JP2009172921A - Discharge pulse setting method - Google Patents

Abstract

To stabilize the discharge of a highly viscous liquid.
The discharge pulse is returned to the reference volume by changing the volume of the pressure chamber of the reference volume so that the liquid having a viscosity of 6 millipascal seconds or more and 20 millipascal seconds or less is discharged from the nozzle. A series of operations is performed by an element that performs an operation for discharging liquid. The ejection pulse has a pre-ejection expansion portion that causes the element to perform an operation to expand the pressure chamber of a reference volume in preparation for ejecting liquid. Then, as the viscosity of the liquid is higher, the amount of potential change per unit time in the expanded portion before discharge is set larger.
[Selection] Figure 12

Description

  The present invention relates to an ejection pulse setting method.

Some liquid ejecting apparatuses such as an ink jet printer expand a pressure chamber of a reference volume before discharging liquid and expand a pressure chamber in a contracted state to a reference volume after discharging liquid (see Patent Document 1). The reason for expanding the pressure chamber before discharging the liquid is to allow the liquid to flow into the pressure chamber or to draw a meniscus (the free surface of the liquid exposed by the nozzle) toward the pressure chamber. Further, the reason for expanding the pressure chamber after the liquid is discharged is to quickly converge excessive vibration of the meniscus after the liquid is discharged.
JP-A-9-52360

In recent years, attempts have been made to eject a liquid having a viscosity higher than that of general ink by using an ink jet technique. It has been found that when such a high-viscosity liquid is ejected with a generally used waveform ejection pulse, the problem arises that the liquid ejection becomes unstable as the liquid ejection frequency is increased. It was. For example, it has been found that the flight curve of the liquid occurs and the discharge amount is insufficient.
The present invention has been made in view of such circumstances, and an object thereof is to stabilize ejection of a liquid having a viscosity higher than that of general ink.

The main invention for achieving the object is as follows:
(A) a pressure chamber communicated with each of the liquid supply unit and the nozzle;
(B) an element that operates to change the volume of the pressure chamber in response to a change in potential;
(C) A discharge pulse for causing the element to perform a series of operations for changing the volume of the pressure chamber of the reference volume to return to the reference volume in order to discharge the liquid from the nozzle, for discharging the liquid In order to prepare, a discharge pulse generation unit that repeatedly generates a discharge pulse having a pre-discharge expansion portion that causes the element to perform an operation for expanding the pressure chamber of the reference volume; and
A method for setting ejection pulses for a liquid ejection apparatus comprising (D),
(E) The viscosity of the liquid is set within a range of 6 millipascal second or more and 20 millipascal second or less,
(F) The higher the viscosity of the liquid, the larger the amount of potential change per unit time in the expanded portion before discharge.
(G) A method for setting ejection pulses.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

(A) a pressure chamber communicated with each of the liquid supply unit and the nozzle; (B) an element that operates to change the volume of the pressure chamber in accordance with a change in potential; A discharge pulse for causing the element to perform a series of operations for changing the volume of a pressure chamber of a reference volume to return to the reference volume in order to discharge the liquid from a nozzle, and to prepare for discharging the liquid A discharge pulse generating section that repeatedly generates a discharge pulse having a pre-discharge expansion portion that causes the element to perform an operation for expanding the pressure chamber of the reference volume, and a liquid discharge apparatus including (D) (E) The viscosity of the liquid is set within a range of 6 millipascal seconds or more and 20 millipascal seconds or less, and (F) the higher the viscosity of the liquid, the ejection pulse setting method is. The vomiting Defining a large potential change amount per unit time in the front expansion portion, it is revealed to be able to realize how to set (G) ejection pulse.
According to such a discharge pulse setting method, the expansion speed of the pressure chamber associated with the pre-discharge expansion portion can be optimized according to the viscosity of the liquid. Thereby, the inflow from the supply unit side to the pressure chamber side can be optimized for a liquid having a viscosity of 6 millipascal seconds or more and 20 millipascal seconds or less. As a result, even if the liquid discharge frequency is increased, a necessary amount of liquid is supplied to the pressure chamber, and the discharge can be stabilized.

In this discharge pulse setting method, the discharge pulse is used to cause the element to perform an operation for expanding the pressure chamber contracted from the reference volume to the reference volume after discharging the liquid. It is preferable that an expansion portion is provided, and a potential change amount per unit time in the expansion portion before discharge is set larger than a potential change amount per unit time in the expansion portion after discharge.
According to such a discharge pulse setting method, the flow of liquid toward the pressure chamber caused by the expansion of the pressure chamber associated with the post-discharge expansion portion can be further enhanced by the expansion of the pressure chamber associated with the pre-discharge expansion portion. it can. Accordingly, even if the liquid discharge frequency is increased, a necessary amount of liquid is supplied to the pressure chamber, and the discharge can be stabilized.

In this ejection pulse setting method, the pre-discharge expansion portion is defined as the first portion of the plurality of portions included in the discharge pulse, and the post-discharge expansion portion is defined as the plurality of portions included in the discharge pulse. Of these, it is preferable to define the last part.
According to such a discharge pulse setting method, after the post-discharge expansion portion of the previous discharge pulse is applied to the element, the pre-discharge expansion portion of the next discharge pulse is applied to the element. As a result, the flow of liquid toward the pressure chamber caused by the expansion of the pressure chamber associated with the post-discharge expansion portion can be efficiently enhanced by the expansion of the pressure chamber associated with the pre-discharge expansion portion.

In this discharge pulse setting method, the higher the liquid discharge frequency is, the higher the discharge frequency of the liquid, the generation start timing of the pre-discharge expansion portion that the subsequent discharge pulse has, and the generation end timing of the post-discharge expansion portion that the previous discharge pulse has It is preferable to set it so that it approaches.
According to such a discharge pulse setting method, the higher the liquid discharge frequency, the shorter the period from the end of expansion of the pressure chamber associated with the post-discharge expansion portion to the start of expansion of the pressure chamber associated with the pre-discharge expansion portion. Thereby, the liquid of the quantity according to the discharge frequency of the liquid can be supplied to the pressure chamber.

In this discharge pulse setting method, at the highest liquid discharge frequency, the generation start timing of the pre-discharge expansion portion that the subsequent discharge pulse has, and the generation end timing of the post-discharge expansion portion that the previous discharge pulse has It is preferable to determine to.
According to such a discharge pulse setting method, the expansion of the pressure chamber associated with the pre-discharge expansion portion is performed following the end of the expansion of the pressure chamber associated with the post-discharge expansion portion. As a result, the liquid can be efficiently supplied to the pressure chamber when the liquid is discharged at the highest discharge frequency where the shortage of the liquid supply is most likely to occur.

In this discharge pulse setting method, the discharge pulse is a discharge portion that causes the element to perform an operation of contracting the pressure chamber to discharge the liquid, and has a maximum potential and a minimum potential in the discharge pulse. Having a discharge portion where the potential changes from one to the other, and defining the pre-discharge expansion portion as a portion where the potential changes from a reference potential corresponding to the reference volume to one of the highest potential and the lowest potential; Preferably, the post-discharge expansion portion is determined as a portion where the potential changes from the other of the highest potential and the lowest potential to the reference potential.
According to such an ejection pulse setting method, it is possible to efficiently perform the ejection of the liquid and the supply of the liquid to the pressure chamber.

In this ejection pulse setting method, the reference potential is determined within the range of 20% or more and 50% or less of the difference between the highest potential and the lowest potential from the other of the highest potential and the lowest potential. It is preferable.
According to such a discharge pulse setting method, the degree of expansion of the pressure chamber by the pre-discharge expansion portion and the degree of expansion of the pressure chamber by the post-discharge expansion portion can be adjusted according to the reference potential. Thereby, supply of the liquid to a pressure chamber can be optimized.

In this discharge pulse setting method, it is preferable that the amount of change in potential per unit time of the expanded portion before discharge is set to be equal to or less than the amount of change that can maintain the shape of the meniscus.
According to such an ejection pulse setting method, ejection can be stabilized.

=== First Embodiment ===
<About the printing system>
The printing system illustrated in FIG. 1 includes a printer 1 and a computer CP. The printer 1 corresponds to a liquid ejecting apparatus, and ejects ink, which is a kind of liquid, toward a medium such as paper, cloth, or film. The medium is an object to which liquid is discharged. The computer CP is communicably connected to the printer 1. In order to cause the printer 1 to print an image, the computer CP transmits print data corresponding to the image to the printer 1.

=== Overview of Printer 1 ===
The printer 1 includes a paper transport mechanism 10, a carriage movement mechanism 20, a drive signal generation circuit 30, a head unit 40, a detector group 50, and a printer-side controller 60.

  The paper transport mechanism 10 transports the paper in the transport direction. The carriage moving mechanism 20 moves the head unit 40 in a predetermined movement direction (for example, the paper width direction). The drive signal generation circuit 30 generates a drive signal COM. This drive signal COM is applied to the head HD (see the piezo element 433, see FIG. 2A) during printing on the paper, and is a series of signals including the ejection pulse PS as shown in FIG. . Here, the ejection pulse PS is a potential change pattern that causes the piezo element 433 to perform a predetermined operation in order to eject droplet-like ink from the head HD. Since the drive signal COM includes the ejection pulse PS, the drive signal generation circuit 30 corresponds to an ejection pulse generation unit. The configuration of the drive signal generation circuit 30 and the ejection pulse PS will be described later. The head unit 40 includes a head HD and a head controller HC. The head HD discharges ink toward the paper. The head controller HC controls the head HD based on the head control signal from the printer-side controller 60. The head HD will be described later. The detector group 50 includes a plurality of detectors that monitor the status of the printer 1. Detection results by these detectors are output to the printer-side controller 60. The printer-side controller 60 performs overall control in the printer 1. The printer controller 60 will also be described later.

=== Main Parts of Printer 1 ===
<About Head HD>
As shown in FIG. 2A, the head HD includes a case 41, a flow path unit 42, and a piezo element unit 43. The case 41 has a box shape in which a housing empty portion 411 for housing and fixing the piezoelectric element unit 43 is provided. The case 41 is made of, for example, a resin material. A flow path unit 42 is joined to the front end surface of the case 41.

  The flow path unit 42 includes a flow path forming substrate 421, a nozzle plate 422, and a vibration plate 423. The nozzle plate 422 is bonded to one surface of the flow path forming substrate 421, and the vibration plate 423 is bonded to the other surface. In the flow path forming substrate 421, a pressure chamber 424, an ink supply path 425, a common ink chamber 426, and the like are formed. The flow path forming substrate 421 is made of, for example, a silicon substrate. The pressure chamber 424 is formed as an elongated chamber in a direction orthogonal to the arrangement direction of the nozzles 427. The ink supply path 425 is a narrow channel portion that communicates between the pressure chamber 424 and the common ink chamber 426. The ink supply path 425 corresponds to a liquid supply unit for supplying liquid to the pressure chamber 424. The common ink chamber 426 is a portion that temporarily stores ink supplied from an ink cartridge (not shown), and corresponds to a common liquid storage chamber.

  In the nozzle plate 422, a plurality of nozzles 427 are provided at predetermined intervals in a predetermined arrangement direction. The nozzle plate 422 is made of, for example, a stainless plate or a silicon substrate.

  The vibration plate 423 has a double structure in which a resin elastic film 429 is laminated on a support plate 428 made of stainless steel, for example. A portion of the vibration plate 423 corresponding to each pressure chamber 424 is formed by etching a stainless plate portion in an annular shape. An island 428a is formed in the ring. The island portion 428a and the elastic film 429a around the island portion constitute a diaphragm portion 423a. The diaphragm portion 423 a is deformed by the piezo element 433 included in the piezo element unit 43 and changes the volume of the pressure chamber 424.

  The piezo element unit 43 includes a piezo element group 431 and a fixed plate 432. The piezo element group 431 has a comb shape. Each comb tooth is a piezo element 433. The front end surface of each piezo element 433 is bonded to the corresponding island portion 428a. The fixing plate 432 supports the piezo element group 431 and serves as an attachment portion for the case 41. The fixing plate 432 is made of, for example, a stainless steel plate and is bonded to the inner wall of the housing space 411.

  The piezo element 433 is a kind of electromechanical conversion element, and corresponds to an element that performs an operation (deformation operation) for applying a pressure change to the liquid in the pressure chamber 424. The piezoelectric element 433 illustrated in FIG. 2A expands and contracts in the element longitudinal direction orthogonal to the stacking direction by applying a potential difference between adjacent electrodes. That is, the electrode includes a common electrode 434 having a predetermined potential and a drive electrode 435 having a potential corresponding to the drive signal COM (ejection pulse PS). The piezoelectric body 436 sandwiched between the electrodes 434 and 435 is deformed to a degree corresponding to the potential difference between the common electrode 434 and the drive electrode 435. The piezoelectric element 433 expands and contracts in the longitudinal direction of the element as the piezoelectric body 436 is deformed. In the present embodiment, the common electrode 434 is set to a ground potential or a bias potential that is higher than the ground potential by a predetermined potential. The piezoelectric element 433 contracts as the potential of the drive electrode 435 becomes higher than the potential of the common electrode 434. On the contrary, it expands as the potential of the drive electrode 435 approaches the potential of the common electrode 434 or becomes lower than the potential of the common electrode 434.

  As described above, the piezo element unit 43 is attached to the case 41 via the fixed plate 432. For this reason, when the piezo element 433 contracts, the diaphragm portion 423 a is pulled in a direction away from the pressure chamber 424. Thereby, the pressure chamber 424 is expanded. On the contrary, when the piezo element 433 is extended, the diaphragm portion 423a is pushed toward the pressure chamber 424 side. As a result, the pressure chamber 424 contracts. Ink in the pressure chamber 424 changes in pressure due to expansion and contraction of the pressure chamber 424. That is, the ink in the pressure chamber 424 is pressurized as the pressure chamber 424 contracts, and the ink in the pressure chamber 424 is depressurized as the pressure chamber 424 expands. Since the expansion / contraction state of the piezo element 433 is determined according to the potential of the drive electrode 435, the volume of the pressure chamber 424 is also determined according to the potential of the drive electrode 435. Therefore, the degree of pressurization and the degree of pressure reduction with respect to the ink in the pressure chamber 424 can be determined by the potential change amount per unit time in the drive electrode 435.

<About ink flow path>
In the head HD, a series of ink flow paths (corresponding to liquid flow paths filled with liquid) from the common ink chamber 426 to the nozzles 427 are provided in accordance with the number of nozzles 427. In the ink flow path, the nozzle 427 and the ink supply path 425 communicate with the pressure chamber 424, respectively. Therefore, when analyzing characteristics such as ink flow, the Helmholtz resonator concept is applied. FIG. 2B is a diagram schematically illustrating the structure of the head HD based on this concept.

  In a general head HD, the length L424 of the pressure chamber 424 is determined within a range of 200 μm to 2000 μm. The width W424 of the pressure chamber 424 is determined in the range of 20 μm to 300 μm, and the height H424 of the pressure chamber 424 is determined in the range of 30 μm to 500 μm. The length L425 of the ink supply path 425 is determined in the range of 50 μm to 2000 μm. The width W425 of the ink supply path 425 is determined in the range of 20 μm to 300 μm, and the height H425 of the ink supply path 425 is determined in the range of 30 μm to 500 μm. Further, the diameter φ427 of the nozzle 427 is determined in the range of 10 μm to 35 μm, and the length L427 of the nozzle 427 is determined in the range of 40 μm to 100 μm.

  Regarding the ink supply path 425, the width W425 and the height H425 are determined to be equal to or smaller than the width W424 and the height H424 of the pressure chamber 424. When one of the width W425 and the height H425 of the ink supply path 425 is aligned with one of the width W424 and the height H424 of the pressure chamber 424, the other of the width W425 and the height H425 of the ink supply path 425 The size is determined to be smaller than the other of the width W424 and the height H424 of the chamber 424.

  In such an ink flow path, ink is ejected from the nozzle 427 by applying a pressure change to the ink in the pressure chamber 424. At this time, the pressure chamber 424, the ink supply path 425, and the nozzle 427 function like a Helmholtz resonator. For this reason, the magnitude of the pressure applied to the ink in the pressure chamber 424 changes in a unique period called a Helmholtz period. That is, pressure vibration occurs in the ink. For this reason, the Helmholtz period is also called the natural vibration period of ink (liquid) in the pressure chamber 424. Due to this Helmholtz period pressure vibration, the meniscus (the free surface of the ink exposed at the nozzle 427) moves periodically within the nozzle 427. Then, by using the pressure change of the natural vibration period, the ink can be efficiently ejected from the nozzle 427, or the pressure change of the ink in the pressure chamber 424 can be canceled efficiently.

  In a general head HD, the natural vibration period in the pressure chamber 424 is determined within a range of 5 μs to 10 μs. For example, in the ink flow path of FIG. 2A, the width W424 of the pressure chamber 424 is 100 μm, the height H424 is 70 μm, the length L424 is 1000 μm, the width W425 of the ink supply path 425 is 50 μm, the height H425 is 70 μm, and the length. When L425 is 500 μm, the diameter φ427 of the nozzle 427 is 30 μm, and the length L427 is 100 μm, the natural vibration period in the pressure chamber 424 is about 8 μs. Note that the natural vibration period also varies depending on the thickness of the partition wall that partitions the adjacent pressure chambers 424, the thickness and compliance of the elastic film 429, and the material of the flow path forming substrate 421 and the nozzle plate 422.

<About the printer-side controller 60>
The printer-side controller 60 performs overall control in the printer 1. For example, the control target unit is controlled based on the print data received from the computer CP and the detection results from each detector, and an image is printed on a sheet. As shown in FIG. 1, the printer-side controller 60 includes an interface unit 61, a CPU 62, and a memory 63. The interface unit 61 exchanges data with the computer CP. The CPU 62 performs overall control of the printer 1. The memory 63 secures an area for storing a computer program, a work area, and the like. The CPU 62 controls each control target unit according to the computer program stored in the memory 63. For example, the CPU 62 controls the paper transport mechanism 10 and the carriage movement mechanism 20. Further, the CPU 62 transmits a head control signal for controlling the operation of the head HD to the head control unit HC, and transmits a control signal for generating the drive signal COM to the drive signal generation circuit 30.

  Here, the control signal for generating the drive signal COM is also called DAC data, and is, for example, digital data of a plurality of bits. This DAC data defines a change pattern of the potential of the generated drive signal COM. Therefore, the DAC data can be said to be data indicating the potential of the drive signal COM and the ejection pulse PS. The DAC data is stored in a predetermined area of the memory 63, and is read out when the drive signal COM is generated and output to the drive signal generation circuit 30.

<About the drive signal generation circuit 30>
The drive signal generation circuit 30 functions as an ejection pulse generation unit, and generates a drive signal COM having an ejection pulse PS based on the DAC data. As shown in FIG. 3, the drive signal generation circuit 30 includes a DAC circuit 31, a voltage amplification circuit 32, and a current amplification circuit 33. The DAC circuit 31 converts digital DAC data into an analog signal. The voltage amplification circuit 32 amplifies the voltage of the analog signal converted by the DAC circuit 31 to a level at which the piezo element 433 can be driven. In this printer 1, the maximum analog signal output from the DAC circuit 31 is 3.3V, whereas the amplified analog signal output from the voltage amplifier circuit 32 (also referred to as a waveform signal for convenience) is 42V at maximum. It is. The current amplifying circuit 33 amplifies the current of the waveform signal from the voltage amplifying circuit 32 and outputs the amplified signal as a drive signal COM. The current amplifier circuit 33 is configured by, for example, a push-pull connected transistor pair.

<About the head controller HC>
The head control unit HC selects a necessary portion of the drive signal COM generated by the drive signal generation circuit 30 based on the head control signal, and applies it to the piezo element 433. Therefore, as shown in FIG. 3, the head controller HC includes a plurality of switches 44 provided for each piezo element 433 in the middle of the supply line of the drive signal COM. Then, the head controller HC generates a switch control signal from the head control signal. By controlling each switch 44 by this switch control signal, a necessary portion (for example, ejection pulse PS) of the drive signal COM is applied to the piezo element 433. At this time, the ejection of ink from the nozzles 427 can be controlled depending on how to select the necessary portions.

<About the drive signal COM>
Next, the drive signal COM generated by the drive signal generation circuit 30 will be described. As shown in FIG. 4, the drive signal COM includes a plurality of ejection pulses PS that are repeatedly generated. These ejection pulses PS have the same waveform. That is, the potential change pattern is the same. As described above, the drive signal COM is applied to the drive electrode 435 included in the piezo element 433. As a result, a potential difference corresponding to the potential change pattern is generated between the common electrode 434 and the fixed potential. As a result, the piezo element 433 expands and contracts according to the potential change pattern, and changes the volume of the pressure chamber 424.

  Although details will be described later, the potential of the ejection pulse PS rises from the intermediate potential VB as the reference potential to the highest potential VH and then falls to the lowest potential VL. Then, it rises to the intermediate potential VB. As described above, the piezo element 433 contracts as the potential of the drive electrode 435 is higher than the potential of the common electrode 434, thereby expanding the volume of the pressure chamber 424. Therefore, when the ejection pulse PS is applied to the piezo element 433, the pressure chamber 424 expands from the reference volume corresponding to the intermediate potential VB to the maximum volume corresponding to the maximum potential VH. Then, it contracts to the minimum volume corresponding to the lowest potential VL and expands to the reference volume. When the maximum volume contracts to the minimum volume, the ink in the pressure chamber 424 is pressurized, and an ink droplet is ejected from the nozzle 427.

  In the illustrated ejection pulse PS, a portion that changes from the highest potential VH to the lowest potential VL corresponds to an ejection portion for ejecting ink. The ink droplet ejection interval is determined by the interval between the ejection portions generated one after the other. For example, in the example of FIG. 4, the solid line drive signal COM is generated for each period Ta in the ejection portion. Thereby, ink droplets are also ejected every period Ta. Further, the one-dot chain line drive signal COM is generated every period Tb in which the ejection portion is longer than the period Ta. As a result, ink droplets are also ejected every period Tb. Therefore, the ejection frequency by the solid line drive signal COM is higher than the ejection frequency by the dashed line drive signal COM.

=== Discharge operation ===
<Overview>
In this type of printer, there is a desire to eject ink at as high a frequency as possible. This is because processing such as printing can be speeded up. Here, an ink having a viscosity sufficiently higher than that of a general ink (about 1 millipascal second), specifically, an ink having a viscosity of 6 to 20 millipascal second (also referred to as a high viscosity ink for convenience). In the case of ejection, there is a problem that if the ejection frequency of the ink is increased, the ejection of the ink becomes unstable. FIG. 5A shows a state where high-viscosity ink is ejected in a stable state. On the other hand, FIG. 5B shows a state in which high viscosity ink is ejected in an unstable state. Comparing these figures, it can be seen that, in an unstable state, there are ink droplets with insufficient flight speed and ink droplets with ejection bends.

  There are various factors that make ink ejection unstable, and one of the factors is considered to be insufficient supply of ink. In the head HD, the ink stored in the common ink chamber 426 is caused to flow into the pressure chamber 424 through the ink supply path 425. Here, with high-viscosity ink, it is considered that the inflow of ink from the common ink chamber 426 side cannot catch up as the ink ejection frequency is increased. For this reason, the ink ejection operation is performed in a state where the ink in the pressure chamber 424 is insufficient, and it is considered that the flying speed of the ink droplet is excessively slow or the flying curvature of the ink droplet occurs.

  In view of such circumstances, the ejection pulse PS of the present embodiment corresponds to a first decompression portion P1 (expansion portion before ejection) for inflating the pressure chamber 424 having a reference volume in preparation for ejection of ink droplets. 6), and a second pressure reducing portion P5 for expanding the contracted pressure chamber 424 to the reference volume after ejection of the ink droplets (hereinafter also referred to as a slope). This corresponds to the expanded portion after discharge (see FIG. 6 and the like). That is, the inclination of the first reduced pressure portion P1 is made larger than the inclination of the second reduced pressure portion P5.

  By using such a discharge pulse PS, the degree of expansion of the pressure chamber 424 associated with the application of the first decompression portion P1 can be made larger than the degree of expansion of the pressure chamber 424 associated with the application of the second decompression portion P5. . In other words, regarding the degree of pressure reduction of the ink in the pressure chamber 424, the degree of pressure reduction caused by the first pressure reduction part P1 can be greater than the pressure reduction degree caused by the second pressure reduction part P5. For this reason, the flow of ink to the pressure chamber 424 generated by the application of the piezo element 433 of the second decompression portion P5 included in the previous ejection pulse PS is changed to that in the first decompression portion P1 included in the later ejection pulse PS. Further enhancement can be achieved by applying the piezo element 433. As a result, even if the ejection frequency of the ink droplet is increased, a necessary amount of ink can be supplied to the pressure chamber 424, and the ejection can be stabilized.

  For the first reduced pressure portion P1, it is preferable to set the potential change amount per unit time to be larger as the viscosity of the ink to be ejected is higher. By using such an ejection pulse PS, the expansion speed of the pressure chamber 424 can be optimized in accordance with the viscosity of the ink. Thereby, the ink can be drawn into the pressure chamber 424 with a strength suitable for the viscosity. As a result, the inflow of ink from the ink supply path 425 side to the pressure chamber 424 side can be optimized, and the ejection can be stabilized even if the ejection frequency of the ink droplets is increased. This will be described in detail below.

<Ink with a viscosity of 20 millipascal second>
6 to 11 show three types of ejection pulses PS1a to PS1c in which the slope of the first decompression portion P1 and the slope of the second decompression portion P5 are different, and the viscosity of each of the ejection pulses PS1a to PS1c is 20 millipascal seconds. It is a figure explaining the state of the meniscus when the ink of this is discharged. Note that the ejection amounts associated with the application of the piezoelectric elements 433 for the ejection pulses PS1a to PS1c are set to be the same.

  FIG. 6 is a diagram illustrating the ejection pulse PS1a in which the slope of the first decompression portion P1 is larger than the slope of the second decompression portion P5. FIG. 7 is a diagram illustrating the state of the meniscus when one ink droplet is ejected by the ejection pulse PS1a of FIG. In FIG. 6, the vertical axis represents the potential of the drive signal COM, and the intermediate potential VB as the reference potential is set to 0V. The horizontal axis is time. In FIG. 7, the vertical axis indicates the meniscus state by the amount of ink, and the horizontal axis indicates time. Regarding the vertical axis, 0 ng indicates the position of the meniscus in the steady state. The larger the value on the positive side, the more the meniscus is pushed out in the discharge direction, and the larger the value on the negative side, the more the meniscus is drawn into the pressure chamber 424 side. In addition, the natural vibration period in the target pressure chamber 424 is 8 μs.

  The ejection pulse PS1a shown in FIG. 6 has a plurality of portions indicated by reference signs P1 to P5. In other words, the ejection pulse PS1a includes a first pressure reducing portion P1, a first potential holding portion P2, a pressurizing portion P3, a second potential holding portion P4, and a second pressure reducing portion P5.

  The first reduced pressure portion P1 is a portion generated from timing t0 to timing t1a. In the first decompression portion P1, the potential at the timing t0 (corresponding to the start potential) is the intermediate potential VB, and the potential at the timing t1a (corresponding to the termination potential) is the maximum potential VH. For this reason, when the first reduced pressure portion P1 is applied, the pressure chamber 424 expands from the reference volume to the maximum volume over the generation period of the first reduced pressure portion P1. Here, the 1st pressure reduction part P1 is produced | generated before the pressurization part P3 which functions as a discharge part. Then, the pressure chamber 424 is expanded as a preparatory operation for ejecting ink droplets. Therefore, the first decompression portion P1 corresponds to the pre-ejection expansion portion, and is the first portion of the plurality of portions constituting the ejection pulse PS1a.

  The intermediate potential VB in the ejection pulse PS1a is higher than the lowest potential VL in the ejection pulse PS1a by 40% of the difference from the highest potential VH to the lowest potential VL in the ejection pulse PS1a (hereinafter also referred to as drive voltage Vh). It has been established. The drive voltage Vh in the ejection pulse PS1a is 30V. Therefore, the intermediate potential VB is 12V higher than the lowest potential VL, and the highest potential VH is 18V higher than the intermediate potential VB. Further, the generation period of the first reduced pressure portion P1 is 2.8 μs. Accordingly, the slope (the amount of change in potential per unit time) of the first decompression portion P1 is about 6.4 V / μs.

  The first potential holding portion P2 is a portion that is generated from timing t1a to timing t2a. The first potential holding portion P2 is constant at the maximum potential VH. For this reason, when the first potential holding portion P2 is applied to the piezo element 433, the pressure chamber 424 maintains the maximum volume over the generation period of the first potential holding portion P2. In this ejection pulse PS1a, the generation period of the first potential holding portion P2 is 1.4 μs.

  The pressurizing part P3 is a part generated from the timing t2a to the timing t3a. The pressurization portion P3 has a start potential of the highest potential VH and a termination potential of the lowest potential VL. For this reason, when the pressurization part P3 is applied to the piezo element 433, the pressure chamber 424 contracts over the generation period of the pressurization part P3 from the maximum volume to the minimum volume. Since the ink is ejected as the pressure chamber 424 contracts, the pressurization portion P3 corresponds to the ejection portion. In the ejection pulse PS1a, the generation period of the pressurization portion P3 is 2.8 μs. Therefore, the inclination of the pressurizing portion P3 is about −10.7 V / μs.

  The second potential holding portion P4 is a constant portion at the lowest potential VL generated from the timing t3a to the timing t4a. When the second potential holding portion P4 is applied to the piezo element 433, the pressure chamber 424 maintains the minimum volume over the generation period of the second potential holding portion P4. In this ejection pulse PS1a, the generation period of the second potential holding portion P4 is 2.8 μs.

  The second decompression portion P5 is a portion generated from timing t4a to timing t5a. In the second decompression portion P5, the start potential is the lowest potential VL and the end potential is the intermediate potential VB. For this reason, when the second reduced pressure portion P5 is applied to the piezo element 433, the pressure chamber 424 expands from the minimum volume to the reference volume over the generation period of the second reduced pressure portion P5. The second decompression portion P5 is generated after the pressurization portion P3 (the last in the ejection pulse PS1a), and an operation for expanding the contracted pressure chamber 424 to the reference volume after ejection of the ink droplet. This corresponds to a post-discharge expansion portion that causes the piezo element 433 to perform. In this ejection pulse PS1a, the generation period of the second reduced pressure portion P5 is 3.6 μs. The potential difference between the intermediate potential VB and the lowest potential VL is 12V. For this reason, the inclination of the second decompression portion P5 is about 3.3 V / μs.

  Next, the operation of the piezo element 433 and the pressure chamber 424 and the ink flow when the ejection pulse PS1a is applied to the piezo element 433 will be described. When the first reduced pressure portion P1 is applied to the piezo element 433, the pressure chamber 424 expands to the maximum volume. Along with this expansion, the ink in the pressure chamber 424 becomes negative pressure, the ink flows into the pressure chamber 424 through the ink supply path 425, and the meniscus is drawn into the pressure chamber 424 in the nozzle 427. Here, in the ejection pulse PS1a, since the inclination of the first reduced pressure portion P1 is determined in consideration of the ink viscosity, the ink can be supplied to the pressure chamber 424 side even if the ink is high viscosity. Such a first reduced pressure portion P1 can be said to be a pre-discharge supply portion for supplying ink to the pressure chamber 424 side before ink discharge.

  The movement of the meniscus toward the pressure chamber 424 is continued even after the application of the first reduced pressure portion P1 is completed. That is, the meniscus moves to the pressure chamber 424 side even during the application period of the first potential holding portion P2 due to the partition wall that partitions the pressure chamber 424, the compliance of the diaphragm 423, and the like. Thereafter, the meniscus is reversed in the discharge direction away from the pressure chamber 424 (timing indicated by reference numeral A1 in FIG. 7). At this time, since the contraction of the pressure chamber 424 accompanying the application of the pressurizing portion P3 is also added, the moving speed of the meniscus is fast. The meniscus that has moved along with the application of the pressurizing portion P3 has a columnar shape. Then, by the time the application of the second potential holding portion P4 to the piezo element 433 is completed, a part of the columnar meniscus on the tip side is cut and discharged in a droplet shape (reference numeral B1 in FIG. 7). Timing shown).

  By the reaction of the discharge, the meniscus returns to the pressure chamber 424 side at a high speed. At this time, the second reduced pressure portion P5 is applied to the piezo element 433. The pressure chamber 424 expands with the application of the second reduced pressure portion P5. With this expansion, the ink in the pressure chamber 424 becomes negative pressure, and the ink flows into the pressure chamber 424 through the ink supply path 425. In the ejection pulse PS1a, the inclination of the second pressure-reducing portion P5 is determined according to the strength of the generated ink flow, so that the ink can be supplied to the pressure chamber 424 side even for high-viscosity ink. . Such a second decompression portion P5 can be said to be a post-discharge supply portion for supplying ink to the pressure chamber 424 side after ink discharge.

  After the second reduced pressure portion P5 is applied, the meniscus gradually changes to a steady state (ink) while switching the movement direction between the discharge side and the pressure chamber 424 (for example, timings indicated by reference numerals C1 and D1 in FIG. 7). Approach the position of 0 ng). The reason why the meniscus approaches the steady state position is thought to be because the ink in the pressure chamber 424 has increased. For this reason, it can be said that ink is supplied from the ink supply path 425 into the pressure chamber 424 while the meniscus is close to the steady state position. The fact that the meniscus has returned to the steady state position means that a sufficient amount of ink has been supplied into the pressure chamber 424. Therefore, if the ejection pulse PS1a is applied to the piezo element 433 after this point, ink ejection failure due to insufficient ink supply can be prevented. In the example of FIG. 7, the meniscus has returned almost to the steady state position when 50 μs has elapsed from the start of application to the piezo element 433 of the first reduced pressure portion P1.

  Thus, there are two reasons why the meniscus quickly returns to the steady state position. The first reason is considered to be that the ink pressure is greatly lowered with the application of the second decompression portion P5 to the piezo element 433. In other words, it is considered that a sufficient amount of ink flows into the pressure chamber 424 due to the ink flow caused by the second reduced pressure portion P5. The second reason is considered to be that the ink pressure is greatly lowered with the application of the first reduced pressure portion P1 to the piezo element 433. That is, it is considered that the ink pressure reduction caused by the second pressure reduction portion P5 is added to the residual vibration of the ink pressure caused by the first pressure reduction portion P1, thereby acting to strengthen the ink flow.

  Here, at the time of continuous ejection of ink droplets, for example, as shown in FIG. 4, after the second reduced pressure portion included in the previous ejection pulse PS is applied to the piezo element 433, the first ejection pulse PS included in the subsequent ejection pulse PS. The reduced pressure portion is applied to the piezo element 433. As the ink droplet ejection frequency increases, the time from the application end timing of the second reduced pressure portion P5 to the application start timing of the first reduced pressure portion P1 becomes shorter. As described above, when the second reduced pressure portion P5 and the first reduced pressure portion P1 are applied to the piezo element 433, an ink flow is generated corresponding to the application of each portion. When the time from the application end timing of the second reduced pressure portion P5 to the application start timing of the first reduced pressure portion P1 becomes shorter, the ink flow caused by the second reduced pressure portion P5 is changed to the pressure caused by the first reduced pressure portion P1. It can be strengthened by the expansion of the chamber 424.

  Further, in the ejection pulse PS1a, the slope (the amount of potential change per unit time) of the first reduced pressure portion P1 is made larger than the slope of the second reduced pressure portion P5. Thereby, the ink flow caused by the first reduced pressure portion P1 can be made stronger than the ink flow caused by the second reduced pressure portion P5. As described above, since the force for flowing ink (negative pressure with respect to the ink in the pressure chamber 424) is increased stepwise, the ink can flow smoothly toward the pressure chamber 424 through the ink supply path 425. And the shortage of ink supply can be suppressed. As a result, ejection of ink droplets at a high frequency can be stabilized.

  FIG. 8 is a diagram for explaining another ejection pulse PS1b in which the slope of the first decompression portion P1 is larger than the slope of the second decompression portion P5. FIG. 9 is a diagram for explaining the state of the meniscus when one ink droplet is ejected by the ejection pulse PS1b of FIG. Note that the ejection pulse PS1b in FIG. 8 and the ejection pulse PS1a in FIG. 6 are different from each other in the slope of the first decompression portion P1 and the slope of the second decompression portion P5. That is, the first decompression portion P1 included in the ejection pulse PS1b of FIG. 8 has a smaller inclination than the first decompression portion P1 included in the ejection pulse PS1a of FIG. In addition, the change width of the potential is also reduced. Further, the second decompression portion P5 included in the ejection pulse PS1b of FIG. 8 has a larger slope than the second decompression portion P5 included in the ejection pulse PS1a of FIG. In addition, the change width of the potential is also increased.

  In FIG. 8, the portion indicated by reference signs P1 to P5 is the ejection pulse PS1b. In this ejection pulse PS1b, the outline of the waveform (potential change pattern) is the same as that of the ejection pulse PS1a in FIG. That is, the parts denoted by the same reference numerals exhibit the same function. In the ejection pulse PS1b of FIG. 8, the intermediate potential VB and the potential change amount of each portion are different from those of the ejection pulse PS1a of FIG.

In the first decompression portion P1, the start potential at the timing t0 is the intermediate potential VB, and the termination potential at the timing t1b is the maximum potential VH. Here, the intermediate potential VB is set to a potential higher by 50% of the drive voltage Vh than the lowest potential VL in the ejection pulse PS1b. The drive voltage Vh in the ejection pulse PS1b is 30V. Therefore, the intermediate potential VB is 15V higher than the lowest potential VL, and the highest potential VH is 15V higher than the intermediate potential VB. Further, the generation period of the first reduced pressure portion P1 is 2.8 μs. Accordingly, the slope of the first reduced pressure portion P1 is about 5.4 V / μs.
The first potential holding portion P2 is a portion that is generated from the timing t1b to the timing t2b and is constant at the highest potential VH. In the ejection pulse PS1b, the generation period of the first potential holding portion P2 is 1.4 μs.
The pressurizing portion P3 is generated from the timing t2b to the timing t3b, and is a portion where the start potential is the highest potential VH and the termination potential is the lowest potential VL. The pressurizing portion P3 corresponds to an ejection portion for ejecting ink, and its generation period is 2.8 μs.
The second potential holding portion P4 is generated from the timing t3b to the timing t4b and is a constant portion at the lowest potential VL. In this ejection pulse PS1b, the generation period of the second potential holding portion P4 is 2.8 μs.
The second decompression portion P5 is generated from timing t4b to timing t5b, and the start potential is the lowest potential VL and the termination potential is the intermediate potential VB. The generation period of the second decompression portion P5 is 3.6 μs. Accordingly, the slope of the second decompression portion P5 is about 4.2 V / μs.

  The slope (about 5.4 V / μs) of the first decompression portion P1 included in the ejection pulse PS1b of FIG. 8 is the slope (about 6.4 V / μs) of the first decompression portion P1 included in the ejection pulse PS1a of FIG. Smaller than. On the other hand, the slope (about 4.2 V / μs) of the second decompression portion P5 of the ejection pulse PS1b in FIG. 8 is the slope (about 3.3 V / μs) of the second decompression portion P5 of the ejection pulse PS1a in FIG. Bigger than. Therefore, the ejection pulse PS1b of FIG. 8 has a smaller difference between the slope of the first decompression portion P1 and the slope of the second decompression portion P5 than the ejection pulse PS1a of FIG.

  Even when the ejection pulse PS1b of FIG. 8 is applied to the piezo element 433, the operation of the piezo element 433 and the pressure chamber 424 until the ink droplet is ejected and the outline of the ink flow in the ink flow path are shown in FIG. This is substantially the same as when the ejection pulse PS1a is applied to the piezo element 433. Therefore, detailed description is omitted. From the comparison between the meniscus state in FIG. 9 and the meniscus state in FIG. 7, the following can be understood.

  First, when the ejection pulse PS1a of FIG. 6 is applied to the piezo element 433, the meniscus returns to the steady state position after about 50 μs has elapsed from the start of application of the first reduced pressure portion P1. On the other hand, when the ejection pulse PS1b of FIG. 8 is applied to the piezo element 433, the meniscus returns to the steady state position after about 100 μs from the start of application of the first reduced pressure portion P1.

  Here, in the present embodiment, the fact that the meniscus has returned to the steady state position after 100 μs has elapsed since the start of application of the first reduced pressure portion P1 can be performed stably even at a high frequency of 40 kHz or higher. This is the standard for judgment. Considering only the time of 100 μs, it seems that the discharge frequency is about 10 kHz at the maximum. However, when the ejection frequency is increased, ink droplets are ejected one after another, so that the ink flow path (a series of flow paths from the common ink chamber to the nozzle 427) is directed from the common ink chamber side to the nozzle 427 side. It is believed that ink flow occurs. It is considered that the ink flow becomes faster as the ejection frequency is increased, and assists the ink flow caused by the first reduced pressure portion P1 and the ink flow caused by the second reduced pressure portion P5. Since the ink is also supplied into the pressure chamber 424 by such an ink flow, the above-described determination criteria are set.

  Second, when the ejection pulse PS1b of FIG. 8 is applied to the piezo element 433, compared to the case where the ejection pulse PS1a of FIG. 6 is applied to the piezo element 433, the amount of meniscus drawing due to the first decompression portion P1 is increased. Is getting smaller. In other words, with respect to the amplitude of the pressure vibration of the ink caused by the first reduced pressure portion P1, the ejection pulse PS1b in FIG. 8 is smaller than the ejection pulse PS1a in FIG. This can be understood from the position of the meniscus at the timing indicated by reference signs A1, A2, the position of the meniscus at the timing indicated by reference signs C1, C2, and D1, D2. The difference in the amplitude of the pressure vibration is considered to affect the meniscus return time. In other words, it is considered that the amount of ink supplied to the pressure chamber 424 after ink droplet ejection is affected. That is, in the ejection pulse PS1b of FIG. 8, the amplitude of the pressure vibration is smaller than that of the ejection pulse PS1a of FIG. 6, so even if the degree of decompression caused by the second decompression portion P5 is higher than that of the ejection pulse PS1a of FIG. It takes time to return.

  FIG. 10 is a diagram for explaining the ejection pulse PS1c of the reference example in which the slope of the first decompression portion P1 is smaller than the slope of the second decompression portion P5. FIG. 11 is a diagram illustrating the state of the meniscus when one ink droplet is ejected by the ejection pulse PS1c of FIG. Note that the ejection pulse PS1c in FIG. 10 and the ejection pulses PS1a and PS1b in FIG. 6 and FIG. 8 differ in the slope of the first decompression portion P1 and the slope of the second decompression portion P5.

  In FIG. 10, the portion indicated by reference signs P1 to P5 is the ejection pulse PS1c. The outline of the waveform of the ejection pulse PS1c is the same as that of the ejection pulses PS1a and PS1b in FIGS. In the ejection pulse PS1c of FIG. 10, the intermediate potential VB and the potential change amount of each part are different from those of the ejection pulses PS1a and PS1b of FIGS.

In the first decompression portion P1, the start potential at the timing t0 is the intermediate potential VB, and the termination potential at the timing t1c is the maximum potential VH. Here, the intermediate potential VB is set to a potential that is higher by 60% of the drive voltage Vh than the lowest potential VL in the ejection pulse PS1c. The drive voltage Vh in the ejection pulse PS1c is 30V. For this reason, the intermediate potential VB is 18V higher than the lowest potential VL, and the highest potential VH is 12V higher than the intermediate potential VB. Further, the generation period of the first reduced pressure portion P1 is 2.8 μs. Accordingly, the slope of the first reduced pressure portion P1 is about 4.3 V / μs.
The first potential holding portion P2 is a portion that is generated from the timing t1c to the timing t2c and is constant at the highest potential VH. In the ejection pulse PS1c, the generation period of the first potential holding portion P2 is 1.4 μs.
The pressure part P3 corresponds to an ejection part for ejecting ink droplets. The pressurization portion P3 is generated from the timing t2c to the timing t3c, and is a portion where the start potential is the highest potential VH and the termination potential is the lowest potential VL. In this ejection pulse PS1c, the generation period of the pressurization portion P3 is 2.8 μs.
The second potential holding portion P4 is generated from timing t3c to timing t4c and is a constant portion at the lowest potential VL. In the ejection pulse PS1c, the generation period of the second potential holding portion P4 is 2.8 μs.
The second decompression portion P5 is generated from timing t4c to timing t5c, and the start potential is the lowest potential VL and the termination potential is the intermediate potential VB. The generation period of the second decompression portion P5 is 3.6 μs. Therefore, the inclination of the second decompression portion P5 is 5 V / μs.

  The slope (about 4.3 V / μs) of the first decompression portion P1 included in the ejection pulse PS1c in FIG. 10 is smaller than the slope (5 V / μs) of the second decompression portion P5. This is different from the ejection pulses PS1a and PS1b shown in FIGS.

  Even when the ejection pulse PS1c of FIG. 10 is applied to the piezo element 433, the operation of the piezo element 433 and the pressure chamber 424 until the ink droplet is ejected and the outline of the ink flow in the ink flow path are shown in FIG. 8 is substantially the same as the case where the ejection pulses PS1a and PS1b in FIG. 8 are applied to the piezo element 433. Therefore, detailed description is omitted. Here, the following can be understood from the comparison between the meniscus state in FIG. 11 and the meniscus state in FIG. 9.

  When the ejection pulse PS1c of FIG. 10 is applied to the piezo element 433, the meniscus has not returned to the steady state position even after about 100 μs has elapsed from the start of application of the first reduced pressure portion P1. The meniscus moving range caused by the ejection pulse PS1c in FIG. 10 is narrower than the meniscus moving range caused by the ejection pulses PS1a and PS1b in FIGS. That is, the amplitude of pressure vibration is small. This means that the position of the meniscus at the timing indicated by reference numeral A3 in FIG. 11 and the position of the meniscus at the timing indicated by reference numeral D3, the position of the meniscus at the timing indicated by reference signs A1 and A2 in FIG. 7 and FIG. This can be understood by comparing with the position of the meniscus at the timing shown in FIG. Then, due to the difference in the meniscus moving range (amplitude of pressure vibration), when the ejection pulse PS1c of FIG. 10 is used, the period until the meniscus returns to the steady state position is long. This is considered to be due to the fact that the ink flow to the pressure chamber 424 side due to the pressure vibration is not sufficient at the time of applying the second reduced pressure portion P5.

<Difference in viscosity>
Next, the influence of the difference in ink viscosity will be described. FIG. 12 is a diagram for explaining another ejection pulse PS2a for ejecting ink having a viscosity of 20 millipascal seconds. FIG. 13 is a diagram for explaining the state of the meniscus when one ink droplet is ejected by the ejection pulse PS2a of FIG. FIG. 14 is a diagram for explaining the ejection pulse PS2b for ejecting ink having a viscosity of 6 millipascal seconds. FIG. 15 is a diagram illustrating the state of the meniscus when one ink droplet is ejected by the ejection pulse PS2b of FIG. As will be described later, the waveform of each of the ejection pulse PS2a in FIG. 12 and the ejection pulse PS2b in FIG. 14 is determined so that the slope of the first decompression portion P1 is larger than the slope of the second decompression portion P5. In these drawings, the natural vibration period in the target pressure chamber 424 is 8 μs.

  In FIG. 12, the portion indicated by reference signs P1 to P5 is the ejection pulse PS2a. In this ejection pulse PS2a, the outline of the waveform is the same as that of each of the ejection pulses PS1a to PS1c described above. That is, after increasing the potential from the intermediate potential VB to the maximum potential VH, the potential is decreased to the minimum potential VL and returned to the intermediate potential VB.

In the first decompression portion P1, the start potential at the timing t1d is the intermediate potential VB, and the termination potential at the timing t2d is the maximum potential VH. Here, the intermediate potential VB is set to a potential that is higher by 30% of the drive voltage Vh than the lowest potential VL in the ejection pulse PS2a. The drive voltage Vh in the ejection pulse PS2a is 25V. Therefore, the intermediate potential VB is 7.5V higher than the lowest potential VL, and the highest potential VH is 17.5V higher than the intermediate potential VB. And the production | generation period of the 1st pressure reduction part P1 is 3 microseconds. For this reason, the inclination of the first decompression portion P1 is about 5.8 V / μs.
The first potential holding portion P2 is a portion that is generated from the timing t2d to the timing t3d and is constant at the maximum potential VH. In this ejection pulse PS2a, the generation period of the first potential holding portion P2 is 2 μs.
The pressure part P3 corresponds to an ejection part for ejecting ink droplets. The pressurization portion P3 is generated from timing t3d to timing t4d, and the start potential is the highest potential VH and the termination potential is the lowest potential VL. In this ejection pulse PS2a, the generation period of the pressurization portion P3 is 3 μs.
The second potential holding portion P4 is generated from the timing t4d to the timing t5d and is a constant portion at the lowest potential VL. In the ejection pulse PS2a, the generation period of the second potential holding portion P4 is 5 μs.
The second decompression portion P5 is generated from timing t5d to timing t6d, and the start potential is the lowest potential VL and the termination potential is the intermediate potential VB. In this ejection pulse PS2a, the generation period of the second reduced pressure portion P5 is 2.3 μs. For this reason, the inclination of the second decompression portion P5 is about 3.3 V / μs.

  As shown in FIG. 13, even when this ejection pulse PS2a is used, the meniscus is sufficiently drawn to the pressure chamber 424 side at timing A4. At timing D4, the meniscus has sufficiently moved to the discharge side. Thus, it can be seen that even when this ejection pulse PS2a is used, the moving range of the meniscus (the amplitude of pressure vibration) is sufficiently large. Accordingly, the meniscus returns to the steady state position when 100 μs has elapsed from the start of application of the first reduced pressure portion P1. Accordingly, it can be said that even with this ejection pulse PS2a, ink droplets can be stably ejected at a high frequency of 40 kHz or more.

  The ejection pulse PS2b shown in FIG. 14 differs from the ejection pulse PS2a in FIG. 12 in the slope of the first decompression portion P1 and the slope of the second decompression portion P5. The first decompression portion P1 is generated from the timing t1e to the timing t2e, the start potential is the intermediate potential VB, and the termination potential is the maximum potential VH. The intermediate potential VB is set to a potential that is higher by 40% of the drive voltage Vh than the lowest potential VL in the ejection pulse PS2b. The drive voltage Vh in the ejection pulse PS2b is 30V. Therefore, the intermediate potential VB is 12V higher than the lowest potential VL, and the highest potential VH is 18V higher than the intermediate potential VB. Further, the generation period of the first reduced pressure portion P1 is 4 μs. Accordingly, the slope of the first reduced pressure portion P1 is 4.5 V / μs.

The first potential holding portion P2 is a portion that is generated from timing t2e to timing t3e. The first potential holding portion P2 is constant at the maximum potential VH. In this ejection pulse PS2b, the generation period of the first potential holding portion P2 is 1.4 μs.
The pressure part P3 corresponds to an ejection part for ejecting ink droplets. In the pressurizing portion P3, the start potential at the timing t3e is the highest potential VH, and the termination potential at the timing t4e is the lowest potential VL. In this ejection pulse PS2b, the generation period of the pressurizing portion P3 is 2.8 μs.
The second potential holding portion P4 is a portion that is generated from the timing t4e to the timing t5e and is constant at the lowest potential VL. In this ejection pulse PS2b, the generation period pwh2 of the second potential holding portion P4 is 2.8 μs.
In the second decompression portion P5, the start potential at the timing t5e is the lowest potential VL, and the termination potential at the timing t6e is the intermediate potential VB. In the ejection pulse PS2b, the generation period of the second reduced pressure portion P5 is 6 μs. Since the difference between the intermediate potential VB and the lowest potential VL is 12V, the slope of the second reduced pressure portion P5 is 2V / μs.

  Even when the ejection pulse PS2b of FIG. 14 is applied to the piezo element 433, the operation of the piezo element 433 and the pressure chamber 424 until the ink droplet is ejected and the outline of the ink flow in the ink flow path are shown in FIG. 8 is substantially the same as the case where the ejection pulses PS1a and PS1b in FIG. 8 are applied to the piezo element 433. Therefore, detailed description is omitted. Here, the following can be understood from the comparison between the meniscus state in FIG. 15 and the meniscus state in FIG. 13.

  Regarding the first decompression portion P1 that affects the degree of meniscus pull-in, the slope (about 5.8 V / μs) of the first decompression portion P1 of the ejection pulse PS2a of FIG. 12 is the first decompression portion of the ejection pulse PS2b of FIG. The slope of the portion P1 (4.5 V / μs) is larger. Further, regarding the second decompression portion P5 that affects the supply of ink to the pressure chamber 424 after ejection, the slope (about 3.3 V / μs) of the second decompression portion P5 that the ejection pulse PS2a of FIG. Is greater than the slope (2 V / μs) of the second decompression portion P5 of the ejection pulse PS2b. That is, it can be said that the ejection pulse PS2a in FIG. 12 has a stronger force that causes the ink to flow toward the pressure chamber 424 than the ejection pulse PS2b in FIG.

  However, if the meniscus pull-in amount at timing A5 is compared with the meniscus pull-in amount at timing A4, the meniscus pull-in amount at timing A5 is larger. Further, when comparing the movement amount of the meniscus from timing C5 to timing D5 with the movement amount of the meniscus from timing C4 to timing D4, the former movement amount is larger. That is, it can be said that the amplitude of pressure vibration is large.

  Further, when comparing the time required for the meniscus to return to the steady state position, in the case of 20 millipascal ink, as shown in FIG. 13, it is about 100 μs after the start of application of the first reduced pressure portion P1. On the other hand, in the case of 6 millipascal ink, as shown in FIG. 15, about 40 μs has elapsed from the start of application of the first reduced pressure portion P1. In this way, with 6 millipascal ink, the meniscus can be returned to a steady state within a time that can sufficiently cope with high-frequency ejection of ink droplets even when the ejection pulse PS2b having a weak force that causes ink flow is used. ing.

  These mean that the higher the ink viscosity, the larger the inclination of the first reduced pressure portion P1, in other words, the degree of reduced pressure of the ink pressure. As described above, the reason is considered that the ink flow (pressure vibration) caused by the first reduced pressure portion P1 assists the ink flow caused by the second reduced pressure portion P5.

  By the way, if the inclination of the first decompression portion P1 is excessively increased, the meniscus is distorted and the amount of ink droplets and the flight direction are deviated from the designed amount and direction. In addition, the meniscus may become bubbles. From these circumstances, the inclination of the first decompression portion P1 is required to be equal to or less than an inclination capable of maintaining the meniscus shape. In this example, it is preferable that the inclination of the first decompression portion P1 is an inclination with a generation period of 1 μs or more. If the inclination is determined in this way, the piezo element 433 can be protected. That is, if the potential of the piezo element 433 is suddenly changed in a short time, an excessively large current flows into the piezo element 433. However, by setting the slope so that the generation period is 1 μs or more, an excessively large current It is possible to prevent a problem that flows.

<About intermediate potential>
FIG. 16 is a diagram illustrating an ejection pulse PS2c for ejecting ink having a viscosity of 20 millipascal seconds, in which the intermediate potential VB is set to 20% of the drive voltage Vh. FIG. 17 is a diagram for explaining the meniscus state when ink is ejected once by the ejection pulse PS2c of FIG.

  In FIG. 16, the portion indicated by reference signs P1 to P5 is the ejection pulse PS2c. In this ejection pulse PS2c, the outline of the waveform is the same as each ejection pulse PS1a described above.

In the first decompression portion P1, the start potential at the timing t1f is the intermediate potential VB, and the termination potential at the timing t2f is the maximum potential VH. The drive voltage Vh in the ejection pulse PS2c is 25V. Therefore, the intermediate potential VB is 5V higher than the lowest potential VL, and the highest potential VH is 20V higher than the intermediate potential VB. And the production | generation period of the 1st pressure reduction part P1 is 2 microseconds. For this reason, the inclination of the first decompression portion P1 is 10 V / μs.
The first potential holding portion P2 is generated from timing t2f to timing t3f. The first potential holding portion P2 is constant at the maximum potential VH. In the ejection pulse PS2c, the generation period of the first potential holding portion P2 is 1 μs.
In the pressurization part P3, the start potential at the timing t3f is the highest potential VH, and the termination potential at the timing t4f is the lowest potential VL. In this ejection pulse PS2c, the generation period of the pressurizing portion P3 is 2 μs.
The second potential holding portion P4 is generated from timing t4f to timing t5f. The second potential holding portion P4 is constant at the lowest potential VL. In this ejection pulse PS2c, the generation period of the second potential holding portion P4 is 5 μs.
In the second decompression portion P5, the start potential at the timing t5f is the lowest potential VL, and the termination potential at the timing t6f is the intermediate potential VB. In this ejection pulse PS2c, the generation period of the second reduced pressure portion P5 is 4 μs. For this reason, the inclination of the second decompression portion P5 is 1.25 V / μs.

  As shown in FIG. 17, even when this ejection pulse PS2c is used, the meniscus is sufficiently drawn to the pressure chamber 424 side at timing A6. At timing D6, the meniscus has sufficiently moved to the discharge side. Thus, it can be seen that even when this ejection pulse PS2c is used, the movement range of the meniscus (the amplitude of pressure vibration) is sufficiently large. Accordingly, the meniscus returns to the steady state position when 100 μs has elapsed from the start of application of the first reduced pressure portion P1. Therefore, it can be said that even with this ejection pulse PS2c, ink droplets can be stably ejected at a high frequency of 40 kHz or higher.

  7, 9, 13, and 17, the slope of the first pressure-reducing portion P <b> 1 is the second in any of a plurality of types of ejection pulses PS <b> 1 a, PS <b> 1 b, PS <b> 2 a, PS <b> 2 c having different intermediate potentials. It can be said that the ejection of ink droplets at a high frequency can be stabilized by setting it to be larger than the inclination of the decompression portion P5.

<Continuous ejection of ink droplets>
As described above, when ink droplets are ejected continuously, after the second decompression portion P5 of the previous ejection pulse PS ends to the piezo element 433, the piezo of the first decompression portion P1 of the next ejection pulse PS. Application to the element 433 is started. In the present embodiment, the application end timing of the second decompression portion P5 and the application start timing of the first decompression portion P1 are closer as the ink droplet ejection frequency is higher. For example, a constant potential portion P6 shown in FIG. 18, more specifically, an intermediate potential VB connecting the end of the second decompression portion P5 included in the previous ejection pulse PS and the start end of the first decompression portion P1 included in the next ejection pulse PS. With respect to a certain portion, the generation time is shortened as the ink droplet ejection frequency increases.
Thereby, at the time of application of the 1st pressure reduction part P1, the influence of the ink flow resulting from the 2nd pressure reduction part P5 can be strengthened, so that the discharge frequency of an ink droplet becomes high. That is, the amount of ink supplied to the pressure chamber 424 can be increased.

  Further, in the present embodiment, as shown in FIG. 19, in the case where ink droplets are ejected at the maximum ejection frequency, the first decompression portion P1 that the next ejection pulse PS has is the second decompression portion that the previous ejection pulse PS has. It is applied following P5. With this configuration, the expansion of the pressure chamber 424 accompanying the application of the first decompression portion P1 is performed following the end of the expansion of the pressure chamber 424 accompanying the application of the second expansion portion. Accordingly, ink can be efficiently supplied to the pressure chamber 424 when ink droplets are ejected at the highest ejection frequency where ink supply is most likely to be insufficient.

  Next, the influence of ink viscosity during high frequency ejection will be considered. FIG. 20 is a diagram illustrating a meniscus state when ink having a viscosity of 20 millipascal seconds is ejected at a frequency of 50 kHz. FIG. 21 is a diagram for explaining the state of the meniscus when ink having a viscosity of 22 millipascal seconds is ejected at a frequency of 50 kHz. FIG. 22 is a diagram illustrating a meniscus state when ink having a viscosity of 6 millipascal seconds is ejected at a frequency of 50 kHz. The results shown in FIGS. 20 and 21 are obtained using the ejection pulse PS1a shown in FIG. Further, the result of FIG. 22 is obtained using the ejection pulse PS2b of FIG.

  As shown in FIG. 20, in the ink having a viscosity of 20 millipascal seconds, the discharge amount is slightly larger than the target discharge amount (20 ng in the figure), but the ink droplet discharge amount is stable in the third and subsequent discharges. You can see that That is, it can be seen that even when ink droplets are ejected at a high frequency of 50 kHz, the ink droplets can be ejected stably. This can be understood from the fact that the positions of the meniscuses at the timing indicated by reference numeral B7 are aligned.

  On the other hand, as shown in FIG. 21, with ink having a viscosity of 22 millipascal seconds, there is some variation in the ink ejection amount. That is, it can be seen that when ink droplets are ejected at a high frequency of 50 kHz, the ejection of ink droplets becomes unstable. This can be understood from the fact that there is a shift in the meniscus position at the timing indicated by reference numeral B8.

  Further, as shown in FIG. 22, in the case of ink having a viscosity of 6 millipascal seconds, the ink discharge amount is larger than the target discharge amount, but the ink droplet discharge amount is stable in the second and subsequent discharges. (Ink can be ejected stably). This can be understood from the fact that the positions of the meniscuses at the timing indicated by reference numeral B9 are aligned.

<Summary>
As can be seen from the above description, in this printer 1, the inclination of the first reduced pressure portion P1 is larger than the inclination of the second reduced pressure portion P5, so that ink is ejected to the pressure chamber 424 side during high-frequency ejection of ink droplets. It can flow efficiently. Thereby, discharge of high viscosity ink can be stabilized. And regarding the inclination of the 1st pressure-reduction part P1, this inclination is enlarged, so that the viscosity of an ink becomes high. Also in this respect, the ink can be efficiently flowed to the pressure chamber 424 side during the high-frequency ejection of the ink droplets, and the ejection of the high viscosity ink can be stabilized.

  In addition, regarding the pressurization portion P3 in each ejection pulse PS (PS1a to PS2c), that is, the ejection portion for ejecting ink, the potential is changed with a constant gradient from the highest potential VH to the lowest potential VL in each ejection pulse PS. It is determined as a part. By defining the pressurizing portion P3 in this manner, the change width of the volume in the pressure chamber 424 can be increased, and the ink discharge amount can be increased. Also, the first decompression portion P1 is configured as a portion that changes the potential from the intermediate potential VB to the maximum potential VH with a constant slope, and the second decompression portion P5 changes the potential from the lowest potential VL to the intermediate potential VB with a constant slope. It is configured as a part to be made. Thus, each of ink ejection and ink supply to the pressure chamber 424 can be performed efficiently. In addition, the terminal end of the first pressure reducing part P1 and the starting end of the pressurizing part P3, and the terminal end of the pressing part P3 and the starting end of the second pressure reducing part P5 are connected by potential holding parts P2 and P4 having a constant potential. . Thereby, the waveform of each ejection pulse PS can be simplified, and it is suitable for ejection at a high frequency of ink.

  Further, in each ejection pulse PS, the starting end potential of the first decompression portion P1 is set to a range from the lowest potential VL to 20% or more and 50% or less of the difference between the highest potential VH and the lowest potential VL. Thereby, the expansion volume of the pressure chamber 424 before ink discharge and the expansion volume of the pressure chamber 424 after ink discharge can be determined in a well-balanced manner. As a result, insufficient supply of ink to the pressure chamber 424 can be suppressed while ensuring the ink droplet ejection speed.

=== About Other Embodiments ===
The above-described embodiment is mainly described with respect to a printing system having the printer 1 as a liquid ejecting apparatus, which includes disclosure of a liquid ejecting method, a liquid ejecting system, an ejection pulse setting method, and the like. ing. Further, this embodiment is intended to facilitate understanding of the present invention and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About other heads>
In the head HD of the above-described embodiment, the type that operates to increase the volume of the pressure chamber 424 as the potential applied by the ejection pulse PS is higher is used as the piezo element 433. Other types of heads may be used. The other head HD ′ shown in FIG. 23 is a type of piezoelectric element that operates to reduce the volume of the pressure chamber 73 as the potential applied by the ejection pulse PS (see FIG. 24) is higher. Used.

  Briefly, the other head HD ′ has a common ink chamber 71, an ink supply port 72, a pressure chamber 73, and a nozzle 74. A plurality of ink flow paths corresponding to the nozzles 74 are provided from the common ink chamber 71 to the nozzles 74 through the pressure chambers 73. The volume of the pressure chamber 73 in other heads HD ′ is changed by the operation of the piezo element 75. That is, a part of the pressure chamber 73 is partitioned by the diaphragm 76, and the piezoelectric element 75 is provided on the surface of the diaphragm 76 on the opposite side to the pressure chamber 73.

  A plurality of piezo elements 75 are provided corresponding to the respective pressure chambers 73. Each piezo element 75 has, for example, a structure in which a piezoelectric body is sandwiched between an upper electrode and a lower electrode (both not shown), and is deformed by applying a potential difference between these electrodes. In this example, when the potential of the upper electrode is raised, the piezoelectric body is charged, and accordingly, the piezo element 75 is bent so as to protrude toward the pressure chamber 73 side. As a result, the pressure chamber 73 is contracted.

  The ejection pulse PS for the other head HD ′ has a waveform shown in FIG. 24, for example. In brief, the ejection pulse PS3a has a waveform obtained by inverting the ejection pulses PS1a to PS2b described above in the potential direction (high and low directions). Accordingly, the ejection pulse PS3a includes a first pressure reducing portion P1 ′, a first potential holding portion P2 ′, a pressurizing portion P3 ′, a second potential holding portion P4 ′, and a second pressure reducing portion P5 ′. .

  The first decompression portion P1 ′ has a start potential of the intermediate potential VB and a termination potential of the lowest potential VL. The first potential holding portion P2 ′ is constant at the lowest potential VL. The pressurizing portion P3 ′ has the lowest potential VL at the start potential and the highest potential VH at the termination potential. The second potential holding portion P4 ′ is constant at the maximum potential VH. In the second decompression portion P5 ′, the start potential is the highest potential VH, and the termination potential is the intermediate potential VB.

  The functions of the portions P1 ′ to P5 ′ included in the ejection pulses PS3a for the other head HD ′ are the same as the functions of the portions P1 to P5 included in the ejection pulses PS1a to PS2b described above. The intermediate potential VB is set to a potential lower by 50% of the drive voltage Vh than the highest potential VH in the ejection pulse PS3a.

  As is apparent from the figure, in the ejection pulse PS3a, the slope of the first reduced pressure portion P1 ′ is larger than the slope of the second reduced pressure portion P5 ′. That is, the amount of potential decrease per unit time increases. Then, when ink having a viscosity of 15 millipascal seconds is ejected using this ejection pulse PS3a, the meniscus becomes steady at the timing when 100 μs has elapsed from the start of application of the first reduced pressure portion P1 ′, as shown in FIG. It has returned to the position of the state. Therefore, even when this ejection pulse PS3a is used, ejection can be stabilized even when ink droplets are ejected at a high ejection frequency of 40 kHz or higher.

  The ejection pulse PS3b in FIG. 26 is a diagram for explaining the ejection pulse of the comparative example. Each part included in the ejection pulse PS3b has the same function as each part included in the ejection pulse PS3a in FIG. The ejection pulse PS3b in FIG. 26 and the ejection pulse PS3a in FIG. 24 differ in the relationship between the slope of the first reduced pressure portion P1 ′ and the slope of the second reduced pressure portion P5 ′. That is, in the ejection pulse PS3b of FIG. 26, the slope of the first reduced pressure portion P1 ′ is smaller than the slope of the second reduced pressure portion P5 ′.

  When ink having a viscosity of 15 millipascal seconds is ejected using this ejection pulse PS3b, the meniscus remains steady even after 100 μs has elapsed from the start of application of the first reduced pressure portion P1 ′, as shown in FIG. It has not returned to the position of the state. From this, it can be said that when this ejection pulse PS3b is used, ejection of ink droplets becomes unstable when ejected at a high ejection frequency of 40 kHz or higher.

  As can be seen from the above description, the relationship between the inclination of the first reduced pressure portion P1 ′ and the inclination of the second reduced pressure portion P5 ′ can be similarly applied to other heads HD ′ having piezo elements 75 of different types. .

<Discharge pulse PS>
In each of the ejection pulses PS (PS1a to PS3a) described above, the first reduced pressure portion P1 (P1 ′) is the first portion in the ejection pulse PS, and the second reduced pressure portion P5 (P5 ′) is the last portion in the ejection pulse PS. Met. The first decompression portion P1 may not be the first portion in the ejection pulse PS as long as it is generated before the pressurization portion P3 as the ejection portion. Similarly, the second decompression portion P5 may not be the last portion in the ejection pulse PS as long as it is generated after the pressurization portion P3.

<Elements that perform discharge operation>
In the printer 1, piezo elements 433 and 75 are used as elements that operate to eject ink. Here, the element that performs the ejection operation is not limited to the piezo elements 433 and 75 described above. Any element that operates according to the applied potential and gives a pressure change to the liquid in the pressure chambers 424 and 73 may be used. For example, a magnetostrictive element may be used. When the piezoelectric elements 433 and 75 are used as the elements as in the above-described embodiment, the volumes of the pressure chambers 424 and 73 can be accurately controlled based on the potential of the ejection pulse PS.

<About other application examples>
In the above-described embodiment, the printer is described as the liquid ejecting apparatus. However, the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporization apparatus, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technology as that of the present embodiment may be applied to various liquid ejection devices to which inkjet technology such as a device and a DNA chip manufacturing device is applied. These methods and manufacturing methods are also within the scope of application.

1 is a block diagram illustrating a configuration of a printing system. FIG. 2A is a cross-sectional view of the head. FIG. 2B is a diagram schematically illustrating the structure of the head. It is a block diagram explaining structures, such as a drive signal generation circuit. It is a figure for demonstrating an example of a drive signal. FIG. 5A is a diagram illustrating a state where high-viscosity ink is stably ejected. FIG. 5B is a diagram illustrating a state where high-viscosity ink is ejected in an unstable state. It is a figure explaining the discharge pulse whose inclination of the 1st pressure reduction part is larger than the inclination of the 2nd pressure reduction part. It is a figure explaining the state of a meniscus when one ink drop is discharged by the discharge pulse of FIG. It is a figure explaining the other discharge pulse whose inclination of a 1st pressure reduction part is larger than the inclination of a 2nd pressure reduction part. It is a figure explaining the state of a meniscus at the time of discharging one ink drop with the discharge pulse of FIG. It is a figure explaining the discharge pulse of the reference example whose inclination of the 1st pressure reduction part is smaller than the inclination of the 2nd pressure reduction part. It is a figure explaining the state of a meniscus when one ink drop is ejected with the ejection pulse of FIG. It is a figure explaining the other discharge pulse for discharging the ink whose viscosity is 20 millipascal second. It is a figure explaining the state of a meniscus at the time of discharging one ink drop with the discharge pulse of FIG. It is a figure explaining the discharge pulse for discharging the ink whose viscosity is 6 millipascal second. It is a figure explaining the state of a meniscus when one ink drop is discharged by the discharge pulse of FIG. FIG. 10 is a diagram illustrating another ejection pulse for ejecting ink having a viscosity of 20 millipascal seconds, in which an intermediate potential is set to 20% of a drive voltage. It is a figure explaining the state of a meniscus when one ink drop is ejected with the ejection pulse of FIG. It is a figure explaining the drive signal produced | generated at the time of continuous discharge of an ink droplet. It is a figure explaining the drive signal produced | generated when an ink drop is made to discharge with the highest discharge frequency. It is a figure explaining the state of the meniscus when ink with a viscosity of 20 millipascal seconds is ejected at a frequency of 50 kHz. It is a figure explaining the state of the meniscus when ink with a viscosity of 22 millipascal seconds is ejected at a frequency of 50 kHz. It is a figure explaining the state of the meniscus when the ink whose viscosity is 6 millipascal second is ejected at a frequency of 50 kHz. It is sectional drawing explaining another head. It is a figure explaining the discharge pulse for other heads. It is a figure explaining the state of a meniscus when one ink drop is ejected with the ejection pulse of FIG. It is a figure explaining the reference example of the discharge pulse for other heads. FIG. 27 is a diagram illustrating a meniscus state when one ink droplet is ejected with the ejection pulse of FIG. 26.

Explanation of symbols

1 printer, 10 paper transport mechanism, 20 carriage movement mechanism,
30 drive signal generation circuit, 31 DAC circuit, 32 voltage amplification circuit,
33 current amplifier circuit, 40 head unit, 41 case,
411 accommodation space, 42 channel unit, 421 channel forming substrate,
422 nozzle plate, 423 diaphragm, 423a diaphragm part,
424 pressure chamber, 425 ink supply path, 426 common ink chamber,
427 nozzle, 428 support plate, 428a island, 429 elastic film,
43 piezo element units, 431 piezo element groups, 432 fixing plate,
433 piezo elements, 434 common electrodes, 435 drive electrodes,
436 piezoelectric bodies, 44 switches, 50 detector groups,
60 printer-side controller, 61 interface unit, 62 CPU,
63 memory, 71 common ink chamber, 72 ink supply port, 73 pressure chamber,
74 nozzles, 75 piezo elements, 76 diaphragm, CP computer,
HD head, HD 'other head, HC head controller,
COM drive signal, PS discharge pulse, P1 (P1 ′) first decompression part,
P2 (P2 ′) first potential holding portion, P3 (P3 ′) pressure portion,
P4 (P4 ′) second potential holding portion, P5 (P5 ′) second decompression portion,
P6 constant potential part

Claims (8)

(A) a pressure chamber communicated with each of the liquid supply unit and the nozzle;
(B) an element that operates to change the volume of the pressure chamber in response to a change in potential;
(C) A discharge pulse for causing the element to perform a series of operations for changing the volume of the pressure chamber of the reference volume to return to the reference volume in order to discharge the liquid from the nozzle, for discharging the liquid In order to prepare, a discharge pulse generation unit that repeatedly generates a discharge pulse having a pre-discharge expansion portion that causes the element to perform an operation for expanding the pressure chamber of the reference volume; and
A method for setting ejection pulses for a liquid ejection apparatus comprising (D),
(E) The viscosity of the liquid is set within a range of 6 millipascal second or more and 20 millipascal second or less,
(F) The higher the viscosity of the liquid, the larger the amount of potential change per unit time in the expanded portion before discharge.
(G) Discharge pulse setting method. It is the setting method of the discharge pulse of Claim 1, Comprising:
The discharge pulse has a post-discharge expansion portion that causes the element to perform an operation for expanding the pressure chamber contracted from the reference volume to the reference volume after the liquid is discharged,
A method for setting an ejection pulse, wherein a potential change amount per unit time in the expanded portion before ejection is set larger than a potential change amount per unit time in the expanded portion after ejection. A discharge pulse setting method according to claim 2,
The pre-discharge expansion portion is defined as the first portion of the plurality of portions of the discharge pulse,
A method for setting an ejection pulse, wherein the post-ejection expansion part is defined as the last part of a plurality of parts of the ejection pulse. It is the setting method of the discharge pulse of Claim 3, Comprising:
The ejection pulse setting is such that the higher the liquid ejection frequency, the closer the generation start timing of the pre-ejection expansion portion of the subsequent ejection pulse is to the generation end timing of the post-ejection expansion portion of the previous ejection pulse. Method. It is the setting method of the discharge pulse of Claim 3, Comprising:
A method for setting a discharge pulse, wherein the generation start timing of the pre-discharge expansion portion included in a subsequent discharge pulse is defined as the generation end timing of the post-discharge expansion portion included in the previous discharge pulse at the highest liquid discharge frequency. A discharge pulse setting method according to any one of claims 2 to 5,
The ejection pulse is an ejection portion that causes the element to perform an operation of contracting the pressure chamber to eject the liquid, and an ejection portion in which the potential changes from one of the highest potential and the lowest potential to the other in the ejection pulse. Have
The pre-discharge expansion portion is defined as a portion where the potential changes from a reference potential corresponding to the reference volume to one of the highest potential and the lowest potential,
The ejection pulse setting method, wherein the post-ejection expansion portion is defined as a portion where the potential changes from the other of the highest potential and the lowest potential to the reference potential. It is the setting method of the discharge pulse of Claim 6, Comprising:
The ejection pulse setting method, wherein the reference potential is set within a range of 20% or more and 50% or less of a difference between the highest potential and the lowest potential from the other of the highest potential and the lowest potential. A discharge pulse setting method according to any one of claims 1 to 7,
A method for setting an ejection pulse, wherein the amount of potential change per unit time of the expanded portion before ejection is set to be equal to or less than the amount of change capable of maintaining the meniscus shape.

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