Liquid ejection device

Abstract

To accurately determine a discharge condition in a discharge part.SOLUTION: A liquid discharge device comprises: a discharge part that discharges liquid charged into a pressure chamber in accordance with displacement of a piezoelectric element; a generation part that generates a driving signal which has a first waveform produced in a first period of time which commences at a first time and displaces the piezoelectric element in a first direction and a second waveform produced in a second period of time which commences at a second time after the first period of time ends and displaces the piezoelectric element in a second direction which is opposite to the first direction; and a detecting part that detects vibrations remaining in the discharge part in a detection period which commences after the second period of time ends. The difference between a time length from the first time to the second time and a time length which is natural multiples of a period of vibrations caused in the discharge part is shorter than one-quarter times the period of vibrations caused in the discharge part.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] In a liquid ejection device such as an inkjet printer, a piezoelectric element provided in a ejection unit included in the liquid ejection device is driven by a drive signal to be displaced, so that a liquid such as ink filled in a pressure chamber provided in the ejection unit is ejected, and an image is formed on a medium such as a recording paper. In such a liquid ejection device, due to the thickening of the liquid filled in the ejection unit, ejection abnormalities may occur where the liquid cannot be normally ejected from the ejection unit. When an ejection abnormality occurs, dots that are supposed to be formed on the medium by the liquid ejected from the ejection unit cannot be accurately formed, and the image quality of the image formed on the medium deteriorates. For this reason, conventionally, a technique has been proposed to prevent a decrease in image quality due to ejection abnormalities by determining the ejection state of the liquid in the ejection unit based on the period of vibration generated in the ejection unit driven by a drive signal (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional technology, when the degree of thickening of the liquid filled in the ejection unit is slight, there is a high possibility that the ejection state in the ejection unit cannot be accurately determined.

Means for Solving the Problems

[0005] In order to solve the above problems, a liquid ejection device according to the present invention includes an ejection unit that ejects a liquid filled in a pressure chamber in response to displacement of a piezoelectric element, a first waveform provided in a first period starting at a first time and displacing the piezoelectric element in a first direction, and a second waveform provided in a second period starting at a second time after the end of the first period and displacing the piezoelectric element in a second direction opposite to the first direction, a generation unit that generates a drive signal having the first waveform and the second waveform, and a detection unit that detects vibration remaining in the ejection unit in a detection period starting after the end of the second period, wherein a difference between a time length from the first time to the second time and a time length that is a natural number multiple of a period of vibration generated in the ejection unit is shorter than a quarter multiple of the period of vibration generated in the ejection unit.

Brief Description of the Drawings

[0006]

Figure 1

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[0007] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each figure, the dimensions and scales of each part are appropriately different from the actual ones. Further, the embodiments described below are preferred specific examples of the present invention, and thus various technically preferable limitations are imposed. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to particularly limit the present invention.

[0008] <<A. Embodiment>> In the present embodiment, an inkjet printer that ejects ink to form an image on a recording paper P will be exemplified to describe a liquid ejection device. In the present embodiment, the ink is an example of "liquid", and the recording paper P is an example of "medium".

[0009] <<1. Outline of Inkjet Printer>> Hereinafter, with reference to FIGS. 1 to 4, an example of the configuration of an inkjet printer 1 according to the present embodiment will be described.

[0010] FIG. 1 is a functional block diagram showing an example of the configuration of the inkjet printer 1.

[0011] As illustrated in FIG. 1, print data Img indicating an image to be formed by the inkjet printer 1 is supplied to the inkjet printer 1 from a host computer such as a personal computer or a digital camera. The inkjet printer 1 executes a printing process for forming an image indicated by the print data Img supplied from the host computer on the recording paper P.

[0012] As illustrated in FIG. 1, the inkjet printer 1 includes a control unit 2 that controls each part of the inkjet printer 1, a head unit 3 provided with a discharge unit D that discharges ink, a drive signal generation unit 4 that generates a drive signal Com for driving the discharge unit D, a conveyance unit 7 that changes the relative position of the recording paper P with respect to the head unit 3, and a determination unit 8 that determines the discharge state of the ink in the discharge unit D.

[0013] In this embodiment, it is assumed that the inkjet printer 1 includes one or more head units 3, one or more drive signal generation units 4 that correspond one-to-one with the one or more head units 3, and one or more determination units 8 that correspond one-to-one with the one or more head units 3. However, hereinafter, for convenience of explanation, as illustrated in FIG. 1, one head unit 3 among the one or more head units 3, one drive signal generation unit 4 provided corresponding to one head unit 3 among the one or more drive signal generation units 4, and one determination unit 8 provided corresponding to one head unit 3 among the one or more determination units 8 will be described by focusing on them.

[0014] The control unit 2 is configured to include one or more CPUs. However, the control unit 2 may be provided with a programmable logic device such as an FPGA instead of or in addition to the CPU. Here, CPU is an abbreviation for Central Processing Unit, and FPGA is an abbreviation for field-programmable gate array. Further, the control unit 2 is configured to include one or both 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).

[0015] As will be described in detail later, the control unit 2 generates signals for controlling the operations of the respective parts of the inkjet printer 1, such as the print signal SI and the waveform designation signal dCom. Here, the waveform designation signal dCom is a digital signal that defines the waveform of the drive signal Com. Also, the drive signal Com is an analog signal for driving the ejection unit D. In the present embodiment, it is assumed that the drive signal Com includes a drive signal Com-A and a drive signal Com-B. The drive signal generation unit 4 includes a DA conversion circuit and generates a drive signal Com having a waveform defined by the waveform designation signal dCom. Also, the print signal SI is a digital signal for designating the type of operation of the ejection unit D. Specifically, the print signal SI is a signal that designates the type of operation of the ejection unit D by designating whether or not to supply the drive signal Com to the ejection unit D.

[0016] As illustrated in FIG. 1, the head unit 3 includes a supply circuit 31, a recording head 32, and a detection circuit 33.

[0017] The recording head 32 includes M ejection units D. Here, the value M is a natural number satisfying "M ≧ 1". In the following, among the M ejection units D provided in the recording head 32, the m-th ejection unit D may be referred to as ejection unit D[m]. Here, the variable m is a natural number satisfying "1 ≦ m ≦ M". Also, in the following, when a component or signal of the inkjet printer 1 corresponds to the ejection unit D[m] among the M ejection units D, a subscript [m] may be attached to the symbol representing the component or signal.

[0018] The supply circuit 31 switches whether to supply the drive signal Com to the ejection unit D[m] based on the print signal SI. In the following, among the drive signals Com, the drive signal Com supplied to the ejection unit D[m] may be referred to as the supply drive signal Vin[m]. Also, the supply circuit 31 switches whether to supply a detection potential signal VX[m] indicating the potential of the upper electrode Zu[m] of the piezoelectric element PZ[m] included in the ejection unit D[m] to the detection circuit 33 based on the print signal SI. Hereinafter, when a detection potential signal VX[m] is supplied from the ejection unit D[m] to the detection circuit 33, the ejection unit D[m] may be referred to as a determination target ejection unit DS. Also, hereinafter, an ejection unit D other than the determination target ejection unit DS may be referred to as a non-determination target ejection unit DP. Note that the piezoelectric element PZ[m] and the upper electrode Zu[m] will be described later with reference to FIG. 3.

[0019] The detection circuit 33 generates a detection signal SK[m] based on the detection potential signal VX[m] supplied from the determination target ejection unit DS via the supply circuit 31. Specifically, the detection circuit 33 generates the detection signal SK[m] by, for example, amplifying the detection potential signal VX[m] and removing noise components.

[0020] The determination unit 8 determines, based on the detection signal SK[m], whether the ink ejection state in the ejection unit D[m] is normal, that is, whether it is a normal ejection state in which no ejection abnormality occurs in the ejection unit D[m], and generates ejection state determination information JH[m] indicating the determination result. Here, ejection abnormality refers to a state in which the ink ejection state in the ejection unit D[m] becomes abnormal, that is, a general term for states in which ink cannot be accurately ejected from the nozzles N provided in the ejection unit D[m]. For example, ejection abnormality includes a state in which ink cannot be ejected from the ejection unit D[m], a state in which the ejection unit D[m] ejects an amount of ink different from the ink ejection amount defined by the drive signal Com, and a state in which the ejection unit D[m] ejects ink at a speed different from the ink ejection speed defined by the drive signal Com, and the like. Note that hereinafter, processing related to the determination of the ink ejection state in the ejection unit D[m] may be referred to as ejection state determination processing. That is, the determination target ejection unit DS is the ejection unit D[m] that is the target of the ejection state determination processing.

[0021] When the printing process is executed, the control unit 2 generates signals for controlling the head unit 3 such as the printing signal SI based on the print data Img. Also, when the printing process is executed, the control unit 2 generates signals for controlling the drive signal generation unit 4 such as the waveform designation signal dCom. Further, when the printing process is executed, the control unit 2 generates signals for controlling the conveyance unit 7. Thereby, in the printing process, the control unit 2 controls the conveyance unit 7 so as to change the relative position of the recording paper P with respect to the head unit 3, and adjusts the presence or absence of ink ejection from the ejection unit D[m], the ink ejection amount, the ink ejection timing, etc., and controls each part of the inkjet printer 1 so that an image corresponding to the print data Img is formed on the recording paper P.

[0022] When the ejection state determination process is executed, the control unit 2 generates a printing signal SI that designates that the ejection unit D[m] is to be driven as the ejection unit DS to be determined, and supplies the printing signal SI to the supply circuit 31. In this case, the printing signal SI designates that a detection potential signal VX[m] is to be supplied from the ejection unit D[m] to the detection circuit 33. Thereafter, in the ejection state determination process, the detection circuit 33 generates a detection signal SK[m] based on the detection potential signal VX[m] supplied via the supply circuit 31 from the ejection unit D[m] driven as the ejection unit DS to be determined. Then, in the ejection state determination process, the determination unit 8 generates ejection state determination information JH[m] based on the detection signal SK[m] supplied from the detection circuit 33.

[0023] FIG. 2 is a perspective view showing an example of a schematic internal structure of the inkjet printer 1.

[0024] As illustrated in FIG. 2, in the present embodiment, it is assumed that the inkjet printer 1 is a serial printer. Specifically, when the inkjet printer 1 executes a printing process, while conveying the recording paper P in the sub-scanning direction, the head unit 3 is reciprocated in the main scanning direction intersecting the sub-scanning direction, and ink is ejected from the ejection unit D[m], thereby forming dots corresponding to the print data Img on the recording paper P. Hereinafter, the +X direction and the -X direction which is the reverse direction thereof are collectively referred to as the "X-axis direction", the +Y direction intersecting the X-axis direction and the -Y direction which is the reverse direction thereof are collectively referred to as the "Y-axis direction", and the +Z direction intersecting the X-axis direction and the Y-axis direction and the -Z direction which is the reverse direction thereof are collectively referred to as the "Z-axis direction". And in the present embodiment, as illustrated in FIG. 2, the direction from the upstream -X side to the downstream +X side is defined as the sub-scanning direction, and the +Y direction and the -Y direction are defined as the main scanning directions. Also, in the present embodiment, as illustrated in FIG. 2, it is assumed that the +Z direction corresponds to the ink ejection direction from the ejection unit D[m].

[0025] As illustrated in FIG. 2, the inkjet printer 1 according to the present embodiment includes a housing 100 and a carriage 110 that can reciprocate in the Y-axis direction within the housing 100 and mounts one or a plurality of head units 3. In the present embodiment, as illustrated in FIG. 2, it is assumed that the carriage 110 stores four ink cartridges 120 that correspond one-to-one to four colors of ink, namely cyan, magenta, yellow, and black. Also, in the present embodiment, as an example, it is assumed that the inkjet printer 1 includes four head units 3 that correspond one-to-one to the four ink cartridges 120. Each ejection unit D[m] receives ink supply from the ink cartridge 120 corresponding to the head unit 3 provided with the ejection unit D[m]. Thereby, each ejection unit D[m] can fill the supplied ink therein and eject the filled ink from the nozzle N. Note that the ink cartridge 120 may be provided outside the carriage 110. The nozzle N will be described later with reference to FIG. 3.

[0026] Also, as described above, the inkjet printer 1 according to the present embodiment includes a conveyance unit 7. As illustrated in FIG. 2, the conveyance unit 7 includes a carriage conveyance mechanism 71 for reciprocating the carriage 110 in the Y-axis direction, a carriage guide shaft 76 that supports the carriage 110 so as to be reciprocable in the Y-axis direction, a medium conveyance mechanism 73 for conveying the recording paper P, and a platen 75 provided on the +Z side of the carriage 110. Therefore, when the printing process is executed, the conveyance unit 7 reciprocates the head unit 3 together with the carriage 110 in the Y-axis direction along the carriage guide shaft 76 by the carriage conveyance mechanism 71, and conveys the recording paper P on the platen 75 in the +X direction by the medium conveyance mechanism 73, thereby changing the relative position of the recording paper P with respect to the head unit 3 and enabling the ink to land on the entire recording paper P.

[0027] FIG. 3 is a schematic partial cross-sectional view of the recording head 32 cut so as to include the discharge portion D[m].

[0028] As illustrated in FIG. 3, the ejection unit D[m] includes a piezoelectric element PZ[m], a cavity 322 filled with ink therein, a nozzle N communicating with the cavity 322, and a diaphragm 321. When the piezoelectric element PZ[m] is driven by a supply drive signal Vin[m], the ink in the cavity 322 is ejected from the nozzle N. The cavity 322 is a space partitioned by a cavity plate 324, a nozzle plate 323 in which the nozzle N is formed, and the diaphragm 321. The cavity 322 communicates with a reservoir 325 via an ink supply port 326. The reservoir 325 communicates with an ink cartridge 120 corresponding to the ejection unit D[m] via an ink intake port 327. The piezoelectric element PZ[m] has an upper electrode Zu[m], a lower electrode Zd[m], and a piezoelectric body Zm[m] provided between the upper electrode Zu[m] and the lower electrode Zd[m]. The lower electrode Zd[m] is electrically connected to a power supply line Ld set to a potential VBS. When a supply drive signal Vin[m] is supplied to the upper electrode Zu[m] and a voltage is applied between the upper electrode Zu[m] and the lower electrode Zd[m], the piezoelectric element PZ[m] is displaced in the +Z direction or the -Z direction according to the applied voltage, and as a result, the piezoelectric element PZ[m] vibrates. The lower electrode Zd[m] is joined to the diaphragm 321. Therefore, when the piezoelectric element PZ[m] is driven by the supply drive signal Vin[m] and vibrates, the diaphragm 321 also vibrates. Then, due to the vibration of the diaphragm 321, the volume of the cavity 322 and the pressure in the cavity 322 change, and the ink filled in the cavity 322 is ejected from the nozzle N.

[0029] FIG. 4 is an explanatory diagram for explaining an example of the arrangement of four head units 3 mounted on the carriage 110 and a total of 4M nozzles N provided in the four head units 3 when the inkjet printer 1 is viewed in plan from the +Z direction.

[0030] As illustrated in FIG. 4, each head unit 3 provided in the carriage 110 is provided with a nozzle row NL. Here, the nozzle row NL is a plurality of nozzles N provided so as to extend in a row in a predetermined direction. In the present embodiment, as an example, a case where each nozzle row NL is composed of M nozzles N arranged so as to extend in the X-axis direction is assumed.

[0031] <<2. Configuration of Head Unit>> Hereinafter, the configuration of the head unit 3 will be described with reference to FIG. 5.

[0032] FIG. 5 is a block diagram showing an example of the configuration of the head unit 3.

[0033] As illustrated in FIG. 5, the head unit 3 includes a supply circuit 31, a recording head 32, and a detection circuit 33. Further, the head unit 3 includes a wiring La to which a drive signal Com-A is supplied from the drive signal generation unit 4, a wiring Lb to which a drive signal Com-B is supplied from the drive signal generation unit 4, and a wiring Ls for supplying a detection potential signal VX[m] to the detection circuit 33.

[0034] As illustrated in FIG. 5, the supply circuit 31 includes M discharge units D[1] to D[M], M switches Wa[1] to Wa[M] corresponding one-to-one to the M discharge units D[1] to D[M], M switches Wb[1] to Wb[M] corresponding one-to-one to the M discharge units D[1] to D[M], M switches Ws[1] to Ws[M] corresponding one-to-one to the M discharge units D[1] to D[M], and a connection state designation circuit 310 for designating the connection state of each switch. Among these, the connection state designation circuit 310 generates a connection state designation signal Qa[m] for designating the on / off of the switch Wa[m], a connection state designation signal Qb[m] for designating the on / off of the switch Wb[m], and a connection state designation signal Qs[m] for designating the on / off of the switch Ws[m] based on at least some of the print signal SI, latch signal LAT, period designation signal Tsig, and change signal CH supplied from the control unit 2. Here, switch Wa[m] switches between conduction and non-conduction of wiring La and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the ejection unit D[m] based on the connection state designation signal Qa[m]. In the present embodiment, switch Wa[m] turns on when the connection state designation signal Qa[m] is at a high level and turns off when it is at a low level. When switch Wa[m] is on, the drive signal Com-A supplied to wiring La is supplied as the supply drive signal Vin[m] to the upper electrode Zu[m] of the ejection unit D[m]. Also, switch Wb[m] switches between conduction and non-conduction of wiring Lb and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the ejection unit D[m] based on the connection state designation signal Qb[m]. In the present embodiment, switch Wb[m] turns on when the connection state designation signal Qb[m] is at a high level and turns off when it is at a low level. When switch Wb[m] is on, the drive signal Com-B supplied to wiring Lb is supplied as the supply drive signal Vin[m] to the upper electrode Zu[m] of the ejection unit D[m]. Also, switch Ws[m] switches between conduction and non-conduction of wiring Ls and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the ejection unit D[m] based on the connection state designation signal Qs[m]. In the present embodiment, switch Ws[m] turns on when the connection state designation signal Qs[m] is at a high level and turns off when it is at a low level. When switch Ws[m] is on, the potential of the upper electrode Zu[m] of the ejection unit D[m] is supplied as the detection potential signal VX[m] to the detection circuit 33 via wiring Ls.

[0035] Also, the detection circuit 33 generates a detection signal SK[m] having a waveform corresponding to the waveform of the detection potential signal VX[m] based on the detection potential signal VX[m] supplied from wiring Ls.

[0036] <<3. Operation of the Head Unit>> Hereinafter, the operation of the head unit 3 will be described with reference to FIGS. 6 and 7.

[0037] In this embodiment, when the inkjet printer 1 executes printing processing or ejection state determination processing, one or a plurality of unit periods TP are set as the operation period of the inkjet printer 1. The inkjet printer 1 according to this embodiment can drive each ejection unit D[m] for printing processing or ejection state determination processing in each unit period TP.

[0038] FIG. 6 is a timing chart for showing the operation of the inkjet printer 1 in the unit period TP. As illustrated in FIG. 6, the control unit 2 outputs a latch signal LAT having a pulse PLL. Thereby, the control unit 2 defines the unit period TP as the period from the rising edge of the pulse PLL to the rising edge of the next pulse PLL. Further, the control unit 2 outputs a change signal CH having a pulse PLC in the unit period TP. Then, the control unit 2 divides the unit period TP into a control period TQ1 from the rising edge of the pulse PLL to the rising edge of the pulse PLC and a control period TQ2 from the rising edge of the pulse PLC to the rising edge of the pulse PLL. Further, the control unit 2 outputs a period designation signal Tsig having a pulse PLT1 and a pulse PLT2 in the unit period TP. Then, the control unit 2 divides the unit period TP into a control period TSS1 from the rising edge of the pulse PLL to the rising edge of the pulse PLT1, a control period TSS2 from the rising edge of the pulse PLT1 to the rising edge of the pulse PLT2, and a control period TSS3 from the rising edge of the pulse PLT2 to the rising edge of the pulse PLL.

[0039] The print signal SI according to this embodiment includes M individual designation signals Sd[1] to Sd[M] that correspond one-to-one with the M ejection units D[1] to D[M]. The individual designation signal Sd[m] designates the driving mode of the ejection unit D[m] in each unit period TP when the inkjet printer 1 executes printing processing or ejection state determination processing. As illustrated in FIG. 6, prior to each unit period TP, the control unit 2 supplies a print signal SI including individual designation signals Sd[1] to Sd[M] to the connection state designation circuit 310 in synchronization with the clock signal CL. Then, in the unit period TP, the connection state designation circuit 310 generates a connection state designation signal Qa[m], a connection state designation signal Qb[m], and a connection state designation signal Qs[m] based on the individual designation signal Sd[m].

[0040] In this embodiment, it is assumed that the ejection unit D[m] can form any one of a large dot, a medium dot smaller than the large dot, and a small dot smaller than the medium dot in the unit period TP. And in this embodiment, the individual designation signal Sd[m] is a value "1" for designating the ejection unit D[m] as the large dot forming ejection unit DP-1 which is a non-judgment target ejection unit DP for ejecting an amount of ink corresponding to a large dot, a value "2" for designating the ejection unit D[m] as the medium dot forming ejection unit DP-2 which is a non-judgment target ejection unit DP for ejecting an amount of ink corresponding to a medium dot, a value "3" for designating the ejection unit D[m] as the small dot forming ejection unit DP-3 which is a non-judgment target ejection unit DP for ejecting an amount of ink corresponding to a small dot, a value "4" for designating the ejection unit D[m] as the dot non-forming ejection unit DP-4 which is a non-judgment target ejection unit DP for not ejecting ink, and a value "5" for designating the ejection unit D[m] as the judgment target ejection unit DS. It is assumed that the individual designation signal Sd[m] can take any one of these five values.

[0041] As illustrated in FIG. 6, in the present embodiment, the drive signal Com-A has a waveform PP1 provided in a control period TQ1 and a waveform PP2 provided in a control period TQ2. Among these, the waveform PP1 is a waveform that returns from the reference potential V0 to the reference potential V0 via a potential VL1 lower than the reference potential V0 and a potential VH1 higher than the reference potential V0. When the supply drive signal Vin[m] having the waveform PP1 is supplied to the ejection unit D[m], the waveform PP1 is defined such that ink corresponding to an ink amount ξ1 is ejected from the ejection unit D[m]. Further, the waveform PP2 is a waveform that returns from the reference potential V0 to the reference potential V0 via a potential VL2 lower than the reference potential V0 and a potential VH2 higher than the reference potential V0. When the supply drive signal Vin[m] having the waveform PP2 is supplied to the ejection unit D[m], the waveform PP2 is defined such that ink corresponding to an ink amount ξ2 is ejected from the ejection unit D[m]. In the present embodiment, the ink amount ξ1 is an ink amount corresponding to a medium dot. Further, in the present embodiment, the ink amount ξ2 is an ink amount less than the ink amount ξ1 and corresponds to a small dot. Further, in the present embodiment, the sum of the ink amount ξ1 and the ink amount ξ2 is an ink amount corresponding to a large dot. In the present embodiment, as an example, when the potential of the supply drive signal Vin[m] supplied to the ejection unit D[m] is at a high potential, it is assumed that the volume of the cavity 322 provided in the ejection unit D[m] becomes smaller compared to the case when the potential is at a low potential. Therefore, when the ejection unit D[m] is driven by the supply drive signal Vin[m] having the waveform PP1 or the waveform PP2, the ink in the ejection unit D[m] is ejected from the nozzle N as the potential of the supply drive signal Vin[m] changes from a low potential to a high potential.

[0042] As illustrated in FIG. 6, in the present embodiment, the drive signal Com-B has a waveform PS provided in a unit period TP. Here, the waveform PS changes from the reference potential V0 to a potential VS3 via a potential VS1 and a potential VS2 in a control period TSS1, maintains the potential VS3 in a control period TSS2, and changes from the potential VS3 to the reference potential V0 in a control period TSS3. In this embodiment, the potential VS1 is higher than the reference potential V0. However, the potential VS1 may be the same as the reference potential V0. Also, in this embodiment, the potential VS2 is lower than the reference potential V0. However, the potential VS2 may be lower than the potential VS1. Further, in this embodiment, the potential VS3 is lower than the reference potential V0 and higher than the potential VS2. However, the potential VS3 may be higher than the potential VS2. Hereinafter, among the waveform PS, the portion that changes from the potential VS1 to the potential VS2 is referred to as waveform PS1, and the portion that changes from the potential VS2 to the potential VS3 in the waveform PS is referred to as waveform PS2. In this embodiment, the waveform PS1 is a waveform for displacing the piezoelectric element PZ[m] in the -Z direction, and the waveform PS2 is a waveform for displacing the piezoelectric element PZ[m] in the +Z direction. Also, hereinafter, among the control period TSS1, the period in which the waveform PS1 is provided is referred to as period T1, the period in which the waveform PS2 is provided in the control period TSS1 is referred to as period T2, the period from the end of period T1 to the start of period T2 is referred to as period TS12, and the period from the end of period T2 to the start of the control period TSS2 is referred to as period TS2k. Also, as described in FIG. 8 to be described later, the time when period T1 starts is referred to as time t11, the time when period T1 ends is referred to as time t12, the time when period T2 starts is referred to as time t21, the time when period T2 ends is referred to as time t22, and the time when the control period TSS2 starts is referred to as time tk. Note that in this embodiment, as an example, it is assumed that the waveform PS is defined so that ink is not ejected from the ejection unit D[m] when the supply drive signal Vin[m] having the waveform PS is supplied to the ejection unit D[m].

[0043] FIG. 7 is an explanatory diagram for explaining the relationship between the individual designation signal Sd[m] and the connection state designation signals Qa[m], Qb[m], and Qs[m] in the unit period TP.

[0044] As illustrated in FIG. 7, when the individual designation signal Sd[m] indicates the value "1" that designates the ejection unit D[m] as the large dot formation ejection unit DP-1 in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal Qa[m] to the high level over the control period TQ1 and the control period TQ2. In this case, the switch Wa[m] is turned on over the unit period TP. For this reason, the ejection unit D[m] is driven by the supply drive signal Vin[m] having the waveforms PP1 and PP2 in the unit period TP, and ejects an amount of ink corresponding to a large dot. Also, when the individual designation signal Sd[m] indicates the value "2" that designates the ejection unit D[m] as the medium dot formation ejection unit DP-2 in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal Qa[m] to the high level in the control period TQ1. In this case, the switch Wa[m] is turned on in the control period TQ1. For this reason, the ejection unit D[m] is driven by the supply drive signal Vin[m] having the waveform PP1 in the unit period TP, and ejects an amount of ink corresponding to a medium dot. Also, when the individual designation signal Sd[m] indicates the value "3" that designates the ejection unit D[m] as the small dot formation ejection unit DP-3 in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal Qa[m] to the high level in the control period TQ2. In this case, the switch Wa[m] is turned on in the control period TQ2. For this reason, the ejection unit D[m] is driven by the supply drive signal Vin[m] having the waveform PP2 in the unit period TP, and ejects an amount of ink corresponding to a small dot. Also, when the individual designation signal Sd[m] indicates the value "4" that designates the ejection unit D[m] as the dot non-formation ejection unit DP-4 in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal Qa[m], the connection state designation signal Qb[m], and the connection state designation signal Qs[m] to the low level over the unit period TP. In this case, the switch Wa[m], the switch Wb[m], and the switch Ws[m] are turned off over the unit period TP. For this reason, the supply drive signal Vin[m] is not supplied to the ejection unit D[m] in the unit period TP, and no ink is ejected from the ejection unit D[m].

[0045] Also, when the individual designation signal Sd[m] indicates the value "5" that designates the discharge unit D[m] as the determination target discharge unit DS in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal Qb[m] to a high level in the control periods TSS1 and TSS3, and sets the connection state designation signal Qs[m] to a high level in the control period TSS2. In this case, the switch Wb[m] is turned on in the control periods TSS1 and TSS3, and the switch Ws[m] is turned on in the control period TSS2. Therefore, when vibration occurs in the discharge unit D[m] as a result of the discharge unit D[m] designated as the determination target discharge unit DS being driven by the supply drive signal Vin[m] having the waveforms PS1 and PS2 in the control period TSS1, the vibration remains in the control period TSS2 as well. And when vibration remains in the discharge unit D[m] in the control period TSS2, the potential of the upper electrode Zu[m] provided in the discharge unit D[m] changes. And when vibration remains in the discharge unit D[m] in the control period TSS2, the potential of the upper electrode Zu[m] is supplied to the detection circuit 33 as the detection potential signal VX[m] via the switch Ws[m]. That is, the waveform of the detection potential signal VX[m] detected from the discharge unit D[m] in the control period TSS2 indicates the waveform of the vibration remaining in the discharge unit D[m] in the control period TSS2. And the waveform of the detection signal SK[m] generated based on the detection potential signal VX[m] detected from the discharge unit D[m] in the control period TSS2 indicates the waveform of the vibration remaining in the discharge unit D[m] in the control period TSS2.

[0046] <<4. Relationship between vibration remaining in discharge unit and drive signal>> Hereinafter, with reference to FIG. 8, the relationship between the drive signal Com and the vibration remaining in the discharge unit D will be described.

[0047] In this embodiment, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS represents a combined vibration BB, which is a combined vibration of the vibration B1 generated by the waveform PS1 and the vibration B2 generated by the waveform PS2, as illustrated in FIG. 8. In this embodiment, the periods TC of the vibration BB, the vibration B1, and the vibration B2 are the natural vibration periods of the determination target ejection unit DS.

[0048] In this embodiment, the control unit 2 controls the drive signal generation unit 4 so that a drive signal Com is generated in which the vibration B1 and the vibration B2 cancel each other out. Specifically, in this embodiment, the waveform PS of the drive signal Com is set such that the time length TX12 from the time t11 when the period T1 for generating the waveform PS1 for generating the vibration B1 starts to the time t21 when the period T2 for generating the waveform PS2 for generating the vibration B2 starts is a natural number multiple of the period TC.

[0049] In this embodiment, the waveform e1 of the vibration B1 at the time t of the control period TSS2 is represented by the following formula (1) when the ink ejection state in the determination target ejection unit DS is normal.

Equation

[0050] Here, the value E1 is the amplitude of the vibration B1 at the time t. The value ω is a value determined based on the acoustic resistance in the ejection unit D, the weight of the ink in the ejection unit D, and the compliance of the ejection unit D. The value θ1 is a value determined based on the time interval between the time t11 and the time t.

[0051] Also, in this embodiment, the waveform e2 of the vibration B2 at the time t is represented by the following formula (2) when the ink ejection state in the determination target ejection unit DS is normal.

Equation

[0052] Here, the value E2 is the amplitude of the vibration B2 at time t. Also, the value θ2 is a value determined based on the time interval between time t21 and time t, and satisfies the following formula (3). In formula (3), the value k is a natural number of 1 or more.

Equation

[0053] In this embodiment, when the ink ejection state in the determination target ejection unit DS is normal, the control unit 2 controls the drive signal generation unit 4 so that the drive signal generation unit 4 generates a drive signal Com such that the amplitudes E1 and E2 are substantially the same. Here, in this specification, "substantially the same" is a concept including cases where, in addition to being exactly the same, it can be regarded as the same considering errors. Therefore, when the ink ejection state in the determination target ejection unit DS is normal, the waveform eb of the vibration BB at time t is represented by the following formula (4).

Equation

[0054] Also, in this embodiment, when the ink in the determination target ejection unit DS thickens and ejection abnormality occurs in the determination target ejection unit DS, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS indicates a combined vibration BBz, which is a combined vibration of the vibration B1z generated by the waveform PS1 and the vibration B2z generated by the waveform PS2, as illustrated in FIG. 8.

[0055] In this embodiment, the waveform e1z of the vibration B1z at time t of the control period TSS2 is represented by the following formula (5). In formula (5), the value E1z is the amplitude of the vibration B1z at time t. The amplitude E1z is smaller than the amplitude E1.

Equation

[0056] Also, in the present embodiment, the waveform e2z of the vibration B2z at time t during the control period TSS2 is represented by the following formula (6). In formula (6), the value E2z is the amplitude of the vibration B2z at time t. The amplitude E2z is smaller than the amplitude E2.

Equation

[0057] And the waveform ebz of the vibration BBz at time t is represented by the following formula (7).

Equation

[0058] Note that when the ink in the determination target discharge unit DS thickens and discharge abnormality occurs in the determination target discharge unit DS, the attenuation rate of the vibration generated in the determination target discharge unit DS becomes higher compared to the case where the ink has not thickened. Also, the time interval between time t11 and time t is longer than the time interval between time t21 and time t. For this reason, in the present embodiment, the degree of attenuation of the vibration generated in the determination target discharge unit DS during the period from time t11 to time t is greater than the degree of attenuation of the vibration generated in the determination target discharge unit DS during the period from time t21 to time t. Therefore, in the present embodiment, even when "E1≒E2" holds between the amplitude E1 and the amplitude E2, the relationship "E1z<E2z" holds between the amplitude E1z and the amplitude E2z. That is, the amplitude of the vibration BBz becomes larger than the amplitude of the vibration BB.

[0059] In this embodiment, the determination unit 8 determines whether the maximum value of the amplitude of the detection potential signal VX is equal to or greater than a predetermined reference amplitude based on the detection signal SK. Then, when the maximum value of the amplitude of the detection potential signal VX is less than the predetermined reference amplitude, the determination unit 8 determines that vibration BB is occurring in the determination target discharge unit DS, determines that the ink discharge state in the determination target discharge unit DS is normal, and generates discharge state determination information JH indicating the determination result. On the other hand, when the maximum value of the amplitude of the detection potential signal VX is equal to or greater than the predetermined reference amplitude, the determination unit 8 determines that vibration BBz is occurring in the determination target discharge unit DS, determines that a discharge abnormality due to thickening has occurred in the determination target discharge unit DS, and generates discharge state determination information JH indicating the determination result.

[0060] Note that in this embodiment, the waveform PS of the drive signal Com is set so that the time length TX12 is a natural multiple of the period TC, but the present invention is not limited to such a mode. For example, the time length TX12 may be determined so as to satisfy the following formula (8).

Equation

[0061] Also, in this embodiment, the values θ1 and θ2 are determined so as to satisfy the above-described formula (3), but the present invention is not limited to such a mode. For example, the values θ1 and θ2 may be determined so as to satisfy the following formula (9).

Equation

[0062] <<5. Reference Example>> Hereinafter, the drive signal Com related to reference will be described with reference to FIG. 9.

[0063] The drive signal Com according to the reference example differs from the drive signal Com according to the embodiment in that the drive signal Com-W is included instead of the drive signal Com-B.

[0064] As illustrated in FIG. 9, the drive signal Com-W changes from the reference potential V0 to a potential VS4 lower than the reference potential V0 and then to a potential VS5 higher than the reference potential V0 during the control period TSS1, maintains the potential VS5 during the control period TSS2, and changes from the potential VS5 to the reference potential V0 during the control period TSS3. Specifically, the drive signal Com-W is provided with a waveform PS1w that changes from the reference potential V0 to the potential VS4 during a period T1w that starts at time t11w and ends at time t12w within the control period TSS1, maintains the potential VS4 during a period TS1w that starts at time t12w and ends at time t21w within the control period TSS1, is provided with a waveform PS2w that changes from the potential VS4 to the potential VS5 during a period T2w that starts at time t21w and ends at time t22w within the control period TSS1, and maintains the potential VS5 during a period TS2w that starts at time t22w and ends at time tk within the control period TSS1. Also in the reference example, as in the embodiment, the supply drive signal Vin having the drive signal Com-W is supplied to the determination target ejection unit DS during the control periods TSS1 and TSS3, and the supply of the drive signal Com is stopped during the control period TSS2. Also in the reference example, as in the embodiment, a detection potential signal VX indicating the potential of the upper electrode Zu is supplied from the determination target ejection unit DS to the detection circuit 33 during the control period TSS2.

[0065] Note that in the reference example, the time length TXw from time t11w to time t21w is determined so as to satisfy the following formula (10).

Equation

[0066] In the reference example, when the ink ejection state in the ejection unit DS to be determined is normal, the detection potential signal VX detected by the detection circuit 33 from the ejection unit DS to be determined indicates a combined vibration BW, which is a combined vibration of the vibration BW1 generated by the waveform PS1w and the vibration BW2 generated by the waveform PS2w, as illustrated in FIG. 9. In the reference example, the drive signal Com-W is set such that the vibration BW1 and the vibration BW2 reinforce each other to generate the vibration BW. Specifically, in the control period TSS2, the waveform ew1 of the vibration BW1 at time t is represented by the following equation (11), the waveform ew2 of the vibration BW2 at time t is represented by the following equation (12), and the waveform ew of the vibration BW at time t is represented by the following equation (13). Here, the amplitude EW1 is the amplitude of the vibration BW1 at time t, and the amplitude EW2 is the amplitude of the vibration BW2 at time t.

Number

[0067] Also, in the reference example, when the ink in the ejection unit DS to be determined thickens and ejection abnormality occurs in the ejection unit DS to be determined, the detection potential signal VX detected by the detection circuit 33 from the ejection unit DS to be determined indicates a combined vibration BWz, which is a combined vibration of the vibration BW1z generated by the waveform PS1w and the vibration BW2z generated by the waveform PS2w, as illustrated in FIG. 9. Specifically, in the control period TSS2, the waveform ew1z of the vibration BW1z at time t is represented by the following equation (14), the waveform ew2z of the vibration BW2z at time t is represented by the following equation (15), and the waveform ewz of the vibration BW at time t is represented by the following equation (16). Here, the amplitude EW1z is the amplitude of the vibration BW1z at time t, and the amplitude EW2z is the amplitude of the vibration BW2z at time t.

Number

[0068] In the reference example, the determination unit 8 determines, based on the detection signal SK, which of the vibrations BW and BWz the vibration occurring in the determination target ejection unit DS corresponds to.

[0069] Thus, in the reference example, the amplitude of the vibration BW is larger than the amplitude of the vibration BW1 and also larger than the amplitude of the vibration BW2. Also, in the reference example, the amplitude of the vibration BWz is larger than the amplitude of the vibration BW1z and also larger than the amplitude of the vibration BW2z. Therefore, according to the reference example, even when the vibration occurring in the determination target ejection unit DS is minute, the detection potential signal VX can be reliably detected by the detection circuit 33.

[0070] However, in the reference example, the amount of change in the amplitude of the vibration BW when the ink thickens in the determination target ejection unit DS, for example, the ratio of the amplitude of the vibration BWz to the amplitude of the vibration BW, is small. Therefore, when the degree of thickening of the ink in the determination target ejection unit DS is small, it may not be possible to accurately determine the ejection state of the ink in the determination target ejection unit DS.

[0071] On the other hand, according to the present embodiment, compared with the reference example, the amount of change in the amplitude of the vibration BB when the ink thickens in the determination target ejection unit DS is large. Specifically, the amount of change in the amplitude of the vibration BB when the ink thickens in the determination target ejection unit DS according to the present embodiment is larger than the amount of change in the amplitude of the vibration BW when the ink thickens in the determination target ejection unit DS according to the reference example. More specifically, for example, the ratio of the amplitude of the vibration BBz to the amplitude of the vibration BB in the present embodiment is larger than the ratio of the amplitude of the vibration BWz to the amplitude of the vibration BW in the reference example. Therefore, according to the present embodiment, compared with the reference example, even when the degree of thickening of the ink in the determination target ejection unit DS is small, it is possible to accurately determine the ejection state of the ink in the determination target ejection unit DS with high sensitivity.

[0072] <<6. Summary of the Embodiment>> As described above, the inkjet printer 1 according to the present embodiment includes a discharge unit D[m] that discharges the ink filled in the cavity 322 in accordance with the displacement of the piezoelectric element PZ[m], a waveform PS1 that is provided in a period T1 starting at time t11 and displaces the piezoelectric element PZ[m] in the -Z direction, and a waveform PS2 that is provided in a period T2 starting at time t21 and displaces the piezoelectric element PZ[m] in the +Z direction, a drive signal generation unit 4 that generates a drive signal Com, and a detection circuit 33 that detects vibrations remaining in the discharge unit D[m] in a control period TSS2 starting after the end of the period T2. The difference between the time length TX12 from time t11 to time t21 and an integer multiple of the vibration period TC generated in the discharge unit D[m] is less than one-fourth of the period TC. The inkjet printer 1 according to the present embodiment can increase, for example, the degree of difference between the amplitude of the vibration BB generated in the discharge unit D[m] when thickening does not occur in the ink filled in the discharge unit D[m] and the amplitude of the vibration BBz generated in the discharge unit D[m] when thickening occurs in the ink filled in the discharge unit D[m], as compared with the reference example. Therefore, according to the present embodiment, for example, even when the degree of thickening of the ink in the discharge unit D[m] is small as compared with the reference example, it is possible to accurately determine the ink discharge state in the discharge unit D[m]. In the present embodiment, the inkjet printer 1 is an example of a "liquid discharge device", the cavity 322 is an example of a "pressure chamber", the time t11 is an example of a "first time", the period T1 is an example of a "first period", the -Z direction is an example of a "first direction", the waveform PS1 is an example of a "first waveform", the time t21 is an example of a "second time", the period T2 is an example of a "second period", the +Z direction is an example of a "second direction", the waveform PS2 is an example of a "second waveform", the drive signal generation unit 4 is an example of a "generation unit", the control period TSS2 is an example of a "detection period", and the detection circuit 33 is an example of a "detection unit".

[0073] Further, the inkjet printer 1 according to the present embodiment may include a determination unit 8 that determines whether the ink filled in the cavity 322 has thickened based on the vibration detected by the detection circuit 33 during the control period TSS2. Therefore, the inkjet printer 1 according to the present embodiment can prevent a decrease in print quality due to thickening of the ink. In the present embodiment, the determination unit 8 is an example of a "determination section".

[0074] Further, in the inkjet printer 1 according to the present embodiment, the amplitude of the vibration B1 generated in the ejection unit D[m] at the time tk by the waveform PS1 and the amplitude of the vibration B2 generated in the ejection unit D[m] at the time tk by the waveform PS2 may be substantially the same. The inkjet printer 1 according to the present embodiment can increase, for example, the degree of difference between the amplitude of the vibration BB generated in the ejection unit D[m] when the ink filled in the ejection unit D[m] has not thickened and the amplitude of the vibration BBz generated in the ejection unit D[m] when the ink filled in the ejection unit D[m] has thickened, as compared with a reference example. Therefore, according to the present embodiment, it is possible to accurately determine the ink ejection state in the ejection unit D[m] even when the degree of thickening of the ink in the ejection unit D[m] is small, for example, as compared with the reference example. In the present embodiment, the vibration B1 is an example of a "first vibration", and the vibration B2 is an example of a "second vibration".

[0075] Further, in the inkjet printer 1 according to the present embodiment, the determination unit 8 may determine that the ink filled in the cavity 322 has thickened when the amplitude of the vibration detected by the detection circuit 33 during the control period TSS2 is equal to or greater than a reference amplitude. Therefore, the inkjet printer 1 according to the present embodiment can prevent a decrease in print quality due to thickening of the ink.

[0076] Also, the inkjet printer 1 according to the present embodiment includes a drive signal generation unit 4 that generates a drive signal Com, a discharge unit D[m] that discharges ink as the drive signal Com is supplied, and a detection circuit 33 that detects vibrations generated in the discharge unit D[m] driven by the drive signal Com. The drive signal generation unit 4 generates a drive signal Com-B that includes a waveform PS1 provided in a period T1 starting at time t11 and causing vibration B1 in the discharge unit D[m], and a waveform PS2 provided in a period T2 starting at time t21 and causing vibration B2 in the discharge unit D[m]. When the discharge unit D[m] is driven by the drive signal Com-B, the detection circuit 33 detects a combined vibration BB of the vibration B1 and the vibration B2 remaining in the discharge unit D[m] in a control period TSS2 starting after the end of the period T2, and the difference between the phase difference between the vibration B1 and the vibration B2 and an odd multiple of Π is smaller than half of Π. The inkjet printer 1 according to the present embodiment can increase, for example, the degree of difference between the amplitude of the vibration BB generated in the discharge unit D[m] when thickening has not occurred in the ink filled in the discharge unit D[m] and the amplitude of the vibration BBz generated in the discharge unit D[m] when thickening has occurred in the ink filled in the discharge unit D[m], as compared with a reference example. Therefore, according to the present embodiment, for example, even when the degree of thickening of the ink in the discharge unit D[m] is small, it is possible to accurately determine the ink discharge state in the discharge unit D[m] as compared with a reference example.

[0077] <<B. Modification Example>> Each of the above embodiments can be variously modified. Specific modification modes are exemplified below. Two or more modes arbitrarily selected from the following examples can be appropriately combined within a range where they do not conflict with each other. For elements in the modification examples exemplified below whose actions and functions are equivalent to those of the embodiments, the reference numerals referred to in the above description are reused, and the detailed description of each is appropriately omitted.

[0078] <<Modification Example 1>> In the above-described embodiment, the drive signal Com supplied to the ejection unit DS to be determined has a waveform PS1 for displacing the piezoelectric element PZ[m] in the -Z direction and a waveform PS2 for displacing the piezoelectric element PZ[m] in the +Z direction. However, the present invention is not limited to such an aspect. The drive signal Com supplied to the ejection unit DS to be determined may have a waveform PS1 for displacing the piezoelectric element PZ[m] in the +Z direction and a waveform PS2 for displacing the piezoelectric element PZ[m] in the +Z direction, or may have a waveform PS1 for displacing the piezoelectric element PZ[m] in the -Z direction and a waveform PS2 for displacing the piezoelectric element PZ[m] in the -Z direction.

[0079] The drive signal Com according to this modification is different from the drive signal Com according to the embodiment in that it includes a drive signal Com-C instead of the drive signal Com-B.

[0080] As illustrated in FIG. 10, the drive signal Com-C has a waveform that changes from the reference potential V0 to the potential VS6 lower than the potential VS2 via the potential VS2 during the control period TSS1, maintains the potential VS6 during the control period TSS2, and changes from the potential VS6 to the reference potential V0 during the control period TSS3. Specifically, during the period T1 of the control period TSS1, the waveform PS1 is provided in the drive signal Com-C. During the period TS13 that starts at time t12 and ends at time t31 within the control period TSS1, the potential VS2 is maintained. During the period T3 that starts at time t31 and ends at time t32 within the control period TSS1, a waveform PS3 that changes from the potential VS2 to the potential VS6 is provided. During the period TS3k that starts at time t32 and ends at time tk within the control period TSS1, the potential VS6 is maintained. Also in this modified example, similar to the embodiment, in the determination target ejection unit DS, a supply drive signal Vin having a drive signal Com-C is supplied during the control periods TSS1 and TSS3, and the supply of the drive signal Com is stopped during the control period TSS2. Also in this modified example, similar to the embodiment, a detection potential signal VX indicating the potential of the upper electrode Zu is supplied from the determination target ejection unit DS to the detection circuit 33 during the control period TSS2.

[0081] In this modified example, the time length TX13 from time t11 to time t31 is determined so as to satisfy the following formula (17).

Equation

[0082] In this modified example, when the ink ejection state in the determination target ejection unit DS is normal, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS indicates a combined vibration BC, which is a combined vibration of the vibration B1 generated by the waveform PS1 and the vibration B3 generated by the waveform PS3, as illustrated in FIG. 10. In this modified example, the drive signal Com-C is set so that the vibration B1 and the vibration B3 cancel each other out. Specifically, during the control period TSS2, the waveform e3 of the vibration B3 at time t is represented by the following formula (18). Here, the amplitude E3 in formula (18) is the amplitude of the vibration B3 at time t. In this modified example, the amplitude E3 is substantially the same as the amplitude E1. Also, the value θ3 in formula (18) is a value determined based on the time interval between time t31 and time t, and satisfies the following formula (19). Also, during the control period TSS2, the waveform ec of the vibration BC at time t is represented by the following formula (20).

Equation

[0083] Also, in this modified example, when the ink in the determination target ejection unit DS thickens and ejection abnormality occurs in the determination target ejection unit DS, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS indicates a combined vibration BCz, which is a combined vibration of the vibration B1z generated by the waveform PS1 and the vibration B3z generated by the waveform PS3, as illustrated in FIG. 10. Specifically, in the control period TSS2, the waveform e3z of the vibration B3z at time t is represented by the following formula (21), and the waveform ecz of the vibration BCz at time t is represented by the following formula (22). Here, the amplitude E3z is the amplitude of the vibration B3z at time t, and the amplitude ECz is the amplitude of the vibration BCz at time t.

Number

[0084] In this modified example, the degree of attenuation of the vibration generated in the determination target ejection unit DS during the period from time t11 to time t is greater than the degree of attenuation of the vibration generated in the determination target ejection unit DS during the period from time t31 to time t. Therefore, in this embodiment, even when "E1≒E3" holds between the amplitude E1 and the amplitude E3, the relationship "E1z<E3z" holds between the amplitude E1z and the amplitude E3z. That is, the amplitude of the vibration BCz is greater than the amplitude of the vibration BC.

[0085] In this modification example, the determination unit 8 determines whether the maximum value of the amplitude of the detection potential signal VX is equal to or greater than a predetermined reference amplitude based on the detection signal SK. Then, when the maximum value of the amplitude of the detection potential signal VX is less than the predetermined reference amplitude, the determination unit 8 assumes that the vibration BC is occurring in the determination target ejection unit DS, determines that the ink ejection state in the determination target ejection unit DS is normal, and generates ejection state determination information JH indicating the determination result. On the other hand, when the maximum value of the amplitude of the detection potential signal VX is equal to or greater than the predetermined reference amplitude, the determination unit 8 assumes that the vibration BCz is occurring in the determination target ejection unit DS, determines that an ejection abnormality due to thickening has occurred in the determination target ejection unit DS, and generates ejection state determination information JH indicating the determination result.

[0086] Note that in this modification example, the drive signal Com is set so that the time length TX13 satisfies the formula (17), but the present invention is not limited to such a mode. For example, the time length TX13 may be determined so as to satisfy the following formula (23).

Number

[0087] Also, in this modification example, the values θ1 and θ3 are determined so as to satisfy the above-described formula (19), but the present invention is not limited to such a mode. For example, the values θ1 and θ3 may be determined so as to satisfy the following formula (24).

Number

[0088] That is, the inkjet printer 1 according to this modification example includes a discharge unit D[m] that discharges the ink filled in the cavity 322 according to the displacement of the piezoelectric element PZ[m], a waveform PS1 that is provided in a period T1 starting at time t11 and displaces the piezoelectric element PZ[m] in the -Z direction, and a waveform PS3 that is provided in a period T3 starting at time t31 and displaces the piezoelectric element PZ[m] in the +Z direction, and a drive signal generation unit 4 that generates a drive signal Com, and a detection circuit 33 that detects vibrations remaining in the discharge unit D[m] during a control period TSS2. The difference between the time length TX13 from time t11 to time t31 and the time length that is an odd multiple of half the period of the vibration generated in the discharge unit D[m] is shorter than one-fourth of the period TC of the vibration generated in the discharge unit D[m]. The inkjet printer 1 according to this modification example can, for example, increase the degree of difference between the amplitude of the vibration BC generated in the discharge unit D[m] when no thickening occurs in the ink filled in the discharge unit D[m] and the amplitude of the vibration BCz generated in the discharge unit D[m] when thickening occurs in the ink filled in the discharge unit D[m], as compared with the reference example. Therefore, according to this embodiment, it is possible to accurately determine the ink discharge state in the discharge unit D[m], for example, even when the degree of thickening of the ink in the discharge unit D[m] is small as compared with the reference example. In this embodiment, time t31 is an example of the "second time", period T3 is an example of the "second period", and waveform PS3 is an example of the "second waveform".

[0089] <<Modification Example 2>> In the above-described embodiment and modification example 1, the amplitude E1 and the amplitude E2 or amplitude E3 were substantially the same, but the present invention is not limited to such a mode. The amplitude E1 and the amplitude E2 or amplitude E3 may be different amplitudes.

[0090] The drive signal Com according to this modification example differs from the drive signal Com according to the embodiment in that it includes a drive signal Com-D instead of the drive signal Com-B.

[0091] As illustrated in FIG. 11, the drive signal Com-D changes from the reference potential V0 to a potential VS7 higher than the potential VS2 via the potential VS2 during the control period TSS1, maintains the potential VS7 during the control period TSS2, and changes from the potential VS7 to the reference potential V0 during the control period TSS3. Specifically, during the period T1 within the control period TSS1 of the drive signal Com-D, a waveform PS1 is provided, during the period TS12 within the control period TSS1, the potential VS2 is maintained, during the period T2 within the control period TSS1, a waveform PS4 that changes from the potential VS2 to the potential VS7 is provided, and during the period TS2k within the control period TSS1, the potential VS7 is maintained. Also in this modification, similar to the embodiment, a supply drive signal Vin having the drive signal Com-D is supplied to the determination target ejection unit DS during the control periods TSS1 and TSS3, and the supply of the drive signal Com is stopped during the control period TSS2. Also in this modification, similar to the embodiment, a detection potential signal VX indicating the potential of the upper electrode Zu is supplied from the determination target ejection unit DS to the detection circuit 33 during the control period TSS2.

[0092] In this modification, when the ink ejection state in the determination target ejection unit DS is normal, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS indicates a combined vibration BD, which is a combined vibration of the vibration B1 generated by the waveform PS1 and the vibration B4 generated by the waveform PS4, as illustrated in FIG. 11. Specifically, during the control period TSS2, the waveform e4 of the vibration B4 at time t is represented by the following formula (25). Here, the amplitude E4 in formula (25) is the amplitude of the vibration B4 at time t. In this modification, the amplitude E4 is smaller than the amplitude E1. Also, the value θ4 in formula (25) is a value determined based on the time interval between time t21 and time t and satisfies the following formula (26). Also, during the control period TSS2, the waveform ed of the vibration BD at time t is represented by the following formula (27).

Equation

[0093] Also, in this modified example, when the ink in the determination target ejection unit DS thickens and ejection abnormality occurs in the determination target ejection unit DS, the detection potential signal VX detected by the detection circuit 33 from the determination target ejection unit DS indicates a combined vibration BDz, which is a combined vibration of the vibration B1z generated by the waveform PS1 and the vibration B4z generated by the waveform PS4, as illustrated in FIG. 11. Specifically, in the control period TSS2, the waveform e4z of the vibration B4z at time t is represented by the following formula (28), and the waveform edz of the vibration BDz at time t is represented by the following formula (29). Here, the amplitude E4z is the amplitude of the vibration B4z at time t, and the amplitude EDz is the amplitude of the vibration BDz at time t.

Equation

[0094] As described above, when the ink in the determination target ejection unit DS thickens, the attenuation rate of the vibration generated in the determination target ejection unit DS becomes higher compared to the case where the ink does not thicken. Also, the time interval between time t11 and time t is longer than the time interval between time t21 and time t. Therefore, in this modified example, the degree of attenuation of the vibration generated in the determination target ejection unit DS during the period from time t11 to time t is greater than the degree of attenuation of the vibration generated in the determination target ejection unit DS during the period from time t21 to time t. Thus, in this modified example, even when "E1 > E4" holds between the amplitude E1 and the amplitude E4, there may be a case where the relationship "E1z < E4z" holds between the amplitude E1z and the amplitude E4z. That is, the phase of the vibration BD becomes substantially the same as the phase of the vibration B1, and the phase of the vibration BDz may be different from the phase of the vibration BD.

[0095] In this modification example, the determination unit 8 determines whether or not the phase difference between the vibration detected by the detection circuit 33 and the vibration B1 is equal to or greater than a predetermined reference value based on the detection signal SK. Then, when the phase difference between the vibration detected by the detection circuit 33 and the vibration B1 is less than the predetermined reference value, the determination unit 8 regards that the vibration BD has occurred in the determination target ejection unit DS, determines that the ink ejection state in the determination target ejection unit DS is normal, and generates ejection state determination information JH indicating the determination result. On the other hand, when the phase difference between the vibration detected by the detection circuit 33 and the vibration B1 is equal to or greater than the predetermined reference value, the determination unit 8 regards that the vibration BDz has occurred in the determination target ejection unit DS, determines that an ejection abnormality due to thickening has occurred in the determination target ejection unit DS, and generates ejection state determination information JH indicating the determination result.

[0096] In the present embodiment, the value θ1 and the value θ4 are determined so as to satisfy the above-described formula (26), but the present invention is not limited to such a mode. For example, the value θ1 and the value θ4 may be determined so as to satisfy the following formula (30).

Equation

[0097] Thus, in the inkjet printer 1 according to this modification example, the amplitude E1 at the time tk of the vibration B1 generated in the ejection unit D[m] by the waveform PS1 is larger than the amplitude E4 at the time tk of the vibration B4 generated in the ejection unit D[m] by the waveform PS4. The inkjet printer 1 according to this modification example can, for example, increase the degree of difference between the phase of the vibration BD generated in the discharge unit D[m] when thickening does not occur in the ink filled in the discharge unit D[m] and the phase of the vibration BDz generated in the discharge unit D[m] when thickening occurs in the ink filled in the discharge unit D[m], as compared with the reference example. Therefore, according to the present embodiment, for example, even when the degree of thickening of the ink in the discharge unit D[m] is small as compared with the reference example, it is possible to accurately determine the ink discharge state in the discharge unit D[m]. Note that in the present embodiment, the waveform PS4 is an example of the "second waveform", and the vibration B4 is an example of the "second vibration".

[0098] Further, in the inkjet printer 1 according to this modification example, the determination unit 8 determines that the ink filled in the cavity 322 has thickened when the phase difference between the phase of the vibration detected by the detection circuit 33 in the control period TSS2 and the vibration B1 is equal to or greater than a predetermined reference value. Therefore, the inkjet printer 1 according to the present embodiment can prevent a decrease in print quality due to thickening of the ink.

[0099] <<Modification Example 3>> In the above-described embodiments and modification examples 1 and 2, the case where the inkjet printer 1 is a serial printer has been exemplified, but the present invention is not limited to such a mode. The inkjet printer 1 may be a so-called line printer in which a plurality of nozzles N are provided in the head unit 3 so as to extend wider than the width of the recording paper P.

Explanation of Reference Numerals

[0100] 1... Inkjet printer, 2... Control unit, 3... Head unit, 4... Drive signal generation unit, 7... Conveyance unit, 8... Determination unit, 31... Supply circuit, 32... Recording head, 33... Detection circuit, D... Discharge unit.

Claims

1. A discharge unit that discharges the liquid filled in the pressure chamber in response to the displacement of the piezoelectric element, provided in a first period starting at a first time, a first waveform that displaces the piezoelectric element in a first direction, and provided in a second period starting at a second time after the end of the first period, a second waveform that displaces the piezoelectric element in a second direction opposite to the first direction, a generation unit that generates a drive signal having the above, in a detection period starting after the end of the second period, a detection unit that detects the vibration remaining in the discharge unit, comprising: the time length from the first time to the second time, and the difference between the time length that is a natural number multiple of the period of the vibration generated in the discharge unit is shorter than one-fourth of the period of the vibration generated in the discharge unit, A liquid discharge device characterized by this.

2. Based on the vibration detected by the detection unit in the detection period, A liquid discharge device according to claim 1, further comprising a determination unit that determines whether or not the liquid filled in the pressure chamber has thickened. characterized by this.

3. The amplitude at the start time of the detection period of the first vibration generated in the discharge unit by the first waveform, and The amplitude at the start time of the detection period of the second vibration generated in the discharge unit by the second waveform are substantially the same, A liquid discharge device according to claim 2, characterized by this.

4. The determination unit When the amplitude of the vibration detected by the detection unit in the detection period is equal to or greater than a reference amplitude, Determine that the liquid filled in the pressure chamber has thickened, A liquid discharge device according to claim 3, characterized by this.

5. The amplitude at the start time of the detection period of the first vibration generated in the discharge unit by the first waveform is greater than the amplitude at the start time of the detection period of the second vibration generated in the discharge unit by the second waveform, A liquid discharge device according to claim 1, characterized by this.

6. Based on the vibration detected by the detection unit in the detection period, A determination unit that determines whether or not the liquid filled in the pressure chamber has thickened is provided, The determination unit When the phase difference between the phase of the vibration detected by the detection unit in the detection period and the first vibration is equal to or greater than a reference value, Determine that the liquid filled in the pressure chamber has thickened, A liquid discharge device according to claim 5, characterized by this.

7. A discharge unit that discharges the liquid filled in the pressure chamber in response to the displacement of the piezoelectric element, Provided in a first period starting at a first time, a first waveform that displaces the piezoelectric element in a first direction, and provided in a second period starting at a second time after the end of the first period, a second waveform that displaces the piezoelectric element in the first direction, a generation unit that generates a drive signal having the above, a detection unit that detects vibration remaining in the ejection unit in a detection period starting after the end of the second period, and is provided with The difference between the time length from the first time to the second time and the time length that is an odd multiple of half the period of the vibration generated in the ejection unit is shorter than one-fourth of the period of the vibration generated in the ejection unit, A liquid ejection device characterized by this.

8. A generation unit that generates a drive signal, an ejection unit that ejects liquid with the supply of the drive signal, a detection unit that detects vibration generated in the ejection unit driven by the drive signal, and is provided with The generation unit is provided in a first period starting at a first time, a first waveform that generates a first vibration in the ejection unit, is provided in a second period starting at a second time after the end of the first period, a second waveform that generates a second vibration in the ejection unit, generates a drive signal for determination including the above, The detection unit when the ejection unit is driven by the drive signal for determination, in a detection period starting after the end of the second period, detects a combined vibration of the first vibration and the second vibration remaining in the ejection unit, The difference between the phase difference between the first vibration and the second vibration and an odd multiple of Π is less than one-half of Π, A liquid ejection device characterized by this. ​ ​ ​

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