Liquid ejection head

Abstract

To provide a liquid discharge head which can re-polarize a piezoelectric actuator.SOLUTION: A liquid discharge head includes piezoelectric actuators, a drive IC, and a switching circuit. The plurality of piezoelectric actuators includes piezoelectric substances, one terminals giving a drive voltage, and other terminals giving a common potential. The drive IC includes a plurality of drive circuits for outputting the drive voltage and driving the piezoelectric actuators at the time of liquid discharge operation, and a plurality of diodes which is connected between output terminals of the respective drive circuits and a reference potential in a non-conductive direction when the drive circuits output the drive voltage. The switching circuit switches whether the other terminals of the piezoelectric actuators are connected to the common potential or a polarization voltage source. The liquid discharge head opens the other power source terminals of the drive IC, switches the switch circuit so as to connect the other terminals to the polarization voltage source, and gives a polarization voltage to the piezoelectric actuators through diodes, at the time of execution of polarization of the piezoelectric substances.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Embodiments of the present invention relate to a liquid ejection head.

Background Art

[0002] A liquid ejection head that supplies a predetermined amount of liquid to a predetermined position is known. The liquid ejection head is mounted on, for example, an inkjet printer, a 3D printer, a dispensing device, etc. An inkjet printer ejects ink droplets from an inkjet head to form an image or the like on the surface of a recording medium. A 3D printer ejects droplets of a modeling material from a modeling material ejection head and cures them to form a three-dimensional object. A dispensing device ejects droplets of a sample and supplies a predetermined amount to a plurality of containers or the like.

[0003] The liquid ejection head has a plurality of channels for ejecting liquid. Each channel includes a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and an actuator for changing the volume of the pressure chamber. The liquid ejection head selects a channel for ejecting liquid from among the plurality of channels and drives it by applying a drive signal to the actuator. When the actuator is driven, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle.

[0004] A piezoelectric actuator that is driven using the piezoelectric effect of a piezoelectric body is polarized in the polarization direction that realizes the function of changing the volume of the pressure chamber. However, the piezoelectric body may undergo polarization degradation, for example, during the manufacturing process of the liquid ejection head or while the liquid ejection head is in normal use. When polarization degradation occurs, the liquid ejection performance of the liquid ejection head may deteriorate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a liquid ejection head capable of polarizing the piezoelectric body of a piezoelectric actuator with a driving IC mounted thereon.

Means for Solving the Problems

[0007] The liquid ejection head according to an embodiment of the present invention includes a piezoelectric actuator, a driving IC (Integrated Circuit), and a switching circuit. The plurality of piezoelectric actuators include a piezoelectric body, one terminal to which a driving voltage is applied, and the other terminal to which a common potential is applied. The driving IC includes a plurality of driving circuits that output the driving voltage to drive the piezoelectric actuator during the liquid ejection operation, and a plurality of diodes respectively connected in a direction that does not conduct when the driving circuit outputs the driving voltage between the output terminal of each driving circuit and the reference potential. The switching circuit switches whether to connect the other terminal of the piezoelectric actuator to the common potential or to a polarization voltage source. The liquid ejection head releases the other power supply terminal of the driving IC during polarization execution of the piezoelectric body, switches the switching circuit to connection with the polarization voltage source, and applies a polarization voltage to the piezoelectric actuator via the diode.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

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

[0010] As an example of an image forming apparatus equipped with the liquid ejection head of the 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 the housing 11 of the inkjet printer 10, there are arranged a cassette 12 for storing a sheet S which is an example of a recording medium, an upstream conveyance path 13 of the sheet S, a conveyance belt 14 for conveying the sheet S taken out from the cassette 12, a plurality of inkjet heads 100 to 103 for ejecting ink droplets toward the sheet S on the conveyance belt 14, a downstream conveyance path 15 of the sheet S, a discharge tray 16, and a control board 17. An operation unit 18 which is a user interface is arranged on the upper side of the housing 11.

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

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

[0013] The conveyance belt 14 is a net-like endless belt having a large number of through holes formed on its surface. The three rollers of the drive roller 141, the driven rollers 142, 143 rotatably support the conveyance belt 14. The motor 205 rotates the conveyance belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. The 105 in the figure indicates the rotation direction of the conveyance belt 14. A negative pressure container 206 is arranged on the back side of the conveyance belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates a negative pressure inside the negative pressure container 206 by the formed air flow, and adsorbs and holds the sheet S on the upper surface of the conveyance belt 14. The 106 in the figure indicates the flow of the air flow.

[0014] The inkjet heads 100 to 103, which are examples of liquid ejection heads, are arranged to face the sheet S adsorbed and held on the conveyance belt 14 with a slight gap of, for example, 1 mm therebetween. The inkjet heads 100 to 103 eject ink droplets toward the sheet S, respectively. The inkjet heads 100 to 103 print an image when the sheet S passes below. Each of the inkjet heads 100 to 103 has the same structure except that the colors of the ejected ink are different. The colors of the ink are, for example, cyan, magenta, yellow, and black.

[0015] The inkjet heads 100 to 103 are each connected to the ink tanks 315 to 318 and the ink supply pressure regulators 321 to 324 via the ink flow paths 311 to 314. Each of the ink tanks 315 to 318 is disposed above each of the inkjet heads 100 to 103. During standby, each of the ink supply pressure regulators 321 to 324 adjusts the pressure inside each of the inkjet heads 100 to 103 to a negative pressure with respect to the atmospheric pressure, for example, -1.2 kPa, so that ink does not leak from the nozzles 24 (see FIG. 2) of the inkjet heads 100 to 103. During image formation, the ink in each of the ink tanks 315 to 318 is supplied to each of the inkjet heads 100 to 103 by the ink supply pressure regulators 321 to 324.

[0016] After image formation, the sheet S is sent from the conveyance belt 14 to the downstream conveyance path 15. The downstream conveyance path 15 is composed of the feed roller pairs 151, 152, 153, 154 and the sheet guide plates 155, 156 that define the conveyance path of the sheet S. The sheet S is sent from the discharge port 157 to the discharge tray 16 via the downstream conveyance path 15. The arrow 107 in the figure indicates the conveyance path of the sheet S.

[0017] Subsequently, the configuration of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 with reference to FIGS. 2 to 6, 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 portion 2 which is an example of a liquid ejection portion. The head portion 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 board 22 which is an example of an intermediate board. The head portion 2 includes a nozzle plate 23 which is an example of a nozzle portion. The head portion 2 is connected to the ink supply pressure regulator 321 in FIG. 1 via the ink flow path 311.

[0019] The nozzles 24 of each channel for ejecting ink are arranged along, for example, the X direction in the first direction of the nozzle plate 23. The nozzle density is set, for example, within the range of 150 to 1200 dpi. The nozzles 24 may be not limited to a single row but may be 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 using a synthetic resin film such as polyimide, for example. The flexible printed wiring board 21 mounts a driving IC (Integrated Circuit) 3 which is a driver chip (hereinafter referred to as the driving IC). The printed board 22 is a rigid through-hole board in which an epoxy resin layer containing glass fibers and a copper wiring layer are laminated multiple times. The driving IC 3 as the control unit temporarily stores the print data sent from the control board 17 of the inkjet printer 10 via the printed board 22, and gives a driving signal to each channel so as to eject ink at a predetermined timing.

[0021] FIGS. 3 to 5 are partial cross-sectional views of the head unit 2. The nozzle plate 23 is joined to one surface of the pressure chamber substrate 4. The nozzle plate 23 is a rectangular plate formed of a resin such as polyimide or a metal such as stainless steel, for example. The diaphragm 41 is joined to one surface of the pressure chamber substrate 4 on the side opposite to the nozzle plate 23. The diaphragm 41 has flexibility to deform when an external force is applied. The diaphragm 41 is a rectangular plate formed of, for example, a flexible polyimide film or metal.

[0022] The pressure chamber 42 is formed in the pressure chamber substrate 4. The plurality of pressure chambers 42 are arranged at the positions of the respective nozzles 24 and are communicated with the nozzles 24 respectively. As an example, the pressure chamber 42 forms a rectangular opening penetrating in the Z direction, for example, in the second direction in the pressure chamber substrate 4, and the openings on both sides are closed by the nozzle plate 23 and the diaphragm 41 respectively, thereby forming a space for filling ink. The pressure chamber 42 communicates with the guide flow path 43 and further communicates with the ink supply manifold 45 through the ink supply port 44 which is an opening hole formed in the diaphragm 41. The guide flow path 43 is formed in a groove shape in the Y direction, for example, in the third direction, on one surface of the pressure chamber substrate 4 on the diaphragm 41 side for each pressure chamber 42. The ink supply manifold 45 is formed in the frame 46 joined to one surface of the diaphragm 41. The ink supply manifold 45 extends in the X direction and communicates with the pressure chambers 42 of the respective channels through the ink supply ports 44 and the guide flow paths 43 of the respective channels. The ink supply manifold 45 as a common ink chamber communicates with the ink flow path 311 (see FIGS. 1 and 2).

[0023] The piezoelectric actuator 5 is arranged on one surface of the diaphragm 41 on the side opposite to the pressure chamber 42. The piezoelectric actuators 5 of the respective channels are arranged at positions facing the pressure chamber 42 and the guide flow path 43 with the diaphragm 41 interposed therebetween. The piezoelectric actuator 5 and the diaphragm 41 are joined with, for example, an adhesive. Each piezoelectric actuator 5 is fixed by joining one surface on the side opposite to the diaphragm 41 in the Z direction to the support member 47 respectively.

[0024] Particularly, as shown in FIG. 3, the piezoelectric actuator 5 is a laminated piezoelectric actuator 5 formed by alternately laminating piezoelectric bodies 51 such as piezo elements, first internal electrodes 52, and second internal electrodes 53 in a layered manner. Each piezoelectric body 51 has its polarization directions arranged in opposite directions to each other, for example, in the Z direction, and is deformed in the d33 mode. The first internal electrode 52 and the second internal electrode 53 are conductive films formed on the main surfaces of the piezoelectric body 51, respectively. The first internal electrode 52 is formed up to one end face of the piezoelectric actuator 5 in the Y direction and is connected to the first external electrode 54 formed on this end face. The second internal electrode 53 is formed up to the other end face of the piezoelectric actuator 5 in the Y direction and is connected to the second external electrode 55 formed on this end face. The dummy layer 58 is made of the same material as the piezoelectric body 51. The dummy layer 58 has internal electrodes provided only on one side and is not deformed because no electric field is applied. The dummy layer 58 serves as a base for fixing the piezoelectric actuator 5 to the support member 47 (see FIG. 4), or serves as a grinding allowance for polishing to achieve accuracy during or after assembly.

[0025] Particularly, as shown in FIG. 4, between the piezoelectric actuators 5 of each channel, a piezoelectric actuator 50 having the same configuration is arranged via a groove 59 and may be, for example, a support column. The piezoelectric actuator 50 is arranged at a position corresponding to the partition wall 40 between adjacent pressure chambers 42. This piezoelectric actuator 50 is not used for the ink ejection operation, but may be used for ink ejection.

[0026] In the case of the piezoelectric actuator 5 in which a plurality of piezoelectric bodies 51 are laminated, as an example, a first internal electrode 52 and a second internal electrode 53 are respectively formed on the main surfaces of the piezoelectric bodies 51 processed into thin plate shapes. Then, after laminating and firing the piezoelectric bodies 51, a voltage is applied between the first internal electrode 52 and the second internal electrode 53 to polarize the piezoelectric bodies 51. Thereafter, a first external electrode 54 and a second external electrode 55 are formed. The piezoelectric body 51 is formed of 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 of a sinterable conductive material such as silver palladium. The first external electrode 54 and the second external electrode 55 are formed of Ni, Cr, Au, etc. by a known method such as a plating method or a sputtering method.

[0027] The first external electrode 54 of each channel is connected to the individual wiring 56 of the flexible printed wiring board 21 respectively. The flexible printed wiring board 21 has a base material 26, individual wirings 56, an adhesive layer 27, and an insulating layer 28. The flexible printed wiring board 21 is arranged such that a region where a solder plating layer 29 is formed faces the first external electrode 54, and the first external electrode 54 of each channel and the individual wiring 56 are electrically and mechanically connected by melting the solder. On the other hand, the second external electrode 55 of each channel is connected to a common wiring (not shown) and is connected to the ground (GND) via the flexible printed wiring board 21, for example.

[0028] FIG. 6 is a circuit diagram of the control system of the inkjet head 100. As shown in FIG. 6, the piezoelectric actuator 5 connects the first external electrode 54 to the individual wiring 56 and connects it to the output terminal of the drive IC 3 via the individual wiring 56. The second external electrode 55 is connected to the common wiring 57 and is connected to the ground (GND) via the common wiring 57. The ground (GND) is an example of a common potential. The connection point of the first external electrode 54 and the individual wiring 56 is one terminal of the piezoelectric actuator 5. The connection point of the second external electrode 55 and the common wiring 57 is the other terminal of the piezoelectric actuator 5. In the following description, one terminal is referred to as an individual terminal and the other terminal is referred to as a common terminal.

[0029] Individual wirings 56 from the individual terminals of each piezoelectric actuator 5 are respectively connected to the output terminals of the drive driver D (i.e., the drive circuit) of the drive IC 3. The drive IC 3 includes an output protection diode 31 that protects the drive driver D. The output protection diode 31 is, for example, a diode with its cathode connected to the output terminal of the drive driver D and its anode connected to the ground (GND) of the drive IC 3. The output protection diode 31 is provided for each drive driver D of each channel. When a parasitic diode is formed by the structure of the transistor in the output circuit, the parasitic diode may be used instead of the output protection diode. The output protection diode 31 or the parasitic diode is an example of a diode connected in a direction that does not conduct when the drive IC 3 outputs a drive voltage between the output terminal of the drive IC 3 and the reference potential. As a preferable example of this reference potential, it is connected to the same ground (GND) as the common potential applied to the common terminal of each piezoelectric actuator 5, but it does not necessarily have to be the same as the common potential applied to the common terminal.

[0030] The drive IC 3 is connected to a power supply (drive power supply) 32 for the drive voltage V1 applied to the piezoelectric actuator 5. The drive power supply 32 has its positive electrode connected to the drive IC 3 and its negative electrode connected to the ground (GND). That is, in this example, a positive voltage is used as the drive voltage V1. The switch SW1 as the first switch turns on and off the connection between the drive power supply 32 and the drive IC 3. The drive IC 3 is connected to the signal line of the print data sent from the control board 17 (see FIG. 1) of the inkjet printer 10. The print data is an example of a control signal. The switch SW2 as the second switch turns on and off the connection between the drive IC 3 and the signal line.

[0031] The common wiring 57 from the common terminal of each piezoelectric actuator 5 is commonly connected to the ground (GND). The polarization circuit 6 for polarizing the piezoelectric actuator 5 is commonly connected to the common terminal of the piezoelectric actuator 5 using a part of the common wiring 57. The switch SW3 as the third switch switches whether to commonly connect the common terminal of the piezoelectric actuator 5 to the ground (GND) or to the polarization circuit 6. The polarization circuit 6 includes a power supply (polarization power supply) 61 for the polarization voltage V2 applied to the piezoelectric actuator 5. The positive electrode of the polarization power supply 61 is connected to the ground (GND) terminal of the drive IC3. That is, the positive electrode of the polarization power supply 61 is connected to the anode of the output protection diode 31. The negative electrode of the polarization power supply 61 is commonly connected to the common terminal of the piezoelectric actuator 5 via the resistor R1 and the resistor R3. The polarization power supply 61 is, for example, a 70V power supply. The polarization power supply 61 is an example of a polarization voltage source. The switch SW4 as the fourth switch, when set to the B side, connects the polarization power supply 61 to the individual terminal of the piezoelectric actuator 5 via the output protection diode 31, and when set to the A side, disconnects this and discharges the capacitor C1 described later.

[0032] The switch SW3 is formed, for example, on the printed circuit board 22 (see FIG. 2). The switch SW3 is an example of a switching circuit that switches whether to connect the other terminal of the piezoelectric actuator 5 to a common potential or to a polarization voltage source. The polarization circuit 6 may be formed, for example, on a separate substrate, connected to the inkjet head 100 during polarization execution, and removed after polarization is completed. Instead of forming the switch SW3 on the printed circuit board 22, it may be configured to perform the function of the switch SW3 by this attachment and detachment. Also, by this attachment and detachment, the polarization circuit 6 may be configured to be shared by a plurality of inkjet heads 100. Polarization is desirably performed, as an example, after assembling the inkjet head 100, when polarization deterioration is a concern, such as when the usage time of the inkjet head 100 reaches a predetermined value. However, the polarization may be re-polarization or initial polarization of the piezoelectric body 51.

[0033] The polarization circuit 6 includes a time constant circuit 62 as a first time constant circuit. The time constant circuit 62 is formed by connecting a capacitor C1 and a resistor R1 in series, and a resistor R2 is further connected between the capacitor C1 and the resistor R1. The resistance value of the resistor R2 is made smaller than the resistance value of the resistor R1. The resistor R2 is a current limiting resistor that protects the capacitor C1 from overcurrent when the switch SW4 is set to the A side to discharge the capacitor C1.

[0034] A resistor R3 is connected between the time constant circuit 62 and the switch SW3 in the polarization circuit 6. The resistor R3 forms a second time constant circuit in combination with the capacitance of the piezoelectric actuator 5. The resistor R3 is a current limiting resistor that protects the piezoelectric actuator 5 from overcurrent when the piezoelectric actuator 5 is connected to the polarization power supply 61. The time constant of the time constant circuit 62 is made larger than the time constant of the second time constant circuit.

[0035] Here, as an example, the case where the capacitance per piezoelectric actuator 5 is 1000 pF and the number of piezoelectric actuators 5 is 300 (i.e., the number of channels is 300) will be described. The polarization power supply 61 uses, for example, a 70 V power supply. The capacitance of the capacitor C1 is, for example, 1 μF. The resistor R1 is, for example, 1 MΩ. The resistor R2 is, for example, 1 kΩ. In this case, the time constant of the time constant circuit 62 is 1 μF × (1 MΩ + 1 kΩ) = approximately 1 second. On the other hand, the resistor R3 that constitutes the second time constant circuit in combination with the capacitance of the piezoelectric actuator 5 is, for example, 1 MΩ. In this case, the time constant of the second time constant circuit is 1000 pF × 300 ch × 1 MΩ = approximately 0.3 seconds. Therefore, the rise time of the polarization voltage to the piezoelectric actuator 5 is limited by the time constant of the time constant circuit 62.

[0036] Subsequently, the ink ejection operation and the polarization operation will be described with reference to FIG. 6. First, in the operation of discharging ink, which is the normal operation, both the switch SW1 of the drive power supply 32 and the switch SW2 of the signal line are turned ON. That is, the drive power supply 32 and the signal line of the print data are connected to the drive IC3. Further, both the switch SW3 and the switch SW4 are set to the A side. That is, the common terminal of the piezoelectric actuator 5 is commonly connected to the ground (GND), and the ground (GND) potential, which is the reference potential, is applied. The ground potential is, for example, 0V.

[0037] Based on the print data, the drive IC3 outputs a drive voltage V1 from the drive driver D of the channel for discharging ink. The drive voltage V1 is a positive voltage lower than the polarization voltage. The drive voltage V1 is applied to the individual terminal of the piezoelectric actuator 5 via the individual wiring 56. By applying the drive voltage V1 to one terminal of the piezoelectric actuator 5 in the standby state, an electric field is applied in the direction of the polarization axis of the piezoelectric body 51, and the piezoelectric actuator 5 is extended to make the volume of the pressure chamber 42 contract. Then, when the potential of one terminal of the piezoelectric actuator 5 is dropped to the ground, the piezoelectric actuator 5 returns to its original state, and at this time, the volume of the pressure chamber 42 relatively expands. As much as the volume of the pressure chamber 42 expands, ink flows into the pressure chamber 42 through the guide channel 43. Then, when the drive voltage V1 is applied to one terminal of the piezoelectric actuator 5 again, the volume of the pressure chamber 42 contracts back to its original state. In this way, the volume of the pressure chamber 42 changes in accordance with the longitudinal vibration of the piezoelectric actuator 5, and ink is discharged from the nozzle 24. During the ink discharge operation, since the polarization power supply 62 is disconnected by the switch SW3, it does not affect the operation of the drive IC3 or the piezoelectric actuator 5.

[0038] Next, in the polarization operation, it is desirable to execute by releasing the other power supply terminals of the drive IC3. In the example of FIG. 6, in order to prevent damage to the drive IC3, it is desirable to turn off the switch SW1 and disconnect the drive power supply 32. Further, it is more preferable to turn off the switch SW2 and also disconnect the signal line from the drive IC3. Then, switch SW3 is switched to the B side, and the common terminal of the piezoelectric actuator 5 is disconnected from the ground (GND) and connected to the negative electrode of the polarization power supply 61 via the resistor R3 and the resistor R1 of the time constant circuit 62. Thereafter, switch SW4 is also switched to the B side, and the positive electrode of the polarization power supply 61 is connected to the ground (GND) terminal of the drive IC3. That is, the positive electrode of the polarization power supply 61 is commonly connected to the piezoelectric actuator 5 of each channel via the output protection diode 31 of each channel.

[0039] In order to improve the voltage efficiency of the piezoelectric actuator 5, a plurality of drive power supplies may be provided. For example, as shown in FIG. 7, a drive power supply 33 that generates a drive voltage V3 is provided and this is supplied to the other terminal of the piezoelectric actuator 5 and the drive circuit. Also in this case, the polarization is executed by turning off both the switch SW1 and the switch SW5 in order to prevent damage to the drive IC3. That is, the other power supply terminals of the drive IC3 are released to execute the polarization. The operation of the other switches during polarization is the same as in the example of FIG. 6.

[0040] Here, before switching the switch SW3 and the switch SW4 to the B side, that is, when they are on the A side, the capacitor C1 (1 μF) is discharged by the resistor R2 (1 kΩ). The voltage of the capacitor C1 (1 μF) is 0 V. After switching the switch SW3 and the switch SW4 to the B side, a charging current flows from the polarization power supply 61 through the resistors R1 and R2 to the capacitor C1 (1 μF), and the voltage of the capacitor C1 (1 μF) rises.

[0041] Then, a voltage corresponding to the voltage rise of the capacitor C1 (1 μF) is applied to the piezoelectric actuator 5 via the output protection diode 31 and the resistor R3 to charge the piezoelectric actuator 5. The voltage applied to the piezoelectric actuator 5 rises from, for example, 0 V according to the time constant of the time constant circuit 62 and saturates at 70 V of the polarization power supply 61. The charging current of the piezoelectric actuator 5 flows through the output protection diode 31 of the drive IC 3. Thus, by applying a polarization voltage to the piezoelectric actuator 5, the polarization of the piezoelectric body 51 is performed.

[0042] By commonly connecting the common terminal of the piezoelectric actuator 5 to the negative electrode of the polarization power supply 61 in this way, and further commonly connecting the positive electrode of the polarization power supply 61 to the piezoelectric actuator 5 via the output protection diodes 31 of all channels, it becomes possible to perform the polarization of the piezoelectric actuators 5 of all channels collectively.

[0043] And by setting the time constant of the time constant circuit 61 large, the current flowing through the piezoelectric actuator 5 via the output protection diode 31 of the drive IC 3 is extremely suppressed, preventing the drive IC 3 and the piezoelectric actuator 5 from being damaged during the polarization operation. Also, for example, a polarization voltage of 70 V enables the polarization of the piezoelectric body 51, but exceeds the allowable upper limit voltage as seen from the drive IC 3. Therefore, a configuration is adopted in which the polarization voltage is applied through the output protection diode 31, and only the forward voltage of the output protection diode 31 (for example, about 0.6 V) is applied to the drive IC 3 to protect the drive IC 3 from the polarization voltage.

[0044] Note that it is possible to connect the polarization power supply 61 to the piezoelectric actuator 5 via the resistor R3 without passing through the time constant circuit 62, and limit the charging current of the piezoelectric actuator 5 by the time constant of the second time constant circuit determined by the capacitance of the piezoelectric actuator 5 and the resistance value of the resistor R3. However, for example, when the number of channels is small, or when the total capacitance obtained by multiplying the capacitance of the piezoelectric actuator 5 by the number of channels is small, it may be necessary to make the resistance value of the resistor R3 extremely large in order to make the time constant of the second time constant circuit equal to or greater than a certain value. In addition, when there is a leakage current in the piezoelectric actuator 5, there is a risk that a sufficient polarization voltage may not be applied to the piezoelectric actuator 5 due to the voltage drop generated in the resistor R3 due to the leakage current. Therefore, it is desirable to provide the time constant circuit 62.

[0045] As described above, according to the above-described embodiment, it is possible to provide the inkjet head 100 capable of polarizing the piezoelectric body 51 of the piezoelectric actuator 5 with the drive IC 3 mounted thereon.

[0046] That is, the multi-channel inkjet head 100 uses the drive IC 3 in which the drive circuits are integrated in order to individually drive a large number of piezoelectric actuators 5. On the other hand, there are various factors that cause deterioration of the polarization of the piezoelectric body 51 of the piezoelectric actuator 5, and it is desirable to enable polarization even when the drive IC 3 is mounted on the inkjet head 100. However, it is necessary to avoid applying a polarization voltage of a high voltage exceeding the allowable upper limit voltage of the drive IC 3 to the drive IC. Therefore, by using the output protection diode 31 of the drive IC 3, it is possible to polarize the piezoelectric actuator 5 without damaging the drive IC 3 even when the drive IC 3 is mounted. The switches SW1 to SW4 are not limited to mechanical switches. A semiconductor switch may be used, or a configuration in which the switches SW1 to SW4 operate by attaching and detaching a connector may also be used.

[0047] Note that in the above-described embodiment, although the driving voltage V1 is a positive voltage, it should be a negative voltage when the polarization direction is reversed compared to this embodiment. When the driving voltage V1 is a negative voltage, for example, in the circuit of FIG. 6, the connections between the positive and negative electrodes of the driving power supply 32, the positive and negative electrodes of the polarization power supply 61, and the cathodes and anodes of the respective output protection diodes 31 are reversed.

[0048] Note that the piezoelectric actuator 5 is not limited to a stacked type in which a plurality of piezoelectric bodies 51 are stacked. The piezoelectric body 51 may be a single-layer piezoelectric actuator. Also, the operation of the actuator when a driving voltage is applied is not limited to longitudinal vibration. Furthermore, it is not limited to the drop-on-demand piezo method and may be applied to the continuous method.

[0049] In the above-described embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection device. However, the liquid ejection device may be a shaping material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0050] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0051] 10 Inkjet printer 100 - 103 Inkjet head 2 Head unit 23 Nozzle plate 24 Nozzle 3 Driving IC 31 Output protection diode 5 Piezoelectric actuator 56 Individual wiring 57 Common wiring 6 Polarization circuit 61 Polarized power supply 62 Time constant circuit D drive driver (drive circuit) SW1~SW4 switches

Claims

1. A plurality of piezoelectric actuators each comprising a piezoelectric body, one terminal for applying a driving voltage, and the other terminal for applying a common potential, a plurality of drive circuits that output the driving voltage to drive the piezoelectric actuators during a liquid ejection operation, and a drive IC (Integrated Circuit) comprising a plurality of diodes each connected in a direction that does not conduct when the drive circuit outputs the driving voltage, between an output terminal of each drive circuit and a reference potential, a switching circuit that switches between connecting the other terminal of the piezoelectric actuator to the common potential or to a polarization voltage source, A liquid ejection head, characterized in that, during polarization of the piezoelectric body, another power supply terminal of the drive IC is opened, the switching circuit is switched to connection with the polarization voltage source, and a polarization voltage is applied to the piezoelectric actuator via the diode.

2. A piezoelectric actuator comprising a piezoelectric body, one terminal for applying a driving voltage, and the other terminal for applying a common potential, a drive IC (Integrated Circuit) that outputs the driving voltage to drive the piezoelectric actuator during a liquid ejection operation, a diode connected in a direction that does not conduct when the drive IC outputs the driving voltage, between an output terminal of the drive IC and a reference potential, a switching circuit that switches between connecting the other terminal of the piezoelectric actuator to the common potential or to a polarization voltage source, A liquid ejection head, characterized by comprising a time constant circuit provided in a circuit that applies a polarization voltage from the polarization voltage source to the piezoelectric actuator.

3. The liquid ejection head according to claim 1, characterized in that a time constant circuit is provided in a circuit that applies the polarization voltage from the polarization voltage source to the piezoelectric actuator.

4. A resistor is connected in series to the other terminal of the piezoelectric actuator to form a second time constant circuit by the electrostatic capacitance of the piezoelectric actuator and the resistor, The liquid ejection head according to claim 2 or 3, characterized in that the time constant of the time constant circuit is larger than the time constant of the second time constant circuit.

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