LIQUID EJECTION DEVICE AND METHOD FOR CONTROLLING LIQUID EJECTION DEVICE

Abstract

To suppress discharge characteristics of liquid droplets from varying.SOLUTION: A liquid discharge apparatus comprises: a plurality of dischargers which each include a nozzle for discharging liquid, a pressure chamber communicating with the nozzle and a driving element for discharging liquid in the pressure chamber through the nozzle; and a driver that generates, for each of the dischargers, an individual drive signal for driving the drive element included in each of the plurality of dischargers, on the basis of a plurality of drive signals which each include a first drive signal having a first waveform and a second drive signal having a second waveform different from the first waveform. The first waveform includes a first contraction waveform in which an electric potential of the first drive signal varies to cause a volume of the pressure chamber to contract. The second waveform includes a second contraction waveform in which an electric potential of the second drive waveform varies to cause the volume of the pressure chamber to change. In one cycle of the plurality of drive signals, a center of one of a time period of the first contraction waveform of the first drive signal and a time period of the second contraction waveform of the second drive signal is located in the other of the time periods.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection apparatus and a method for controlling the liquid ejection apparatus. [Background technology]

[0002] Patent Document 1 discloses a liquid ejection device that prints an image by ejecting a liquid such as ink from a plurality of nozzles using a piezoelectric element. For example, a drive signal having a drive waveform corresponding to image data is supplied to one electrode of the piezoelectric element, and a constant bias voltage signal is supplied to the other electrode of the piezoelectric element. The drive signal is generated, for example, by selecting a common drive signal corresponding to the image data from a plurality of common drive signals that cause different amounts of droplets to be ejected from the nozzles. For example, one common drive signal from the plurality of common drive signals has a drive waveform that causes the nozzles to eject an amount of droplets corresponding to that common drive signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-64112 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the amount of current flowing through the wiring to which the common drive signal is supplied changes depending on the drive waveform of the common drive signal, the potential of the bias voltage signal supplied to the piezoelectric element may fluctuate. If the potential of the bias voltage signal fluctuates, the droplet ejection characteristics may change, and the droplet landing position may deviate from the predetermined position. If the droplet landing position deviates from the predetermined position, the quality of the printed image will deteriorate. Therefore, it is desirable to suppress changes in the droplet ejection characteristics in liquid ejection devices. [Means for solving the problem]

[0005] In order to solve the above problems, the liquid ejection device of the present invention comprises a plurality of ejection units including a nozzle that ejects liquid, a pressure chamber connected to the nozzle, and a drive element that ejects the liquid in the pressure chamber from the nozzle, and a drive unit that generates individual drive signals for each of the plurality of ejection units based on a plurality of drive signals including a first drive signal having a first waveform and a second drive signal having a second waveform different from the first waveform, wherein the first waveform includes a first contraction waveform in which the potential of the first drive signal changes to contract the volume of the pressure chamber, and the second waveform includes a second contraction waveform in which the potential of the second drive signal changes to contract the volume of the pressure chamber, and during one cycle of the plurality of drive signals, the center of one of the period of the first contraction waveform of the first drive signal and the period of the second contraction waveform of the second drive signal is located within the period of the other.

[0006] Furthermore, a control method for a liquid ejection device according to the present invention is a control method for a liquid ejection device having a plurality of ejection sections, each including a nozzle that ejects liquid, a pressure chamber connected to the nozzle, and a drive element that ejects the liquid in the pressure chamber from the nozzle, wherein an individual drive signal that drives the drive element included in each of the plurality of ejection sections is generated for each ejection section based on a plurality of drive signals including a first drive signal having a first waveform and a second drive signal having a second waveform different from the first waveform, wherein the first waveform includes a first contraction waveform in which the potential of the first drive signal changes to contract the volume of the pressure chamber, and the second waveform includes a second contraction waveform in which the potential of the second drive signal changes to contract the volume of the pressure chamber, and wherein in one cycle of the plurality of drive signals, the center of one of the periods of the first contraction waveform of the first drive signal and the second contraction waveform of the second drive signal is located within the center of the other period. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram illustrating an example of the configuration of an inkjet printer according to an embodiment of the invention. [Figure 2]FIG. 1 is a perspective view illustrating an example of a schematic internal structure of an inkjet printer. [Figure 3] FIG. 4 is a cross-sectional view illustrating an example of the structure of a discharge portion. [Figure 4] FIG. 2 is a plan view showing an example of the arrangement of nozzles in a head unit. [Figure 5] FIG. 2 is a block diagram showing an example of the configuration of a head unit. [Figure 6] 4 is a timing chart illustrating an example of a signal supplied to a head unit. [Figure 7] 7 is an explanatory diagram for explaining an operation when the drive signal shown in FIG. 6 is supplied to a head unit. FIG. [Figure 8] 10A and 10B are explanatory diagrams for explaining one cause of deviation in ink landing position when large dots and small dots are mixed; [Figure 9] 10 is an explanatory diagram for explaining the influence of a change in the potential of a bias voltage signal on the potential difference between a drive signal and a bias voltage signal; FIG. [Figure 10] 10A and 10B are explanatory diagrams showing experimental results when the timing relationship between the drive signals for large dots and small dots is changed. [Figure 11] 10 is a timing chart illustrating an example of a drive signal in the first modified example. [Figure 12] FIG. 10 is an explanatory diagram for explaining the timing relationship of drive signals in a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of 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 those of the actual parts. Furthermore, since the embodiments described below are preferred examples of the present invention, various technically preferable limitations are applied, 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. Embodiment] In this embodiment, a liquid ejection device will be described using an inkjet printer that ejects ink onto recording paper to form an image. Note that in this embodiment, ink is an example of a "liquid." First, the configuration of a drive signal generation unit 4 according to this embodiment will be described with reference to FIG. 1.

[0010] FIG. 1 is a block diagram showing an example of the configuration of an inkjet printer 1 according to an embodiment of the invention.

[0011] Print data IMG indicating the image to be formed by the inkjet printer 1 is supplied to the inkjet printer 1 from a host computer such as a personal computer or digital camera. The inkjet printer 1 executes a printing process to form the image indicated by the print data IMG supplied from the host computer on a medium. In this embodiment, the medium is assumed to be recording paper P shown in Figure 2, which will be described later.

[0012] The inkjet printer 1 has a control unit 2 that controls each part of the inkjet printer 1, a head unit 3 that has ejection units D that eject ink, and a drive signal generation unit 4 that generates a plurality of drive signals COM for driving the ejection units D. The inkjet printer 1 also has a transport unit 7 that changes the relative position of the recording paper P with respect to the head unit 3, and a maintenance unit 8 that executes maintenance processing to maintain the ejection units D that are provided in the head unit 3.

[0013] In this embodiment, it is assumed that the head units 3 and the drive signal generation units 4 correspond to each other. For example, the inkjet printer 1 may have multiple head units 3 and multiple drive signal generation units 4 that correspond one-to-one to the multiple head units 3. Alternatively, the inkjet printer 1 may have one head unit 3 and one drive signal generation unit 4 that corresponds one-to-one to the single head unit 3. In this embodiment, it is assumed that the inkjet printer 1 has four head units 3 and four drive signal generation 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 generation units 4 that is provided to correspond to one of the head units 3, as shown in FIG. 1.

[0014] The control unit 2 is configured to include one or more central processing units (CPUs). Note that the control unit 2 may be configured to include a programmable logic device such as a field-programmable gate array (FPGA) instead of or in addition to a CPU. The control unit 2 is also configured to include one or both of a volatile memory such as a random access memory (RAM) and a non-volatile memory such as a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), or a programmable ROM (PROM).

[0015] As will be described in detail below, the control unit 2 generates signals such as a print signal SI and a waveform designation signal dCOM for controlling the operation of each part of the inkjet printer 1. Here, the waveform designation signal dCOM is a digital signal that defines the waveform of each of the multiple drive signals COM. Furthermore, each drive signal COM is an analog signal for driving a discharge section D. In this embodiment, as shown in FIG. 6 and other figures described below, it is assumed that the multiple drive signals COM include a drive signal COMa and a drive signal COMb. Furthermore, the print signal SI is a digital signal for specifying the type of operation of the discharge section D. Specifically, the print signal SI is a signal that specifies whether or not to supply each drive signal COM to the discharge section D, thereby specifying the type of operation of the discharge section D.

[0016] The drive signal generating unit 4 includes, for example, a DAC (Digital Analog Converter), and generates a plurality of drive signals COM based on a waveform designation signal dCOM supplied from the control unit 2. For example, each of the plurality of drive signals COM generated by the drive signal generating unit 4 includes a waveform defined by the waveform designation signal dCOM. The drive signal generating unit 4 outputs the plurality of drive signals COM generated based on the waveform designation signal dCOM to a supply circuit 31 included in the head unit 3.

[0017] The head unit 3 has a supply circuit 31 and a recording head 32. The supply circuit 31 is an example of a "drive unit."

[0018] The recording head 32 has M discharge sections D. The value M is a natural number greater than or equal to 1. Below, the mth 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." Also, below, when a component or signal of the inkjet printer 1 corresponds to a discharge section D[m] among the M discharge sections D, the subscript [m] may be added to the symbol representing the component or signal.

[0019] The supply circuit 31 switches whether or not to supply each drive signal COM to the discharge section D[m] based on the print signal SI. Note that, hereinafter, as shown in FIG. 5 and other figures described later, of the multiple drive signals COM, the drive signal COM supplied to the discharge section D[m] may be referred to as an individual drive signal Vin[m].

[0020] 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 print signals 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 waveform designation signals dCOM, for controlling the drive signal generation 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 P with respect to the head unit 3, while also adjusting the presence or absence of ink ejection from the ejection unit D[m], the amount of ink ejection, the timing of ink ejection, and so on. In this way, the control unit 2 controls each part of the inkjet printer 1 so that an image corresponding to the print data IMG is formed on the recording paper P.

[0021] As described above, in this embodiment, the inkjet printer 1 executes maintenance processes. For example, the maintenance processes include a flushing process that discharges ink from the ejection section D, a wiping process that uses a wiper to wipe off foreign matter such as ink adhering to the vicinity of the nozzles N of the ejection section D, and a pumping process that uses a tube pump or the like to suck ink from inside the ejection section D. The nozzles N will be described later with reference to FIG. 3.

[0022] The maintenance unit 8 has a discharged ink receiving section 80 for receiving the discharged ink when the ink is discharged from the discharge section D during the flushing process, a wiper for wiping off foreign matter such as ink adhering to the vicinity of the nozzles N of the discharge section D, and a tube pump for sucking ink, air bubbles, etc. from the discharge section D. The discharged ink receiving section 80 will be described later in FIG. 2. The wiper and tube pump are not shown in the drawings. Next, the general internal structure of the inkjet printer 1 will be described with reference to FIG. 2.

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

[0024] 2, this embodiment assumes that the inkjet printer 1 is a serial printer. Specifically, when performing a printing process, the inkjet printer 1 transports the recording paper P in the sub-scanning direction, while reciprocating the head unit 3 in the main scanning direction that intersects the sub-scanning direction, and ejects ink from the ejection units D[m] to form dots on the recording paper P according to the print data IMG.

[0025] For ease of explanation, a three-axis Cartesian coordinate system having mutually orthogonal X, Y, and Z axes will be introduced as appropriate below. Furthermore, hereinafter, the direction indicated by the X-axis arrow will be referred to as the +X direction, and the direction opposite to the +X direction will be referred to as the -X direction. The direction indicated by the Y-axis arrow will be referred to as the +Y direction, and the direction opposite to the +Y direction will be referred to as the -Y direction. Furthermore, hereinafter, the +X direction and the -X direction will sometimes be referred to as the X direction without any particular distinction, and the +Y direction and the -Y direction will sometimes be referred to as the Y direction without any particular distinction. Furthermore, the +Z direction and the -Z direction will sometimes be referred to as the Z direction without any particular distinction. Furthermore, in this embodiment, the +X direction is the sub-scanning direction, and the +Y direction and the -Y direction are the main scanning directions. In this embodiment, as shown in FIG. 2, the −Z direction is the ejection direction of ink from the ejection section D[m].

[0026] The inkjet printer 1 according to this embodiment has a housing 100 and a carriage 110 that can move back and forth in the Y direction within the housing 100 and that has four head units 3 mounted thereon.

[0027] In this embodiment, it is assumed that the carriage 110 stores four ink cartridges 120 that correspond one-to-one to the four colors of ink: cyan, magenta, yellow, and black. As described above, it is also assumed in this embodiment that the inkjet printer 1 has four head units 3 that correspond one-to-one to the four ink cartridges 120. Each ejection section D[m] receives a supply of ink from the ink cartridge 120 that corresponds 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 nozzles N. Note that the ink cartridges 120 may also be provided outside the carriage 110.

[0028] As described with reference to FIG. 1 , the inkjet printer 1 according to this embodiment also includes a transport unit 7. The transport unit 7 includes a carriage transport mechanism 71 for reciprocating the carriage 110 in the Y direction, and a carriage guide shaft 76 that supports the carriage 110 so that it can reciprocate in the Y direction. The transport unit 7 also includes a medium transport mechanism 73 for transporting the recording paper P, and a platen 75 that is disposed in the −Z direction relative to the carriage 110. For example, during a printing process, the carriage transport mechanism 71 reciprocates the head unit 3 together with the carriage 110 along the carriage guide shaft 76 in the Y direction, and the medium transport mechanism 73 transports the recording paper P on the platen 75 in the +X direction. Therefore, during a printing process, the transport unit 7 causes the carriage transport mechanism 71 and the medium transport mechanism 73 to perform the above-described operations, thereby changing the relative position of the recording paper P with respect to the head unit 3 and enabling ink to land on the entire recording paper P.

[0029] Next, the general structure of the recording head 32 will be described with reference to FIG.

[0030] Fig. 3 is a cross-sectional view for explaining an example of the structure of the discharge portion D. Note that Fig. 3 schematically shows a cross section of a portion of the recording head 32 when the recording head 32 is cut so as to include the discharge portion D[m].

[0031] The ejection unit D[m] has 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 ejection unit D[m] ejects ink in the cavity CV from the nozzle N when the piezoelectric element PZ[m] is driven by an individual drive signal Vin[m]. The cavity CV is an example of a "pressure chamber," and the piezoelectric element PZ is an example of a "drive element."

[0032] The cavity CV is a space defined by a cavity plate 324, a nozzle plate 323 in which nozzles N are formed, and a vibration plate 321. The cavity CV is in communication with a reservoir 325 via an ink supply port 326. The reservoir 325 is in communication 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 Zb[m] provided between the upper electrode Zu[m] and the lower electrode Zd[m]. The upper electrode Zu[m] is electrically connected to wiring Li to which an individual drive signal Vin[m] is supplied. The lower electrode Zd[m] is electrically connected to wiring Ld to which a bias voltage signal VBS is supplied. Then, when an individual drive signal Vin[m] is supplied to the upper electrode Zu[m], a voltage is applied between the upper electrode Zu[m] and the lower electrode Zd[m]. The piezoelectric element PZ[m] is displaced in the +Z direction or the -Z direction depending on the voltage applied between the upper electrode Zu[m] and the lower electrode Zd[m]. The lower electrode Zd is an example of a "bias electrode."

[0033] In this way, the piezoelectric element PZ[m] vibrates in response to the voltage applied between the upper electrode Zu[m] and the lower electrode Zd[m]. The lower electrode Zd[m] is joined to the diaphragm 321. Therefore, when the piezoelectric element PZ[m] is driven to vibrate by the individual drive signal Vin[m], the diaphragm 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 in the cavity CV to be ejected from the nozzle N.

[0034] In this embodiment, as an example, it is assumed that the potential of the individual drive signal Vin[m] supplied to the discharge section D[m] changes from low to high, causing the piezoelectric element PZ to be displaced in the -Z direction. That is, in this embodiment, it is assumed that when the potential of the individual drive signal Vin[m] supplied to the discharge section D[m] is high, the volume of the cavity CV provided in the discharge section D[m] becomes smaller than when the potential is low.

[0035] Next, an example of the arrangement of the nozzles N will be described with reference to FIG.

[0036] Fig. 4 is a plan view showing an example of the arrangement of nozzles N in a head unit 3. Fig. 4 shows an example of the arrangement of four head units 3 mounted on a carriage 110 and a total of 4M nozzles N provided in the four head units 3 when the inkjet printer 1 is viewed from above in the -Z direction.

[0037] Each head unit 3 provided on the carriage 110 is provided with a nozzle row NL. Here, the nozzle row NL is a plurality of nozzles N arranged to extend in a row in a predetermined direction. In this embodiment, it is assumed as an example that each nozzle row NL is composed of M nozzles N arranged to extend in the X direction.

[0038] Next, an overview of the head unit 3 will be described with reference to FIGS.

[0039] FIG. 5 is a block diagram showing an example of the configuration of the head unit 3.

[0040] As described in FIG. 1, the head unit 3 has a supply circuit 31 and a recording head 32. The head unit 3 also has a wiring La to which a drive signal COMa is supplied from the drive signal generating unit 4, a wiring Lb to which a drive signal COMb is supplied from the drive signal generating unit 4, and a wiring Li[m] that supplies an individual drive signal Vin[m] to the discharge section D[m]. The drive signal COMa is an example of one of the "first drive signal" and "second drive signal," and the drive signal COMb is an example of the other of the "first drive signal" and "second drive signal." In this embodiment, the operation of the head unit 3 and the like will be described by taking the drive signal COMa as an example of the "second drive signal" and the drive signal COMb as an example of the "first drive signal."

[0041] The supply circuit 31 includes M switches Wa[1] to Wa[M] that correspond one-to-one to the M discharge sections D[1] to D[M], M switches Wb[1] to Wb[M] that correspond one-to-one to the M discharge sections D[1] to D[M], and a connection state designation circuit 310. The connection state designation circuit 310 designates the connection states of the M switches Wa and the M switches Wb. For example, the connection state designation circuit 310 generates connection state designation signals Qa[m] and Qb[m] based on at least a portion of the print signal SI and the latch signal LAT supplied from the control unit 2. The connection state designation signal Qa[m] designates the on / off state of the switch Wa[m], and the connection state designation signal Qb[m] designates the on / off state of the switch Wb[m].

[0042] The switch Wa[m] switches between conduction and non-conduction between the wiring La 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 Qa[m]. That is, the switch Wa[m] switches between conduction and non-conduction between the wiring La and the wiring Li[m] connected to the upper electrode Zu[m] based on the connection state designation signal Qa[m]. In this embodiment, the switch Wa[m] is turned on when the connection state designation signal Qa[m] is high level and turned off when it is low level. When the switch Wa[m] is on, the drive signal COMa supplied to the wiring La is supplied as an individual drive signal Vin[m] to the upper electrode Zu[m] of the discharge section D[m] via the wiring Li[m].

[0043] The switch Wb[m] switches between conduction and non-conduction between the wiring Lb 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 Qb[m]. That is, the switch Wb[m] switches between conduction and non-conduction between the wiring Lb and the wiring Li[m] connected to the upper electrode Zu[m] based on the connection state designation signal Qb[m]. In this embodiment, the switch Wb[m] is turned on when the connection state designation signal Qb[m] is high level and turned off when the connection state designation signal Qb[m] is low level. When the switch Wb[m] is on, the drive signal COMb supplied to the wiring Lb is supplied as an individual drive signal Vin[m] to the upper electrode Zu[m] of the discharge section D[m] via the wiring Li[m].

[0044] Next, the operation of the head unit 3 will be described with reference to FIG.

[0045] In this embodiment, when the inkjet printer 1 executes a printing process or a flushing 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 or the flushing process.

[0046] FIG. 6 is a timing chart for explaining an example of a signal supplied to the head unit 3. In FIG.

[0047] The control unit 2 outputs a latch signal LAT having a pulse PLL. As a result, the control unit 2 defines a unit period TP as the period from the rising edge of the pulse PLL to the rising edge of the next pulse PLL. The unit period TP is, for example, the drive cycle of M discharge sections D. In this embodiment, it is assumed that one cycle of a plurality of drive signals COM is the unit period TP.

[0048] The print signal SI according to this embodiment 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] specifies the drive mode of the discharge section D[m] during each unit period TP when the inkjet printer 1 executes a printing process or a flushing process. For example, 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 status designation circuit 310 in synchronization with the clock signal CL. The connection status designation circuit 310 then generates the connection status designation signals Qa[m] and Qb[m] during that unit period TP based on the individual designation signal Sd[m].

[0049] 7, which will be described later, it is assumed that the discharge unit D[m] can form either large dots DL or small dots DS that are smaller than the large dots DL during the unit period TP in which the printing process is performed. For example, the discharge unit D[m] is designated by the individual designation signal Sd[m] as either a discharge unit D that forms large dots DL, a discharge unit D that forms small dots DS, or a discharge unit D that does not form dots during the unit period TP in which the printing process is performed.

[0050] The drive signal COMa has a waveform PA. For example, the drive signal COMa has a pulse of the waveform PA provided in a unit period TP. The waveform PA is a waveform in which the potential of the drive signal COMa changes from a reference potential V0 to a potential VLa1, a potential VHa1, a potential VLa2, and a potential VHa2, before returning to the reference potential V0. The potentials VLa1 and VLa2 are lower than the reference potential V0, and the potentials VHa1 and VHa2 are higher than the reference potential V0. The relationship between the potentials VLa1 and VLa2 and the relationship between the potentials VHa1 and VHa2 are not particularly limited, but are determined based on the ink ejection characteristics of the ejection section D, etc. In this embodiment, it is assumed that the potential VLa1 is lower than the potential VLa2, and the potential VHa1 is lower than the potential VHa2. The waveform PA is an example of a "second waveform." The ink ejection characteristics include, for example, the amount of ink ejected as droplets and the ejection speed of the ejected droplets.

[0051] Hereinafter, the portion of the waveform PA where the potential of the drive signal COMa changes from the reference potential V0 to the potential VLa1 will be referred to as waveform Pa1, and the portion where the potential of the drive signal COMa is maintained at the potential VLa1 will be referred to as waveform Pa2. The portion of the waveform PA where the potential of the drive signal COMa changes from the potential VLa1 to the potential VHa1 will be referred to as waveform Pa3, and the portion where the potential of the drive signal COMa is maintained at the potential VHa1 will be referred to as waveform Pa4. The portion of the waveform PA where the potential of the drive signal COMa changes from the potential VHa1 to the potential VLa2 will be referred to as waveform Pa5, and the portion where the potential of the drive signal COMa is maintained at the potential VLa2 will be referred to as waveform Pa6. The portion of the waveform PA where the potential of the drive signal COMa changes from the potential VLa2 to the potential VHa2 will be referred to as waveform Pa7, and the portion where the potential of the drive signal COMa is maintained at the potential VHa2 will be referred to as waveform Pa8. The portion of the waveform PA where the potential of the drive signal COMa changes from the potential VHa2 to the reference potential V0 is also referred to as a waveform Pa9. That is, the waveform PA includes waveforms Pa1, Pa2, Pa3, Pa4, Pa5, Pa6, Pa7, Pa8, and Pa9.

[0052] The waveforms Pa1, Pa5, and Pa9 are waveforms for displacing the piezoelectric element PZ in the +Z direction. That is, the waveforms Pa1, Pa5, and Pa9 are waveforms in which the potential of the drive signal COMa changes to expand the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PA, the waveforms Pa1, Pa5, and Pa9 correspond to expansion elements that change the potential of the drive signal COMa to drive the piezoelectric element PZ so as to expand the volume of the cavity CV. The waveform Pa1 is an example of a "second expansion waveform."

[0053] The waveforms Pa3 and Pa7 are waveforms for displacing the piezoelectric element PZ in the -Z direction. In other words, the waveforms Pa3 and Pa7 are waveforms in which the potential of the drive signal COMa changes to contract the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PA, the waveforms Pa3 and Pa7 correspond to contraction elements that change the potential of the drive signal COMa to drive the piezoelectric element PZ so as to contract the volume of the cavity CV. The waveform Pa3 is an example of a "second contraction waveform."

[0054] Waveforms Pa2, Pa4, Pa6, and Pa8 are waveforms for maintaining the position of piezoelectric element PZ in the Z direction. For example, among the multiple elements constituting the pulse of waveform PA, waveforms Pa2 and Pa6 correspond to expansion maintaining elements that maintain the potential of drive signal COMa in order to drive piezoelectric element PZ so as to maintain the volume of cavity CV expanded by waveform Pa1 or Pa5. Also, for example, among the multiple elements constituting the pulse of waveform PA, waveforms Pa4 and Pa8 correspond to contraction maintaining elements that maintain the potential of drive signal COMa in order to drive piezoelectric element PZ so as to maintain the volume of cavity CV contracted by waveform Pa3 or Pa7.

[0055] The waveform PA is determined so that when an individual drive signal Vin[m] having the waveform PA is supplied to the discharge section D[m], an amount of ink corresponding to a small dot DS is discharged from the discharge section D[m]. The amount of ink corresponding to the small dot DS is an example of a "second amount." Note that, as described with reference to FIG. 3 , this embodiment assumes that when the potential of the individual drive signal Vin[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 individual drive signal Vin[m] having the waveform PA, the waveform Pa3, which changes the potential of the individual drive signal Vin[m] from low to high, causes the ink in the discharge section D[m] to be discharged from the nozzle N.

[0056] The drive signal COMb has a waveform PB. For example, the drive signal COMb has a pulse of the waveform PB provided in the unit period TP. The waveform PB is a waveform in which the potential of the drive signal COMb goes from a reference potential V0, passes through a potential VLb1 lower than the reference potential V0, passes through a potential VHb1 higher than the reference potential V0, and returns to the reference potential V0. The waveform PB is an example of a "first waveform."

[0057] Hereinafter, the portion of the waveform PB where the potential of the drive signal COMb changes from the reference potential V0 to the potential VLb1 will be referred to as waveform Pb1, and the portion where the potential of the drive signal COMb is maintained at the potential VLb1 will be referred to as waveform Pb2. Furthermore, the portion of the waveform PB where the potential of the drive signal COMb changes from the potential VLb1 to the potential VHb1 will be referred to as waveform Pb3, and the portion where the potential of the drive signal COMb is maintained at the potential VHb1 will be referred to as waveform Pb4. Furthermore, the portion of the waveform PB where the potential of the drive signal COMb changes from the potential VHb1 to the reference potential V0 will be referred to as waveform Pb5. That is, the waveform PB includes waveforms Pb1, Pb2, Pb3, Pb4, and Pb5.

[0058] The waveforms Pb1 and Pb5 are waveforms for displacing the piezoelectric element PZ in the +Z direction. That is, the waveforms Pb1 and Pb5 are waveforms in which the potential of the drive signal COMb changes to expand the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PB, the waveforms Pb1 and Pb5 correspond to expansion elements that change the potential of the drive signal COMb in order to drive the piezoelectric element PZ so as to expand the volume of the cavity CV. The waveform Pb1 is an example of a "first expansion waveform."

[0059] The waveform Pb3 is a waveform for displacing the piezoelectric element PZ in the -Z direction. In other words, the waveform Pb3 is a waveform in which the potential of the drive signal COMb changes to contract the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PB, the waveform Pb3 corresponds to a contraction element that changes the potential of the drive signal COMb to drive the piezoelectric element PZ so as to contract the volume of the cavity CV. The waveform Pb3 is an example of a "first contraction waveform."

[0060] Waveforms Pb2 and Pb4 are waveforms for maintaining the position of piezoelectric element PZ in the Z direction. For example, among the multiple elements constituting the pulse of waveform PB, waveform Pb2 corresponds to an expansion maintaining element that maintains the potential of drive signal COMb in order to drive piezoelectric element PZ so as to maintain the volume of cavity CV expanded by waveform Pb1. Furthermore, for example, among the multiple elements constituting the pulse of waveform PB, waveform Pb4 corresponds to a contraction maintaining element that maintains the potential of drive signal COMb in order to drive piezoelectric element PZ so as to maintain the volume of cavity CV contracted by waveform Pb3.

[0061] The waveform PB is determined so that when an individual drive signal Vin[m] having the waveform PB is supplied to the discharge section D[m], an amount of ink equivalent to a large dot DL is discharged from the discharge section D[m]. The amount of ink equivalent to a large dot DL is an example of a "first amount." When the discharge section D[m] is driven by the individual drive signal Vin[m] having the waveform PB, the waveform Pb3, which changes the potential of the individual drive signal Vin[m] from low to high, causes the ink in the discharge section D[m] to be discharged from the nozzle N.

[0062] In this embodiment, the drive signal COMa includes only pulses of the waveform PA that perform one ejection operation within the unit period TP, and the drive signal COMb includes only pulses of the waveform PB that perform one ejection operation within the unit period TP. This makes it possible to suppress deterioration of the ejection characteristics even when, for example, the ejection section D is driven at a frequency of 50 kHz or more. Each of the drive signals COMa and COMb may have pulses that perform two or more ejection operations within the unit period TP.

[0063] Here, it has been confirmed through experiments by the inventors that by matching the first timing, which is the center Ca12 of the period Ta12 of the waveform Pa3, and the second timing, which is the center Cb12 of the period Tb12 of the waveform Pb3, in the unit period TP, it is possible to suppress changes in the ink ejection characteristics of the ejection section D. In this specification, "match" includes not only a perfect match, but also a match that can be considered to occur when an error is taken into consideration.

[0064] 6, in the unit period TP, the first timing Cb12, which is the center Cb12 of the period Tb12 of the waveform Pb3 of the drive signal COMb, and the second timing Ca12, which is the center Ca12 of the period Ta12 of the waveform Pa3 of the drive signal COMa, coincide with each other. As a result, in this embodiment, it is possible to suppress changes in the ink ejection characteristics of the ejection section D.

[0065] Although it is preferable that the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3, coincide with each other, the first timing does not have to coincide with the second timing. For example, as long as the center of one of the period Ta12 of the waveform Pa3 and the period Tb12 of the waveform Pb3 in the unit period TP is located within the other of the periods Ta12 and Tb12, the first timing does not have to coincide with the second timing. Even in this case, changes in the ink ejection characteristics of the ejection section D can be suppressed.

[0066] 6, in the unit period TP, the center of one of the period Ta10 of the waveform Pa1 of the drive signal COMa and the period Tb10 of the waveform Pb1 of the drive signal COMb is located within the other period. For example, in the unit period TP, the center Ca10 of the period Ta10 of the waveform Pa1 of the drive signal COMa is located within the period Tb10 of the waveform Pb1 of the drive signal COMb. Note that in the example shown in FIG. 6, in the unit period TP, the center Cb10 of the period Tb10 of the waveform Pb1 is located outside the period Ta10 of the waveform Pa1, but the center Cb10 may be located within the period Ta10 of the waveform Pa1.

[0067] Next, the operation of this embodiment will be described with reference to FIG. 7 when compared with a comparative example in which the center Ca12 of the period Ta12 of the waveform Pa3 is located outside the period Tb12 of the waveform Pb3.

[0068] Fig. 7 is an explanatory diagram for explaining the operation when the drive signals COMa and COMb shown in Fig. 6 are supplied to the head unit 3. The left column of Fig. 7 shows this embodiment in which the center Ca12 of the period Ta12 of the waveform Pa3 is located within the period Tb12 of the waveform Pb3. The right column of Fig. 7 shows a comparison example in which the center Ca12 of the period Ta12 of the waveform Pa3 is located outside the period Tb12 of the waveform Pb3, as a form for comparison with this embodiment.

[0069] 7 shows experimental results for the case where the drive signals COMa and COMb of the present embodiment and the comparative example are designed so that the landing positions in the Y direction of the ink ejected from the M ejection units D coincide with each other when all the ink ejected from the M ejection units D are small dots DS or large dots DL during the same unit period TP. As described above, the present embodiment and the comparative example differ in that the center Ca12 of the period Ta12 of the waveform Pa3 is located within or outside the period Tb12 of the waveform Pb3, but the other configurations are the same. Also, in FIG. 7, when ink ejected from the ejection unit D is a large dot DL, the ink ejected from the ejection unit D separates into a main droplet and a satellite droplet smaller than the main droplet. However, the satellite droplets are not shown for clarity.

[0070] Among the M ejection sections D, if one of two adjacent ejection sections D ejects ink for large dots DL and the other of the two adjacent ejection sections D ejects ink for small dots DS during the same unit period TP, the ink landing positions in the Y direction of the large dots DL and the small dots DS will differ. In this embodiment, where the center Ca12 of the period Ta12 of waveform Pa3 is located within the period Tb12 of waveform Pb3, the difference ΔYa in the landing positions of the large dots DL and the small dots DS is smaller than the difference ΔYb in the landing positions of the large dots DL and the small dots DS in the comparative example. That is, in this embodiment, when large dots DL and small dots DS are mixed during the same unit period TP, the deviation between the ink landing positions of the large dots DL and the ink landing positions of the small dots DS can be made smaller than in the comparative example. As a result, this embodiment can prevent a decrease in the quality of the printed image. Furthermore, the small deviation between the ink landing positions of the large dots DL and the ink landing positions of the small dots DS indicates that there is little change in the ink ejection characteristics when dots of the same size are ejected from M ejection sections D in the same unit period TP compared to when M ejection sections D eject dots of different sizes. Therefore, in this embodiment, it is possible to suppress changes in the ink ejection characteristics due to the combination of sizes of dots ejected from M ejection sections D in the same unit period TP.

[0071] Next, referring to Figure 8, we will explain one cause of the deviation between the ink landing positions of large dots DL and small dots DS that occurs when large dots DL and small dots DS are mixed in the ejection from M ejection sections D during the same unit period TP, in the comparison shown in the right column of Figure 7.

[0072] FIG. 8 is an explanatory diagram for explaining one cause of deviation in ink landing position when large dots DL and small dots DS are mixed in the ejection from M ejection sections D in the same unit period TP in the above-mentioned comparative example.

[0073] In the same unit period TP, if all of the ink ejected from the M ejection sections D are small dots DS, then all of the individual drive signals Vin supplied to the M ejection sections D become drive signals COMa. In addition, in the same unit period TP, if all of the ink ejected from the M ejection sections D are large dots DL, then all of the individual drive signals Vin supplied to the M ejection sections D become drive signals COMb. Note that, hereinafter, the drive signals COMa and COMb may be referred to as the drive signal COM without any particular distinction being made.

[0074] Here, an individual drive signal Vin[m] is supplied to each upper electrode Zu[m] of the M discharge units D, while a bias voltage signal VBS that maintains a constant voltage is commonly supplied via wiring Ld to the lower electrodes Zd[1] to Zd[M] of the M discharge units D. At this time, when the potential of the bias voltage signal VBS changes in accordance with an increase or decrease in the current flowing in accordance with a change in the potential of the individual drive signal Vin[m] supplied to the upper electrode Zu[m], the potential of the bias voltage signal VBS changes at the lower electrodes Zd[1] to Zd[M] of all discharge units D.

[0075] For example, if all of the ink ejected from the M ejection sections D during the same unit period TP are small dots DS, and if all of the ink ejected from the M ejection sections D are large dots DL, the potential of the bias voltage signal VBS changes at the timing of the potential change of the drive signal COM. As shown in the bias voltage signal VBS (COMa only) in the second row of FIG. 8, if all of the ink ejected from the M ejection sections D during the same unit period TP are small dots DS, the potential of the bias voltage signal VBS changes in the portions corresponding to waveforms Pa1, Pa3, Pa5, and Pa7, where the potential changes. In particular, the portion corresponding to waveform Pa3, where the amount and width of potential change per unit time are larger than the other portions, shows a large change, including the peak Vpa. In comparison, the potential fluctuation of the bias voltage signal VBS is small in the portions corresponding to waveforms Pa2, Pa4, Pa6, and Pa8, where the potential is maintained, and waveform Pa9, where the potential change is gradual. Similarly, as shown in the bias voltage signal VBS (COMb only) in the fourth row of FIG. 8, when all the ink ejected from the M ejection sections D during the same unit period TP are large dots DL, the potential of the bias voltage signal VBS fluctuates significantly in the portions corresponding to waveforms Pb1 and Pb3, where the potential changes. In particular, the portion corresponding to waveform Pb3, where the amount and width of potential change per unit time are larger than in other portions, including the peak Vpb, fluctuates significantly. In comparison, the potential of the bias voltage signal VBS fluctuates less in the portions corresponding to waveforms Pb2 and Pb4, where the potential is maintained, and waveform Pb5, where the potential change is gradual. In other words, the potential of the bias voltage signal VBS supplied to the lower electrode Zd of the piezoelectric element PZ fluctuates in response to potential changes in the drive signal COM. Therefore, when large dots DL and small dots DS are mixed in the ink ejected from the M ejection sections D during the same unit period TP, the potential of the bias voltage signal VBS is affected by both the potential changes corresponding to drive signals COMa and COMb.As shown in the bias voltage signal VBS (COMa and COMb mixed) in the fifth row of Figure 8, when large dots DL and small dots DS are mixed in the ink ejected from M ejection sections D during the same unit period TP, the potential of the bias voltage signal VBS fluctuates significantly in the portions corresponding to waveforms Pa1, Pa3, Pa5, and Pa7, where the potential of the drive signal COMa changes, and waveforms Pb1 and Pb3, where the potential of the drive signal COMb changes. For example, the potential of the bias voltage signal VBS changes to a potential corresponding to the sum of the potential changes caused by the change in drive signal COMa and the potential changes caused by the change in drive signal COMb. Therefore, when large dots DL and small dots DS are mixed, the potential of the bias voltage signal VBS changes even at timings that would not change if all the ink ejected from M ejection sections D were large dots DL. For example, the portion corresponding to waveform Pb2, which had small potential fluctuations in the bias voltage signal VBS (COMb only), experiences large potential fluctuations, including peak Vpa, in the bias voltage signal VBS (COMa and COMb mixed), due to the influence of waveform Pa3 of drive signal COMa.

[0076] Thus, in comparison, when large dots DL and small dots DS are mixed in the ink ejected from the M ejection units D during the same unit period TP, for example, the potential difference between the drive signal COMb and the bias voltage signal VBS is different from the potential difference between the drive signal COMb and the bias voltage signal VBS when all the ink ejected from the M ejection units D is large dots DL. If the potential difference between the drive signal COMb and the bias voltage signal VBS differs from the value assumed in the design, for example, the ink ejection characteristics of the ejection units D will vary from the expected characteristics. As shown in Figure 8, the portion of the bias voltage signal VBS corresponding to the waveform Pb2 of the drive signal COMb does not change significantly when all the ink ejected from the M ejection units D is large dots DL, but when large dots DL and small dots DS are mixed, it changes due to the influence of the waveform Pa3 of the drive signal COMa. On the other hand, the portion of the bias voltage signal VBS corresponding to the waveform Pa2 of the drive signal COMa shows similar changes when all the ink ejected from the M ejection sections D are small dots DS and when there is a mixture of large dots DL and small dots DS. For this reason, in a comparison example in which the drive signal is designed so that the landing positions when all the ink ejected from the M ejection sections D are large dots DL and the landing positions when all the ink ejected from the M ejection sections D are small dots DS coincide, when there is a mixture of large dots DL and small dots DS, a deviation occurs in the landing positions of the ink between the large dots DL and the small dots DS.

[0077] Next, with reference to FIG. 9, the influence of a change in the potential of the bias voltage signal VBS on the potential difference between the drive signal COMb and the bias voltage signal VBS in the comparative example will be described.

[0078] Figure 9 is an explanatory diagram for explaining, in comparison, the effect of a change in the potential of the bias voltage signal VBS on the potential difference between the drive signal COMb and the bias voltage signal VBS supplied to the upper electrode Zu[m] of the discharge section D[m] that discharges the large dot DL when large dots DL and small dots DS are mixed in the discharge from M discharge sections D in the same unit period TP. The first row of Figure 9 shows the comparative drive signal COMb as the individual drive signal Vin[m] supplied to the upper electrode Zu[m]. The second row of Figure 9 shows the bias voltage signal VBS supplied to the lower electrode Zd[m]. The third row of Figure 9 shows the potential difference COMb-VBS between the drive signal COMb and the bias voltage signal VBS at the discharge section D[m]. Note that to make it easier to understand the explanation of the change in discharge characteristics due to the contraction element of the drive signal COMb between cases where there is a potential change in the bias voltage signal VBS due to the influence of waveform Pa3 of the drive signal COMa and cases where there is not, the potential change in the bias voltage signal VBS due to the influence of waveforms other than waveform Pa3 is not shown in Figure 9.

[0079] 2, the piezoelectric element PZ is displaced in accordance with the potential difference between the drive signal COMb supplied to the upper electrode Zu and the bias voltage signal VBS supplied to the lower electrode Zd. For example, as shown in the comparative example, if the peak of the potential change in the bias voltage signal VBS due to the influence of the potential change in the waveform Pa3 of the drive signal COMa occurs before the start of the waveform Pb3, which is the contraction element of the drive signal COMb, the amount of change corresponding to the contraction element of the potential difference between the drive signal COMb and the bias voltage signal VBS increases compared to when the potential of the bias voltage signal VBS does not change before the start of the waveform Pb3.

[0080] In the example shown in FIG. 9, the potential of the bias voltage signal VBS increases by a potential ΔV from a potential VBS0 before the start of the waveform Pb3. This is because the period Ta12 of the waveform Pa3 precedes the period Tb12 of the waveform Pb3, and the potential of the bias voltage signal VBS increases by a potential ΔV in response to the increase or decrease in current accompanying the potential change of the waveform Pa3. The potential of the bias voltage signal VBS then returns to the original potential VBS0 before the potential of the drive signal COMb reaches a potential VHb1. In this case, the difference between the potential VLb1 and the value obtained by adding the potential ΔV to the potential VBS0 corresponds to the start point of the amount of change corresponding to the contraction element of the potential difference between the drive signal COMb and the bias voltage signal VBS. Furthermore, the difference between the potential VHb1 and the potential VBS0 corresponds to the end point of the amount of change corresponding to the contraction element of the potential difference between the drive signal COMb and the bias voltage signal VBS. Therefore, the value obtained by adding the potential ΔV to the difference between the potentials VHb1 and VLb1 corresponds to the amount of change APb2 that corresponds to the contraction factor of the potential difference between the drive signal COMb and the bias voltage signal VBS.

[0081] In contrast, if the potential of the bias voltage signal VBS does not change due to waveform Pa3 before period Tb12 of waveform Pb3, the difference between potentials VHb1 and VLb1 corresponds to a change amount APb1, which corresponds to the contraction element of the potential difference between drive signal COMb and bias voltage signal VBS. Hereinafter, the changes APb1 and APb2, which correspond to the contraction element of the potential difference between drive signal COMb and bias voltage signal VBS, may be collectively referred to as the change amount APb. For example, if the increasing peak of the potential change of the bias voltage signal VBS occurs before the start of waveform Pb3, which is the contraction element, the change amount APb is larger than when the potential of the bias voltage signal VBS does not change before the start of waveform Pb3. In the example shown in FIG. 9, the change amount APb2 is the sum of the change amount APb1 and a potential ΔV.

[0082] When the change APb, which corresponds to the contraction element of the potential difference between the drive signal COMb and the bias voltage signal VBS, increases, the displacement of the piezoelectric element PZ increases, and the droplet ejection speed increases. That is, when the increasing peak of the potential change of the bias voltage signal VBS occurs before the start of the waveform Pb3, which is the contraction element, the displacement of the piezoelectric element PZ increases, and the ejection speed increases. For example, in the comparative example shown in FIG. 8, the increasing peak of the potential change of the bias voltage signal VBS (mixed COMa and COMb) corresponding to the peak Vpa of the waveform Pa3 occurs before the start of the waveform Pb3, which is the contraction element, and therefore the ink ejection characteristics of the ejection unit D ejecting large dots DL change. In contrast, in this embodiment, by positioning the center Ca12 of the period Ta12 of the waveform Pa3 within the period Tb12 of the waveform Pb3, when large dots DL and small dots DS are mixed in the ejection from the M ejection units D in the same unit period TP, the effect of the potential change of the bias voltage signal VBS on the ink ejection characteristics of the ejection unit D ejecting large dots DL can be reduced. As another comparative example, if the period Tb12 of the waveform Pb3 of the drive signal COMb is positioned before the period Ta12 of the waveform Pa3 of the drive signal COMa, the increasing peak of the bias voltage signal VBS corresponding to the increase or decrease in current accompanying the change in potential of the waveform Pa3 will be present before the start of the waveform Pa3, which is the contraction element, and the ink ejection characteristics of the ejection units D that eject small dots DS will change. In contrast, in this embodiment, by positioning the center Cb12 of the period Tb12 of the waveform Pb3 within the period Ta12 of the waveform Pa3, it is possible to reduce the impact of changes in the potential of the bias voltage signal VBS on the ink ejection characteristics of the ejection units D that eject small dots DS when large dots DL and small dots DS are mixed in the ejection from the M ejection units D in the same unit period TP.

[0083] In this embodiment, as described with reference to FIG. 6 and other figures, the center of one of the periods Ta12 of the waveform Pa3 of the drive signal COMa and the period Tb12 of the waveform Pb3 of the drive signal COMb in the unit period TP is located within the other of the periods Ta12 and Tb12. This allows, for example, the timing of the peak Vpa of the potential change of the bias voltage signal VBS due to the waveform Pa3 to be closer to the timing of the peak Vpb of the potential change of the bias voltage signal VBS due to the waveform Pb3. As a result, in this embodiment, when large dots DL and small dots DS are mixed, the potential of the bias voltage signal VBS can be prevented from changing at a timing that would not change if the ink ejected from the M ejection units D were all large dots DL or all small dots DS. Therefore, in this embodiment, changes in the ink ejection characteristics of the ejection units D can be prevented.

[0084] Furthermore, when focusing on the potential change of the bias voltage signal VBS, the drive signals COMa and COMb may be determined as follows. For example, the drive signals COMa and COMb may be determined so that the timing of the peak Vpb of the potential change of the bias voltage signal VBS due to the waveform Pb3 and the timing of the peak Vpa of the potential change of the bias voltage signal VBS due to the waveform Pa3 coincide with each other. Even in this form, when large dots DL and small dots DS are mixed, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing that would not change if the ink ejected from the M ejection sections D were all large dots DL or all small dots DS.

[0085] The timing of peak Vpb of the potential change of bias voltage signal VBS due to waveform Pb3 corresponds to the timing when the potential fluctuation of lower electrode Zd becomes greatest during period Tb12 of waveform Pb3 in piezoelectric element PZ to which individual drive signal Vin including waveform Pb3 is supplied. Also, the timing of peak Vpa of the potential change of bias voltage signal VBS due to waveform Pa3 corresponds to the timing when the potential fluctuation of lower electrode Zd becomes greatest during period Ta12 of waveform Pa3 in piezoelectric element PZ to which individual drive signal Vin including waveform Pa3 is supplied.

[0086] For example, assume that the individual drive signal Vin[m] supplied to the discharge unit D[m] includes a waveform Pb3, and the individual drive signal Vin[n] supplied to the discharge unit D[n] includes a waveform Pa3. Here, the variable n is a natural number that satisfies "1≦n≦M" and is different from the variable m. In this case, one of the discharge units D[m] and D[n] is an example of a "first discharge unit," and the other of the discharge units D[m] and D[n] is an example of a "second discharge unit." Furthermore, one of the lower electrodes Zd[m] and Zd[n] is an example of a "first bias electrode," and the other of the lower electrodes Zd[m] and Zd[n] is an example of a "second bias electrode." For example, if the discharge unit D[m] corresponds to the "first discharge unit," the lower electrode Zd[m] corresponds to the "first bias electrode." In the above assumption, the timing at which the potential fluctuation of the lower electrode Zd[m] is greatest during the period Tb12 of the waveform Pb3 and the timing at which the potential fluctuation of the lower electrode Zd[n] is greatest during the period Ta12 of the waveform Pa3 may be made to coincide with each other. Even in this case, it is possible to suppress changes in the ink ejection characteristics of the ejection section D.

[0087] Next, with reference to FIG. 10, experimental results obtained when the timing relationship between the drive signals COMa and COMb is changed will be described.

[0088] FIG. 10 is an explanatory diagram showing the results of an experiment in which the timing relationship between the small dot drive signal COMa and the large dot drive signal COMb is changed.

[0089] 10 indicates the ratio of the difference between a first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3 of the drive signal COMb, and a second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3 of the drive signal COMa, to the period Tb12. Hereinafter, the ratio of the difference between the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3, to the period Tb12 will also be referred to as the timing difference between the waveforms Pa3 and Pb3.

[0090] Furthermore, the double circles in Fig. 10 indicate that the relationship between the ink landing positions of the large dots DL and the small dots DS is good when large dots DL and small dots DS are mixed. The single circles in Fig. 10 indicate that the difference in the ink landing positions of the large dots DL and small dots DS is within the acceptable range when large dots DL and small dots DS are mixed. The triangles in Fig. 10 indicate that the difference in the ink landing positions of the large dots DL and small dots DS is outside the acceptable range when large dots DL and small dots DS are mixed.

[0091] As shown in FIG. 10, when the timing difference between waveforms Pa3 and Pb3 is within ±5%, the ink landing positions of large dots DL and small dots DS are in good agreement. For example, when the timing difference between waveforms Pa3 and Pb3 is within ±5%, the ink landing positions of large dots DL and small dots DS coincide with each other. Alternatively, when the timing difference between waveforms Pa3 and Pb3 is within ±5%, the difference in ink landing positions between large dots DL and small dots DS is small. When the timing difference between waveforms Pa3 and Pb3 is within ±15%, the difference in ink landing positions between large dots DL and small dots DS when large dots DL and small dots DS are mixed is within the acceptable range. When the timing difference between waveforms Pa3 and Pb3 is ±20% or more, the difference in ink landing positions between large dots DL and small dots DS when large dots DL and small dots DS are mixed is outside the acceptable range.

[0092] For this reason, in this embodiment, in the unit period TP, the center of one of the period Ta12 of the waveform Pa3 of the drive signal COMa and the period Tb12 of the waveform Pb3 of the drive signal COMb is located within the other of the periods Ta12 and Tb12. Preferably, in the unit period TP, the difference between the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3 of the drive signal COMb, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3 of the drive signal COMa, is within ±15% of the period Tb12. More preferably, in the unit period TP, the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3, coincide with each other.

[0093] As described above, in this embodiment, the inkjet printer 1 includes a plurality of ejection sections D, each including a nozzle N that ejects ink, a cavity CV that communicates with the nozzle N, and a piezoelectric element PZ that ejects ink from the cavity CV through the nozzle N; and a supply circuit 31. The supply circuit 31 generates an individual drive signal Vin for each ejection section D, driving the piezoelectric element PZ included in each of the plurality of ejection sections D, based on a plurality of drive signals COM, including a drive signal COMb having a waveform PB and a drive signal COMa having a waveform PA different from the waveform PB. The waveform PB includes a waveform Pb3, in which the potential of the drive signal COMb changes to contract the volume of the cavity CV. The waveform PA includes a waveform Pa3, in which the potential of the drive signal COMa changes to contract the volume of the cavity CV. Within one cycle of the plurality of drive signals COM, for example, within a unit period TP, the center of one of the period Tb12 of the waveform Pb3 of the drive signal COMb and the period Ta12 of the waveform Pa3 of the drive signal COMa is located within the center of the other period.

[0094] Thus, in this embodiment, the center of one of the period Tb12 of the waveform Pb3 and the period Ta12 of the waveform Pa3 of the drive signal COMa in the unit period TP is located within the other period. As a result, in this embodiment, even when the potential of the bias voltage signal VBS supplied to the piezoelectric element PZ varies depending on the waveforms Pa3 and Pb3, the influence of the potential change of the bias voltage signal VBS on the ink ejection characteristics of the ejection section D can be reduced. For example, in this embodiment, the timing of the peak Vpa of the potential change of the bias voltage signal VBS due to the waveform Pa3 and the timing of the peak Vpb of the potential change of the bias voltage signal VBS due to the waveform Pb3 can be made closer to each other. As a result, in this embodiment, when an individual drive signal Vin including the waveform PB and an individual drive signal Vin including the waveform PA are mixed, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing that would not normally change. For example, when all the individual drive signals Vin include only the waveform PA, or when all the individual drive signals Vin include only the waveform PB, the timing at which the potential of the bias voltage signal VBS does not change corresponds to the timing at which the potential of the bias voltage signal VBS should not change. In this way, in this embodiment, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing at which it should not change, and therefore it is possible to prevent changes in the ink ejection characteristics of the ejection section D. As a result, in this embodiment, it is possible to prevent the ink landing position from shifting from a predetermined position, and therefore it is possible to prevent a deterioration in the quality of the printed image.

[0095] In this embodiment, the inkjet printer 1 includes a lower electrode Zd[m] provided in each of the ejection sections D[m] and supplied with a bias voltage signal VBS, and a lower electrode Zd[n] provided in each of the ejection sections D[n] and supplied with a bias voltage signal VBS. The inkjet printer 1 also includes wiring Ld that supplies the bias voltage signal VBS to the lower electrode Zd[m] and the lower electrode Zd[n]. When the individual drive signal Vin[m] supplied to the ejection section D[m] includes the waveform Pb3 and the individual drive signal Vin[n] supplied to the ejection section D[n] includes the waveform Pa3, the timing at which the potential fluctuation of the lower electrode Zd[m] is greatest during the period Tb12 of the waveform Pb3 coincides with the timing at which the potential fluctuation of the lower electrode Zd[n] is greatest during the period Ta12 of the waveform Pa3 within the unit period TP.

[0096] In this case as well, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing when it would not normally change, and therefore it is possible to prevent the ink ejection characteristics of the ejection section D from changing.

[0097] Furthermore, in this embodiment, in the unit period TP, the difference between the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3 of the drive signal COMb, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3 of the drive signal COMa, may be within ±15% of the period Tb12 of the waveform Pb3. Even in this case, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing when it would not normally change, and therefore it is possible to prevent changes in the ink ejection characteristics of the ejection section D.

[0098] Furthermore, in this embodiment, the first timing, which is the center Cb12 of the period Tb12 of the waveform Pb3, and the second timing, which is the center Ca12 of the period Ta12 of the waveform Pa3, may coincide with each other. In this case, it is possible to further prevent the potential of the bias voltage signal VBS from changing at a timing at which it would not normally change. Therefore, even when the first timing and the second timing coincide with each other, it is possible to further prevent the ink ejection characteristics of the ejection section D from changing.

[0099] Up to this point, we have explained how to set the timing of the waveform Pa3 of the drive signal COMa and the waveform Pb3 of the drive signal COMb. Similarly, it is possible to set the timing of the waveforms Pa1, Pa3, Pa5, and Pa7 of the drive signal COMa, which cause a potential change in the bias voltage signal VBS, and the waveforms Pb1 and Pb3 of the drive signal COMb. In this embodiment, the waveform PB further includes a waveform Pb1 in which the potential of the drive signal COMb changes to expand the volume of the cavity CV, and the waveform PA further includes a waveform Pa1 in which the potential of the drive signal COMa changes to expand the volume of the cavity CV. The waveform Pb3 is a waveform that appears after the period Tb10 of the waveform Pb1. The volume of the cavity CV that expands due to the potential change of the waveform Pb1 contracts due to the potential change of the waveform Pb3. The waveform Pa3 is a waveform that appears after the period Ta10 of the waveform Pa1. The volume of the cavity CV that expands due to the potential change of the waveform Pa1 contracts due to the potential change of the waveform Pa3. In the unit period TP, the center of one of the period Tb10 of the waveform Pb1 of the drive signal COMb and the period Ta10 of the waveform Pa1 of the drive signal COMa is located within the other period. Even in this case, the potential of the bias voltage signal VBS can be prevented from changing at a timing when it would not normally change, thereby preventing changes in the ink ejection characteristics of the ejection section D. In particular, by setting waveforms Pa1 and Pb1, and waveforms Pa3 and Pb3, whose potentials change before ink is ejected from nozzle N, to prevent the potential of bias voltage signal VBS from changing at a timing when it would not normally change, it is possible to further prevent the ink ejection characteristics of ejection section D from changing.

[0100] Furthermore, in this embodiment, when the piezoelectric element PZ is driven by a potential change of the waveform Pb3, it contracts the volume of the cavity CV to eject a first amount of ink from the nozzle N. The first amount is, for example, an amount of ink corresponding to a large dot DL. When the piezoelectric element PZ is driven by a potential change of the waveform Pa3, it contracts the volume of the cavity CV to eject a second amount of ink from the nozzle N. The second amount is, for example, an amount of ink corresponding to a small dot DS. In this case, even if large dots DL and small dots DS are mixed, for example, the potential of the bias voltage signal VBS can be prevented from changing at a timing that would not change if the ink ejected from the multiple ejection units D were all large dots DL or all small dots DS. Therefore, even in this case, it is possible to prevent the potential of the bias voltage signal VBS from changing at a timing that would not normally change, thereby preventing changes in the ink ejection characteristics of the ejection units D.

[0101] [2. Modifications] Each of the above embodiments can be modified in various ways. Specific modified embodiments are exemplified below. Two or more embodiments arbitrarily selected from the following examples can be combined as appropriate within a range that does not contradict each other. In the modified examples exemplified below, elements whose actions and functions are equivalent to those of the embodiments will be designated by the same reference numerals as in the above description, and detailed descriptions of each will be omitted as appropriate.

[0102] [First Modification] In the above-described embodiment, the multiple drive signals COM include the drive signals COMa and COMb, but the present invention is not limited to this. For example, the multiple drive signals COM may include the drive signal COMc shown in FIG. 11 in addition to the drive signals COMa and COMb.

[0103] Fig. 11 is a timing chart for explaining an example of the drive signal COM in Modification 1. Elements similar to those explained in Figs. 1 to 10 are given the same reference numerals, and detailed explanations will be omitted.

[0104] 11, the multiple drive signals COM include the drive signals COMa and COMb, and the drive signal COMc, which have been described with reference to Fig. 6 etc. The drive signal COMc is an example of a "third drive signal."

[0105] The drive signal COMc has a waveform PC. For example, the drive signal COMc has a pulse of the waveform PC provided in the unit period TP. The waveform PC is a waveform in which the potential of the drive signal COMc changes from a reference potential V0, passes through a potential VLc1 that is lower than the reference potential V0, and returns to the reference potential V0. The waveform PC is an example of a "third waveform."

[0106] Hereinafter, the portion of the waveform PC where the potential of the drive signal COMc changes from the reference potential V0 to the potential VLc1 will be referred to as the waveform Pc1, and the portion where the potential of the drive signal COMc is maintained at the potential VLc1 will be referred to as the waveform Pc2. Also, the portion of the waveform PC where the potential of the drive signal COMc changes from the potential VLc1 to the reference potential V0 will be referred to as the waveform Pc3. That is, the waveform PC includes the waveforms Pc1, Pc2, and Pc3.

[0107] The waveform Pc1 is a waveform for displacing the piezoelectric element PZ in the +Z direction. That is, the waveform Pc1 is a waveform in which the potential of the drive signal COMc changes so as to expand the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PC, the waveform Pc1 corresponds to the expansion element that changes the potential of the drive signal COMc in order to drive the piezoelectric element PZ so as to expand the volume of the cavity CV.

[0108] The waveform Pc3 is a waveform for displacing the piezoelectric element PZ in the -Z direction. In other words, the waveform Pc3 is a waveform in which the potential of the drive signal COMc changes to contract the volume of the cavity CV. Therefore, among the multiple elements that make up the pulse of the waveform PC, the waveform Pc3 corresponds to a contraction element that changes the potential of the drive signal COMc in order to drive the piezoelectric element PZ to contract the volume of the cavity CV. In this modified example, when the piezoelectric element PZ is driven by the potential change of the waveform Pc3, it contracts the volume of the cavity CV and agitates the ink in the nozzle N without ejecting ink from the nozzle N. The waveform Pc3 is an example of a "third contraction waveform."

[0109] The waveform Pc2 is a waveform for maintaining the position of the piezoelectric element PZ in the Z direction. For example, among the multiple elements that make up the pulse of the waveform PC, the waveform Pc2 corresponds to an expansion maintaining element that maintains the potential of the drive signal COMc in order to drive the piezoelectric element PZ so as to maintain the volume of the cavity CV that has expanded due to the waveform Pc1.

[0110] The waveform PC is determined so that when an individual drive signal Vin[m] having the waveform PC is supplied to a discharge section D[m], the liquid in the nozzle N is agitated without causing the nozzle N to discharge ink.

[0111] In the unit period TP, the center Cc12 of the period Tc12 of the waveform Pc3 of the drive signal COMc is located within at least one of the period Ta12 of the waveform Pa3 of the drive signal COMa and the period Tb12 of the waveform Pb3 of the drive signal COMb. This reduces the effect that the potential change of the bias voltage signal VBS due to the waveform Pc3 has on the ink ejection characteristics when the ejection section D ejects ink in response to the drive signal COMa or COMb.

[0112] As in the example shown in FIG. 11, the center Cc12 may be located within both the periods Ta12 and Tb12.

[0113] In this modification, the first timing Cb12, which is the center Cb12 of the period Tb12 of the waveform Pb3, the second timing Ca12, which is the center Ca12 of the period Ta12 of the waveform Pa3, and the third timing Cc12, which is the center Cc12 of the period Tc12 of the waveform Pc3 may coincide with each other. Even in this case, it is possible to suppress changes in the ink ejection characteristics of the ejection section D.

[0114] 11, the center Cc10 of the period Tc10 of the waveform Pc1 of the drive signal COMc is located within the period Tb10 of the waveform Pb1 of the drive signal COMb in the unit period TP. Even in this case, if all of the ink ejected from the M ejection units D in the same unit period TP are large dots DL, and if dots including large dots DL are ejected from some of the M ejection units D while ink is not ejected from the remaining units at a timing when the potential of the bias voltage signal VBS does not normally change, the bias voltage signal VBS can be prevented from changing before the waveform Pb1 of the drive signal COMb, thereby preventing changes in the ink ejection characteristics of the ink ejection units D. In the example shown in FIG. 11, the center Cc10 is located within the period Tb10 of the waveform Pb1 of the drive signal COMb, but before the period Ta10 of the waveform Pa1 of the drive signal COMa. However, the center Cc10 may be located within both the periods Ta10 and Tb10.

[0115] In this modified example, one of the drive signals COMa and COMb may be omitted. In this case, the drive signal COMc is another example of a "second drive signal." For example, the multiple drive signals COM may include drive signals COMb and COMc, or may include drive signals COMa and COMc. When drive signal COMa is omitted and the multiple drive signals COM include drive signals COMb and COMc, drive signal COMb corresponds to the "first drive signal" and drive signal COMc corresponds to the "second drive signal." Furthermore, when drive signal COMb is omitted and the multiple drive signals COM include drive signals COMa and COMc, drive signal COMa corresponds to the "first drive signal" and drive signal COMc corresponds to the "second drive signal."

[0116] As described above, this modification also achieves the same effects as the above-described embodiment. Furthermore, in this modification, the multiple drive signals COM further include a drive signal COMc having a waveform PC different from the waveforms PA and PB. The waveform PC includes a waveform Pc3 in which the potential of the drive signal COMc changes to contract the volume of the cavity CV. In the unit period TP, the center Cc12 of the period Tc12 of the waveform Pc3 of the drive signal COMc is located within at least one of the period Ta12 of the waveform Pa3 of the drive signal COMa and the period Tb12 of the waveform Pb3 of the drive signal COMb. When driven by the potential change of the waveform Pc3, the piezoelectric element PZ contracts the volume of the cavity CV and agitates the ink in the nozzle N without ejecting ink from the nozzle N. In this modification, supplying the drive signal COMc to the ejection section D prevents ink from thickening.

[0117] Furthermore, in this modified example, one of the drive signals COMa and COMb may be omitted. For example, in the above-described embodiment, the multiple drive signals COM may have a drive signal COMc instead of the drive signal COMa. In this case, when the piezoelectric element PZ is driven by a potential change of the waveform Pb3, it contracts the volume of the cavity CV and ejects ink from the nozzle N. Furthermore, when the piezoelectric element PZ is driven by a potential change of the waveform Pc3, it contracts the volume of the cavity CV and agitates the ink in the nozzle N without ejecting ink from the nozzle N. Even when the multiple drive signals COM have a drive signal COMc instead of the drive signal COMa, the same effects as in the above-described embodiment can be obtained.

[0118] [Second Modification] In the above-described embodiment, the first timing Cb12, which is the center Cb12 of the period Tb12 of the waveform Pb3, and the second timing Ca12, which is the center Ca12 of the period Ta12 of the waveform Pa3, are coincident with each other, but the present invention is not limited to this. For example, in the unit period TP, the timing at which the current flowing through the line Li in response to a potential change in the waveform Pb3 is maximized may be coincident with the timing at which the current flowing through the line Li in response to a potential change in the waveform Pa3 is maximized.

[0119] 12 is an explanatory diagram for explaining the timing relationship between the drive signals COMa and COMb in the second modified example. Elements similar to those explained in FIGS. 1 to 11 are given the same reference numerals, and detailed explanations will be omitted.

[0120] In this modified example, it is assumed that the individual drive signal Vin[m] supplied to the discharge unit D[m] includes a waveform Pb3, and the individual drive signal Vin[n] supplied to the discharge unit D[n] includes a waveform Pa3. In this case, one of the discharge units D[m] and D[n] is an example of a "first discharge unit," and the other of the discharge units D[m] and D[n] is an example of a "second discharge unit." Furthermore, one of the wirings Li[m] and Li[n] is an example of a "first wiring," and the other of the wirings Li[m] and Li[n] is an example of a "second wiring." For example, if the discharge unit D[m] corresponds to the "first discharge unit," the wiring Li[m] corresponds to the "first wiring."

[0121] A current ILD[m] flows through the wiring Li[m] that supplies the individual drive signal Vin[m] to the discharge section D[m] in response to potential changes in the individual drive signal Vin[m]. For example, the waveform of the current ILD[m] that flows through the wiring Li[m] in response to potential changes in the waveform Pb3 has a peak ILDp[m]. Furthermore, a current ILD[n] flows through the wiring Li[n] that supplies the individual drive signal Vin[n] to the discharge section D[n] in response to potential changes in the individual drive signal Vin[n]. For example, the waveform of the current ILD[m] that flows through the wiring Li[n] in response to potential changes in the waveform Pa3 has a peak ILDp[n].

[0122] In this modification, the drive signals COMa and COMb are determined so that the timing of the peak ILDp[m] of the current ILD[m] and the timing of the peak ILDp[n] of the current ILD[n] coincide with each other during the unit period TP. That is, in this modification, the timing at which the current ILD[m] flowing through the wiring Li[m] reaches its maximum in response to a change in the potential of the waveform Pb3 coincides with the timing at which the current ILD[n] flowing through the wiring Li[n] reaches its maximum in response to a change in the potential of the waveform Pa3. In this case, the peaks of the potential changes in the bias voltage signal VBS due to the current ILD[m] and the peaks of the potential changes in the bias voltage signal VBS due to the current ILD[n] coincide with or approach each other. Therefore, in this modification, the potential of the bias voltage signal VBS can be prevented from changing at a timing at which it would not normally change, thereby preventing changes in the ink ejection characteristics of the ejection section D.

[0123] As described above, this modification also achieves the same effects as the above-described embodiment. For example, in this modification, the inkjet printer 1 includes a wiring Li[m] that supplies an individual drive signal Vin[m] to a discharge section D[m] among the multiple discharge sections D, and a wiring Li[n] that supplies an individual drive signal Vin[n] to a discharge section D[n] among the multiple discharge sections D. If the individual drive signal Vin[m] supplied to the discharge section D[m] includes waveform Pb3 and the individual drive signal Vin[n] supplied to the discharge section D[n] includes waveform Pa3, the timing at which the current ILD[m] flowing through the wiring Li[m] reaches its maximum in response to a change in the potential of waveform Pb3 coincides with the timing at which the current ILD[n] flowing through the wiring Li[n] reaches its maximum in response to a change in the potential of waveform Pa3. Therefore, this modification also prevents the potential of the bias voltage signal VBS from changing at a timing at which it would not normally change. As a result, this modification also prevents changes in the ink ejection characteristics of the discharge section D.

[0124] [Third Modification] In the above-described embodiment and modified example, the piezoelectric element PZ is displaced in the -Z direction when the potential of the individual drive signal Vin[m] changes from a low potential to a high potential, but the present invention is not limited to such an embodiment. For example, a piezoelectric element PZ that is displaced in the -Z direction when the potential of the individual drive signal Vin[m] changes from a high potential to a low potential may be used. In this case, for example, the potential of the drive signal COM changes from a low potential to a high potential in a portion corresponding to an expansion element, and changes from a high potential to a low potential in a portion corresponding to a contraction element. In this modified example, the same effects as those of the above-described embodiment and modified example can be obtained.

[0125] [Fourth Modification] In the above-described embodiment and modified example, each head unit 3 has one nozzle row NL, but the present invention is not limited to this. For example, each head unit 3 may have multiple nozzle rows NL. In this modified example, the same effects as those of the above-described embodiment and modified example can be obtained.

[0126] [Fifth Modification] In the above-described embodiment and modified example, the inkjet printer 1 has four head units 3, but the present invention is not limited to this. For example, the inkjet printer 1 may have one to three head units 3, or five or more head units 3.

[0127] [Sixth Modification] In the above-described embodiment and modified example, the inkjet printer 1 is a serial printer, but the present invention is not limited to this. For example, the inkjet printer 1 may be a so-called line printer in which the head unit 3 has multiple nozzles N that extend wider than the width of the recording paper P. This modified example also provides the same effects as the above-described embodiment and modified example. [Explanation of symbols]

[0128] 1...inkjet printer, 2...control unit, 3...head unit, 4...drive signal generation unit, 7...transport unit, 8...maintenance unit, 31...supply circuit, 32...recording head, D...ejection section, N...nozzle

Claims

1. a plurality of ejection units each including a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and a drive element that ejects the liquid in the pressure chamber from the nozzle; a drive unit that generates, for each of the plurality of ejection units, an individual drive signal that drives the drive element included in each of the plurality of ejection units, based on a plurality of drive signals including a first drive signal having a first waveform and a second drive signal having a second waveform different from the first waveform; Equipped with The first waveform is a first contraction waveform in which the potential of the first drive signal changes so as to contract the volume of the pressure chamber; Including, The second waveform is a second contraction waveform in which the potential of the second drive signal changes so as to contract the volume of the pressure chamber; Including, In one cycle of the plurality of drive signals, the center of one of the first contraction waveform period of the first drive signal and the second contraction waveform period of the second drive signal is located within the other period. A liquid ejection device characterized by:

2. a first wiring that supplies the individual drive signal to a first ejection unit among the plurality of ejection units; a second wiring that supplies the individual drive signal to a second ejection unit among the plurality of ejection units; and when the individual drive signal supplied to the first discharge section includes the first contraction waveform and the individual drive signal supplied to the second discharge section includes the second contraction waveform, in one cycle, a timing at which the current flowing through the first wiring in response to a potential change of the first contraction waveform becomes maximum and a timing at which the current flowing through the second wiring in response to a potential change of the second contraction waveform becomes maximum coincide with each other. The liquid ejection device according to claim 1 .

3. a first bias electrode provided in a first ejection unit among the plurality of ejection units, to which a bias voltage signal is supplied; a second bias electrode provided in a second ejection section among the plurality of ejection sections, to which the bias voltage signal is supplied; Wiring for supplying the bias voltage signal to the first bias electrode and the second bias electrode; and when the individual drive signal supplied to the first ejection unit includes the first contraction waveform and the individual drive signal supplied to the second ejection unit includes the second contraction waveform, in one cycle, the timing at which the potential fluctuation of the first bias electrode becomes maximum during the period of the first contraction waveform and the timing at which the potential fluctuation of the second bias electrode becomes maximum during the period of the second contraction waveform coincide with each other. The liquid ejection device according to claim 1 .

4. In one cycle, a difference between a first timing that is the center of a period of the first contraction waveform of the first drive signal and a second timing that is the center of a period of the second contraction waveform of the second drive signal is within ±15% of the period of the first contraction waveform. The liquid ejection device according to claim 1 .

5. In one cycle, the first timing and the second timing coincide with each other.

5. The liquid ejection device according to claim 4.

6. The first waveform is a first expansion waveform in which the potential of the first drive signal changes so as to expand the volume of the pressure chamber; Further including, The second waveform is a second expansion waveform in which the potential of the second drive signal changes so as to expand the volume of the pressure chamber; Further including, the first contraction waveform is a waveform that occurs after a period of the first expansion waveform, The volume of the pressure chamber expanded by the potential change of the first expansion waveform is contracted by the potential change of the first contraction waveform, the second contraction waveform is a waveform that occurs after a period of the second expansion waveform, the volume of the pressure chamber expanded by the potential change of the second expansion waveform is contracted by the potential change of the second contraction waveform, In one cycle, the center of one of the period of the first expansion waveform of the first drive signal and the period of the second expansion waveform of the second drive signal is located within the other period.

6. The liquid ejection device according to claim 1, wherein the ejection head is a nozzle.

7. The driving element is When driven by a potential change of the first contraction waveform, the volume of the pressure chamber is contracted to eject a first amount of liquid from the nozzle; When driven by the potential change of the second contraction waveform, the volume of the pressure chamber is contracted to eject a second amount of liquid from the nozzle.

7. The liquid ejection device according to claim 1, wherein the ejection head is a nozzle.

8. The plurality of drive signals are a third drive signal having a third waveform different from the first waveform and the second waveform; The third waveform is a third contraction waveform in which the potential of the third drive signal changes so as to contract the volume of the pressure chamber; Including, In one cycle, the center of the period of the third contraction waveform of the third drive signal is located within at least one of the period of the first contraction waveform of the first drive signal and the period of the second contraction waveform of the second drive signal, The driving element is When driven by a potential change of the third contraction waveform, the volume of the pressure chamber is contracted to agitate the liquid in the nozzle without ejecting the liquid from the nozzle.

8. The liquid ejection device according to claim 7.

9. A method for controlling a liquid ejection device having a plurality of ejection units including nozzles that eject liquid, pressure chambers that communicate with the nozzles, and drive elements that eject the liquid in the pressure chambers from the nozzles, the method comprising: generating, for each ejection section, an individual drive signal that drives the drive element included in each of the plurality of ejection sections, based on a plurality of drive signals including a first drive signal having a first waveform and a second drive signal having a second waveform different from the first waveform; The first waveform is a first contraction waveform in which the potential of the first drive signal changes so as to contract the volume of the pressure chamber; Including, The second waveform is a second contraction waveform in which the potential of the second drive signal changes so as to contract the volume of the pressure chamber; Including, In one cycle of the plurality of drive signals, the center of one of the first contraction waveform period of the first drive signal and the second contraction waveform period of the second drive signal is located within the other period. A method for controlling a liquid ejection device.

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