JP2021186990A - Liquid discharge head - Google Patents

Abstract

To provide a liquid discharge head fewer in power consumption than the conventional head.SOLUTION: An objective liquid discharge head comprises a pressure chamber, an actuator and an application part. In the pressure chamber, its volume in such a state that the actuator does not operate is a reference volume and a liquid is stored therein. The actuator changes the volume of the pressure chamber in response to an impressed driving signal. The application part impresses the driving signal to the actuator. The driving signal includes a vibration pulse lessening the volume of the pressure chamber compared to the reference volume, and an ejection waveform which is impressed after the vibration pulse and ejects a liquid from a nozzle communicated with the pressure chamber. The ejection waveform includes an expansion pulse enlarging the volume of the pressure chamber compared to the reference volume, and a reduction pulse impressed after the expansion pulse and lessening the volume of the pressure chamber compared to the reference volume. The pulse width of the vibration pulse is larger than 1/4 cycle in a main acoustic resonance frequency of the liquid in the pressure chamber, and the pulse width of the expansion pulse is a half period in the main acoustic resonance frequency.SELECTED DRAWING: Figure 11

Description

Embodiments of the present invention relate to a liquid discharge head.

A liquid ejection device (inkjet printer) equipped with a liquid ejection head (inkjet head) for ejecting a liquid such as ink from a nozzle is known. Such a liquid discharge head applies a drive signal to the actuator to discharge the liquid by the operation of the actuator. The liquid discharge head consumes a large amount of power due to the drive signal. Therefore, it is desired that the liquid discharge head reduces the electric power consumed by applying the drive signal.

Japanese Unexamined Patent Publication No. 2019-12398

An object to be solved by the embodiment of the present invention is to provide a liquid discharge head having lower power consumption than the conventional one.

The liquid discharge head of the embodiment includes a pressure chamber, an actuator, and an application unit. The volume of the pressure chamber when the actuator is not operating is the reference volume. The pressure chamber houses the liquid. The actuator changes the volume of the pressure chamber according to the applied drive signal. The application unit applies the drive signal to the actuator. The drive signal includes a vibration pulse and one discharge waveform. The vibration pulse reduces the volume of the pressure chamber to be smaller than the reference volume. The discharge waveform is applied after the vibration pulse, and the liquid is discharged from the nozzle communicating with the pressure chamber. The discharge waveform includes an expansion pulse and a reduction pulse. The expansion pulse expands the volume of the pressure chamber to be larger than the reference volume. The reduction pulse is applied after the expansion pulse to reduce the volume of the pressure chamber to be smaller than the reference volume. The pulse width of the vibration pulse is larger than the quarter period at the main acoustic resonance frequency of the liquid in the pressure chamber. The pulse width of the extended pulse is a half cycle at the main acoustic resonance frequency.

The schematic diagram which shows an example of the structure of the inkjet recording apparatus which concerns on 1st Embodiment and 2nd Embodiment. The perspective view which shows an example of the inkjet head shown in FIG. The schematic diagram of the ink supply apparatus shown in FIG. The plan view of the head substrate applicable to the inkjet head shown in FIG. FIG. 4 is a cross-sectional view taken along the line AA of the head substrate shown in FIG. The perspective view of the head substrate shown in FIG. The figure which shows the state of a pressure chamber. The figure which shows the state which one pressure chamber was expanded. The figure which shows the state which one pressure chamber was contracted. The figure which shows the structural example of the drive circuit which concerns on 1st Embodiment. The figure which shows an example of the drive waveform which concerns on 1st Embodiment. The figure which shows an example of the conventional drive waveform. The figure which shows the state which one pressure chamber was expanded. The figure which shows the structural example of the drive circuit which concerns on 2nd Embodiment.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the figure, the same or equivalent parts are designated by the same reference numerals. In addition, each drawing used for the description of the embodiment may be shown by appropriately changing the scale of each part for the sake of explanation.

[First Embodiment]
FIG. 1 is a schematic diagram showing an example of the configuration of an inkjet recording apparatus 1 including an inkjet head according to the first embodiment.
The inkjet recording device 1 forms an image on an image forming medium S or the like using a liquid recording material such as ink. As an example, the inkjet recording apparatus 1 includes a plurality of liquid ejection units 2, a head support mechanism 3 that movably supports the liquid ejection unit 2, and a medium support mechanism 4 that movably supports the image forming medium S. Be prepared. The image forming medium S is, for example, sheet-shaped paper or the like. The inkjet recording device 1 is an example of a liquid ejection device.

As shown in FIG. 1, a plurality of liquid discharge units 2 are supported by the head support mechanism 3 in a state of being arranged in parallel in a predetermined direction. The head support mechanism 3 is attached to a belt 6 hung on a roller 5. The inkjet recording device 1 can move the head support mechanism 3 in the main scanning direction M orthogonal to the transport direction of the image forming medium S by rotating the roller 5. The liquid ejection unit 2 integrally includes an inkjet head 10 and an ink supply device 20. The liquid ejection unit 2 performs an ejection operation of ejecting a liquid I such as ink from the inkjet head 10. As an example, the inkjet recording apparatus 1 is a scanning method for forming a desired image on an image forming medium S arranged opposite to each other by performing a liquid ejection operation while reciprocating the head support mechanism 3 in the main scanning direction M. Is. Alternatively, the inkjet recording device 1 may be a single-pass system in which the liquid ejection operation is performed without moving the head support mechanism 3. In this case, it is not enough to provide the roller 5 and the belt 6. Further, in this case, the head support mechanism 3 is fixed to, for example, the housing of the inkjet recording device 1. Further, in this case, the transport direction of the image forming medium S is, for example, the M direction. The inkjet head 10 is an example of a liquid ejection head.

Each of the plurality of liquid ejection units 2 corresponds to, for example, one of four colors of ink of CMYK (cyan, magenta, yellow, and key (black)). That is, each of the plurality of liquid ejection units 2 corresponds to any of cyan ink, magenta ink, yellow ink, and black ink. Then, each of the plurality of liquid ejection units 2 ejects ink of the corresponding color. The liquid ejection unit 2 can continuously eject one or a plurality of droplets of ink of the corresponding color with respect to one pixel on the image forming medium S. The larger the number of times of continuous ejection, the larger the amount of droplets that land on one pixel. Therefore, the larger the number of times of continuous ejection, the darker the corresponding color appears. As a result, the inkjet recording device 1 can express the gradation of the image formed on the image forming medium S.

FIG. 2 is a perspective view showing an example of the inkjet head 10. The inkjet head 10 includes a nozzle 101, a head substrate 102, a drive circuit 103, and a manifold 104.

The manifold 104 includes an ink supply port 105 and an ink discharge port 106. The ink supply port 105 is a supply port for supplying the liquid I to the nozzle 101. Further, the ink discharge port 106 is a liquid I discharge port. The nozzle 101 ejects a droplet of liquid I supplied from the ink supply port 105 in response to a drive signal given from the drive circuit 103. The liquid I that has not been ejected from the nozzle 101 is ejected from the ink ejection port 106.

FIG. 3 is a schematic view of the ink supply device 20 used in the inkjet recording device 1. The ink supply device 20 is a device that supplies the liquid I to the inkjet head 10. The ink supply device 20 includes a supply-side ink tank 21, a discharge-side ink tank 22, a supply-side pressure adjustment pump 23, a transport pump 24, a discharge-side pressure adjustment pump 25, and a supply pump 26. These are connected by a tube through which the liquid I can flow.

The supply-side ink tank 21 is connected to the ink supply port 105 via a tube. The supply-side ink tank 21 supplies the liquid I to the ink supply port 105 of the inkjet head 10.
The discharge side ink tank 22 is connected to the ink discharge port 106 via a tube. The discharge side ink tank 22 temporarily stores the liquid I discharged from the ink discharge port 106 of the inkjet head 10.

The supply-side pressure adjusting pump 23 adjusts the pressure of the supply-side ink tank 21.
The transport pump 24 recirculates the liquid I stored in the discharge-side ink tank 22 to the supply-side ink tank 21 via a tube.
The discharge side pressure adjusting pump 25 adjusts the pressure of the discharge side ink tank 22.
The supply pump 26 sends the liquid I in the ink cartridge 30 to the supply side ink tank 21 of the ink supply device 20.
The ink cartridge 30 includes a tank capable of holding the liquid I. Further, the ink cartridge 30 stores liquid information. The liquid information is information about the liquid I in the ink cartridge 30.

The inkjet head 10 will be described in more detail.
FIG. 4 is a plan view of the head substrate 102 applicable to the inkjet head 10. In FIG. 4, the internal structure of the head substrate 102 is shown by partially not showing the lower left of the nozzle plate 109 in the drawing. FIG. 5 is a sectional view taken along line AA of the head substrate 102 shown in FIG. FIG. 6 is a perspective view of the head substrate 102 shown in FIG.

As shown in FIGS. 4 and 5, the head substrate 102 includes a piezoelectric member 107, an ink flow path member 108, a nozzle plate 109, a frame member 110, and a plate wall 111. Further, the ink flow path member 108 is formed with an ink supply hole 112 and an ink discharge hole 113. The space surrounded by the ink flow path member 108, the nozzle plate 109, the frame member 110, and the plate wall 111 and in which the ink supply hole 112 is formed is the ink supply path 114. Further, the space surrounded by the ink flow path member 108, the nozzle plate 109, the frame member 110, and the plate wall 111 and in which the ink discharge hole 113 is formed is the ink discharge path 117. The ink supply hole 112 communicates with the ink supply path 114. The ink discharge hole 113 communicates with the ink discharge path 117. The ink supply hole 112 is fluidly connected to the ink supply port 105 of the manifold 104. The ink discharge hole 113 is fluidly connected to the ink discharge port 106 of the manifold 104.

The piezoelectric member 107 has a plurality of long grooves extending from the ink supply path 114 to the ink discharge path 117. These elongated grooves become part of the pressure chamber 115 or the air chamber 116. The pressure chamber 115 and the air chamber 116 are formed every other one. That is, in the piezoelectric member 107, the pressure chamber 115 and the air chamber 116 are alternately formed. The air chamber 116 is formed by closing both ends of the long groove with a plate wall 111. By closing both ends of the long groove with the plate wall 111, the liquid I of the ink supply path 114 and the ink discharge path 117 is prevented from flowing into the air chamber 116. A groove is formed at a portion of the plate wall 111 in contact with the pressure chamber 115. As a result, the liquid I flows into the pressure chamber 115 from the ink supply passage 114, and the liquid I is discharged from the pressure chamber 115 into the ink discharge passage 117. Further, the pressure chamber 115 accommodates the inflowing liquid I.

As shown in FIGS. 6 to 9, the piezoelectric member 107 includes a wiring electrode 119 (1192, 1194, 1196, ...), A wiring electrode 121 (1211, 1213, 1215, ...), And a wiring electrode 122 (1221, 1223, ...). 1225, ...) Is formed. Electrodes 120, which will be described later, are formed on the inner surfaces of the piezoelectric members of the pressure chamber 115 and the air chamber 116. The wiring electrode 119 electrically connects the electrode 120 and the drive circuit 103. The ink flow path member 108, the frame member 110, and the plate wall 111 are preferably made of, for example, a material having a small dielectric constant and a small difference in thermal expansion coefficient from the piezoelectric member. As these materials, for example, alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), aluminum nitride (AlN), lead zirconate titanate (PZT), or the like is used. Is possible.

As shown in FIGS. 7 to 9, the piezoelectric member 107 is formed by laminating the piezoelectric member 1071 and the piezoelectric member 1072. 7 to 9 are views showing the state of the pressure chamber. The polarization directions of the piezoelectric member 1071 and the piezoelectric member 1072 are opposite to each other along the plate thickness direction. The piezoelectric member 107 is formed with a plurality of long grooves connected in parallel from the ink supply path 114 to the ink discharge path 117.

Electrodes 120 (1202, 1204, 1206, ...), Electrodes 123 (1231, 1233, 1235, ...) And electrodes 125 (1251, 1253, 1255, ...) Are formed on the inner surface of each elongated groove. The space surrounded by the long groove and one surface of the nozzle plate 109 covering the long groove becomes the pressure chamber 115 and the air chamber 116. In the example of FIG. 7, each of the spaces indicated by the reference numerals 1152, 1154, 1156, ... Is the pressure chamber 115, and each of the spaces indicated by the reference numerals 1161, 1163, 1165, ... Is the air chamber 116.

As described above, the pressure chambers 115 and the air chambers 116 are arranged alternately. The electrode 120 is connected to the drive circuit 103 through the wiring electrode 119. The piezoelectric member 107 constituting the partition wall of the pressure chamber 115 is sandwiched by the electrodes 120 provided on the inner surface of each elongated groove. The piezoelectric member 107 and the electrode 120 constitute the actuator 118.

The drive circuit 103 applies an electric field to the actuator 118 by a drive signal. The actuator 118 is sheared and deformed by the applied electric field with the joint portion between the piezoelectric member 1071 and the piezoelectric member 1072 as the top, as in the actuators 1184 and 1185 of FIG. The volume of the pressure chamber 115 changes due to the deformation of the actuator 118. Due to the change in the volume of the pressure chamber 115, the liquid I inside the pressure chamber 115 is pressurized or depressurized. By this pressurization or depressurization, the liquid I is discharged from the nozzle 101 (1012, 1014, 1016, ...). As the piezoelectric member 107, for example, lead zirconate titanate (PZT: Pb (Zr, Ti) O ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. Lead zirconate titanate (PZT) having a high piezoelectric constant is preferable.

The electrode 120 has, for example, a two-layer structure of nickel (Ni) and gold (Au). The electrode 120 is uniformly formed in the long groove by, for example, a plating method. As a method for forming the electrode 120, a sputtering method or a thin-film deposition method can be used in addition to the plating method. The elongated groove has, for example, a shape of 1.5 to 2.5 [mm] in the longitudinal direction, a depth of 15.0 to 300.0 [μm], and a width of 30.0 to 110.0 [μm], and is 70 to 180 [. They are arranged in parallel with a pitch of [μm]. As mentioned above, the long groove becomes part of the pressure chamber 115 or the air chamber 116. The pressure chamber 115 and the air chamber 116 are arranged alternately.

The nozzle plate 109 is adhered on the piezoelectric member 107. A nozzle 101 is formed in the central portion of the pressure chamber 115 of the nozzle plate 109 in the longitudinal direction. The material of the nozzle plate 109 is, for example, a polyimide film. Alternatively, the material of the nozzle plate 109 may be a metal material such as stainless steel, an inorganic material such as single crystal silicon, or a resin material such as a polyimide film.

The inkjet head 10 described above has an ink supply path 114 at one end of the pressure chamber 115, an ink discharge path 117 at the other end, and a nozzle 101 at the center of the pressure chamber 115. The inkjet head 10 is not limited to this configuration example. For example, the inkjet head may have a nozzle at one end of the pressure chamber 115 and an ink supply path at the other end.

Next, the operating principle of the inkjet head 10 according to the present embodiment will be described with reference to FIGS. 7 to 9.
FIG. 7 shows a head substrate 102 in a state where a ground voltage is applied to all the electrodes via wiring electrodes. The electrodes are the electrode 120, the electrode 123, and the electrode 124. In FIG. 7, since all the electrodes have the same potential, no electric field is applied to the actuators 1181 to 1188. Therefore, the actuators 1181 to 1188 are not deformed. The volume of the pressure chamber 1154 at this time is the volume in the state where the actuator is not operating, and is an example of the reference volume.

FIG. 8 shows the head substrate 102 in a state where the voltage Va is applied only to the electrode 1204. In the state shown in FIG. 8, a potential difference occurs between the electrode 1204 and the electrodes 1243 and 1235 on both sides of the electrode 1204. The actuator 1184 and the actuator 1185 are shear-deformed so as to expand the volume of the pressure chamber 1154 due to the applied potential difference. Here, when the voltage of the electrode 1204 is returned from Va to the ground voltage, the actuator 1184 and the actuator 1185 return from the state of FIG. 8 to the state of FIG. 7.

Further, in FIG. 9, the volume of the pressure chamber 1154 is reduced. In FIG. 9, the actuator 1184 and the actuator 1185 are deformed into a shape opposite to that shown in FIG.
FIG. 9 shows a head substrate 102 in a state where the electrode 1204 is used as a ground voltage and a voltage Va is applied only to the electrode 1243 and the electrode 1235. In the state shown in FIG. 9, a potential difference (opposite electric field) opposite to that in FIG. 8 occurs between the electrode 1204 and the electrodes 1243 and 1235 on both sides of the electrode 1204. Due to these potential differences, the actuator 1184 and the actuator 1185 undergo shear deformation in the direction opposite to the shape shown in FIG. Here, when the voltage of the electrode 1243 and the electrode 1235 is returned from Va to the ground voltage, the actuator 1184 and the actuator 1185 return from the state of FIG. 9 to the state of FIG. 7.
In the actuator 1184, the electrode 1204 is an example of the first electrode. Further, in the actuator 1184, the electrode 1243 is an example of the second electrode. In the actuator 1185, the electrode 1204 is an example of the first electrode. Further, in the actuator 1185, the electrode 1235 is an example of the second electrode. The other actuator 118 also includes a first electrode and a second electrode.

When transitioning from the state of FIG. 8 to the state of FIG. 7 and from the state of FIG. 7 to the state of FIG. 9, the volume of the pressure chamber 115 decreases, so that the pressure of the liquid I in the pressure chamber 115 rises. Then, the droplets are ejected from the nozzle 101.

FIG. 10 is a diagram showing a configuration example of the drive circuit 103. The drive circuit 103 shown in FIG. 10 is partially omitted. The drive circuit 103 includes a voltage switching unit 31 (311, 312, ...), A voltage switching unit 32 (321, 322, ...), And a voltage control unit 33. The drive circuit 103 includes, for example, voltage switching units 31 as many as the number of pressure chambers 115 inside the inkjet head 10. Further, the drive circuit 103 includes, for example, as many voltage switching units 32 as there are pressure chambers 115 inside the inkjet head 10.

The drive circuit 103 is connected to the first voltage source 40 and the second voltage source 41. The drive circuit 103 selectively supplies the voltages supplied from the first voltage source 40 and the second voltage source 41 to the wiring electrodes 119, 121, and 122. In the example shown in FIG. 10, the output voltage of the first voltage source 40 is a ground voltage, and the voltage value thereof is VO (VO = 0 [V]). Further, the voltage value indicated by the output voltage of the second voltage source 41 is Va. The voltage value Va is a voltage higher than that of VO.

The voltage switching unit 31 and the voltage switching unit 32 are composed of, for example, a semiconductor switch.
Each voltage switching unit 31 is connected to the wiring electrode 119. That is, the voltage switching unit 311 is connected to the wiring electrode 1192, the voltage switching unit 312 is connected to the wiring electrode 1194, and the voltage switching unit 313 is connected to the wiring electrode 1196. The same applies to the voltage switching 314, the voltage switching 315, and so on.
Each voltage switching unit 32 is connected to the wiring electrode 121 and the wiring electrode 122. That is, the voltage switching unit 321 is connected to the wiring electrode 1221 and the wiring electrode 1213, the voltage switching unit 322 is connected to the wiring electrode 1223 and the wiring electrode 1215, and the voltage switching unit 323 is connected to the wiring electrode 1225 and the wiring electrode 1217. The same applies to the voltage switching unit 324, the voltage switching unit 325, and so on.

Further, the voltage switching unit 31 and the voltage switching unit 32 are connected to the first voltage source 40 and the second voltage source 41 via the wiring drawn into the drive circuit 103.
The voltage switching unit 31 has a changeover switch for switching the voltage source connected to the wiring electrode 119. The voltage switching unit 31 uses this switch to select a voltage source to be connected to the wiring electrode 119 from the first voltage source 40 and the second voltage source 41. For example, the voltage switching unit 311 connects any one of the first voltage source 40 or the second voltage source 41 to the wiring electrode 1192 by the changeover switch.
The voltage switching unit 32 has a switching switch for switching the voltage source connected to the wiring electrode 121 and the wiring electrode 122. The voltage switching unit 32 uses this switch to select a voltage source to be connected to the wiring electrode 121 and the wiring electrode 122 from the first voltage source 40 and the second voltage source 41. For example, the voltage switching unit 321 connects any one of the first voltage source 40 or the second voltage source 41 with the wiring electrode 1221 and the wiring electrode 1213 by the changeover switch.

The voltage control unit 33 is connected to each of the voltage switching unit 31 and the voltage switching unit 32. The voltage control unit 33 outputs a command indicating which voltage source to select from the first voltage source 40 and the second voltage source 41 to each voltage switching unit 31 and the voltage switching unit 32. For example, the voltage control unit 33 receives print data from the outside of the drive circuit 103, and determines the switching timing of the voltage source in each voltage switching unit 31 and the voltage switching unit 32. Then, the voltage control unit 33 outputs a command to select either the first voltage source 40 or the second voltage source 41 to the voltage switching unit 31 and the voltage switching unit 32 at the determined switching timing. The voltage switching unit 31 switches the voltage source connected to the wiring electrode 119 according to the command from the voltage control unit 33. The voltage switching unit 32 switches the voltage source connected to the wiring electrode 121 and the wiring electrode 122 according to the command from the voltage control unit 33.
The first voltage source 40 is an example of the first voltage source. The second voltage source 41 is an example of the second voltage source.

FIG. 11 is a diagram showing an example of a drive waveform of a drive signal given to the actuator 118 by the drive circuit 103. The drive waveform 515 shows an example of a drive waveform when five droplets are continuously ejected. The drive waveform 512 shows an example of a drive waveform when two droplets are continuously ejected. The drive waveform 511 shows an example of the drive waveform when one droplet is continuously ejected. The illustration of the drive waveform 513 and the drive waveform 514 when the number of droplets to be continuously ejected is 3 or 4 is omitted. The drive waveforms 511 to 515 are collectively referred to as a drive waveform 51.

In FIG. 11, the horizontal axis is time and the vertical axis is potential difference. The potential difference is the potential difference of the electrode 120 with reference to the potential of the electrode 123 or the electrode 124. The potential difference indicates the voltage of the electrode 120. The drive waveform 51 shown in FIG. 11 assumes the potential difference of the electrode 1204 shown in FIG. 7. The air chambers 116 on both sides of the electrode 1204 are an air chamber 1163 and an air chamber 1165. Further, the electrodes on the electrode 1204 side of the air chambers 1163 and the inner walls of the air chambers 1165 on both sides of the electrode 1204 are the electrodes 1243 and the electrodes 1235. The wiring electrodes connected to the electrode 1243 and the electrode 1235 are the wiring electrode 1223 and the wiring electrode 1215. Therefore, when the drive waveform 51 is applied to the electrode 1204, the potential difference shown in FIG. 11 is the potential difference of the electrodes 1204 based on the potentials of the wiring electrode 1223 and the wiring electrode 1215 (electrode 1243 and electrode 1235).

When the voltage of the drive waveform 51 applied to the electrode 1204 is 0, the pressure chamber 1154 is in the state shown in FIG. 7, and the volume does not change. Further, when the voltage of the drive waveform 51 applied to the electrode 1204 is Va, the pressure chamber 1154 is in the state shown in FIG. 8, and the volume expands. Further, when the voltage of the drive waveform 51 applied to the electrode 1204 is −Va, the pressure chamber 1154 is in the state shown in FIG. 9, and the volume is reduced.

The drive waveform 51 includes a vibration pulse and a discharge waveform in this order. The vibration pulse is applied to generate a pressure vibration to facilitate the ejection of the droplet. The ejection waveform is applied to eject the droplet from the nozzle 101. The discharge waveform is an example of a discharge waveform in which the liquid I is discharged from the nozzle 101.

Each pulse included in the drive waveform 51 has a rising time and a falling time. Therefore, each pulse has a waveform close to a trapezoid. Therefore, it can be said that each pulse is a trapezoidal wave.

The drive waveform 511 includes one discharge waveform, the drive waveform 512 includes two continuous discharge waveforms, ..., And the drive waveform 515 includes five continuous discharge waveforms. For example, the drive waveform 515 shown in FIG. 11 includes a vibration pulse and a first discharge waveform to a fifth discharge waveform in this order. Further, the drive waveform 512 includes a vibration pulse, a first discharge waveform, and a second discharge waveform in this order. The drive waveform 511 includes the vibration pulse and the first discharge waveform in this order. The number of discharge waveforms included in the drive waveform 51 is N.

The drive circuit 103 first starts applying a vibration pulse. The vibration pulse is, for example, a falling waveform having an sp width in which the voltage changes in the order of 0 and −Va. The width indicates the time from the start of application of the pulse to the end of application. Therefore, the sp width indicates that the time from the start of application of the pulse to the end of application is sp. With the start of application of the vibration pulse, the potential difference of the electrode 1204 changes from 0 to −Va. Then, the voltage of the electrode 1204 is held at −Va until the application of the vibration pulse is completed. The total of the time until the potential difference of the electrode 1204 falls from 0 to −Va and the time when the potential difference of the electrode 1204 is held at −Va is the time sp.
When the application of the vibration pulse is started, the volume of the pressure chamber 1154 is reduced, and the liquid I in the pressure chamber 1154 is pressurized. The pressurization due to the start of application of the vibration pulse shall be such that the droplets are not ejected from the nozzle 101.

The voltage control unit 33 controls the voltage switching unit 31 and the voltage switching unit 32 for applying the vibration pulse. By this control, the voltage switching unit 31 connects the first voltage source 40 and the wiring electrode 1194. Then, the voltage switching unit 32 connects the second voltage source 41 to the wiring electrode 1223 and the wiring electrode 1215. As a result, as shown in FIG. 9, the volume of the pressure chamber 1154 is reduced.

The drive circuit 103 ends the application of the vibration pulse after a predetermined time sp has elapsed from the start of the application of the vibration pulse. Then, the drive circuit 103 starts applying the first discharge waveform at the same time as the application of the vibration pulse is completed. The discharge waveform of the drive waveform 51 is, for example, a trapezoidal wave whose voltage changes in the order of −Va, 0, Va, 0, −Va. Further, the discharge waveform includes an expansion pulse and a reduction pulse in this order.

The extended pulse is a rising waveform having a dp width in which the voltage changes in the order of −Va, 0, Va. That is, the time from the start of application of the extended pulse to the end of application is the time dp (dpA, dpB, dpC, ...). With the start of application of the expansion pulse, the potential difference of the electrode 1204 changes from −Va to Va. Then, the voltage of the electrode 1204 is held in Va until the end of application of the expansion pulse. The total of the time from which the potential difference of the electrode 1204 rises from −Va to Va and the time when the potential difference of the electrode 1204 is held in Va is the time dp. The width of the first extended pulse is time dpA. The width of the second extended pulse is time dpB. The width of the third extended pulse is time dpC. The width of the fourth extended pulse is time dpD. The width of the fifth extended pulse is the time dpE.
By the end of application of the vibration pulse and the start of application of the first expansion pulse, the volume of the pressure chamber 1154 is expanded and the pressure of the liquid I in the pressure chamber 1154 is reduced. Further, the volume of the pressure chamber 1154 is expanded and the pressure of the liquid I in the pressure chamber 1154 is reduced by the end of application of the (k-1) th discharge waveform and the start of application of the kth expansion pulse. In addition, k is an arbitrary integer of 2 or more and N or less.

The voltage control unit 33 controls the voltage switching unit 31 and the voltage switching unit 32 for applying the extended pulse. By this control, the voltage switching unit 31 connects the second voltage source 41 and the wiring electrode 1194. Then, the voltage switching unit 32 connects the first voltage source 40 with the wiring electrode 1223 and the wiring electrode 1215. As a result, as shown in FIG. 8, the volume of the pressure chamber 1154 is expanded.

The reduction pulse is a falling waveform in which the voltage changes in the order of Va, 0, −Va. The start of application of the reduction pulse coincides with the end of application of the expansion pulse. With the start of application of the reduction pulse, the potential difference of the electrode 1204 changes from −Va to Va. Then, the voltage of the electrode 1204 is held at −Va until the application of the reduction pulse is completed.
By the end of application of the expansion pulse and the start of application of the reduction pulse, the volume of the pressure chamber 1154 is reduced, and the pressure of the liquid I in the pressure chamber 1154 rises. As a result, the liquid I in the pressure chamber 1154 is discharged as droplets from the nozzle 101.

The voltage control unit 33 controls the voltage switching unit 31 and the voltage switching unit 32 for applying the reduction pulse. By this control, the voltage switching unit 31 connects the first voltage source 40 and the wiring electrode 1194. Then, the voltage switching unit 32 connects the second voltage source 41 to the wiring electrode 1223 and the wiring electrode 1215. As a result, as shown in FIG. 9, the volume of the pressure chamber 1154 is reduced.

In the pressure chamber 1154, the potential difference from 0 to the potential difference-Va due to the start of application of the vibration pulse, and the rise from the potential difference-Va to the potential difference Va due to the end of application of the vibration pulse and the start of application of the first discharge waveform. Pressure vibration is generated in the liquid I. By lowering the potential difference of the electrode 1204 from Va to −V in accordance with this pressure vibration, the ejection force of the droplet can be increased. Therefore, by bringing the time sp and the time dpA close to the half-cycle AL of the pressure vibration of the liquid I in the pressure chamber 115, the discharge force of the first discharge waveform can be increased. In order to obtain a strong discharge force, it is preferable that the time sp and the time dpA are in the range of 0.5AL or more and 1.5AL or less. Further, it is more preferable that the discharge force of the first discharge waveform can be maximized by matching the time sp and the time dpA with AL. The half cycle AL of the pressure vibration is half the time of the natural vibration cycle (cycle at the main acoustic resonance frequency) of the liquid I in the pressure chamber 115.

The time from the center of the (k-1) th expansion pulse to the center of the kth expansion pulse is 2UL. The center of the pulse is the center point between the start and end of application of the pulse. The discharge force of the k-th discharge waveform can be increased by starting to apply the k-th discharge waveform in time with the vibration generated in the pressure chamber 1154 by the (k-1) th discharge waveform. Therefore, it is preferable to set the time 2UL to 2AL.

The time from the center of the expansion pulse of the Nth discharge waveform to the end of application of the reduction pulse is 2.5 VL. When the application of the reduction pulse of the Nth discharge waveform is completed, the potential difference of the electrode 1204 changes from −Va to 0. The reduction pulse of the Nth discharge waveform is a suppression pulse. The suppression pulse is applied to suppress the residual vibration. In the drive waveform 511, the first discharge waveform is the Nth discharge waveform. Therefore, the reduction pulse of the first discharge waveform of the drive waveform 511 is a suppression pulse.

The time 2.5 VL from the center of the expansion pulse of the Nth discharge waveform to the end of application of the reduction pulse is, for example, in the range of 2AL to 3AL. Within this range, the suppression pulse has a function of suppressing residual vibration. Preferably, 2.5VL = 2.5AL. In this case, the vibration having a phase opposite to the vibration generated by the Nth discharge waveform is applied to the pressure chamber 1154 by the suppression pulse, and the residual vibration in the pressure chamber 1154 is suppressed. In addition, VL = UL may be used.

Although the electrode 1204 has been described above as a representative, the same applies to the other electrodes 120 (electrode 1202 and electrode 1206, electrode 1208, electrode 1210, ...).

As described above, the liquid ejection unit 2 changes the amount of droplets landing on one pixel according to the number of droplets continuously ejected to the image forming medium S, thereby realizing gradation expression. In the first embodiment, the gradation is in 6 stages of 0 to 5. When the droplet is landed on the image forming medium S while transporting the image forming medium S in the direction perpendicular to the ejection direction of the droplet, the landing position deviation of the continuously ejected droplet on the image forming medium S is large. Small is desirable. In order to reduce the landing position deviation, it is desirable that the velocity of the droplet ejected later among the droplets ejected continuously is the same as or higher than the velocity of the droplet ejected before that. Further, when the velocity of the droplet ejected last is extremely higher than that of the droplet ejected first, the landing position shift becomes large.

Therefore, consider adjusting the velocity of the droplet ejected by the drive waveform.
First, consider the drive waveform 512 that continuously ejects two droplets. The pressure vibration in the pressure chamber 115 generated by the vibration pulse and the first ejection waveform is attenuated by ejecting the first droplet from the nozzle 101. Further, the pressure vibration is attenuated by the viscous resistance in the pressure chamber 115. Here, the second expansion pulse, which is the Nth discharge waveform, is applied at the timing when the time from the center of the first expansion pulse to the center of the second expansion pulse becomes 2UL. As a result, it is possible to compensate for the damping component of the pressure vibration against the pressure vibration damped by the above-mentioned factors and the like. As a result, a ejection force for ejecting the second droplet is obtained. If the attenuation of the pressure vibration and the addition of the pressure vibration due to the second discharge waveform are about the same, the discharge speeds of the first droplet and the second droplet are almost the same. That is, the second ejection waveform plays a role of maintaining the pressure vibration required for the second droplet ejection. The m-th droplet means a droplet ejected by the m-th ejection waveform. However, m is an integer of 1 or more and N or less.

Here, for example, even if the width dpB of the second ejection waveform is AL, if the ejection speed of the second droplet is slower than the first ejection speed, the width sp of the vibration pulse is made smaller than AL. Or think about making it bigger. This is likely to occur when the viscosity of the liquid I is high or the flow path resistance of the pressure chamber 115 is high. If the width sp of the vibration pulse is made smaller or larger than AL, the phase of the pressure vibration generated in the pressure chamber 115 by the vibration pulse and the phase of the pressure vibration generated in the pressure chamber 115 by the first pulse deviate from each other. Therefore, by making the width sp of the vibration pulse smaller or larger than AL, the ejection speed of the first droplet can be made smaller than when the width sp of the vibration pulse is AL.

Further, the ejection speed of the second droplet can be reduced by making the width dpB of the second ejection waveform smaller or larger than AL. When the viscosity of the liquid I is low or the flow path resistance of the pressure chamber is small, the ejection speed of the second droplet increases when the pulse width dpB width is close to AL. As a result, the first droplet and the second droplet may be coalesced, and the velocity of the coalesced droplet may be extremely higher than the velocity of the droplet ejected by the waveform 511. As a result, the landing position shift may be larger than the position where the first droplet lands on the image forming medium S. Therefore, it is necessary to adjust the width dpB so that the ejection speed of the second droplet does not become too large as compared with the ejection speed of the first droplet. From the viewpoint of reducing the voltage Va, it is preferable to maximize the ejection force of the drive waveform in the first droplet ejection without residual vibration due to the prior droplet ejection. For this purpose, the width sp and the width dpA are preferably close to AL, and more preferably matched with AL.

Further, the ejection speed of the second droplet can be adjusted by making the time 2UL from the center of the first ejection waveform to the center of the second ejection waveform smaller or larger than 2AL. However, in order to strengthen the pressure vibration in the pressure chamber 115 generated by the vibration pulse and the first discharge waveform by the pressure vibration generated by the second discharge waveform, the time 2UL is 1.5AL to 2.5AL. It is preferably within the range of. When the time 2UL is less than 1.5AL and the range is 2.5AL to 3.5AL, the phase of the pressure vibration generated by the second discharge waveform is inverted with respect to the pressure vibration generated by the first discharge waveform. Therefore, the pressure vibration cannot be strengthened.

Next, consider the drive waveform 515 that continuously ejects five droplets. The five droplets are ejected from the nozzle 101 at the timing of falling from the potential difference Va to the potential difference − Va in each of the first ejection waveform to the fifth ejection waveform. Here, when the time 2UL is set to 2AL, the ratio of the droplet velocity ejected in the latter half to the droplet velocity at the beginning (droplet velocity in the latter half / droplet velocity at the beginning) becomes large.

Similar to the drive waveform 512, the second and subsequent ejection waveforms of the drive waveform 515 play a role of maintaining the pressure vibration required for the second and subsequent droplet ejection. If the flow path resistance in the inkjet head 10 such as the pressure chamber 115 is low due to the viscosity of the liquid I, the flow path structure, etc., the discharge force applied to maintain the pressure vibration required for the second and subsequent droplet discharges. Is smaller, so the widths dpB to dpE can be made smaller or larger than AL. From the viewpoint of reducing the voltage Va, the width sp and the width dpA are preferably close to AL, and more preferably matched with AL.

Further, by making the time 2UL smaller or larger than 2AL, the second and subsequent discharge speeds can be adjusted. However, since the residual vibration (pressure vibration) generated in the nth discharge waveform is strengthened by the pressure vibration generated in the n + 1th discharge waveform, the time 2UL is preferably in the range of 1.5AL to 2.5AL. ..

In the drive waveform of the present embodiment, the discharge force is obtained by matching the phases of the residual vibration in the pressure chamber 115 and the discharge waveform. Further, the magnitude of the residual vibration generated by the application of the drive waveform changes depending on the viscosity of the liquid I, the flow path structure of the inkjet head, the material of the flow path of the inkjet head, and the like. Therefore, it is necessary to adjust the ratio of each waveform parameter such as time sp, time dpA to time dpE, and time UL of the drive waveform according to the viscosity of the liquid I, the type of the inkjet head, and the like.

〔Example〕
An embodiment for carrying out the above embodiment will be described by way of examples. The embodiments do not limit the scope of the above embodiments.

The examples were performed using a simulation by numerical analysis. The displacement generated in the actuator was calculated by structural analysis. The fluid flow in the pressure chamber after being displaced by the actuator was calculated by compressible fluid analysis. The behavior of the droplets ejected from the nozzle was calculated by surface fluid analysis.

The scope of structural analysis will be described with reference to FIGS. 4 and 5. The vertical range in FIG. 5 is a range including the piezoelectric member 107 forming the pressure chamber 115 and the nozzle plate 109. The range in the left-right direction in FIG. 5 is a range including the piezoelectric member 107 and the plate wall 111. The vertical range in FIG. 4 is the range from the AA line of the pressure chamber 115 to the adjacent air chamber 201. The boundary surface having a normal in the vertical direction in FIG. 4 was defined as a symmetric boundary. The vertical direction in FIG. 4 is the depth direction in FIG.

The range of the compressible fluid analysis was the range including the pressure chamber. The boundary between the ink supply path and the ink discharge path and the pressure chamber was set as a free inflow condition. The pressure value near the nozzle in the pressure chamber was used as the input condition for surface fluid analysis to analyze the liquid surface of the nozzle. As a result, the liquid flow rate flowing into the nozzle from the pressure chamber in the surface fluid analysis was input to the compressible fluid analysis as the outflow flow rate in the vicinity of the nozzle in the pressure chamber. Then, coupled analysis was performed.

(Numerical analysis 1)
Numerical analysis 1 is a simulation of a case where a liquid I having a viscosity of about 30 [mPas] and a specific density of about 0.85 is discharged by an inkjet head 10 as a first embodiment. The AL of the simulation model of the inkjet head 10 of the first embodiment was about 2 μsec.

Here, if the actuator is regarded as a capacitor and the internal resistance, wiring resistance and other energy loss of the drive circuit 103 are regarded as resistors, the voltage source, the drive circuit 103, the wiring electrode 119, the wiring electrode 121 and the wiring electrode 122, and The circuit connecting the actuators can be likened to an RC series circuit. Consider the case where the voltage source is switched in this RC series circuit. The rise and fall times of each trapezoidal wave of the drive waveform correlate with the time constant of the RC circuit, and indicate the charge time or discharge time required for the voltage change inside the capacitor when the voltage source connected to the capacitor changes. ing. In the embodiment, the drive waveform of the simulation model is set by setting the rise and fall time of each pulse of the drive waveform 51 to about 0.2 μsec.

In the numerical analysis 1, a simulation was performed when the inkjet head 10 of the embodiment ejected droplets according to the drive waveforms 511 to 515. The waveform parameters at this time were UL = AL, sp = AL, and dpA = AL. In addition, as shown in Table 1, simulations were performed with various changes in dpB to dpE, and the velocities of the droplets at the 1st to 5th drops in each waveform width were obtained. The results are shown in Table 1. When a plurality of droplets were united in the middle, the velocity of the combined droplets was described in the velocity column of the first droplet of the combined plurality of droplets. In addition, "←" is described in the velocity column of the droplets other than the beginning of the plurality of combined droplets. Further, the velocity ratio between the velocity of the last droplet (hereinafter referred to as "last drop velocity") and the velocity of the first droplet (hereinafter referred to as "first drop velocity") is also shown. However, when all the droplets of the 1st to 5th drops are coalesced, it is described as "coalescence" instead of the velocity ratio.

When the number of drops in Table 1 is 5, that is, when looking at the drive waveform 515, it can be seen that the closer the dpE is to AL, the faster the last drop velocity is relative to the first drop velocity. When the drop number is 4, that is, for the drive waveform 514, the last drop velocity with respect to the first drop velocity becomes faster as the dpD approaches AL, and when the dpD is 0.6AL, the last drop is combined with the first drop. .. When the number of drops is 3, that is, the drive waveform 513 has the same tendency as the case where the number of drops is 4. It can be seen that the ratio of the speeds of the first droplet and the last droplet can be adjusted by adjusting each waveform width in this way.

The inkjet recording apparatus 1 forms one dot on the image forming medium S by landing a plurality of droplets ejected by the driving waveform 512 to the driving waveform 515 on the image forming medium S. Therefore, in order to prevent the landing positions of the plurality of droplets from being separated on the image forming medium S, the plurality of droplets are united or the speed of the last droplet is higher than the speed of the first droplet of the plurality of droplets. It is desirable that the speed increases. Here, Table 1 shows the discharge rate and the speed ratio when the dpB is variously changed when the drop number is 2. Looking at Table 1, it can be seen that the last drop velocity is higher than the first drop velocity by setting dpB to 0.5 AL or more. Therefore, the dpB is preferably 0.5 AL or more. However, the speed of the 1st drop when the number of drops is 2 and the dpB is 0.5AL is about 1 [m / s] smaller than the speed of the 1st drop when the number of drops is 1. This is a result of the fact that each droplet is connected without being divided immediately after ejecting a plurality of droplets, and each droplet is pulled by the surface tension, thereby interacting with the speed of each droplet. .. In order to keep the landing positions of the dots on the image forming medium S, it is desirable that the velocity difference of the leading drop is small regardless of the number of drops. Therefore, it is desirable that the head drop velocity when the drop number is 2 is close to 9.7 [m / s], which is the head drop velocity when the drop number is 1. Therefore, it is particularly preferable that dpB is 0.6AL.

Further, Table 1 shows the discharge rate and the speed ratio when the dpB is set to 0.6AL and the dpC is variously changed in the drive waveform 513 as in the drive waveform 512. Looking at Table 1, it can be seen that by setting the dpC to 0.4AL or more, the final drop velocity becomes larger than the first drop velocity or all the droplets are coalesced. Therefore, the dpC is preferably 0.4AL or more. Since it is desirable that the velocity difference of the first drop is small regardless of the number of drops, the dpC is particularly preferably 0.4AL. The dpC may be set to 0.5AL in order to give priority to the coalescence of the droplets.

Further, Table 1 shows the discharge rate and the speed ratio in the drive waveform 514 when dpB is 0.6AL and dpC is 0.4AL and dpD is variously changed as in the drive waveform 513. Looking at Table 1, it can be seen that by setting the dpD to 0.5 AL or more, the final drop velocity becomes larger than the first drop velocity or all the droplets are coalesced. Therefore, the dpC is preferably 0.5 AL or more. Since it is desirable that the speed difference of the first drop is small regardless of the number of drops, the dpD is particularly preferably 0.5 AL. The dpD may be set to 0.6AL in order to give priority to the coalescence of the droplets.

Further, in Table 1, the discharge rate and the speed ratio when dpB is 0.6AL, dpC is 0.4AL, and dpD is 0.5AL and dpE is variously changed in the drive waveform 515 as in the drive waveform 514. Is shown. Looking at Table 1, it can be seen that by setting the dpE to 0.5AL or more, the final drop velocity becomes larger than the first drop velocity or all the droplets are coalesced. Therefore, the dpE is preferably 0.5AL or more. Since it is desirable that the speed difference of the head drop is small regardless of the number of drops, the dpE is particularly preferably 0.5AL.

(Numerical analysis 2)
In the numerical analysis 2, as a second embodiment, a simulation was carried out in the case where the liquid I having a viscosity of about 50 [mPas] and a specific density of about 0.85 was discharged by the inkjet head 10. The AL of the simulation model of the inkjet head 10 of the second embodiment was about 2 μsec as in the first embodiment.
In the numerical analysis 2, the simulation was carried out in the same manner as in the numerical analysis 1. The results are shown in Table 2.

In the numerical analysis 2, each waveform width was adjusted in the same manner as in the case of the numerical analysis 1, and dpB was set to 0.8AL, dpC was set to 0.5AL, dpD was set to 0.5AL, and dpE was set to 0.6AL.

FIG. 12 is a diagram showing a drive waveform 52 of a comparative example. The drive waveforms 521 to 525 are collectively referred to as a drive waveform 52. The drive waveform 525 shows an example of the drive waveform when five droplets are continuously ejected. The drive waveform 522 shows an example of a drive waveform when two droplets are continuously ejected. The drive waveform 521 shows an example of a drive waveform when one droplet is continuously ejected. The illustration of the drive waveform 523 and the drive waveform 524 when the number of droplets to be continuously ejected is 3 or 4 is omitted.
The drive waveform 52 includes a vibration pulse, a discharge pulse, and a suppression pulse in this order. The number of discharge pulses included in the drive waveform 52 is N.

The drive circuit 103 that applies the drive waveform 52 first starts applying the vibration pulse. The vibration pulse is a trapezoidal wave with an sp width in which the voltage changes in the order of 0 and −Vb. With the start of application of the vibration pulse, the voltage of the electrode 1204 changes from 0 to −Vb. Then, the voltage of the electrode 1204 is held at −Vb until the application of the vibration pulse is completed. The sum of the time until the voltage of the electrode 1204 drops from 0 to −Vb and the time when the voltage of the electrode 1204 is held at −Vb is the time sp. The pressurization at the start of application by the vibration pulse shall be such that the droplets are not ejected from the nozzle 101.

The drive circuit 103 ends the application of the vibration pulse after a predetermined time sp has elapsed from the start of the application of the vibration pulse. Then, the drive circuit 103 starts applying the first discharge pulse. The discharge pulse is a trapezoidal wave having a dpX width in which the potential difference changes in the order of 0, Vb, and 0. With the end of application of the vibration pulse and the start of application of the discharge pulse, the voltage of the electrode 1204 changes from −Vb to Vb via 0. Then, the voltage of the electrode 1204 is held in Vb until the application of the first pulse is completed. The total of the time until the voltage of the electrode 1204 rises from 0 to Vb and the time when the voltage of the electrode 1204 is held in Vb is the time dpX.
The drive circuit 103 ends the application of the first discharge pulse after a predetermined time dpX elapses from the start of application of the first discharge pulse. With the end of application of the discharge pulse, the voltage of the electrode 1204 changes from Vb to 0. Then, the voltage of the electrode 1204 is held at 0 until the application of the next pulse is started.
When the application of the discharge pulse is completed, the volume of the pressure chamber 115d is contracted, and the liquid I in the pressure chamber 115d is pressurized. As a result, the liquid I in the pressure chamber 115d is discharged as droplets from the nozzle 101.

The drive circuit 103 applies N discharge pulses. The time from the center of the (k-1) th discharge pulse to the center of the kth discharge pulse is 2UL.

After the application of the Nth discharge pulse is completed, the drive circuit 103 starts applying the suppression pulse so that the time from the center of the Nth discharge pulse to the center of the suppression pulse is 2UL for a predetermined time.
The suppression pulse of the drive waveform 52 is a trapezoidal wave having a cp width in which the potential difference changes in the order of 0, −Vb, and 0. With the start of application of the suppression pulse, the voltage of the electrode 1204 changes from 0 to −Vb. Then, the voltage of the electrode 1204 is held at −Vb until the application of the suppression pulse is completed. The total of the time until the voltage of the electrode 1204 drops from 0 to −Vb and the time when the voltage of the electrode 1204 is held at −Vb is the time cp.

(Numerical analysis 3)
Here, a simulation was performed in which the same liquid I was ejected to the inkjet head 10 with the drive waveform 511 of the example and the drive waveform 521 of the comparative example, and the potential difference V required to obtain the same droplet velocity was compared. The parameters of the liquid I were a viscosity of about 30 [mPas] and a specific gravity of about 0.85, as in the numerical analysis 1.
Table 1 shows the waveform width and potential difference Va of the drive waveform 511 in the numerical analysis 3. That is, Va = 20 [V]. The discharge speed at this time is 9.7 [m / s] as shown in Table 1.
The drive waveform 521 was simulated with the waveform parameters set to sp = AL, dpX = AL, 2UL = 2AL, and cp = AL. In this case, when the potential difference Vb required for the inkjet head 10 to eject the droplet at 9.7 [m / s] using the drive waveform 521 was examined, it was about 24.8 [V].

(Numerical analysis 4)
In the numerical analysis 4, the parameters of the liquid I were set to the same viscosity as the numerical analysis 2 with a viscosity of about 50 [mPas] and a specific gravity of about 0.85, and the same comparison as with the numerical analysis 3 was performed.
Table 2 shows each waveform width and potential difference Va of the drive waveform 511 in the numerical analysis 4. That is, Va = 27.5 [V]. The discharge speed at this time is 8.8 [m / s] as shown in Table 2.
In this case, the potential difference Vb required for the inkjet head 10 to eject the droplet at 8.8 [m / s] using the drive waveform 521 was examined and found to be about 33.1 [V].

As the results of the numerical analysis 3 and the numerical analysis 4 show, the drive waveform 511 of the embodiment can discharge the liquid I with a lower potential difference V than the drive waveform 521 of the comparative example. Therefore, the drive circuit 103 using the drive waveform 511 can be driven with a lower potential difference than the conventional drive waveform. Therefore, the inkjet head 10 of the embodiment has lower power consumption than the conventional one, and can reduce the cost.

(Numerical analysis 5)
The same liquid I was discharged from the drive waveform 515 of the example and the drive waveform 525 of the comparative example, and the potential difference V required to obtain the same droplet velocity was compared. The parameters of the liquid I were a viscosity of about 30 [mPas] and a specific gravity of about 0.85, as in the numerical analysis 3.
The waveform width and potential difference Va of the drive waveform 515 in the numerical analysis 5 are as shown in Table 1. That is, Va = 20 [V], sp = AL, dpA = AL, dpB = 0.6AL, dpC = 0.4AL, dpD = 0.5AL, dpE = 0.5. The head drop velocity at this time is 10.4 [m / s] as shown in Table 1.
For the drive waveform 525, the total of the vibration pulse width sp and the time to return the potential difference from -Vb to 0 is set to 0.7AL so that the last drop velocity is larger than the first drop velocity, and dpX = AL, 2UL = 2AL, cp. = AL. In this case, the potential difference Vb required for the inkjet head 10 to eject the droplet at the head drop speed of 10.4 [m / s] using the drive waveform 525 was about 28.6 [V].

As the result of the numerical analysis 5 shows, the drive waveform 515 of the embodiment can discharge the liquid I with a lower potential difference V than the drive waveform 525 of the comparative example. Further, as can be seen by comparing with the result of the numerical analysis 3, the effect of reducing the potential difference V is greater when the number of droplets to be continuously ejected is 5 times than when the number of droplets is continuously ejected once.
Under the condition that the viscosity of the liquid I is 30 [mPas], the viscous resistance of the flow path in the head is large, and the residual vibration generated at the time of ejecting the first droplet is greatly attenuated. Therefore, when the sp width is AL in the drive waveform 525, the head drop speed is faster than the last drop speed. In order to make the last drop velocity of the drive waveform 525 faster than the first drop velocity, the first drop velocity needs to be slower than the last drop velocity, and the sp width must be smaller than AL or larger than AL. As a result, the required potential difference Vb of the drive waveform 525 is larger than that of the drive waveform 521 that requires only one droplet to be ejected.

As described above, the voltage source, the drive circuit 103, the wiring electrode 119, the wiring electrode 121 and the wiring electrode 122, and the circuit connecting the actuator can be regarded as an RC series circuit. The power consumption of this RC series circuit is proportional to the number of trapezoidal waves included in the drive waveform, and is proportional to the square of the potential difference.
The drive waveform 515 includes five trapezoidal waves having a height Va whose potential difference changes in the order of 0, Va, 0. The drive waveform 515 includes six trapezoidal waves having a height −V that changes in the order of potential difference 0, −Va, and 0. Therefore, the drive waveform 515 includes 11 trapezoidal waves in total.
On the other hand, the drive waveform 525 includes five trapezoidal waves having a height of Va. The drive waveform 525 includes two trapezoidal waves having a height of −Va. Therefore, the drive waveform 525 includes a total of seven trapezoidal waves.

（１）式より、実施例の駆動波形５１５は、比較例の駆動波形５２５の７７％程度の消費電力であることが分かる。すなわち、実施例の駆動波形５１５は、粘度が３０［ｍＰａｓ］の液体Ｉを用いる場合において、従来と比べて２３％程度消費電力を抑えることができる。 Therefore, the power consumption of the drive waveform 515 of the embodiment with respect to the comparative example 525 can be estimated by the following equation (1). Note that da in equation (1) is the number of trapezoidal waves in the drive waveform 515. Then, db in the equation (1) is the number of trapezoidal waves in the drive waveform 525.

From the equation (1), it can be seen that the drive waveform 515 of the embodiment consumes about 77% of the drive waveform 525 of the comparative example. That is, in the drive waveform 515 of the embodiment, when the liquid I having a viscosity of 30 [mPas] is used, the power consumption can be suppressed by about 23% as compared with the conventional case.

(Numerical analysis 6)
In the numerical analysis 6, the parameters of the liquid I were set to the same viscosity as the numerical analysis 2 and the numerical analysis 4 with a viscosity of about 50 [mPas] and a specific gravity of about 0.85, and the same comparison as the numerical analysis 5 was performed.
Table 2 shows the waveform width and potential difference Va of the drive waveform 515 in the numerical analysis 6. That is, Va = 27.5 [V], sp = AL, dpA = AL, dpB = 0.8AL, dpC = 0.5AL, dpD = 0.5AL, dpE = 0.6. The head drop velocity at this time is 8.9 [m / s] as shown in Table 1.
For the drive waveform 525, the total of the vibration pulse width sp and the time to return the potential difference from -Vb to 0 is 0.4AL so that the last drop velocity is larger than the first drop velocity, and dpX = AL, 2UL = 2AL, cp. = AL. In this case, the potential difference Vb required for the inkjet head 10 to eject the droplet at the head drop speed of 8.9 [m / s] using the drive waveform 525 was about 46.2 [V].

（２）式より、実施例の駆動波形５１５は、比較例の駆動波形５２５の５６％程度の消費電力であることが分かる。すなわち、実施例の駆動波形５１５は、粘度が５０［ｍＰａｓ］の液体Ｉを用いる場合において、従来と比べて４４％程度消費電力を抑えることができる。 As for the numerical analysis 6, the power consumption of the drive waveform 515 of the embodiment with respect to the comparative example 525 can be estimated by the following equation (2) as in the numerical analysis 5.

From the equation (2), it can be seen that the drive waveform 515 of the embodiment consumes about 56% of the drive waveform 525 of the comparative example. That is, in the drive waveform 515 of the embodiment, when the liquid I having a viscosity of 50 [mPas] is used, the power consumption can be suppressed by about 44% as compared with the conventional case.

The first embodiment can be modified as follows.
The method of applying a voltage for deforming the pressure chamber 1154 is not limited to the examples of FIGS. 7 to 9.
For example, the drive circuit makes the electrode 1243, the electrode 1204, and the electrode 1235 have the same potential by applying the same voltage to all the electrodes 1243, 1204, and 1235. As a result, the actuator 1184 and the actuator 1185 are in a non-deformed state. At this time, the pressure chamber 1154 is not deformed as in the case of FIG. 7. For this purpose, the drive circuit connects, for example, the second voltage source 41 to the electrode 1243, the electrode 1204 and the electrode 1235.

For example, the drive circuit applies a voltage Va / 2 to the electrode 1204 and applies a voltage −Va / 2 to the electrodes 1243 and 1235 on both sides thereof. As a result, the potential difference Va is applied to the actuator 1184 and the actuator 1185 as in the case of FIG. Then, the actuator 1184 and the actuator 1185 are deformed so as to expand the volume of the pressure chamber 1154 as in the case of FIG.

For example, the drive circuit applies a voltage −Va / 2 to the electrode 1204 and applies a voltage Va / 2 to the electrodes 1243 and 1235 on both sides thereof. As a result, the potential difference − Va is applied to the actuator 1184 and the actuator 1185 as in the case of FIG. Then, the actuator 1184 and the actuator 1185 are deformed so as to contract the volume of the pressure chamber 1154 as in the case of FIG.

[Second Embodiment]
The configuration of the inkjet recording device 1 according to the second embodiment is the same as that of FIGS. 1 to 6 of the first embodiment. Therefore, the description of the relevant portion will be omitted.

However, the inkjet recording apparatus 1 of the second embodiment applies a voltage as shown in FIG. 13 instead of FIG. 8 when expanding the volume of the pressure chamber 1154.
FIG. 13 shows a head substrate 102 in a state where the electrode 1204 is used as a ground voltage and a voltage −Va is applied only to the electrode 1243 and the electrode 1235. In the state shown in FIG. 13, a potential difference similar to that in FIG. 8 occurs between the electrode 1204 and the electrodes 1243 and 1235 on both sides of the electrode 1204. Due to these potential differences, the actuator 1184 and the actuator 1185 are sheared and deformed so as to expand the volume of the pressure chamber 1154, similar to the shape shown in FIG.

The inkjet recording device 1 of the second embodiment includes a drive circuit 1032 as shown in FIG. 14 instead of the drive circuit 103 of FIG. FIG. 14 is a diagram showing a configuration example of the drive circuit 1032. The drive circuit 1032 includes a voltage control unit 35. The drive circuit 1032 includes voltage switching units 34 as many as the number of pressure chambers 115 inside the inkjet head 10. However, FIG. 14 illustrates the voltage switching unit 341, the voltage switching unit 342, and the voltage switching unit 343 as the voltage switching unit 34, and the illustration of the voltage switching unit 344 and subsequent units is omitted.
The third voltage source 42 is an example of the third voltage source. The drive circuit 1032 is an example of an application unit.

The drive circuit 1032 is connected to the first voltage source 40, the second voltage source 41, and the third voltage source 42. The drive circuit 1032 connects the first voltage source 40 to each wiring electrode 119. Therefore, the electrode 120 on the inner wall of the pressure chamber is connected to the first voltage source 40 via the wiring electrode 119. As a result, the voltage of each wiring electrode 119 and each electrode 120 becomes a ground voltage. Further, the drive circuit 1032 selectively supplies the voltages supplied from the first voltage source 40, the second voltage source 41, and the third voltage source 42 to the wiring electrodes 121 and 122. The voltage value indicated by the output voltage of the third voltage source 42 is −Va.

Each voltage switching unit 34 is connected to the wiring electrode 121 and the wiring electrode 122. That is, the voltage switching unit 341 is connected to the wiring electrode 1221 and the wiring electrode 1213, the voltage switching unit 342 is connected to the wiring electrode 1223 and the wiring electrode 1215, and the voltage switching unit 343 is connected to the wiring electrode 1225 and the wiring electrode 1217.

The voltage switching unit 341 connects any of the first voltage source 40, the second voltage source 41, and the third voltage source 42 with the wiring electrode 1221 and the wiring electrode 1213 under the control of the voltage control unit 35. The voltage switching unit 342 connects any of the first voltage source 40, the second voltage source 41, and the third voltage source 42 with the wiring electrode 1223 and the wiring electrode 1215 under the control of the voltage control unit 35. The voltage switching unit 343 connects any of the first voltage source 40, the second voltage source 41, and the third voltage source 42 with the wiring electrode 1225 and the wiring electrode 1217 under the control of the voltage control unit 35. The same applies to the voltage switching unit 344, the voltage switching unit 345, and so on.

In the example of FIG. 14, the wiring electrode 119 connected to the electrode 120 of the pressure chamber wall is connected to the first voltage source 40 inside the drive circuit 1032. However, this wiring electrode may be connected to the first voltage source 40 outside the drive circuit. In this case, the wiring electrodes connected to the drive circuit are only those connected to the electrodes on the air chamber wall.

The inkjet head 10 of the second embodiment expands or contracts the pressure chamber by applying a positive or negative voltage to the electrodes 123 and 124 that are not in contact with the liquid I. As for the inkjet head 10 of the second embodiment, the electrode 120 in contact with the liquid I has the first voltage source 40 regardless of whether the pressure chamber is in the state of FIG. 7, the state of FIG. 13, or the state of FIG. Connecting. That is, the electrode 120 has a ground voltage regardless of the state of the pressure chamber. Therefore, the liquid I has a small change in potential and no potential difference occurs. Therefore, the inkjet head 10 of the second embodiment can eject the liquid I whose properties are likely to change due to an electrochemical reaction without changing its properties.

The above embodiment can be modified as follows.
The gradation of the inkjet recording apparatus 1 of the above embodiment has 6 levels of 0 to 5. However, the number of gradations of the inkjet recording device 1 is not limited. Further, the drive waveform of the embodiment may be one that continuously ejects more than five droplets.

The inkjet recording device 1 of the embodiment is an inkjet printer that forms a two-dimensional image with ink on the image forming medium S. However, the inkjet recording apparatus of the embodiment is not limited to this. The inkjet recording device of the embodiment may be, for example, a 3D printer, an industrial manufacturing machine, a medical machine, or the like. When the inkjet recording device of the embodiment is a 3D printer, an industrial manufacturing machine, a medical machine, or the like, the inkjet recording device of the embodiment may, for example, provide a material or a binder for solidifying the material. A three-dimensional object is formed by ejecting from the inkjet head.

The inkjet recording apparatus 1 of the embodiment includes four liquid ejection units 2, and the color of the liquid I used by each liquid ejection unit 2 is cyan, magenta, yellow, or black. However, the number of liquid ejection units 2 included in the inkjet recording device is not limited to four, and may not be limited to four. Further, the color and characteristics of the liquid I used by each liquid discharge unit 2 are not limited.
Further, the liquid ejection unit 2 can also eject transparent glossy ink, ink that develops color when irradiated with infrared rays, ultraviolet rays, or the like, or other special inks. Further, the liquid ejection unit 2 may be capable of ejecting a liquid other than ink. The liquid I discharged by the liquid discharge unit 2 may be a dispersion liquid such as a suspension. Examples of the liquid other than the ink ejected by the liquid ejection unit 2 include a liquid containing conductive particles for forming a wiring pattern of a printed wiring substrate, a liquid containing cells for artificially forming a tissue or an organ, and the like. , Binders such as adhesives, waxes, liquid resins and the like.

Each numerical value in the above embodiment allows an error within the range in which the object of the present invention is achieved.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Inkjet recording device, 2 ... Liquid discharge unit, 10 ... Inkjet head, 31, 32, 34 ... Voltage switching unit, 33, 35 ... Voltage control unit, 101, 1012, 1014, 1016 ... Nozzle , 103, 1032 ... Drive circuit, 107, 1071, 1072 ... Hydraulic member, 115, 1152, 1154, 1156 ... Pressure chamber, 116, 1161, 1163, 1165, 1167 ... Air chamber, 117 ... Ink discharge Road, 118, 1181-1187 ... Actuator, 119, 121, 122, 1192, 1194, 1196, 1211, 1213, 1215, 1217, 1221, 1223, 1225, 1227 ... Wiring electrode, 120, 123, 124, 1202 , 1204, 1206, 1231, 1233, 1235, 1237, 1241, 1243, 1245, 1247 ... Electrode

Claims (5)

The volume in which the actuator is not operating is the reference volume, and the pressure chamber that houses the liquid and
The actuator that changes the volume of the pressure chamber according to the applied drive signal, and
A unit for applying the drive signal to the actuator is provided.
The drive signal is
A vibration pulse that reduces the volume of the pressure chamber to be smaller than the reference volume,
The discharge waveform includes one discharge waveform applied after the vibration pulse and discharging a liquid from a nozzle communicating with the pressure chamber, and the discharge waveform expands the volume of the pressure chamber to be larger than the reference volume. The expansion pulse and the reduction pulse applied after the expansion pulse and reducing the volume of the pressure chamber to be smaller than the reference volume are included.
The pulse width of the vibration pulse is larger than the quarter period at the main acoustic resonance frequency of the liquid in the pressure chamber.
The liquid discharge head, wherein the pulse width of the extended pulse of the discharge waveform is a half cycle at the main acoustic resonance frequency. The volume in which the actuator is not operating is the reference volume, and the pressure chamber that houses the liquid and
The actuator that changes the volume of the pressure chamber according to the applied drive signal, and
A unit for applying the drive signal to the actuator is provided.
The drive signal is
A vibration pulse that reduces the volume of the pressure chamber to be smaller than the reference volume,
The discharge waveform includes a plurality of discharge waveforms applied after the vibration pulse to discharge the liquid from a nozzle communicating with the pressure chamber, and the discharge waveform expands the volume of the pressure chamber to be larger than the reference volume. Includes a pulse and a reduction pulse applied after the expansion pulse that reduces the volume of the pressure chamber to be smaller than the reference volume.
The pulse width of the vibration pulse is larger than the quarter period at the main acoustic resonance frequency of the liquid in the pressure chamber.
The liquid discharge head, wherein the pulse width of the extended pulse of the first discharge waveform is a half cycle at the main acoustic resonance frequency. The actuator comprises a first electrode and a second electrode.
The application part is
By connecting the same voltage source of either the first voltage source or the second voltage source to both the first electrode and the second electrode, the volume of the pressure chamber is set to the reference volume, and the first voltage source is used. By connecting the first voltage source to the electrode and connecting the second voltage source to the second electrode, the volume of the pressure chamber is reduced to be smaller than the reference volume.
By connecting the second voltage source to the first electrode and connecting the first voltage source to the second electrode, the volume of the pressure chamber is expanded so as to be larger than the reference volume.
The liquid discharge head according to claim 1 or 2. The actuator comprises a first electrode and a second electrode.
The application part is
By connecting the first voltage source to the first electrode and the second electrode, the volume of the pressure chamber is set to the reference volume, and the first voltage source is connected to the first electrode. By connecting a second voltage source to the electrode 2, the volume of the pressure chamber is reduced to be smaller than the reference volume.
By connecting the first voltage source to the first electrode and connecting the third voltage source to the second electrode, the volume of the pressure chamber is expanded so as to be larger than the reference volume.
The liquid discharge head according to claim 1 or 2. The extended pulse included in the discharge waveform after the first one is such that the speed of the liquid discharged by the discharge waveform after the first one is faster than the speed of the liquid discharged by the first discharge waveform. The liquid discharge head according to claim 2, which has a wide pulse width.

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