Liquid discharge device

Abstract

To provide a liquid discharge device that can be improved in displacement characteristics.SOLUTION: A liquid discharge device comprises a liquid discharge head that has a first electrode, a second electrode and a piezoelectric body provided between the first electrode and the second electrode, and a voltage application part that applies a reference voltage that does not vary with time to the first electrode and applies a driving voltage that varies with time to the second electrode, so as to drive the piezoelectric body to discharge liquid, where when a drive frequency of the piezoelectric body discharging liquid is defined as a first driving frequency, an anti-voltage of the piezoelectric body obtained when driving the piezoelectric body at the first drive frequency is defined as a first anti-voltage, a drive frequency lower than the first drive frequency is defined as a second drive frequency, and an anti-voltage of the piezoelectric body obtained when driving the piezoelectric body at the second drive frequency is defined as a second anti-voltage, a differential between the reference voltage and the minimum value of the driving voltage is larger than the first anti-voltage and is smaller than the second anti-voltage.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a liquid ejection device.

Background Art

[0002] Conventionally, a liquid ejection device including a liquid ejection head that ejects a liquid such as ink onto a medium such as printing paper has been proposed. As such a liquid ejection device, a piezoelectric inkjet printer is known. In the piezoelectric method, a piezoelectric element that vibrates a diaphragm constituting a part of the wall surface of a pressure chamber is used.

[0003] In the liquid ejection head described in Patent Document 1, by applying a drive voltage to the piezoelectric element, the pressure in the pressure chamber is changed, and ink droplets are ejected from nozzles arranged opposite to the respective pressure chambers. In this liquid ejection head, the minimum value of the voltage applied to the piezoelectric body is set to be larger than the anti-voltage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By making the minimum value of the voltage applied to the piezoelectric body larger than the anti-voltage, the voltage range applied to the piezoelectric body can be made within a range where polarization reversal does not occur, so that the displacement amount of the piezoelectric element can be increased.

[0006] However, through the inventors' studies, it has been found that due to the rate-determining factor of the circuit, the counter electromotive voltage in the high-frequency band is smaller than that in the normal frequency band. That is, in the high-frequency band, if a voltage applied to the piezoelectric body is set to be larger than, for example, the counter electromotive voltage in the normal frequency band, the actual counter electromotive voltage shifts to the negative side, so there is a margin in the usable range. The present invention aims to perform piezoelectric body driving with improved displacement characteristics as much as possible considering the driving frequency.

Means for Solving the Problems

[0007] A liquid ejection device according to a preferred embodiment of the present invention includes a liquid ejection head having a first electrode, a second electrode, and a piezoelectric body provided between the first electrode and the second electrode, and a voltage application unit that applies a reference voltage that does not change over time to the first electrode and a driving voltage that changes over time to the second electrode to drive the piezoelectric body and eject liquid. The liquid ejection device is such that when the driving frequency of the piezoelectric body when ejecting liquid is a first driving frequency, the counter electromotive voltage of the piezoelectric body obtained when driving the piezoelectric body at the first driving frequency is a first counter electromotive voltage, a driving frequency lower than the first driving frequency is a second driving frequency, and the counter electromotive voltage of the piezoelectric body obtained when driving the piezoelectric body at the second driving frequency is a second counter electromotive voltage, the difference between the reference voltage and the minimum value of the driving voltage is larger than the first counter electromotive voltage and smaller than the second counter electromotive voltage.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Note that the dimensions or scales of each part in the drawings are appropriately different from the actual ones, and there are also parts that are schematically shown for easy understanding. Further, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

[0010] The following description will be made using the X-axis, Y-axis, and Z-axis that intersect each other as appropriate. One direction along the X-axis is referred to as the X1 direction, and the direction opposite to the X1 direction is referred to as the X2 direction. The directions opposite to each other along the Y-axis are referred to as the Y1 direction and the Y2 direction. The directions opposite to each other along the Z-axis are referred to as the Z1 direction and the Z2 direction. Looking in the direction along the Z-axis is referred to as "plan view". The Z-axis is typically a vertical axis. However, the Z-axis does not have to be a vertical axis. Further, the X-axis, Y-axis, and Z-axis typically intersect at right angles to each other, but are not limited thereto, and may intersect at an angle within a range of 80° or more and 100° or less, for example.

[0011] 1. This Embodiment 1-1. Overall Configuration of the Liquid Discharge Device 100 FIG. 1 is a configuration diagram schematically showing a liquid ejection device 100 according to the present embodiment. The liquid ejection device 100 is an inkjet printing device that ejects ink, which is an example of a liquid, as droplets onto a medium 12. The medium 12 is typically printing paper. Note that the medium 12 is not limited to printing paper, and may be a printing target of any material such as a resin film or a fabric, for example.

[0012] As shown in FIG. 1, a liquid container 14 for storing ink is attached to the liquid ejection device 100. Specific examples of the liquid container 14 include a cartridge that is detachable from the liquid ejection device 100, a bag-shaped ink pack formed of a flexible film, and an ink tank that can be refilled with ink. Note that the type of ink stored in the liquid container 14 is arbitrary.

[0013] The liquid ejection device 100 includes a control unit 20, a conveyance mechanism 22, a movement mechanism 24, and a liquid ejection head 26. The control unit 20 includes, for example, a processing circuit such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array) and a storage circuit such as a semiconductor memory, and controls the operations of the respective elements of the liquid ejection device 100. The control unit 20 includes a voltage application unit 29 that ejects ink from the nozzles by controlling the driving of a piezoelectric element 44, which will be described later.

[0014] The conveyance mechanism 22 conveys the medium 12 in the Y2 direction under the control of the control unit 20. The movement mechanism 24 reciprocates the liquid ejection head 26 in the X1 direction and the X2 direction under the control of the control unit 20. In the example shown in FIG. 1, the movement mechanism 24 includes a substantially box-shaped carrier 242 called a carriage that houses the liquid ejection head 26, and a conveyor belt 244 to which the carrier 242 is fixed. Note that the number of liquid ejection heads 26 mounted on the carrier 242 is not limited to one, and may be a plurality. In addition to the liquid ejection head 26, the liquid container 14 may be mounted on the carrier 242.

[0015] Under the control of the control unit 20, the liquid ejection head 26 ejects ink supplied from the liquid container 14 toward the medium 12 in the Z2 direction from each of a plurality of nozzles. By performing this ejection in parallel with the conveyance of the medium 12 by the conveyance mechanism 22 and the reciprocating movement of the liquid ejection head 26 by the movement mechanism 24, an image made of ink is formed on the surface of the medium 12.

[0016] 1-2. Overall Structure of Liquid Ejection Head FIG. 2 is an exploded perspective view of the liquid ejection head 26 shown in FIG. 1. FIG. 3 is a cross-sectional view of a part of the liquid ejection head shown in FIG. 2, which is a cross-sectional view taken along line III-III in FIG. 2. As shown in FIG. 2, the liquid ejection head 26 has a plurality of nozzles N arranged in a direction along the Y-axis. In the example shown in FIG. 2, the plurality of nozzles N are divided into a first row L1 and a second row L2 that are arranged at intervals in a direction along the X-axis. Each of the first row L1 and the second row L2 is a set of a plurality of nozzles N linearly arranged in a direction along the Y-axis. Elements related to each nozzle N in the first row L1 and elements related to each nozzle N in the second row L2 in the liquid ejection head 26 are substantially symmetric to each other in the direction along the X-axis. In the following description, elements corresponding to the first row L1 will be mainly described, and the description of elements corresponding to the second row L2 will be omitted as appropriate.

[0017] Note that the positions in the direction along the Y-axis of the plurality of nozzles N in the first row L1 and the plurality of nozzles N in the second row L2 may coincide with each other or may be different. Also, elements related to each nozzle N in one of the first row L1 and the second row L2 may be omitted.

[0018] As shown in FIGS. 2 and 3, the liquid ejection head 26 has a nozzle plate 62, a vibration absorber 64, a flow path substrate 32, a pressure chamber substrate 34, a diaphragm 36, a wiring substrate 46, a housing portion 48, and a drive circuit 50. Each of the nozzle plate 62, the vibration absorber 64, the flow path substrate 32, the pressure chamber substrate 34, the diaphragm 36, the wiring substrate 46, and the housing portion 48 is a plate-shaped member that is long in the direction along the Y-axis. The nozzle plate 62, the flow path substrate 32, the pressure chamber substrate 34, the diaphragm 36, and the wiring substrate 46 are arranged in the Z1 direction in this order.

[0019] The nozzle plate 62 is a plate-like member in which a plurality of nozzles N are formed. Each of the plurality of nozzles N is a circular through-hole through which ink passes. The nozzle N discharges ink by the vibration of the diaphragm 36. The nozzle plate 62 is joined to the flow path substrate 32 by, for example, an adhesive.

[0020] In the flow path substrate 32, flow paths for supplying ink to the plurality of nozzles N are formed. Specifically, in the flow path substrate 32, a space Ra, a plurality of supply flow paths 322, a plurality of communication flow paths 324, and a supply liquid chamber 326 are formed. The space Ra is an elongated opening extending in the direction along the Y-axis in a plan view when viewed in the direction along the Z-axis. Each of the supply flow path 322 and the communication flow path 324 is a through-hole formed for each nozzle N. The supply liquid chamber 326 is an elongated space extending in the direction along the Y-axis across the plurality of nozzles N, and communicates the space Ra and the plurality of supply flow paths 322 with each other. Each of the plurality of communication flow paths 324 overlaps with one nozzle N corresponding to the communication flow path 324 in a plan view. The pressure chamber substrate 34 is joined to the flow path substrate 32 by, for example, an adhesive.

[0021] In the pressure chamber substrate 34, a plurality of pressure chambers C are formed. The plurality of pressure chambers C are arranged in the direction along the Y-axis. Each pressure chamber C is formed for each nozzle N and is an elongated space extending in the direction along the X-axis in a plan view. The pressure chamber C is a space located between the flow path substrate 32 and the diaphragm 36. The pressure chamber C communicates with the nozzle N via the communication flow path 324 and communicates with the space Ra via the supply flow path 322 and the supply liquid chamber 326.

[0022] Each of the nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34 is manufactured, for example, by processing a single-crystal silicon substrate using dry etching, wet etching, or the like. However, other known methods may be appropriately used for manufacturing each of the nozzle plate 62, the flow path substrate 32, and the pressure chamber substrate 34.

[0023] The diaphragm 36 is disposed on the surface of the pressure chamber substrate 34 facing the Z2 direction. The diaphragm 36 is a plate-like member that can vibrate elastically.

[0024] On the surface of the diaphragm 36 facing the Z1 direction, a plurality of piezoelectric elements 44 corresponding to the nozzles N are arranged. Each piezoelectric element 44 has an elongated shape extending in a direction along the X-axis in plan view. The plurality of piezoelectric elements 44 correspond to the plurality of pressure chambers C and are arranged in a direction along the Y-axis. The piezoelectric element 44 deforms when a voltage is applied. When the diaphragm 36 vibrates in conjunction with the deformation, the pressure in the pressure chamber C fluctuates, and the ink is discharged from the nozzle N.

[0025] The housing portion 48 is a case for storing the ink supplied to the plurality of pressure chambers C. As shown in FIG. 3, a space Rb is formed in the housing portion 48. The space Rb in the housing portion 48 and the space Ra in the flow path substrate 32 communicate with each other. The space composed of the space Ra and the space Rb functions as a liquid storage chamber R, which is a reservoir for storing the ink supplied to the plurality of pressure chambers C. Ink is supplied to the liquid storage chamber R through an inlet 482 formed in the housing portion 48. The ink in the liquid storage chamber R is supplied to the pressure chamber C through the supply liquid chamber 326 and each supply flow path 322.

[0026] The vibration absorber 64 is a flexible film that constitutes the wall surface of the liquid storage chamber R. The vibration absorber 64 is a compliance substrate that absorbs the pressure fluctuations of the ink in the liquid storage chamber R.

[0027] The wiring board 46 is a plate-like member on which wirings for electrically connecting the drive circuit 50 and the plurality of piezoelectric elements 44 are formed. The surface of the wiring board 46 facing the Z2 direction is joined to the diaphragm 36 via a plurality of conductive bumps B. On the other hand, the drive circuit 50 is mounted on the surface of the wiring board 46 facing the Z1 direction. The drive circuit 50 is an IC (Integrated Circuit) chip that outputs a drive voltage Com and a reference voltage E0 for driving each piezoelectric element 44. Note that the wiring board 46 is not limited to a rigid board, and may be, for example, an FPC (Flexible Printed Circuits) or an FFC (Flexible Flat Cable). In this case, the drive circuit 50 may be mounted on the wiring board 46, or the wiring board 46 may also serve as the external wiring 52.

[0028] As shown in FIG. 2, the end of the external wiring 52 is joined to the surface of the wiring board 46 facing the Z1 direction. The external wiring 52 is composed of connection components such as, for example, an FPC (Flexible Printed Circuits) or an FFC (Flexible Flat Cable). A plurality of wirings 461 for electrically connecting the external wiring 52 and the drive circuit 50, and a plurality of wirings 462 to which the drive voltage Com and the reference voltage E0 output from the drive circuit 50 are supplied are formed on the wiring board 46.

[0029] 1-3. Diaphragm 36 and Piezoelectric Element 44 FIG. 4 is an enlarged cross-sectional view of a part of the liquid ejection head 26 shown in FIG. 3. The diaphragm 36 shown in FIG. 4 vibrates in response to the drive of the piezoelectric body 443 included in the piezoelectric element 44 described later. The diaphragm 36 has a first layer 361 and a second layer 362. The first layer 361 and the second layer 362 are laminated in this order in the Z1 direction.

[0030] The first layer 361 is an elastic film made of, for example, silicon oxide (SiO 2 ). The elastic film is formed, for example, by thermally oxidizing one surface of a single-crystalline silicon substrate. The second layer 362 is made of, for example, zirconium oxide (ZrO 2It is an insulating film composed of []. The insulating film is formed, for example, by forming a layer of zirconium by sputtering and then thermally oxidizing the layer. Zirconium oxide has excellent electrical insulation, mechanical strength, and toughness. Therefore, by including the second layer 362 containing zirconium oxide in the diaphragm 36, the characteristics of the diaphragm 36 can be enhanced.

[0031] Note that other layers such as metal oxides may be interposed between the first layer 361 and the second layer 362. Also, part or all of the diaphragm 36 may be integrally formed with the pressure chamber substrate 34. Further, the diaphragm 36 may be composed of a single material layer.

[0032] The pressure chamber C of the pressure chamber substrate 34 is formed, for example, by anisotropically etching a silicon single crystal substrate. Although not shown, the planar shape of the pressure chamber C is rectangular. However, the planar shape of the pressure chamber C is not limited to this and is arbitrary. For example, when formed by anisotropic etching on a silicon single crystal substrate with a plane orientation of (110), the planar shape of the pressure chamber C in plan view is a parallelogram.

[0033] The piezoelectric element 44 overlaps the pressure chamber C in plan view. The piezoelectric element 44 has a second electrode 442, a seed layer 444, a piezoelectric body 443, and a first electrode 441, and these are laminated in this order in the Z1 direction. Note that other layers such as a layer for enhancing adhesion may be appropriately interposed between the layers of the piezoelectric element 44 or between the piezoelectric element 44 and the diaphragm 36.

[0034] The second electrode 442 is an individual electrode that is arranged separately from each other for each piezoelectric element 44. Specifically, a plurality of second electrodes 442 extending in the direction along the X axis are arranged at intervals in the direction along the Y axis. A drive voltage Com for discharging ink from the nozzle N is applied to the second electrode 442 of each piezoelectric element 44.

[0035] Examples of the material of the second electrode 442 include metal materials such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu), or alloys. The second electrode 442 may be a single layer or multiple layers. For example, the second electrode 442 has a first layer made of titanium (Ti), a second layer made of platinum (Pt), and a third layer made of iridium (Ir), and these are laminated in this order in the Z1 direction. Further, the second electrode 442 is formed by, for example, a known film formation technique such as a sputtering method, and a known processing technique using photolithography and etching, etc.

[0036] The first electrode 441 is a strip-shaped common electrode that extends in the direction along the Y-axis so as to be continuous across a plurality of piezoelectric elements 44. A reference voltage E0 is applied to the first electrode 441.

[0037] Examples of the material of the first electrode 441 include metal materials such as aluminum (Al), nickel (Ni), gold (Au), and copper (Cu), or alloys. The first electrode 441 may be a single layer or multiple layers. For example, the first electrode 441 has, for example, a layer made of iridium, a layer made of iridium oxide (IrOx), a layer made of titanium oxide (TiOx), and a layer made of iridium, and these are laminated in this order from the piezoelectric body 443. The first electrode 441 is formed by, for example, a known film formation technique such as a sputtering method, and a known processing technique using photolithography and etching, etc.

[0038] The piezoelectric body 443 is disposed between the first electrode 441 and the second electrode 442. The piezoelectric body 443 is, for example, strip-shaped and extends along the Y-axis, and is separated for each piezoelectric element 44 by forming a plurality of notches. Note that the piezoelectric body 443 may be provided individually for a plurality of piezoelectric elements 44.

[0039] The piezoelectric body 443 is composed of a piezoelectric material having a perovskite crystal structure represented by the general composition formula ABO 3 For example, as the piezoelectric material, lead titanate (PbTiO 3) Lead zirconate titanate (PZT: Pb(Zr,Ti)O 3 ) Lead zirconate (PbZrO 3 ) Lead lanthanum titanate ((Pb,La)TiO 3 ) Lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O 3 ) Lead zirconium titanate niobate (Pb(Zr,Ti,Nb)O 3 ) Lead zirconium titanate magnesium niobate (Pb(Zr,Ti)(Mg,Nb)O 3 ) and potassium sodium niobate (KNN), etc. Among them, lead zirconate titanate (PZT) is preferably used as the constituent material of the piezoelectric body 443. Note that the piezoelectric body 443 may contain a small amount of other elements such as impurities.

[0040] The piezoelectric body 443 is formed, for example, by forming a precursor layer of the piezoelectric body 443 by a sol-gel method or a MOD (metal organic decomposition) method and firing the precursor layer to crystallize it. The piezoelectric body 443 may be a single layer or a plurality of layers.

[0041] The seed layer 444 is disposed between the second electrode 442 and the piezoelectric body 443. The seed layer 444 is provided in the same region as the second electrode 442 and has the same shape in a plan view. Note that the seed layer 444 only needs to be disposed between the second electrode 442 and the piezoelectric body 443. The seed layer 444 may be provided, for example, in the same region as the piezoelectric body 443 and have the same shape in a plan view.

[0042] The seed layer 444 has the function of improving the orientation of the piezoelectric body 443 when forming the piezoelectric body 443. Specifically, the seed layer 444 is composed of, for example, titanium (Ti). When the seed layer 444 is composed of titanium, when forming the piezoelectric body 443, island-shaped Ti serves as crystal nuclei to improve the orientation of the piezoelectric body 443. The seed layer 444 containing titanium is formed by, for example, known film formation techniques such as sputtering and known processing techniques such as photolithography and etching. Note that the seed layer 444 may be regarded as a part of the second electrode 442.

[0043] Also, the seed layer 444 is not limited to the configuration composed of titanium, and may be composed of, for example, a complex oxide having a perovskite structure containing lead, iron, and titanium as constituent elements. In this case, when forming the piezoelectric body 443, the orientation of the piezoelectric body 443 is improved because the piezoelectric body 443 is affected by the crystal structure of the seed layer 444. The complex oxide is, for example, a solid solution of BiFeO 3 and PbTiO 3 and is represented by (Bi,Pb)(Fe,Ti)O 3 . The seed layer 444 in the case of being composed of such a complex oxide is formed, for example, by forming a precursor layer of the complex oxide by the sol-gel method or the MOD method and firing and crystallizing the precursor layer. Note that the seed layer 444 may be omitted.

[0044] In the piezoelectric element 44 described above, the piezoelectric body 443 deforms according to the voltage applied between the first electrode 441 and the second electrode 442. A drive voltage Com corresponding to the ejection amount of the ink is applied to the second electrode 442. A constant reference voltage E0 is applied to the first electrode 441 regardless of the ejection amount of the ink. When a voltage difference is generated between the first electrode 441 and the second electrode 442 due to the application of the drive voltage Com and the reference voltage E0, the piezoelectric body 443 deforms.

[0045] 1-4. Drive Voltage Com, Reference Voltage E0, and Applied Voltage Ea FIG. 5 is a diagram for explaining the drive voltage Com and the reference voltage E0. The horizontal axis shown in FIG. 5 is time, and the vertical axis is voltage [V].

[0046] The drive voltage Com changes over time. The drive voltage Com includes a drive waveform WCom. The drive waveform WCom is repeated at a unit period Tu. The drive waveform WCom includes an intermediate voltage Ek, a maximum voltage En, and a minimum voltage Em. The maximum voltage En is the maximum value of the drive voltage Com. The minimum voltage Em is the minimum value of the drive voltage Com. The drive waveform WCom decreases from the intermediate voltage Ek to the minimum voltage Em, maintains the minimum voltage Em, then increases from the minimum voltage Em to the maximum voltage En, maintains the maximum voltage En, and then decreases to the intermediate voltage Ek. Note that the drive waveform WCom shown in FIG. 5 is an example, and the drive voltage Com may have other waveforms.

[0047] The reference voltage E0 does not change over time and is constant. In the illustrated example, the reference voltage E0 is a voltage value higher than the minimum voltage Em of the drive voltage Com, but is not limited thereto.

[0048] As described above, the piezoelectric body 443 is provided between the first electrode 441 and the second electrode 442. The piezoelectric body 443 is driven by the voltage difference between the reference voltage E0 applied to the first electrode 441 and the drive voltage Com applied to the second electrode 442. An applied voltage Ea, which is the difference between the reference voltage E0 and the drive voltage Com, is supplied to the piezoelectric body 443.

[0049] FIG. 6 is an illustration of the applied voltage Ea, which is the actual voltage applied to the piezoelectric body 443 when the drive voltage Com shown in FIG. 5 is applied to the first electrode 441 and the reference voltage E0 is applied to the second electrode 442. That is, the applied voltage Ea shown in FIG. 6 is obtained by subtracting the reference voltage E0 from the drive voltage Com shown in FIG. 5 at each time.

[0050] The horizontal axis shown in FIG. 6 is time, and the vertical axis is voltage [V]. The applied voltage Ea includes the waveform WEa. The waveform WEa includes the intermediate voltage EK, the maximum voltage EN, and the minimum voltage EM. The maximum voltage EN is the difference between the maximum voltage En of the driving voltage Com and the reference voltage E0. The minimum voltage EM is the difference between the minimum voltage Em of the driving voltage Com and the reference voltage E0. Note that the waveform WEa shown in FIG. 6 is an example and varies depending on the driving voltage Com and the reference voltage E0.

[0051] Since the reference voltage E0 is constant, the voltage range RE of the applied voltage Ea is equal to the voltage range RE of the driving voltage Com.

[0052] As described above, the piezoelectric body 443 deforms according to the voltage applied between the first electrode 441 and the second electrode 442. First, by lowering the voltage from the intermediate voltage EK to the minimum voltage EM, that is, by discharging, the piezoelectric element 44 and the diaphragm 36 deform so as to bend in the Z1 direction. As a result, ink is taken into the pressure chamber C. Next, by raising the voltage from the minimum voltage EM to the maximum voltage EN, that is, by charging, the piezoelectric element 44 and the diaphragm 36 deform so as to bend in the Z2 direction. As a result, the ink in the pressure chamber C is discharged from the nozzle.

[0053] 1-5. Characteristics of the piezoelectric body 443 FIG. 7 is an illustration of a hysteresis curve showing the relationship between the voltage and polarization of the piezoelectric body 443. FIG. 8 is an illustration of the butterfly curve of the piezoelectric body 443. In FIG. 7, the horizontal axis is voltage [V], and the vertical axis is polarization [μC / cm 2 . In FIG. 8, the horizontal axis is voltage [V], and the vertical axis is the displacement amount [nm] of the diaphragm 36. The vertical axis can also be regarded as the strain amount of the piezoelectric body 443. Note that the displacement amount of the diaphragm 36 indicates how much it has been displaced toward the Z2 side, that is, the pressure chamber C side, with the position where the diaphragm 36 is on the most Z1 side, that is, the side opposite to the pressure chamber C, being set to 0. That is, the displacement amount of the diaphragm 36 indicates the relative position based on the position on the most Z1 side.

[0054] During the period when the intermediate voltage EK in FIG. 6 changes to the minimum voltage EM, the voltage decreases toward the counter-voltage -Ec, which is the voltage in the counter-field along the path Rcv1 of the hysteresis curve shown in FIG. 7, and the polarization changes to the negative side. That is, it changes as shown by the arrow a1. At this time, in the butterfly curve shown in FIG. 8, the displacement amount changes to the negative side along the path Rsv1. And when the counter-voltage -Ec is reached, the diaphragm 36 is at the most Z1 side, and the displacement amount of the diaphragm 36 becomes 0. Note that the counter-field is the magnitude of the electric field when the polarization is 0 μC / cm 2 is the magnitude of the electric field at that time.

[0055] Next, during the period when the minimum voltage EM in FIG. 6 changes to the maximum voltage EN, it moves from the path Rcv1 to the path Rcv2 of the hysteresis curve shown in FIG. 7, and the polarization changes to the positive side by the voltage range RE. At this time, in the butterfly curve shown in FIG. 8, it moves from the path Rsv1 to the path Rsv2, and the displacement amount of the diaphragm 36 changes to the positive side. And the displacement amount of the diaphragm 36 becomes the displacement amount corresponding to the maximum voltage EN. During this period, as the diaphragm 36 is displaced toward the Z2 side, the ink is ejected.

[0056] Here, by setting the minimum voltage EM to be equal to or higher than the counter-voltage -Ec, the voltage range RE applied to the piezoelectric body 443 can be set within a range where the polarization inversion does not occur completely. Therefore, the displacement amounts of the piezoelectric element 44 and the diaphragm 36 can be increased. In particular, by setting the minimum voltage EM to the counter-voltage -Ec, the displacement amount can be maximized. For example, as shown in FIG. 8, by setting the minimum voltage EM to the counter-voltage -Ec, the displacement amount SX can be increased. Since the counter-voltage -Ec is the minimum voltage in the range where the polarization inversion does not occur, by setting the counter-voltage -Ec to the minimum voltage EM, the displacement amount SX can be increased.

[0057] Therefore, in order to increase the displacement amount, it is preferable that the minimum voltage EM is set to the counter voltage -Ec. However, through the inventors' studies, it has been found that due to the rate-determining factor of the circuit or the like, the counter voltage -Ec becomes smaller in the high-frequency band than in the normal frequency band. That is, it has been found that the counter voltage -Ec has frequency dependence. This counter voltage -Ec is the counter voltage -Ec in measurement, which is different from the counter voltage as a physical property value of the piezoelectric body 443 defined from the electric field resistance of the piezoelectric material and the film thickness of the piezoelectric body 443. Hereinafter, the "counter voltage as a physical property value" and the "counter voltage -Ec in measurement" will be described separately. Also, through the inventors' studies, it has been found that the counter voltage -Ec in measurement in the normal frequency band is approximated to the counter voltage as a physical property value.

[0058] FIG. 9 is an illustration of the hysteresis curves of the piezoelectric body 443 at various driving frequencies. FIG. 9 shows the respective hysteresis curves of the piezoelectric body 443 at 0.1 [kHz], 1 [kHz], and 10 [kHz].

[0059] As shown in FIG. 9, when the driving frequency changes, the hysteresis curve is displaced, and the counter voltage -Ec of the measured value is displaced. The counter voltage -Ec of the measured value is displaced to the negative side as the driving frequency increases. In the hysteresis measurement, a ferroelectric property evaluation system FCE-1S manufactured by Toyo Technica was used. By applying a triangular wave pulse with a voltage range of 25 [V] to the piezoelectric element 44 and observing the polarization as its response, the hysteresis curve shown in FIG. 9 was obtained.

[0060] For example, let the maximum usable value of the maximum voltage EN be Emax. In this case, at a normal driving frequency of 0.1 [kHz], by setting the counter electromotive voltage -Ec as the minimum voltage EM and the maximum voltage EN as Emax, the displacement amount can be increased as shown by S1. However, at a high driving frequency of 1 [kHz], if the counter electromotive voltage -Ec at 0.1 [kHz] is set as the minimum voltage EM, as shown by S2, the displacement amount will become small. In the high-frequency band, it is necessary to set the minimum voltage EM taking into account the displacement of the measured counter electromotive voltage -Ec. At 1 [kHz], by setting the measured counter electromotive voltage -Ec at 1 [kHz] as the minimum voltage EM and the maximum voltage EN as Emax, a large displacement amount as shown by S1 can be obtained.

[0061] FIG. 10 is a diagram showing the relationship between the driving frequency and the measured counter electromotive voltage -Ec. As shown in FIG. 10, the driving frequency is approximately stable at about -1.9 [V] when it is 0.1 [Hz] or more and less than 100 [Hz]. The measured counter electromotive voltage -Ec at this driving frequency is close to the counter electromotive voltage as a physical property value. On the other hand, it can be seen that as the driving frequency increases, the measured counter electromotive voltage -Ec changes in a direction smaller than -1.9 [V].

[0062] In particular, the measured counter electromotive voltage -Ec at 1000 [Hz], that is, 1 [kHz] or more, is significantly smaller than the measured counter electromotive voltage -Ec at 0.1 [Hz] or more and less than 100 [Hz]. That is, the measured counter electromotive voltage -Ec at 1 [kHz] or more is significantly smaller than the counter electromotive voltage as a physical property value. In the high-frequency band of 1 [kHz] or more, it is considered that the contribution of the delay due to the rate-determining of the circuit or the like is added. By setting the minimum voltage EM in consideration of the change in the measured counter electromotive voltage -Ec in this high-frequency driving band, the displacement amounts of the piezoelectric element 44 and the diaphragm 36 can be made even larger than before.

[0063] Here, let the driving frequency of the piezoelectric body 443 when discharging ink be the first driving frequency F1. Let the counter electromotive voltage -Ec of the piezoelectric body 443 obtained when driving the piezoelectric body 443 at the first driving frequency F1 be the first counter electromotive voltage E1. Let the driving frequency lower than the first driving frequency F1 be the second driving frequency F2. The second driving frequency F2 is not, for example, the driving frequency when discharging ink. Let the counter electromotive voltage -Ec of the piezoelectric body 443 obtained when driving the piezoelectric body 443 at the second driving frequency F2 be the second counter electromotive voltage E2. In this case, the minimum voltage EM, which is the difference between the reference voltage E0 and the minimum voltage Em that is the minimum value of the driving voltage Com, is larger than the first counter electromotive voltage E1 and smaller than the second counter electromotive voltage E2. That is, the minimum voltage EM is set between the first counter electromotive voltage E1 and the second counter electromotive voltage E2.

[0064] By being within the range where the minimum voltage EM is applied, compared to the case of being outside the range, in high-frequency driving, the displacement amount of the piezoelectric element 44 can be increased within the range where polarization reversal does not occur. For this reason, piezoelectric body driving with improved displacement characteristics in high-frequency driving can be performed. Therefore, the ink discharge amount in high-frequency driving can be made larger than before. Thus, high-quality printing performance corresponding to high-frequency driving can be provided compared to before.

[0065] Note that each of the first counter electromotive voltage E1 and the second counter electromotive voltage E2 is the counter electromotive voltage -Ec in measurement and is different from the counter electromotive voltage as a physical property value.

[0066] For example, 1000 [Hz] corresponds to the first driving frequency F1. -2.3 [V] corresponds to the first counter electromotive voltage E1. 10 [Hz] corresponds to the second driving frequency F2. -1.9 [V] corresponds to the second counter electromotive voltage E2. In this case, the minimum voltage EM is set to be larger than -3 [V] and smaller than -1.9 [V]. Thereby, the displacement amount of the piezoelectric element 44 can be increased within the range where polarization reversal does not occur.

[0067] Note that the first driving frequency F1 is not limited to 1000 [Hz], and any frequency may be used as long as it is the driving frequency of the piezoelectric body 443 when discharging the ink. Also, the second driving frequency F2 is not limited to 10 [Hz], and any frequency may be used as long as it is smaller than the first driving frequency F1.

[0068] In addition, it is preferable that the minimum voltage EM, which is the difference between the reference voltage E0 and the minimum value of the driving voltage Com, is closer to the first counter voltage E1 than to the second counter voltage E2. By having the minimum voltage EM closer to the first counter voltage E1, the displacement amount of the piezoelectric element 44 can be increased compared to the case where it is closer to the second counter voltage E2.

[0069] For example, when 1000 [Hz] corresponds to the first driving frequency F1 and 10 [Hz] corresponds to the second driving frequency F2, it is preferable to set the minimum voltage EM to a voltage closer to -2.3 [V] than -1.9 [V]. By setting the minimum voltage EM to a voltage closer to -2.3 [V], the displacement amount of the piezoelectric element 44 can be increased compared to the case where it is set to a voltage closer to -1.9 [V].

[0070] Also, the first driving frequency F1 is preferably greater than 1 [kHz]. At high frequencies of 1 [kHz] or more, the measured counter voltage -Ec tends to change in a direction smaller than the counter voltage in the normal frequency band and the counter voltage as a physical property value. Considering this, it is preferable that the first driving frequency F1 is greater than 1 [kHz].

[0071] From the above viewpoints, the first driving frequency F1 is more preferably greater than 50 [kHz], and even more preferably greater than 80 [kHz]. As shown in FIG. 9, when exceeding 80 [kHz], the measured counter voltage -Ec is significantly smaller than the measured counter voltage -Ec in the normal frequency band of 0.1 [Hz] or more and less than 100 [Hz]. For this reason, it is particularly preferable that the first driving frequency F1 is greater than 80 [kHz].

[0072] Further, the second drive frequency F2 is preferably greater than 10 [Hz] and less than 100 [Hz]. When the second drive frequency F2 is 10 [Hz] or less, it may be difficult to obtain stable driving due to the influence of leakage current as compared with the case where it is greater than 10 [Hz]. Further, when the second drive frequency F2 is greater than 100 [Hz], depending on the value of the first drive frequency F1, the setting range of the minimum voltage EM becomes very narrow, which is not suitable for convenience.

[0073] FIG. 11 is a graph showing the evaluation results of the displacement amount of the piezoelectric element 44. FIG. 12 is a table showing the evaluation results of the displacement amount of the piezoelectric element 44. The displacement amount of the piezoelectric element 44 was evaluated by the following method. The evaluation results in FIGS. 11 and 12 are the results when the drive frequency is 80 [kHz].

[0074] As a measuring device, an arbitrary waveform generator AFG3022C (Tektronix), a voltage amplifier HAS4011 (NF Circuit Design Block), an oscilloscope HDO4024 (Teiedyne Lecroy), and a laser displacement system NLV-2500 (Polytec) were used. The voltage waveform shown in FIG. 6, which outputs an electrical waveform from the arbitrary waveform generator and amplifies it 10 times with the voltage amplifier, is applied to the piezoelectric element 44 having a planar area of 97680 μm 2 The displacement amount of the piezoelectric element 44 is detected with a laser displacement meter. Then, the detected displacement amount is converted into a voltage and captured by the oscilloscope.

[0075] The voltage range RE, which is the difference between the maximum voltage EN and the minimum voltage EM in FIG. 6, was fixed at 25V. Also, the minimum voltage EM was varied in the range of -10[V] or more and 1[V] or less. The intermediate voltage EK was set to the value in the middle of the maximum voltage EN and the minimum voltage EM, that is, (EN - EM) / 2. Also, the change from the intermediate voltage EK to the minimum voltage EM, from the minimum voltage EM to the maximum voltage EN, and from the maximum voltage EN to the intermediate voltage EK was made in 2 μs each. Also, the holding time of each of the minimum voltage EM and the maximum voltage EN was set to 98 μs. Also, the displacement amount of the piezoelectric element 44 was defined as the difference between the value of the laser displacement meter 88 μs after the transition from the intermediate voltage EK to the minimum voltage EM and the value of the laser displacement meter 88 μs after the transition from the minimum voltage EM to the maximum voltage EN.

[0076] FIG. 12 is a table showing the displacement amount [nm] at specific several minimum voltages EM among the results shown in FIG. 11. In the results shown in FIG. 11, the displacement amount is the largest at -3.8[V], and the displacement amount decreases when it is smaller or larger than -3.8[V]. Also, as can be seen from FIG. 12, Examples 1, 2, 3, and 4 have larger displacement amounts than Examples 5, 6, and 7. That is, it can be seen that a larger displacement amount can be obtained when the minimum voltage EM is smaller than -1.9[V] or larger than -1.9[V]. Further, as shown in FIG. 11, it can be seen that the range where the minimum voltage EM is -4.2[V] or more and -1.9[V] or less has a larger displacement amount than when it is larger than -1.9[V].

[0077] Note that the evaluation results in FIGS. 11 and 12 are the results when the driving frequency is 80[kHz] as described above. As shown in FIG. 11, when the driving frequency is 80[kHz], the maximum value, that is, the peak of the displacement amount, is -3.8[V].

[0078] Even at frequencies other than 80 [kHz] for the driving frequency, a relationship similar to the relationship between the voltage and the displacement amount shown in FIG. 11 is exhibited. And the peak of the displacement amount at each driving frequency is as shown in FIG. 10. Therefore, for example, when the driving frequency is 10 [kHz], the peak of the displacement amount is about -3.4 [V]. Also, for example, when the driving frequency is 1 [kHz], the peak of the displacement amount is about -2.3 [V].

[0079] As described above, by setting the minimum voltage EM to be greater than the first withstand voltage E1 and less than the second withstand voltage E2, it is possible to perform piezoelectric body driving with improved displacement characteristics in high-frequency driving compared to the prior art. Therefore, it is possible to provide high-quality printing performance corresponding to high-frequency driving compared to the prior art.

[0080] Also, not limited to the case where the piezoelectric body 443 is PZT, but also in the case of other piezoelectric materials, particularly piezoelectric materials having a perovskite crystal structure, it is the same as the above description. That is, even for other piezoelectric materials, by setting the minimum voltage EM to be greater than the first withstand voltage E1 and less than the second withstand voltage E2, it is possible to provide high-quality printing performance corresponding to high-frequency driving.

[0081] 2. Modification The embodiments exemplified above can be variously modified. Specific modification modes applicable to the above-described embodiments are exemplified below. Two or more modes arbitrarily selected from the following examples can be appropriately combined within a range that does not conflict with each other.

[0082] In the foregoing embodiments, the second driving frequency F2 is not the driving frequency when discharging ink. That is, it is not performed except for the mode of driving the piezoelectric body 443 at a high frequency. However, if a mode of driving the piezoelectric body 443 at a high frequency is to be executed, even in a form in which a mode of driving the piezoelectric body 443 at a low frequency is executed in addition thereto, the same effects as those in the embodiments can be obtained in the mode of driving the piezoelectric body 443 at a high frequency. That is, the first mode of driving the piezoelectric body 443 at the first driving frequency F1 and the second mode of driving the piezoelectric body 443 at the second driving frequency F2 may be switched and executed. Therefore, the liquid discharge device 100 may include a first mode of discharging ink at the first driving frequency F1 and a second mode of discharging ink at the second driving frequency F2.

[0083] In the foregoing embodiments, the case where the driving voltage Com is a positive voltage has been described by way of assumption, but it may be a negative voltage. Even in this case, the applied voltage Ea is set based on the same idea as the technical idea in each embodiment. In the foregoing description, the "first counter voltage" and the "second counter voltage" are the measured negative counter voltage -Ec, but may be the measured positive counter voltage.

[0084] The "liquid discharge head" may be a circulation type head having a so-called circulation flow path. Further, the "liquid discharge head" is not limited to a serial head and may be a line head.

[0085] In addition to devices dedicated to printing, the "liquid discharge device" can be adopted in various devices such as facsimile machines and copy machines. The use of the liquid discharge device is not limited to printing. For example, a liquid discharge device that discharges a solution of a coloring material is used as a manufacturing device for forming a color filter of a display device such as a liquid crystal display panel. Further, a liquid discharge device that discharges a solution of a conductive material is used as a manufacturing device for forming wirings and electrodes of a wiring board. Further, a liquid discharge device that discharges a solution of an organic substance related to a living body is used, for example, as a manufacturing device for manufacturing a biochip.

[0086] The present invention has been described based on the preferred embodiments, but the present invention is not limited to the above-described embodiments. Further, the configuration of each part of the present invention can be replaced with any configuration that exhibits the same function as that of the above-described embodiments, and any configuration can be added.

Explanation of Reference Numerals

[0087] 12... medium, 26... liquid ejection head, 29... voltage application unit, 36... diaphragm, 44... piezoelectric element, 100... liquid ejection device, 441... first electrode, 442... second electrode, 443... piezoelectric body, C... pressure chamber, E0... reference voltage, E1... first counter voltage, E2... second counter voltage, EK... intermediate voltage, EM... minimum voltage, EN... maximum voltage, Ea... applied voltage, Ek... intermediate voltage, Em... minimum voltage, En... maximum voltage, RE... voltage range, F1... first driving frequency, F2... second driving frequency, N... nozzle, SX... displacement amount, Sy... displacement amount, -Ec... counter voltage.

Claims

1. a liquid ejection head having a first electrode, a second electrode, and a piezoelectric body provided between the first electrode and the second electrode; a voltage application unit that applies a reference voltage that does not change over time to the first electrode and a drive voltage that changes over time to the second electrode to drive the piezoelectric body and eject liquid, The driving frequency of the piezoelectric body when discharging liquid is a first driving frequency, a coercive voltage of the piezoelectric body obtained when the piezoelectric body is driven at the first driving frequency is called a first coercive voltage; A drive frequency lower than the first drive frequency is defined as a second drive frequency. When a coercive voltage of the piezoelectric body obtained when the piezoelectric body is driven at the second drive frequency is defined as a second coercive voltage, A liquid ejection apparatus, wherein a difference between the reference voltage and a minimum value of the driving voltage is greater than the first coercive voltage and less than the second coercive voltage.

2. 2. The liquid ejection apparatus according to claim 1, wherein the difference between the reference voltage and the minimum value of the drive voltage is closer to the first coercive voltage than to the second coercive voltage.

3. 3. The liquid ejection apparatus according to claim 1, wherein the first driving frequency is greater than 1 kHz.

4. 4. The liquid ejection device according to claim 3, wherein the first drive frequency is greater than 50 kHz.

5. 4. The liquid ejection device according to claim 3, wherein the first drive frequency is greater than 80 kHz.

6. 3. The liquid ejection apparatus according to claim 1, wherein the second drive frequency is greater than 10 Hz and less than 100 Hz.

7. 3. The liquid ejection apparatus according to claim 1, wherein the second drive frequency is not a drive frequency for ejecting liquid.

8. 3. The liquid ejection device according to claim 1, wherein the liquid ejection device is capable of switching between a first mode in which the piezoelectric body is driven at the first drive frequency and a second mode in which the piezoelectric body is driven at the second drive frequency.

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