Liquid dispensing device and control method for liquid dispensing head

Abstract

To suppress mist from being generated.SOLUTION: A driving signal for a driving element includes a first driving waveform including a first contraction waveform whose potential changes from a first potential to a second potential so that volumes of a pressure chamber are contracted, and a second driving waveform including a second contraction waveform whose potential changes from the first potential to the second potential so that the volumes of the pressure chamber are contracted. The first contraction waveform includes a first partial waveform whose potential changes from the first potential to a first intermediate potential, a second partial waveform whose potential is kept at the first intermediate potential and a third partial waveform whose potential changes from the first intermediate potential to the second potential. The second contraction waveform includes a fourth partial waveform whose potential changes from the first potential to a second intermediate potential, a fifth partial waveform whose potential is kept at the second intermediate potential and a sixth partial waveform whose potential changes from the second intermediate potential to the second potential. The driving element makes a nozzle discharge first liquid droplets in accordance with the first driving waveform, and makes the nozzle discharge second liquid droplets in accordance with the second driving waveform, so that the second liquid droplets unite with the first liquid droplets before the first liquid droplets impact in a medium.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a liquid ejection apparatus and a control method for a liquid ejection head.

Background Art

[0002] There is known a liquid ejection apparatus that prints an image by ejecting a liquid such as ink from a plurality of nozzles using a piezoelectric element. In this type of liquid ejection apparatus, for example, the piezoelectric element contracts a pressure chamber communicating with the nozzle in response to a drive signal including a pulse that causes ink to be ejected from the nozzle, thereby ejecting ink in the pressure chamber from the nozzle. Further, as a control method for a liquid ejection apparatus, a method is known in which a plurality of pulses are supplied to a piezoelectric element, and a plurality of droplets ejected from each nozzle are combined before they land on a print medium. For example, Patent Document 1 discloses a printing apparatus including: an ejection head that ejects droplets from a nozzle to a predetermined position on a print medium; and a control unit that outputs, to the ejection head, a drive waveform capable of combining a plurality of droplets at a distance equal to or less than 1 / 2 of the distance from the nozzle to the print medium.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] Incidentally, compared with low-viscosity ink, high-viscosity ink has a longer tail trailing the ink ejected from the nozzle, which makes mist more likely to occur. Mist is fine mist-like ink droplets. When mist occurs, the quality of a printed image is lower than that when no mist occurs. Therefore, it is desired to suppress the occurrence of mist in liquid ejection apparatuses.

Means for Solving the Problem

[0005] To solve the above problems, the liquid dispensing device according to the present invention comprises a liquid dispensing head having a nozzle for dispensing droplets, a pressure chamber communicating with the nozzle, and a dispensing section including a drive element that imparts pressure fluctuations to the liquid in the pressure chamber in response to a drive signal, and a control unit that controls the supply of the drive signal to the drive element, wherein the drive signal includes a first drive waveform and a second drive waveform that occurs after the first drive waveform, the first drive waveform includes a first expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, and a first contraction waveform in which the potential of the drive signal changes from a first potential to a second potential so as to contract the volume of the pressure chamber, the second drive waveform includes a second expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, and a second contraction waveform in which the potential of the drive signal changes from a first potential to a second potential so as to contract the volume of the pressure chamber The first contraction waveform includes a first partial waveform in which the potential of the drive signal changes from a first potential to a first intermediate potential between the first potential and the second potential, a second partial waveform in which the potential of the drive signal is maintained at the first intermediate potential, and a third partial waveform in which the potential of the drive signal changes from the first intermediate potential to the second potential; the second contraction waveform includes a fourth partial waveform in which the potential of the drive signal changes from a first potential to a second intermediate potential between the first potential and the second potential, a fifth partial waveform in which the potential of the drive signal is maintained at the second intermediate potential, and a sixth partial waveform in which the potential of the drive signal changes from the second intermediate potential to the second potential; the drive element, upon being supplied with the drive signal, discharges a first droplet from the nozzle in accordance with the first drive waveform, and discharges a second droplet from the nozzle in accordance with the second drive waveform, such that the second droplet merges with the first droplet before it hits the medium.

[0006] Furthermore, the liquid discharge head control method according to the present invention is a control method for a liquid discharge head having a discharge unit including a nozzle for discharging droplets, a pressure chamber communicating with the nozzle, and a drive element that causes pressure fluctuations in the liquid in the pressure chamber in response to a drive signal, wherein the drive signal includes a first drive waveform and a second drive waveform that occurs after the first drive waveform, the first drive waveform includes a first expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, and a first contraction waveform in which the potential of the drive signal changes from a first potential to a second potential so as to contract the volume of the pressure chamber, the second drive waveform includes a second expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, and a second contraction waveform in which the potential of the drive signal changes from a first potential to a second potential so as to contract the volume of the pressure chamber, the first contraction waveform is in which the potential of the drive signal changes to a first potential The second contraction waveform includes a first partial waveform that changes from a potential to a first intermediate potential between the first potential and the second potential, a second partial waveform in which the potential of the drive signal is maintained at the first intermediate potential, and a third partial waveform in which the potential of the drive signal changes from the first intermediate potential to the second potential, wherein the second contraction waveform includes a fourth partial waveform in which the potential of the drive signal changes from the first potential to a second intermediate potential between the first potential and the second potential, a fifth partial waveform in which the potential of the drive signal is maintained at the second intermediate potential, and a sixth partial waveform in which the potential of the drive signal changes from the second intermediate potential to the second potential, and controls the supply of the drive signal to the drive element, wherein the drive element, upon being supplied with the drive signal, discharges a first droplet from the nozzle in accordance with the first drive waveform, and discharges a second droplet from the nozzle in accordance with the second drive waveform, such that the second droplet merges with the first droplet before it hits the medium. [Brief explanation of the drawing]

[0007] [Figure 1] This block diagram shows an example of the configuration of an inkjet printer according to an embodiment of the present invention. [Figure 2] This is a perspective view showing an example of the general internal structure of an inkjet printer. [Figure 3] This is a cross-sectional view illustrating an example of the structure of the discharge section. [Figure 4] This is a plan view showing an example of nozzle arrangement in a head unit. [Figure 5] This is a block diagram showing an example of a head unit configuration. [Figure 6] This is a timing chart illustrating an example of a signal supplied to the head unit. [Figure 7] Figure 6 is an explanatory diagram illustrating the operation when the drive signal shown is supplied to the head unit. [Figure 8] This is an explanatory diagram showing the experimental results of measuring the length of satellite droplets. [Figure 9] This is a timing chart illustrating an example of a drive signal in the first modified example. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part have been appropriately changed from those of the actual parts. Furthermore, the embodiments described below are preferred specific examples of the present invention and are subject to various technically preferred limitations, but the scope of the present invention is not limited to these embodiments unless otherwise stated in the following description.

[0009] [1. Embodiments] In this embodiment, an inkjet printer that ejects ink onto recording paper to form an image will be used as an example to explain the liquid ejection device. In this embodiment, ink is an example of a "liquid," and recording paper is an example of a "medium."

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

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

[0012] The inkjet printer 1 includes a control unit 2 that controls various parts of the inkjet printer 1, a head unit 3 equipped with an ink ejection unit D for ejecting ink, and a drive signal generation unit 4 that generates a drive signal COM for driving the ejection unit D. Furthermore, the inkjet printer 1 includes a transport unit 7 for changing the relative position of the recording paper P with respect to the head unit 3, and a maintenance unit 8 that performs maintenance processing for maintaining the ejection unit D provided on the head unit 3.

[0013] In this embodiment, we assume that the head unit 3 and the drive signal generation unit 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 with 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 to one head unit 3. In this embodiment, we assume that the inkjet printer 1 has four head units 3 and four drive signal generation units 4 that correspond one-to-one with the four head units 3. However, for the sake of explanation, in the following, as illustrated in Figure 1, we may focus on one head unit 3 out of the four head units 3 and one drive signal generation unit 4 provided in correspondence with one head unit 3 out of the four drive signal generation units 4. Note that the head unit 3 is an example of a "liquid ejection head".

[0014] The control unit 2 is configured to include one or more CPUs (Central Processing Units). Note that the control unit 2 may be configured to include a programmable logic device such as an FPGA (field-programmable gate array) instead of or in addition to the CPU. Further, the control unit 2 is configured to include one or both of volatile memory such as RAM (Random Access Memory) and non-volatile memory such as ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), or PROM (Programmable ROM).

[0015] Although details will be described later, the control unit 2 generates signals for controlling the operation of each part of the inkjet printer 1, such as a print signal SI and a waveform designation signal dCOM. Here, the waveform designation signal dCOM is a digital signal that defines the waveform of the drive signal COM. Further, the drive signal COM is an analog signal for driving the ejection unit D. Further, the print signal SI is a digital signal for designating the type of operation of the ejection unit D. Specifically, the print signal SI is a signal that designates the type of operation of the ejection unit D by designating whether or not the drive signal COM is to be supplied to the ejection unit D. Note that the control unit 2 is an example of a "control section".

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

[0017] The head unit 3 includes a supply circuit 31 and a recording head 32.

[0018] The recording head 32 has M ejection sections D. The value M is a natural number of 1 or greater. Hereinafter, among the M ejection sections D provided in the recording head 32, the m-th ejection section D may be referred to as ejection section D[m]. Here, the variable m is a natural number satisfying "1≦m≦M". Further, hereinafter, when a component, signal or the like of the inkjet printer 1 corresponds to the ejection section D[m] among the M ejection sections D, a subscript [m] may be added to the reference numeral representing the component, signal or the like.

[0019] The supply circuit 31 switches whether to supply the drive signal COM to the ejection section D[m] based on the print signal SI. Hereinafter, as shown in FIG. 5 and the like which will be described later, the drive signal COM supplied to the ejection section D[m] may be referred to as an individual drive signal Vin[m].

[0020] As described above, in the present embodiment, the inkjet printer 1 executes a printing process. When the printing process is executed, the control unit 2 generates signals for controlling the head unit 3, such as the print signal SI, based on print data IMG. Further, when the printing process is executed, the control unit 2 generates signals for controlling the drive signal generation unit 4, such as a waveform designation signal dCOM. Furthermore, when the printing process is executed, the control unit 2 generates signals for controlling the conveyance unit 7. Accordingly, in the printing process, the control unit 2 controls the conveyance unit 7 to change the relative position of the recording paper P with respect to the head unit 3, and adjusts the presence / absence of ink ejection from the ejection section D[m], the ink ejection amount, the ink ejection timing and the like. In this way, the control unit 2 controls each part of the inkjet printer 1 such that an image corresponding to the print data IMG is formed on the recording paper P.

[0021] Furthermore, as described above, in this embodiment, the inkjet printer 1 performs maintenance processing. For example, the maintenance processing includes a flushing process to discharge ink from the ejection unit D, a wiping process to wipe off foreign matter such as ink adhering to the vicinity of the nozzle N of the ejection unit D with a wiper, and a pumping process to suck out the ink inside the ejection unit D with a tube pump or the like. The nozzle N will be described later in Figure 3.

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

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

[0024] As shown in Figure 2, in this embodiment, it is assumed that the inkjet printer 1 is a serial printer. Specifically, when the inkjet printer 1 performs a printing process, it transports the recording paper P in the sub-scanning direction, and while reciprocating the head unit 3 in the main scanning direction intersecting the sub-scanning direction, it ejects ink from the ejection unit D [m] to form dots on the recording paper P corresponding to the print data IMG.

[0025] For the sake of explanation, a three-axis Cartesian coordinate system with mutually orthogonal X, Y, and Z axes will be introduced as appropriate below. In the following, the direction pointed to by the X-axis arrow will be referred to as the +X direction, and the opposite direction will be referred to as the -X direction. The direction pointed to by the Y-axis arrow will be referred to as the +Y direction, and the opposite direction will be referred to as the -Y direction. The direction pointed to by the Z-axis arrow will be referred to as the +Z direction, and the opposite direction will be referred to as the -Z direction. In the following, the +X and -X directions may be referred to as the X direction without any particular distinction, and the +Y and -Y directions may be referred to as the Y direction without any particular distinction. In addition, the +Z and -Z directions may 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 and -Y directions are the main scanning directions. Furthermore, in this embodiment, as illustrated in Figure 2, the -Z direction is defined as the ink ejection direction from the ejection unit D[m].

[0026] The inkjet printer 1 according to this embodiment includes a housing 100 and a carriage 110 that is capable of reciprocating within the housing 100 in the Y direction and is equipped with four head units 3.

[0027] In this embodiment, it is assumed that the carriage 110 houses four ink cartridges 120, each corresponding one-to-one with four inks: cyan, magenta, yellow, and black. Furthermore, as described above, this embodiment assumes that the inkjet printer 1 has four head units 3, each corresponding one-to-one with the four ink cartridges 120. Each ejection unit D[m] receives ink from the ink cartridge 120 corresponding to the head unit 3 on which the ejection unit D[m] is located. As a result, each ejection unit D[m] can fill itself with the supplied ink and eject the filled ink from the nozzle N. Note that the ink cartridges 120 may be located outside the carriage 110.

[0028] Furthermore, the inkjet printer 1 according to this embodiment has a transport unit 7, as described in Figure 1. The transport unit 7 has 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. In addition, the transport unit 7 has a media transport mechanism 73 for transporting the recording paper P, and a platen 75 provided in the -Z direction relative to the carriage 110. For example, in the 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 media transport mechanism 73 transports the recording paper P on the platen 75 in the +X direction. Therefore, in the printing process, the transport unit 7 changes the relative position of the recording paper P with respect to the head unit 3 by causing the carriage transport mechanism 71 and the media transport mechanism 73 to perform the above operations, thereby enabling ink to land on the entire recording paper P. In this embodiment, it is assumed that multiple ink droplets that merge before landing on the recording paper P are ejected from the nozzle N. An ink droplet is, for example, a particle of ink. Note that an ink droplet is an example of a "liquid droplet".

[0029] Next, the general structure of the recording head 32 will be described with reference to Figure 3.

[0030] Figure 3 is a cross-sectional view illustrating an example of the structure of the ejection section D. Note that Figure 3 schematically shows a portion of the recording head 32 when the recording head 32 is cut to include the ejection section D[m].

[0031] The ejection unit D[m] includes a piezoelectric element PZ[m], a cavity CV filled with ink, a nozzle N communicating with the cavity CV, and a diaphragm 321. The ejection unit D[m] ejects the ink from the cavity CV through the nozzle N when the piezoelectric element PZ[m] is driven by an individual drive signal Vin[m]. Note that the cavity CV is an example of a "pressure chamber," and the piezoelectric element PZ is an example of a "drive element."

[0032] Cavity CV is a space partitioned by a cavity plate 324, a nozzle plate 323 on which the nozzle N is formed, and a diaphragm 321. Cavity CV is in communication with a reservoir 325 via an ink supply port 326. The reservoir 325 is in communication with an ink cartridge 120 corresponding to the ejection section D[m] via an ink intake port 327.

[0033] The piezoelectric element PZ[m] imparts pressure fluctuations to the ink in the cavity CV in response to an individual drive signal Vin[m]. For example, the piezoelectric element PZ[m] has an upper electrode Zu[m], a lower electrode Zd[m], and a piezoelectric element 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 the individual drive signal Vin[m] is supplied. The lower electrode Zd[m] is electrically connected to wiring Ld to which the bias voltage signal VBS is supplied. When the 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 in response to the voltage applied between the upper electrode Zu[m] and the lower electrode Zd[m].

[0034] Thus, 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 and vibrates by the individual drive signal Vin[m], the diaphragm 321 also vibrates. As a result of the vibration of the diaphragm 321, the volume of the cavity CV and the pressure inside the cavity CV change, and the ink filled in the cavity CV is ejected from the nozzle N.

[0035] In this embodiment, as an example, we assume that the piezoelectric element PZ is displaced in the -Z direction when the potential of the individual drive signal Vin[m] supplied to the ejection unit D[m] changes from a low potential to a high potential. That is, in this embodiment, we assume that when the potential of the individual drive signal Vin[m] supplied to the ejection unit D[m] is high, the volume of the cavity CV provided by the ejection unit D[m] becomes smaller compared to when the potential is low. Also in this embodiment, among the surfaces of the nozzle plate 323, the surface in the -Z direction, which is the ink ejection direction, is also called the nozzle surface NSF.

[0036] Next, an example of nozzle N arrangement will be described with reference to Figure 4.

[0037] Figure 4 is a plan view showing an example of the arrangement of nozzles N in the head unit 3. In Figure 4, when the inkjet printer 1 is viewed from the -Z direction, an example of the arrangement of the four head units 3 mounted on the carriage 110 and the total of 4M nozzles N provided on these four head units 3 is shown.

[0038] Each head unit 3 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, as an example, we assume that each nozzle row NL consists of M nozzles N arranged to extend in the X direction.

[0039] Next, we will describe the overview of the head unit 3 with reference to Figures 5 and 6.

[0040] Figure 5 is a block diagram showing an example of the configuration of the head unit 3.

[0041] As described in Figure 1, the head unit 3 has a supply circuit 31 and a recording head 32. The head unit 3 also has wiring La to which the drive signal COM is supplied from the drive signal generation unit 4, and wiring Li [m] to which the individual drive signal Vin [m] is supplied to the ejection unit D [m].

[0042] The supply circuit 31 has M switches Wa[1] to Wa[M] that correspond one-to-one with M discharge units D[1] to D[M], and a connection state specification circuit 310. The connection state specification circuit 310 specifies the connection state of each of the M switches Wa. For example, the connection state specification circuit 310 generates a connection state specification signal Qa[m] that specifies the on or off state of switch Wa[m] based on at least some of the print signal SI and latch signal LAT supplied from the control unit 2.

[0043] Switch Wa[m] switches between conductivity and non-conductivity between wiring La and the upper electrode Zu[m] of piezoelectric element PZ[m] provided in the discharge section D[m], based on the connection status specification signal Qa[m]. That is, switch Wa[m] switches between conductivity and non-conductivity between wiring La and wiring Li[m] connected to the upper electrode Zu[m], based on the connection status specification signal Qa[m]. In this embodiment, switch Wa[m] is turned on when the connection status specification signal Qa[m] is high level and turned off when it is low level. When switch Wa[m] is turned on, the drive signal COM supplied to wiring La is supplied as an individual drive signal Vin[m] to the upper electrode Zu[m] of the discharge section D[m] via wiring Li[m].

[0044] Next, the operation of the head unit 3 will be explained with reference to Figure 6.

[0045] In this embodiment, when the inkjet printer 1 performs 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 unit D[m] for the printing process or the flushing process.

[0046] Figure 6 is a timing chart illustrating an example of the signals supplied to the head unit 3.

[0047] The control unit 2 outputs a latch signal LAT having a pulse PLL. This allows the control unit 2 to define a unit period TP as the period from the rising edge of one pulse PLL to the rising edge of the next pulse PLL. The unit period TP is, for example, the period required to form one dot on the recording paper P corresponding to each nozzle N. In this embodiment, it is assumed that two ink droplets are ejected from the nozzle N within the same unit period TP, and that these two ink droplets merge before landing on the recording paper P, thereby forming one dot on the recording paper P. The unit period TP is, for example, the drive cycle of M ejection units D. In this embodiment, it is assumed that one cycle of the drive signal COM is equal to 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 with M ejection units D[1] to D[M]. The individual designation signals Sd[m] specify the mode of driving the ejection units D[m] in each unit period TP when the inkjet printer 1 performs a printing process or a flushing process. For example, prior to each unit period TP, the control unit 2 supplies the print signal SI, which includes the M individual designation signals Sd[1] to Sd[M], to the connection state designation circuit 310 in synchronization with the clock signal CL. The connection state designation circuit 310 then generates a connection state designation signal Qa[m] based on the individual designation signals Sd[m] in the unit period TP. In this way, the control unit 2 controls the supply of a drive signal COM to each of the M piezoelectric elements PZ by supplying the print signal SI, which includes the M individual designation signals Sd[1] to Sd[M], to the connection state designation circuit 310.

[0049] For example, during a unit period TP in which the printing process is performed, the ejection unit D[m] is designated by an individual designation signal Sd[m] to be either an ejection unit D that forms dots or an ejection unit D that does not form dots.

[0050] The drive signal COM has waveforms PD1 and PD2 arranged in time series. In the example shown in Figure 6, waveform PD2 is a waveform that occurs after waveform PD1. That is, the drive signal COM has waveform PD1 and waveform PD2 which occurs after waveform PD1. Furthermore, the drive signal COM includes waveform PW1, in which the potential of the drive signal COM is maintained at the potential V0 at the start of waveform PD1 before the start of waveform PD1, and waveform PW2, which connects waveform PD1 and waveform PD2, in which the potential of the drive signal COM is maintained at the potential V0 at the start of waveform PD2. Thus, the drive signal COM has, for example, pulses of waveform PD1 and pulses of waveform PD2 provided in a unit period TP.

[0051] Waveforms PD1 and PD2 are examples of "multiple drive waveforms." Therefore, waveform PD1 is an example of the "second-to-last drive waveform," and waveform PD2 is an example of the "last drive waveform." In other words, waveform PD1 is an example of the "first drive waveform," and waveform PD2 is an example of the "second drive waveform." Also, waveform PW1 is an example of the "first standby waveform," and waveform PW2 is an example of the "second standby waveform." Hereafter, waveforms PD1 and PD2 will be referred to simply as waveform PD without any particular distinction. Similarly, waveforms PW1 and PW2 will be referred to simply as waveform PW.

[0052] As will be explained in detail later, waveforms PD1 and PD2 are waveforms for ejecting ink droplets from nozzle N. For example, in the same unit period TP, a first ink droplet ejected from nozzle N by waveform PD1 and a second ink droplet ejected from nozzle N by waveform PD2 merge before landing on the recording paper P. The first ink droplet is an example of a "first droplet," and the second ink droplet is an example of a "second droplet." Hereafter, the first ink droplet will also be referred to as the first ink droplet, and the second ink droplet will also be referred to as the second ink droplet. First, waveform PD1 will be explained.

[0053] Waveform PD1 is, for example, a waveform in which the potential of the drive signal COM returns to potential V0, passing through potentials VL, V1, and VH. Potential V0 is, for example, a reference potential. Potential VL is a potential lower than potential V0 and is the lowest potential of waveform PD1. Potential VH is a potential higher than potential V0 and is the highest potential of waveform PD1. Potential V1 is a potential between potential V0 and potential VL. Potential VL is an example of a "first potential," potential VH is an example of a "second potential," and potential V1 is an example of a "first intermediate potential." Potentials VL, VH, V1, V0, and potential V2 (described later) are each determined, for example, based on the ink ejection characteristics of the ejection unit D. Ink ejection characteristics include, for example, the amount of ink ejected as ink droplets and the speed of the ejected ink droplets.

[0054] In the following, the portion of waveform PD1 in which the potential of the drive signal COM changes from potential V0 to potential VL is also referred to as waveform Pep1, and the portion in which the potential of the drive signal COM is maintained at potential VL is also referred to as waveform Peh1. Furthermore, the portion of waveform PD1 in which the potential of the drive signal COM changes from potential VL to potential VH is also referred to as waveform Pcn1, and the portion in which the potential of the drive signal COM is maintained at potential VH is also referred to as waveform Pch1. In addition, the portion of waveform PD1 in which the potential of the drive signal COM changes from potential VH to potential V0 is also referred to as waveform Pdm1. That is, waveform PD1 includes waveforms Pep1, Peh1, Pcn1, Pch1, and Pdm1.

[0055] Waveform Pep1 is a waveform that displaces the piezoelectric element PZ in the +Z direction. In other words, waveform Pep1 is a waveform in which the potential of the drive signal COM changes in such a way that the volume of the cavity CV expands. Therefore, waveform Pep1 corresponds to the expansion element among the multiple elements that make up the pulse of waveform PD1, which changes the potential of the drive signal COM in order to drive the piezoelectric element PZ to expand the volume of the cavity CV. When the volume of the cavity CV expands, the surface of the ink inside the nozzle N is pulled in the +Z direction, which is the opposite direction to the ejection direction. Hereafter, the pulling of the surface of the ink inside the nozzle N in the opposite direction to the ejection direction may be referred to as "pull". Note that waveform Pep1 is an example of a "first expansion waveform".

[0056] Waveform Peh1 is a waveform used to maintain the position of the piezoelectric element PZ in the Z direction. For example, among the multiple elements that make up the pulse of waveform PD1, waveform Peh1 corresponds to the expansion maintenance element that maintains the potential of the drive signal COM in order to drive the piezoelectric element PZ to maintain the volume of the cavity CV that has expanded due to waveform Peh1. In the example shown in Figure 6, waveform Peh1 connects waveform Peh1 and waveform Pcn1, and is a waveform in which the potential of the drive signal COM is maintained at the potential VL at the end of waveform Peh1. Note that waveform Peh1 is an example of a "first expansion maintenance waveform".

[0057] Waveform Pcn1 is the waveform that displaces the piezoelectric element PZ in the -Z direction. In other words, waveform Pcn1 is the waveform in which the potential of the drive signal COM changes in such a way that the volume of the cavity CV contracts. Therefore, waveform Pcn1 corresponds to the contraction element among the multiple elements that make up the pulse of waveform PD1, which changes the potential of the drive signal COM in order to drive the piezoelectric element PZ to contract the volume of the cavity CV. When the volume of the cavity CV contracts, the surface of the ink in the nozzle N is pushed out in the -Z direction, which is the ejection direction. Hereafter, pushing the surface of the ink in the nozzle N in the ejection direction may be referred to as "pushing".

[0058] Furthermore, waveform Pcn1 includes waveform PcnF1 in which the potential of the drive signal COM changes from potential VL to potential V1, waveform PcnS1 in which the potential of the drive signal COM is maintained at potential V1, and waveform PcnT1 in which the potential of the drive signal COM changes from potential V1 to potential VH. Therefore, in waveform Pcn1, the contraction of the cavity CV volume occurs in two stages. Waveform Pcn1 is an example of the "first contraction waveform". Waveform PcnF1 is an example of the "first partial waveform", waveform PcnS1 is an example of the "second partial waveform", and waveform PcnT1 is an example of the "third partial waveform".

[0059] Furthermore, in this embodiment, as explained in Figure 3, it is assumed that when the potential of the individual drive signal Vin[m] is high, the volume of the cavity CV in the ejection unit D[m] becomes smaller compared to when the potential is low. Therefore, when the drive signal COM is supplied to the ejection unit D[m] as the individual drive signal Vin[m], the ink in the ejection unit D[m] is ejected from the nozzle N as the first ink droplet by the waveform Pcn1, which changes the potential of the individual drive signal Vin[m] from low to high potential.

[0060] In this embodiment, as described above, the volume of the cavity CV is contracted in two stages by waveform Pcn1. Hereafter, among the waveforms that correspond to the contraction element, the waveform in which the volume of the cavity CV is contracted in two stages will also be referred to as a two-stage push waveform. Furthermore, below, among the waveforms that correspond to the contraction element, the waveform in which the volume of the cavity CV is contracted in a single stage without being divided into multiple stages will be referred to as a simple push waveform in contrast to the two-stage push waveform.

[0061] In this embodiment, since waveform Pcn1 is a two-stage push waveform, the amount of ink droplets ejected by the first stage push by waveform PcnF1 is less than the amount of ink droplets ejected by a simple push waveform. Therefore, in this embodiment, the speed of the main droplets that form dots is slower than the speed of the ink droplets ejected by the simple push waveform. Also, in this embodiment, since the potential of the drive signal COM is maintained at the potential at the end of waveform PcnF1 by waveform PcnS1, a constriction occurs in the satellite droplets that follow the main droplets. Then, the satellite droplets are separated from the ink in nozzle N by a second stage push by waveform PcnT1, for example. The speed of the satellite droplets also increases with the second stage push. As a result, the satellite droplets are more likely to merge with the main droplets, and a portion of the satellite droplets is absorbed by the main droplets. As a result, in this embodiment, the size of the main droplets can be increased while the size of the satellite droplets can be decreased.

[0062] Waveform Pch1 is a waveform used to maintain the position of the piezoelectric element PZ in the Z direction. For example, among the multiple elements that make up the pulse of waveform PD1, waveform Pch1 corresponds to the contraction maintenance element that maintains the potential of the drive signal COM in order to drive the piezoelectric element PZ to maintain the volume of the cavity CV that has contracted by waveform Pcn1. In the example shown in Figure 6, waveform Pch1 is a waveform in which the potential of the drive signal COM is maintained at the potential VH at the end of waveform Pch1. Note that waveform Pch1 is an example of a "first contraction maintenance waveform".

[0063] Waveform Pdm1 is a waveform that displaces the piezoelectric element PZ in the +Z direction. For example, waveform Pdm1 is a waveform in which the potential of the drive signal COM changes in order to expand the volume of the cavity CV, which has been contracted by waveform Pcn1, and to dampen the residual vibration of the ink in the cavity CV. That is, waveform Pdm1 is a waveform in which the potential of the drive signal COM changes from potential VH to potential V0 in order to expand the volume of the cavity CV, which has been maintained by waveform Pch1, and to dampen the residual vibration of the ink in the cavity CV. Therefore, waveform Pdm1 corresponds to a vibration damping element among the multiple elements that make up the pulse of waveform PD1, which changes the potential of the drive signal COM in order to drive the piezoelectric element PZ in order to expand the volume of the cavity CV and dampen the residual vibration of the ink in the cavity CV. Note that waveform Pdm1 is an example of the "first vibration damping waveform".

[0064] For example, the vibration of the ink in cavity CV occurring up to waveform Pcn1 is combined with the vibration generated by waveform Pdm1 at a timing corresponding to the length of waveform Pch1. That is, the piezoelectric element PZ[m] expands the volume of cavity CV in response to the potential change of waveform Pdm1, thereby dampening the vibration of the ink in cavity CV. Thus, waveform PD1 is a so-called pull-push-pull waveform.

[0065] Next, we will explain waveform PD2. Waveform PD2 is also a pull-push-pull waveform, similar to waveform PD1. We will omit detailed explanations of elements that are the same as those in waveform PD1.

[0066] Waveform PD2 is, for example, a waveform in which the potential of the drive signal COM returns to potential V0, passing through potentials VL, V2, and VH. Potential V2 is the potential between potential V0 and potential VL. For example, potentials V1 and V2 are set such that the velocity of the second ink droplet ejected from nozzle N by waveform PD2 is faster than the velocity of the first ink droplet ejected from nozzle N by waveform PD1. Note that potential V2 is an example of a "second intermediate potential".

[0067] In the following, the portion of waveform PD2 in which the potential of the drive signal COM changes from potential V0 to potential VL is also referred to as waveform Pep2, and the portion in which the potential of the drive signal COM is maintained at potential VL is also referred to as waveform Peh2. Furthermore, the portion of waveform PD2 in which the potential of the drive signal COM changes from potential VL to potential VH is also referred to as waveform Pcn2, and the portion in which the potential of the drive signal COM is maintained at potential VH is also referred to as waveform Pch2. In addition, the portion of waveform PD2 in which the potential of the drive signal COM changes from potential VH to potential V0 is also referred to as waveform Pdm2. That is, waveform PD2 includes waveforms Pep2, Peh2, Pcn2, Pch2, and Pdm2. Furthermore, waveform Pcn2 includes waveform PcnF2 in which the potential of the drive signal COM changes from potential VL to potential V2, waveform PcnS2 in which the potential of the drive signal COM is maintained at potential V2, and waveform PcnT2 in which the potential of the drive signal COM changes from potential V2 to potential VH.

[0068] Waveform PD2 is similar to waveform PD1, except for the potential change amount of waveform PcnF2. For example, waveform Pcn2 is a waveform in which the potential of the drive signal COM changes so as to contract the volume of cavity CV which has expanded due to waveform Pep2, causing an ink droplet to be ejected from nozzle N, and it corresponds to the same contraction element as waveform Pcn1. Therefore, when the drive signal COM is supplied to the ejection unit D[m] as an individual drive signal Vin[m], the ink in the ejection unit D[m] is ejected from nozzle N as a second ink droplet by waveform Pcn2, in which the potential of the individual drive signal Vin[m] changes from a low potential to a high potential.

[0069] Waveform Pep2 corresponds to an expansion element similar to waveform Pep1, and waveform Peh2 corresponds to an expansion maintenance element similar to waveform Peh1. Furthermore, waveform Pch2 corresponds to a contraction maintenance element similar to waveform Pch1, and waveform Pdm2 corresponds to a vibration damping element similar to waveform Pdm1. Here, waveform Pep2 is an example of a "second expansion waveform," waveform Peh2 is an example of a "second expansion maintenance waveform," and waveform Pcn2 is an example of a "second contraction waveform." Furthermore, waveform PcnF2 is an example of a "fourth partial waveform," waveform PcnS2 is an example of a "fifth partial waveform," and waveform PcnT2 is an example of a "sixth partial waveform." Furthermore, waveform Pch2 is an example of a "second contraction maintenance waveform," and waveform Pdm2 is an example of a "second vibration damping waveform."

[0070] In the following, waveforms Pep1 and Pep2 will also be referred to simply as waveform Pep without any particular distinction. Similarly, waveforms Peh1 and Peh2 will also be referred to simply as waveform Peh, and waveforms Pcn1 and Pcn2 will also be referred to simply as waveform Pcn. Furthermore, waveforms Pch1 and Pch2 will also be referred to simply as waveform Pch, and waveforms Pdm1 and Pdm2 will also be referred to simply as waveform Pdm. Additionally, waveforms PcnF1 and PcnF2 will also be referred to simply as waveform PcnF, waveforms PcnS1 and PcnS2 will also be referred to simply as waveform PcnS, and waveforms PcnT1 and PcnT2 will also be referred to simply as waveform PcnT.

[0071] In this embodiment, the elements of waveforms PD1 and PD2 are defined such that the velocity of the second ink droplet produced by waveform PD2 is faster than the velocity of the first ink droplet produced by waveform PD1. As a result, in this embodiment, the second ink droplet can be combined with the first ink droplet produced by waveform Pcn1 before it lands on the recording paper P. Below, we will mainly explain the setting conditions for the elements of waveforms PD1 and PD2 and the setting of waveform PW, focusing on the setting conditions for making the velocity of the second ink droplet produced by waveform PD2 faster than the velocity of the first ink droplet produced by waveform PD1.

[0072] The first setting condition is that the potential change of waveform PcnF2 is greater than the potential change of waveform PcnF1. For example, the potential V2 at the end of waveform PcnF2 is higher than the potential V1 at the end of waveform PcnF2. In this way, the first setting condition adjusts the potential change of waveform PcnF that performs the first stage of the two-stage contraction of the cavity CV, that is, the waveform PcnF when the ink droplet is ejected from nozzle N. When the potential change of waveform PcnF that ejects the ink droplet from nozzle N is large, the ejection speed of the ink droplet is faster compared to when the potential change of waveform PcnF is small. Therefore, according to the first setting condition, the speed of the second ink droplet produced by waveform PD2 is faster than the speed of the first ink droplet produced by waveform PD1.

[0073] The second setting condition is that the rate of potential change per unit time of waveform PcnT1 is smaller than the rate of potential change per unit time of waveform PcnT2. In this way, the second setting condition adjusts the rate of potential change per unit time of waveform PcnT that performs the second stage of the two-stage contraction of the cavity CV, i.e., the waveform PcnT that separates the ink droplet from the ink in nozzle N. When the rate of potential change per unit time of waveform PcnT that separates the ink droplet from the ink in nozzle N is small, the ink droplet ejection speed is slower compared to when the rate of potential change per unit time of waveform PcnT is large. Therefore, the second setting condition makes the speed of the second ink droplet produced by waveform PD2 faster than the speed of the first ink droplet produced by waveform PD1.

[0074] The third setting condition is that the difference between the period Tsm1 before ink ejection in waveform PD1 and half the natural vibration period of the ejection unit D is greater than the difference between the period Tsm2 before ink ejection in waveform PD2 and half the natural vibration period of the ejection unit D. For example, period Tsm1 is the period from the start of waveform Pep1 to the start of waveform Pcn1, and is the sum of the period Tep1 of waveform Pep1 and the period Teh1 of waveform Peh1. Similarly, period Tsm2 is the period from the start of waveform Pep2 to the start of waveform Pcn2, and is the sum of the period Tep2 of waveform Pep2 and the period Teh2 of waveform Peh2. Thus, under the first setting condition, the relationship between the period Tsm1, which is the sum of the period Tep1 of waveform Pep1 and the period Teh1 of waveform Peh1, the period Tsm2, which is the sum of the period Tep2 of waveform Pep2 and the period Teh2 of waveform Peh2, and the natural vibration period of the discharge unit D is adjusted. Hereafter, periods Tsm1 and Tsm2 will be referred to simply as period Tsm without any particular distinction.

[0075] Here, the natural vibration period of the discharge unit D is, for example, the natural vibration period that represents the natural vibration periods of M discharge units D. For example, the natural vibration period that represents the natural vibration periods of M discharge units D may be the natural vibration period of one of the M discharge units D. Alternatively, the natural vibration period that represents the natural vibration periods of M discharge units D may be the average value of the natural vibration periods of N discharge units D, or it may be the maximum or minimum value among the natural vibration periods of N discharge units D. Note that the value N is a natural number that satisfies "2 ≤ N ≤ M".

[0076] When the difference between the period Tsm from the start of waveform Pep to the start of waveform Pcn and half the natural vibration period of the ejection unit D is small, the ink droplet ejection speed is faster compared to when the difference between the period Tsm and half the natural vibration period of the ejection unit D is large. Therefore, under the third setting condition, the speed of the second ink droplet produced by waveform PD2 becomes faster than the speed of the first ink droplet produced by waveform PD1.

[0077] In the example shown in Figure 6, the period Teh1 of waveform Peh1 is made shorter than the period Teh2 of waveform Peh2, so that the difference between period Tsm and half the natural vibration period of the discharge section D is greater for waveform PD1 than for waveform PD2.

[0078] The fourth setting condition is that the period Tpw2 of waveform PW2 is shorter than the period Tpw1 of waveform PW1. The fifth setting condition is that the period Tpw2 of waveform PW2 is between one-sixth and one-fifth of the natural vibration period of the ejection unit D. The velocity of the second ink droplet is adjusted, for example, by adjusting the period Tpw2 of waveform PW2. Therefore, by either or both of the fourth and fifth setting conditions, the velocity of the second ink droplet produced by waveform PD2 can be made faster than the velocity of the first ink droplet produced by waveform PD1.

[0079] The sixth setting condition is that the rate of potential change per unit time of waveform Pep2 is greater than the rate of potential change per unit time of waveform Pep1. When the rate of potential change per unit time of waveform Pep, which corresponds to the expansion element, is large, the ink droplet ejection speed is faster than when the rate of potential change per unit time of waveform Pep is small. Therefore, according to the seventh setting condition, the speed of the second ink droplet produced by waveform PD2 is faster than the speed of the first ink droplet produced by waveform PD1.

[0080] The setting conditions for making the velocity of the second ink droplet produced by waveform PD2 faster than the velocity of the first ink droplet produced by waveform PD1 are not limited to the first to sixth setting conditions described above. For example, a setting condition other than those described above may be that the potential change amount of waveform Pep2 is greater than the potential change amount of waveform Pep1. Specifically, the initial potential of waveform Pep2 may be higher than the initial potential of waveform Pep1. In addition, in this embodiment, all of the above setting conditions may be adopted, or some of the setting conditions may be adopted.

[0081] Furthermore, in this embodiment, the waveforms PcnF, PcnS, and PcnT of waveforms Pcn1 and Pcn2 are set to shorten the length of the satellite droplet. For example, the period TcnS1 of waveform PcnS1 and the period TcnS2 of waveform PcnS2 may be between one-fifth and one-quarter of the natural vibration period of the discharge unit D. In this embodiment, by adjusting the lengths of periods TcnS1 and TcnS2, the interval between the first push and the second push can be adjusted. That is, in this embodiment, by adjusting the lengths of periods TcnS1 and TcnS2, the second push can be performed at the timing when the length of the satellite droplet is shortened.

[0082] Alternatively, the potential change amounts of waveform PcnF1 and waveform PcnF2 may be one-third or less of the potential change amount from potential VL to potential VH. For example, in a simple push waveform, when the potential change amount is large, the speed of the ink droplet is faster than when the potential change amount is small, but the trail attached to the ink becomes longer, resulting in a longer satellite droplet length. Therefore, in this embodiment, the length of the satellite droplet can be shortened by reducing the potential change amount of waveform PcnF corresponding to the first-stage push waveform. In this embodiment, since waveform Pcn is a two-stage push waveform, the speed of the ink droplet can be adjusted to a desired speed by adjusting waveform PcnT corresponding to the second-stage push waveform.

[0083] Thus, in this embodiment, the length of the satellite droplet can be shortened, thereby suppressing the generation of mist. As a result, in this embodiment, a decrease in the quality of the printed image can be suppressed.

[0084] Next, referring to Figure 7, we will explain the operation when the drive signal COM shown in Figure 6 is supplied to the head unit 3.

[0085] Figure 7 is an explanatory diagram illustrating the operation when the drive signal COM shown in Figure 6 is supplied to the head unit 3. Figure 7 schematically shows the process by which the first ink droplet Idp1, ejected from nozzle N by waveform PD1, and the second ink droplet Idp2, ejected from nozzle N by waveform PD2, combine. The dashed arrows in the figure indicate the forces applied to ink droplets Idp1, Idp2, and Idp12. Ink droplet Idp12 is the combined ink droplet of the first ink droplet Idp1 and the second ink droplet Idp2.

[0086] In the following, ink droplets Idp1, Idp2, and Idp12 will be referred to simply as ink droplet Idp without any particular distinction. Furthermore, in the following, the portion of the edge of ink droplet Idp facing the ejection direction (-Z) will be referred to as the tip of ink droplet Idp, and the portion facing the opposite direction (+Z) will be referred to as the rear end of ink droplet Idp.

[0087] For example, at time T10, the waveform PcnF1 is applied to the piezoelectric element PZ. As a result, the first ink droplet Idp1 begins to be ejected from the nozzle N. At time T20, the tip of the first ink droplet Idp1 has moved in the -Z direction compared to the tip of the first ink droplet Idp1 at time T10. Note that at time T20, the first ink droplet Idp1 has not separated from the ink in the nozzle N.

[0088] At time T30, the first ink droplet Idp1 separates from the ink in nozzle N. That is, the first ink droplet Idp1 separates from the ink in nozzle N before it combines with the second ink droplet Idp2. Therefore, in this embodiment, the influence of the first ink droplet Idp1 on the discharge amount of the subsequent second ink droplet Idp2 can be reduced. As a result, in this embodiment, the amount of the second ink droplet Idp2 can be easily adjusted to a desired amount. This makes it possible to suppress the complexity of setting the waveform PD2 for discharging a desired amount of the second ink droplet Idp2, for example, in this embodiment.

[0089] At time T40, the tip of the second ink droplet Idp2 is located in the -Z direction relative to the nozzle surface NSF, and in the +Z direction relative to the rear end of the first ink droplet Idp1. In other words, at time T40, the second ink droplet Idp2 is not combined with the first ink droplet Idp1. Also, at time T40, the second ink droplet Idp2 is not separated from the ink in nozzle N.

[0090] At time T50, the tip of the second ink droplet Idp2 merges with the rear end of the first ink droplet Idp1. This forms an ink droplet Idp12, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2. Note that at time T50, the second ink droplet Idp2 has not separated from the ink in nozzle N. In other words, the second ink droplet Idp2 merges with the first ink droplet Idp1 before separating from the ink in nozzle N.

[0091] Furthermore, at time T50, the first ink droplet Idp1 has not separated into a main droplet and a satellite droplet. That is, the first ink droplet Idp1 combines with the second ink droplet Idp2 without separating into a main droplet and a satellite droplet. Here, for example, if the second ink droplet Idp2 combines with the satellite droplet of the first ink droplet Idp1 after the first ink droplet Idp1 has separated into a main droplet and a satellite droplet, the speed of the second ink droplet Idp2, which has combined with the satellite droplet of the first ink droplet Idp1, will decrease. In this case, the second ink droplet Idp2 may not be able to catch up with the main droplet of the first ink droplet Idp1 before it hits the recording paper P, and may not combine with the first ink droplet Idp1. In contrast, in this embodiment, as described above, the first ink droplet Idp1 combines with the second ink droplet Idp2 without separating into a main droplet and a satellite droplet. As a result, in this embodiment, a decrease in the velocity of the second ink droplet Idp2 can be suppressed, and the second ink droplet Idp2 can combine with the first ink droplet Idp1 before landing on the recording paper P.

[0092] Furthermore, at time T50, the second ink droplet Idp2 has not separated into a main droplet and a satellite droplet. In other words, the second ink droplet Idp2 merges with the first ink droplet Idp1 before separating into a main droplet and a satellite droplet.

[0093] For example, at time T50, the tip of the second ink droplet Idp2 comes into contact with the first ink droplet Idp1, causing the velocity of the tip of the second ink droplet Idp2 to increase. This increase in velocity of the tip of the second ink droplet Idp2 generates a reaction force between the tip and the trailing portion of the second ink droplet Idp2. This reaction force between the tip and trailing portions of the second ink droplet Idp2 causes the velocity of the trailing portion to decrease. This prevents the length of the trailing portion from increasing.

[0094] Here, focusing on the position of the tip of the ink droplet Idp, the second ink droplet Idp2 merges with the first ink droplet Idp1 at a distance of twice the distance Z10 from the nozzle surface NSF. Distance Z10 is the distance from the nozzle surface NSF to the tip of the first ink droplet Idp1 when it separates from the ink in the nozzle N. Note that twice the distance Z10 is just one example of the "first distance". In the example shown in Figure 7, the distance Z20 from the nozzle surface NSF to the tip of the second ink droplet Idp2 when the first ink droplet Idp1 and the second ink droplet Idp2 merge is shorter than distance Z10. That is, the second ink droplet Idp2 may merge with the first ink droplet Idp1 at a distance of Z10 from the nozzle surface NSF.

[0095] At time T60, the second ink droplet Idp2 separates from the ink in nozzle N. That is, the ink droplet Idp12, formed by the fusion of the first ink droplet Idp1 and the second ink droplet Idp2, separates from the ink in nozzle N. Note that a force in the +Z direction is applied to the tail portion of ink droplet Idp12, which is the trailing end portion, near the tip of ink droplet Idp12, due to the reaction force generated at time T50.

[0096] Furthermore, in this embodiment, as described above, the tip of the second ink droplet Idp2 merges with the first ink droplet Idp1 while the second ink droplet Idp2 is connected to the ink in the nozzle N. Therefore, in this embodiment, when the ink droplet Idp12, formed by the merging of the first ink droplet Idp1 and the second ink droplet Idp2, separates from the ink in the nozzle N, the portion of the ink droplet Idp12 that is separated from the ink in the nozzle N is pulled in the -Z direction. As a result, a force in the -Z direction is applied to the portion of the trailing portion of the ink droplet Idp12 that is close to the nozzle surface NSF. Consequently, the velocity of the trailing portion of the trailing portion of the ink droplet Idp12 increases.

[0097] At time T70, ink droplet Idp12 separates into a main droplet Mdp12 and a satellite droplet Sdp12 that follows the main droplet Mdp12. That is, after the second ink droplet Idp2 merges with the first ink droplet Idp1, the ink droplet Idp12 formed by the merger of the first ink droplet Idp1 and the second ink droplet Idp2 separates into a main droplet Mdp12 and a satellite droplet Sdp12. A force in the +Z direction is applied to the tip of the satellite droplet Sdp12 due to the reaction force generated between the main droplet Mdp12 and the satellite droplet Sdp12, so the velocity of the satellite droplet Sdp12 decreases. Therefore, the length of the satellite droplet Sdp12 is suppressed, for example, as shown at time T80.

[0098] Furthermore, focusing on the position of the tip of the ink droplet Idp, the ink droplet Idp12 formed by the fusion of the first ink droplet Idp1 and the second ink droplet Idp2 may separate into a main droplet Mdp12 and a satellite droplet Sdp12 at a predetermined distance from the nozzle surface NSF. In the example shown in Figure 7, the distance Z30 from the nozzle surface NSF to the tip of the ink droplet Idp12 when it separates into a main droplet Mdp12 and a satellite droplet Sdp12 is shorter than twice the distance Z10. That is, the predetermined distance may be twice the distance Z10.

[0099] Thus, in this embodiment, the piezoelectric element PZ ejects a first ink droplet Idp1 from the nozzle N in accordance with the waveform PD1 when a drive signal COM is supplied. The piezoelectric element PZ also ejects a second ink droplet Idp2 from the nozzle N in accordance with the waveform PD2, such that it combines with the first ink droplet Idp1 before it lands on the recording paper P. In the example shown in Figure 7, the piezoelectric element PZ ejects a second ink droplet Idp2 from the nozzle N in accordance with the waveform PD2, such that it combines with the first ink droplet Idp1 before the second ink droplet Idp2 separates into a main droplet and a satellite droplet that follows the main droplet.

[0100] In this embodiment, by supplying a drive signal COM including two waveforms PD1 and PD2, which include a two-stage push waveform, to the piezoelectric element PZ, it is possible to form a desired amount of main droplet Mdp12 while suppressing an increase in the length of the satellite droplet Sdp12.

[0101] Furthermore, in this embodiment, the supply of waveform Pep2, which corresponds to the expansion element of waveform PD2, to the piezoelectric element PZ may be started between the time PD1 is supplied to the piezoelectric element PZ and the time T30 when the first ink droplet Idp1 separates from the ink in the nozzle N. In this case as well, it is possible to suppress the length of the satellite droplet Sdp12 from increasing.

[0102] Next, we will explain the experimental results of measuring the length of satellite droplets, referring to Figure 8.

[0103] Figure 8 is an explanatory diagram showing the experimental results of measuring the length of satellite droplets. Figure 8 shows the results of an ink ejection experiment when the viscosity of the ink in nozzle N, measured at a shear rate of 200 [1 / sec], is 100 millipascal seconds or higher. The vertical axis of Figure 8 represents the length of satellite droplets, and the horizontal axis represents the number of ink ejections per unit period TP. The open circles in the figure indicate the length of satellite droplets when the piezoelectric element PZ is driven by a waveform PD including a two-stage push waveform, while the filled circles indicate the length of satellite droplets when the piezoelectric element PZ is driven by a simple push waveform, contrasted with the two-stage push waveform. The simple push waveform, as explained in Figure 6, is a waveform in which the volume contraction of the cavity CV occurs in a single step without being divided into multiple stages.

[0104] When ejecting high-viscosity ink with a simple push waveform, the amount of potential change in the waveform Pcn required to eject the ink at a predetermined speed must be larger compared to when ejecting low-viscosity ink with a simple push waveform. When the amount of potential change in the waveform Pcn is large, the ink trail becomes longer and the length of the satellite droplet increases compared to when the amount of potential change in the waveform Pcn is small. For example, as shown in Figure 8, when the piezoelectric element PZ is driven by a simple push waveform so that ink is ejected once per unit period TP, the length of the satellite droplet is approximately 1100 [μm].

[0105] In contrast, when the piezoelectric element PZ is driven by a waveform PD including a two-stage push waveform so that ink is ejected once per unit period TP, the length of the satellite droplet is approximately 300 [μm]. In other words, by using a two-stage push waveform, the length of the satellite droplet can be shortened by approximately 800 [μm] compared to when a simple push waveform is used.

[0106] Furthermore, when the piezoelectric element PZ is driven by a waveform PD including a two-stage push waveform so that ink is ejected twice in a unit period TP, the length of the satellite droplet is approximately 200 [μm]. Also, when the piezoelectric element PZ is driven by a waveform PD including a two-stage push waveform so that ink is ejected three times in a unit period TP, the length of the satellite droplet is approximately 200 [μm]. Thus, in this embodiment, even when the number of ink ejections in a unit period TP is increased, the length of the satellite droplet can be suppressed by driving the piezoelectric element PZ with a waveform PD including a two-stage push waveform.

[0107] Thus, in this embodiment, even when the viscosity of the ink in nozzle N is high, for example, when the viscosity of the ink is 10 millipascal seconds or more, it is possible to suppress the length of the satellite droplet from becoming longer. Figure 8 shows the measurement results of the length of the satellite droplet when ink with a viscosity of 100 millipascal seconds or more is dispensed, as described above. In other words, in this embodiment, even when the viscosity of the ink in nozzle N is 100 millipascal seconds or more, it is possible to suppress the length of the satellite droplet from becoming longer.

[0108] In this embodiment, the inkjet printer 1 includes a head unit 3 and a control unit 2. The head unit 3 has an ejection section D that includes a nozzle N for ejecting ink, a cavity CV communicating with the nozzle N, and a piezoelectric element PZ that applies pressure fluctuations to the ink in the cavity CV in response to a drive signal COM. The control unit 2 controls the supply of the drive signal COM to the piezoelectric element PZ. The drive signal COM includes waveform PD1 and waveform PD2 which is later than waveform PD1.

[0109] In this embodiment, the piezoelectric element PZ ejects a first ink droplet Idp1 from the nozzle N in accordance with the waveform PD1 when a drive signal COM is supplied. The piezoelectric element PZ also ejects a second ink droplet Idp2 from the nozzle N in accordance with the waveform PD2, such that it combines with the first ink droplet Idp1 before it lands on the recording paper P. For example, in this embodiment, the piezoelectric element PZ ejects a second ink droplet Idp2 from the nozzle N in accordance with the waveform PD2, such that it combines with the first ink droplet Idp1 before the second ink droplet Idp2 separates into a main droplet and a satellite droplet that follows the main droplet. In this embodiment, after the second ink droplet Idp2 merges with the first ink droplet Idp1, the combined ink droplet Idp12 of the second ink droplet Idp2 and the first ink droplet Idp1 separates into a main droplet Mdp12 and a satellite droplet Sdp12.

[0110] Thus, in this embodiment, the second ink droplet Idp2 merges with the first ink droplet Idp1 before separating into a main droplet and a satellite droplet. Therefore, in this embodiment, when the second ink droplet Idp2 comes into contact with the first ink droplet Idp1, the reaction force generated between the main droplet and the satellite droplet of the second ink droplet Idp2 before they separate is applied to the satellite droplet. This reaction force applied to the satellite droplet shortens its length. In other words, in this embodiment, it is possible to suppress the length of the satellite droplet Sdp12 separated from the main droplet Mdp12 of the ink droplet Idp12 formed by the merging of the first ink droplet Idp1 and the second ink droplet Idp2. Therefore, in this embodiment, the generation of mist can be suppressed. As a result, in this embodiment, a decrease in the quality of the printed image can be suppressed.

[0111] Furthermore, in this embodiment, the first ink droplet Idp1 may be separated from the ink in the nozzle N before it combines with the second ink droplet Idp2. In this case, the influence of the first ink droplet Idp1 on the subsequent discharge amount of the second ink droplet Idp2 can be reduced. As a result, in this embodiment, the amount of the second ink droplet Idp2 can be easily adjusted to a desired amount. This makes it possible to ensure a desired discharge amount when discharging the second ink droplet Idp2 in this embodiment.

[0112] Furthermore, in this embodiment, the first ink droplet Idp1 may combine with the second ink droplet Idp2 without separating into a main droplet and a satellite droplet. For example, if the satellite droplet separated from the main droplet of the first ink droplet Idp1 combines with the second ink droplet Idp2, the speed of the second ink droplet Idp2 decreases. In this case, the second ink droplet Idp2 may not catch up to the main droplet of the first ink droplet Idp1 before landing on the recording paper P, and may not combine with the first ink droplet Idp1. For this reason, in this embodiment, for example, the piezoelectric element PZ may eject the first ink droplet Idp1 and the second ink droplet Idp2 from the nozzle N so that the first ink droplet Idp1 combines with the second ink droplet Idp2 without separating into a main droplet and a satellite droplet. In this case, it is possible to suppress the decrease in the velocity of the second ink droplet Idp2 and to prevent the second ink droplet Idp2 from merging with the first ink droplet Idp1 before it lands on the recording paper P.

[0113] Furthermore, in this embodiment, the second ink droplet Idp2 may combine with the first ink droplet Idp1 before separating from the ink in the nozzle N. In this case, for example, when the ink droplet Idp12 formed by the combination of the first ink droplet Idp1 and the second ink droplet Idp2 separates from the ink in the nozzle N, the portion of the ink droplet Idp12 that is separated from the ink in the nozzle N is pulled in the discharge direction, which is the -Z direction. As a result, a force in the -Z direction is applied to the portion of the trailing portion of the ink droplet Idp12 that is close to the nozzle surface NSF. Consequently, the velocity of the trailing portion of the trailing portion of the ink droplet Idp12 increases. In this case, it is possible to suppress an increase in the length of the trailing portion of the ink droplet Idp12, and thus suppress an increase in the length of the satellite droplet Sdp12.

[0114] Furthermore, in this embodiment, the second ink droplet Idp2 may merge with the first ink droplet Idp1 at a distance of a first distance from the nozzle surface NSF. The first distance is twice the distance Z10 from the nozzle surface NSF to the tip of the first ink droplet Idp1 when the first ink droplet Idp1 separates from the ink in the nozzle N. In this case as well, it is possible to suppress the length of the satellite droplet Sdp12 from becoming longer.

[0115] Furthermore, in this embodiment, waveform PD1 includes waveform Pep1, in which the potential of the drive signal COM changes to potential VL so as to expand the volume of the cavity CV, and waveform Pcn1, in which the potential of the drive signal COM changes from potential VL to potential VH so as to contract the volume of the cavity CV. Waveform PD2 includes waveform Pep2, in which the potential of the drive signal COM changes to potential VL so as to expand the volume of the cavity CV, and waveform Pcn2, in which the potential of the drive signal COM changes from potential VL to potential VH so as to contract the volume of the cavity CV. Waveform Pcn1 includes waveform PcnF1, in which the potential of the drive signal COM changes from potential VL to potential V1 between potential VL and potential VH, waveform PcnS1, in which the potential of the drive signal COM is maintained at potential V1, and waveform PcnT1, in which the potential of the drive signal COM changes from potential V1 to potential VH. Waveform Pcn2 includes waveform PcnF2 in which the potential of the drive signal COM changes from potential VL to potential V2, which is between potential VL and potential VH; waveform PcnS2 in which the potential of the drive signal COM is maintained at potential V2; and waveform PcnT2 in which the potential of the drive signal COM changes from potential V2 to potential VH.

[0116] Thus, in this embodiment, each waveform Pcn of waveforms PD1 and PD2 included in the drive signal COM is a two-stage push waveform in which the volume contraction of the cavity CV is performed in two stages. That is, in this embodiment, the piezoelectric element PZ is driven by a drive signal COM that includes two waveforms PD1 and PD2, which include a two-stage push waveform. As a result, in this embodiment, it is possible to form a desired amount of main droplet Mdp12 while suppressing an increase in the length of the satellite droplet Sdp12.

[0117] Furthermore, in this embodiment, the period TcnS1 of waveform PcnS1 and the period TcnS2 of waveform PcnS2 may be between one-fifth and one-quarter of the natural vibration period of the discharge unit D. In this case as well, the length of the satellite droplet Sdp12 can be shortened.

[0118] Furthermore, in this embodiment, the potential change amounts of waveform PcnF1 and waveform PcnF2 may be one-third or less of the potential change amount from potential VL to potential VH. In this case as well, the length of the satellite droplet Sdp12 can be shortened.

[0119] Furthermore, in this embodiment, the potential change of waveform PcnF2 may be greater than the potential change of waveform PcnF1. When the potential change of waveform PcnF that ejects ink droplets from nozzle N is large, the ejection speed of ink droplets becomes faster compared to when the potential change of waveform PcnF is small. Therefore, in this embodiment, by making the potential change of waveform PcnF2 larger than the potential change of waveform PcnF1, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

[0120] Furthermore, in this embodiment, the amount of potential change per unit time of waveform PcnT1 may be smaller than the amount of potential change per unit time of waveform PcnT2. When the amount of potential change per unit time of waveform PcnT, which separates the ink droplet from the ink in the nozzle N, is small, the ink droplet ejection speed becomes slower compared to when the amount of potential change per unit time of waveform PcnT is large. Therefore, in this embodiment, by making the amount of potential change per unit time of waveform PcnT1 smaller than the amount of potential change per unit time of waveform PcnT2, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

[0121] Furthermore, in this embodiment, waveform PD1 further includes waveform Peh1, which connects waveform Pep1 and waveform Pcn1, and maintains the potential of the drive signal COM at potential VL to maintain the volume of cavity CV. Waveform PD2 further includes waveform Peh2, which connects waveform Pep2 and waveform Pcn2, and maintains the potential of the drive signal COM at potential VL to maintain the volume of cavity CV. The difference between the combined period Tsm1, which is the period Tep1 of waveform Pep1 and the period Teh1 of waveform Peh1, and half the natural vibration period of the discharge unit D may be greater than the difference between the combined period Tsm2, which is the period Tep2 of waveform Pep2 and the period Teh2 of waveform Peh2, and half the natural vibration period of the discharge unit D. When the difference between the period Tsm from the start of waveform Pep to the start of waveform Pcn and the period of half the natural vibration period of the ejection unit D is small, the ink droplet ejection speed is faster compared to when the difference between the period Tsm and the period of half the natural vibration period of the ejection unit D is large. Therefore, in this embodiment, by making the difference between the period Tsm and the period of half the natural vibration period of the ejection unit D larger for waveform PD1 than for waveform PD2, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

[0122] Furthermore, in this embodiment, waveform PD1 further includes waveform Pch1 in which the potential of the drive signal COM is maintained at potential VH so as to maintain the volume of cavity CV contracted by waveform Pcn1, and waveform Pdm1 in which the potential of the drive signal COM changes so as to expand the volume of cavity CV maintained by waveform Pch1. Waveform PD2 further includes waveform Pch2 in which the potential of the drive signal COM is maintained at potential VH so as to maintain the volume of cavity CV contracted by waveform Pcn2, and waveform Pdm2 in which the potential of the drive signal COM changes so as to expand the volume of cavity CV maintained by waveform Pch2. The drive signal COM further includes waveform PW1 in which the potential of the drive signal COM is maintained at the potential V0 at the start of waveform Pep1 before the start of waveform Pep1, and waveform PW2 in which waveform Pdm1 and waveform Pep2 are connected and the potential of the drive signal COM is maintained at the potential V0 at the start of waveform Pep2. The duration Tpw2 of waveform PW2 may be shorter than the duration Tpw1 of waveform PW1. In this case as well, the velocity of the second ink droplet Idp2 can be made faster than the velocity of the first ink droplet Idp1.

[0123] Furthermore, in this embodiment, the period Tpw2 of the waveform PW2 may be between one-sixth and one-fifth of the natural vibration period of the ejection unit D. In this case as well, the velocity of the second ink droplet Idp2 can be made faster than the velocity of the first ink droplet Idp1.

[0124] Furthermore, in this embodiment, the potential change of waveform Pep2 may be greater than the potential change of waveform Pep1. In this case as well, the velocity of the second ink droplet Idp2 can be made faster than the velocity of the first ink droplet Idp1.

[0125] Furthermore, in this embodiment, the amount of potential change per unit time of waveform Pep2 may be greater than the amount of potential change per unit time of waveform Pep1. When the amount of potential change per unit time of waveform Pep, which corresponds to the expansion element, is large, the ink droplet ejection speed becomes faster compared to when the amount of potential change per unit time of waveform Pep is small. Therefore, in this embodiment, by making the amount of potential change per unit time of waveform Pep2 greater than the amount of potential change per unit time of waveform Pep1, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

[0126] Thus, in this embodiment, the ejection speed of the second ink droplet Idp2 from the nozzle N is faster than the ejection speed of the first ink droplet Idp1 from the nozzle N. As a result, in this embodiment, the first ink droplet Idp1 and the second ink droplet Idp2 can be combined before the first ink droplet Idp1 lands on the recording paper P.

[0127] Furthermore, in this embodiment, the viscosity of the ink in nozzle N may be 10 millipascal seconds or more. In this embodiment, even when the viscosity of the ink in nozzle N is high, the length of the satellite droplet Sdp12 can be shortened.

[0128] [2. Variant] Each of the above forms can be modified in various ways. Specific examples of modifications are given below. Two or more forms arbitrarily selected from the following examples can be combined as appropriate, within the bounds of mutual consistency. In the modified examples given below, for elements whose function or action is equivalent to that of the embodiments, the same reference numerals used in the above description will be reused, and detailed explanations of each will be omitted as appropriate.

[0129] [First variation] In the embodiments described above, the drive signal COM is illustrated as including two waveform PDs provided in a unit period TP, but the present invention is not limited to such embodiments. For example, the drive signal COM may include three or more waveform PDs provided in a unit period TP.

[0130] Figure 9 is a timing chart illustrating an example of the drive signal COM in the first modified example. Elements similar to those described in Figures 1 to 8 are denoted by the same reference numerals, and detailed explanations are omitted. In the example shown in Figure 9, three ink droplets are ejected from the nozzle N in the same unit period TP, and these three ink droplets merge before landing on the recording paper P, forming a single dot on the recording paper P. The three ink droplets are an example of "multiple droplets".

[0131] The drive signal COM shown in Figure 9 is the same as the drive signal COM shown in Figure 6, except that waveforms PD3 and PW3 are added to the drive signal COM shown in Figure 6. For example, the drive signal COM has waveforms PD1, PD2 and PD3 that give pressure fluctuations to the ink in the cavity CV, waveform PW1 that connects waveforms PD3 and PD1, waveform PW2 that connects waveforms PD1 and PD2, and waveform PW3. For example, waveform PD3 is a waveform that precedes waveform PD1. Also, waveform PW3 is a waveform in which the potential of the drive signal COM is maintained at the potential V0 at the start of waveform PD3 before the start of waveform PD3.

[0132] Waveforms PD1, PD2, and PD3 are examples of "multiple drive waveforms." Hereafter, waveforms PD1, PD2, and PD3 will also be referred to simply as waveform PD without any particular distinction.

[0133] Waveform PD3 is a pull-push-pull waveform, similar to waveform PD1. Detailed explanations of elements similar to waveform PD1 are omitted.

[0134] Waveform PD3 is, for example, a waveform in which the potential of the drive signal COM returns to potential V0, passing through potentials VL, V3, and VH. Potential V3 is the potential between potential V0 and potential VL. For example, potentials V1 and V3 are set such that the velocity of the ink droplet Idp ejected from nozzle N by waveform PD1 is faster than the velocity of the ink droplet Idp ejected by nozzle N by waveform PD3. For example, potential V3 is a lower potential than potential V1.

[0135] In the following, the portion of waveform PD3 in which the potential of the drive signal COM changes from potential V0 to potential VL is also referred to as waveform Pep3, and the portion in which the potential of the drive signal COM is maintained at potential VL is also referred to as waveform Peh3. Furthermore, the portion of waveform PD3 in which the potential of the drive signal COM changes from potential VL to potential VH is also referred to as waveform Pcn3, and the portion in which the potential of the drive signal COM is maintained at potential VH is also referred to as waveform Pch3. In addition, the portion of waveform PD3 in which the potential of the drive signal COM changes from potential VH to potential V0 is also referred to as waveform Pdm3. That is, waveform PD3 includes waveforms Pep3, Peh3, Pcn3, Pch3, and Pdm3. Furthermore, waveform Pcn3 includes waveform PcnF3 in which the potential of the drive signal COM changes from potential VL to potential V3, waveform PcnS3 in which the potential of the drive signal COM is maintained at potential V3, and waveform PcnT3 in which the potential of the drive signal COM changes from potential V3 to potential VH.

[0136] Waveform PD3 is similar to waveform PD1, except for the potential change amount of waveform PcnF3. For example, waveform Pcn3 is a waveform in which the potential of the drive signal COM changes so as to contract the volume of the cavity CV which has expanded due to waveform Pep3, causing an ink droplet Idp to be ejected from nozzle N, and it corresponds to the same contraction element as waveform Pcn1. Therefore, when the drive signal COM is supplied to the ejection unit D[m] as an individual drive signal Vin[m], the ink in the ejection unit D[m] is ejected from nozzle N as the first ink droplet Idp by waveform Pcn3, in which the potential of the individual drive signal Vin[m] changes from a low potential to a high potential. In the example shown in Figure 9, the ink droplet Idp ejected from nozzle N by waveform PD1 is the second ink droplet Idp, and the ink droplet Idp ejected from nozzle N by waveform PD2 is the third ink droplet Idp.

[0137] Waveform Pep3 corresponds to an expansion element similar to waveform Pep1, and waveform Peh3 corresponds to an expansion maintenance element similar to waveform Peh1. Furthermore, waveform Pch3 corresponds to a contraction maintenance element similar to waveform Pch1, and waveform Pdm3 corresponds to a vibration damping element similar to waveform Pdm1. Here, waveforms Pep1, Pep2, and Pep3 are examples of "expansion waveforms," ​​waveforms Peh1, Peh2, and Peh3 are examples of "expansion maintenance waveforms," ​​and waveforms Pcn1, Pcn2, and Pcn3 are examples of "contraction waveforms." Furthermore, waveforms PcnF1, PcnF2, and PcnF3 are examples of "first waveforms," ​​waveforms PcnS1, PcnS2, and PcnS3 are examples of "second waveforms," ​​and waveforms PcnT1, PcnT2, and PcnT3 are examples of "third waveforms."

[0138] In this modified example, the elements of waveforms PD1 and PD2 are defined such that the velocity of the third ink droplet Idp produced by waveform PD2 is faster than the velocity of the second ink droplet Idp produced by waveform PD1. Similarly, the elements of waveforms PD1 and PD3 are defined such that the velocity of the second ink droplet Idp produced by waveform PD1 is faster than the velocity of the first ink droplet Idp produced by waveform PD3. The setting conditions for making the velocity of the second ink droplet Idp produced by waveform PD1 faster than the velocity of the first ink droplet Idp produced by waveform PD3 are the same as the setting conditions 1 to 6 described in Figure 6. For example, in the explanation of the setting conditions 1 to 6, the elements of waveform PD1 and waveform PD2 are replaced with the elements of waveform PD3 and waveform PD1, respectively.

[0139] Furthermore, in this modified example, waveforms PcnF3, PcnF3, and PcnT3 included in waveform Pcn3 are set to shorten the length of the satellite droplet, similar to waveforms PcnF, PcnS, and PcnT of waveforms Pcn1 and Pcn2, respectively.

[0140] As described above, the same effects as those of the embodiment described can be obtained in this modified version as well. For example, in this modified version, multiple ink droplets Idp can be ejected from the nozzle N in the same unit period TP so that they combine before landing on the recording paper P. In addition, in this modified version as well, it is possible to suppress the length of satellite droplets that separate from the combined ink droplets Idp. Therefore, in this modified version as well, the generation of mist can be suppressed, and the deterioration of the quality of the printed image can be suppressed.

[0141] [Second variation] In the embodiments and modifications described above, the amount of the second ink droplet Idp2 may be greater than or equal to the amount of the first ink droplet Idp1. In these modifications as well, the same effects as in the embodiments and modifications described above can be obtained.

[0142] [Third variation] In the embodiments and modifications described above, the case in which the piezoelectric element PZ is displaced in the -Z direction due to a change in the potential of the individual drive signal Vin[m] from a low potential to a high potential was illustrated, but the present invention is not limited to such embodiments. For example, a piezoelectric element PZ that is displaced in the -Z direction due to a change in the potential of the individual drive signal Vin[m] 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 the part corresponding to the expansion element, and changes from a high potential to a low potential in the part corresponding to the contraction element. The same effects as those of the embodiments and modifications described above can be obtained in this modification as well.

[0143] [Fourth variation] In the embodiments and modifications described above, the case in which each head unit 3 has one nozzle row NL is illustrated, but the present invention is not limited to such embodiments. For example, each head unit 3 may have multiple nozzle rows NL. In this modification as well, the same effects as in the embodiments and modifications described above can be obtained.

[0144] [Fifth variation] The embodiments and modifications described above illustrate the case where the inkjet printer 1 has four head units 3, but the present invention is not limited to such embodiments. For example, the inkjet printer 1 may have one to three head units 3, or it may have five or more head units 3.

[0145] [Sixth variation] In the embodiments and modifications described above, the initial potential of waveform Pep1, which corresponds to the expansion element of waveform PD1, may be lower than the initial potential of waveform Pep2, which corresponds to the expansion element of waveform PD2. In this case as well, the velocity of the ink droplet Idp ejected from nozzle N by waveform PD2 will be faster than the velocity of the ink droplet Idp ejected from nozzle N by waveform PD1. The same effects as those of the embodiments and modifications described above can be obtained in this modification as well.

[0146] [9th variation] In the embodiments and modifications described above, the case in which the inkjet printer 1 is a serial printer is illustrated, but the present invention is not limited to such embodiments. For example, the inkjet printer 1 may be a so-called line printer in which a plurality of nozzles N in the head unit 3 are provided so as to extend wider than the width of the recording paper P. In this modification as well, the same effects as in the embodiments and modifications described above can be obtained.

[0147] [10th variation] In the embodiments and modifications described above, the case in which there is one drive signal COM is illustrated, but the present invention is not limited to such embodiments. For example, in addition to the drive signal COM shown in Figure 6, the drive signal COM may include drive signals having waveforms different from the waveforms PD1 and PD2 of the drive signal COM. In this modification as well, the same effects as in the embodiments and modifications described above can be obtained. [Explanation of Symbols]

[0148] 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 unit, N... Nozzle.

Claims

1. A liquid discharge head having a discharge section that includes a nozzle for discharging droplets, a pressure chamber communicating with the nozzle, and a drive element that causes pressure fluctuations in the liquid in the pressure chamber in response to a drive signal, A control unit that controls the supply of the drive signal to the drive element, Equipped with, The drive signal has a plurality of drive waveforms within one cycle, including a first drive waveform and a second drive waveform that occurs after the first drive waveform. The first drive waveform is, A first expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, A first contraction waveform in which the potential of the drive signal changes from the first potential to the second potential so as to contract the volume of the pressure chamber, Including, The second drive waveform is, A second expansion waveform in which the potential of the drive signal changes to the first potential so as to expand the volume of the pressure chamber, A second contraction waveform in which the potential of the drive signal changes from the first potential to the second potential so as to contract the volume of the pressure chamber, Includes, The first contraction waveform is, A first partial waveform in which the potential of the drive signal changes from the first potential to a first intermediate potential between the first potential and the second potential, A second partial waveform in which the potential of the drive signal is maintained at the first intermediate potential, A third partial waveform in which the potential of the drive signal changes from the first intermediate potential to the second potential, Includes, The second contraction waveform is, A fourth partial waveform in which the potential of the drive signal changes from the first potential to a second intermediate potential between the first potential and the second potential, A fifth partial waveform in which the potential of the drive signal is maintained at the second intermediate potential, A sixth partial waveform in which the potential of the drive signal changes from the second intermediate potential to the second potential, Includes, The aforementioned drive element is When the aforementioned drive signal is supplied, In accordance with the first drive waveform, a first droplet is discharged from the nozzle. In accordance with the second drive waveform, a second droplet is discharged from the nozzle such that it merges with the first droplet before the first droplet lands on the medium. The multiple droplets discharged from the nozzle according to the multiple drive waveforms merge before impact with the medium. The first drive waveform is the second to last drive waveform among the plurality of drive waveforms, The second drive waveform is the last drive waveform among the plurality of drive waveforms. A liquid dispensing device characterized by the following features.

2. The duration of the second partial waveform and the duration of the fifth partial waveform are between one-fifth and one-quarter of the natural vibration period of the discharge unit. The liquid dispensing device according to feature 1.

3. The potential change in the first partial waveform and the potential change in the fourth partial waveform are less than or equal to one-third of the potential change from the first potential to the second potential. The liquid dispensing device according to feature 1 or 2.

4. The potential change of the fourth partial waveform is greater than the potential change of the first partial waveform. A liquid dispensing device according to any one of claims 1 to 3.

5. The rate of potential change per unit time of the third partial waveform is smaller than the rate of potential change per unit time of the sixth partial waveform. A liquid dispensing device according to any one of claims 1 to 4.

6. The first drive waveform is, The first expansion waveform and the first contraction waveform are connected to form a first expansion maintenance waveform in which the potential of the drive signal is maintained at the first potential in order to maintain the volume of the pressure chamber. Furthermore, The second drive waveform is, The second expansion waveform and the second contraction waveform are connected to form a second expansion maintenance waveform in which the potential of the drive signal is maintained at the first potential in order to maintain the volume of the pressure chamber. Furthermore, The difference between the combined period of the first expansion waveform and the first expansion maintenance waveform and the period of half the natural vibration period of the discharge unit is greater than the difference between the combined period of the second expansion waveform and the second expansion maintenance waveform and the period of half the natural vibration period of the discharge unit. A liquid dispensing device according to any one of claims 1 to 5.

7. The first drive waveform is, A first contraction maintenance waveform is provided in which the potential of the drive signal is maintained at the second potential in order to maintain the volume of the pressure chamber contracted by the first contraction waveform, A first vibration damping waveform in which the potential of the drive signal changes to expand the volume of the pressure chamber maintained by the first contraction maintenance waveform, It further includes, The second drive waveform is, A second contraction maintenance waveform is provided, in which the potential of the drive signal is maintained at the second potential in order to maintain the volume of the pressure chamber contracted by the second contraction waveform, A second vibration damping waveform is provided, in which the potential of the drive signal changes to expand the volume of the pressure chamber maintained by the second contraction maintenance waveform, It further includes, The aforementioned drive signal is A first standby waveform is provided before the start of the first expansion waveform, in which the potential of the drive signal is maintained at the potential at the start of the first expansion waveform, The first vibration damping waveform and the second expansion waveform are connected to form a second standby waveform in which the potential of the drive signal is maintained at the potential at the start of the second expansion waveform, It further includes, The duration of the second standby waveform is shorter than the duration of the first standby waveform. A liquid dispensing device according to any one of claims 1 to 6.

8. The duration of the second standby waveform is between one-sixth and one-fifth of the natural vibration period of the discharge unit. The liquid dispensing device according to feature 7.

9. The potential change of the second expansion waveform is greater than the potential change of the first expansion waveform. A liquid dispensing device according to any one of claims 1 to 8.

10. The rate of potential change per unit time of the second expansion waveform is greater than the rate of potential change per unit time of the first expansion waveform. A liquid dispensing device according to any one of claims 1 to 9.

11. The discharge speed of the second droplet from the nozzle is faster than the discharge speed of the first droplet from the nozzle. A liquid dispensing device according to any one of claims 1 to 10.

12. The amount of the second droplet is greater than or equal to the amount of the first droplet. A liquid dispensing device according to any one of claims 1 to 11.

13. Each of the plurality of drive waveforms is An expansion waveform in which the potential of the drive signal changes to the first potential so as to expand the volume of the pressure chamber, A contraction waveform in which the potential of the drive signal changes from the first potential to the second potential so as to contract the volume of the pressure chamber, Includes, The aforementioned contraction waveform is A first waveform in which the potential of the drive signal changes from the first potential to a potential between the first potential and the second potential, A second waveform in which the potential of the drive signal is maintained at the potential at the end of the first waveform, A third waveform in which the potential of the drive signal changes from the potential at the end of the first waveform to the second potential, Includes, In the second to last drive waveform, the expansion waveform is the first expansion waveform, the contraction waveform is the first contraction waveform, the first waveform is the first partial waveform, the second waveform is the second partial waveform, and the third waveform is the third partial waveform. In the aforementioned final drive waveform, the expansion waveform is the second expansion waveform, the contraction waveform is the second contraction waveform, the first waveform is the fourth partial waveform, the second waveform is the fifth partial waveform, and the third waveform is the sixth partial waveform. A liquid dispensing device according to any one of claims 1 to 12.

14. The viscosity of the liquid inside the nozzle is 10 millipascal seconds or more. A liquid dispensing device according to any one of claims 1 to 13.

15. A control method for a liquid discharge head having a discharge section that includes a nozzle for discharging droplets, a pressure chamber communicating with the nozzle, and a drive element that causes pressure fluctuations in the liquid within the pressure chamber in response to a drive signal, The drive signal has a plurality of drive waveforms within one cycle, including a first drive waveform and a second drive waveform that occurs after the first drive waveform. The first drive waveform is, A first expansion waveform in which the potential of the drive signal changes to a first potential so as to expand the volume of the pressure chamber, A first contraction waveform in which the potential of the drive signal changes from the first potential to the second potential so as to contract the volume of the pressure chamber, Including, The second drive waveform is, A second expansion waveform in which the potential of the drive signal changes to the first potential so as to expand the volume of the pressure chamber, A second contraction waveform in which the potential of the drive signal changes from the first potential to the second potential so as to contract the volume of the pressure chamber, Includes, The first contraction waveform is, A first partial waveform in which the potential of the drive signal changes from the first potential to a first intermediate potential between the first potential and the second potential, A second partial waveform in which the potential of the drive signal is maintained at the first intermediate potential, A third partial waveform in which the potential of the drive signal changes from the first intermediate potential to the second potential, Includes, The second contraction waveform is, A fourth partial waveform in which the potential of the drive signal changes from the first potential to a second intermediate potential between the first potential and the second potential, A fifth partial waveform in which the potential of the drive signal is maintained at the second intermediate potential, A sixth partial waveform in which the potential of the drive signal changes from the second intermediate potential to the second potential, Includes, Control the supply of the drive signal to the drive element, The aforementioned drive element is When the aforementioned drive signal is supplied, In accordance with the first drive waveform, a first droplet is discharged from the nozzle. In accordance with the second drive waveform, a second droplet is discharged from the nozzle such that it merges with the first droplet before the first droplet lands on the medium. The multiple droplets discharged from the nozzle according to the multiple drive waveforms merge before impact with the medium. The first drive waveform is the second to last drive waveform among the plurality of drive waveforms, The second drive waveform is the last drive waveform among the plurality of drive waveforms. A method for controlling a liquid dispensing head, characterized by the features described above.

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