Liquid ejection device

Abstract

To provide a liquid ejection device, which can eject liquid more stably.SOLUTION: A driving signal includes a plurality of ejection pulses corresponding to a plurality of droplets that are integrated before impacting on a medium. A first ejection pulse comprises a first expansion element, whose potential varies from first potential to second potential, and which drives the driving element to enlarge volumes of a pressure chamber. A second ejection pulse succeeding the first ejection pulse comprises a second expansion element, whose potential varies from fourth potential to fifth potential, and which drives the driving element to enlarge volumes of the pressure chamber. A time length in a first period of time that is a period of time during which the potential of the second expansion element varies from the fourth potential to the fifth potential is longer than a time length of a second period of time that is a period of time during which the potential of the first expansion element varies from the first potential to the second potential.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] A liquid ejection device such as an inkjet printer drives a piezoelectric element provided in an ejection section of the liquid ejection device with a drive signal, causing a liquid such as ink filled in a pressure chamber provided in the ejection section to be ejected as droplets from a nozzle, thereby forming an image on a medium such as recording paper.

[0003] In such liquid ejection devices, as described in Patent Document 1, for example, a droplet ejected from a nozzle and another droplet ejected from the nozzle after the first droplet is ejected may be merged before landing on a medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-140761 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the drive cycle of the ejection unit is shortened to meet the recent demand for faster printing speeds, the interval between the ejection of one droplet from the nozzle and the ejection of another droplet becomes shorter, resulting in a problem of unstable ejection of the other droplets. [Means for solving the problem]

[0006] A liquid ejection device according to one aspect of the present invention includes an ejection section having a nozzle that ejects liquid to be landed on a medium, a pressure chamber that is connected to the nozzle and through which the liquid flows, and a drive element that generates a pressure fluctuation in the liquid in the pressure chamber when a drive signal is supplied, and a drive signal generation section that generates the drive signal, the drive signal including a plurality of ejection pulses corresponding to a plurality of droplets that combine before landing on the medium, a first ejection pulse that is the first in chronological order among the plurality of ejection pulses includes a first expansion element that changes from a first potential to a second potential and drives the drive element to expand the volume of the pressure chamber, and a second expansion element that changes from the second potential to a third potential and drives the drive element to expand the volume of the pressure chamber expanded by the first expansion element. a first ejection element that contracts the nozzle and ejects droplets from the nozzle, and a second ejection pulse that is next to the first ejection pulse in chronological order among the multiple ejection pulses changes from a fourth potential to a fifth potential, driving the driving element to expand the volume of the pressure chamber, and a second ejection element that changes from the fifth potential to a sixth potential, contracting the volume of the pressure chamber expanded by the second expansion element and ejecting droplets from the nozzle, wherein the length of a first period during which the second expansion element changes from the fourth potential to the fifth potential is longer than the length of a second period during which the first expansion element changes from the first potential to the second potential. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a functional block diagram illustrating an example of the configuration of an inkjet printer 1. [Diagram 2] FIG. 1 is a perspective view showing an example of a schematic internal structure of an inkjet printer 1. [Diagram 3] 2 is a schematic partial cross-sectional view of a recording head 32. FIG. [Figure 4] 2 is a block diagram showing an example of the configuration of a head unit 3. FIG. [Diagram 5] 4 is a timing chart showing various signals such as a drive signal Com supplied to the head unit 3. [Figure 6]FIG. 11 is an explanatory diagram for explaining an individual designation signal Sd[m]. [Figure 7] 11 is an example of a timing chart showing a drive signal Com in a conventional example. [Figure 8] 4 is an example of a timing chart showing a drive signal Com in the first embodiment. [Figure 9] 13 is an example of a timing chart showing a drive signal Com in the second embodiment. [Figure 10] FIG. 1 is an enlarged view of waveform PP6(2). [Figure 11] 13 is an example of a timing chart showing a drive signal Com in the third embodiment. [Figure 12] 13 is an example of a timing chart showing a drive signal Com in the fourth embodiment. [Figure 13] 13 is an example of a timing chart showing a drive signal Com in the fifth embodiment. [Figure 14] 13 is an example of a timing chart showing a drive signal Com in Modification 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments for carrying out the present invention will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part are appropriately different from the actual ones. In addition, since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0009] 1: First embodiment In this embodiment, the liquid ejecting device will be described by taking as an example an inkjet printer that ejects ink to form an image on recording paper PR.

[0010] 1-1: Overview of inkjet printers An example of the configuration of an inkjet printer 1 according to this embodiment will be described below with reference to FIGS.

[0011] FIG. 1 is a functional block diagram showing an example of the configuration of an inkjet printer 1.

[0012] 1, print data Img indicating an image to be formed by the inkjet printer 1 is supplied from a host computer such as a personal computer or digital camera to the inkjet printer 1. The inkjet printer 1 executes a printing process to form, on recording paper PR, an image indicated by the print data Img supplied from the host computer.

[0013] The inkjet printer 1 comprises a control unit 2 that controls each part of the inkjet printer 1, a head unit 3 provided with an ejection section D that ejects ink, a drive signal generation unit 4 that generates a drive signal Com for driving the ejection section D, and a transport unit 7 that changes the relative position of the recording paper PR with respect to the head unit 3.

[0014] Note that ink is an example of a "liquid," and recording paper PR is an example of a "medium." Furthermore, the inkjet printer 1 that ejects ink is an example of a "liquid ejection device." The drive signal generation unit 4 that generates the drive signal Com that drives the head unit 3 is configured to include, for example, one or more electric circuits, and is an example of a "drive signal generation section."

[0015] In this embodiment, it is assumed that the inkjet printer 1 includes one or more head units 3, and one or more drive signal generating units 4 that correspond one-to-one to the one or more head units 3. Specifically, in this embodiment, it is assumed that the inkjet printer 1 includes four head units 3, and four drive signal generating units 4 that correspond one-to-one to the four head units 3. However, for ease of explanation, the following description may focus on one of the four head units 3 and one of the four drive signal generating units 4 that is provided to correspond to one of the head units 3, as shown in FIG.

[0016] The control unit 2 is configured to include one or more CPUs. However, the control unit 2 may include a programmable logic device such as an FPGA instead of or in addition to a CPU. Here, CPU is an abbreviation for Central Processing Unit, and FPGA is an abbreviation for field-programmable gate array. The control unit 2 also includes a memory. The memory 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).

[0017] Although details will be described later, the control unit 2 generates signals for controlling the operation of each part of the inkjet printer 1, such as a print signal SI and a waveform designation signal dCom. Here, the waveform designation signal dCom is a digital signal that defines the waveform of the drive signal Com. The drive signal Com is an analog signal for driving the discharge section D. The drive signal generation unit 4 includes a DA conversion circuit and generates the drive signal Com having a waveform defined by the waveform designation signal dCom. The print signal SI is a digital signal that designates the type of operation of the discharge section D. Specifically, the print signal SI is a signal that designates whether or not to supply the drive signal Com to the discharge section D, thereby designating the type of operation of the discharge section D.

[0018] As shown in FIG. 1, the head unit 3 includes a supply circuit 31 and a recording head 32.

[0019] The recording head 32 has M discharge sections D. Here, the value M is a natural number that satisfies "M≧1". In the following, the m-th discharge section D of the M discharge sections D provided in the recording head 32 may be referred to as discharge section D[m]. Here, the variable m is a natural number that satisfies "1≦m≦M". In the following, when a component or signal of the inkjet printer 1 corresponds to a discharge section D[m] of the M discharge sections D, the subscript [m] may be added to the symbol representing the component or signal.

[0020] The supply circuit 31 switches whether or not to supply the drive signal Com to the discharge section D[m] based on the print signal SI. In the following, the drive signal Com supplied to the discharge section D[m] may be referred to as the supply drive signal Vin[m].

[0021] As described above, in this embodiment, the inkjet printer 1 executes a printing process. When the printing process is executed, the control unit 2 generates signals, such as a print signal SI, for controlling the head unit 3 based on the print data Img. When the printing process is executed, the control unit 2 also generates signals, such as a waveform designation signal dCom, for controlling the drive signal generating unit 4. When the printing process is executed, the control unit 2 also generates signals for controlling the transport unit 7. In this way, during the printing process, the control unit 2 controls the transport unit 7 to change the relative position of the recording paper PR with respect to the head unit 3, while adjusting the presence or absence of ink ejection from the ejection section D[m], the amount of ink ejection, the timing of ink ejection, and the like, 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 PR.

[0022] FIG. 2 is a perspective view showing an example of a schematic internal structure of the inkjet printer 1. As shown in FIG.

[0023] 2, this embodiment assumes that the inkjet printer 1 is a serial printer. Specifically, when executing a printing process, the inkjet printer 1 transports the recording paper PR in the X1 direction, while reciprocating the head unit 3 in the Y1 direction that intersects with the X1 direction, and in the Y2 direction that is the opposite direction to the Y1 direction, to eject ink from the ejection units D[m], thereby forming dots Dt on the recording paper PR according to the print data Img. Hereinafter, the X1 direction and its opposite X2 direction will be collectively referred to as the "X-axis direction", the Y1 direction intersecting the X-axis direction and its opposite Y2 direction will be collectively referred to as the "Y-axis direction", and the Z1 direction intersecting the X-axis and Y-axis directions and its opposite Z2 direction will be collectively referred to as the "Z-axis direction". In this embodiment, as an example, a description will be given assuming that the X-axis direction, the Y-axis direction, and the Z-axis direction are mutually orthogonal. However, the present invention is not limited to this aspect. It is sufficient that the X-axis direction, the Y-axis direction, and the Z-axis direction intersect with each other. In this embodiment, the Z1 direction is the direction in which ink is ejected from the ejection section D[m].

[0024] As shown in FIG. 2, the inkjet printer 1 according to this embodiment includes a housing 100, and a carriage 110 that is capable of reciprocating within the housing 100 in the Y-axis direction and that has four head units 3 mounted thereon. In this embodiment, as shown in FIG. 2, it is assumed that the carriage 110 stores four ink cartridges 120 in one-to-one correspondence with the four colors of ink: cyan, magenta, yellow, and black. Also, in this embodiment, it is assumed that the inkjet printer 1 includes four head units 3 in one-to-one correspondence with the four ink cartridges 120, as described above. Each ejection section D[m] receives a supply of ink from the ink cartridge 120 corresponding to the head unit 3 in which the ejection section D[m] is provided. This allows each ejection section D[m] to fill itself with the supplied ink and eject the filled ink from the nozzle N. Note that the ink cartridges 120 may be provided outside the carriage 110.

[0025] As described above, the inkjet printer 1 according to this embodiment also includes a transport unit 7. As shown in Fig. 2, the transport unit 7 includes a carriage transport mechanism 71 for reciprocating the carriage 110 in the Y axis direction, a carriage guide shaft 76 that supports the carriage 110 so that it can reciprocate in the Y axis direction, a medium transport mechanism 73 for transporting the recording paper PR, and a platen 75 provided in the Z1 direction of the carriage 110. Thus, when a printing process is performed, the transport unit 7 causes the carriage transport mechanism 71 to reciprocate the head unit 3 together with the carriage 110 along the carriage guide shaft 76 in the Y axis direction, and the medium transport mechanism 73 to transport the recording paper PR on the platen 75 in the X1 direction, thereby changing the relative position of the recording paper PR with respect to the head unit 3 and enabling ink to land on the entire recording paper PR.

[0026] FIG. 3 is a schematic partial cross-sectional view of the recording head 32, in which the recording head 32 is cut so as to include the ejection portion D[m].

[0027] As shown in FIG. 3, the ejection section D[m] includes a piezoelectric element PZ[m], a cavity CV filled with ink, a nozzle N communicating with the cavity CV, and a vibration plate 321. The cavity CV is an example of a "pressure chamber." The piezoelectric element PZ[m] is an example of a "drive element." The ejection section D[m] ejects ink in the cavity CV from the nozzle N by driving the piezoelectric element PZ[m] with a supply drive signal Vin[m]. The cavity CV is a space defined by a cavity plate 324, a nozzle plate 323 in which the nozzle N is formed, and the vibration plate 321. The cavity CV communicates with a reservoir 325 via an ink supply port 326. The reservoir 325 communicates with the ink cartridge 120 corresponding to the ejection section 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 the power supply line LD set to the potential VBS. Then, when the 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 Z1 direction or the Z2 direction according to the applied voltage. As a result, the piezoelectric element PZ[m] vibrates. The lower electrode Zd[m] is joined to the vibration plate 321. Therefore, when the piezoelectric element PZ[m] is driven to vibrate by the supply drive signal Vin[m], the vibration plate 321 also vibrates. The vibration of the diaphragm 321 changes the volume of the cavity CV and the pressure within the cavity CV, causing the ink filled within the cavity CV to be ejected from the nozzle N.

[0028] During the printing process, some of the ink ejected from the nozzles N becomes a mist before landing on the recording paper PR, and floats inside the housing 100.

[0029] 1-2: Head unit overview Hereinafter, an overview of the head unit 3 will be described with reference to FIGS.

[0030] FIG. 4 is a block diagram showing an example of the configuration of the head unit 3. As shown in FIG.

[0031] 4, the head unit 3 includes a supply circuit 31 and a recording head 32. The head unit 3 also includes wiring LC to which the drive signal Com is supplied from the drive signal generating unit 4.

[0032] As shown in FIG. 4, the supply circuit 31 includes M switches WS[1] to WS[M] each having a one-to-one correspondence with the M discharge sections D[1] to D[M], and a connection state designation circuit 310 that designates the connection state of each switch. The connection state designation circuit 310 generates a connection state designation signal QS[m] that designates the on / off state of the switch WS[m] based on at least some of the signals of the print signal SI, the latch signal LAT, and the change signal CH supplied from the control unit 2. The switch WS[m] switches between electrical continuity and non-conduction between the wiring LC and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the discharge section D[m] based on the connection state designation signal QS[m]. In this embodiment, the switch WS[m] is turned on when the connection state designation signal QS[m] is at a high level, and turned off when the connection state designation signal QS[m] is at a low level. When the switch WS[m] is turned on, the drive signal Com supplied to the wiring LC is supplied to the upper electrode Zu[m] of the discharge section D[m] as the supply drive signal Vin[m].

[0033] In this embodiment, when the inkjet printer 1 executes a printing process, one or more unit periods TP are set as the operating period of the inkjet printer 1. In each unit period TP, the inkjet printer 1 according to this embodiment can drive each ejection section D[m] for the printing process.

[0034] FIG. 5 is a timing chart showing various signals such as the drive signal Com supplied to the head unit 3 during the unit period TP.

[0035] 5, the control unit 2 outputs a latch signal LAT having a pulse PLL, whereby the control unit 2 defines a unit period TP as a period from the rising edge of the pulse PLL to the rising edge of the next pulse PLL. Moreover, the control unit 2 outputs a change signal CH having a pulse PLC in a unit period TP. The control unit 2 then divides the unit period TP into a drive period TQ1 from the rising edge of the pulse PLL to the rising edge of the pulse PLC, and a drive period TQ2 from the rising edge of the pulse PLC to the rising edge of the pulse PLL.

[0036] As shown in FIG. 5, the print signal SI includes M individual designation signals Sd[1] to Sd[M] that correspond one-to-one to the M discharge sections D[1] to D[M]. The individual designation signal Sd[m] designates the driving mode of the discharge section D[m] in each unit period TP when the inkjet printer 1 executes a printing process. Prior to each unit period TP, the control unit 2 supplies the print signal SI including the M individual designation signals Sd[1] to Sd[M] to the connection state designation circuit 310 in synchronization with the clock signal CL. Then, the connection state designation circuit 310 generates a connection state designation signal QS[m] based on the individual designation signal Sd[m] during the unit period TP.

[0037] In this embodiment, it is assumed that during the unit period TP in which the printing process is executed, the ejection section D[m] is capable of forming any of the following dots Dt: a large dot made of ink with an ink amount ξ1, a medium dot made of ink with an ink amount ξ2 which is less than the ink amount ξ1, or a small dot made of ink with an ink amount ξ3 which is less than the ink amount ξ2.

[0038] FIG. 6 is an explanatory diagram for explaining the individual designation signal Sd[m].

[0039] As shown in FIG. 6, in this embodiment, the individual designation signal Sd[m] can take one of four values ​​in the unit period TP in which the print process is executed: a value "1" that designates the discharge section D[m] as a large dot forming discharge section DP-1, a value "2" that designates the discharge section D[m] as a medium dot forming discharge section DP-2, a value "3" that designates the discharge section D[m] as a small dot forming discharge section DP-3, and a value "4" that designates the discharge section D[m] as a non-dot forming discharge section DP-N. Here, the large dot forming discharge section DP-1 is the discharge section D that forms a large dot in the unit period TP. The medium dot forming discharge section DP-2 is the discharge section D that forms a medium dot in the unit period TP. The small dot forming discharge section DP-3 is the discharge section D that forms a small dot in the unit period TP. The non-dot forming discharge section DP-N is the discharge section D that does not form a dot in the unit period TP.

[0040] Let us return to the explanation given in FIG. As shown in Fig. 5, in this embodiment, the driving signal Com has a waveform P1 provided in the unit period TP. The waveform P1 has a waveform PA1-1 provided in the driving period TQ1 and a waveform PA2-1 provided in the driving period TQ2. Note that, among the driving signal Com, the ejection pulse corresponding to the waveform PA1-1 is an example of a "first ejection pulse." Also, among the driving signal Com, the ejection pulse corresponding to the waveform PA2-1 is an example of a "second ejection pulse." The potential of the waveform P1 at the start of the unit period TP is the reference potential V0. Also, the potential of the waveform P1 at the end of the unit period TP is the reference potential V0. The waveform PA1-1 is a waveform that goes from a reference potential V0 through a potential VL1 that is lower than the reference potential V0 to a potential VH1. In this embodiment, it is assumed that VH1 is equal to V0. The waveform PA1-1 is determined so that when a supply drive signal Vin[m] having the waveform PA1-1 is supplied to the ejection section D[m], ink equivalent to an ink amount φ1 is ejected from the ejection section D[m]. Moreover, the waveform PA2-1 is a waveform that goes from a potential VH1 to a potential VL2 lower than the reference potential V0, and a potential VH2 higher than the reference potential V0, and then returns to the reference potential V0. When a supply drive signal Vin[m] having the waveform PA2-1 is supplied to the discharge section D[m], the waveform PA2-1 is determined so that ink equivalent to the ink amount φ2 is discharged from the discharge section D[m]. When a supply drive signal Vin[m] having the waveform PA1-1 and the waveform PA2-1 is supplied to the discharge section D[m], the waveforms PA1-1 and PA2-2 are determined so that a droplet discharged from the discharge section D[m] by the waveform PA1-1 and a droplet discharged from the discharge section D[m] by the waveform PA1-2 are combined before landing on the medium, and the combined droplet corresponds to the ink amount ξ1.

[0041] In this embodiment, it is assumed that the ink amount ξ1 corresponds to an ink amount equal to or greater than the sum of the ink amount φ1 and the ink amount φ2, the ink amount ξ2 corresponds to the ink amount φ2, and the ink amount ξ3 corresponds to the ink amount φ1.

[0042] 6, when the individual designation signal Sd[m] indicates a value of "1" that designates the discharge section D[m] as the large dot forming discharge section DP-1 in the unit period TP, the connection state designation circuit 310 sets the connection state designation signal QS[m] to a high level in the drive period TQ1 and the drive period TQ2. In this case, the switch WS[m] is turned on in the drive period TQ1 and the drive period TQ2. Therefore, the discharge section D[m] is driven by the supply drive signal Vin[m] having the waveforms PA1-1 and PA2-1 in the unit period TP, and discharges ink of the ink amount ξ1 corresponding to a large dot. Furthermore, when the individual designation signal Sd[m] indicates a value of "2" that designates the discharge section D[m] as a medium dot forming discharge section DP-2 during the unit period TP, the connection state designation circuit 310 sets the connection state designation signal QS[m] to a low level during the drive period TQ1, and to a high level during the drive period TQ2. In this case, the switch WS[m] is turned off during the drive period TQ1, and turned on during the drive period TQ2. Therefore, the discharge section D[m] is driven by the supply drive signal Vin[m] having the waveform PA2-1 during the unit period TP, and discharges ink of the ink amount ξ2 corresponding to a medium dot. Furthermore, when the individual designation signal Sd[m] indicates a value of "3" that designates the discharge section D[m] as the small dot forming discharge section DP-3 during the unit period TP, the connection state designation circuit 310 sets the connection state designation signal QS[m] to a high level during the drive period TQ1 and to a low level during the drive period TQ2. In this case, the switch WS[m] is turned on during the drive period TQ1 and turned off during the drive period TQ2. Therefore, the discharge section D[m] is driven by the supply drive signal Vin[m] having the waveform PA1-1 during the unit period TP, and discharges ink of an ink amount ξ3 corresponding to a small dot. Furthermore, when the individual designation signal Sd[m] indicates a value of "4" that designates the discharge section D[m] as a non-dot-forming discharge section DP-N during the unit period TP, the connection state designation circuit 310 sets the connection state designation signal QS[m] to a low level during the unit period TP. In this case, the switch WS[m] is turned off during the unit period TP. Therefore, the discharge section D[m] is not driven by the supply drive signal Vin[m] having the waveform PA1-1 or the waveform PA2-1 during the unit period TP, and does not discharge ink.

[0043] 1-3: Waveform of the driving signal Com in the first embodiment 7 is an example of a timing chart showing the driving signal Com in the first embodiment. In FIG. 7, the potential VL=the potential VL1=the potential VL2. The potential VH1 is equal to the reference potential V0. In the example shown in FIG. 7, the potential VH2 is a potential higher than the potential VH1. The potential VL is a potential lower than the reference potential V0. As illustrated in FIG. 7, in the first embodiment, a unit period TP is divided into nine control periods Q1 to Q3 and Q6 to Q11.

[0044] Here, the waveform PA1-1 includes, in chronological order, a waveform PP1 provided in a control period Q1, a waveform PP2 provided in a control period Q2, and a waveform PP3(1) provided in a control period Q3. The waveform PP1 changes from a reference potential V0 to a potential VL1. The waveform PP2 maintains the potential VL1 from the end of the waveform PP1 to the beginning of the waveform PP3(1). The waveform PP3(1) changes from the potential VL1 to the potential VH1. In addition, in the present invention, "one signal maintains one potential in one period" is a concept that includes not only the case where "one signal maintains a potential equal to one potential in one period", but also the case where "one signal maintains a potential equal to one potential in one period by design", and the case where "if noise is eliminated, one signal can be regarded as maintaining a potential equal to one potential in one period".

[0045] Further, the waveform PA2-1 includes, in chronological order, a waveform PP7 provided in the control period Q7, a waveform PP8 provided in the control period Q8, a waveform PP9 provided in the control period Q9, a waveform PP10 provided in the control period Q10, and a waveform PP11 provided in the control period Q11. The waveform PP7 is a waveform that changes from a potential VH1 to a potential VL2. The waveform PP8 is a waveform that maintains the potential VL2. The waveform PP9 is a waveform that changes from a potential VL2 to a potential VH2. The waveform PP10 is a waveform that maintains the potential VH2. The waveform PP11 is a waveform that changes from a potential VH2 to a reference potential V0.

[0046] The waveform PP6 connects the waveform PA1-1 and the waveform PA2-1 in the control period Q6. In Fig. 7, the waveform PP6 maintains the potential VH1. As described above, in the example shown in Fig. 7, the potential VH1 is equal to the reference potential V0. The inkjet printer 1 can ensure printing gradation by making the period from the rising edge to the falling edge of the pulse PLC in the change signal CH be included in the period from the beginning to the end of the waveform PP6.

[0047] In this embodiment, as an example, it is assumed that when the potential of the supply drive signal Vin[m] supplied to the discharge section D[m] is high, the volume of the cavity CV of the discharge section D[m] is smaller than when the potential is low. Therefore, when the discharge section D[m] is driven by the supply drive signal Vin[m] having the waveform PA1-1 or the like, the ink in the discharge section D[m] is discharged from the nozzle N by changing the potential of the supply drive signal Vin[m] from low to high. However, as an alternative, when the potential of the supply drive signal Vin[m] is high, the volume of the cavity CV of the discharge section D[m] may be larger than when the potential is low. In this case, the high and low potentials in each embodiment described below are reversed.

[0048] In the waveform PP1 in the control period Q1, the potential of the drive signal Com changes from a high potential to a low potential, so that the volume of the cavity CV expands. In the waveform PP2 in the control period Q2, the potential of the drive signal Com is maintained at the potential VL1, and therefore the volume of the cavity CV is also maintained. In the waveform PP3(1) of the control period Q3, the potential of the drive signal Com changes from a low potential to a high potential, so that the volume of the cavity CV contracts and a droplet is ejected from the nozzle N. In the waveform PP6 in the control period Q6, the potential of the drive signal Com is maintained at the potential VH1, and therefore the volume of the cavity CV is also maintained. In the waveform PP7 in the control period Q7, the potential of the drive signal Com changes from a high potential to a low potential, so that the volume of the cavity CV expands. In the waveform PP8 of the control period Q8, the potential of the drive signal Com is maintained at the potential VL2, and therefore the volume of the cavity CV is also maintained. In the waveform PP9 of the control period Q9, the potential of the drive signal Com changes from a low potential to a high potential, so that the volume of the cavity CV contracts and a droplet is ejected from the nozzle N. In the waveform PP10 of the control period Q10, the potential of the drive signal Com is maintained at the potential VH2, and therefore the volume of the cavity CV is also maintained. In the waveform PP11 of the control period Q11, the potential of the drive signal Com changes from a high potential to a low potential, so that the volume of the cavity CV expands.

[0049] After the waveform PP is supplied to the piezoelectric element PZ, the waveform PP10 and the waveform PP11 expand the volume of the cavity CV at the timing when the pressure of the ink in the cavity CV increases due to the pressure vibration remaining in the ink in the ejection portion D, thereby suppressing the residual vibration of the liquid in the ejection portion D. The waveform PP11 is an example of a "vibration damping element."

[0050] The duration of control period Q7, which is the period during which the potential changes from VH1 to VL2 in the waveform PP7, is longer than the duration of control period Q1, which is the period during which the potential changes from the reference potential V0 to the potential VL1 in the waveform PP1. Preferably, the duration of control period Q7 is 1.5 to 3 times the duration of control period Q1.

[0051] If the length of control period Q7 is shorter than the length of control period Q1, the droplets ejected by waveform PA2-1 will elongate and become more likely to become constricted in shape, causing ink to more easily splash from nozzle N. By making the length of control period Q7 longer than the length of control period Q1, the inkjet printer 1 can reduce ink splash from nozzle N.

[0052] In other words, the rate of change from the potential VH1 to the potential VL2 in the waveform PP7 is smaller than the rate of change from the reference potential V0 to the potential VL1 in the waveform PP1.

[0053] The waveform PP7 monotonically decreases from the potential VH1 to the potential VL2. In the example shown in Fig. 7, the waveform PP7 monotonically decreases, but alternatively, when the potential VL2 is higher than the reference potential V0, the waveform PP7 may monotonically increase to either the potential VH1 or the potential VL2.

[0054] In either case, the waveform PP7 does not have a sustain element that maintains a constant potential for a predetermined time or more. Here, the "predetermined time" is, for example, a period of 0.1 TC or more. In this embodiment, "TC" represents the natural vibration period generated in the ink in the ejection section D.

[0055] Compared to when the waveform PP7 has a sustaining element, there is no need to temporarily stop the expansion of the cavity CV, so the inkjet printer 1 can be driven at a higher speed.

[0056] 7, the time length from the start of waveform PP1 to the start of waveform PP7 is 0.85Tc or more and 1.15Tc or less. In other words, the total time length of control period Q1, control period Q2, control period Q3, and control period Q6 is 0.85Tc or more and 1.15Tc or less. The length of the period from the beginning of waveform PP3(1) to the beginning of waveform PP9 is 1Tc or more and 1.4Tc or less. In other words, the total length of control period Q3, control period Q6, control period Q7, and control period Q8 is 1Tc or more and 1.4Tc or less. The time length from the end of waveform PP3(1) to the end of waveform PP9 is 1Tc or more and 1.4Tc or less. In other words, the total time length of control period Q6, control period Q7, control period Q8, and control period Q9 is 1Tc or more and 1.4Tc or less. Moreover, the waveform PP6 connects the waveform PA1-1 and the waveform PA2-1. The waveform PP6 is an example of a "connecting element." The waveform PP6 connects from the end of the waveform PP3(1) to the beginning of the waveform PP7, and maintains a constant potential. The waveform PP6 of this embodiment maintains the potential VH1 over a period of 0.3Tc or more and 0.5Tc or less.

[0057] Since the period during which the waveform PP6 maintains the potential VH1 is 0.5Tc or less, the first shot droplets ejected by the waveform PP3(1) and the second shot droplets ejected by the waveform PP9 can be more reliably combined. As a result, the ink ejection weight is ensured. In addition, by reliably combining the first shot droplets and the second shot droplets, the ejection weight to the correct position is ensured compared to a case in which at least one of the first shot droplets and the second shot droplets does not land accurately. In addition, since the first shot liquid and the second shot liquid combine before landing, the straightness of the droplets is improved compared to a case in which they fly separately without combining.

[0058] 7, the potential difference between potentials VL2 and VH2 in the waveform PP9 is equal to or greater than the potential difference between potentials VL1 and VH1 in the waveform PP3(1). The potential difference between potentials VL1 and VH1 in the waveform PP3(1) is equal to or greater than 0.6 times the potential difference between potentials VL2 and VH2 in the waveform PP9. In this specification, the "potential difference between potentials A and B" refers to the absolute value of the difference between potentials A and B.

[0059] By ensuring that the potential difference in the waveform PP3(1) is at least a predetermined amount, it is possible to eject a desired amount of ink or more.

[0060] Moreover, the rate of change from the potential VL2 to the potential VH2 in the waveform PP9 is greater than the rate of change from the potential VL1 to the potential VH1 in the waveform PP3(1).

[0061] Therefore, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ejection weight of ink.

[0062] The duration of the period from the beginning of waveform PP1 to the beginning of waveform PP3(1) is 0.45Tc or more and 0.55Tc or less. In other words, the sum of the durations of control periods Q1 and Q2 is 0.45Tc or more and 0.55Tc or less. The duration of the period from the beginning of waveform PP7 to the beginning of waveform PP9 is 0.6Tc to 0.8Tc, in other words, the sum of the durations of control periods Q7 and Q8 is 0.6Tc to 0.8Tc.

[0063] Because the length of time from the beginning of waveform PP1 to the beginning of waveform PP3(1) is shorter than the length of time from the beginning of waveform PP7 to the beginning of waveform PP9, the inkjet printer 1 can reduce ink splattering.

[0064] Moreover, the waveform PA1-1 has a waveform PP2 that maintains a potential VL1 from the end of the waveform PP1 to the beginning of the waveform PP3(1). Moreover, the waveform PA2-1 has a waveform PP8 that maintains a potential VL2 from the end of the waveform PP7 to the beginning of the waveform PP9. The duration of each of the periods of the waveform PP2 and the waveform PP8 is not less than 0.2Tc and not more than 0.4Tc. In other words, the duration of each of the control periods Q2 and Q8 is not less than 0.2Tc and not more than 0.4Tc.

[0065] Since the duration of the waveform PP2 and the duration of the waveform PP8 are within a predetermined range, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0066] The reference potential V0 in the waveform PP1 is an example of a "first potential." The potential VL1 in the waveform PP1 is an example of a "second potential." The waveform PP1 is an example of a "first expansion element." The waveform PP2 is an example of a "first maintenance element." The potential VL1 in the waveform PP3(1) is an example of a "second potential." The potential VH1 in the waveform PP3(1) is an example of a "third potential." The waveform PP3(1) is an example of a "first ejection element."

[0067] Furthermore, the potential VH1 in the waveform PP7 is an example of a "fourth potential." The potential VL2 in the waveform PP7 is an example of a "fifth potential." The waveform PP7 is an example of a "second expansion element." The waveform PP8 is an example of a "second maintenance element." The potential VL2 in the waveform PP9 is an example of a "fifth potential." The potential VH2 in the waveform PP9 is an example of a "sixth potential." The waveform PP9 is an example of a "second ejection element." Furthermore, the reference potential V0 in the waveform PP11 is an example of a "seventh potential."

[0068] Moreover, control period Q7 is an example of a "first period." Control period Q1 is an example of a "second period."

[0069] 1-4: Waveform of the drive signal Com0 in the comparative example FIG. 8 is an example of a timing chart showing the drive signal Com0 in the comparative example. As illustrated in FIG. 8, in the comparative example, the driving signal Com0 has a waveform P0 provided in a unit period TP0.

[0070] The waveform P0 of the comparative example includes a waveform PA1-0 and a waveform PA2-0. When a supply drive signal Vin[m] having the waveforms PA1-0 and PA2-0 of the comparative example is supplied to the discharge section D[m], the waveforms PA1-0 and PA2-0 are determined so that the droplets discharged from the discharge section D[m] by the waveform PA1-0 and the droplets discharged from the discharge section D[m] by the waveform PA2-0 are combined before landing on the medium, and the combined droplets correspond to the ink amount ξ1. The waveform PA1-0 includes a waveform PP10, a waveform PP20, a waveform PP30, a waveform PP40, and a waveform PP50. The waveforms PP10 and PP20 in the waveform PA1-0 according to the comparative example are similar to the waveforms PP1 and PP2 in the present embodiment. However, in the waveform PA1-0 of the comparative example, the waveform PP30 changes from the potential VL to the potential VH2 beyond the reference potential V0, and then the waveform PP40 maintains the potential VH2, and then the waveform PP50 changes from the potential VH2 to the reference potential V0. The waveform PA1-0 of the comparative example ensures the amount of ink to be ejected by the waveform PP30 that changes from the potential VL to the potential VH2 beyond the reference potential V0, and suppresses the residual vibration of the ink in the ejection section D that occurs after the supply of the waveform PP30 by driving the waveforms PP40 and PP50, thereby suppressing the ejection of droplets from the ejection section D by driving the next waveform PA2-0 from becoming unstable.

[0071] In the case where the distance from the nozzle N to the medium is longer than usual, the droplets discharged from the nozzle N are affected by air resistance and surrounding air currents during flight, making it difficult to land them at the desired position. Therefore, by combining droplets discharged continuously from the nozzle N to increase their weight, it is possible to maintain straightness and suppress mist formation, thereby improving the landing accuracy. In addition, there is an increasing demand for faster printing speeds of inkjet printers 1 in order to improve productivity. Specifically, as an example, a driving frequency of 30 kHz or more may be required for the piezoelectric element PZ. However, in order to achieve a driving frequency of 30 kHz or more, as shown in FIG. 8, when the driving signal Com0 in the unit period TP0 includes waveforms for two shots, namely, the waveform PA1-0 and the waveform PA2-0, it is necessary to shorten each of the control periods Q1 to Q11 in order to achieve a driving frequency of 30 kHz or more for the piezoelectric element PZ while ensuring the landing accuracy of the droplets discharged from the nozzle N. However, simply shortening each control period Q1 to Q11 may cause the ejection to become unstable or the ink to easily splash from the nozzle N due to interference between the pressure vibration and the residual vibration generated by driving the waveforms PA1-0 and PA2-0. As a method for suppressing the ejection instability and the ink splash caused by the interference of the residual vibration, it is possible to shorten the period Tc of the residual vibration generated in the ejection section D[m] when the piezoelectric element PZ[m] is driven. However, if the structure of the cavity CV is changed to shorten the period Tc, the amount of ink ejected will decrease. In addition, if the pressure vibration generated by driving the piezoelectric element PZ[m] is simply weakened in order to suppress the ejection instability and the ink splash caused by the interference of the residual vibration, the amount of ink ejected will also decrease. The decrease in the amount of ink droplets will result in a decrease in the amount of ink that hits the medium per unit time in printing by the inkjet printer 1, and the printing efficiency will decrease. On the other hand, in the waveform PA1-1 of the waveform P1 of this embodiment, the end of the waveform PP3(1), which changes from the potential VL1 to the potential VH1, is directly connected to the waveform PP6, and the unit period TP does not include the control period Q4 and the control period Q5 shown in the comparative example. Furthermore, by configuring the waveforms PP1 to PP3(1) and PP6 to PP11 of the waveform P1 as described above, the unit period TP of the waveform P1 of this embodiment can be shortened compared to the unit period TP0 of the waveform P0 of the comparative example, while ensuring the discharge amount and discharge stability, and the multiple droplets discharged during the unit period TP can be reliably merged, and the merged droplets can be landed at an accurate position on the medium. Therefore, the inkjet printer 1 of this embodiment can increase the printing speed while ensuring the print quality.

[0072] 1-5: Advantages of the First Embodiment The inkjet printer 1 according to this embodiment includes a discharge section D and a drive signal generating unit 4. The discharge section D includes a nozzle N[m] that discharges ink to land on the recording paper PR, a cavity CV[m] that communicates with the nozzle N[m] and through which the ink flows, and a piezoelectric element PZ[m] that generates a pressure fluctuation in the ink in the cavity CV when a drive signal Com is supplied. The drive signal generating unit 4 generates the drive signal Com. The drive signal Com includes multiple waveforms PA that correspond to multiple droplets that combine before landing on the recording paper PR. The first waveform PA1-1 of the multiple waveforms PA in chronological order includes a waveform PP1 and a waveform PP3(1). The waveform PP1 drives the piezoelectric element PZ[m] to change from a reference potential V0 to a potential VL1 and to expand the volume of the cavity CV[m]. The waveform PP3(1) changes from potential VL1 to potential VH1, contracting the volume of the cavity CV[m] expanded by the waveform PP1, and ejecting droplets from the nozzle N[m]. The waveform PA2-1 next to the waveform PA1-1 in chronological order among the multiple waveforms PA includes a waveform PP7 and a waveform PP9. The waveform PP7 changes from potential VH1 to potential VL2, and drives the piezoelectric element PZ[m] to expand the volume of the cavity CV[m]. The waveform PP9 changes from potential VL2 to potential VH2, contracting the volume of the cavity CV[m] expanded by the waveform PP7, and ejecting droplets from the nozzle N[m]. The time length of the control period Q7, which is the period during which the waveform PP7 changes from potential VH1 to potential VL2, is longer than the time length of the control period Q1, which is the period during which the waveform PP1 changes from reference potential V0 to potential VL1.

[0073] The inkjet printer 1 can reduce ink scattering from the nozzle N[m] by making the duration of the control period Q7 longer than the duration of the control period Q1.

[0074] Moreover, the time length of the control period Q7 is 1.5 times or more and 3 times or less than the time length of the control period Q1.

[0075] The inkjet printer 1 can reduce ink scattering from the nozzle N [m] by setting the duration of the control period Q7 to be between 1.5 and 3 times the duration of the control period Q1.

[0076] Moreover, the rate of change of the potential in the waveform PP7 from the potential VH1 to the potential VL2 is smaller than the rate of change of the potential in the waveform PP1 from the reference potential V0 to the potential VL1.

[0077] The inkjet printer 1 can reduce ink scattering from the nozzle N[m] by making the rate of potential change from potential VH1 to potential VL2 in the waveform PP7 smaller than the rate of potential change from reference potential V0 to potential VL1 in the waveform PP1.

[0078] Moreover, the waveform PA1-1 includes a waveform PP2 that is an element that maintains a potential VL1 from the end of the waveform PP1 to the beginning of the waveform PP3(1), and the waveform PP1 starts with the waveform PP1 and ends with the waveform PP3(1). The drive signal Com includes a waveform PP6 that maintains a potential VH1 from the end of the waveform PA1-1 to the beginning of the waveform PA1-2. The waveform PP7 monotonically increases or decreases from the potential VH1 to the potential VL2.

[0079] Because the waveform PA1-1 is composed of waveforms PP1, PP2, and PP3(1), and the waveform PP7 does not have a sustain element that maintains a constant potential for a specified period of time or longer, the inkjet printer 1 can be driven at high speed.

[0080] Furthermore, if the natural vibration period of the vibration generated in the ejection section D[m] when the piezoelectric element PZ[m] is driven by the drive signal Com is Tc, the time length of the period from the start of the waveform PP1 to the start of the waveform PP7 is greater than or equal to 0.85Tc and less than or equal to 1.15Tc.

[0081] Because the time length from the start of waveform PP1 to the start of waveform PP7 falls within a predetermined range, the first shot of droplets ejected by waveform PP3 and the second shot of droplets ejected by waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0082] Furthermore, if the natural vibration period of the vibration generated in the ejection section D[m] when the piezoelectric element PZ[m] is driven by the drive signal Com is Tc, the time length of the period from the start of the waveform PP3(1) to the start of the waveform PP9 is greater than or equal to 1Tc and less than or equal to 1.4Tc.

[0083] Because the time length from the start of waveform PP3(1) to the start of waveform PP9 falls within a predetermined range, the first shot of droplets ejected by waveform PP3(1) and the second shot of droplets ejected by waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0084] Furthermore, if the natural vibration period of the vibration generated in the ejection section D[m] when the piezoelectric element PZ[m] is driven by the drive signal Com is Tc, the time length of the period from the end of the waveform PP3(1) to the end of the waveform PP9 is greater than or equal to 1Tc and less than or equal to 1.4Tc.

[0085] Because the time length from the end of waveform PP3(1) to the end of waveform PP9 falls within a predetermined range, the first shot of droplets ejected by waveform PP3(1) and the second shot of droplets ejected by waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0086] The drive signal Com also includes a waveform PP6 that connects the waveforms PA1-1 and PA2-1. The waveform PP6 is connected to the waveform PP3(1). If the natural vibration period of the vibration generated in the discharge portion D[m] when the piezoelectric element PZ[m] is driven by the drive signal Com is Tc, the waveform PP6 includes an element that maintains the potential VH1 over a period of 0.3Tc to 0.5Tc.

[0087] By keeping the period during which the waveform PP6 maintains the potential VH1 within a predetermined range, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0088] Moreover, the potential difference between the potentials VL2 and VH2 in the waveform PP9 is equal to or greater than the potential difference between the potentials VL1 and VH1 in the waveform PP3(1).

[0089] Therefore, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ejection weight of ink.

[0090] Moreover, the potential difference between the potentials VL1 and VH1 in the waveform PP3(1) is 0.6 times or more the potential difference between the potentials VL2 and VH2 in the waveform PP9.

[0091] By ensuring that the potential difference in the waveform PP3(1) is equal to or greater than a predetermined amount, it is possible to reduce cases in which ink is not ejected due to the waveform PP3(1).

[0092] Moreover, the waveform PA2-1 further includes a waveform PP11 which changes from the potential VH2 to the reference potential V0 and suppresses the vibration of the liquid in the discharge section D. The potential difference between potential VL2 and potential VH2 in waveform PP9 of waveform PA2-1 is larger than the potential difference between potential VL1 and potential VH1 in waveform PP3(1), but waveform PP11 can suppress residual vibrations in the ejection section D, thereby stabilizing the ejection by waveform PA1-1 in the next unit period TP.

[0093] Moreover, the rate of change of potential from the potential VL2 to the potential VH2 in the waveform PP9 is greater than the rate of change of potential from the potential VL1 to the potential VH1 in the waveform PP3(1).

[0094] Therefore, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ejection weight of ink.

[0095] The time length from the beginning of waveform PP1 to the beginning of waveform PP3(1) is 0.45Tc or more and 0.55Tc or less. The time length from the beginning of waveform PP7 to the beginning of waveform PP9 is 0.6Tc or more and 0.8Tc or less.

[0096] Because the length of time from the beginning of waveform PP1 to the beginning of waveform PP3(1) is shorter than the length of time from the beginning of waveform PP7 to the beginning of waveform PP9, the inkjet printer 1 can reduce ink splattering.

[0097] Moreover, the waveform PA1-1 has a waveform PP2 that maintains a potential VL1 from the end of the waveform PP1 to the beginning of the waveform PP3(1). The waveform PA2-1 has a waveform PP8 that maintains a potential VL2 from the end of the waveform PP7 to the beginning of the waveform PP9. The time length of each of the waveforms PP2 and PP8 is 0.2Tc or more and 0.4Tc or less.

[0098] Since the time lengths of the waveforms PP2 and PP8 are within a predetermined range, the first shot of droplets ejected by the waveform PP3(1) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined, thereby ensuring the ink ejection weight.

[0099] The driving signal Com is set to the reference potential V0 at the start of a unitary period TP in which a plurality of waveforms PA are provided, and is set to the reference potential V0 at the end of the unitary period TP. The driving signal Com also includes a waveform PP6 that connects the waveforms PA1-1 and PA2-1. The waveform PP6 maintains the potential VH1.

[0100] For this reason, the inkjet printer 1 can ensure printing gradation by making the period from the rising edge to the falling edge of the pulse PLC in the change signal CH be included in the period from the beginning to the end of the waveform PP6.

[0101] 2: Second embodiment The liquid ejection device according to the second embodiment will be described below with reference to Fig. 9. The configuration of the liquid ejection device according to this embodiment is the same as that of the liquid ejection device according to the first embodiment, except for the waveform of the drive signal Com. Therefore, the following mainly describes the waveform of the drive signal Com in this embodiment.

[0102] 2-1: Waveform of the driving signal Com in the second embodiment FIG. 9 is an example of a timing chart showing the driving signal Com in the second embodiment. 9, in this embodiment, the driving signal Com has a waveform P2 provided in the unit period TP. Below, the characteristics of the waveform P2 will be described, focusing mainly on the differences between the waveform P2 and the waveform P1 according to the first embodiment.

[0103] Waveform P2 has waveform PP6(2) instead of waveform PP6 of waveform P1, and waveform PP7(2) instead of waveform PP7 of waveform P1. Waveform PP7(2) includes a contraction element that contracts cavity CV and a maintenance element that maintains the contraction before expanding the volume of cavity CV with a second expansion element, as described below.

[0104] 9, potential VL=potential VL1=potential VL2. Potential VL is a potential lower than reference potential V0. Potential VH1 is equal to reference potential V0. Potentials VH2 and VH3 are potentials higher than potential VH1. Moreover, potential VH2 is a potential higher than potential VH3.

[0105] The waveform P2 includes a waveform PA1-2 and a waveform PA2-2. The waveform PA1-2 is an example of a "first ejection pulse" corresponding to the waveform PA1-1. The waveform PA2-2 is an example of a "second ejection pulse" corresponding to the waveform PA2-1. The waveform PA1-2 includes a waveform PP1, a waveform PP2, and a waveform PP3(2). The waveform PP1, like the waveform PP1 in the waveform P1, changes from a reference potential V0 to a potential VL1 in the control period Q1. The waveform PP2, like the waveform PP2 in the waveform P1, maintains the potential VL1 in the control period Q2. The waveform PP3(2), like the waveform PP3(1) in the waveform P1, changes from a potential VL1 to a potential VH1 in the control period Q3.

[0106] The waveform PA2-2 includes a waveform PP7(2), a waveform PP8, a waveform PP9, a waveform PP10, and a waveform PP11. The waveform PP7(2) changes from a potential VH1 to a potential VH3 in a control period Q7, maintains the potential VH3 for a predetermined period, and then changes from the potential VH3 to a potential VL2. The waveform PP8 maintains the potential VL2 in the control period Q8, similar to the waveform PP8 in the waveform P1. The waveform PP9 changes from a potential VL2 to a potential VH2 in the control period Q9, similar to the waveform PP9 in the waveform P1. The waveform PP10 maintains the potential VH2 in the control period Q10, similar to the waveform PP10 in the waveform P1. The waveform PP11 changes from a potential VH2 to a reference potential V0 in the control period Q11, similar to the waveform PP11 in the waveform P1. The waveform PP6(2) connects the end of PP3(2), which is the end of the waveform PA1-2, to the beginning of the waveform PP71, which is the beginning of the waveform PA2-2, during the control period Q6. The waveform PP6(2) maintains the potential VH1.

[0107] FIG. 10 is an enlarged view of waveforms PP6(2) and PP7(2). The waveform PP6(2) connects the end of the waveform PP3(2) included in the waveform PA1-2 to the beginning of the waveform PP71, which is the beginning of the waveform PP7(2) included in the waveform PA2-2. The potential at the end of the waveform PP3(2) is the potential VH1. The potential at the beginning of the waveform PP71 is the potential VH1. As described above, the potential VH1 is equal to the reference potential V0. The control period Q7 includes, in chronological order, a control period Q71, a control period Q72, and a control period Q73. The waveform PP7(2) includes a waveform PP71 provided in the control period Q71, a waveform PP72 provided in the control period Q72, and a waveform PP73 provided in the control period Q73. The waveform PP71 is a waveform that changes from a potential VH1 to a potential VH3, and is an example of a "pre-contraction element" that contracts the volume of the cavity CV before the second expansion element. The waveform PP72 is a waveform that maintains the potential VH3, and is an example of a "maintenance element" that maintains the volume of the cavity CV contracted by the waveform PP71.

[0108] Because waveform PP6(2) is a waveform that maintains potential VH1, the inkjet printer 1 can ensure the proper gradation of printing by ensuring that the period from the rising edge to the falling edge of pulse PLC in change signal CH is included in the period from the beginning to the end of waveform PP6(2).

[0109] In addition, in the example shown in Figure 9, the waveform PP7(2) changes the waveform PP71 from potential VH1 to potential VH3, so that the potential difference between potential VH3 and potential VL2 in the waveform PP73 can be made greater than or equal to the potential difference between reference potential V0 and potential VL1 in the waveform PP1.

[0110] Therefore, the first shot of droplets ejected by the waveform PP3(2) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined. Also, the ejection weight of the ink is ensured.

[0111] Furthermore, by having waveform PP72 that maintains a potential between waveforms PP71 and PP73, waveform PP7(2) can prevent ejection from becoming unstable due to interference between residual vibrations caused by driving waveform PP71 and pressure fluctuations caused by driving waveform PP73.

[0112] In the example shown in FIG. 9, the reference potential V0 in the waveform PP1 is an example of a "first potential". The potential VL1 in the waveform PP1 is an example of a "second potential". The waveform PP1 is an example of a "first expansion element". The waveform PP2 is an example of a "first sustain element". The potential VL1 in the waveform PP3(2) is an example of a "second potential". The potential VH1 in the waveform PP3(2) is an example of a "third potential". The waveform PP3(2) is an example of a "first ejection element". The waveform PP6(2) is an example of a "connection element". The potential VH3 in the waveform PP73 of the waveform PP7(2) is an example of a "fourth potential". The potential VL2 in the waveform PP73 of the waveform PP7(2) is an example of a "fifth potential". The waveform PP73 of the waveform PP7(2) is an example of a "second expansion element". The potential VL2 in the waveform PP9 is an example of a "fifth potential." The potential VH2 in the waveform PP9 is an example of a "sixth potential." The waveform PP9 is an example of a "second ejection element." The reference potential V0 in the waveform PP11 is an example of a "seventh potential." The waveform PP11 is an example of a "vibration damping element." The waveform PP6(2) is an example of a "connection element."

[0113] 2-2: Advantages of the Second Embodiment In the inkjet printer 1 according to the second embodiment, the potential difference between the potential VH3 and the potential VL2 in the waveform PP73 of the waveform PP7(2) is equal to or greater than the potential difference between the reference potential V0 and the potential VL1 in the waveform PP1.

[0114] Therefore, the first shot of droplets ejected by the waveform PP3(2) and the second shot of droplets ejected by the waveform PP9 can be more reliably combined. Also, the ejection weight of the ink is ensured.

[0115] 3: Third embodiment The liquid ejection device according to the third embodiment will be described below with reference to Fig. 11. The configuration of the liquid ejection device according to this embodiment is the same as that of the liquid ejection device according to the first embodiment, except for the waveform of the drive signal Com. Therefore, the following mainly describes the waveform of the drive signal Com in this embodiment.

[0116] 3-1: Waveform of the driving signal Com in the third embodiment FIG. 11 is an example of a timing chart showing the driving signal Com in the third embodiment. 11, in this embodiment, the driving signal Com has a waveform P3 provided in the unit period TP. The following describes the characteristics of the waveform P3, focusing mainly on the differences between the waveform P3 and the waveform P1 according to the first embodiment.

[0117] The waveform P3 does not have waveforms corresponding to the waveforms PP10 and PP11 of the waveform P1.

[0118] 11, the potential VL=potential VL1. The potential VL is lower than the reference potential V0. The potential VL2 is lower than the reference potential V0 and the potential VL1. Moreover, the potentials VH1 and VH2 are equal to the reference potential V0.

[0119] The waveform P3 includes a waveform PA1-3 and a waveform PA2-3. The waveform PA1-3 is an example of a "first ejection pulse" corresponding to the waveform PA1-1. The waveform PA2-3 is an example of a "second ejection pulse." The waveforms PA1-3 include a waveform PP1, a waveform PP2, and a waveform PP3(3). The waveform PP1, like the waveform PP1 in the waveform P1, changes from a reference potential V0 to a potential VL1 in the control period Q1. The waveform PP2, like the waveform PP2 in the waveform P1, maintains the potential VL1 in the control period Q2. The waveform PP3(3), like the waveform PP3(1) in the waveform P1, changes from a potential VL1 to a potential VH1 in the control period Q3.

[0120] The waveform PA2-3 includes a waveform PP7(3), a waveform PP8(3), and a waveform PP9(3). That is, unlike the waveform PA2-1 according to the first embodiment, the waveform PA2-3 does not include the waveform PP10 and the waveform PP11. The waveform PP7(3) changes from the potential VH1 to the potential VL2 in the control period Q7. The waveform PP8(3) maintains the potential VL2 in the control period Q8. The waveform PP9(3) changes from the potential VL2 to the potential VH2 in the control period Q9. The potential VH2 is equal to the reference potential V0.

[0121] The waveform PP6 connects the end of PP3(3), which is the end of the waveform PA1-3, to the beginning of the waveform PP7(3), which is the beginning of the waveform PA2-3. The waveform PP6 maintains the potential VH1, similar to the waveform PP6 in the first embodiment. As described above, the potential VH1 is equal to the reference potential V0.

[0122] In the example shown in FIG. 11, the potential VH1 in the waveform PP1 is an example of a "first potential". The potential VL1 in the waveform PP1 is an example of a "second potential". The waveform PP1 is an example of a "first expansion element". The waveform PP2 is an example of a "first sustain element". The potential VL1 in the waveform PP3(3) is an example of a "second potential". The potential VH1 in the waveform PP3(3) is an example of a "third potential". The waveform PP3(3) is an example of a "first ejection element". The potential VH1 in the waveform PP7(3) is an example of a "fourth potential". The potential VL2 in the waveform PP7(3) is an example of a "fifth potential". The waveform PP7(3) is an example of a "second expansion element". The potential VL2 in the waveform PP8(3) is an example of a "fifth potential". The waveform PP8(3) is an example of a "second sustain element". The potential VL2 in the waveform PP9(3) is an example of a “fifth potential.” The potential VH2 in the waveform PP9(3) is an example of a “sixth potential.” The waveform PP9(3) is an example of a “second ejection element.”

[0123] 3-2: Advantages of the Third Embodiment The inkjet printer 1 according to the third embodiment provides the same effects as the inkjet printer 1 according to the first embodiment.

[0124] 4: Fourth embodiment The liquid ejection device according to the fourth embodiment will be described below with reference to Fig. 12. The configuration of the liquid ejection device according to this embodiment is the same as that of the liquid ejection device according to the first embodiment, except for the waveform of the drive signal Com. Therefore, the following mainly describes the waveform of the drive signal Com in this embodiment.

[0125] 4-1: Waveform of the driving signal Com in the fourth embodiment FIG. 12 is an example of a timing chart showing the driving signal Com in the fourth embodiment. 12, in this embodiment, the driving signal Com has a waveform P4 provided in the unit period TP. The following describes the characteristics of the waveform P4, focusing mainly on the differences between the waveform P4 and the waveform P1 according to the first embodiment.

[0126] The waveform P4 has a waveform PP11(4) instead of the waveform PP11 of the waveform P1.

[0127] 12, potential VL=potential VL1=potential VL2. Potential VL is a potential lower than reference potential V0. Potential VL3 is a potential between potential VL and reference potential V0. Potential VH1 is equal to reference potential V0. Potential VH2 is a potential higher than potential VH1.

[0128] The waveform P4 includes waveforms PA1-4 and PA2-4. The waveforms PA1-4 correspond to the waveform PA1-1. The waveforms PA2-4 correspond to the waveform PA2-1. The waveforms PA1-4 include waveforms PP1, PP2, and PP3(4). The waveform PP1 changes from the reference potential V0 to potential VL1 during the control period Q1. The waveform PP2 maintains the potential VL1 during the control period Q2. The waveform PP3(4), like the waveform PP3(1), changes from potential VL1 to potential VH1 during the control period Q3.

[0129] The waveform PA2-4 includes a waveform PP7, a waveform PP8, a waveform PP9, a waveform PP10, and a waveform PP11(4). The waveform PP7 changes from a potential VH1 to a potential VL2 in the control period Q7. The waveform PP8 maintains a potential VL2 in the control period Q8. The waveform PP9 changes from a potential VL2 to a potential VH2 in the control period Q9. The waveform PP10 maintains a potential VH2 in the control period Q10. The waveform PP11(4) changes from a potential VH2 to a potential VL3 in the control period Q11, then maintains the potential VL3, and then changes from the potential VL3 to the reference potential V0.

[0130] The waveform PP6 maintains the potential VH1, similarly to the waveform PP6 according to the first embodiment. As described above, the potential VH1 is equal to the reference potential V0.

[0131] In the example shown in FIG. 12, the control period Q11 includes, in chronological order, a control period Q111, a control period Q112, and a control period Q113. The waveform PP11(4) includes a waveform PP111 provided in the control period Q111, a waveform PP112 provided in the control period Q112, and a waveform PP113 provided in the control period Q113. The waveform PP111 is a waveform that changes from a potential VH2 to a potential VL3, and has the effect of expanding the volume of the cavity CV by the waveform PP111 at the timing when the pressure of the ink in the cavity CV increases due to the pressure vibration remaining in the ink in the discharge section D after the second discharge element, thereby suppressing the residual vibration of the liquid in the discharge section D. The potential difference from the potential VH2 to the potential VL3 of the waveform PP111 of this embodiment is larger than the potential difference from the potential VH2 to the reference potential V0 of the waveform PP11 of the first embodiment, and the residual vibration can be further attenuated. Thereafter, at the timing when the pressure of the ink in the cavity CV drops due to the residual vibration of the ink in the ejection portion D, the volume of the cavity CV is contracted by the waveform PP113, which has the effect of further suppressing the residual vibration of the liquid in the ejection portion D. In other words, the waveform PA2-4 includes the waveform PP11(4) as a vibration suppression element that suppresses the residual vibration of the ink in the ejection portion D[m]. The waveform PP11(4) suppresses the vibration of the ink in the ejection portion D[m], thereby stabilizing the ejection of ink from the nozzle N in the next unit period TP.

[0132] In the example shown in FIG. 12, the reference potential V0 in the waveform PP1 is an example of a "first potential". The potential VL1 in the waveform PP1 is an example of a "second potential". The waveform PP1 is an example of a "first expansion element". The waveform PP2 is an example of a "first sustain element". The potential VL1 in the waveform PP3(4) is an example of a "second potential". The potential VH1 in the waveform PP3(4) is an example of a "third potential". The waveform PP3(4) is an example of a "first ejection element". The potential VH1 in the waveform PP7 is an example of a "fourth potential". The potential VL2 in the waveform PP7 is an example of a "fifth potential". The waveform PP7 is an example of a "second expansion element". The potential VL2 in the waveform PP9 is an example of a "fifth potential". The potential VH2 in the waveform PP9 is an example of a "sixth potential". The waveform PP9 is an example of a "second ejection element". The potential VL3 in the waveform PP11(4) is an example of a "seventh potential." The waveform PP11(4) is an example of a "vibration damping element." The waveform PP6 is an example of a "connection element."

[0133] 4-2: Advantages of the Fourth Embodiment In the inkjet printer 1 according to the fourth embodiment, the waveform PA2-4 includes a waveform P11(4) as a vibration damping element that suppresses the vibration of the ink in the ejection section D[m] by changing from potential VH2 to potential VL3, and then changing from potential VL3 to reference potential V0.

[0134] By suppressing the vibration of the ink in the ejection section D[m], the ejection of ink from the nozzle N is stabilized.

[0135] 5: Fifth embodiment A liquid ejection device according to the fifth embodiment will be described below with reference to Fig. 13. The configuration of the liquid ejection device according to this embodiment is the same as that of the liquid ejection device according to the first embodiment, except for the waveform of the drive signal Com. Therefore, the following mainly describes the waveform of the drive signal Com in this embodiment.

[0136] 5-1: Waveform of the driving signal Com in the fifth embodiment FIG. 13 is an example of a timing chart showing the driving signal Com in the fifth embodiment. 13, in this embodiment, the driving signal Com has a waveform P5 provided in the unit period TP. The following describes the characteristics of the waveform P5, focusing mainly on the differences between the waveform P5 and the waveform P1 according to the first embodiment.

[0137] The waveform P5 has a waveform PP7(5) instead of the waveform PP7 of the waveform P1. The waveform PP7(5) is a waveform in which the rate of potential change changes in two stages.

[0138] 13, potential VL=potential VL1=potential VL2. Potential VL is a potential lower than reference potential V0. Potential VL4 is a potential between potential VL and potential VH1. Potential VH1 is equal to reference potential V0. Potential VH2 is a potential higher than potential VH1.

[0139] The waveform P5 includes a waveform PA1-5 and a waveform PA2-5. The waveform PA1-5 is an example of a "first ejection pulse" corresponding to the waveform PA1-1. The waveform PA2-5 is an example of a "second ejection pulse" corresponding to the waveform PA2-1. The waveform PA1-5 includes a waveform PP1, a waveform PP2, and a waveform PP3(5). The waveform PP1 changes from a reference potential V0 to a potential VL1 during the control period Q1. The waveform PP2 maintains the potential VL1 during the control period Q2. The waveform PP3(5), like the waveform PP3(1), changes from a potential VL1 to a potential VH1 during the control period Q3.

[0140] The waveform PA2-5 includes a waveform PP7(5), a waveform PP8, a waveform PP9, a waveform PP10, and a waveform PP11. The waveform PP7(5) changes from a potential VH1 to a potential VL2 in the control period Q7. The waveform PP8 maintains a potential VL2 in the control period Q8. The waveform PP9 changes from a potential VL2 to a potential VH2 in the control period Q9. The waveform PP10 maintains a potential VH2 in the control period Q10. The waveform PP11 changes from a potential VH2 to a reference potential V0 in the control period Q11.

[0141] Furthermore, control period Q7 includes, in chronological order, control period Q71 and control period Q72. Waveform PP7(5) includes waveform PP71 provided in control period Q71 and waveform PP72 provided in control period Q72. Waveform PP71 is a waveform that changes from potential VH1 to potential VL4. Waveform PP72 is a waveform that changes from potential VL4 to potential VL2. As described above, potential VL4 is a potential between potential VH1 and potential VL2.

[0142] The rate of potential change from the potential VL4 to the potential VL2 in the waveform PP72 is greater than the rate of potential change from the potential VH1 to the potential VL4 in the waveform PP71.

[0143] Also, the potential difference between the potentials VH1 and VL4 in the waveform PP71 is preferably 25% or less of the potential difference between the potentials VL4 and VL2 in the waveform PP72.

[0144] 13, the inkjet printer 1 expands the volume of the cavity CV in two stages using waveforms PP71 and PP72, and by making the first stage of expansion slower than the second stage of expansion, it is possible to suppress a sudden meniscus change after ink is ejected by waveform PP3(5). As a result, the ejection of ink from the ejection section D[m] is stabilized.

[0145] Moreover, the waveform PP6 maintains the potential VH1. As described above, the potential VH1 is equal to the reference potential V0. For this reason, the inkjet printer 1 ensures that the period from the rising edge to the falling edge of the pulse PLC in the change signal CH is included in the period from the beginning to the end of the waveform PP6, thereby ensuring the proper printing gradation.

[0146] In the example shown in FIG. 13, the reference potential V0 in the waveform PP1 is an example of a "first potential". The potential VL1 in the waveform PP1 is an example of a "second potential". The waveform PP1 is an example of a "first expansion element". The waveform PP2 is an example of a "first sustain element". The potential VL1 in the waveform PP3(5) is an example of a "second potential". The potential VH1 in the waveform PP3(5) is an example of a "third potential". The waveform PP3(5) is an example of a "first ejection element". The potential VH1 in the waveform PP7(5) is an example of a "fourth potential". The potential VL2 in the waveform PP7(5) is an example of a "fifth potential". The waveform PP7(5) is an example of a "second expansion element". The potential VL2 in the waveform PP9 is an example of a "fifth potential". The potential VH2 in the waveform PP9 is an example of a "sixth potential". The waveform PP9 is an example of a "second ejection element." The reference potential V0 in the waveform PP11 is an example of a "seventh potential." The waveform PP11 is an example of a "vibration suppression element."

[0147] Moreover, waveform PP71 is an example of a "first partial element." Waveform PP72 is an example of a "second partial element." Potential VL4 in waveforms PP71 and PP72 is an example of an "eighth potential." The potential change rate from potential VH1 to potential VL4 in waveform PP71 is an example of a "first potential change rate." The potential change rate from potential VL4 to potential VL2 in waveform PP72 is an example of a "second potential change rate."

[0148] 5-2: Advantages of the Fifth Embodiment In the inkjet printer 1 according to this embodiment, the waveform PP7 includes a waveform PP71 that changes from the potential VH1 at a first potential change rate, and a waveform PP72 that changes at a second potential change rate that is greater than the first potential change rate, following the waveform PP71 in chronological order.

[0149] Therefore, the ink jet printer 1 can suppress abrupt changes in the meniscus after ink is ejected by the waveform PP3(5), and as a result, the ejection of ink from the ejection section D[m] is stabilized.

[0150] Furthermore, in the inkjet printer 1 according to this embodiment, the waveform PP71 changes from a potential VH1 to a potential VL4 between the potentials VH1 and VL2. The waveform PP72 changes from a potential VL4 to a potential VL2. The potential difference between the potentials VH1 and VL4 is 25% or less of the potential difference between the potentials VL4 and VL2.

[0151] Therefore, the ink jet printer 1 can suppress abrupt changes in the meniscus after ink is ejected by the waveform PP3(5), and as a result, the ejection of ink from the ejection section D[m] is stabilized.

[0152] 6: Variations Each of the above embodiments may be modified in various ways. Specific modified aspects are exemplified below. The aspects exemplified below and the aspects shown in the above embodiment may be appropriately combined within a range that does not contradict each other. Note that, for elements in the modified examples exemplified below that have the same actions and functions as the embodiment, the reference numerals referenced in the above description are used and detailed descriptions of each are appropriately omitted.

[0153] 6-1: Variation 1 In the above embodiment, the drive signal generating unit 4 generates the drive signal Com consisting of one type of drive signal. However, the drive signal generating unit 4 may generate the drive signal Com including multiple types of drive signals. As an example, the drive signal Com may include a drive signal Com-A and a drive signal Com-B.

[0154] In this case, the supply circuit 31 includes two types of switches, not shown, a switch Wa[m] and a switch Wb[m], in addition to the switch WS[m]. The connection state designation circuit 310 generates a connection state designation signal Qa[m] that designates the on / off state of the switch Wa[m] and a connection state designation signal Qb[m] that designates the on / off state of the switch Wb[m] based on at least some of the signals of the print signal SI, the latch signal LAT, and the change signal CH that are supplied from the control unit 2.

[0155] When the switch Wa[m] is turned on based on the connection state designation signal Qa[m], the drive signal Com-A is supplied to the upper electrode Zu[m] of the discharge section D[m] as the supply drive signal Vin[m]. When the switch Wb[m] is turned on based on the connection state designation signal Qb[m], the drive signal Com-B is supplied to the upper electrode Zu[m] of the discharge section D[m] as the supply drive signal Vin[m].

[0156] If the drive signal Com-A has the same waveform as the drive signal Com in the above embodiment, and both the drive signal Com-A and the drive signal Com-B include a waveform PP6 that maintains the reference potential V0 as the potential VH1, and are set to the reference potential V0 at the start and end of the unit period TP, the inkjet printer 1 can seamlessly switch between supplying the drive signal Com-A or the drive signal Com-B to the upper electrode Zu[m] of the ejection section D[m]. As a result, the inkjet printer 1 can ensure the proper gradation in printing.

[0157] 6-2: Variation 2 The liquid ejection device according to this modified example will be described below with reference to Fig. 14. The configuration of the liquid ejection device according to this modified example is the same as that of the liquid ejection device according to the first embodiment, except for the waveform of the drive signal Com. Therefore, the following mainly describes the waveform of the drive signal Com in this modified example.

[0158] FIG. 14 is an example of a timing chart showing the drive signal Com in this modified example. 14, in the modified example, the driving signal Com has a waveform P6 provided in the unit period TP. The following describes the characteristics of the waveform P6, focusing mainly on the differences between the waveform P6 and the waveform P1 according to the first embodiment.

[0159] In the waveform P1, the potential VL1 is equal to the potential VL2, but in the waveform P6, the potential VL1 and the potential VL2 are different potentials. Also, in the waveform P1, the potential VH1 is equal to the reference potential V0, but in the waveform P6, the potential VH1 and the reference potential V0 are different potentials.

[0160] 14, the potentials VL1 and VL2 are lower than the reference potential V0. The potential VL1 is lower than the potential VL2. The potentials VH1 and VH2 are higher than the reference potential V0. The potential VH2 is higher than the potential VH1. The potential VL2 may be higher than the potential VL1.

[0161] The waveform P6 includes a waveform PA1-6 and a waveform PA2-6. The waveform PA1-6 is an example of a "first ejection pulse" corresponding to the waveform PA1-1. The waveform PA2-6 is an example of a "second ejection pulse" corresponding to the waveform PA2-1. The waveform PA1-6 includes a waveform PP1, a waveform PP2, and a waveform PP3 (6). The waveform PP1 changes from a reference potential V0 to a potential VL1 during the control period Q1. The waveform PP2 maintains the potential VL1 during the control period Q2. The waveform PP3 changes from a potential VL1 to a potential VH1 during the control period Q3.

[0162] The waveform PA2-6 includes a waveform PP7(6), a waveform PP8, a waveform PP9(6), a waveform PP10, and a waveform PP11. The waveform PP7(6) changes from a potential VH1 to a potential VL2 in the control period Q7. The waveform PP8 maintains the potential VL2 in the control period Q8. The waveform PP9(6) changes from a potential VL2 to a potential VH2 in the control period Q9. The waveform PP10 maintains the potential VH2 in the control period Q10. The waveform PP11 changes from a potential VH2 to a reference potential V0 in the control period Q11. Because waveform PP6(6) is a waveform that maintains potential VH1, the inkjet printer 1 can ensure the proper gradation of printing by ensuring that the period from the rising edge to the falling edge of pulse PLC in change signal CH is included in the period from the beginning to the end of waveform PP6(6).

[0163] In the example shown in FIG. 14, the reference potential V0 in the waveform PP1 is an example of a "first potential". The potential VL1 in the waveform PP1 is an example of a "second potential". The waveform PP1 is an example of a "first expansion element". The waveform PP2 is an example of a "first sustain element". The potential VL1 in the waveform PP3 is an example of a "second potential". The potential VH1 in the waveform PP3 is an example of a "third potential". The waveform PP3 is an example of a "first ejection element". The potential VH1 in the waveform PP7 is an example of a "fourth potential". The potential VL2 in the waveform PP7 is an example of a "fifth potential". The waveform PP7 is an example of a "second expansion element". The potential VL2 in the waveform PP9 is an example of a "fifth potential". The potential VH2 in the waveform PP9 is an example of a "sixth potential". The waveform PP9 is an example of a "second ejection element". The reference potential V0 in the waveform PP11 is an example of a "seventh potential." The waveform PP11 is an example of a "vibration damping element." The waveform PP6(6) is an example of a "connection element."

[0164] 6-3: Variation 3 In the waveform P1 according to the first embodiment, the waveform PP7 monotonically decreases within the control period Q7. However, the waveform PP7 may have a period during which it maintains a substantially constant potential during part of the control period Q7. This is also true for the waveform P2 according to the second embodiment to the waveform P5 according to the fifth embodiment, and the waveform P6 according to the second modification.

[0165] 6-4: Variation 4 In the embodiment and modification 2, the waveform PP9 increases monotonically within the control period Q9. However, the waveform PP9 may have a period during which a substantially constant potential is maintained during part of the control period Q9.

[0166] 6-5: Variation 5 In the above embodiment and modification 2, the unit period TP includes only two pulses, the first ejection pulse and the second ejection pulse, but it is also possible to include one or more pulses after the second ejection pulse. [Explanation of symbols]

[0167] 1: inkjet printer, 2: control unit, 3: head unit, 4: drive signal generation unit, 7: transport unit, 31: supply circuit, 32: recording head, 71: carriage transport mechanism, 73: medium transport mechanism, 100: housing, 321: diaphragm, CH: change signal, Com: drive signal, D: ejection section, N: nozzle, PLC, PLL: pulse, TP: unit period, Tc: natural vibration period, V0: reference potential, VBS, VH1, VH2, VL, VL1, VL2: potential

Claims

1. an ejection unit having a nozzle that ejects liquid to be landed on a medium, a pressure chamber that communicates with the nozzle and through which the liquid flows, and a drive element that generates a pressure fluctuation in the liquid in the pressure chamber when a drive signal is supplied; A drive signal generating unit that generates the drive signal; Equipped with the drive signal includes a plurality of ejection pulses corresponding to a plurality of droplets that combine before landing on a medium; The first ejection pulse among the plurality of ejection pulses in chronological order is a first expansion element that changes from a first potential to a second potential and drives the drive element to expand the volume of the pressure chamber; a first ejection element that changes from the second potential to a third potential to contract the volume of the pressure chamber expanded by the first expansion element, and ejects a droplet from the nozzle; A second ejection pulse next to the first ejection pulse in chronological order among the plurality of ejection pulses is a second expansion element that changes from a fourth potential to a fifth potential and drives the drive element to expand the volume of the pressure chamber; a second ejection element that changes from the fifth potential to a sixth potential to contract the volume of the pressure chamber expanded by the second expansion element, and ejects a droplet from the nozzle; A liquid ejection device, wherein the length of a first period during which the second expansion element changes from the fourth potential to the fifth potential is longer than the length of a second period during which the first expansion element changes from the first potential to the second potential.

2. The time length of the first period is 1.5 times or more and 3 times or less than the time length of the second period. The liquid ejection device according to claim 1 .

3. a rate of change of potential in the second expansion element from the fourth potential to the fifth potential is smaller than a rate of change of potential in the first expansion element from the first potential to the second potential; The liquid ejection device according to claim 1 .

4. a potential difference between the fourth potential and the fifth potential in the second expansion element is equal to or greater than a potential difference between the first potential and the second potential in the first expansion element; The liquid ejection device according to claim 1 .

5. the first ejection pulse comprises a first sustain element that sustains the second potential from an end of the first expansion element to a beginning of the first ejection element; the first ejection pulse beginning with the first expansion element and ending with the first ejection element; the drive signal includes a connection element that maintains a constant potential from the end of the first ejection pulse to the start of the second ejection pulse, the second expansion element monotonically increases or decreases from the fourth potential to the fifth potential; The liquid ejection device according to claim 1 .

6. When the drive element is driven by the drive signal, a natural vibration period of the vibration generated in the ejection portion is defined as Tc, and the time length from the start of the first expansion element to the start of the second expansion element is 0.85Tc or more and 1.15Tc or less. The liquid ejection device according to claim 1 .

7. When the natural vibration period of the vibration generated in the ejection unit when the drive element is driven by the drive signal is Tc, the time length from the start of the first ejection element to the start of the second ejection element is 1Tc or more and 1.4Tc or less. The liquid ejection device according to claim 1 .

8. When the natural vibration period of the vibration generated in the ejection unit when the drive element is driven by the drive signal is Tc, the time length from the end of the first ejection element to the end of the second ejection element is 1Tc or more and 1.4Tc or less. The liquid ejection device according to claim 1 .

9. the drive signal includes a connection element that connects the first ejection pulse and the second ejection pulse, the connection element is connected to the first ejection element, and maintains the third potential for a period of 0.3Tc or more and 0.5Tc or less, where Tc is a natural vibration period of vibration generated in the ejection portion when the drive element is driven by the drive signal; The liquid ejection device according to claim 1 .

10. a potential difference between the fifth potential and the sixth potential in the second ejection element is equal to or greater than a potential difference between the second potential and the third potential in the first ejection element; The liquid ejection device according to claim 9.

11. a potential difference between the second potential and the third potential in the first ejection element is 0.6 times or more a potential difference between the fifth potential and the sixth potential in the second ejection element; The liquid ejection device according to claim 10.

12. The second ejection pulse further comprises: a vibration damping element that changes from the sixth potential to a seventh potential and suppresses vibration of the liquid in the ejection portion; The liquid ejection device according to claim 11.

13. a rate of change in potential from the fifth potential to the sixth potential in the second ejection element is greater than a rate of change in potential from the second potential to the third potential in the first ejection element; The liquid ejection device according to claim 1 .

14. the second expansion element includes a first partial element which is an element that changes from the fourth potential at a first potential change rate, and a second partial element which is an element that changes at a second potential change rate that is greater than the first potential change rate and is placed after the first partial element in time series order; The liquid ejection device according to claim 1 .

15. the first subelement changes from the fourth potential to an eighth potential between the fourth potential and the fifth potential; the second subelement changes from the eighth potential to the fifth potential; a potential difference between the fourth potential and the eighth potential is 25% or less of a potential difference between the eighth potential and the fifth potential; The liquid ejection device according to claim 14.

16. When the drive element is driven by the drive signal, the natural vibration period of the vibration generated in the ejection portion is denoted by Tc, The time length of the period from the start of the first expansion element to the start of the first discharge element is 0.45Tc or more and 0.55Tc or less, The time length of the period from the start of the second expansion element to the start of the second discharge element is 0.6Tc or more and 0.8Tc or less. The liquid ejection device according to claim 1 .

17. the first ejection pulse comprises a first sustain element that sustains the second potential from an end of the first expansion element to a beginning of the first ejection element; the second ejection pulse comprises a second sustain element that sustains the fifth potential from an end of the second expansion element to a beginning of the second ejection element; a duration of each of the first sustain element and the second sustain element is not less than 0.2 Tc and not more than 0.4 Tc; The liquid ejection device according to claim 16.

18. The drive signal is the potential is set to the first potential at the start of a unit period during which the plurality of ejection pulses are provided, and the potential is set to the first potential at the end of the unit period; a connection element that connects the first ejection pulse and the second ejection pulse; the connecting element maintains the first potential; The liquid ejection device according to claim 1 .

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