Liquid discharge head

Abstract

To provide a liquid discharge head capable of stably discharging liquid.SOLUTION: A liquid discharge head of an embodiment includes a plurality of pressure chambers, a diaphragm, and a plurality of piezoelectric actuators. The plurality of pressure chambers communicate with nozzles, respectively. The diaphragm constitutes a part of a barrier wall of the pressure chambers and has a plurality of irregularities on a surface thereof. The plurality of piezoelectric actuators are arranged on the surface having the irregularities, of the diaphragm. The number of the plurality of piezoelectric actuators is larger than the number of pressure chambers communicating with the nozzles. The plurality of piezoelectric actuators include: first piezoelectric actuators that are each arranged for each pressure chamber communicating with the nozzle at a position facing a projection part of the diaphragm, each push the projection part to change volume of the pressure chamber to discharges liquid from the nozzle; and second piezoelectric actuator that are each not arranged at a position corresponding to each pressure chamber communicating with the nozzle and are each wired so as to be able measure a terminal voltage.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a liquid ejection head. [Background technology]

[0002] Liquid ejection heads that supply a predetermined amount of liquid to a predetermined position are known. Liquid ejection heads are mounted on, for example, inkjet printers, 3D printers, and dispensing devices. Inkjet printers eject ink droplets from an inkjet head to form images or the like on the surface of a recording medium. 3D printers eject modeling material droplets from a modeling material ejection head, harden them, and form three-dimensional objects. Dispensing devices eject sample droplets and supply them in predetermined amounts to multiple containers or the like.

[0003] A liquid ejection head has multiple channels for ejecting liquid. Each channel is equipped with a nozzle for ejecting liquid, a pressure chamber that communicates with the nozzle, a vibration plate that forms part of the partition wall of the pressure chamber, and an actuator that presses the vibration plate to change the volume of the pressure chamber. The liquid ejection head selects a channel from among the multiple channels to eject liquid, and drives the actuator by applying a drive waveform to it. When the actuator is driven to press the vibration plate, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle.

[0004] The diaphragm has a thin section so that it distorts when pressed by the actuator. The actuator presses on the thicker section. Therefore, when assembling a liquid ejection head, precision is required in aligning the actuator and diaphragm. However, not only is it difficult to align them correctly, it is also difficult to confirm that they have been aligned correctly after assembly. If the actuator is not aligned correctly with the diaphragm, it may affect the liquid ejection characteristics. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-334949 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-95769 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-73898 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a liquid ejection head that can eject liquid stably. [Means for solving the problem]

[0007] A liquid ejection head according to an embodiment of the present invention includes a plurality of pressure chambers, a vibration plate, and a plurality of piezoelectric actuators. Each of the pressure chambers communicates with a nozzle. The vibration plate forms part of the partition wall of the pressure chamber and has a plurality of projections and recesses on its surface. The plurality of piezoelectric actuators are arranged on the surface of the vibration plate with projections and the number of piezoelectric actuators is greater than the number of pressure chambers communicating with the nozzle. The plurality of piezoelectric actuators include a first piezoelectric actuator that is arranged for each pressure chamber communicating with the nozzle at a position facing a projection of the vibration plate, and that uses deformation due to the inverse piezoelectric effect to press the projection, changing the volume of the pressure chamber and ejecting liquid from the nozzle; and a second piezoelectric actuator that is not arranged at a position corresponding to the pressure chamber communicating with the nozzle, but is wired so that the electromotive force generated at a terminal due to the piezoelectric effect can be measured. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating the overall configuration of an inkjet printer equipped with an inkjet head according to an embodiment. [Figure 2] FIG. 2 is a perspective view of the inkjet head. [Figure 3] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 4]FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 5] FIG. 2 is a partially enlarged plan view of a head portion of the inkjet head. [Figure 6] FIG. 2 is a circuit diagram of the inkjet head. [Figure 7] 3A to 3C are diagrams illustrating an assembly process of the inkjet head. [Figure 8] This is a driving waveform applied to the piezoelectric actuator of the inkjet head. [Figure 9] 3A to 3C are diagrams illustrating the operation of the piezoelectric actuator. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a liquid ejection head according to an embodiment will be described in detail with reference to the accompanying drawings, in which the same components are denoted by the same reference numerals.

[0010] As an example of an image forming apparatus equipped with a liquid ejection head according to an embodiment, an inkjet printer 10 that prints an image on a recording medium will be described. Fig. 1 shows a schematic configuration of the inkjet printer 10. Inside a housing 11, the inkjet printer 10 has arranged therein: a cassette 12 that stores sheets S, which are an example of a recording medium; an upstream transport path 13 for the sheets S; a transport belt 14 that transports the sheets S removed from the cassette 12; a plurality of inkjet heads 100-103 that eject ink droplets toward the sheets S on the transport belt 14; a downstream transport path 15 for the sheets S; an ejection tray 16; and a control board 17. An operation unit 18, which serves as a user interface, is located on the upper side of the housing 11.

[0011] Image data to be printed on the sheet S is generated by, for example, a computer 200, which is an externally connected device. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 via a cable 201 and connectors 202 and 203.

[0012] A pickup roller 204 supplies sheets S one by one from the cassette 12 to the upstream conveying path 13. The upstream conveying path 13 is composed of a pair of feed rollers 131 and 132 and sheet guide plates 133 and 134. The sheets S are fed via the upstream conveying path 13 onto the upper surface of the conveying belt 14. An arrow 104 in the figure indicates the conveying path of the sheets S from the cassette 12 to the conveying belt 14.

[0013] The conveyor belt 14 is a mesh-like endless belt with many through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, support the conveyor belt 14 so that it can rotate freely. A motor 205 rotates the drive roller 141 to rotate the conveyor belt 14. The motor 205 is an example of a drive device. In the figure, 105 indicates the direction of rotation of the conveyor belt 14. A negative pressure container 206 is disposed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates an airflow that creates a negative pressure inside the negative pressure container 206, causing the sheet S to be attracted and held on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

[0014] Inkjet heads 100-103, which are an example of liquid ejection heads, are arranged to face sheet S, which is held by suction on conveyor belt 14, with a small gap of, for example, 1 mm between them. Each of inkjet heads 100-103 ejects ink droplets toward sheet S. As sheet S passes below inkjet heads 100-103, they print an image. Each of inkjet heads 100-103 has the same structure except for the color of ink they eject. The ink colors are, for example, cyan, magenta, yellow, and black.

[0015] The inkjet heads 100-103 are connected to ink tanks 315-318 and ink supply pressure adjusters 321-324 via ink flow paths 311-314, respectively. Each ink tank 315-318 is located above the corresponding inkjet head 100-103. During standby, each ink supply pressure adjuster 321-324 adjusts the pressure inside each inkjet head 100-103 to a negative pressure, e.g., -1.2 kPa, relative to atmospheric pressure to prevent ink from leaking from the nozzles 24 (see FIG. 2) of the inkjet heads 100-103. During image formation, ink from each ink tank 315-318 is supplied to each inkjet head 100-103 by the ink supply pressure adjusters 321-324.

[0016] After the image is formed, the sheet S is sent from the conveyor belt 14 to a downstream conveying path 15. The downstream conveying path 15 is made up of pairs of feed rollers 151, 152, 153, and 154, and sheet guide plates 155 and 156 that define the conveying path of the sheet S. The sheet S passes through the downstream conveying path 15 and is sent from a discharge port 157 to a discharge tray 16. An arrow 107 in the figure indicates the conveying path of the sheet S.

[0017] Next, we will explain the configuration of the inkjet heads 100 to 103. Below, we will explain the inkjet head 100 with reference to Figures 2 to 5, but the inkjet heads 101 to 103 have the same structure as the inkjet head 100.

[0018] As shown in Fig. 2, the inkjet head 100 includes a head unit 2, which is an example of a liquid ejection unit. The head unit 2 is connected to a flexible printed wiring board 21, which is an example of a film wiring board. The flexible printed wiring board 21 is connected to a printed circuit board 22, which is an example of a relay board. The head unit 2 includes a nozzle plate 23, which is an example of a nozzle unit. The head unit 2 is connected to the ink supply pressure adjustment device 321 of Fig. 1 via an ink flow path 311.

[0019] The nozzles 24 of each channel that ejects ink are arranged along a first direction, for example, the X direction, of the nozzle plate 23. The nozzle density is set within a range of 150 to 1200 dpi, for example. The nozzles 24 are not limited to being arranged in a single row, but may be arranged in multiple rows. The detailed configuration of the head unit 2 will be described later.

[0020] The flexible printed wiring board 21 is a flexible printed wiring board made of a synthetic resin film such as polyimide. The flexible printed wiring board 21 is equipped with a driver chip, a driving integrated circuit (IC) 3 (hereinafter referred to as the driving IC). The printed circuit board 22 is a hard through-hole board made by laminating multiple layers of glass fiber-reinforced epoxy resin and copper wiring layers. The driving IC 3, which serves as the control unit for the inkjet head 100, temporarily stores print data sent via the printed circuit board 22 from the control board 17, which is equipped with a CPU and serves as the control unit for the inkjet printer 10, and sends driving signals to each channel to eject ink at predetermined timing.

[0021] 3 to 5 are partial cross-sectional views of the head unit 2. The nozzle plate 23 is bonded to one surface of the pressure chamber substrate 4. The nozzle plate 23 is a rectangular plate made of, for example, a resin such as polyimide or a metal such as stainless steel.

[0022] The vibration plate 41 is bonded to one surface of the pressure chamber substrate 4 opposite the nozzle plate 23. The vibration plate 41 is flexible enough to deform when an external force is applied. The vibration plate 41 is a flexible rectangular plate made of, for example, metal or polyimide film. The vibration plate 41 has an uneven surface with multiple protrusions 411 and multiple recesses 412 (see FIG. 4). FIGS. 4(b) and 4(c) only show the vibration plate 41 to make the uneven surface easier to understand. FIG. 4(b) is a cross-sectional view, and FIG. 4(c) is a plan view of the uneven surface. The protrusions 411 and recesses 412 are alternately arranged in the X direction. Such unevenness is formed by, for example, etching. As an example, the thickness of the vibration plate 41 is 8 μm for the protrusions 411 and 4 μm for the recesses 412. The alignment of the vibration plate 41 with the piezoelectric actuators 5 (511, 512) will be described later.

[0023] The pressure chambers 42 are formed in the pressure chamber substrate 4. The multiple pressure chambers 42 are arranged at the positions of the nozzles 24 and are each connected to one of the nozzles 24. As an example, the pressure chambers 42 are formed by forming rectangular openings that penetrate in the second direction, for example, the Z direction, in the pressure chamber substrate 4, and closing the openings on both sides with the nozzle plate 23 and the diaphragm 41, respectively, to form spaces to be filled with ink. In other words, the diaphragm 41 constitutes part of the partition wall of the pressure chamber 42.

[0024] The pressure chambers 42 communicate with guide channels 43 having narrowed portions, and further communicate with an ink supply manifold 45 via ink supply ports 44, which are openings formed in the vibration plate 41. The guide channels 43 are formed in the shape of grooves in a third direction, for example, the Y direction, on one surface of the pressure chamber substrate 4 facing the vibration plate 41, for each pressure chamber 42. The ink supply manifold 45 is formed within a frame 46 joined to one surface of the vibration plate 41. The ink supply manifold 45 extends in the X direction and communicates with the pressure chambers 42 of each channel via the ink supply ports 44 and guide channels 43 of each channel. The ink supply manifold 45, which serves as a common ink chamber, communicates with the ink channels 311 (see FIGS. 1 and 2).

[0025] The piezoelectric actuators 5 (511, 512) are arranged on the uneven surface of the vibration plate 41. The piezoelectric actuators 5 (511, 512) include a first piezoelectric actuator 511 that forms a channel for ejecting ink from the nozzle 24, and a second piezoelectric actuator 512 that is not used for ejecting ink. Therefore, the number of piezoelectric actuators 5 (511, 512) is greater than the number of pressure chambers 42 that communicate with the nozzle 24. The second piezoelectric actuators 512 that are not used for ejecting ink are not arranged in positions corresponding to the pressure chambers 42 that communicate with the nozzle 24, but are used for measuring electromotive force. The electromotive force is measured to check whether the convex portions 411 of the vibration plate 41 and the first piezoelectric actuator 511 are correctly aligned, as will be described in detail later.

[0026] The piezoelectric actuators 5 (511, 512) are arranged alternately with the support columns 50 along the arrangement direction of the nozzles 24 in the X direction. The first piezoelectric actuators 511 constituting the ejection channels are arranged at positions facing the pressure chambers 42, sandwiching the convex portions 411 of the vibration plate 41. The width of the convex portions 411 in the X direction is set to be the same as the column width of the first piezoelectric actuator 511. Therefore, the concave portions 412 of the vibration plate 41 are located in the gaps 59 between the first piezoelectric actuators 511 and the support columns 50, and become the portions that are distorted when the first piezoelectric actuators 511 are driven. The width of the convex portions 411 in the Y direction (see FIG. 4(c)) is also set to be the same as the column width of the first piezoelectric actuator 511 in the Y direction.

[0027] The pillars 50 on both sides of the first piezoelectric actuator 511 are disposed at positions facing the partition walls 40 between adjacent pressure chambers 42, with the convex portions 411 of the vibration plate 41 sandwiched between them. The width of the convex portions 411 in the X direction is set to be the same as the column width of the pillars 50. The width of the convex portions 411 in the Y direction (see FIG. 4(c)) is also set to be the same as the column width of the pillars 50 in the Y direction.

[0028] A plurality of second piezoelectric actuators 512 (for example, two) are arranged at one end of the arrangement of the piezoelectric actuators 5 (511, 512) in the X direction. At least one of the second piezoelectric actuators 512 is arranged in a position facing the partition wall 40, with the convex portion 411 of the vibration plate 41 in between. The width of the convex portion 411 in the X direction is set so that a portion faces the column width of the second piezoelectric actuator 512. In other words, the second piezoelectric actuator 512 faces the convex portion 411 with an area narrower than that of the first piezoelectric actuator 511. The narrow area is one-third or less. The width of the convex portion 411 in the Y direction (see FIG. 4(c)) is set to be the same as the column width of the second piezoelectric actuator 512 in the Y direction.

[0029] Furthermore, at least one of the second piezoelectric actuators 512 is disposed at a position facing the recessed portion 412 of the vibration plate 41. In other words, this second piezoelectric actuator 512 is not in contact with the vibration plate 41. Note that the second piezoelectric actuator 512 facing the protruding portion 411 and the second piezoelectric actuator 512 facing the recessed portion 412 do not have to be disposed at a position corresponding to the pressure chamber 42 communicating with the nozzle 24, and may be disposed at a position other than the position corresponding to the partition wall 40, such as an air chamber. However, for measuring electromotive force, which will be described later, a position corresponding to the partition wall 40 is preferable.

[0030] The piezoelectric actuators 5 (511, 512) and the diaphragm 41 are bonded together, for example, with an adhesive (except for the one facing the recess 412). Each piezoelectric actuator 5 (511, 512) is fixed by bonding one surface opposite the diaphragm 41 in the Z direction to the support member 47. As shown in FIG. 3 , the piezoelectric actuators 5 (511, 512) are multilayer piezoelectric actuators formed by alternately stacking piezoelectric bodies 51 such as piezoelectric elements (e.g., piezo elements), first internal electrodes 52, and second internal electrodes 53. The piezoelectric bodies 51 are arranged with their polarization directions opposite to each other in the Z direction, for example, and are deformed in the d33 mode. The first internal electrodes 52 and the second internal electrodes 53 are conductive films formed on the main surfaces of the piezoelectric bodies 51. The first internal electrodes 52 are formed up to one end surface of each piezoelectric actuator 5 (511, 512) in the Y direction and are connected to the first external electrodes 54 formed on this end surface. The second internal electrodes 53 are formed up to the other end faces of the piezoelectric actuators 5 (511, 512) in the Y direction, and are connected to the second external electrodes 55 formed on these end faces.

[0031] The dummy layer 58 is made of the same material as the piezoelectric body 51. The dummy layer 58 does not have an internal electrode and is not subjected to an electric field, so it does not deform. The dummy layer 58 serves as a base for fixing the piezoelectric actuators 5 (511, 512) to the support member 47 (see FIG. 4), or as a polishing allowance for polishing to achieve precision during or after assembly. The piezoelectric actuators 5 (511, 512) integrated by the dummy layer 58 constitute an actuator block 500. The support pillar 50 may be a dummy actuator formed in the same manner as the piezoelectric actuators 5 (511, 512). In this case, the support pillar 50 is also included in the actuator block 500. However, instead of being formed from a dummy actuator, the support pillar 50 may be formed from a separate member.

[0032] In the case of a piezoelectric actuator 5 (511, 512) in which multiple piezoelectric bodies 51 are stacked, for example, a first internal electrode 52 and a second internal electrode 53 are formed on the main surfaces of each piezoelectric body 51 processed into a thin plate. The piezoelectric bodies 51 are then stacked together and fired to form a single body. Then, a first external electrode 54 and a second external electrode 55 are formed. The piezoelectric bodies 51 are then polarized using a polarization voltage. The piezoelectric bodies 51 are formed from a lead-containing piezoelectric material such as lead zirconate titanate (PZT) or a lead-free piezoelectric material such as sodium potassium niobate. The first internal electrode 52 and the second internal electrode 53 are formed from a sinterable conductive material such as silver-palladium. The first external electrode 54 and the second external electrode 55 are formed from Ni, Cr, Au, or the like using a known method such as plating or sputtering.

[0033] The first external electrodes 54 of each channel that ejects ink are connected to individual wiring 56 of the flexible printed wiring board 21 (see FIG. 3). The flexible printed wiring board 21 includes a substrate 26, individual wiring 56, an adhesive layer 27, and an insulating layer 28. The flexible printed wiring board 21 is disposed so that the area where the solder plating layer 29 is formed faces the first external electrodes 54, and the first external electrodes 54 and the individual wiring 56 of each channel are electrically and mechanically connected by melting the solder. Instead of solder, anisotropic conductive film (ACF), anisotropic conductive paste (ACP), non-conductive film (NCF), non-conductive paste (NCP), or the like may be used for fixing and for anisotropic conductive connection in the thickness direction. Meanwhile, the second external electrodes 55 of each channel are connected to a common wiring (not shown) and, for example, connected to ground (GND) via the flexible printed wiring board 21.

[0034] FIG. 6 shows an example of a drive circuit for the inkjet head 100. As shown in FIG. 6, the first piezoelectric actuator 511 of each channel (#1ch to #nch) has its first external electrode 54 connected to an individual wiring 56, which is connected to the output terminal of the drive driver D (i.e., the drive circuit) of the drive IC 3. The connection point between the first external electrode 54 and the individual wiring 56 is the individual terminal of the first piezoelectric actuator 511. The second external electrode 55 is connected to a common wiring 57 and is connected to a common potential. The connection point between the second external electrode 55 and the common wiring 57 is the common terminal of the first piezoelectric actuator 511.

[0035] The driving IC 3 is connected to a power supply 7 for a driving voltage V1 and a power supply 70 for a driving voltage V2 that are applied to the first piezoelectric actuator 511 when ejecting ink. The positive terminals of the power supplies 7 and 70 are connected to the driving IC 3, and the negative terminals are connected to ground (GND). The driving IC 3 is connected to a signal line for print data sent from the control board 17 (see FIG. 1), which is the control unit of the inkjet printer 10. The print data is an example of a control signal. A common wiring 57 from the common terminal of the first piezoelectric actuator 511 is connected to ground (GND).

[0036] The second piezoelectric actuator 512 has its first external electrode 54 and second external electrode 55 connected to an inspection jig 8. The inspection jig 8 is preferably detachably connected to the inkjet head 100 and removed once the inspection is complete. The inspection jig 8 includes a detection circuit 81 that measures the electromotive force of the second piezoelectric actuator 512. The detection circuit 81 is composed of a reset switch 82 and a voltmeter 83. The detection circuit 81 connects wiring to the first external electrode 54 and the second external electrode 55 of the second piezoelectric actuator 512 and measures the voltage between the terminals at the connection point. In other words, the detection circuit 81 is configured to be able to measure the terminal voltage of the second piezoelectric actuator 512. As another example, connection terminals for connecting the wiring of the detection circuit 81 may be provided on the flexible printed wiring board 21 or the printed circuit board 22, making the wiring of the detection circuit 81 detachable.

[0037] The following describes alignment when assembling the inkjet head 100 using the detection circuit 81. As shown in FIG. 7, the inkjet head 100 is made up of a first structure formed by bonding together a nozzle plate 23, a pressure chamber substrate 4, and a diaphragm 41. The second structure is formed by bonding together an actuator block 500 and a support member 47. The first structure and the second structure, which have been assembled separately, are then aligned and bonded together. At this time, alignment may be performed after applying uncured adhesive to the bonding surfaces, or the adhesive may be applied after confirming that proper alignment can be achieved.

[0038] When aligning the first structure and the second structure, it is important to align the center line of the convex portion 411 of the vibration plate 41 in the X direction with the center line of the column width of the opposing first piezoelectric actuator 511. The first piezoelectric actuator 511, which is driven during ink ejection, presses the convex portion 411 of the vibration plate 41 to distort the concave portions 412 on both sides of it, thereby changing the volume of the pressure chamber 42. Therefore, it is necessary to correctly align the first piezoelectric actuator 511 and the convex portion 411 in the X direction. Similarly, for the support column 50, it is desirable that the center line of the convex portion 411 of the vibration plate 41 in the X direction with the center line of the column width of the opposing support column 50. However, it is difficult to correctly align the multiple first piezoelectric actuators 511 with the multiple convex portions 411 of the vibration plate 41. Furthermore, since the bonding area cannot be optically observed after bonding, it is difficult to determine whether the alignment is correct.

[0039] Therefore, a second piezoelectric actuator 512 is provided. Prior to joining the first structure and the second structure described above, a detection circuit 81 that measures the electromotive force of the second piezoelectric actuator 512 turns on a reset switch 82 to discharge the charge accumulated in the second piezoelectric actuator 512. Next, after turning off the reset switch 82, the first structure and the second structure are aligned and pressed together. When pressed together, if the second piezoelectric actuator 512 is compressed, an electromotive force is generated due to the piezoelectric action of the piezoelectric element, and this is detected by a voltmeter 83. When pressed together, if the second piezoelectric actuator 512 is not compressed, no electromotive force is generated due to the piezoelectric action of the piezoelectric element, and the value of the voltmeter 83 does not change.

[0040] One of the second piezoelectric actuators 512 faces the recessed portion 412 of the diaphragm 41, so if they face each other correctly, the value on the voltmeter 83 will not change. One of the second piezoelectric actuators 512 faces a part of the protruding portion 411 of the diaphragm 41, so if they face each other correctly, the value on the voltmeter 83 will change. In other words, when the electromotive force of the second piezoelectric actuator 512 facing the recessed portion 412 is not detected and the electromotive force of the second piezoelectric actuator 512 facing the protruding portion 411 is detected, it can be determined that they are correctly aligned or that even a slight misalignment is within an allowable range that does not affect the ejection of ink.

[0041] In contrast, if the first structure is shifted in either direction in the X direction and the second piezoelectric actuator 512 that should face the recess 412 runs onto one of the protrusions 411, the value of the voltmeter 83 will change. In this case, it is determined that the alignment is incorrect, and the alignment of the first structure and the second structure is redone before the adhesive hardens.

[0042] Another of the second piezoelectric actuators 512 faces the convex portion 411 of the diaphragm 41, so if they face each other correctly, the value on the voltmeter 83 will change. In contrast, if the first structure is shifted to one side in the X direction (the left side of the paper in FIG. 7) and the second piezoelectric actuator 512 is in a position that does not face the convex portion 411, the value on the voltmeter 83 will not change. In this case, it is determined that the alignment is not correct, and the alignment of the first structure and the second structure is redone. Conversely, if the first structure is shifted to the other side (the right side of the paper in FIG. 7), the value on the voltmeter 83 will still change, but since the value on the voltmeter 83 of the second piezoelectric actuator 512 facing the concave portion 412 changes as described above, it can be determined that the alignment is not correct.

[0043] As described above, by checking the presence or absence of electromotive force of the second piezoelectric actuator 512 during the bonding process, it is possible to determine whether the X-direction positions of the first piezoelectric actuator 511 and the convex portion 411 of the diaphragm 41 are correct. In addition, by arranging both the second piezoelectric actuator 512 facing the concave portion 412 and the second piezoelectric actuator facing the convex portion 411, it is possible to determine in which direction the misalignment in the X-direction exists. Therefore, when realigning the first structure and the second structure, it is also possible to determine how to correct the position. Alternatively, the fine adjustment stage can be used to first check the position without applying adhesive, and after confirming that the position is correct, adhesive can be applied and fixed. A thermosetting resin adhesive can also be used, and after confirming that the position is correct, it can be heat-cured. Furthermore, by capturing the timing at which an electromotive force is generated in the second piezoelectric actuator 512 facing the convex portion 411, it is possible to know the timing at which the first structure and the second structure come into contact, and it is also possible to adjust the positional relationship in the Z direction between the first structure and the second structure during bonding, thereby preventing poor contact between the first structure and the second structure or, conversely, damage due to excessive pressure.

[0044] In this embodiment, the electromotive force of the piezoelectric effect generated in the second piezoelectric actuator 512 is measured using a voltmeter 83 as the inspection jig 8, but the detection jig 8 is not limited to this. For example, if an impedance analyzer is used as the inspection jig 8 to monitor the impedance of the terminals of the second piezoelectric actuator 512, it can be determined whether or not the piezoelectric actuators 5 (511, 512, excluding the one facing the recessed portion 412) have hit the convex portion 411 of the diaphragm 41 from a change in resonance characteristics when the piezoelectric actuators 5 hit the convex portion 411 of the diaphragm 41. For example, if a capacitance meter is used as the inspection jig 8 to monitor the capacitance of the terminals of the second piezoelectric actuator 512, it can be determined whether or not the piezoelectric actuators 5 (511, 512, excluding the one facing the recessed portion 412) have hit the convex portion 411 of the diaphragm 41 from a decrease in capacitance when the piezoelectric actuators 5 hit the convex portion 411 of the diaphragm 41 and are restrained.

[0045] The tolerance for misalignment between the first piezoelectric actuator 511 and the convex portion 411 of the diaphragm 41 can be adjusted by adjusting the distance (L1 in FIG. 7) between the second piezoelectric actuator 512 facing the concave portion 412 and the convex portion 411 of the adjacent diaphragm 41. Similarly, the tolerance for misalignment can also be adjusted by adjusting the overlap amount (L2 in FIG. 7) of the second piezoelectric actuator 512 facing the convex portion 411. Note that, as a preferred example, both the second piezoelectric actuator 512 facing the concave portion 412 and the second piezoelectric actuator facing the convex portion 411 are disposed, but either one may be used. Alternatively, a set of the second piezoelectric actuator 512 facing the concave portion 412 and the second piezoelectric actuator facing the convex portion 411 may be disposed on both ends of the arrangement of the piezoelectric actuators 5 (511, 512) in the X direction.

[0046] Thereafter, a frame 46 that forms the ink supply manifold 45 is attached, and the flexible printed wiring board 21 and the printed circuit board 22 are connected to assemble the inkjet head 100 shown in FIG.

[0047] Next, the ink ejection operation will be described with reference to Figures 8 and 9. Each driver D of the driver IC 3 applies a drive waveform to the individual electrode 54 of the first piezoelectric actuator 511 using drive voltages V1, V2, and ground (GND). The voltage V1 is, for example, 20V. The voltage V2 is, for example, 10V. The ground (GND) is, for example, 0V. Which channel's first piezoelectric actuator 511 is driven is based on, for example, print data. Figure 8 shows an example of a drive waveform applied to the first piezoelectric actuator 511.

[0048] As shown in FIG. 8, when the first piezoelectric actuator 511 is driven with a ground potential applied to the common electrode 55, a voltage V2 is applied to the individual electrode 54 to place the actuator in a standby state. When the voltage V2 is applied, an electric field is applied in the direction of the polarization axis of the piezoelectric body 51. Due to the inverse piezoelectric effect of the piezoelectric element, the first piezoelectric actuator 511 expands in the stacking direction (Z direction), reducing the volume of the pressure chamber 42, as shown in FIG. 9(a). This is performed prior to the ink ejection timing. Then, at the ink ejection timing (time t1 in FIG. 8), the potential of the individual electrode 54 is first lowered to ground (GND). As shown in FIG. 9(b), the expanded first piezoelectric actuator 511 returns to its original state, i.e., contracts relatively, and the volume of the pressure chamber 42 expands relatively. Ink flows into the pressure chamber 42 via the guide channel 43 by the amount of expansion of the pressure chamber 42.

[0049] Then, for example, after half the pressure vibration period of the head unit 2 has elapsed, if a voltage V2 is applied to the individual electrode 54 at time t2 in FIG. 8, the first piezoelectric actuator 511 expands in the stacking direction (Z direction), as shown in FIG. 9(c), causing the volume of the pressure chamber 42 to relatively shrink, resulting in the ejection of an ink droplet R from the nozzle 24. Then, for example, after half the pressure vibration period of the head unit 2 has elapsed, at time t3 in FIG. 8, a voltage V1 is applied to the individual electrode 54, and then returned to voltage V2 a predetermined time later at time t4. The expansion (FIG. 9(d)) and return (FIG. 9(a)) of the first piezoelectric actuator 511 at this time reduces and returns the volume of the pressure chamber 42, and this operation damps residual vibration. In this way, the volume of the pressure chamber 42 changes in accordance with the longitudinal vibration of the first piezoelectric actuator 511 in the stacking direction, allowing ink to be ejected.

[0050] As described above, according to the above-described embodiment, it is possible to provide an inkjet head 100 that can stably eject ink by using the second piezoelectric actuator 512 to correctly align the first piezoelectric actuator 511, which is driven during ink ejection operation, with the convex portion 411 of the vibration plate 41. Furthermore, although alignment in the X direction has been described in detail as a preferred example, it may also be applied to alignment in the Y direction.

[0051] The piezoelectric actuator 5 is not limited to a laminated type in which multiple piezoelectric bodies 51 are stacked. The piezoelectric body 51 may be a single-layer piezoelectric actuator. Furthermore, the operation of the actuator when a drive voltage is applied is not limited to longitudinal vibration. Furthermore, it is not limited to a drop-on-demand piezoelectric system, and may be applied to a continuous system.

[0052] In the above embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection device, but the liquid ejection device may also be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0053] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0054] 10. Inkjet printer 100~103 Inkjet head 24 nozzles 3 Driver IC 41 Vibration plate 411 Convex 412 recess 42 Pressure Chamber 5 Piezoelectric Actuators 511 First Piezoelectric Actuator 512 Second Piezoelectric Actuator

Claims

1. a plurality of pressure chambers each communicating with a nozzle; a vibration plate that forms a part of the partition wall of the pressure chamber and has a plurality of projections and recesses on its surface; a plurality of piezoelectric actuators arranged on a surface of the vibration plate having irregularities, the number of which is greater than the number of pressure chambers communicating with the nozzles; The plurality of piezoelectric actuators include a first piezoelectric actuator that is disposed for each pressure chamber communicating with the nozzle at a position facing the convex portion of the vibration plate, and that presses the convex portion to change the volume of the pressure chamber, thereby discharging liquid from the nozzle; a second piezoelectric actuator that is not disposed at a position corresponding to a pressure chamber that communicates with the nozzle, and that is wired so that a terminal voltage can be measured.

2. 2. The liquid ejection head according to claim 1, wherein at least one of the second piezoelectric actuators faces a recess of the vibration plate.

3. 2. The liquid ejection head according to claim 1, wherein at least one of the second piezoelectric actuators faces the convex portion of the vibration plate over an area smaller than that of the first piezoelectric actuator.

4. 4. The liquid ejection head according to claim 3, wherein the small area is equal to or less than one-third of the area of ​​the first piezoelectric actuator facing the convex portion of the vibration plate.

5. A liquid ejection head as described in claim 3, characterized in that the second piezoelectric actuator facing the convex portion of the vibration plate generates an electromotive force in the wiring due to the piezoelectric effect of the piezoelectric element when the piezoelectric actuator and the vibration plate are correctly aligned.

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