Driving method for liquid ejection device

Abstract

To provide a driving method for a liquid ejection device capable of suppressing degradation of print quality.SOLUTION: There is provided a driving method for a liquid ejection device which includes: a piezoelectric element in which a piezoelectric body is disposed between a first electrode and a second electrode; a pressure chamber; a drive signal generation unit configured to generate a plurality of combinations of a first drive signal that is supplied to the first electrode and includes a potential change element that changes in potential from a start potential to an end potential over a predetermined potential difference and a second drive signal that is supplied to the second electrode and includes a potential maintaining element that maintains a constant potential; and a detection unit configured to detect, as a residual vibration signal, a change in electromotive force of the piezoelectric element corresponding to a residual pressure change in liquid in the pressure chamber after the potential change element is supplied to the first electrode, and the potential maintaining element is supplied to the second electrode in each of the plurality of combinations. The potential difference between the end potential of the potential change element of the first drive signal and the potential maintaining element of the second drive signal is different from each other among the plurality of combinations. The detection unit specifies a first displacement characteristic of the piezoelectric element on the basis of the plurality of combinations of residual vibration signals.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to a driving method for a liquid ejection device.

Background Art

[0002] Liquid ejection devices that eject liquids such as ink onto media such as printing paper have been proposed conventionally.

[0003] The liquid ejection device described in Patent Document 1 includes a nozzle plate having nozzles for ejecting ink, a flow path substrate having pressure chambers provided corresponding to the nozzles, and a piezoelectric element for changing the pressure of the ink inside the pressure chambers. The piezoelectric element includes an upper electrode, a lower electrode, and a piezoelectric body disposed therebetween. The piezoelectric body deforms according to the applied driving voltage, that is, the potential difference between the upper electrode film and the lower electrode film. By causing pressure fluctuations in the ink inside the pressure chamber using the deformation of the piezoelectric body, droplets are ejected from the nozzles.

[0004] In such a liquid ejection device, based on the piezoelectric characteristics of the piezoelectric body, a driving voltage corresponding to the amount of liquid to be ejected from the nozzle is set.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Generally, the piezoelectric characteristics of the piezoelectric body are measured during the manufacture of the liquid ejection device. However, the piezoelectric characteristics of the piezoelectric body change as the printing time of the liquid ejection device elapses. For this reason, when the driving voltage based on the piezoelectric characteristics set at the time of manufacture is used, the amount of liquid ejected from the nozzle may gradually change. As a result, color differences and the like may occur, and there is a risk of affecting the print quality.

Means for Solving the Problem

[0007] A driving method of a liquid ejection device according to an aspect of the present disclosure includes a piezoelectric element including a first electrode, a second electrode, and a piezoelectric body disposed between the first electrode and the second electrode, a pressure chamber whose volume changes according to the displacement of the piezoelectric element, a first driving signal including a potential change element that is supplied to the first electrode and changes in potential over a predetermined potential difference from a start potential to an end potential, and a second driving signal including a potential maintaining element that is supplied to the second electrode and maintains a constant potential. A driving signal generation unit that generates a plurality of combinations of the second driving signal, and in each of the plurality of combinations, after supplying the potential change element to the first electrode and the potential maintaining element to the second electrode, the electromotive force of the piezoelectric element corresponding to the pressure change remaining in the liquid in the pressure chamber is detected as a residual vibration signal. A detection unit, and a driving method of a liquid ejection device, wherein the potential difference between the end potential of the potential change element of the first driving signal and the potential maintaining element of the second driving signal is different for each of the plurality of combinations, and the detection unit is based on the plurality of combinations of the residual vibration signals. Identify the first displacement characteristics of the piezoelectric element.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments according to the present disclosure will be described with reference to the accompanying drawings. Note that the dimensions and scales of each part in the drawings are appropriately different from the actual ones, and there are also parts schematically shown for easy understanding. In addition, the scope of the present disclosure 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. In the following, one direction along the X-axis is the X1 direction, and the direction opposite to the X1 direction is the X2 direction. Similarly, the directions opposite to each other along the Y-axis are the Y1 direction and the Y2 direction. The directions opposite to each other along the Z-axis are the Z1 direction and the Z2 direction. Typically, the Z-axis is a vertical axis, and the Z2 direction corresponds to the downward direction in the vertical direction. However, the Z-axis does not have to be a vertical axis. In addition, the X-axis, Y-axis, and Z-axis typically intersect each other at right angles, 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] A: First Embodiment A1: Overall Configuration of Liquid Discharge Device FIG. 1 is a schematic diagram showing a configuration example of a liquid ejection device 100 according to the first embodiment. The liquid ejection device 100 is an inkjet printing device that ejects a liquid such as ink as droplets onto a medium 11. The medium 11 is, for example, printing paper. Note that the medium 11 is not limited to printing paper, and may be a printing target made of any material such as a resin film or a fabric.

[0012] As shown in FIG. 1, the liquid ejection device 100 includes a liquid container 12, a control unit 21, a conveyance mechanism 22, a movement mechanism 23, and a liquid ejection head 20.

[0013] The liquid container 12 stores ink. Specific examples of the liquid container 12 include a cartridge that is detachable from the liquid ejection device 100, a bag-shaped ink pack composed 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 12 is arbitrary.

[0014] The control unit 21 controls the operations of the respective elements of the liquid ejection device 100. The control unit 21 includes, for example, one or more processing circuits such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array), and one or more storage circuits such as a semiconductor memory.

[0015] The conveyance mechanism 22 conveys the medium 11 in the Y1 direction under the control of the control unit 21. The movement mechanism 23 reciprocates the liquid ejection head 20 along the X axis under the control of the control unit 21. The movement mechanism 23 includes a substantially box-shaped carriage 231 that houses the liquid ejection head 20, and an endless conveyor belt 232 to which the carriage 231 is fixed. Note that the number of liquid ejection heads 20 mounted on the carriage 231 is not limited to one, and may be a plurality. In addition to the liquid ejection head 20, the aforementioned liquid container 12 may be mounted on the carriage 231.

[0016] The liquid ejection head 20 ejects ink supplied from the liquid container 12 from each of a plurality of nozzles onto the medium 11 under the control of a control unit 21 based on the print data Img. By performing this ejection in parallel with the conveyance of the medium 11 by the conveyance mechanism 22 and the reciprocating movement of the liquid ejection head 20 by the movement mechanism 23, an image corresponding to the print data Img by the ink is formed on the surface of the medium 11.

[0017] A2: Electrical Configuration of the Liquid Ejection Device 100 FIG. 2 is a diagram showing the electrical configuration of the liquid ejection device 100 according to the first embodiment. As shown in FIG. 2, the liquid ejection head 20 includes a head chip 3 and a drive control unit 30. In the illustrated example, one head chip 3 is shown, but a plurality of head chips 3 may be provided.

[0018] The head chip 3 has a plurality of piezoelectric elements 34. The drive control unit 30 switches whether to supply the drive signal Com output from the control unit 21 as a supply drive signal Vin to each of the plurality of piezoelectric elements 34 of the head chip 3 under the control of the control unit 21.

[0019] Note that the head chip 3 has M piezoelectric elements 34. M is a natural number of 1 or more. Hereinafter, among the M piezoelectric elements 34, the m-th piezoelectric element 34 may be referred to as piezoelectric element 34[m]. m is a natural number satisfying "1 ≤ m ≤ M". Further, hereinafter, when a component or signal etc. of the liquid ejection head 20 corresponds to the piezoelectric element 34[m], a subscript m may be attached to the symbol representing the component or signal etc.

[0020] As shown in FIG. 2, the control unit 21 includes a control unit 51, a storage unit 52, a drive signal generation unit 54, and a detection unit 50.

[0021] The control unit 51 has a function of controlling the operations of each part of the liquid ejection device 100 and a function of processing various data. The control unit 51 includes, for example, a processor such as one or more CPUs (Central Processing Units). Note that the control unit 51 may include a programmable logic device such as an FPGA (field-programmable gate array) instead of or in addition to the CPU. Also, when the control unit 51 is composed of a plurality of processors, the plurality of processors may be mounted on different substrates or the like.

[0022] The storage unit 52 stores various programs executed by the control unit 51 and various data such as print data Img processed by the control unit 51. The storage unit 52 includes, for example, one or both semiconductor memories of a volatile memory such as a RAM (Random Access Memory) and a non-volatile memory such as a ROM (Read Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a PROM (Programmable ROM). The print data Img is supplied from an external device 200 such as a personal computer or a digital camera. Note that the storage unit 52 may be configured as a part of the control unit 51.

[0023] The drive signal generation unit 54 includes a circuit that generates a drive signal Com for driving each piezoelectric element 34. Examples of the drive signal Com include a first drive signal ComB, a second drive signal VBS, and a third drive signal ComA, which will be described later. Each of the first drive signal ComB and the third drive signal ComA includes an element whose potential changes across a predetermined potential difference. The first drive signal ComB is a signal related to the detection of the residual vibration of the piezoelectric element 34. The residual vibration is the vibration remaining in the ink in the pressure chamber C after the volume of the pressure chamber C1 has changed due to the driving of the piezoelectric element 34. The third drive signal ComA is a signal related to the ejection of the ink. Also, the second drive signal VBS includes an element that maintains a constant potential.

[0024] The drive signal generation unit 54 has, for example, a DA conversion circuit and an amplification circuit. The drive signal generation unit 54 converts the waveform designation signal dCom into an analog signal by means of the DA conversion circuit, and the analog signal is amplified by the amplification circuit and output. Among the waveforms included in the first drive signal ComB or the third drive signal ComA, the signal of the waveform actually supplied to the piezoelectric element 34 is the aforementioned supply drive signal Vin. The waveform designation signal dCom is a digital signal for defining each waveform and potential of the drive signal Com.

[0025] The control unit 51 controls the operations of the respective parts of the liquid ejection device 100 by executing the program stored in the storage unit 52. By executing the program, the control unit 51 generates a control signal Sk1, a control signal Sk2, a print data signal SI, a waveform designation signal dCom, a latch signal LAT, a change signal CH, a period designation signal Ts, and a clock signal CLK as signals for controlling the operations of the respective parts of the liquid ejection device 100.

[0026] The control signal Sk2 is a signal for controlling the drive of the conveyance mechanism 22. The control signal Sk1 is a signal for controlling the drive of the moving mechanism 23. The print data signal SI is a digital signal for designating the operating state of the piezoelectric element 34. The latch signal LAT, the change signal CH, and the period designation signal Ts are timing signals that are used in combination with the print data signal SI and define the ink ejection timing from each nozzle of the head chip 3. These timing signals are generated, for example, based on the output of an encoder that detects the position of the aforementioned carriage 231.

[0027] A3: Specific structure of the head chip 3 FIG. 3 is a cross-sectional view for explaining the configuration of the head chip 3 shown in FIG. 2. The Z-axis is an axis along the ink ejection direction by the head chip 3. Looking from the Z1 direction or the Z2 direction is referred to as "plan view".

[0028] Although illustration is omitted, the head chip 3 includes a plurality of nozzles N arranged along the Y-axis. The plurality of nozzles N are arranged side by side at intervals along the X-axis and are divided into two nozzle rows. Each of the two nozzle rows is a set of a plurality of nozzles N linearly arranged along the Y-axis. The head chip 3 has a structure in which elements related to each nozzle N in one of the two nozzle rows and elements related to each nozzle N in the other row are arranged in a substantially plane-symmetrical manner. In the following description, elements corresponding to one of the two nozzle rows will be mainly described, and the description of elements corresponding to the other row will be omitted as appropriate.

[0029] As shown in FIG. 3, the head chip 3 includes a flow path structure 3a, a plurality of piezoelectric elements 34, a sealing substrate 35, a housing portion 36, and a wiring substrate 39.

[0030] The flow path structure 3a is a structure in which flow paths for supplying ink to each of the plurality of nozzles N are formed inside. The flow path structure 3a is composed of a communication plate 31, a pressure chamber substrate 32, a diaphragm 33, a nozzle substrate 37, and a vibration absorber 38.

[0031] Each member constituting the flow path structure 3a is a long plate-like member along the Y-axis. The pressure chamber substrate 32 and the housing portion 36 are installed on the surface of the communication plate 31 in the Z1 direction. The nozzle substrate 37 and the vibration absorber 38 are installed on the surface of the communication plate 31 in the Z2 direction. For example, each member is fixed to each other by an adhesive.

[0032] The nozzle substrate 37 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 for discharging ink. For example, the nozzle substrate 37 is manufactured by processing a single crystal substrate of silicon (Si) using semiconductor manufacturing technologies such as photolithography and etching.

[0033] The communication plate 31 is formed with a plurality of throttle portions 312, a plurality of communication channels 314, a communication space Ra, and a common channel Rb. Each of the throttle portion 312 and the communication channel 314 extends in the Z2 direction and is a through hole formed for each nozzle N. The communication channel 314 overlaps the nozzle N in plan view. The communication space Ra is an opening formed in a long shape along the Y-axis. The common channel Rb extends along the Y-axis. The common channel Rb communicates with the communication space Ra and overlaps the communication space Ra in plan view. The common channel Rb communicates with the plurality of throttle portions 312. Further, the communication space Ra communicates the common channel Rb and the external channel of the head chip 3 via a space Rc described later.

[0034] A plurality of pressure chambers C1 are formed in the pressure chamber substrate 32. The pressure chamber C1 is located between the communication plate 31 and the diaphragm 33 and is a space formed by the wall surface 320 of the pressure chamber substrate 32. The pressure chamber C1 is formed for each nozzle N. The pressure chamber C1 is a long space extending in the X1 direction. The plurality of pressure chambers C1 are arranged along the Y-axis. One end of the pressure chamber C1 in the X1 direction communicates with the nozzle N via the communication channel 314. The throttle portion 312 communicates with the other end of the pressure chamber C1 in the X1 direction. The throttle portion 312 has a smaller cross-sectional area than the pressure chamber C1. Further, the pressure chamber C1, the nozzle N, the communication channel 314, and the throttle portion 312 constitute an individual channel 300 for each nozzle N.

[0035] The communication plate 31 and the pressure chamber substrate 32 are manufactured by processing a semiconductor substrate such as a single crystal silicon substrate.

[0036] Above the pressure chamber C1, a diaphragm 33 that can be elastically deformed is disposed. The diaphragm 33 is laminated on the pressure chamber substrate 32 and contacts the surface of the pressure chamber substrate 32 opposite to the communication plate 31. The diaphragm 33 is a plate-like member formed in a long rectangular shape along the Y-axis in plan view. The thickness direction of the diaphragm 33 is parallel to the Z2 direction. The pressure chamber C1 communicates with the communication flow path 314 and the throttle portion 312. Therefore, the pressure chamber C1 communicates with the nozzle N through the communication flow path 314 and communicates with the communication space Ra through the throttle portion 312. In FIG. 3, for ease of explanation, the pressure chamber substrate 32 and the diaphragm 33 are illustrated as separate substrates, but in actuality, they are laminated on one silicon substrate.

[0037] Piezoelectric elements 34 are formed for each pressure chamber C1 on the surface of the diaphragm 33 opposite to the pressure chamber C1. The piezoelectric elements 34 are long in the X-axis direction in plan view. The piezoelectric elements 34 are drive elements that are driven when a drive signal is applied. The piezoelectric elements 34 include two electrodes and a piezoelectric body disposed between these electrodes. The piezoelectric elements 34 cause the ink in the pressure chamber C1 to be ejected from the nozzle N by varying the pressure of the ink in the pressure chamber C1. The piezoelectric element 43 vibrates the diaphragm 33 as it deforms when a drive signal Com is supplied. Along with this vibration, the pressure chamber C1 expands and contracts, causing the pressure of the ink in the pressure chamber C1 to vary.

[0038] The housing portion 36 is a case for storing the ink supplied to the plurality of pressure chambers C1 and is formed, for example, by injection molding of a resin material. A space Rc and a supply port 361 are formed in the housing portion 36. The supply port 361 is a pipe through which ink is supplied from the liquid container 12 and communicates with the space Rc. The space Rc of the housing portion 36 and the communication space Ra of the communication plate 31 communicate with each other. The common space R common to the plurality of nozzles N is constituted by the aforementioned communication space Ra, the common flow path Rb, and the space Rc. The common space R functions as a liquid storage chamber for storing the ink supplied to the plurality of pressure chambers C1. The ink stored in the common space R branches to each throttle portion 312 and is supplied and filled in the plurality of pressure chambers C1 in parallel.

[0039] The vibration absorber 38 is a flexible film that constitutes the wall surface of the communication space Ra and absorbs the pressure fluctuations of the ink in the common space R. The vibration absorber 38 is, for example, a laminate of an ink-resistant resin film, a SUS (stainless steel) member that holds the resin film and has spring properties, and a fixing plate that protects the resin film and the SUS member.

[0040] The sealing substrate 35 is a structure that protects the plurality of piezoelectric elements 34 and reinforces the mechanical strength of the pressure chamber substrate 32 and the diaphragm 33, and is fixed to the surface of the diaphragm 33 with, for example, an adhesive. The plurality of piezoelectric elements 34 are housed inside the recess formed on the surface of the sealing substrate 35 that faces the diaphragm 33. Further, the wiring substrate 39 is inserted through the through-hole 362 of the housing portion 36 and the through-hole 353 of the sealing substrate 35. The wiring substrate 39 is joined to the surface of the diaphragm 33. The wiring substrate 39 is a mounting component on which a plurality of wirings for electrically connecting the control unit 21 and the head chip 3 are formed. As the wiring substrate 39, for example, a TCP (Tape Carrier Package) or an FPC (Flexible Printed Circuit) or the like is used. A drive signal Com for driving the aforementioned piezoelectric element 34 is supplied from the wiring substrate 39 to each piezoelectric element 34.

[0041] When the piezoelectric element 34 contracts due to energization, the diaphragm 33 is bent and deflected in a direction in which the volume of the pressure chamber C1 decreases, the pressure in the pressure chamber C1 rises, and ink droplets are ejected from the nozzle N. At this time, the pressure also propagates from the pressure chamber C1 toward the throttle portion 312, and ink also flows through the throttle portion 312 into the common flow path Rb. After the ink is ejected, the piezoelectric element 34 returns to its original position. At this time, the ink in the common flow path Rb from the nozzle N also vibrates. Then, when the meniscus of the nozzle N is restored, ink is supplied from the throttle portion 312 at the same time. Through the above series of operations, ink is ejected from the nozzle N.

[0042] 1-4. Configuration of the drive control unit 30 FIG. 4 is a diagram showing a configuration example of the drive control unit 30 shown in FIG. 2. The drive control unit 30 supplies a drive signal Com as a drive signal Vin to the piezoelectric element 34. The piezoelectric element 34 [m] has a first electrode Zu [m] and a second electrode Zd [m] as two electrodes.

[0043] Also, examples of the drive signal Com include a first drive signal ComB, a second drive signal VBS, and a third drive signal ComA. The first drive signal ComB is a signal related to the generation of a residual vibration signal. The third drive signal ComA is a signal related to ejection.

[0044] Wiring LHa, LHb, LHs, and LHd are connected to the drive control unit 30. The wiring LHa is a signal line that transmits the third drive signal ComA. The wiring LHb is a signal line that transmits the first drive signal ComB. The wiring LHs is a signal line that transmits the residual vibration signal Vout. The wiring LHs is connected to the detection unit 50. The wiring LHd is a power supply line to which the second drive signal VBS is supplied.

[0045] The drive control unit 30 also includes a plurality of switches SW and a connection state specifying circuit 301 that specifies the connection states of the plurality of switches. The plurality of switches SW includes M switches SWa (SWa [1] to SWa [M]), M switches SWb (SWb [1] to SWb [M]), and M switches SWs (SWs [1] to SWs [M]). Each switch SW is, for example, a transmission gate.

[0046] The switch SWa [m] is a switch that switches between conduction (on) and non-conduction (off) between the wiring LHa for transmitting the third drive signal ComA and the piezoelectric element 34 [m]. The switch SWb [m] is a switch that switches between conduction (on) and non-conduction (off) between the wiring LHb for transmitting the first drive signal ComB and the piezoelectric element 34 [m]. The switch SWs [m] is a switch that switches between conduction (on) and non-conduction (off) between the wiring LHs for transmitting the residual vibration signal Vout and the piezoelectric element 34 [m].

[0047] The connection state specifying circuit 301 generates a connection state specifying signal SL for specifying the on / off states of the respective switches SW based on the print data signal SI. Examples of the connection state specifying signal SL include connection state specifying signals SLa[m], SLb[m], and SLs[m].

[0048] The connection state specifying signal SLa[m] is a signal for specifying the on / off state of the switch SWa[m]. The switch SWa[m] is in the on state when the connection state specifying signal SLa[m] is at a high level and in the off state when it is at a low level. The drive control unit 30 switches the on / off state of the switch SWa1[m] to switch whether to supply, as the supply drive signal Vin, part or all of the waveform included in the third drive signal ComA to the first electrode Zu[m] of the piezoelectric element 34[m].

[0049] The connection state specifying signal SLb[m] is a signal for specifying the on / off state of the switch SWb[m]. The switch SWb[m] is in the on state when the connection state specifying signal SLb[m] is at a high level and in the off state when it is at a low level. The drive control unit 30 switches the on / off state of the switch SWb[m] to switch whether to supply, as the supply drive signal Vin, part or all of the waveform included in the first drive signal ComB to the first electrode Zu[m] of the piezoelectric element 34[m].

[0050] The connection state specifying signal SLs[m] is a signal for specifying the on / off state of the switch SWs[m]. The switch SWs[m] is in the on state when the connection state specifying signal SLs[m] is at a high level and in the off state when it is at a low level. The drive control unit 30 switches the on / off state of the switch SWs[m] to switch whether to make the residual vibration signal Vout detectable from the piezoelectric element 34[m].

[0051] The period during which the switch SWa[m] is on, the period during which the switch SWb[m] is on, and the period during which the switch SWs[m] is on do not overlap with each other. That is, the switches SWa[m], SWb[m], and SWs[m] are exclusively on. Also, a wiring LHd is electrically connected to the second electrode Zd[m] of the piezoelectric element 34[m], and the second drive signal VBS is supplied thereto.

[0052] For example, with the second drive signal VBS being supplied to the second electrode Zd[m], when the switch SWa[m] is on, the third drive signal ComA is supplied to the first electrode Zu[m] of the piezoelectric element 34[m]. By supplying these signals, a voltage corresponding to the potential difference between the first electrode Zu[m] and the second electrode Zd[m] is applied to the piezoelectric element 34[m]. As a result, the piezoelectric element 34[m] is driven, the pressure in the pressure chamber C1 fluctuates, and ink is ejected from the nozzle N.

[0053] Also, for example, with the second drive signal VBS being supplied to the second electrode Zd[m], when the switch SWb[m] is on, the first drive signal ComB is supplied to the first electrode Zu[m] of the piezoelectric element 34[m]. When these signals are supplied, a voltage corresponding to the potential difference between the first electrode Zu[m] and the second electrode Zd[m] is applied to the piezoelectric element 34[m]. As a result, the piezoelectric element 34[m] causes pressure fluctuations of a strength at which ink is not ejected from the nozzle N in the pressure chamber C1. Also, for example, when the switch SWs[m] is turned on immediately after the switch SWb[m] is turned on, the residual vibration signal Vout is detected by the detection unit 50.

[0054] A5: Waveform of the drive signal Com FIG. 5 is a diagram for explaining the waveform of the drive signal Com in the first embodiment. As shown in FIG. 5, the latch signal LAT includes a pulse PlsL for defining a repeating period Tu. The period Tu corresponds to a printing period for forming dots by ink from the nozzle N on the medium 11. The period Tu is defined, for example, as the period from the rising edge of the pulse PlsL to the rising edge of the next pulse PlsL.

[0055] The change signal CH includes a pulse PlsC for dividing the period Tu into a preceding control period Tua and a succeeding control period Tub. The control period Tua is, for example, the period from the rising edge of the pulse PlsL to the rising edge of the pulse PlsC. The control period Tub is, for example, the period from the rising edge of the pulse PlsC to the rising edge of the pulse PlsL. Further, the period designation signal Ts includes pulses PlsT1 and PlsT2 for dividing the period Tu into control periods Tsa, Tsb, and Tsc. The control period Tsa is the period from the rising edge of the pulse PlsL to the rising edge of the pulse PlsT1. The control period Tsb is the period from the rising edge of the pulse PlsT1 to the rising edge of the pulse PlsT2. The control period Tsc is the period from the rising edge of the pulse PlsT2 to the rising edge of the next pulse PlsL.

[0056] The third drive signal ComA includes a potential pulse related to ink ejection. Specifically, the third drive signal ComA has a discharge waveform P1 of medium dots provided in the control period Tua and a discharge waveform P2 of small dots provided in the control period Tub.

[0057] The discharge waveform P1 is a waveform that decreases from the reference potential E0 to the lowest potential EL1 lower than the reference potential E0, then rises to the highest potential EH1 higher than the reference potential E0 through the discharge potential change element E1, and then returns to the reference potential E0. In the example of FIG. 5, the discharge potential change element E1 is a rising edge from the lowest potential EL1 to the highest potential EH1. The discharge potential change element E1 is an element that changes the volume of the pressure chamber C1 so as to cause pressure fluctuations in the ink in the pressure chamber C1 to such an extent that ink droplets are ejected from the nozzle N communicating with the pressure chamber C1.

[0058] The ejection waveform P2 is a waveform that drops from the reference potential E0 to the lowest potential EL2 lower than the reference potential E0, then rises to the highest potential EH2 higher than the reference potential E0 through the ejection potential change element E2, and then returns to the reference potential E0. In the example of FIG. 5, the ejection potential change element E2 is a rising edge from the lowest potential EL2 to the highest potential EH2. The ejection potential change element E2 is an element that changes the volume of the pressure chamber C1 so as to cause pressure fluctuations in the ink in the pressure chamber C1 to such an extent that ink droplets are ejected from the nozzle N communicating with the pressure chamber C1.

[0059] The potential difference between the highest potential EH1 and the lowest potential EL1 of the ejection waveform P1 is larger than the potential difference between the lowest potential EL2 and the highest potential EH2 of the ejection waveform P2. In the ejection waveforms P1 and P2, the potentials at the start and end are set to the reference potential E0.

[0060] By appropriately combining the ejection waveforms P1 and P2 in the period Tu, dots of different sizes, namely large dots, medium dots, and small dots, can be ejected from the nozzle N. That is, by switching the on / off of the aforementioned switch SWa[m] by the drive control unit 30 in the control periods Tua and Tub, part or all of the ejection waveforms P1 and P2 are supplied to the piezoelectric element 34[m] as the supply drive signal Vin for each period Tu. As a result, dots of different sizes, namely large dots, medium dots, and small dots, can be dropped onto the medium 11 for each period Tu.

[0061] The first drive signal ComB includes a potential pulse for detecting residual vibration. In the illustrated example, the first drive signal ComB has a detection waveform P3 provided in the period Tu. Specifically, the detection waveform P3 is a potential pulse that drives the piezoelectric element 34 so as to cause pressure fluctuations in the pressure chamber C1 that do not eject ink from the nozzle N. The potential difference between the highest potential EH3 and the lowest potential EL3 of the detection waveform P3 is smaller than the potential difference between the highest potential EH2 and the lowest potential EL2 of the ejection waveform P2. In the detection waveform P3, the potentials at the start and end are set to the reference potential E0.

[0062] The waveform P3 for detection rises from the reference potential E0 to the highest potential EH3 that is higher than the reference potential E0, and then, after passing through the potential change element E3, it drops to the lowest potential EL3 that is lower than the reference potential E0 and then returns to the reference potential E0. The potential change element E3 is an element whose potential changes over a predetermined potential difference from the highest potential EH3 as the "start potential" to the lowest potential EL3 as the "end potential". In the illustrated example, the potential change element E3 is a falling edge from the highest potential EH3 to the lowest potential EL3.

[0063] The connection state specifying circuit 301 sets the connection state specifying signal SLb[m] to a high level during the control periods Tsa and Tsc, and sets it to a low level during the control period Tsb. During the control period Tsa, the piezoelectric element 34[m] is displaced with a strength such that ink is not ejected from the nozzle N by the potential change element E3. As a result, the piezoelectric element 34[m] vibrates, and the vibration of the liquid in the pressure chamber C caused by this vibration remains also during the control period Tsb. Then, during the control period Tsb, the piezoelectric element 34[m] exhibits a potential corresponding to the electromotive force of the piezoelectric element 34[m] due to the residual vibration during the control period Tsa. The said potential is detected as the residual vibration signal Vout during the control period Tsb.

[0064] Also, the second drive signal VBS is an offset potential. The second drive signal VBS includes a potential maintaining element E4 that maintains a constant potential.

[0065] A6: Waveform of the residual vibration signal Vout FIG. 6 is a diagram showing the residual vibration signal Vout. As shown in FIG. 6, the residual vibration signal Vout is detected during the control period Tsb. The residual vibration has a natural vibration frequency determined by the shape of the nozzle N, the shape of the individual flow path, the weight of the ink in the flow path of the head chip 3, and the viscosity of the ink. When there is a discharge abnormality, the natural vibration frequency and amplitude of the residual vibration change compared to the normal state. Discharge abnormalities occur, for example, when the piezoelectric element 34 fails and cannot be displaced, when air bubbles are mixed into the individual flow path, when foreign matter adheres near the nozzle N, when the ink has thickened, and the like. By detecting the residual vibration, such discharge abnormalities can be detected.

[0066] A7. Estimation of Discharge Performance of Liquid Discharge Device 100 In addition to the above-described discharge abnormalities, although there are no discharge abnormalities, if the printing time of the liquid discharge device 100 is long, color differences and the like may occur and the print quality may deteriorate.

[0067] In the liquid discharge device 100, based on the piezoelectric characteristics of the piezoelectric body of the piezoelectric element 34, a drive signal Com corresponding to the liquid volume to be discharged from the nozzle N is set. The piezoelectric characteristics of the piezoelectric body of the piezoelectric element 34 change with the passage of the printing time of the liquid discharge device 100. That is, the piezoelectric characteristics of the piezoelectric body of the piezoelectric element 34 change when the piezoelectric element 34 is continuously driven. For this reason, when the drive signal Com based on the piezoelectric characteristics set at the time of manufacturing the liquid discharge device 100 is used, if the piezoelectric element 34 is continuously driven, the liquid volume discharged from the nozzle N may gradually change. As a result, although it is not the above-described discharge abnormality, there is a possibility that the discharge performance deteriorates such as color difference.

[0068] When the piezoelectric element 34 is continuously driven, the hysteresis characteristics of the piezoelectric element 34 change. In particular, the breakdown voltage of the piezoelectric element 34 changes. By detecting this change in the breakdown voltage, the change in the piezoelectric characteristics of the piezoelectric element 34 can be estimated.

[0069] In the detection of the aforementioned residual vibration, when one or both of the first drive signal ComB and the second drive signal VBS are changed to change the voltage applied to the piezoelectric body of the piezoelectric element 34, the piezoelectric effect is lost near the counter voltage. Therefore, near the counter voltage, a phenomenon occurs where the residual vibration is not detected. By utilizing this phenomenon, the counter voltage of the piezoelectric element 34 can be specified. In the present embodiment, the counter voltage corresponds to the "displacement characteristic" of the piezoelectric element 34.

[0070] Specifically, the drive signal generation unit 54 generates a plurality of combinations of the first drive signal ComB supplied to the first electrode Zu and the second drive signal VBS supplied to the second electrode Zd[m]. In the plurality of combinations, the potential difference D between the lowest potential EL3 corresponding to the end potential of the potential change element E3 of the first drive signal ComB and the potential maintenance element E4 of the second drive signal VBS is different from each other. Then, the detection unit 50 detects the residual vibration signal Vout in each of the plurality of combinations, and specifies the displacement characteristic corresponding to the counter voltage based on the residual vibration signals Vout of the plurality of combinations.

[0071] A8. Driving Method of Liquid Discharge Device 100 FIG. 7 is a diagram for explaining the driving method of the liquid discharge device 100 according to the first embodiment. FIG. 8 is a diagram for explaining steps S01 and S02 included in each of the first step S1 and the second step S2 of FIG. 7. Hereinafter, the driving method of the liquid discharge device 100 for specifying the displacement characteristic of the piezoelectric element 34[m] and the driving method of the liquid discharge device 100 for estimating the deterioration of the piezoelectric element 34[m] are shown.

[0072] As shown in FIG. 7, the driving method of the liquid discharge device 100 includes a first step S1 of specifying a first displacement characteristic at a first timing, a second step S2 of specifying a second displacement characteristic at a second timing, and a third step S3 of estimating the deterioration of the piezoelectric element 34[m]. The second timing is a timing after a predetermined period from the first timing.

[0073] As shown in FIG. 8, in each of the first step S1 and the second step S2, it includes a step S01 of detecting the residual vibration signal Vout and a step S02 of specifying the displacement characteristics of the piezoelectric element 34. The displacement characteristics of the piezoelectric element 34[m] specified at the first timing of the first step S1 are the first displacement characteristics, and the displacement characteristics of the piezoelectric element 34[m] specified at the second timing of the second step S2 are the second displacement characteristics. The driving method of the liquid ejection device 100 for specifying the first displacement characteristics and the second displacement characteristics is the same except that the specified timings are different.

[0074] In step S01, every time the drive control unit 30 supplies each of a plurality of sets, which are combinations in which at least one of the first drive signal ComB and the second drive signal VBS is different, to the piezoelectric element 34[m], the detection unit 50 detects the residual vibration signal Vout corresponding to each set. The plurality of sets of combinations of the first drive signal ComB and the second drive signal VBS are generated by the drive signal generation unit 54.

[0075] In step S02, based on the residual vibration signal Vout corresponding to each of the plurality of sets detected in step S01, the detection unit 50 specifies the displacement characteristics of the piezoelectric element 34[m].

[0076] A8-1. Step S01 FIG. 9 is a diagram for explaining a plurality of sets of a first drive signal ComB and a second drive signal VBS supplied to the piezoelectric element 34[m] in step S01. As shown in FIG. 9, in step S01, the drive signal generation unit 54 generates a plurality of sets of combinations of the first drive signal ComB and the second drive signal VBS by changing the potential of the potential maintenance element E4 of the second drive signal VBS. For example, for each combination of the first drive signal ComB and the second drive signal VBS, the potential is increased as indicated by arrow A1 from the second drive signal VBS shown by the solid line to the second drive signal VBS shown by the broken line, thereby generating the plurality of sets. In the present embodiment, in the generation of the plurality of sets, the potential and waveform of the first drive signal ComB are not changed. Therefore, the potential and waveform of the first drive signal ComB are equal to each other in the plurality of sets. As a result, the plurality of sets of the first drive signal ComB and the second drive signal VBS have different potential differences D for each combination.

[0077] FIG. 10 is a diagram showing the temporal change for explaining step S01. Hereinafter, step S01 for specifying the displacement characteristics will be exemplified with reference to FIG. 10. In the following example, the drive signal generation unit 54 generates K sets of combinations of the first drive signal ComB and the second drive signal VBS. K is a plurality and is a natural number of 2 or more. The K sets are denoted as the first set to the Kth set. Hereinafter, among the K sets, the kth set may be referred to as the kth set. In addition, elements or signals corresponding to the first set to the Kth set may be appended with subscripts 1 to K.

[0078] In the example of FIG. 10, a case where K continuous periods Tu are shown is shown. In the K periods Tu, the drive control unit 30 supplies K sets of combinations of the first drive signal ComB and the second drive signal VBS to the piezoelectric element 34[m]. In addition, the detection unit 50 detects K residual vibration signals Vout in the K periods Tu. In the illustrated example, the K periods Tu are continuous, but they do not have to be continuous.

[0079] As shown in FIG. 10, in period Tu_1, a combination of the first driving signal ComB of the first set and the second driving signal VBS_1 is supplied to the piezoelectric element 34[m]. Specifically, the first driving signal ComB is supplied to the first electrode Zu[m], and the second driving signal VBS_1 is supplied to the second electrode Zd[m]. Therefore, in the control period Tsa of period Tu_1, the piezoelectric element 34[m] changes its displacement state from the displacement state corresponding to the potential difference between the reference potential E0 and the potential maintaining element E4 to the displacement state corresponding to the potential difference between the highest potential EH3 and the potential maintaining element E4, and then changes to the displacement state corresponding to the potential difference D_1 between the lowest potential EL3 and the potential maintaining element E4. Further, in the control period Tsb of period Tu_1, the piezoelectric element 34[m] in the displacement state corresponding to the potential difference D_1 exhibits a potential corresponding to the electromotive force due to the piezoelectric effect of the piezoelectric element 34[m] caused by the residual vibration of the pressure fluctuation of the liquid in the pressure chamber C during the control period Tsa. The potential corresponding to the electromotive force of the piezoelectric element 34[m] is detected by the detection unit 50 as the residual vibration signal Vout_1.

[0080] In the next period Tu_2 of period Tu_1, a combination of the first driving signal ComB of the second set and the second driving signal VBS_2 is supplied to the piezoelectric element 34[m]. Specifically, the first driving signal ComB is supplied to the first electrode Zu[m], and the second driving signal VBS_2 is supplied to the second electrode Zd[m]. Therefore, in the control period Tsa of period Tu_2, the piezoelectric element 34[m] changes its displacement state from the displacement state corresponding to the potential difference between the reference potential E0 and the potential maintaining element E4 to the displacement state corresponding to the potential difference between the highest potential EH3 and the potential maintaining element E4, and then maintains the displacement state corresponding to the potential difference D_2 between the lowest potential EL3 and the potential maintaining element E4. Further, in the control period Tsb of period Tu_2, the piezoelectric element 34[m] in the displacement state corresponding to the potential difference D_2 exhibits a potential corresponding to the electromotive force due to the piezoelectric effect of the piezoelectric element 34[m] caused by the residual vibration of the pressure fluctuation of the liquid in the pressure chamber C during the control period Tsa. The potential corresponding to the electromotive force of the piezoelectric element 34[m] is detected by the detection unit 50 as the residual vibration signal Vout_2.

[0081] The second set of the combination of the first drive signal ComB and the second drive signal VBS_2 is different from the first set of the combination of the first drive signal ComB and the second drive signal VBS_1. Specifically, the potential of the potential maintaining element E4 of the second drive signal VBS_2 is different from the potential of the potential maintaining element E4 of the second drive signal VBS_1. As a result, the potential difference between the reference potential E0 and the potential maintaining element E4, the potential difference between the highest potential EH3 and the potential maintaining element E4, and the potential difference D between the lowest potential EL3 and the potential maintaining element E4 are different between the first set and the second set. That is, since the potential difference D_2 is different from the potential difference D_1, the displacement state of the piezoelectric element 34[m] when detecting the residual vibration signal Vout is different between the first set and the second set. In the example of FIG. 9, the potential of the potential maintaining element E4 of the second drive signal VBS_2 is higher than the potential of the potential maintaining element E4 of the second drive signal VBS_1, and the potential difference D_2 is smaller than the potential difference D_1.

[0082] In the period Tu_k, the combination of the k-th set of the first drive signal ComB and the second drive signal VBS_k is supplied to the piezoelectric element 34[m]. Specifically, the first drive signal ComB is supplied to the first electrode Zu[m], and the second drive signal VBS_k is supplied to the second electrode Zd[m]. Therefore, in the control period Tsa within the period Tu_k, the piezoelectric element 34[m] changes its displacement state from the displacement state corresponding to the potential difference between the reference potential E0 and the potential maintaining element E4 to the displacement state corresponding to the potential difference between the highest potential EH3 and the potential maintaining element E4, and then changes to the displacement state corresponding to the potential difference D_k between the lowest potential EL3 and the potential maintaining element E4. Further, in the control period Tsb within the period Tu_k, the piezoelectric element 34[m] in the displacement state corresponding to the potential difference D_k exhibits a potential corresponding to the electromotive force due to the piezoelectric effect of the piezoelectric element 34[m] caused by the residual vibration of the pressure fluctuation of the liquid in the pressure chamber C during the control period Tsa. The potential corresponding to the electromotive force of the piezoelectric element 34[m] is detected by the detection unit 50 as the residual vibration signal Vout_k.

[0083] The k-th combination of the first drive signal ComB and the second drive signal VBS_k is different from the combinations before and after the k-th one. Specifically, the potential of the potential holding element E4 of the second drive signal VBS_k is different from the potentials of the potential holding elements E4 of the combinations before and after the k-th one. As a result, the potential difference D_k is different from the potential differences D of the combinations before and after the k-th one. In the example of FIG. 9, the absolute value of the potential difference D_k is the smallest among the plurality of combinations. Here, the potential difference D in the present embodiment can be the value obtained by subtracting the potential holding element E4 from the lowest potential EL3. Therefore, in the present embodiment, when the potential of the potential holding element E4 is lower than the lowest potential EL3, the potential difference D becomes a positive value, and when the potential of the potential holding element E4 is higher than the lowest potential EL3, the potential difference D becomes a negative value.

[0084] During the period Tu_K, the combination of the first drive signal ComB and the second drive signal VBS_K of the K-th combination is supplied to the piezoelectric element 34[m]. Specifically, the first drive signal ComB is supplied to the first electrode Zu[m], and the second drive signal VBS_K is supplied to the second electrode Zd[m]. Therefore, during the control period Tsa within the period Tu_K, the piezoelectric element 34[m] changes its displacement state from the displacement state corresponding to the potential difference between the reference potential E0 and the potential holding element E4 to the displacement state corresponding to the potential difference between the highest potential EH3 and the potential holding element E4, and then changes to the displacement state corresponding to the potential difference D_K between the lowest potential EL3 and the potential holding element E4. Further, during the control period Tsb within the period Tu_K, the piezoelectric element 34[m] in the displacement state corresponding to the potential difference D_K exhibits a potential corresponding to the electromotive force due to the piezoelectric effect of the piezoelectric element 34[m] caused by the residual vibration of the pressure fluctuation of the liquid in the pressure chamber C during the control period Tsa. The potential corresponding to the electromotive force of the piezoelectric element 34[m] is detected by the detection unit 50 as the residual vibration signal Vout_K.

[0085] The K-th combination of the first drive signal ComB and the second drive signal VBS_K is different from the combinations of the sets before the K-th set. Specifically, the potential of the potential maintaining element E4 of the second drive signal VBS_K is different from the potential of each potential maintaining element E4 of the sets before the K-th set. As a result, the potential difference D_K is different from each potential difference D of the sets before the K-th set.

[0086] In the above manner, the detection unit 50 detects K residual vibration signals Vout.

[0087] A8-2. Step S02 In step S02, the detection unit 50 specifies the displacement characteristics corresponding to the piezoelectric voltage of the piezoelectric element 34[m] based on the K residual vibration signals Vout. When the potential difference between the first electrode Zu[m] and the second electrode Zd[m] of the piezoelectric element 34[m] is near the piezoelectric voltage, the piezoelectric effect is lost. Therefore, as described above, when changing the potential difference D, which is the voltage applied to the piezoelectric body of the piezoelectric element 34, in the detection of the residual vibration signal Vout, when the potential difference D is near the piezoelectric voltage, a phenomenon occurs where the residual vibration is not detected. By utilizing this phenomenon, the displacement characteristics, which are the piezoelectric voltage of the piezoelectric element 34, can be specified.

[0088] For example, the displacement characteristics are specified from the amplitude state of the residual vibration signal Vout shown in FIG. 6 described above. Specifically, for example, it is specified based on the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of the K residual vibration signals Vout and the potential difference D. Examples of the frequency analysis include Fourier transform.

[0089] FIG. 11 is a graph showing the relationship between the spectral intensity and the potential difference D. The horizontal axis of FIG. 11 is the aforementioned potential difference D, and the vertical axis is the spectral intensity of the natural vibration frequency (Tc) of the residual vibration as a predetermined frequency component obtained from the frequency analysis, as shown in FIG. 11. Also, the result of the first timing is indicated by the line segment L1, and the result of the second timing is indicated by the line segment L2.

[0090] When the potential difference D is changed, the spectral intensity of the natural vibration frequency changes. This correlates with the fact that when the potential difference between the first electrode Zu[m] and the second electrode Zd[m] of the piezoelectric element 34[m] is changed, the displacement amount, which is the amount of strain of the piezoelectric element 34[m], changes. Also, when the potential difference D between the first electrode Zu[m] and the second electrode Zd[m] of the piezoelectric element 34[m] is near the counter voltage, no residual vibration is detected and the spectral intensity becomes the minimum value. Therefore, the potential difference D at which the spectral intensity becomes the minimum value corresponds to the counter voltage. That is, the potential difference D corresponding to the minimum value corresponds to the displacement characteristic. Therefore, by specifying the potential difference D at which the spectral intensity becomes the minimum value through frequency analysis, the potential difference D can be specified as the counter voltage, that is, the displacement characteristic.

[0091] As described above, in step S02, the detection unit 50 characterizes the displacement characteristic, which is the counter voltage of the piezoelectric element 34[m], by performing frequency analysis on each of the K sets of potential differences D and the residual vibration signal Vout.

[0092] And the aforementioned steps S01 and S02 are performed in the first step S1 and the second step S2, respectively.

[0093] A8-3. Third step S3 In the third step S3, the detection unit 50 estimates the deterioration of the piezoelectric element 34[m]. As shown in FIG. 11, the line segment L1 at the first timing and the line segment L2 at the second timing do not coincide with each other, and the line segment L2 at the second timing is shifted to the lower potential side compared to the line segment L1 at the first timing. And the potential difference D corresponding to the minimum value M2 of the spectral intensity at the second timing is shifted to the lower potential side compared to the potential difference D corresponding to the minimum value M1 of the spectral intensity at the first timing. As can be seen from FIG. 11, as time elapses, the potential difference D has shifted, and thus the displacement characteristic, which is the withstand voltage, has shifted. This is because during the period from the first timing to the second timing, the hysteresis characteristics of the piezoelectric element 34[m] change according to the time during which the voltage was applied to the piezoelectric element 34[m], the magnitude of the applied voltage, and the temperature of the piezoelectric element 34[m], etc., and the main change is the shift of the withstand voltage. Therefore, by detecting the shift amount of the withstand voltage, it is possible to determine the degree of change in the hysteresis characteristics of the piezoelectric element 34[m].

[0094] In the storage unit 52, correlation data between the electric field strength (applied voltage) applied to the piezoelectric element 34[m] and the displacement amount of the piezoelectric element 34[m] corresponding to the shift amount of the withstand voltage is stored in advance. Alternatively, in the storage unit 52, correlation data between the target ink ejection amount and the correction amount of the third drive signal ComA corresponding to the shift amount of the withstand voltage is stored. Also, a table of the correction amount of the third drive signal ComA corresponding to the withstand voltage of the piezoelectric element 34[m] can be stored in the storage unit 52 in advance.

[0095] The detection unit 50 obtains a correction value of the third drive signal ComA based on the shift amount of the potential difference D corresponding to the anti-voltage at the second timing with respect to the potential difference D corresponding to the anti-voltage at the first timing and the correlation data stored in the storage unit 52. For example, the difference between the first displacement characteristic and the second displacement characteristic corresponding to the shift amount of the anti-voltage is determined as the degree of deterioration of the piezoelectric element 34, which is an example of the change state of the displacement characteristic of the piezoelectric element 34[m]. Then, the detection unit 50 obtains a correction value of the third drive signal ComA according to the degree of deterioration based on the correlation data stored in the storage unit 52. Based on this result, the control unit 51 corrects the waveform data corresponding to the third drive signal ComA and generates a waveform designation signal dCom. The drive signal generation unit 54 generates the third drive signal ComA for ejection from the corrected waveform designation signal dCom. Thereby, the ejection amount from the nozzle by the third drive signal ComA after the second timing can be corrected to the ejection amount at the first timing. Note that the difference between the first displacement characteristic and the second displacement characteristic corresponds to "characteristic information" including the displacement characteristic. Also, for example, the detection unit 50 obtains a correction amount of the third drive signal ComA according to the anti-voltage based on the table stored in the storage unit 52. The control unit 51 corrects the waveform data corresponding to the third drive signal ComA using the correction amount obtained by the detection unit 50 and generates a waveform designation signal dCom. The drive signal generation unit 54 generates the third drive signal ComA for ejection from the corrected waveform designation signal dCom. Thereby, the ejection amount from the nozzle by the third drive signal ComA can be corrected to an appropriate amount.

[0096] According to the method as described above, based on a plurality of residual vibration signals Vout detected using each of a plurality of combinations in which at least one of the first drive signal ComB and the second drive signal VBS is different, the displacement characteristics of the piezoelectric element 34[m] can be specified. Further, based on the difference between the first displacement characteristics specified at the first timing and the second displacement characteristics specified at the second timing, the deterioration state of the piezoelectric element 34[m] can be determined. By correcting the third drive signal ComA according to the specified displacement characteristics and degree of deterioration of the piezoelectric element 34, the discharge amount can be made an appropriate amount, so that the possibility of deterioration of discharge performance such as color difference can be reduced.

[0097] As described above, the driving method of the liquid ejection device 100 for specifying the first displacement characteristics of the piezoelectric element 34[m] has been described. As described above, the detection unit 50 detects the residual vibration signal Vout for each of a plurality of sets in which the potential differences D are different from each other, and specifies the first displacement characteristics corresponding to the piezoelectric voltage based on the plurality of sets of residual vibration signals Vout. That is, the first displacement characteristics are specified based on the plurality of sets of residual vibration signals Vout detected through steps S01 and S02. The residual vibration signal Vout is a signal indicating a change in the electromotive force corresponding to a change in the pressure remaining in the ink in the pressure chamber C1 of the piezoelectric element 34 that is displaced according to the potential difference D after the potential change element E3 is supplied to the first electrode Zu[m] and the potential maintaining element E4 is supplied to the second electrode Zd[m].

[0098] In this way, the first displacement characteristics of the piezoelectric element 34[m] can be specified using the residual vibration signal Vout. The detection of the residual vibration signal Vout is a function also used for detecting ejection abnormalities of each nozzle N, and it is not necessary to separately mount a measuring device or the like on the liquid ejection device 100 in order to specify the displacement characteristics of the piezoelectric element 34[m]. In addition, the third drive signal ComA for ejection can be appropriately corrected according to the first displacement characteristic specified using the residual vibration signal Vout. Further, by using the first displacement characteristic specified using the residual vibration signal Vout, the deterioration of the piezoelectric element 34 can be estimated. That is, the durability of the piezoelectric element 34 can be estimated. Therefore, by performing correction of the ink ejection amount or the like based on the estimated result, it is possible to reduce the risk of deterioration of ejection performance such as color difference. Thus, deterioration of print quality can be suppressed.

[0099] In addition, in the present embodiment, the first displacement characteristic includes the coercive voltage. The coercive voltage shows a particularly significant change when the piezoelectric element 34 is continuously driven. Further, by specifying the coercive voltage, the hysteresis characteristic of the piezoelectric element 34 can be estimated. Therefore, capturing the change in the coercive voltage is suitable for estimating the change in the hysteresis characteristic of the piezoelectric element 34, that is, the deterioration of the piezoelectric element 34.

[0100] Note that in the above description, the first displacement characteristic was the coercive voltage, but it may include characteristics of the piezoelectric element 34 other than the coercive voltage. Similarly, the second displacement characteristic may also be a characteristic other than the coercive voltage. For example, the change gradient of the spectral intensity with respect to the change in the potential difference D can be used as the displacement characteristic. Specifically, the spectral intensity corresponding to each of at least two predetermined potential differences D is detected by the above-described detection method. From the detected spectral intensity and potential difference D, information regarding the change gradient of the spectral intensity with respect to the change in the potential difference D is obtained. The information regarding the change gradient of the spectral intensity with respect to the change in the potential difference D may be an nth-order function formula approximating the correlation between the potential difference D and the spectral intensity (n is a natural number of 1 or more). In the storage unit 52, a plurality of types of displacement characteristics corresponding to the degree of deterioration of the piezoelectric element 34 obtained in advance by experiments or the like, and the correction amount of the third drive signal ComA corresponding to the plurality of types of displacement characteristics are stored. From the plurality of types of displacement characteristics stored in the storage unit 52, the one corresponding to the detected displacement characteristic is selected, and the third drive signal ComA can be corrected with the correction amount of the third drive signal ComA corresponding to the selected displacement characteristic.

[0101] However, it is preferable that the first displacement characteristic indicates a change in the displacement amount of the piezoelectric element 34 corresponding to a change in the potential difference D between the first electrode Zu and the second electrode Zd. The change in the displacement amount of the piezoelectric element 34 corresponding to the change in the potential difference D between the first electrode Zu and the second electrode Zd corresponds to the hysteresis curve of the piezoelectric element 34, and the coercive voltage can be obtained. For example, in addition to the coercive voltage, the first displacement characteristic may be a voltage corresponding to a specific polarization in the hysteresis curve of the piezoelectric element 34. Similarly, it is preferable that the second displacement characteristic also indicates a change in the displacement amount of the piezoelectric element 34 corresponding to a change in the potential difference D between the first electrode Zu and the second electrode Zd. Also, the second displacement characteristic may be a voltage corresponding to a specific polarization in the hysteresis curve of the piezoelectric element 34.

[0102] Also, as described above, the drive signal generation unit 54 generates a third drive signal ComA related to ejection. The third drive signal ComA includes ejection potential change elements E1 and E2 shown in FIG. 5. The ejection potential change elements E1 and E2 are elements that are supplied to the first electrode Zu and displace the piezoelectric element 34 so as to cause pressure fluctuations in the ink in the pressure chamber C1 to such an extent that ink is ejected from the nozzle N communicating with the pressure chamber C1. The first displacement characteristic is specified using a first drive signal ComB different from such a third drive signal ComA.

[0103] The deterioration of the piezoelectric element 34 progresses according to the applied voltage, environmental temperature, and humidity. Therefore, when printing continues with a predetermined third drive signal ComA at a predetermined environmental temperature and humidity, it is possible to predict a certain degree of deterioration progress state from the energization time. However, the waveform shape including the potential of the third drive signal ComA related to ejection may be changed since the manufacture to achieve a desired ejection amount and ejection speed adapted to printing. In addition, the environment where the liquid ejection device 100 is installed varies. Therefore, it has been difficult to estimate the deterioration of the piezoelectric element 34 simply from the cumulative time of driving the piezoelectric element 34 using the third drive signal ComA or the like. However, according to the method described above, the first displacement characteristic of the current piezoelectric element 34 is specified using the first drive signal ComB. For this reason, deterioration can be estimated based on the displacement characteristic of the current piezoelectric element 34 detected using the first drive signal ComB, rather than estimating from the cumulative application time of the third drive signal ComA which may be different from the actual usage situation.

[0104] Further, the drive signal generation unit 54 generates a third drive signal ComA corrected according to the difference between the first displacement characteristic and the second displacement characteristic which are characteristic information. In this way, the waveform included in the third drive signal ComA related to ejection is corrected. Specifically, the lowest potential EL1 and the highest potential EH1 of the ejection potential change element E1, and the lowest potential EL2 and the highest potential EH2 of the ejection potential change element E2 are set. In this way, by using the characteristic information including the difference in the displacement characteristics of the piezoelectric element 34 detected using the common first drive signal ComB at the first timing and the second timing, the waveform of the third drive signal ComA related to ejection can be corrected based on the more accurate difference in the characteristic information of the piezoelectric element at the first timing and the second timing. Therefore, even if the piezoelectric element 34 is driven for a long period of time, deterioration of the print quality can be suppressed.

[0105] Also, in the examples shown in FIGS. 9 and 10 described above, the potentials and waveforms of the first drive signal ComB are equal to each other in multiple sets. Therefore, each of the highest potential EH3 corresponding to the start potential and the lowest potential EL3 corresponding to the end potential of the potential change element E3 of the first drive signal ComB is equal to each other in multiple sets. For this reason, the potential differences between the highest potential EH3 and the lowest potential EL3 are equal to each other in multiple sets. On the other hand, the potentials maintained by the potential maintenance element E4 of the second drive signal VBS are different from each other in multiple sets. Thereby, in multiple sets, the correlation between the potential difference D and the residual vibration signal Vout can be detected without considering the variation in the potential difference between the highest potential EH3 and the lowest potential EL3 of the potential change element E3.

[0106] The second drive signal VBS is easier to change in potential than the first drive signal ComB. For this reason, by changing the potential maintained by the potential maintenance element E4 of the second drive signal VBS, multiple sets with different potential differences D can be easily generated.

[0107] Also, when the potential change element E3 of the first drive signal ComB described above is supplied, the volume of the pressure chamber C1 when the highest potential EH3 corresponding to the start potential is applied is smaller than the volume of the pressure chamber C1 when the lowest potential EL3 corresponding to the end potential is applied. That is, when the potential change element E3 is supplied, the meniscus in the nozzle is drawn in the direction of the pressure chamber C1 rather than in the droplet ejection direction. By causing such a potential change, it is possible to more reliably prevent the ink from being ejected from the nozzle N due to the driving of the piezoelectric element 34.

[0108] Also, as described above, at the first timing, the first displacement characteristic is specified. At the second timing, the second displacement characteristic is specified. The detection unit 50 determines the degree of deterioration of the piezoelectric element 34, which is an example of the change state of the displacement characteristic of the piezoelectric element 34, based on the difference between the first displacement characteristic and the second displacement characteristic. By using two or more displacement characteristics specified at two or more timings that are different in time, the change state of the displacement characteristic of the piezoelectric element 34 can be estimated. Therefore, correction of the third drive signal ComA applied to the ejection can be performed based on the estimated change state of the displacement characteristic.

[0109] The first displacement characteristic is specified from the amplitude states of a plurality of residual vibration signals Vout detected at the first timing. Similarly, the second displacement characteristic is specified from the amplitude states of a plurality of residual vibration signals Vout detected at the second timing. The residual vibration signal Vout is generated by the piezoelectric effect of the piezoelectric element 34. Therefore, since a change in the piezoelectric effect due to deterioration of the piezoelectric element 34 appears as a change in the amplitude state of the residual vibration signal Vout, the displacement characteristic can be specified using the amplitude state of the residual vibration signal Vout.

[0110] The first displacement characteristic is specified based on the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals Vout detected at the first timing and the potential difference D. Similarly, the second displacement characteristic is specified based on the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals Vout detected at the second timing and the potential difference D. Thus, by obtaining the displacement characteristic using frequency analysis, the displacement characteristic can be specified easily and quickly.

[0111] Furthermore, the first displacement characteristic is the breakdown voltage of the piezoelectric element specified from the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals Vout detected at the first timing and the potential difference D. Similarly, the second displacement characteristic is the breakdown voltage of the piezoelectric element specified from the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals Vout detected at the second timing and the potential difference D. That is, the first displacement characteristic and the second displacement characteristic are the breakdown voltages as described above. Catching a change in the breakdown voltage is suitable for estimating deterioration of the piezoelectric element 34. Therefore, by obtaining the displacement characteristic using frequency analysis, the displacement characteristic can be specified accurately, easily, and quickly.

[0112] In addition, the displacement characteristics may be characterized by a method other than frequency analysis. For example, the displacement characteristics may be specified using curve fitting processing. Specifically, the first displacement characteristics may be specified based on the correlation between the amplitude of the residual vibration obtained by subjecting a plurality of detected residual vibration signals Vout at the first timing to curve fitting processing and the potential difference D. Similarly, the second displacement characteristics may be specified based on the correlation between the amplitude of the residual vibration obtained by subjecting a plurality of detected residual vibration signals Vout at the second timing to curve fitting processing and the potential difference D.

[0113] FIG. 12 is a model formula in the curve fitting process. In the model formula of FIG. 12, Ac is the amplitude of the residual vibration. τ1 is the decay time constant of the residual vibration. δ3 is the phase of the decay component of the residual vibration. ωc is each frequency of the residual vibration. δ1 is the phase of the vibration component of the residual vibration. τ2 is the decay time constant of the vibration of the circuit. δ4 is the phase of the decay component of the vibration of the circuit. ωm is each frequency of the vibration of the circuit. δ2 is the phase of the vibration component of the vibration of the circuit. Vbg is the background voltage. Vbg corresponds to, for example, the lowest potential EL3 of the first drive signal ComB. Vsig is the coefficient of the vibration component of the natural vibration frequency of the piezoelectric element 34.

[0114] For each of the plurality of sets, the detection unit 50 calculates the coefficient Vsig of the vibration component of the natural vibration frequency of the residual vibration by curve fitting. Then, the detection unit 50 detects the minimum value of the plurality of sets of coefficients Vsig and characterizes the potential difference D corresponding to the minimum value as the counter voltage, that is, the displacement characteristics. By using such curve fitting processing, the displacement characteristics can be obtained quickly and easily.

[0115] 2. Second Embodiment For elements whose operations and functions are the same as those of the first embodiment described above in the embodiments illustrated below, the reference numerals used in the description of the first embodiment are reused and the detailed description of each is omitted as appropriate. In the second embodiment, the step of detecting the residual vibration signal Vout in step S01 is different from that of the first embodiment.

[0116] FIG. 13 is a diagram for explaining step S01 in the second embodiment. In the present embodiment, in step S01, the drive signal generation unit 54 generates a second drive signal VBS in which the potential of the potential maintenance element E4 is a predetermined potential and is constant, and a first drive signal ComB having sequentially different potentials, thereby generating a plurality of sets of combinations of the first drive signal ComB and the second drive signal VBS.

[0117] As shown in FIG. 13, without changing the waveform shape of the first drive signal ComB, the overall potential of the first drive signal ComB is changed. For example, by decreasing the potential as indicated by arrow A1 from the first drive signal ComB shown by the solid line to the first drive signal ComB shown by the broken line, the plurality of sets are generated. In the present embodiment, the potential of the second drive signal VBS is not changed. Therefore, the potential and waveform of the second drive signal VBS are equal to each other in the plurality of sets.

[0118] Therefore, in the present embodiment, the potentials of the first drive signal ComB are different from each other in the plurality of sets. Therefore, the lowest potential EL3 corresponding to the end potential of the potential change element E3 of the first drive signal ComB is different from each other in the plurality of sets. On the other hand, the potential maintained by the potential maintenance element E4 of the second drive signal VBS is equal to each other in the plurality of sets. Thereby, the plurality of sets of the first drive signal ComB and the second drive signal VBS have different potential differences D for each combination.

[0119] Also in this embodiment, similar to the first embodiment, by changing the potential of the first drive signal ComB, a plurality of sets having different potential differences D can be generated.

[0120] In addition, in the present embodiment, the potential difference between the highest potential EH3 corresponding to the start potential of the potential change element E3 and the lowest potential EL3 corresponding to the end potential is equal for a plurality of sets. By varying the first drive signal ComB for each set without changing the potential difference, a plurality of sets with different potential differences D can be easily generated. As a result, in a plurality of sets, the correlation between the potential difference D and the residual vibration signal Vout can be detected without considering the variation in the potential difference between the highest potential EH3 and the lowest potential EL3 of the potential change element E3.

[0121] 3. Modification Each of the embodiments illustrated above can be variously modified. Specific modification modes applicable to the above-described embodiments are illustrated below. Two or more modes arbitrarily selected from the following illustrations can be appropriately combined within a range that does not conflict with each other.

[0122] In the above-described embodiment, either the first drive signal ComB or the second drive signal VBS was changed for each of the plurality of sets. However, both the first drive signal ComB and the second drive signal VBS may be changed for each of the plurality of sets. It is only necessary that the potential difference D is different for the plurality of sets.

[0123] In addition, in the above-described embodiment, the displacement characteristics were specified at two timings, the first timing and the second timing, but the displacement characteristics may be specified at more timings.

[0124] Further, the liquid ejection device 100 may have a circulation mechanism for circulating the ink in the flow path inside the head chip 3.

[0125] In the above-described embodiment, one piezoelectric element 34 was provided for one nozzle N, but a plurality of piezoelectric elements 34 may be provided for one nozzle N.

[0126] In each of the above-described embodiments, a serial liquid ejection device 100 that reciprocates a carriage 231 on which a liquid ejection head 20 is mounted was illustrated, but the present disclosure is also applicable to a line liquid ejection device in which a plurality of nozzles N are distributed over the entire width of the medium 11.

[0127] The liquid ejection device 100 exemplified in the above-described form may be adopted not only in devices dedicated to printing but also in various devices such as facsimile machines and copying machines, and the applications of the present disclosure are not particularly limited. However, the application of the liquid ejection device is not limited to printing. For example, a liquid ejection device that ejects 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. In addition, a liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device for forming wirings and electrodes of a wiring board. Further, a liquid ejection device that ejects a solution of an organic substance related to a living body is used, for example, as a manufacturing device for manufacturing a biochip.

[0128] 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

[0129] 3... head chip, 3a... flow path structure, 20... liquid ejection head, 21... control unit, 30... drive control unit, 34... piezoelectric element, 50... detection unit, 51... control unit, 52... storage unit, 54... drive signal generation unit, 100... liquid ejection device, C1... pressure chamber, Com... drive signal, ComA... third drive signal, ComB... first drive signal, D... potential difference, E0... reference potential, E1... ejection potential change element, E2... ejection potential change element, E3... potential change element, E4... potential maintenance element, EH1... highest potential, EH2... highest potential, EH3... highest potential, EL1... lowest potential, EL2... lowest potential, EL3... lowest potential, M1... minimum value, M2... minimum value, N... nozzle, P1... ejection waveform, P2... ejection waveform, P3... detection waveform, S01... step, S02... step, S1... first step, S2... second step, S3... third step, SL... connection state designation signal, SW... switch, T... period, Tu... period, VBS... second drive signal, Vin... supply drive signal, Vout... residual vibration signal, Zd... first electrode, Zu... second electrode.

Claims

1. A piezoelectric element including a first electrode, a second electrode, and a piezoelectric body disposed between the first electrode and the second electrode; A pressure chamber whose volume changes according to the displacement of the piezoelectric element; A drive signal generation unit that generates a plurality of combinations of a first drive signal including a potential change element that is supplied to the first electrode and changes in potential across a predetermined potential difference from a start potential to an end potential, and a second drive signal that is supplied to the second electrode and includes a potential maintenance element that maintains a constant potential; A detection unit that, in each of the plurality of combinations, after supplying the potential change element to the first electrode and the potential maintenance element to the second electrode, detects a change in the electromotive force of the piezoelectric element corresponding to a pressure change remaining in the liquid in the pressure chamber as a residual vibration signal; A driving method for a liquid ejection device, comprising: The potential difference between the end potential of the potential change element of the first drive signal and the potential maintenance element of the second drive signal is different for each of the plurality of combinations; The detection unit specifies a first displacement characteristic of the piezoelectric element based on the residual vibration signals of the plurality of combinations; A driving method for a liquid ejection device, characterized by the above.

2. The first displacement characteristic includes the piezoelectric voltage of the piezoelectric element; The driving method for a liquid ejection device according to claim 1.

3. The first displacement characteristic indicates a change in the displacement amount of the piezoelectric element corresponding to a change in the potential difference between the first electrode and the second electrode; The driving method for a liquid ejection device according to claim 1.

4. The drive signal generation unit further generates a third drive signal including a discharge potential change element that is supplied to the first electrode and displaces the piezoelectric element so as to cause pressure fluctuations in the liquid in the pressure chamber to such an extent that droplets are discharged from a nozzle communicating with the pressure chamber, Sets the minimum potential and the maximum potential of the discharge potential change element according to the characteristic information including the first displacement characteristic; The driving method for a liquid ejection device according to claim 1.

5. The end potential of the potential change element of the first drive signal is different for each of the plurality of combinations; The potentials maintained by the potential maintenance elements of the second drive signals are equal to each other for the plurality of combinations; The driving method for a liquid ejection device according to claim 1.

6. The end potential of the potential change element of the first drive signal is equal for each of the plurality of combinations; The potentials maintained by the potential maintenance elements of the second drive signals are different for each of the plurality of combinations; The driving method for a liquid ejection device according to claim 1.

7. When the potential change element of the first drive signal is supplied, the volume of the pressure chamber when the start potential is applied is smaller than the volume of the pressure chamber when the end potential is applied. The driving method of the liquid ejection device according to claim 1.

8. The potential differences between the start potential and the end potential of the potential change element are equal to each other in the plurality of sets. The driving method of the liquid ejection device according to claim 1.

9. At a first timing, specify the first displacement characteristics for each of the plurality of sets, at a second timing after a predetermined period from the first timing, detect the residual vibration signal for each of the plurality of sets, specify the second displacement characteristics of the piezoelectric element based on the residual vibration signals of the plurality of sets, The detection unit determines the change state of the displacement characteristics of the piezoelectric element based on the difference between the first displacement characteristics and the second displacement characteristics. The driving method of the liquid ejection device according to claim 1.

10. The first displacement characteristics are specified from the amplitude states of a plurality of residual vibration signals detected at the first timing, The second displacement characteristics are specified from the amplitude states of a plurality of residual vibration signals detected at the second timing. The driving method of the liquid ejection device according to claim 9.

11. The first displacement characteristics are based on the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals detected at the first timing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. specified, The second displacement characteristics are based on the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals detected at the second timing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. specified, The driving method of the liquid ejection device according to claim 10.

12. The first displacement characteristics are the withstand voltage of the piezoelectric element specified from the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals detected at the first timing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. The second displacement characteristic is the piezoelectric voltage of the piezoelectric element specified from the correlation between the spectral intensity of a predetermined frequency component obtained from the frequency analysis of a plurality of residual vibration signals detected at the second timing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. Determining a change state of the displacement characteristic of the piezoelectric element based on the difference between the piezoelectric voltage of the piezoelectric element that is the first displacement characteristic and the piezoelectric voltage of the piezoelectric element that is the second displacement characteristic. The driving method of the liquid ejection device according to claim 11.

13. The first displacement characteristic is specified based on the correlation between the amplitude of the residual vibration obtained by subjecting the plurality of residual vibration signals detected at the first timing to curve fitting processing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. The second displacement characteristic is specified based on the correlation between the amplitude of the residual vibration obtained by subjecting the plurality of residual vibration signals detected at the second timing to curve fitting processing and the potential difference between the end potential of the potential change element and the potential maintained by the potential maintaining element. The driving method of the liquid ejection device according to claim 10.

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