplet ejection head of claim 1, wherein, in a planar view, the outer edge of the first groove portion is farthest from the outer edge of the electrode body in the first direction among the first direction, a second direction that is the opposite direction to the first direction, a third direction perpendicular to the first direction and the second direction, and a fourth direction that is the opposite direction to the third direction. A nozzle for ejecting droplets;
A pressure chamber connected to the nozzle;
a piezoelectric actuator having a flat plate shape and including a piezoelectric element that deforms when a voltage is applied to the piezoelectric element to deform the pressure chamber ; and
a flow path member having a flat plate shape and including a plurality of the pressure chambers;
a reinforcing plate located between the flow path member and the piezoelectric element;
having
The piezoelectric element is
a surface electrode facing the pressure chamber;
a first groove portion located around the surface electrode and extending in a shape corresponding to an outer shape of the surface electrode;
having
When viewed from above, the flow path member and the reinforcing plate are larger than the piezoelectric actuator,
the flow path member has a first through hole in a region located outside the piezoelectric actuator,
the reinforcing plate has a second through hole at a position corresponding to the first through hole,
The second through hole is larger than the first through hole in a plan view;
A droplet ejection head that satisfies the following formula (1), where the maximum value of the distance between the outer edge of the pressure chamber and the outer edge of the first groove portion in a planar view is A1 and the minimum value is A2, and the maximum value of the distance between the outer edge of the surface electrode and the outer edge of the first groove portion in a planar view is B1 and the minimum value is B2 .
A1-A2<B1-B2...(1) the first groove portion penetrates the piezoelectric actuator in a thickness direction,
The reinforcing plate is
The droplet ejection head according to claim 5 , further comprising a second groove portion on an adhesive surface to be bonded to the piezoelectric actuator, the second groove portion being located outside the first groove portion and the pressure chamber in a plan view perspective. The second groove portion is
a plurality of individual grooves extending along peripheries of two or more of the pressure chambers in a plan view;
a collecting groove portion communicating with the plurality of individual groove portions,
the flow path member has a communication hole communicating with the collecting groove portion,
The droplet ejection head according to claim 6 , wherein the communication hole opens to a surface opposite to a surface bonded to the reinforcing plate. the reinforcing plate has a column portion in contact with the piezoelectric actuator inside the second groove,
The droplet ejection head according to claim 6 , wherein the piezoelectric actuator has a bump at a position overlapping with the column portion in a plan view. The droplet ejection head according to claim 1 ;
A control unit that controls the droplet ejection head. The droplet ejection head according to claim 1 ;
and an arm that holds the droplet ejection head.

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