EP4674626A1

EP4674626A1 - Droplet discharge head and recording device

Info

Publication number: EP4674626A1
Application number: EP24763937.0A
Authority: EP
Inventors: Makoto TOGO; Nobuaki YAMAKUCHI; Daisuke Hozumi
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2023-02-28
Filing date: 2024-02-27
Publication date: 2026-01-07
Also published as: JP2025175181A; JPWO2024181458A1; JP2025032021A; JP7615417B1; CN120677066A; WO2024181458A1; JP7751061B2

Abstract

A liquid droplet ejection head according to the present disclosure includes a nozzle, a pressure chamber, and a piezoelectric element. The nozzle ejects liquid droplets. The pressure chamber connects to the nozzle. The piezoelectric element deforms the pressure chamber by being deformed upon application of voltage. The piezoelectric element includes a surface electrode and a first groove. The surface electrode faces the pressure chamber. The first groove is positioned around the surface electrode and extends in a shape corresponding to an outer shape of the surface electrode. Where in plane perspective, a maximum distance and a minimum distance between an outer edge of the pressure chamber and an outer edge of the first groove are defined as A1 and A2, respectively, and in plan view, a maximum distance and a minimum distance between an outer edge of the surface electrode and the outer edge of the first groove are defined as B1 and B2, respectively, the following Equation (1) is satisfied:

A 1 - A 2 < B 1 - B 2

Description

TECHNICAL FIELD

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

BACKGROUND OF INVENTION

A known printing device is an inkjet printer or an inkjet plotter using an inkjet recording method. A liquid droplet ejection head for ejecting liquid is installed in such a printing device utilizing an inkjet method.
The liquid droplet ejection head ejects liquid in a pressure chamber from the nozzle by driving a piezoelectric element positioned above the pressure chamber to change the pressure in the pressure chamber. The piezoelectric element includes a piezoelectric body, an internal electrode located inside the piezoelectric body, and a surface electrode located on a surface of the piezoelectric body.
Patent Document 1 discloses an inkjet head including a piezoelectric element in which a groove surrounding a surface electrode is formed around the surface electrode for the purpose of reducing the occurrence of crosstalk between the piezoelectric elements.

CITATION LIST

PATENT LITERATURE

Patent Document 1: JP 2003-311954 A

SUMMARY

A liquid droplet ejection head according to one aspect of the present disclosure includes a nozzle, a pressure chamber, and a piezoelectric element. The nozzle ejects liquid droplets. The pressure chamber connects to the nozzle. The piezoelectric element deforms the pressure chamber by being deformed upon application of voltage. The piezoelectric element includes a surface electrode and a first groove. The surface electrode faces the pressure chamber. The first groove is positioned around the surface electrode and extends in a shape corresponding to an outer shape of the surface electrode. Where in plane perspective, a maximum distance and a minimum distance between an outer edge of the pressure chamber and an outer edge of the first groove are defined as A1 and A2, respectively, and in plan view, a maximum distance and a minimum distance between an outer edge of the surface electrode and the outer edge of the first groove are defined as B1 and B2, respectively, the following Equation (1) is satisfied: $A 1 - A 2 < B 1 - B 2$

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a printer according to a 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 a liquid droplet ejection head according to the first embodiment.
FIG. 4 is a schematic plan view illustrating a main portion of a head body according to the first embodiment.
FIG. 5 is a schematic enlarged view of a region V illustrated in FIG. 4.
FIG. 6 is a schematic cross-sectional view taken along a line VI-VI of FIG. 5.
FIG. 7 is a schematic plan view of a piezoelectric element according to the first embodiment.
FIG. 8 is a schematic plan view of a piezoelectric element according to the first embodiment.
FIG. 9 is a schematic plan view of a piezoelectric element according to the first embodiment.
FIG. 10 is a schematic plan view of a piezoelectric element according to the first embodiment.
FIG. 11 is a schematic plan view of a piezoelectric element according to the first embodiment.
FIG. 12 is a schematic cross-sectional view of a reinforcement plate and a channel member according to the first embodiment.
FIG. 13 is a schematic cross-sectional view illustrating a main portion of a head body according to the first embodiment.
FIG. 14 is a schematic plan view illustrating a main portion of the head body according to the first embodiment.
FIG. 15 is a plan view illustrating a configuration of a reinforcement plate according to the first embodiment.
FIG. 16 is a schematic plan view illustrating a configuration of a piezoelectric element according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments for implementing a liquid droplet ejection head and a recording device according to the present disclosure (hereinafter referred to as "embodiments") will be described with reference to the accompanying drawings. Note that the disclosure is not limited by the embodiments. The embodiments can also be combined as appropriate as long as no inconsistencies arise in the process. In the following embodiments, the same parts are denoted by the same reference signs, and redundant descriptions are omitted.
In the following embodiments, expressions such as "certain", "orthogonal", "perpendicular", and "parallel" may be used, but these expressions need not mean exactly "certain", "orthogonal", "perpendicular", and "parallel". In other words, each of the expressions described above allows for deviations in, for example, manufacturing accuracy, or installation accuracy.
Additionally, in the drawings referenced below, to facilitate understanding, an orthogonal coordinate system may be defined, in which the X-axis direction, Y-axis direction, and Z-axis direction are mutually orthogonal, and the positive Z-axis direction is set as the vertically upward direction. Furthermore, in some cases, the rotational direction about the vertical axis may be referred to as the θ direction.
The groove of the inkjet head described in Patent Document 1 is formed by bonding a channel unit including a plurality of pressure chambers and an actuator unit including a piezoelectric element, and then performing laser processing with reference to the position of the surface electrode.
In order to increase the driven displacement of the piezoelectric element, it is preferable that the groove is formed along the edge of the pressure chamber in plane perspective. However, when the actuator unit is bonded to the channel unit, the actuator unit may be bonded deviating from the desired position on the channel unit. In other words, the position of the surface electrode with respect to the pressure chamber may deviate from the desired position. In the related art described above, the groove is formed based on the position of the surface electrode. Thus, when the position of the surface electrode deviates from the desired position, the groove is arranged not along the edge of the pressure chamber, and as a result, the driven displacement of the piezoelectric element may become smaller than the desired value.
Thus, it is desired to provide an inkjet head in which the driven displacement of the piezoelectric element hardly decreases even when the positional deviation between the pressure chamber and the surface electrode occurs.

First Embodiment

Configuration of Printer

First, an outline of a printer 1, which is an example of a recording device according to a first embodiment, will be described with reference to FIGs. 1 and 2. FIG. 1 is a schematic side view of the printer 1 according to the first embodiment, and FIG. 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 illustrated in FIG. 1, the printer 1 includes a paper feed roller 2, a pair of guide rollers 3, an applicator 4, a head case 5, a plurality of transport rollers 6, a plurality of frames 7, a plurality of liquid droplet ejection heads 8, a pair of transport rollers 9, a dryer 10, a pair of transport rollers 11, a sensor unit 12, and a collection roller 13.
The printer 1 further includes a controller 14 that controls the paper feed roller 2, the pair of guide rollers 3, the applicator 4, the head case 5, the plurality of transport rollers 6, the plurality of frames 7, the plurality of liquid droplet ejection heads 8, the pair of transport rollers 9, the dryer 10, the pair of transport rollers 11, the sensor unit 12, and the collection roller 13.
The printer 1 records images or characters on a printing paper P by causing liquid droplets to land on the printing paper P. The printing paper P is an example of a recording medium. The printing paper P is wound around the paper feed roller 2 before use. The printer 1 transports the printing paper P from the paper feed roller 2 to the inside of the head case 5 through the pair of guide rollers 3 and the applicator 4.
The applicator 4 uniformly applies a coating agent to the printing paper P. This can apply surface treatment to the printing paper P, so that the printing quality of the printer 1 can be improved.
The head case 5 accommodates the plurality of transport rollers 6, the plurality of frames 7, and the plurality of liquid droplet ejection heads 8. The inside of the head case 5 forms a space isolated from the outside except for a portion connected to the outside such as a portion where the printing paper P enters and leaves.
In the internal space of the head case 5, at least one of the controlling factors such as temperature, humidity, and air pressure is controlled by the controller 14 as required. The transport rollers 6 transport the printing paper P to the vicinity of the liquid droplet ejection heads 8 inside the head case 5.
The frame 7 is a rectangular flat plate and positioned above and in proximity to the printing paper P transported by the transport rollers 6. As illustrated in FIG. 2, the frame 7 is positioned such that the longitudinal direction thereof is orthogonal to a transport direction of the printing paper P. The plurality (e.g., four) of frames 7 are positioned inside the head case 5 along the transport direction of the printing paper P.
A liquid, for example, ink, is supplied from a liquid tank (not illustrated) to the liquid droplet ejection head 8. The liquid droplet ejection head 8 ejects liquid droplets supplied from the liquid tank.
The controller 14 controls the liquid droplet ejection heads 8 based on data such as images and characters to eject the liquid droplets toward the printing paper P. The distance between the liquid droplet ejection head 8 and the printing paper P is, for example, about 0.5 to 20 mm.
The liquid droplet ejection head 8 is fixed to the frame 7. The liquid droplet ejection head 8 has both ends in the longitudinal direction, which are, for example, fixed to the frame 7. The liquid droplet ejection head 8 is positioned such that the longitudinal direction thereof is orthogonal 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 liquid droplet ejection heads 8 are fixed inside the printer 1. Note that the printer 1 according to the first embodiment is not limited to the line printer, but may be a so-called serial printer. The serial printer is a printer that alternately performs the operation of recording and the transport of the printing paper P. This operation of recording is performed while moving the liquid droplet ejection head 8 in a direction crossing the transport direction of the printing paper P, for example, by reciprocating in a direction substantially orthogonal to the transport direction.
As illustrated in FIG. 2, a plurality of (e.g., five) the liquid droplet ejection heads 8 are fixed in one frame 7. FIG. 2 illustrates an example in which three of the liquid droplet ejection heads 8 are positioned on the front side and two of them are positioned on the rear side in the transport direction of the printing paper P. The liquid droplet ejection heads 8 are positioned such that the centers thereof do not overlap each other in the transport direction of the printing paper P.
The plurality of liquid droplet ejection heads 8 positioned in one frame 7 constitute a head group 8A. Four of the head groups 8A are positioned along the transport direction of the printing paper P. The same color ink is supplied to the liquid droplet ejection heads 8 belonging to the same head group 8A. Thus, the printer 1 can perform printing with four colors of ink by using the four head groups 8A.
The colors of the ink ejected from the respective head groups 8A are, for example, magenta (M), yellow (Y), cyan (C), and black (K). The controller 14 can print a color image on the printing paper P by controlling each of the head groups 8A and ejecting inks of a plurality of colors onto the printing paper P.
Note that, in order to treat the surface of the printing paper P, the liquid droplet ejection heads 8 may eject the coating agent onto the printing paper P.
The number of the liquid droplet ejection heads 8 included in one of the head groups 8A or the number of the head groups 8A mounted on the printer 1 can be changed as appropriate in accordance with a printing object or printing conditions. For example, when the color to be printed on the printing paper P is a single color and the printing range can be covered by one liquid droplet ejection head 8, the number of liquid 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 pair of 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 by the dryer 10 is transported by the pair of transport rollers 11 and collected by the collection roller 13.
In the printer 1, drying the printing paper P with the dryer 10 can reduce adhesion of the printing paper P wound in an overlapping manner, and rubbing of undried liquid at the collection roller 13.
The sensor unit 12 is constituted by, for example, a position sensor, a speed sensor, or a temperature sensor. Based on information from the sensor unit 12, the controller 14 can determine the state of each unit of the printer 1 and control each unit of the printer 1.
The printer 1 described above uses the printing paper P as the printing object (i.e., the recording medium), but the printing object in the printer 1 is not limited to the printing paper P. For example, the printing object may be rolled cloth.
Instead of directly transporting the printing paper P itself, the printer 1 may transport the object placed on a transport belt. By using the transport belt, the printer 1 can use a sheet of paper, a cut cloth, wood, a tile, or the like as the printing object.
The printer 1 may print wiring patterns of an electronic device by ejecting liquid droplets containing conductive particles from the liquid droplet ejection heads 8. The printer 1 may also eject a predetermined amount of a liquid chemical agent or liquid droplets containing the chemical agent from the liquid droplet ejection heads 8 onto a reaction vessel or the like to produce chemicals.

Configuration of Liquid Droplet Ejection Head

The configuration of the liquid droplet ejection head 8 according to the first embodiment will be described below with reference to FIG. 3. FIG. 3 is a schematic exploded perspective view of the liquid droplet ejection head 8 according to the first embodiment.
The liquid droplet ejection head 8 includes a head body 20, a wiring portion 30, a casing 40, and a pair of heat dissipation plates 45. The head body 20 includes a channel member 21, a reinforcement plate 172 (see FIG. 4), a piezoelectric actuator 22 (see FIG. 4), and a reservoir 23.
In the following description, for convenience, a direction in which the head body 20 is provided in the liquid droplet ejection head 8 may be represented as "lower", and a direction in which the casing 40 is provided with respect to the head body 20 may be represented as "upper".
The channel member 21 of the head body 20 has a substantially flat plate shape, and includes 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 includes an opening (not illustrated), and a liquid is supplied from the reservoir 23 to the inside of the channel member 21 through the opening.
A plurality of ejection holes 163 (see FIG. 6) for ejecting the liquid to the printing paper P are located in the second surface 21b. The flow channel member 21 has therein a flow path, through which liquid flows from the first surface 21a to the second surface 21b.
The reinforcement plate 172 is located on the first surface 21a of the channel member 21. The reinforcement plate 172 includes a first surface 172a facing the first surface 21a of the channel member 21 and a second surface 172b (see FIG. 6) located on the opposite side of the first surface 172a.
The piezoelectric actuator 22 is located on the first surface 172a of the reinforcement plate 172. The piezoelectric actuator 22 includes a plurality of piezoelectric elements 170 (see FIG. 6). The flexible substrate 31 of the wiring portion 30 is electrically connected to the piezoelectric actuator 22.
The reservoir 23 is located on the piezoelectric actuator 22. The reservoir 23 is provided with openings 23a at both ends in the main scanning direction, which is orthogonal to the transport direction of the printing paper P and parallel to the printing paper P. The reservoir 23 internally includes a channel, and the liquid is supplied to the reservoir 23 from the outside through the openings 23a. The reservoir 23 supplies liquid to the channel member 21. The reservoir 23 also stores liquid supplied to the channel member 21.
The wiring portion 30 includes the flexible substrate 31, a wiring board 32, a plurality of driver ICs 33, a pressing member 34, and an elastic member 35. The flexible substrate 31 transmits, to the head body 20, a predetermined signal transmitted from the outside. As illustrated in FIG. 3, the liquid droplet ejection head 8 according to the first embodiment may include 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 drawn upward so as to pass through a slit 23b of the reservoir 23, and is electrically connected to the wiring board 32. Thus, the piezoelectric actuator 22 of the head body 20 can be electrically connected to the outside.
The wiring board 32 is positioned above the head body 20. The wiring board 32 distributes signals to a plurality of driver ICs 33.
The plurality of driver ICs 33 are positioned on one main surface of the flexible substrate 31. As illustrated in FIG. 3, in the liquid droplet ejection head 8 according to the first embodiment, two driver ICs 33 are provided on one flexible substrate 31, but the number of the driver ICs 33 provided on one flexible substrate 31 is not limited to two.
The driver IC 33 drives the piezoelectric actuator 22 of the head body 20 based on the driving signal sent from the controller 14 (see FIG. 1). This causes the driver IC 33 to drive the liquid droplet ejection head 8.
The pressing member 34 is substantially U-shaped in cross-sectional view, and presses the driver ICs 33 on the flexible substrate 31 toward the heat dissipation plate 45 from the inside. Thus, in the first embodiment, heat generated when the driver IC 33 is driven can be efficiently dissipated to the heat dissipation plate 45 on the outside.
The elastic member 35 is provided so as to come into contact with the outer wall of the pressing member (not illustrated) of the pressing member 34. By providing such the elastic member 35, the possibility can be reduced that the pressing member 34 damages the flexible substrate 31 when the pressing member 34 presses the driver ICs 33.
The elastic member 35 is made of, for example, a foam double-sided tape. The heat dissipation of the driver IC 33 can be improved by using, for example, a non-silicon heat conductive sheet as the elastic member 35. Note that it is not necessary to provide the elastic member 35.
The casing 40 is positioned on the head body 20 so as to cover the wiring portion 30. Thus, the casing 40 can seal the wiring portion 30. The casing 40 is made of, for example, resin or metal.
The casing 40 has a box shape extending long in the main scanning direction, and has a first opening 40a and a second opening 40b on a pair of side surfaces facing each other along the main scanning direction. The casing 40 has a third opening 40c on the lower surface and a fourth opening 40d on the upper surface.
In the first opening 40a, one of the heat dissipation plates 45 is positioned to close the first opening 40a, and in the second opening 40b, the other of the heat dissipation plates 45 is positioned to close the second opening 40b.
Each of the heat dissipation plates 45 is provided to extend in the main scanning direction, and is made of a metal or alloy or the like, having high heat dissipation property. Each of the heat dissipation plates 45 is provided in contact with the corresponding driver ICs 33 to dissipate heat generated in those driver ICs 33.
The pair of heat dissipation plates 45 are each fixed to the casing 40 by screws (not illustrated). Thus, the casing 40, to which the heat dissipation plates 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 opened.
The third opening 40c is positioned so as to face the reservoir 23. The flexible substrates 31 and the pressing member 34 are inserted into the third opening 40c.
The fourth opening 40d is provided to allow a connector (not illustrated) provided on the wiring board 32 to be inserted therein. When the space between the connector and the fourth opening 40d is sealed with resin or the like, liquid or dust is less likely to enter the casing 40.
The casing 40 includes an insulation portion 40e. The insulation portion 40e is disposed adjacent to the first opening 40a and the second opening 40b, and protrudes outward from the side surface of the casing 40 along the main scanning direction.
The insulation portion 40e is formed so as to extend in the main scanning direction. That is, the insulation portion 40e is positioned between the heat dissipation plate 45 and the head body 20. Thus, by providing the insulation portion 40e in the casing 40, the heat generated in the driver ICs 33 is less likely to be transmitted to the head body 20 through the heat dissipation plate 45.
FIG. 3 illustrates an example of the configuration of the liquid droplet ejection head 8, and may further include members other than those illustrated in FIG. 3.

Configuration of Head Body

The configuration of the head body 20 according to the first embodiment will be described below. FIG. 4 is a schematic plan view illustrating a main portion of the head body 20 according to the first embodiment.
As described above, the head body 20 includes the channel member 21, the reinforcement plate 172, and the piezoelectric actuator 22. The channel member 21, the reinforcement plate 172, and the piezoelectric actuator 22 each have a flat plate shape, and are positioned in this order from the lower side of the head body 20 (see FIG. 6).
As illustrated in FIG. 4, the channel member 21 and the reinforcement plate 172 are larger than the piezoelectric actuator 22. Specifically, the width of the channel member 21 and the reinforcement plate 172 in the longitudinal direction is larger than the width of the piezoelectric actuator 22 in the longitudinal direction. The width of the channel member 21 and the reinforcement plate 172 in the lateral direction is larger than the width of the piezoelectric actuator 22 in the lateral direction.
The channel member 21 includes a first through hole 21c in a region located outside the piezoelectric actuator 22. First through holes 21c are formed, for example, at both ends of the channel member 21 in the longitudinal direction.
The reinforcement 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 located above the first through hole 21c and at a position overlapping the first through hole 21c in plan view. The first through hole 21c and the second through hole 172g will be described below with reference to FIG. 13.
The piezoelectric actuator 22 is positioned substantially at the center of the reinforcement plate 172. The piezoelectric actuator 22 includes an ejection region 24. A plurality of piezoelectric elements 170 are arranged in the ejection region 24.
FIG. 5 is a schematic enlarged view of the region V illustrated in FIG. 4. FIG. 5 is a plan view of the piezoelectric element 170 viewed from a direction perpendicular to the surface of a piezoelectric ceramic body 171. In FIG. 5, a first groove 100 described below is omitted.
As illustrated in FIG. 5, the plurality of piezoelectric elements 170 are arranged at positions corresponding to the plurality of pressure chambers 162 of the channel member 21, respectively. Specifically, the plurality of piezoelectric elements 170 are each arranged so that an electrode body 174a of a surface electrode 174 described below is positioned above a pressure chamber 162.
The configuration of the channel member 21 including the pressure chamber 162 will now be described. FIG. 6 is a schematic cross-sectional view taken along a line VI-VI of FIG. 5. The line VI-VI illustrated in FIG. 5 is a straight line passing through a center point P1 of the electrode body 174a of the surface electrode 174 described below and a center point P2 of a connecting electrode 175 described below.
As illustrated in FIG. 6, the channel member 21 has a laminated structure in which a plurality of plates are laminated. Specifically, the channel member 21 includes a cavity plate 21A, a base plate 21B, an aperture (throttle) plate 21C, a supply plate 21D, manifold plates 21E, 21F, 21G, a cover plate 21H, and a nozzle plate 211. These plates are arranged in this order from the first surface 21a side of the channel member 21. These plates are formed of a metal such as stainless steel (SUS).
The plates constituting the channel member 21 have many holes. The thickness of each plate is about 10 µm to 300 µm. This can increase the accuracy of hole formation. The plates are laminated in alignment so that these holes communicate with each other to constitute an individual channel 164 and a supply manifold 161.
In the channel member 21, the supply manifold 161 and the ejection hole 163 are connected by the individual channel 164. The supply manifold 161 is positioned on the second surface 21b side inside the channel member 21, and the ejection hole 163 is positioned at the second surface 21b of the channel member 21.
The individual channel 164 includes the pressure chamber 162 and an individual supply channel 165. The pressure chamber 162 is positioned on the first surface 21a of the channel member 21, and the individual supply channel 165 is a channel connecting the supply manifold 161 and the pressure chamber 162.
The individual supply channel 165 includes a throttle 166 which is narrower than other parts. The throttle 166 is narrower in width than other parts of the individual supply channel 165, so that the channel resistance is high. Thus, when the channel resistance of the throttle 166 is high, the pressure generated in the pressure chamber 162 is difficult to escape to the supply manifold 161.
Next, the configuration of the piezoelectric element 170 and the reinforcement plate 172 will be described with reference to FIGs. 5 and 6. As illustrated in FIGs. 5 and 6, the piezoelectric element 170 includes the piezoelectric ceramic body 171, the reinforcement plate 172, an internal electrode 173, the surface electrode 174, and the connecting electrode 175.
The piezoelectric ceramic body 171 has a flat plate shape. The piezoelectric ceramic body 171 is positioned on the first surface 21a of the channel member 21 via the reinforcement plate 172.
The piezoelectric ceramic body 171 includes, for example, a plurality of piezoelectric ceramic layers 171a and 171b. Each of the piezoelectric ceramic layers 171a and 171b has, for example, a thickness of about 20 µm. Each of the piezoelectric ceramic layers 171a and 171b extends over a plurality of pressure chambers 162. The plurality of piezoelectric elements 170 share one piezoelectric ceramic body 171.
As the piezoelectric ceramic layers 171a and 171b, a ceramic material of lead zirconate titanate (PZT) having ferroelectricity, can be used.
In this example, the piezoelectric ceramic body 171 includes two piezoelectric ceramic layers 171a and 171b, but may include three or more piezoelectric ceramic layers.
A piezoelectric ceramic layer 171b is an example of a diaphragm. The diaphragm does not need 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 positioned between the two piezoelectric ceramic layers 171a and 171b. The internal electrode 173 is formed in the region between a piezoelectric ceramic layer 171a and the piezoelectric ceramic layer 171b over substantially the entire surface in the plane direction. That is, the internal electrode 173 overlaps all the pressure chambers 162 in the region facing the piezoelectric actuator 22. The internal electrode 173 functions as a common electrode shared by the plurality of piezoelectric elements 170.
For example, a metal material such as Ag-Pd system can be used for the internal electrode 173. The thickness of the internal electrode 173 is about 2 µm, for example.
The internal electrode 173 is electrically connected to a connecting electrode (not illustrated) located on the surface of the piezoelectric ceramic body 171 through a via hole formed in the piezoelectric ceramic layer 171a. The connecting electrode for the internal electrode 173 is grounded and held at a ground potential.
The surface electrode 174 includes the electrode body 174a and a lead electrode 174b. The electrode body 174a is positioned in a region facing the pressure chamber 162. The electrode body 174a is one size smaller than the pressure chamber 162 and has a shape substantially similar to that of the pressure chamber 162.
As illustrated in FIG. 5, the first embodiment illustrates, as an example, a case where the pressure chamber 162 and the electrode body 174a are circular in plane perspective. However, the shapes of the pressure chamber 162 and the electrode body 174a are not limited to this example. This point will be described below with reference to FIG. 16.
The lead electrode 174b is lead out from the electrode body 174a. The lead electrode 174b extends linearly toward the connecting electrode 175 described below. That is, the lead electrode 174b includes at its end a portion that is led outside the region facing the pressure chamber 162, and the connecting electrode 175 is positioned at this portion.
The electrode body 174a and the lead electrode 174b, of the surface electrode 174 may be made of a metal material such as Au system.
The connecting electrode 175 has a convex shape having a thickness of about 15 µm, for example. The connecting electrode 175 is located on the surface of the piezoelectric ceramic body 171 and is connected to the surface electrode 174. Specifically, the connecting electrode 175 is located on the lead electrode 174b and is electrically connected to the electrode body 174a via the lead electrode 174b. The connecting electrode 175 is electrically coupled to an electrode provided on the flexible substrate 31 (see FIG. 3).
The connecting electrode 175 contains metals that are more likely to cause ion migration than those (e.g., Au) contained in the surface electrode 174. For example, the connecting electrode 175 contains Ag, Cu, Sn, Pb, and Ni. Specifically, silver-palladium containing glass frit is used as the connecting electrode 175. The connecting electrode 175 is an example of a bump.
The piezoelectric actuator 22 includes a dummy connecting electrode 25 in addition to the connecting electrode 175, which is required for electrical connection between the surface electrode 174 and the flexible substrate 31. The dummy connecting electrode 25 has a convex shape, for example, and is located on the surface of the piezoelectric ceramic body 171. The dummy connecting electrode 25 is an example of a bump.
The plurality of surface electrodes 174 are individually electrically connected to the controller 14 (see FIG. 1) through the connecting electrodes 175, the flexible substrates 31, and wirings, respectively, in order to individually control the potential. When the surface electrode 174 and the internal electrode 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, acts as an active portion that is deformed by the piezoelectric effect.
The reinforcement plate 172 has a flat plate shape. The reinforcement plate 172 is positioned between the channel member 21 and the piezoelectric element 170. Specifically, the reinforcement plate 172 is located between the first surface 21a of the channel member 21 and the back surface of the piezoelectric ceramic body 171 on the opposite side of the surface where the surface electrode 174 is located. The reinforcement plate 172 extends over a plurality of the pressure chambers 162, and constitutes a ceiling portion of the plurality of the pressure chambers 162. The plurality of piezoelectric elements 170 share one reinforcement plate 172.
The head body 20 is not necessarily required to include the reinforcement plate 172. In this case, the piezoelectric ceramic body 171 constitutes a ceiling portion of a plurality of pressure chambers 162.
That is, the piezoelectric element 170 is constituted by the surface electrode 174, and a portion that faces the pressure chamber 162 in the piezoelectric actuator 22. This portion is composed of the piezoelectric ceramic layer 171a, the reinforcement plate 172, and the internal electrode 173. The piezoelectric element 170 is unimorphically deformed to press the pressure chamber 162 and eject liquid from the ejection hole 163. The ejection hole 163 is an example of a nozzle penetrating the nozzle plate 211.

Configuration of First Groove

FIGs. 7 to 9 are schematic plan views of the piezoelectric element 170 according to the first embodiment. In FIGs. 7 to 9, the size of the first groove 100 is exaggerated to facilitate understanding.
As illustrated in FIG. 7, the piezoelectric element 170 includes the first groove 100. The first groove 100 is positioned around (outside) the electrode body 174a at the surface electrode 174 in plan view, and extends in a shape corresponding to the outer shape of the electrode body 174a. That is, the first groove 100 has a shape substantially similar to the outer shape of the electrode body 174a in plan view.
For example, in the example illustrated in FIG. 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 longitudinal ends of the first groove 100 are positioned outside the lead electrode 174b with the lead electrode 174b sandwiched between the longitudinal ends. Specifically, one longitudinal end of the first groove 100 faces one side surface of the lead electrode 174b, and the other end faces the other side surface of the lead electrode 174b.
Thus, by providing the first groove 100 around the electrode body 174a, the rigidity of the piezoelectric ceramic body 171 can be reduced, so that the driven displacement of the piezoelectric element 170 can be increased as compared with the case where the first groove 100 is not provided.
Here, as illustrated in FIG. 7, when the outer edge of the first groove 100 is formed along the outer edge of the pressure chamber 162 in plane perspective, the driven displacement of the piezoelectric element 170 can be increased, as compared with the case where the outer edge of the first groove 100 is formed not along the outer edge of the pressure chamber 162.
However, when the piezoelectric actuator 22 is bonded to the channel member 21, the piezoelectric actuator 22 may be bonded deviating from the desired position on the channel member 21. In other words, the position of the surface electrode 174 with respect to the pressure chamber 162 may deviate from the desired position. FIGs. 8 and 9 illustrate the piezoelectric element 170 when the position of the surface electrode 174 with respect to the pressure chamber 162 deviates from the desired position (e.g., the position illustrated in FIG. 7). For example, when the first groove 100 is formed based on the position of the surface electrode 174, a problem arises in that the position of the surface electrode 174 deviates from the desired position. As a result, the outer edge of the first groove 100 is positioned not along the outer edge of the pressure chamber 162, and thus, the driven displacement of the piezoelectric element 170 may become smaller than the desired value.
Thus, the first groove 100 is formed 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 100 is as illustrated in FIG. 8. Here, the maximum and minimum distances between the outer edge of the pressure chamber 162 and the outer edge of the first groove 100 are defined as A1 and A2, respectively. Similarly, the maximum and minimum distances between the outer edge of the surface electrode 174 and the outer edge of the first groove 100 are defined as B1 and B2, respectively. Then, based on these definitions, the configuration may satisfy the following Equation (1): $A 1 - A 2 < B 1 - B 2$
In this configuration, the position shift between the outer edge of the pressure chamber 162 and the outer edge of the first groove 100 is smaller than the position shift between the outer edge of the electrode body 174a and the outer edge of the first groove 100. That is, the first groove 100 is positioned more along the outer edge of the pressure chamber 162 than along the outer edge of the surface electrode 174, and the driven displacement of the piezoelectric element 170 is hardly reduced even when the position shift between the pressure chamber 162 and the surface electrode 174 occurs.
The configuration of the pressure chamber 162, the surface electrode 174 and the first groove 100 is as illustrated in FIG. 9. Here, the maximum and minimum distances between the center point P3 of the pressure chamber 162 and the outer edge of the first groove 100 are defined as C1 and C2, respectively. Similarly, the maximum and minimum distances between the center point P1 of the surface electrode 174 and the outer edge of the first groove 100 are defined as D1 and D2, respectively. Then, based on these definitions, the configuration may satisfy the following Equation (2): $C 1 - C 2 < D 1 - D 2$
In this configuration, the position shift between the center of the pressure chamber 162 and the outer edge of the first groove 100 is smaller than the position shift between the center of the electrode body 174a and the outer edge of the first groove 100. That is, the first groove 100 is positioned to correspond more to the center point P3 of the pressure chamber 162 than to the center point P1 of the surface electrode 174, so that the driven displacement of the piezoelectric element 170 is hardly reduced even when the position shift between the pressure chamber 162 and the surface electrode 174 occurs.
The first groove 100 penetrates the piezoelectric actuator 22 in the thickness direction (see FIG. 10). In such a configuration, since the rigidity of the piezoelectric ceramic body 171 can be made lower than in the case where the first groove 100 does not penetrate the piezoelectric actuator 22, the driven displacement of the piezoelectric element 170 can be further increased.
Note that the first groove 100 is not necessarily required to penetrate the piezoelectric actuator 22.
Positional Relationship of First Groove, Pressure Chamber, and Surface Electrode The positional relationship of the first groove 100, the pressure chamber 162, and the surface electrode 174 according to the first embodiment, will be described below. FIG. 10 is a schematic plan view of the piezoelectric element 170 according to the first embodiment.
As illustrated in FIG. 10, it is assumed that the lead electrode 174b extends from the electrode body 174a in the positive X-axis positive direction (an example of the first direction). At this time, it is assumed that a part of the outer edge of the first groove 100 is located outside the outer edge of the pressure chamber 162 in the plane perspective. Then, the outer edge of the first groove 100 may be farthest apart from the outer edge of the pressure chamber in the X-axis positive direction among the X-axis positive direction, the X-axis negative direction (example of the second direction), the Y-axis positive direction (example of the third direction), and the Y-axis negative direction (example of the fourth direction).
The same may apply to the positional relationship between the first groove 100 and the electrode body 174a. That is, the outer edge of the first groove 100 may be farthest apart from the outer edge of the electrode body 174a in the X-axis positive direction among the X-axis positive direction, X-axis negative direction, Y-axis positive direction, and Y-axis negative direction.
As illustrated in FIG. 10, the lead electrode 174b is positioned on the X-axis positive direction side of the electrode body 174a, so that the first groove 100 is not provided around the lead electrode 174b so as not to overlap the lead electrode 174b. Thus, the area of the first groove 100 in the X-axis positive direction among the 4 directions is smaller than the area of the first groove 100 in each of the other 3 directions. Thus, when the outer edge of the first groove 100 is farthest apart from the outer edge of the pressure chamber 162 in the X-axis positive direction among the 4 directions, the driven displacement of the piezoelectric element 170 is less likely to decrease as compared with in the other directions.
The same applies to the positional relationship between the first groove 100 and the electrode body 174a. When the outer edge of the first groove 100 and the center of the electrode body 174a are the farthest apart in the X-axis positive direction among the 4 directions, the driven displacement of the piezoelectric element 170 is less likely to decrease than in the other directions.
Positional Relationship between First Groove and Surface Electrode The positional relationship between the first groove 100 and the surface electrode 174 according to the first embodiment, will be described below. FIG. 11 is a schematic plan view of the piezoelectric element 170 according to the first embodiment.
As described above with reference to FIG. 8, even when the position of the surface electrode 174 deviates from the desired position with respect to the pressure chamber 162, in the first embodiment, the first groove 100 is formed along the outer edge of the pressure chamber 162 in order to cause the driven displacement of the piezoelectric element 170 less likely to reduce.
Here, when the pressure chamber 162 and the surface electrode 174 are displaced in the left-right direction (Y-axis direction) by a threshold value or more, once the first groove 100 is formed along the outer edge of the pressure chamber 162, the first groove 100 may overlap the surface electrode 174. As a result, a part of the surface electrode 174 is shaved. In particular, when the lead electrode 174b of the surface electrode 174 is shaved, the wiring is cut off, and the ejecting function may be reduced (lost).
Thus, the first groove 100 is formed so as to ensure a certain interval or more from the lead electrode 174b. Specifically, it is supposed that the distance between one end and the other end of the first groove 100 is defined as E1, a width of the lead electrode 174b is defined as E2, and the average value of the distance between the outer edge of the surface electrode 174 and the inner edge of the first groove 100 is defined as E3, as illustrated in FIG. 11. Then, the configuration of the first groove 100 and the surface electrode 174 may satisfy the following Equation (3): $(E 1 - E 2) / 2 > E 3$
With this configuration, the lead electrode 174b is less likely to be shaved even when the position shift in the left-right direction (Y-axis direction) occurs between the surface electrode 174 and the first groove 100. As a result, as compared with the case where the lead electrode 174b is shaved out of the surface electrode 174, the processing failure can be quickly determined by the electrostatic capacitance inspection and the effect on the ejection function can be reduced.
Size Relationship between First Through Hole and Second Through Hole The size relationship between the first through hole 21c and the second through hole 172g according to the first embodiment, will be described below. FIG. 12 is a schematic cross-sectional view of the reinforcement plate 172 and the channel member 21 according to the first embodiment.
As described above with reference to FIG. 4, the channel member 21 includes the first through holes 21c in a region located outside the piezoelectric actuator 22. The reinforcement plate 172 includes the second through holes 172g at a position corresponding to the first through hole 21c. In this case, as illustrated in FIG. 12, the second through hole 172g may be larger than the first through hole 21c in plane perspective. With this configuration, the position of the first through hole 21c of the channel member 21 becomes clear in plan view, so that the position of the outer edge of the pressure chamber 162 of the channel member 21 can be easily grasped by using the position of the first through hole 21c as a mark. Thus, when the first groove 100 is formed in the piezoelectric actuator 22 after bonding the piezoelectric actuator 22, the reinforcement plate 172 and the piezoelectric actuator 22, the first groove 100 can be easily formed in a position along the outer edge of the pressure chamber 162 with the first through hole 21c as a reference.
Although the first through hole 21c and the second through hole 172g are both circular in plan view, 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 Reinforcement Plate

Next, the configuration of the reinforcement plate 172 according to the first embodiment will be described with reference to FIGs. 13 to 15. FIG. 13 is a schematic cross-sectional view illustrating the main portion of the head body 20 according to the first embodiment. FIG. 14 is a schematic plan view illustrating the main portion of the head body 20 according to the first embodiment. FIG. 15 is a plan view illustrating the configuration of the reinforcement plate 172 according to the first embodiment.
As illustrated in FIG. 13, the reinforcement plate 172 may include a second groove 172c on the second surface 172b, which is a bonding surface with the piezoelectric actuator 22. As illustrated in FIG. 14, the second groove 172c is formed in a position that does not overlap the first groove 100 and the pressure chamber 162 in the plane perspective. Specifically, the second groove 172c is positioned outside the first groove 100 and the pressure chamber 162 in the plane perspective. The dashed line illustrated in FIG. 14 indicates the side wall portion of the second groove 172c.
Thus, by forming the second groove 172c on the bonding surface of the reinforcement plate 172 with the piezoelectric actuator 22, excess adhesive or air bubbles can be released (poured) into the second groove 172c, when the piezoelectric actuator 22 and the reinforcement plate 172 are bonded. Thus, unevenness of transfer or biting of air bubbles can be reduced, and thus, dispersion of ejection characteristics can be reduced. By forming the second groove 172c at a position not to overlap the first groove 100 and the pressure chamber 162, as compared with the case where the second groove 172c is formed at a position to overlap the first groove 100 and the pressure chamber 162, the possibility that the first groove 100 and the pressure chamber 162 communicate with each other when the first groove 100 is formed, can be reduced.
As illustrated in FIG. 15, the second groove 172c includes a plurality of individual grooves 172e and a collective groove 172f. The plurality of individual grooves 172e extend along the periphery of 2 or more pressure chambers 162 among the plurality of pressure chambers in plane perspective. The collective groove 172f communicates with the plurality of individual groove 172e.
The channel member 21 includes a communication hole 21d communicating with the collective groove 172f. The communication hole 21d opens on the second surface 21b (see FIG. 6), which is opposite to the bonding surface with the reinforcement plate 172 of the channel member 21.
That is, the communication hole 21d of the channel member 21 communicates with the individual groove 172e of the second groove 172c through the collective groove 172f. Thus, when the piezoelectric actuator 22 and the reinforcement plate 172 are bonded together, the outgas or bubbles flowing into the second groove 172c are released to the outside of the liquid droplet ejection head 8 through the individual groove 172e, the collective groove 172f, and the communication hole 21d. Accordingly, the internal pressure of the second groove 172c is hardly increased, and as a result, the dispersion of the ejection characteristics can be reduced.
As illustrated in FIG. 13, the reinforcement plate 172 includes pillars 172d inside the second groove 172c. One end of a pillar 172d is positioned in the piezoelectric actuator 22, and the other end is positioned in the reinforcement plate 172.
The pillar 172d is arranged at a position to overlap with the connecting electrode 175 or the dummy connecting electrode 25, which are located on the surface of the piezoelectric actuator 22 in plane perspective. In other words, in the reinforcement plate 172, the groove is not formed vertically below the connecting electrode 175 or the dummy connecting electrode 25.
When the flexible substrate 31 and the piezoelectric actuator 22 are electrically connected, a certain pressure is applied to the connecting electrode 175 and the dummy connecting electrode 25. Thus, when the groove is formed vertically below the connecting electrode 175 or the dummy connecting electrode 25, this has a risk that the head body 20 may not receive the pressure and a crack may occur. Thus, when the pillar 172d is formed inside the second groove 172c and overlaps with the connecting electrode 175 or the dummy connecting electrode 25 in the plane perspective as described above, the pressure can be received by the pillar 172d, and the crack may not occur in the head body 20.
As described above, according to the liquid droplet ejection head 8 according to the first embodiment, the driven displacement of the piezoelectric element 170 is hardly reduced even when the position shift between the pressure chamber 162 and the surface electrode 174 occurs.

Second Embodiment

Shape of Piezoelectric Element

FIG. 16 is a schematic plan view illustrating the configuration of the piezoelectric element 170 according to a second embodiment. The shape of the piezoelectric element 170 is not limited to the shape illustrated in FIG. 5. For example, as illustrated in FIG. 16, the shape of the piezoelectric element 170 may be a bowling pin.
Specifically, in plan view, the pressure chamber 162 may have a diamond shape with rounded corners. In this case, the electrode body 174a of the surface electrode 174 also has a diamond shape with rounded corners in plan view in accordance with the shape of the pressure chamber 162. The lead electrode 174b extends linearly from a sharp corner of a plurality of corners of the electrode body 174a toward the connecting electrode 175. The connecting electrode 175 is circular in plan view.
In this case also, the piezoelectric element 170 may include the first groove 100 (not illustrated here) positioned around the electrode body 174a in the surface electrode 174 and extending in a shape corresponding to the outer shape of the electrode body 174a. In this case also, the first groove 100 may be formed along the outer edge of the pressure chamber 162.
In one embodiment, (1) a liquid droplet ejection head (e.g., liquid droplet ejection head 8) includes: a nozzle (e.g., ejection hole 163); a pressure chamber (e.g., pressure chamber 162); and a piezoelectric element (e.g., piezoelectric element 170). The nozzle ejects liquid droplets. The pressure chamber connects to the nozzle. The piezoelectric element deforms the pressure chamber by being deformed upon application of voltage. The piezoelectric element includes: a surface electrode (e.g., surface electrode 174); and a first groove (e.g., first groove 100). The surface electrode faces the pressure chamber. The first groove is positioned around the surface electrode and extends in a shape corresponding to an outer shape of the surface electrode. Where in plane perspective, a maximum distance and a minimum distance between an outer edge of the pressure chamber and an outer edge of the first groove are defined as A1 and A2, respectively, and in plan view, a maximum distance and a minimum distance between an outer edge of the surface electrode and the outer edge of the first groove are defined as B1 and B2, respectively, the following Equation (1) is satisfied: $A 1 - A 2 < B 1 - B 2$
(2) A liquid droplet ejection head includes: a nozzle; a pressure chamber; and a piezoelectric element. The nozzle ejects liquid droplets. The pressure chamber connects to the nozzle. The piezoelectric element deforms the pressure chamber by being deformed upon application of voltage. The piezoelectric element includes: a surface electrode; and a first groove. The surface electrode faces the pressure chamber. The first groove is positioned around the surface electrode and extends in a shape corresponding to an outer shape of the surface electrode. The pressure chamber and the surface electrode are circular in plane perspective, and where in plane perspective, a maximum distance and a minimum distance between a center of the pressure chamber and an outer edge of the first groove are defined as C1 and C2, respectively, and in plan view, a maximum distance and a minimum distance between a center of the surface electrode and the outer edge of the first groove are defined as D1 and D2, respectively, the following Equation (2) may be satisfied: $C 1 - C 2 < D 1 - D 2$
(3) In the liquid droplet ejection head according to above (1) or (2), the surface electrode includes: an electrode body (e.g., electrode body 174a) positioned in a region facing the pressure chamber; and a lead electrode (e.g., lead electrode 174b) extending from the electrode body in a first direction, and when in plane perspective, a portion of the outer edge of the first groove is positioned outside the outer edge of the pressure chamber, the outer edge of the first groove may be farthest apart from the outer edge of the pressure chamber in the first direction among the first direction, a second direction opposite to the first direction, a third direction orthogonal to the first direction and the second direction, and a fourth direction opposite to the third direction.
(4) In the liquid droplet ejection head according to above (1) or (2), the surface electrode includes: an electrode body positioned in a region facing the pressure chamber; and a lead electrode extending from the electrode body in a first direction and in plan view, the outer edge of the first groove may be farthest apart from an outer edge of the electrode body in the first direction among the first direction, a second direction opposite to the first direction, a third direction orthogonal to the first direction and the second direction, and a fourth direction opposite to the third direction.
(5) In the liquid droplet ejection head according to any one of above (1) to (4), the pressure chamber is circular in plane perspective, the surface electrode includes: an electrode body positioned in a region facing the pressure chamber, the electrode body being circular in plan view; and a lead electrode extending from the electrode body in a first direction, the first groove has an arc shape surrounding the electrode body and positioned outside the lead electrode with the lead electrode sandwiched between both ends, and where in plan view, a distance between one end and the other end of the first groove is defined as E1, a width of the lead electrode is defined as E2, and an average distance between the outer edge of the surface electrode and an inner edge of the first groove is defined as E3, the following Equation (3) may be satisfied: $(E 1 - E 2) / 2 > E 3$
(6) The liquid droplet ejection head according to any one of above (1) to (5) includes: a piezoelectric actuator (e.g., piezoelectric actuator 22)having a flat plate shape and including a plurality of the piezoelectric elements; a channel member (e.g., channel member 21) having a flat plate shape and including a plurality of the pressure chambers; and a reinforcement plate (e.g., reinforcement plate 172) positioned between the channel member and the piezoelectric elements, in which in plane perspective, the channel member and the reinforcement plate are larger than the piezoelectric actuator, the channel member includes a first through hole (e.g., first through hole 21c) in a region positioned outside the piezoelectric actuator, the reinforcement plate includes a second through hole (e.g., second through hole 172g) at a position corresponding to the first through hole, and in plane perspective, the second through hole may be larger than the first through hole.
(7) In the liquid droplet ejection head according to above (6), the first groove penetrates through the piezoelectric actuator in a thickness direction, and the reinforcement plate may include a second groove (e.g., second groove 172c) on a bonding surface with the piezoelectric actuator, and positioned outside the first groove and the pressure chamber in plane perspective.
(8) In the liquid droplet ejection head according to above (7), the second groove includes: a plurality of individual grooves (e.g., individual grooves 172e) extending along peripheries of two or more of the plurality of the pressure chambers in plane perspective; and a collective groove (e.g., collective groove 172f) communicating with the plurality of individual grooves, the channel member includes a communication hole (e.g., communication hole 21d) communicating with the collective groove, and the communication hole may open on a surface opposite to the bonding surface with the reinforcement plate.
(9) In the liquid droplet ejection head according to above (7) or (8), the reinforcement plate may include a pillar (e.g., pillar 172d) in contact with the piezoelectric actuator inside the second groove, and the piezoelectric actuator may include a bump (e.g., connecting electrode 175, dummy connecting electrode 25) at a position overlapping the pillar in plane perspective.
(10) A recording device (e.g., printer 1) may include: the liquid droplet ejection head according to any one of above (1) to (9); and a controller (e.g., controller 14) configured to control the liquid droplet ejection head.
(11) A recording device may include: the liquid droplet ejection head according to any one of above (1) to (9); and an arm holding the liquid droplet ejection head.
The embodiments disclosed herein should be considered exemplary in all respects and not restrictive. Indeed, the embodiments described above may be embodied in various forms. The embodiments described above may also be omitted, replaced, or modified in various forms without departing from the scope and spirit of the attached claims.
For example, the present disclosure may be applied to a recording device (painting robot) including the liquid droplet ejection head and an arm holding the liquid droplet ejection head. The painting robot can be used for vehicle body painting. The liquid droplet ejection head used for the painting robot may eject paint with high viscosity with a short paint ejecting interval and a large ejection amount. Thus, deterioration of ejection performance due to reduction of the driven displacement of the piezoelectric element and non-ejection due to disconnection may greatly affect the painting quality.
However, when the present disclosure is applied, reduction of the driven displacement of the piezoelectric element can be decreased, dispersion of the displacement between the pressure chambers can be reduced, and the probability of occurrence of non-ejection due to disconnection can be reduced. Thus, the painting quality can be improved even when used for the painting robot.

REFERENCE SIGNS

1 Printer
8 Liquid droplet ejection head
14 Controller
20 Head body
21 Channel member
21c First through hole
21d Communication hole
22 Piezoelectric actuator
25 Dummy connecting electrode
100 First groove
162 Pressure chamber
163 Ejection hole
170 Piezoelectric element
171 Piezoelectric ceramic body
172 Reinforcement plate
172c Second groove
172d Pillar
172e Individual groove
172f Collective groove
172g Second through hole
173 Internal electrode
174 Surface electrode
174a Electrode body
174b Lead electrode
175 Connecting electrode

Claims

A liquid droplet ejection head comprising:
a nozzle configured to eject liquid droplets;

a pressure chamber connecting to the nozzle; and

a piezoelectric element configured to deform the pressure chamber by being deformed upon application of voltage, wherein

the piezoelectric element comprises:
a surface electrode facing the pressure chamber; and

a first groove positioned around the surface electrode, and extending in a shape corresponding to an outer shape of the surface electrode, and

where in plane perspective, a maximum distance and a minimum distance between an outer edge of the pressure chamber and an outer edge of the first groove are defined as A1 and A2, respectively, and in plan view, a maximum distance and a minimum distance between an outer edge of the surface electrode and the outer edge of the first groove are defined as B1 and B2, respectively, the following Equation (1) is satisfied: $A 1 - A 2 < B 1 - B 2$
A liquid droplet ejection head comprising:
a nozzle configured to eject liquid droplets;

a pressure chamber connecting to the nozzle; and

a piezoelectric element configured to deform the pressure chamber by being deformed upon application of voltage, wherein

the piezoelectric element comprises:
a surface electrode facing the pressure chamber; and

a first groove positioned around the surface electrode, and extending in a shape corresponding to an outer shape of the surface electrode,

the pressure chamber and the surface electrode are circular in plane perspective, and

where in plane perspective, a maximum distance and a minimum distance between a center of the pressure chamber and an outer edge of the first groove are defined as C1 and C2, respectively, and in plan view, a maximum distance and a minimum distance between a center of the surface electrode and the outer edge of the first groove are defined as D1 and D2, respectively, the following Equation (2) is satisfied: $C 1 - C 2 < D 1 - D 2$
The liquid droplet ejection head according to claim 1, wherein
the surface electrode comprises:
an electrode body positioned in a region facing the pressure chamber; and

a lead electrode extending from the electrode body in a first direction, and

when in plane perspective, a portion of the outer edge of the first groove is positioned outside the outer edge of the pressure chamber, the outer edge of the first groove is farthest apart from the outer edge of the pressure chamber in the first direction among the first direction, a second direction opposite to the first direction, a third direction orthogonal to the first direction and the second direction, and a fourth direction opposite to the third direction.
The liquid droplet ejection head according to claim 1, wherein
the surface electrode comprises:
an electrode body positioned in a region facing the pressure chamber; and

a lead electrode extending from the electrode body in a first direction, and

in plan view, the outer edge of the first groove is farthest apart from an outer edge of the electrode body in the first direction among the first direction, a second direction opposite to the first direction, a third direction orthogonal to the first direction and the second direction, and a fourth direction opposite to the third direction.
The liquid droplet ejection head according to claim 1, wherein
the pressure chamber is circular in plane perspective,

the surface electrode comprises:
an electrode body positioned in a region facing the pressure chamber, the electrode body being circular in plan view; and

a lead electrode extending from the electrode body in a first direction,

the first groove has an arc shape surrounding the electrode body and positioned outside the lead electrode with the lead electrode sandwiched between both ends, and

where in plan view, a distance between one end and the other end of the first groove is defined as E1, a width of the lead electrode is defined as E2, and an average distance between the outer edge of the surface electrode and an inner edge of the first groove is defined as E3, the following Equation (3) is satisfied: $(E 1 - E 2) / 2 > E 3$
The liquid droplet ejection head according to claim 1, comprising:
a piezoelectric actuator having a flat plate shape and comprising a plurality of the piezoelectric elements;

a channel member having a flat plate shape and comprising a plurality of the pressure chambers; and

a reinforcement plate positioned between the channel member and the piezoelectric elements, wherein,

in plane perspective, the channel member and the reinforcement plate are larger than the piezoelectric actuator,

the channel member comprises a first through hole in a region positioned outside the piezoelectric actuator,

the reinforcement plate comprises a second through hole at a position corresponding to the first through hole, and

in plane perspective, the second through hole is larger than the first through hole.
The liquid droplet ejection head according to claim 6, wherein
the first groove penetrates through the piezoelectric actuator in a thickness direction, and

the reinforcement plate comprises a second groove on a bonding surface with the piezoelectric actuator and positioned outside the first groove and the pressure chamber in plane perspective.
The liquid droplet ejection head according to claim 7, wherein
the second groove comprises:
a plurality of individual grooves extending along peripheries of two or more of the plurality of the pressure chambers in plane perspective; and

a collective groove communicating with the plurality of individual grooves,

the channel member comprises a communication hole communicating with the collective groove, and

the communication hole opens on a surface opposite to the bonding surface with the reinforcement plate.
The liquid droplet ejection head according to claim 7, wherein
the reinforcement plate comprises a pillar in contact with the piezoelectric actuator inside the second groove, and

the piezoelectric actuator comprises a bump at a position overlapping the pillar in plane perspective.
A recording device comprising:
the liquid droplet ejection head according to claim 1; and

a controller configured to control the liquid droplet ejection head.
A recording device comprising:
the liquid droplet ejection head according to claim 1; and

an arm holding the liquid droplet ejection head.