JP2023129891A - Control method of liquid discharge head and liquid discharge device - Google Patents

Abstract

To suppress mist from being generated.SOLUTION: A control method of a liquid discharge head, which has a discharging part which includes a nozzle for discharging liquid droplets, a pressure chamber communicated with the nozzle and a driving element that gives pressure fluctuation to liquid in the pressure chamber in response to a driving signal, controls supply of the driving signal to the driving element, where the driving signal includes a first driving waveform and a second driving waveform subsequent to the first driving waveform. The driving element makes the nozzle discharge first liquid droplets, in accordance with the first driving waveform, by being supplied with the driving signal, 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 second liquid droplets are separated into main droplets and satellite droplets following the main droplets.SELECTED DRAWING: Figure 7

Description

The present invention relates to a method of controlling a liquid ejection head and a liquid ejection apparatus.

2. Description of the Related Art Liquid ejecting devices are known that print images by ejecting liquid such as ink from a plurality of nozzles using piezoelectric elements. In this type of liquid ejection device, for example, a piezoelectric element contracts a pressure chamber communicating with the nozzle in response to a drive signal that includes a pulse that causes ink to be ejected from the nozzle, thereby ejecting ink within the pressure chamber from the nozzle. . Furthermore, as a method of controlling a liquid ejecting device, 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 landing on a print medium. For example, Patent Document 1 describes an ejection head that ejects droplets from a nozzle to a predetermined position on a print medium, and a method that allows multiple droplets to coalesce at a distance of 1/2 or less of the distance from the nozzle to the print medium. A printing apparatus is disclosed that includes a control section that outputs a driving waveform to an ejection head.

Japanese Patent Application Publication No. 2017-140761

By the way, ink with a high viscosity has a long trail of ink ejected from a nozzle and is more likely to generate mist than ink with a low viscosity. Note that the mist is a fine mist of ink droplets. When mist is generated, the quality of the printed image is lower than when no mist is generated. Therefore, in liquid ejection devices, it is desired to suppress the generation of mist.

In order to solve the above problems, a method for controlling a liquid ejection head according to the present invention includes a nozzle for ejecting droplets, a pressure chamber communicating with the nozzle, and a pressure applied to the liquid in the pressure chamber according to a drive signal. A method of controlling a liquid ejection head having an ejection section including a drive element that provides fluctuation, wherein the drive signal includes a first drive waveform and a second drive waveform subsequent to the first drive waveform, The supply of a drive signal to the drive element is controlled, and when the drive signal is supplied, the drive element ejects a first droplet from the nozzle according to the first drive waveform, and In accordance with a second drive waveform, a second droplet is sent from the nozzle to the first droplet before the second droplet is separated into a main droplet and a satellite droplet following the main droplet. Discharge so that they coalesce.

Further, the liquid ejection device according to the present invention includes an ejection section including a nozzle that ejects droplets, a pressure chamber communicating with the nozzle, and a drive element that applies pressure fluctuations to the liquid in the pressure chamber according to a drive signal. a control unit that controls supply of the drive signal to the drive element, and the drive signal includes a first drive waveform and a second drive waveform subsequent to the first drive waveform. The drive element includes a waveform, and when supplied with the drive signal, the drive element ejects a first droplet from the nozzle according to the first drive waveform, and ejects the first droplet from the nozzle according to the second drive waveform. A second droplet is ejected from the nozzle such that the second droplet merges with the first droplet before separating into a main droplet and a satellite droplet following the main droplet.

1 is a block diagram showing an example of the configuration of an inkjet printer according to an embodiment of the present invention. FIG. 1 is a perspective view showing an example of a schematic internal structure of an inkjet printer. FIG. 3 is a cross-sectional view for explaining an example of the structure of a discharge section. FIG. 3 is a plan view showing an example of the arrangement of nozzles in the head unit. FIG. 2 is a block diagram showing an example of the configuration of a head unit. 5 is a timing chart for explaining an example of a signal supplied to a head unit. FIG. 7 is an explanatory diagram for explaining an effect when the drive signal shown in FIG. 6 is supplied to the head unit. FIG. 2 is an explanatory diagram showing experimental results of measuring the length of satellite droplets. It is a timing chart for explaining an example of a drive signal in a 1st modification.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each figure, the dimensions and scale of each part are appropriately different from the actual ones. Furthermore, since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached thereto. Unless there is a statement to that effect, it is not limited to these forms.

[1. Embodiment]
In this embodiment, a liquid ejecting apparatus will be described using an example of an inkjet printer that forms an image by ejecting ink onto recording paper. Note that in this embodiment, ink is an example of a "liquid" and recording paper is an example of a "medium."

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

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

The inkjet printer 1 includes a control unit 2 that controls each part of the inkjet printer 1, a head unit 3 that is provided with an ejection section D that ejects ink, and a drive signal that generates a drive signal COM for driving the ejection section D. It has a generation unit 4. 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 for performing maintenance processing for maintaining the ejection section D provided in the head unit 3. have

In this embodiment, it is assumed that the head unit 3 and the drive signal generation unit 4 correspond to each other. For example, the inkjet printer 1 may include a plurality of head units 3 and a plurality of drive signal generation units 4 in one-to-one correspondence with the plurality of head units 3. Alternatively, the inkjet printer 1 may include one head unit 3 and one drive signal generation unit 4 corresponding to the one head unit 3. In this embodiment, it is assumed that the inkjet printer 1 includes four head units 3 and four drive signal generation units 4 in one-to-one correspondence with the four head units 3. However, in the following, for convenience of explanation, as illustrated in FIG. In some cases, the explanation will focus on one drive signal generation unit 4 provided at the same time. Note that the head unit 3 is an example of a "liquid ejection head."

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. The control unit 2 also includes volatile memories such as RAM (Random Access Memory), and non-volatile memories such as ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), or PROM (Programmable ROM). The memory is configured to include one or both of the following.

Although details will be described later, the control unit 2 generates signals for controlling the operations 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 section D. Further, the print signal SI is a digital signal for specifying the type of operation of the ejection section D. Specifically, the print signal SI is a signal that specifies the type of operation of the ejection section D by specifying whether or not the drive signal COM is supplied to the ejection section D. Note that the control unit 2 is an example of a "control unit".

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 a 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.

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

The recording head 32 has M ejection sections D. Note that the value M is a natural number of 1 or more. Hereinafter, the m-th ejection section D among the M ejection sections D provided in the recording head 32 may be referred to as an ejection section D[m]. Here, the variable m is a natural number that satisfies "1≦m≦M". In addition, in the following, when a component, signal, etc. of the inkjet printer 1 corresponds to the ejection part D [m] among the M ejection parts D, the code for representing the component or signal, etc. A subscript [m] may be added.

The supply circuit 31 switches whether or not to supply the drive signal COM to the ejection section D[m] based on the print signal SI. In addition, below, as shown in FIG. 5 etc. mentioned later, the drive signal COM supplied to the discharge part D[m] may be called an individual drive signal Vin[m].

As described above, in this embodiment, the inkjet printer 1 executes printing processing. When printing processing is executed, the control unit 2 generates a signal for controlling the head unit 3, such as a print signal SI, based on the print data IMG. Furthermore, when printing processing is executed, the control unit 2 generates a signal for controlling the drive signal generation unit 4, such as a waveform designation signal dCOM. Further, the control unit 2 generates a signal for controlling the transport unit 7 when printing processing is executed. Accordingly, in the printing process, the control unit 2 controls the transport unit 7 to change the relative position of the recording paper P with respect to the head unit 3, and determines whether or not ink is ejected from the ejection section D[m]. Adjust the ejection amount, ink ejection timing, etc. In this way, the control unit 2 controls each part of the inkjet printer 1 so that an image corresponding to the print data IMG is formed on the recording paper P.

Furthermore, as described above, in this embodiment, the inkjet printer 1 executes maintenance processing. For example, the maintenance process includes a flushing process to discharge ink from the ejection part D, a wiping process to wipe off foreign matter such as ink adhering to the vicinity of the nozzle N of the ejection part D with a wiper, and a tube pump or the like to remove the ink in the ejection part D. This includes a pumping process for suctioning. The nozzle N will be described later with reference to FIG.

The maintenance unit 8 includes a discharged ink receiving section 80 for receiving the discharged ink when the ink in the discharge section D is discharged in the flushing process, and a discharged ink receiving section 80 for receiving the discharged ink when the ink in the discharge section D is discharged in the flushing process, and a foreign matter such as ink attached to the vicinity of the nozzle N of the discharge section D. It has a wiper for wiping away ink and a tube pump for sucking ink, air bubbles, etc. inside the discharge part D. Note that the discharged ink receiving section 80 will be described later with reference to FIG. Further, illustrations of the wiper and tube pump are omitted. Next, a schematic internal structure of the inkjet printer 1 will be described with reference to FIG. 2.

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

As shown in FIG. 2, this embodiment assumes that the inkjet printer 1 is a serial printer. Specifically, when performing printing processing, the inkjet printer 1 transports the recording paper P in the sub-scanning direction and moves the head unit 3 back and forth in the main scanning direction that intersects with the sub-scanning direction. By ejecting ink from D[m], dots corresponding to the print data IMG are formed on the recording paper P.

In the following, for convenience of explanation, a three-axis orthogonal coordinate system having an X axis, a Y axis, and a Z axis that are orthogonal to each other will be introduced as appropriate. Furthermore, hereinafter, the direction pointed by the X-axis arrow will be referred to as the +X direction, and the direction opposite to the +X direction will be referred to as the -X direction. The direction pointed by the Y-axis arrow is called the +Y direction, and the opposite direction to the +Y direction is called the -Y direction. The direction pointed by the Z-axis arrow is called the +Z direction, and the opposite direction to the +Z direction is called the -Z direction. Furthermore, hereinafter, the +X direction and the -X direction may be referred to as the X direction without any particular distinction, and the +Y direction and the -Y direction may be referred to as the Y direction without any particular distinction. Further, the +Z direction and the -Z direction may be referred to as the Z direction without any particular distinction. Further, in this embodiment, the +X direction is the sub-scanning direction, and the +Y direction and the -Y direction are the main scanning direction. Further, in this embodiment, as illustrated in FIG. 2, the −Z direction is the ink ejection direction from the ejection portion D[m].

The inkjet printer 1 according to the present embodiment includes a housing 100 and a carriage 110 that is capable of reciprocating in the Y direction within the housing 100 and on which four head units 3 are mounted.

In this embodiment, it is assumed that the carriage 110 stores four ink cartridges 120 that correspond one-to-one to four color inks: cyan, magenta, yellow, and black. Further, in this embodiment, as described above, it is assumed that the inkjet printer 1 has four head units 3 in one-to-one correspondence with the four ink cartridges 120. Each ejection portion D[m] receives ink supply from the ink cartridge 120 corresponding to the head unit 3 in which the ejection portion D[m] is provided. Thereby, each discharge portion D[m] can fill the inside with the supplied ink and discharge the filled ink from the nozzle N. Note that the ink cartridge 120 may be provided outside the carriage 110.

Further, the inkjet printer 1 according to the present embodiment includes the transport unit 7, as described in FIG. The transport unit 7 includes a carriage transport mechanism 71 for reciprocating the carriage 110 in the Y direction, and a carriage guide shaft 76 for supporting the carriage 110 in a reciprocating manner in the Y direction. Further, the transport unit 7 includes a medium transport mechanism 73 for transporting the recording paper P, and a platen 75 provided in the −Z direction with respect to the carriage 110. For example, in printing processing, the carriage transport mechanism 71 moves the head unit 3 back and forth along the carriage guide shaft 76 together with the carriage 110 in the Y direction, and the medium transport mechanism 73 moves the recording paper P on the platen 75 in the +X direction. transport. Therefore, in the printing process, the conveyance unit 7 changes the relative position of the recording paper P with respect to the head unit 3 by causing the carriage conveyance mechanism 71 and the medium conveyance mechanism 73 to perform the above-described operations. Allows ink to land. In this embodiment, a case is assumed in which a plurality of ink droplets are ejected from the nozzle N, which coalesce before landing on the recording paper P. An ink droplet is, for example, a droplet of ink. Note that the ink droplet is an example of a "droplet."

Next, the general structure of the recording head 32 will be described with reference to FIG. 3.

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

The ejection portion 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 in the cavity CV from the nozzle N by driving the piezoelectric element PZ[m] with the 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."

Cavity CV is a space defined by cavity plate 324, nozzle plate 323 in which nozzle N is formed, and diaphragm 321. Cavity CV communicates with reservoir 325 via ink supply port 326. The reservoir 325 communicates with the ink cartridge 120 corresponding to the discharge portion D[m] via the ink intake port 327.

The piezoelectric element PZ[m] applies pressure fluctuations to the ink within the cavity CV according to the individual drive signal Vin[m]. For example, the piezoelectric element PZ[m] includes 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 the wiring Li to which the individual drive signal Vin[m] is supplied. The lower electrode Zd[m] is electrically connected to the wiring Ld to which the bias voltage signal VBS is supplied. Then, by supplying the individual drive signal Vin[m] to the upper electrode Zu[m], a voltage is applied between the upper electrode Zu[m] and the lower electrode Zd[m]. The piezoelectric element PZ[m] is displaced in the +Z direction or the -Z direction depending on the voltage applied between the upper electrode Zu[m] and the lower electrode Zd[m].

In this way, the piezoelectric element PZ[m] vibrates according to the voltage applied between the upper electrode Zu[m] and the lower electrode Zd[m]. A lower electrode Zd[m] is bonded 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. Then, the volume of the cavity CV and the pressure inside the cavity CV change due to the vibration of the diaphragm 321, and the ink filled inside the cavity CV is ejected from the nozzle N.

In this embodiment, as an example, when the piezoelectric element PZ is displaced in the −Z direction due to the potential of the individual drive signal Vin[m] supplied to the discharge portion D[m] changing from a low potential to a high potential. Assume that That is, in this embodiment, when the potential of the individual drive signal Vin[m] supplied to the ejection section D[m] is a high potential, compared to a case where the potential is a low potential, the ejection section D[m] has a lower potential. Assume that the volume of the cavity CV becomes smaller. Furthermore, 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 referred to as a nozzle surface NSF.

Next, an example of the arrangement of the nozzles N will be described with reference to FIG. 4.

FIG. 4 is a plan view showing an example of the arrangement of nozzles N in the head unit 3. Note that FIG. 4 shows four head units 3 mounted on the carriage 110 and a total of 4M nozzles provided on the four head units 3 when the inkjet printer 1 is viewed from above in the −Z direction. An example of the arrangement of N is shown.

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

Next, an overview of the head unit 3 will be described with reference to FIGS. 5 and 6.

FIG. 5 is a block diagram showing an example of the configuration of the head unit 3. As shown in FIG.

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

The supply circuit 31 includes M switches Wa[1] to Wa[M] in one-to-one correspondence with M discharge portions D[1] to D[M], and a connection state designation circuit 310. The connection state designation circuit 310 designates the connection state of each of the M switches Wa. For example, the connection state designation circuit 310 generates a connection state designation signal Qa that designates on/off of the switch Wa[m] based on the print signal SI supplied from the control unit 2 and at least part of the latch signal LAT. Generate [m].

The switch Wa[m] establishes conduction between the wiring La and the upper electrode Zu[m] of the piezoelectric element PZ[m] provided in the discharge portion D[m] based on the connection state designation signal Qa[m]. and non-conducting. That is, the switch Wa[m] switches conduction or non-conduction between the wiring La and the wiring Li[m] connected to the upper electrode Zu[m] based on the connection state designation signal Qa[m]. In this embodiment, the switch Wa[m] is turned on when the connection state designation signal Qa[m] is at a high level, and turned off when it is at a low level. When the switch Wa[m] is turned on, the drive signal COM supplied to the wiring La connects the wiring Li[m] to the upper electrode Zu[m] of the discharge part D[m] as an individual drive signal Vin[m]. Supplied via

Next, the operation of the head unit 3 will be explained with reference to FIG.

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

FIG. 6 is a timing chart for explaining an example of signals supplied to the head unit 3.

The control unit 2 outputs a latch signal LAT with a pulse PLL. Thereby, the control unit 2 defines a unit period TP as a period from the rising edge of the pulse PLL to the rising edge of the next pulse PLL. The unit period TP is, for example, a period during which one dot corresponding to each nozzle N is formed on the recording paper P. In this embodiment, two ink droplets are ejected from the nozzle N during the same unit period TP, and one dot is formed on the recording paper P by combining the two ink droplets before landing on the recording paper P. Assume that The unit period TP is, for example, a driving cycle of the M discharge units D. In this embodiment, it is assumed that one cycle of the drive signal COM is a unit period TP.

The print signal SI according to the present embodiment includes M individual designation signals Sd[1] to Sd[M] that correspond one-to-one to the M ejection units D[1] to D[M]. The individual designation signal Sd[m] designates the driving mode of the ejection section D[m] in each unit period TP when the inkjet printer 1 executes printing processing or flushing processing. For example, the control unit 2 synchronizes the print signal SI including M individual designation signals Sd[1] to Sd[M] with the clock signal CL and sends it to the connection state designation circuit 310 prior to each unit period TP. supply Then, the connection state designation circuit 310 generates the connection state designation signal Qa[m] based on the individual designation signal Sd[m] in the unit period TP. In this way, the control unit 2 supplies the print signal SI including the M individual designation signals Sd[1] to Sd[M] to the connection state designation circuit 310, thereby controlling each of the M piezoelectric elements PZ. control the supply of the drive signal COM.

For example, in the unit period TP during which printing processing is executed, the ejection unit D[m] is selected as either the ejection unit D that forms dots or the ejection unit D that does not form dots, according to the individual designation signal Sd[m]. specified.

The drive signal COM has waveforms PD1 and PD2 arranged in time series. In the example shown in FIG. 6, waveform PD2 is a waveform after waveform PD1. That is, the drive signal COM has a waveform PD1 and a waveform PD2 subsequent to the waveform PD1. Further, the drive signal COM connects the waveform PW1 in which the potential of the drive signal COM is maintained at the potential V0 at the start of the waveform PD1 before the start of the waveform PD1, and the waveform PD1 and the waveform PD2. The waveform PW2 includes a waveform PW2 in which the potential of the drive signal COM is maintained at the potential V0 of the drive signal COM. In this way, the drive signal COM has, for example, a pulse of the waveform PD1 and a pulse of the waveform PD2 provided in the unit period TP.

Waveforms PD1 and PD2 are examples of "a plurality of 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". That is, waveform PD1 is an example of a "first drive waveform," and waveform PD2 is an example of a "second drive waveform." Further, the waveform PW1 is an example of a "first standby waveform," and the waveform PW2 is an example of a "second standby waveform." Below, waveforms PD1 and PD2 are also referred to as waveform PD without particular distinction. Similarly, waveforms PW1 and PW2 are also referred to as waveform PW.

The details will be described later, but the waveforms PD1 and PD2 are waveforms for ejecting ink droplets from the nozzle N. For example, in the same unit period TP, the first ink droplet ejected from the nozzle N according to the waveform PD1 and the second ink droplet ejected from the nozzle N according to the waveform PD2 arrive on the recording paper P. Combine. The first ink droplet is an example of a "first droplet," and the second ink droplet is an example of a "second droplet." In the following, the first ink drop is also referred to as a first ink drop, and the second ink drop is also referred to as a second ink drop. First, waveform PD1 will be explained.

The waveform PD1 is, for example, a waveform in which the potential of the drive signal COM is from the potential V0, passes through the potential VL, the potential V1, and the potential VH, and then returns to the potential V0. The potential V0 is, for example, a reference potential. The potential VL is lower than the potential V0 and is the lowest potential of the waveform PD1. Potential VH is higher than potential V0 and is the highest potential of waveform PD1. Further, the potential V1 is a potential between the potential V0 and the potential VL. Note that the potential VL is an example of a "first potential," the potential VH is an example of a "second potential," and the potential V1 is an example of a "first intermediate potential." Each of the potential VL, the potential VH, the potential V1, the potential V0, and the potential V2, which will be described later, is determined based on, for example, the ink ejection characteristics of the ejection portion D. Examples of the ink ejection characteristics include the amount of ink ejected as ink droplets and the speed of the ejected ink droplets.

Below, in the waveform PD1, a portion where the potential of the drive signal COM changes from the potential V0 to the potential VL is also referred to as a waveform Pep1, and a portion where the potential of the drive signal COM is maintained at the potential VL is also referred to as a waveform Peh1. be done. Furthermore, in the waveform PD1, a portion where the potential of the drive signal COM changes from the potential VL to the potential VH is also referred to as a waveform Pcn1, and a portion where the potential of the drive signal COM is maintained at the potential VH is also referred to as a waveform Pch1. Ru. Furthermore, a portion of the waveform PD1 where the potential of the drive signal COM changes from the potential VH to the potential V0 is also referred to as a waveform Pdm1. That is, waveform PD1 includes waveforms Pep1, Peh1, Pcn1, Pch1, and Pdm1.

The waveform Pep1 is a waveform for displacing the piezoelectric element PZ in the +Z direction. That is, the waveform Pep1 is a waveform in which the potential of the drive signal COM changes so as to expand the volume of the cavity CV. Therefore, the waveform Pep1 corresponds to an expansion element that changes the potential of the drive signal COM in order to drive the piezoelectric element PZ to expand the volume of the cavity CV, among the multiple elements that make up the pulse of the waveform PD1. do. When the volume of the cavity CV expands, the surface of the ink inside the nozzle N is drawn in the +Z direction, which is the opposite direction to the ejection direction. Hereinafter, pulling 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 the waveform Pep1 is an example of a "first expansion waveform."

The waveform Peh1 is a waveform for maintaining the position of the piezoelectric element PZ in the Z direction. For example, the waveform Peh1 maintains the potential of the drive signal COM in order to drive the piezoelectric element PZ so as to maintain the volume of the cavity CV expanded by the waveform Pep1 among the plurality of elements making up the pulse of the waveform PD1. This corresponds to the expansion maintenance element. In the example shown in FIG. 6, the waveform Peh1 is a waveform that connects the waveform Pep1 and the waveform Pcn1, and maintains the potential of the drive signal COM at the potential VL at the end of the waveform Pep1. Note that the waveform Peh1 is an example of a "first expansion maintenance waveform."

The waveform Pcn1 is a waveform for displacing the piezoelectric element PZ in the −Z direction. That is, the waveform Pcn1 is a waveform in which the potential of the drive signal COM changes so as to contract the volume of the cavity CV. Therefore, the waveform Pcn1 corresponds to a contraction element that changes the potential of the drive signal COM in order to drive the piezoelectric element PZ so as to contract the volume of the cavity CV, among the plurality of elements making up the pulse of the waveform PD1. do. When the volume of the cavity CV contracts, the surface of the ink inside the nozzle N is pushed out in the −Z direction, which is the ejection direction. Hereinafter, pushing out the surface of the ink inside the nozzle N in the ejection direction may be referred to as pushing.

Further, the waveform Pcn1 includes a waveform PcnF1 in which the potential of the drive signal COM changes from the potential VL to the potential V1, a waveform PcnS1 in which the potential of the drive signal COM is maintained at the potential V1, and a waveform PcnS1 in which the potential of the drive signal COM changes from the potential V1 to the potential V1. It includes a waveform PcnT1 that changes to VH. Therefore, in the waveform Pcn1, the volume of the cavity CV is contracted in two stages. Note that the waveform Pcn1 is an example of a "first contraction waveform." Further, the waveform PcnF1 is an example of a "first partial waveform," the waveform PcnS1 is an example of a "second partial waveform," and the waveform PcnT1 is an example of a "third partial waveform."

Furthermore, in the present embodiment, as described in FIG. 3, when the potential of the individual drive signal Vin[m] is high, the cavity provided in the ejection part D[m] is It is assumed that the CV volume becomes small. Therefore, when the drive signal COM is supplied to the ejection part D[m] as the individual drive signal Vin[m], the waveform Pcn1 in which the potential of the individual drive signal Vin[m] changes from a low potential to a high potential causes the ejection Ink in portion D[m] is ejected from nozzle N as the first ink droplet.

In this embodiment, as described above, the volume of the cavity CV is contracted in two stages according to the waveform Pcn1. Hereinafter, among the waveforms corresponding to the contraction elements, the waveform in which the volume of the cavity CV is contracted in two stages is also referred to as a two-stage push waveform. In addition, among the waveforms corresponding to the contraction element, a waveform in which the volume of the cavity CV is contracted in one step without being divided into multiple steps will be referred to as a simple push waveform in comparison with a two-step push waveform. There are cases.

In this embodiment, since the waveform Pcn1 is a two-step push waveform, the amount of ink droplets ejected by the first push of the waveform PcnF1 is smaller than the amount of ink droplets ejected by the simple push waveform. Therefore, in this embodiment, among the ink droplets, the speed of the main droplet forming a dot is slower than the speed of the ink droplet ejected by the simple push waveform. Further, in this embodiment, since the potential of the drive signal COM is maintained at the potential at the end of the waveform PcnF1 by the waveform PcnS1, a constriction occurs in the satellite droplet following the main droplet among the ink droplets. Then, the satellite droplet is separated from the ink in the nozzle N by, for example, the second stage push using the waveform PcnT1. Furthermore, the speed of the satellite droplet increases due to the second push. This makes it easier for the satellite droplets to coalesce into the main droplet, and some of the satellite droplets are absorbed by the main droplet. As a result, in this embodiment, the size of the satellite droplet can be reduced while increasing the size of the main droplet.

The waveform Pch1 is a waveform for maintaining the position of the piezoelectric element PZ in the Z direction. For example, the waveform Pch1 maintains the potential of the drive signal COM in order to drive the piezoelectric element PZ so as to maintain the volume of the cavity CV contracted by the waveform Pcn1 among a plurality of elements making up the pulse of the waveform PD1. This corresponds to the contraction maintenance element. In the example shown in FIG. 6, the waveform Pch1 is a waveform in which the potential of the drive signal COM is maintained at the potential VH at the end of the waveform Pch1. Note that the waveform Pch1 is an example of a "first contraction maintenance waveform."

The waveform Pdm1 is a waveform for displacing the piezoelectric element PZ in the +Z direction. For example, the waveform Pdm1 is a waveform in which the potential of the drive signal COM changes so as to expand the volume of the cavity CV that has been contracted by the waveform Pcn1 and dampen the residual vibration of the ink in the cavity CV. That is, in the waveform Pdm1, the potential of the drive signal COM changes from the potential VH to the potential V0 so as to expand the volume of the cavity CV maintained by the waveform Pch1 and dampen the residual vibration of the ink in the cavity CV. It is a waveform. Therefore, the waveform Pdm1 is one of the plurality of elements making up the pulse of the waveform PD1 in order to drive the piezoelectric element PZ so as to expand the volume of the cavity CV and attenuate the residual vibration of the ink within the cavity CV. , corresponds to a vibration damping element that changes the potential of the drive signal COM. Note that the waveform Pdm1 is an example of a "first damping waveform."

For example, the vibrations of the ink within the cavity CV that have been generated up to the waveform Pcn1 are combined with the vibrations that are generated by the waveform Pdm1 at a timing that corresponds to the length of the waveform Pch1. That is, the piezoelectric element PZ[m] expands the volume of the cavity CV in accordance with the potential change of the waveform Pdm1, and damps the vibration of the ink within the cavity CV. In this way, the waveform PD1 is a so-called pull-push-pull waveform.

Next, waveform PD2 will be explained. Waveform PD2 is also a pull-push-pull waveform similar to waveform PD1. Detailed description of elements similar to waveform PD1 will be omitted.

The waveform PD2 is, for example, a waveform in which the potential of the drive signal COM returns from the potential V0 to the potential V0 through the potential VL, the potential V2, and the potential VH. Potential V2 is a potential between potential V0 and potential VL. For example, the potentials V1 and V2 are set such that the speed of the second ink droplet ejected from the nozzle N according to the waveform PD2 is faster than the speed of the first ink droplet ejected from the nozzle N according to the waveform PD1. It will be done. Note that the potential V2 is an example of a "second intermediate potential".

Below, in the waveform PD2, a portion where the potential of the drive signal COM changes from the potential V0 to the potential VL is also referred to as a waveform Pep2, and a portion where the potential of the drive signal COM is maintained at the potential VL is also referred to as a waveform Peh2. be done. Furthermore, in the waveform PD2, a portion where the potential of the drive signal COM changes from the potential VL to the potential VH is also referred to as a waveform Pcn2, and a portion where the potential of the drive signal COM is maintained at the potential VH is also referred to as a waveform Pch2. Ru. Furthermore, a portion of the waveform PD2 where the potential of the drive signal COM changes from the potential VH to the potential V0 is also referred to as a waveform Pdm2. That is, waveform PD2 includes waveforms Pep2, Peh2, Pcn2, Pch2, and Pdm2. Furthermore, the waveform Pcn2 includes a waveform PcnF2 in which the potential of the drive signal COM changes from the potential VL to the potential V2, a waveform PcnS2 in which the potential of the drive signal COM is maintained at the potential V2, and a waveform PcnS2 in which the potential of the drive signal COM changes from the potential V2 to the potential V2. It includes a waveform PcnT2 that changes to VH.

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

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

Below, waveforms Pep1 and Pep2 are also referred to as waveform Pep without particular distinction. Similarly, waveforms Peh1 and Peh2 are also referred to as waveform Peh, and waveforms Pcn1 and Pcn2 are also referred to as waveform Pcn. Further, waveforms Pch1 and Pch2 are also referred to as waveform Pch, and waveforms Pdm1 and Pdm2 are also referred to as waveform Pdm. Further, waveforms PcnF1 and PcnF2 are also referred to as waveform PcnF, waveforms PcnS1 and PcnS2 are also referred to as waveform PcnS, and waveforms PcnT1 and PcnT2 are also referred to as waveform PcnT.

Here, in this embodiment, each element of waveforms PD1 and PD2 is determined so that the speed of the second ink droplet according to waveform PD2 is faster than the speed of the first ink droplet according to waveform PD1. Thereby, in this embodiment, the second ink droplet can be combined with the first ink droplet according to the waveform Pcn1 before it lands on the recording paper P. Below, among the settings of each element of waveforms PD1 and PD2 and the settings of waveform PW, setting conditions for making the speed of the second ink droplet according to waveform PD2 faster than the speed of the first ink droplet according to waveform PD1 will be described. I will mainly explain.

The first setting condition is that the amount of potential change in waveform PcnF2 is larger than the amount of potential change in waveform PcnF1. For example, the potential V2 at the end of the waveform PcnF2 is higher than the potential V1 at the end of the waveform PcnF2. In this way, under the first setting condition, the waveform PcnF that performs the first stage of contraction of the volume of the cavity CV that is performed in two stages, that is, when an ink droplet is ejected from the nozzle N, The amount of potential change in the waveform PcnF is adjusted. When the amount of potential change in the waveform PcnF that causes ink droplets to be ejected from the nozzle N is large, the ink droplet ejection speed becomes faster than when the amount of potential change in the waveform PcnF is small. Therefore, according to the first setting condition, the speed of the second ink droplet according to the waveform PD2 is faster than the speed of the first ink droplet according to the waveform PD1.

The second setting condition is that the amount of potential change per unit time of waveform PcnT1 is smaller than the amount of potential change per unit time of waveform PcnT2. In this way, under the second setting condition, the waveform PcnT performs the second stage of contraction of the volume of the cavity CV, which is performed in two stages, that is, the ink droplet is separated from the ink in the nozzle N. The amount of potential change per unit time of the waveform PcnT is adjusted. When the amount of potential change per unit time of the waveform PcnT that separates the ink droplet from the ink in the nozzle N is small, the ejection speed of the ink droplet becomes slower than when the amount of potential change per unit time of the waveform PcnT is large. . Therefore, according to the second setting condition, the speed of the second ink droplet according to the waveform PD2 is faster than the speed of the first ink droplet according to the waveform PD1.

The third setting condition is that the difference between the period Tsm1 before ink ejection in the waveform PD1 and a period half the natural vibration period of the ejection part D is the difference between the period Tsm2 before ink ejection in the waveform PD2 and the period Tsm1 before ink ejection in the waveform PD2. This is larger than the difference from the period of one half of the natural vibration period of D. For example, the period Tsm1 is a period from the start of the waveform Pep1 to the start of the waveform Pcn1, and is the sum of the period Tep1 of the waveform Pep1 and the period Teh1 of the waveform Peh1. Further, the period Tsm2 is a period from the start of the waveform Pep2 to the start of the waveform Pcn2, and is a period that is the sum of the period Tep2 of the waveform Pep2 and the period Teh2 of the waveform Peh2. In this way, under the first setting condition, the period Tsm1 is the sum of the period Tep1 of the waveform Pep1 and the period Teh1 of the waveform Peh1, the period Tsm2 is the sum of the period Tep2 of the waveform Pep2 and the period Teh2 of the waveform Peh2, and The relationship between part D and the natural vibration period is adjusted. Below, periods Tsm1 and Tsm2 are also referred to as period Tsm without particular distinction.

Here, the natural vibration period of the discharge portion D is, for example, a natural vibration period that represents the natural vibration period of the M discharge portions D. For example, the natural vibration period representing the natural vibration period of the M discharge portions D may be the natural vibration period of one of the M discharge portions D. Alternatively, the natural vibration period representing the natural vibration period of the M discharge portions D may be the average value of the natural vibration periods of the N discharge portions D, or the natural vibration period of the N discharge portions D. It may be the maximum value or the minimum value. Note that the value N is a natural number that satisfies "2≦N≦M."

If the difference between the period Tsm from the start of the waveform Pep to the start of the waveform Pcn and the period that is half of the natural vibration period of the discharge section D is small, the period Tsm and the period that is half the natural vibration period of the discharge section D The ink droplet ejection speed becomes faster than when the difference from the period is large. Therefore, according to the third setting condition, the speed of the second ink droplet according to the waveform PD2 is faster than the speed of the first ink droplet according to the waveform PD1.

In the example shown in FIG. 6, by making the period Teh1 of the waveform Peh1 shorter than the period Teh2 of the waveform Peh2, the difference between the period Tsm and the period of half of the natural vibration period of the discharge part D can be calculated from the waveform The waveform PD1 is made larger than PD2.

The fourth setting condition is that the period Tpw2 of the waveform PW2 is shorter than the period Tpw1 of the waveform PW1. Further, the fifth setting condition is that the period Tpw2 of the waveform PW2 has a length of 1/6 or more and 1/5 or less of the natural vibration period of the discharge portion D. The speed of the second ink droplet is adjusted, for example, by adjusting the period Tpw2 of the waveform PW2. Therefore, by using one or both of the fourth setting condition and the fifth setting condition, the speed of the second ink droplet according to the waveform PD2 can be made faster than the speed of the first ink droplet according to the waveform PD1.

The sixth setting condition is that the amount of potential change per unit time of waveform Pep2 is larger than the amount of potential change per unit time of waveform Pep1. When the amount of potential change per unit time of the waveform Pep corresponding to the expansion element is large, the ejection speed of the ink droplet becomes faster than when the amount of potential change per unit time of the waveform Pep is small. Therefore, according to the seventh setting condition, the speed of the second ink droplet based on waveform PD2 is faster than the speed of the first ink droplet based on waveform PD1.

Note that the setting conditions for making the speed of the second ink droplet according to waveform PD2 faster than the speed of the first ink droplet according to waveform PD1 are not limited to the above-mentioned first to sixth setting conditions. For example, a setting condition other than the above-mentioned setting condition may be that the amount of change in potential of waveform Pep2 is larger than the amount of change in potential of waveform Pep1. Specifically, the potential at the start of waveform Pep2 may be higher than the potential at the start of waveform Pep1. Moreover, in this embodiment, all the setting conditions among the plurality of setting conditions described above may be adopted, or a part of the plurality of setting conditions may be adopted.

Furthermore, in this embodiment, each of the waveforms PcnF, PcnS, and PcnT of the waveforms Pcn1 and Pcn2 is set so that the length of the satellite droplet is short. For example, the period TcnS1 of the waveform PcnS1 and the period TcnS2 of the waveform PcnS2 may have a length of 1/5 or more and 1/4 or less of the natural vibration period of the discharge portion D. In this embodiment, by adjusting the lengths of the periods TcnS1 and TcnS2, it is possible to adjust the interval from the first push to the second push. That is, in this embodiment, by adjusting the lengths of the periods TcnS1 and TcnS2, the second stage push can be performed at the timing when the length of the satellite droplet becomes shorter.

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

In this manner, in this embodiment, the length of the satellite droplet can be shortened, so that generation of mist can be suppressed. As a result, in this embodiment, it is possible to suppress deterioration in the quality of printed images.

Next, with reference to FIG. 7, the operation when the drive signal COM shown in FIG. 6 is supplied to the head unit 3 will be described.

FIG. 7 is an explanatory diagram for explaining the effect when the drive signal COM shown in FIG. 6 is supplied to the head unit 3. Note that FIG. 7 schematically shows a process in which the first ink droplet Idp1 ejected from the nozzle N according to the waveform PD1 and the second ink droplet Idp2 ejected from the nozzle N according to the waveform PD2 are combined. There is. Further, the broken line arrows in the figure indicate the forces applied to the ink droplets Idp1, Idp2, Idp12, etc. Note that the ink droplet Idp12 is an ink droplet that is a combination of the first ink droplet Idp1 and the second ink droplet Idp2.

In the following, ink droplets such as ink droplets Idp1, Idp2, and Idp12 are also referred to as ink droplets Idp without particular distinction. In addition, in the following, the part of the edge of the ink droplet Idp in the -Z direction, which is the ejection direction, is also referred to as the tip of the ink droplet Idp, and the part in the +Z direction, which is the opposite direction to the ejection direction, is referred to as the tip of the ink droplet Idp. Also called the rear end of.

For example, at time T10, application of waveform PcnF1 to piezoelectric element PZ is started. As a result, the first ink droplet Idp1 starts to be ejected from the nozzle N. At time T20, the tip of the first ink droplet Idp1 moves in the -Z direction more than 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 inside the nozzle N.

At time T30, the first ink droplet Idp1 separates from the ink inside the nozzle N. That is, the first ink droplet Idp1 separates from the ink in the nozzle N before combining with the second ink droplet Idp2. Therefore, in this embodiment, the influence of the first ink droplet Idp1 on the ejection 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. Thereby, for example, in the present embodiment, it is possible to suppress the setting of the waveform PD2 for ejecting the desired amount of second ink droplets Idp2 from becoming complicated.

At time T40, the leading end of the second ink droplet Idp2 is located in the -Z direction relative to the nozzle surface NSF, and is located in the +Z direction relative to the trailing end of the first ink droplet Idp1. That is, at time T40, the second ink droplet Idp2 has not merged with the first ink droplet Idp1. Furthermore, at time T40, the second ink droplet Idp2 has not separated from the ink inside the nozzle N.

At time T50, the leading end of the second ink droplet Idp2 merges with the trailing end of the first ink droplet Idp1. As a result, an ink droplet Idp12 is formed by combining 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 inside the nozzle N. That is, the second ink droplet Idp2 is combined with the first ink droplet Idp1 before separating from the ink in the nozzle N.

Furthermore, at time T50, the first ink droplet Idp1 has not been separated into a main droplet and a satellite droplet. That is, the first ink droplet Idp1 is combined 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 is combined with the satellite droplet of the first ink droplet Idp1 after the first ink droplet Idp1 is separated into a main droplet and a satellite droplet, The velocity of the second ink drop Idp2 that has merged with the satellite drop decreases. In this case, the second ink droplet Idp2 may not catch up with the main droplet of the first ink droplet Idp1 by the time it lands on the recording paper P, and may not combine with the first ink droplet Idp1. In contrast, in the present embodiment, as described above, the first ink droplet Idp1 is not separated into the main droplet and the satellite droplet, but is combined with the second ink droplet Idp2. As a result, in the present embodiment, it is possible to suppress the speed of the second ink droplet Idp2 from decreasing, and it is possible to prevent the second ink droplet Idp2 from being combined with the first ink droplet Idp1 before landing on the recording paper P. can.

Furthermore, at time T50, the second ink droplet Idp2 has not been separated into a main droplet and a satellite droplet. That is, the second ink droplet Idp2 is combined with the first ink droplet Idp1 before being separated into a main droplet and a satellite droplet.

For example, at time T50, the tip of the second ink droplet Idp2 comes into contact with the first ink droplet Idp1, so that the speed of the tip of the second ink droplet Idp2 increases. As the speed of the tip of the second ink droplet Idp2 increases, a reaction force is generated between the tip of the second ink droplet Idp2 and the trailing portion that is the trailing edge of the second ink droplet Idp2. . The reaction force generated between the leading end and trailing end of the second ink droplet Idp2 reduces the speed of the trailing portion of the second ink droplet Idp2. This suppresses the length of the trailing portion from increasing.

Here, when 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 twice the distance Z10 from the nozzle surface NSF. The distance Z10 is the distance from the nozzle surface NSF to the tip of the first ink droplet Idp1 when the first ink droplet Idp1 is separated from the ink in the nozzle N. Note that the distance twice the distance Z10 is an example of a "first distance." In the example shown in FIG. 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 are combined is shorter than the distance Z10. That is, the second ink droplet Idp2 may be combined with the first ink droplet Idp1 by a distance Z10 from the nozzle surface NSF.

At time T60, the second ink droplet Idp2 separates from the ink inside the nozzle N. That is, the ink droplet Idp12, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2, is separated from the ink in the nozzle N. Note that a force in the +Z direction is applied to a portion of the trailing portion that is the rear end portion of the ink droplet Idp12 that is close to the tip portion of the ink droplet Idp12 due to the reaction force generated at time T50.

Further, 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 the present embodiment, when the ink droplet Idp12, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2, is separated from the ink in the nozzle N, among the ink droplets Idp12, the ink droplet in the nozzle N is The cut portion with the ink is pulled in the -Z direction. As a result, a force in the −Z direction is applied to a portion of the trailing portion of the ink droplet Idp12 that is close to the nozzle surface NSF. As a result, the speed of the trailing end portion of the trailing portion of the ink droplet Idp12 increases.

At time T70, the ink droplet Idp12 is separated into a main droplet Mdp12 and a satellite droplet Sdp12 following the main droplet Mdp12. That is, after the second ink droplet Idp2 is combined with the first ink droplet Idp1, the ink droplet Idp12, which is the combination of the first ink droplet Idp1 and the second ink droplet Idp2, is combined with the main droplet Mdp12 and the satellite droplet Sdp12. Separate into Since 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, the speed of the satellite droplet Sdp12 decreases. Therefore, for example, as shown at time T80, the length of the satellite droplet Sdp12 is suppressed from increasing.

Further, when focusing on the position of the tip of the ink droplet Idp, the ink droplet Idp12, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2, becomes the main droplet Mdp12 by a predetermined distance from the nozzle surface NSF. It may be separated into satellite droplet Sdp12. In the example shown in FIG. 7, the distance Z30 from the nozzle surface NSF to the tip of the ink droplet Idp12 when the ink droplet Idp12 is separated into the main droplet Mdp12 and the satellite droplet Sdp12 is shorter than twice the distance Z10. That is, the predetermined distance may be twice the distance Z10.

In this manner, in this embodiment, the piezoelectric element PZ ejects the first ink droplet Idp1 from the nozzle N according to the waveform PD1 by being supplied with the drive signal COM. Furthermore, the piezoelectric element PZ causes the second ink droplet Idp2 from the nozzle N to coalesce into the first ink droplet Idp1 before the first ink droplet Idp1 lands on the recording paper P according to the waveform PD2. , discharge. Note that in the example shown in FIG. 7, the piezoelectric element PZ separates the second ink droplet Idp2 from the nozzle N according to the waveform PD2, and the second ink droplet Idp2 is a main droplet and a satellite droplet following the main droplet. The ink droplets are ejected so as to coalesce into a first ink droplet Idp1 before separating into two ink droplets.

In this embodiment, by supplying the drive signal COM including the two waveforms PD1 and PD2 including the two-stage push waveform to the piezoelectric element PZ, the length of the satellite droplet Sdp12 can be adjusted while forming the desired amount of the main droplet Mdp12. can be suppressed from becoming too long.

Further, in the present embodiment, after the waveform PD1 is supplied to the piezoelectric element PZ until the time T30 when the first ink droplet Idp1 separates from the ink in the nozzle N, the waveform corresponding to the expansion element of the waveform PD2 Supply of Pep2 to the piezoelectric element PZ may be started. Also in this case, it is possible to suppress the length of the satellite droplet Sdp12 from increasing.

Next, with reference to FIG. 8, experimental results of measuring the length of satellite droplets will be described.

FIG. 8 is an explanatory diagram showing experimental results of measuring the length of satellite droplets. Note that FIG. 8 shows the results of an ink ejection experiment when the viscosity of the ink in the nozzle N measured at a shear rate of 200 [1/sec] was 100 milliPascal seconds or more. The vertical axis in FIG. 8 indicates the length of the satellite droplet, and the horizontal axis in FIG. 8 indicates the number of ink ejections in the unit period TP. In addition, the white circles in the figure indicate the length of the satellite droplet when the piezoelectric element PZ is driven by the waveform PD including the two-stage push waveform, and the black circles in the figure indicate the length of the satellite droplet when the piezoelectric element PZ is driven by the waveform PD including the two-stage push waveform. The length of the satellite droplet is shown when the piezoelectric element PZ is driven by a simple push waveform. Note that, as explained in FIG. 6, the simple push waveform is a waveform in which the volume of the cavity CV is contracted in one step without being divided into multiple steps.

When ejecting ink with high viscosity using a simple push waveform, it is necessary to increase the amount of potential change in the waveform Pcn to eject ink at a predetermined speed, compared to when ejecting ink with low viscosity using a simple push waveform. be. When the amount of potential change in waveform Pcn is large, the ink trail becomes longer and the length of the satellite droplet becomes longer than when the amount of potential change in waveform Pcn is small. For example, as shown in FIG. 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 about 1100 [μm].

On the other hand, 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 about 300 [μm]. That is, by using the two-stage push waveform, the length of the satellite droplet can be made approximately 800 [μm] shorter than when the simple push waveform is used.

Further, 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 about 200 [μm]. Further, even when the piezoelectric element PZ is driven by the waveform PD including the two-stage push waveform so that ink is ejected three times in the unit period TP, the length of the satellite droplet is about 200 [μm]. As described above, in this embodiment, even when the number of times of ink ejection in the unit period TP is increased, the length of the satellite droplet can be increased by driving the piezoelectric element PZ with the waveform PD including the two-stage push waveform. It is possible to prevent this from happening.

In this way, in this embodiment, even when the viscosity of the ink in the 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 increasing. I can do it. Note that, as described above, FIG. 8 shows the measurement results of the length of satellite droplets when ink having a viscosity of 100 milliPascal seconds or more is ejected. That is, in this embodiment, even when the viscosity of the ink in the nozzle N is 100 milliPascal seconds or more, it is possible to suppress the length of the satellite droplet from increasing.

As described above, in this embodiment, the inkjet printer 1 includes the head unit 3 and the control unit 2. The head unit 3 includes a nozzle N that discharges ink, a cavity CV that communicates with the nozzle N, and a discharge section D that includes a piezoelectric element PZ that applies pressure fluctuations to the ink within the cavity CV in accordance with 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 a waveform PD1 and a waveform PD2 subsequent to the waveform PD1.

In this embodiment, the piezoelectric element PZ ejects the first ink droplet Idp1 from the nozzle N according to the waveform PD1 by being supplied with the drive signal COM. Furthermore, the piezoelectric element PZ causes the second ink droplet Idp2 from the nozzle N to coalesce into the first ink droplet Idp1 before the first ink droplet Idp1 lands on the recording paper P according to the waveform PD2. , discharge. For example, in the present embodiment, the piezoelectric element PZ controls the second ink droplet Idp2 from the nozzle N according to the waveform PD2, the second ink droplet Idp2 from the nozzle N to the main droplet, and a satellite droplet following the main droplet. The ink droplets are ejected so as to coalesce into a first ink droplet Idp1 before separating into two ink droplets. In this embodiment, after the second ink droplet Idp2 is combined with the first ink droplet Idp1, the ink droplet Idp12, which is the combination of the second ink droplet Idp2 and the first ink droplet Idp1, becomes the main droplet Mdp12. and satellite droplet Sdp12.

Thus, in this embodiment, the second ink droplet Idp2 coalesces into the first ink droplet Idp1 before separating into a main droplet and a satellite droplet. Therefore, in the present embodiment, as the second ink droplet Idp2 comes into contact with the first ink droplet Idp1, the second ink droplet Idp2 is generated between the main droplet and the satellite droplet before they are separated from each other. A reaction force is applied to the satellite drop. By applying a reaction force to the satellite droplet, the length of the satellite droplet becomes shorter. That is, 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, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2, from increasing. . Therefore, in this embodiment, generation of mist can be suppressed. As a result, in this embodiment, it is possible to suppress deterioration in the quality of printed images.

Further, in this embodiment, the first ink droplet Idp1 may be separated from the ink in the nozzle N before being combined with the second ink droplet Idp2. In this case, the influence of the first ink droplet Idp1 on the ejection 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. Thereby, in this embodiment, a desired ejection amount can be ensured in ejecting the second ink droplet Idp2.

Further, in the present embodiment, the first ink droplet Idp1 may be combined with the second ink droplet Idp2 without being separated into a main droplet and a satellite droplet. For example, when a satellite droplet separated from the main droplet of the first ink droplet Idp1 and the second ink droplet Idp2 are combined, the speed of the second ink droplet Idp2 decreases. In this case, the second ink droplet Idp2 may not catch up with the main droplet of the first ink droplet Idp1 by the time it lands on the recording paper P, and may not combine with the first ink droplet Idp1. Therefore, in the present embodiment, for example, the piezoelectric element PZ is configured to move the first ink droplet Idp1 so that the first ink droplet Idp1 is combined with the second ink droplet Idp2 without separating into a main droplet and a satellite droplet. Idp1 and the second ink droplet Idp2 may be ejected from the nozzle N. In this case, it is possible to prevent the speed of the second ink droplet Idp2 from decreasing, and it is possible to prevent the second ink droplet Idp2 from coalescing into the first ink droplet Idp1 before landing on the recording paper P. .

Furthermore, in the present embodiment, the second ink droplet Idp2 may be combined 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, which is a combination of the first ink droplet Idp1 and the second ink droplet Idp2, is separated from the ink in the nozzle N, the ink droplet Idp12 is separated from the ink in the nozzle N. The cut portion is pulled in the −Z direction, which is the discharge direction. As a result, a force in the −Z direction is applied to a portion of the trailing portion of the ink droplet Idp12 that is close to the nozzle surface NSF. As a result, the speed of the trailing end portion of the trailing portion of the ink droplet Idp12 increases. In this case, it is possible to suppress the length of the trailing portion of the ink droplet Idp12 from increasing, and it is possible to suppress the length of the satellite droplet Sdp12 from increasing.

Further, in the present embodiment, the second ink droplet Idp2 may be combined with the first ink droplet Idp1 within 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 is separated from the ink in the nozzle N. Also in this case, it is possible to suppress the length of the satellite droplet Sdp12 from increasing.

In the present embodiment, the waveform PD1 includes a waveform Pep1 in which the potential of the drive signal COM changes to the potential VL so as to expand the volume of the cavity CV, and a waveform Pep1 in which the potential of the drive signal COM changes to the potential VL so as to expand the volume of the cavity CV. It includes a waveform Pcn1 in which the potential changes from the potential VL to the potential VH. The waveform PD2 includes a waveform Pep2 in which the potential of the drive signal COM changes to the potential VL so as to expand the volume of the cavity CV, and a waveform Pep2 in which the potential of the drive signal COM changes from the potential VL to the potential VH so as to contract the volume of the cavity CV. It includes a waveform Pcn2 that changes to . Waveform Pcn1 includes waveform PcnF1 in which the potential of drive signal COM changes from potential VL to potential V1 between potential VL and potential VH, waveform PcnS1 in which the potential of drive signal COM is maintained at potential V1, and drive signal COM. includes a waveform PcnT1 in which the potential of PcnT1 changes from potential V1 to potential VH. Waveform Pcn2 includes waveform PcnF2 in which the potential of drive signal COM changes from potential VL to potential V2 between potential VL and potential VH, waveform PcnS2 in which the potential of drive signal COM is maintained at potential V2, and drive signal COM. PcnT2 includes a waveform PcnT2 in which the potential of PcnT2 changes from potential V2 to potential VH.

As described above, 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 of the cavity CV is contracted in two stages. That is, in this embodiment, the piezoelectric element PZ is driven by the drive signal COM including two waveforms PD1 and PD2 including a two-stage push waveform. Thereby, in this embodiment, it is possible to form a desired amount of main droplets Mdp12 while suppressing an increase in the length of satellite droplets Sdp12.

Further, in the present embodiment, the period TcnS1 of the waveform PcnS1 and the period TcnS2 of the waveform PcnS2 may have a length of 1/5 or more and 1/4 or less of the natural vibration period of the discharge portion D. Also in this case, the length of the satellite droplet Sdp12 can be shortened.

Further, in the present embodiment, the amount of potential change in the waveform PcnF1 and the amount of potential change in the waveform PcnF2 may be one-third or less of the amount of potential change from the potential VL to the potential VH. Also in this case, the length of the satellite droplet Sdp12 can be shortened.

Further, in the present embodiment, the amount of potential change of waveform PcnF2 may be larger than the amount of potential change of waveform PcnF1. When the amount of potential change in the waveform PcnF that causes ink droplets to be ejected from the nozzle N is large, the ink droplet ejection speed becomes faster than when the amount of potential change in the waveform PcnF is small. Therefore, in this embodiment, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1 by making the amount of potential change of the waveform PcnF2 larger than the amount of potential change of the waveform PcnF1. can.

Furthermore, in the present 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 the waveform PcnT that separates the ink droplet from the ink in the nozzle N is small, the ejection speed of the ink droplet becomes slower than when the amount of potential change per unit time of the waveform PcnT is large. . Therefore, in the present embodiment, by making the amount of potential change per unit time of the waveform PcnT1 smaller than the amount of potential change per unit time of the waveform PcnT2, the speed of the second ink droplet Idp2 is increased from that of the first ink droplet Idp1. can be faster than the speed of

In the present embodiment, the waveform PD1 further includes a waveform Peh1 that connects the waveform Pep1 and the waveform Pcn1 and maintains the potential of the drive signal COM at the potential VL so as to maintain the volume of the cavity CV. Waveform PD2 connects waveform Pep2 and waveform Pcn2, and further includes a waveform Peh2 in which the potential of drive signal COM is maintained at potential VL so as to maintain the volume of cavity CV. The difference between the period Tsm1, which is the sum of the period Tep1 of the waveform Pep1 and the period Teh1 of the waveform Peh1, and the period of half the natural vibration period of the discharge part D is the difference between the period Tep2 of the waveform Pep2 and the period Teh2 of the waveform Peh2. It may be larger than the difference between the combined period Tsm2 and a period that is half of the natural vibration period of the discharge section D. If the difference between the period Tsm from the start of the waveform Pep to the start of the waveform Pcn and the period that is half of the natural vibration period of the discharge section D is small, the period Tsm and the period that is half the natural vibration period of the discharge section D The ink droplet ejection speed becomes faster than when the difference from the period is large. Therefore, in the present embodiment, by making the difference between the period Tsm and the period half the natural vibration period of the ejection portion D larger in the waveform PD1 than in the waveform PD2, the velocity of the second ink droplet Idp2 is increased. can be made faster than the velocity of the first ink droplet Idp1.

In the present embodiment, the waveform PD1 includes a waveform Pch1 in which the potential of the drive signal COM is maintained at the potential VH so as to maintain the volume of the cavity CV contracted by the waveform Pcn1, and a cavity maintained by the waveform Pch1. It further includes a waveform Pdm1 in which the potential of the drive signal COM changes so as to expand the volume of the CV. The waveform PD2 is a waveform Pch2 in which the potential of the drive signal COM is maintained at the potential VH so as to maintain the volume of the cavity CV contracted by the waveform Pcn2, and a waveform Pch2 in which the volume of the cavity CV maintained by the waveform Pch2 is expanded. further includes a waveform Pdm2 in which the potential of the drive signal COM changes. The drive signal COM connects the waveform PW1 in which the potential of the drive signal COM is maintained at the potential V0 at the start of the waveform Pep1 before the start of the waveform Pep1, the waveform Pdm1, and the waveform Pep2, and the potential at the start of the waveform Pep2. It further includes a waveform PW2 in which the potential of the drive signal COM is maintained at V0. The period Tpw2 of the waveform PW2 may be shorter than the period Tpw1 of the waveform PW1. Even in this case, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

Further, in the present embodiment, the period Tpw2 of the waveform PW2 may have a length of one-sixth or more and one-fifth or less of the natural vibration period of the discharge portion D. Even in this case, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

Further, in the present embodiment, the amount of potential change in waveform Pep2 may be larger than the amount of potential change in waveform Pep1. Even in this case, the speed of the second ink droplet Idp2 can be made faster than the speed of the first ink droplet Idp1.

Further, in the present embodiment, the amount of potential change per unit time of waveform Pep2 may be larger than the amount of potential change per unit time of waveform Pep1. When the amount of potential change per unit time of the waveform Pep corresponding to the expansion element is large, the ejection speed of the ink droplet becomes faster than when the amount of potential change per unit time of the waveform Pep is small. Therefore, in the present embodiment, by making the amount of potential change per unit time of the waveform Pep2 larger than the amount of potential change per unit time of the waveform Pep1, the speed of the second ink droplet Idp2 is increased from that of the first ink droplet Idp1. can be faster than the speed of

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. Thereby, 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.

Further, in this embodiment, the viscosity of the ink within the nozzle N may be 10 milliPascal seconds or more. In this embodiment, even when the viscosity of the ink in the nozzle N is high, the length of the satellite droplet Sdp12 can be shortened.

[2. Modified example]
Each of the above embodiments may be modified in various ways. Specific modes of modification are illustrated below. Two or more aspects arbitrarily selected from the following examples may be combined as appropriate within the scope of not contradicting each other. In addition, in the modified examples illustrated below, the reference numerals referred to in the above description will be used for elements whose operations and functions are equivalent to those in the embodiment, and detailed descriptions of each will be omitted as appropriate.

[First modification]
In the embodiment described above, the case where the drive signal COM includes two waveforms PD provided in the unit period TP has been exemplified, but the present invention is not limited to such an aspect. For example, the drive signal COM may include three or more waveforms PD provided in a unit period TP.

FIG. 9 is a timing chart for explaining an example of the drive signal COM in the first modification. Elements similar to those described in FIGS. 1 to 8 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the example shown in FIG. 9, three ink droplets are ejected from the nozzle N during the same unit period TP, and the three ink droplets coalesce before landing on the recording paper P, resulting in one dot being recorded. It is formed on paper P. Three ink droplets are an example of "multiple droplets."

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

Note that the waveforms PD1, PD2, and PD3 are examples of "a plurality of drive waveforms." Below, waveforms PD1, PD2, and PD3 are also referred to as waveform PD without particular distinction.

Waveform PD3 is a pull-push-pull waveform similar to waveform PD1. Detailed description of elements similar to waveform PD1 will be omitted.

The waveform PD3 is, for example, a waveform in which the potential of the drive signal COM returns from the potential V0 to the potential V0 through the potential VL, the potential V3, and the potential VH. Potential V3 is a potential between potential V0 and potential VL. For example, the potentials V1 and V3 are determined such that the speed of the ink droplet Idp ejected from the nozzle N according to the waveform PD1 is faster than the speed of the ink droplet Idp ejected from the nozzle N according to the waveform PD3. For example, the potential V3 is a potential lower than the potential V1.

Below, in the waveform PD3, a portion where the potential of the drive signal COM changes from the potential V0 to the potential VL is also referred to as a waveform Pep3, and a portion where the potential of the drive signal COM is maintained at the potential VL is also referred to as a waveform Peh3. be done. Furthermore, in the waveform PD3, a portion where the potential of the drive signal COM changes from the potential VL to the potential VH is also referred to as a waveform Pcn3, and a portion where the potential of the drive signal COM is maintained at the potential VH is also referred to as a waveform Pch3. Ru. Furthermore, a portion of the waveform PD3 where the potential of the drive signal COM changes from the potential VH to the potential V0 is also referred to as a waveform Pdm3. That is, waveform PD3 includes waveforms Pep3, Peh3, Pcn3, Pch3, and Pdm3. Furthermore, the waveform Pcn3 includes a waveform PcnF3 in which the potential of the drive signal COM changes from the potential VL to the potential V3, a waveform PcnS3 in which the potential of the drive signal COM is maintained at the potential V3, and a waveform PcnS3 in which the potential of the drive signal COM changes from the potential V3 to the potential V3. It includes a waveform PcnT3 that changes to VH.

Waveform PD3 is the same waveform as waveform PD1 except for the amount of change in potential of waveform PcnF3. For example, the waveform Pcn3 is a waveform in which the potential of the drive signal COM changes so that the volume of the cavity CV expanded by the waveform Pep3 is contracted and the ink droplet Idp is ejected from the nozzle N. Applies to the element. Therefore, when the drive signal COM is supplied to the ejection part D[m] as the individual drive signal Vin[m], the waveform Pcn3 in which the potential of the individual drive signal Vin[m] changes from a low potential to a high potential causes the ejection part The ink within D[m] is ejected from the nozzle N as the first ink droplet Idp. In the example shown in FIG. 9, the ink droplet Idp ejected from the nozzle N according to the waveform PD1 is the second ink droplet Idp, and the ink droplet Idp ejected from the nozzle N according to the waveform PD2 is the third ink droplet Idp. droplet Idp.

Note that the waveform Pep3 corresponds to an expansion element similar to the waveform Pep1, and the waveform Peh3 corresponds to an expansion maintenance element similar to the waveform Peh1. Further, waveform Pch3 corresponds to a contraction maintaining 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 "contraction waveforms." This is an example. Further, 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." ” is an example.

Here, also in this modification, each element of the waveforms PD1 and PD2 is set so that the speed of the third ink droplet Idp according to the waveform PD2 is faster than the speed of the second ink droplet Idp according to the waveform PD1. determined. Similarly, each element of waveforms PD1 and PD3 is determined so that the speed of the second ink droplet Idp according to waveform PD1 is faster than the speed of the first ink droplet Idp according to waveform PD3. Note that the setting conditions for making the speed of the second ink droplet Idp according to waveform PD1 faster than the speed of the first ink droplet Idp according to waveform PD3 are from the first setting condition to the sixth setting condition explained in FIG. This is the same as the setting conditions. For example, in the description of the first setting condition to the sixth setting condition, the elements of the waveform PD1 and the elements of the waveform PD2 are replaced with the elements of the waveform PD3 and the element of the waveform PD1, respectively.

Also in this modification, waveforms PcnF3, PcnF3, and PcnT3 included in waveform Pcn3 are set so that the length of the satellite droplet is short, similar to waveforms PcnF, PcnS, and PcnT of waveforms Pcn1 and Pcn2, respectively. Ru.

As described above, the same effects as in the above-described embodiment can be obtained also in this modification. For example, in this modification, the plurality of ink droplets Idp can be ejected from the nozzle N during the same unit period TP so that the plurality of ink droplets Idp coalesce before landing on the recording paper P. Also in this modification, it is possible to suppress the length of a satellite droplet that is separated from an ink droplet Idp that is a combination of a plurality of ink droplets Idp from becoming longer. Therefore, in this modification as well, generation of mist can be suppressed, and deterioration in the quality of printed images can be suppressed.

[Second modification]
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. Also in this modification, the same effects as in the embodiment and modification described above can be obtained.

[Third modification]
In the above-described embodiments and modifications, the piezoelectric element PZ is displaced in the -Z direction as the potential of the individual drive signal Vin[m] changes from a low potential to a high potential. It is not limited to this embodiment. For example, a piezoelectric element PZ that is displaced in the −Z direction when the potential of the individual drive signal Vin[m] changes from a high potential to a low potential may be used. In this case, for example, the potential of the drive signal COM changes from a low potential to a high potential in a portion corresponding to the expansion element, and from a high potential to a low potential in a portion corresponding to the contraction element. Also in this modification, the same effects as in the embodiment and modification described above can be obtained.

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

[Fifth modification]
In the above-described embodiments and modified examples, the case where the inkjet printer 1 has four head units 3 was illustrated, but the present invention is not limited to such an embodiment. For example, the inkjet printer 1 may have one or more and three or less head units 3, or may have five or more head units 3.

[Sixth variation]
In the above-described embodiments and modified examples, the potential at the start of waveform Pep1 corresponding to the expansion element of waveform PD1 may be lower than the potential at the start of waveform Pep2 corresponding to the expansion element of waveform PD2. . In this case as well, the speed of the ink droplet Idp ejected from the nozzle N according to the waveform PD2 is faster than the speed of the ink droplet Idp ejected from the nozzle N according to the waveform PD1. Also in this modification, the same effects as in the embodiment and modification described above can be obtained.

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

[10th modification]
In the embodiments and modifications described above, the case where there is one drive signal COM is exemplified, but the present invention is not limited to such an embodiment. For example, the drive signal COM may include, in addition to the drive signal COM shown in FIG. 6, a drive signal having a waveform different from the waveforms PD1 and PD2 of the drive signal COM. Also in this modification, the same effects as in the embodiment and modification described above can be obtained.

DESCRIPTION OF SYMBOLS 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... Discharge part, N... Nozzle .

Claims (20)

1. A method of controlling a liquid ejection head having an ejection section including a nozzle that ejects droplets, a pressure chamber communicating with the nozzle, and a drive element that applies pressure fluctuations to the liquid in the pressure chamber according to a drive signal, the method comprising:
The drive signal includes a first drive waveform and a second drive waveform subsequent to the first drive waveform,
controlling supply of the drive signal to the drive element;
The drive element is
By supplying the drive signal,
ejecting a first droplet from the nozzle according to the first drive waveform;
In accordance with the second driving waveform, a second droplet is sent from the nozzle to the first droplet before the second droplet is separated into a main droplet and a satellite droplet following the main droplet. Discharge so as to coalesce into
A method for controlling a liquid ejection head, characterized in that: After the second droplet is combined with the first droplet, the droplet obtained by combining the second droplet and the first droplet is separated into the main droplet and the satellite droplet. ,
The method of controlling a liquid ejection head according to claim 1, characterized in that: the first droplet separates from the liquid in the nozzle before combining with the second droplet;
The method of controlling a liquid ejection head according to claim 1, characterized in that: The first droplet is combined with the second droplet without separating into the main droplet and the satellite droplet.
The method of controlling a liquid ejection head according to claim 1, characterized in that: the second droplet coalesces with the first droplet before separating from the liquid in the nozzle;
The method of controlling a liquid ejection head according to claim 1, characterized in that: The second droplet merges with the first droplet by a first distance from the nozzle surface,
The first distance is twice the distance from the nozzle surface to the tip of the first droplet when the first droplet is separated from the liquid in the nozzle.
6. The method of controlling a liquid ejection head according to claim 5, wherein the method further comprises: controlling a liquid ejection head according to claim 1; 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 a 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;
including;
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;
including;
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;
including,
7. The method of controlling a liquid ejection head according to claim 1, wherein: The amount of potential change of the fourth partial waveform is larger than the amount of potential change of the first partial waveform.
8. The method of controlling a liquid ejection head according to claim 7. The amount of potential change per unit time of the third partial waveform is smaller than the amount of potential change per unit time of the sixth partial waveform.
9. The method of controlling a liquid ejection head according to claim 7 or 8. The first drive waveform is
a first expansion maintenance waveform in which the first expansion waveform and the first contraction waveform are connected, and the potential of the drive signal is maintained at the first potential so as to maintain the volume of the pressure chamber;
In addition, it includes
The second drive waveform is
a second expansion maintenance waveform that connects the second expansion waveform and the second contraction waveform and maintains the potential of the drive signal at the first potential so as to maintain the volume of the pressure chamber;
In addition, it includes
The difference between the period of the first expansion waveform and the period of the first expansion maintenance waveform and the period of one half of the natural vibration period of the discharge section is the difference between the period of the second expansion waveform and the period of the first expansion waveform. greater than the difference between the combined period of the second expansion maintenance waveform and a period of one-half of the natural vibration period of the discharge section;
The method for controlling a liquid ejection head according to any one of claims 7 to 9. The first drive waveform is
a first contraction maintenance waveform in which the potential of the drive signal is maintained at the second potential so as to maintain the volume of the pressure chamber contracted by the first contraction waveform;
a first vibration suppression waveform in which the potential of the drive signal changes so as to expand the volume of the pressure chamber maintained by the first contraction maintenance waveform;
further including;
The second drive waveform is
a second contraction maintenance waveform in which the potential of the drive signal is maintained at the second potential so as to maintain the volume of the pressure chamber contracted by the second contraction waveform;
a second damping waveform in which the potential of the drive signal changes so as to expand the volume of the pressure chamber maintained by the second contraction maintaining waveform;
further including;
The drive signal is
a first standby waveform in which the potential of the drive signal is maintained at the potential at the start of the first expansion waveform before the first expansion waveform starts;
a second standby waveform that connects the first damping waveform and the second expansion waveform, and maintains the potential of the drive signal at the potential at the start of the second expansion waveform;
further including;
The period of the second standby waveform is shorter than the period of the first standby waveform.
The method for controlling a liquid ejection head according to any one of claims 7 to 10. The period of the second standby waveform has a length of one-sixth or more and one-fifth or less of the natural vibration period of the discharge part.
12. The method of controlling a liquid ejection head according to claim 11. The amount of change in potential of the second expansion waveform is greater than the amount of change in potential of the first expansion waveform.
13. The method of controlling a liquid ejection head according to claim 7, wherein: The amount of potential change per unit time of the second expansion waveform is larger than the amount of potential change per unit time of the first expansion waveform.
14. The method of controlling a liquid ejection head according to claim 7, wherein: The ejection speed of the second droplet from the nozzle is faster than the ejection speed of the first droplet from the nozzle.
The method for controlling a liquid ejection head according to any one of claims 1 to 14. The amount of the second droplet is greater than or equal to the amount of the first droplet,
16. The method of controlling a liquid ejection head according to claim 1, wherein: The drive signal has a plurality of drive waveforms including the first drive waveform and the second drive waveform within one cycle,
The plurality of droplets ejected from the nozzle according to the plurality of drive waveforms coalesce before landing on 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 of the plurality of drive waveforms,
17. The method of controlling a liquid ejection head according to claim 1, wherein: The drive signal has a plurality of drive waveforms including the first drive waveform and the second drive waveform within one cycle,
The plurality of droplets ejected from the nozzle according to the plurality of drive waveforms coalesce before landing on 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 of the plurality of drive waveforms,
Each of the plurality of drive waveforms is
an 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 contraction waveform in which the potential of the drive signal changes from the first potential to a second potential so as to contract the volume of the pressure chamber;
including;
The 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;
including,
7. The method of controlling a liquid ejection head according to claim 1, wherein: The viscosity of the liquid in the nozzle is 10 milliPascal seconds or more,
The method for controlling a liquid ejection head according to any one of claims 1 to 18. a liquid ejection head having an ejection section including a nozzle that ejects droplets, a pressure chamber communicating with the nozzle, and a drive element that applies pressure fluctuations to the liquid in the pressure chamber according to a drive signal;
a control unit that controls supply of the drive signal to the drive element;
Equipped with
The drive signal includes a first drive waveform and a second drive waveform subsequent to the first drive waveform,
The drive element is
By supplying the drive signal,
ejecting a first droplet from the nozzle according to the first drive waveform;
In accordance with the second driving waveform, a second droplet is sent from the nozzle to the first droplet before the second droplet is separated into a main droplet and a satellite droplet following the main droplet. Discharge so as to coalesce into
A liquid ejection device characterized by:

Images