JP2018161749A - Inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the power consumption reduction and the high-speed driving when discharging ink droplets using a multidrop type.SOLUTION: An inkjet head comprises a pressure chamber, a nozzle, an actuator, and a drive circuit. The drive circuit includes a first waveform generation part, a second waveform generation part, a waveform formation part, and a waveform unit selection part. The first waveform generation part generates a driving waveform unit for causing one drop to be discharged. The second waveform generation part generates a driving waveform unit for discharging a plurality of drops. The waveform formation part connects the driving waveform unit generated from the first waveform generation part and the driving waveform unit generated from the second waveform generation part to form a driving waveform signal. The waveform unit selection part selects a driving waveform unit to be validated according to the print data from the drive waveform signal formed by the waveform formation part and applies it to the actuator.SELECTED DRAWING: Figure 7

Description

  Embodiments described herein relate generally to an inkjet head.

  The ink-jet head employs a multi-drop method for adjusting the number of ink droplets ejected from one nozzle when performing gradation printing. In the conventional multi-drop method, a drive waveform for ejecting one drop of ink droplet from a nozzle is repeated as many times as necessary. Therefore, as the number of ink droplets increases, the number of operations of the actuator increases, resulting in an increase in power consumption. In addition, since the driving time increases in proportion to the number of ink droplets, there is a problem that it is difficult to increase the driving frequency.

  For this reason, power consumption can be reduced by reducing the number of actuator operations when ejecting multiple ink droplets from the nozzles using the multi-drop method, and the drive time can be shortened. An ink jet head capable of realizing high speed driving is desired.

Japanese Patent No. 5871851 Japanese Patent No. 4815364

  The problem to be solved by the embodiments of the present invention is to provide an ink jet head capable of realizing reduction in power consumption and high-speed driving when ink droplets are ejected by the multi-drop method.

  In one embodiment, an ink jet head includes a pressure chamber that stores ink, a nozzle that communicates with the pressure chamber, an actuator that is provided corresponding to the pressure chamber, and that displaces the volume of the pressure chamber, and a drive that drives the actuator. Circuit. The drive circuit includes a first waveform generator, a second waveform generator, a waveform generator, and a waveform unit selector. The first waveform generator generates a drive waveform unit for discharging one drop. The second waveform generator generates a drive waveform unit for discharging a plurality of drops. The waveform generator generates a drive waveform signal by connecting the drive waveform unit generated from the first waveform generator and the drive waveform unit generated from the second waveform generator. The waveform unit selection unit selects a drive waveform unit to be valid according to the print data from the drive waveform signal generated by the waveform generation unit, and applies it to the actuator.

The disassembled perspective view of an inkjet head. The perspective view which expanded partially one of the piezoelectric members arranged in two rows on the base material of an inkjet head. The expanded sectional view of the part which cut | disconnected the inkjet head in the longitudinal direction by the F3-F3 arrow line of FIG. The top view which expanded one side of the piezoelectric member of an inkjet head partially. Sectional drawing which cut | disconnected the inkjet head by F5-F5 arrow line of FIG. Sectional drawing which cut | disconnected the inkjet head by the F6-F6 arrow line of FIG. FIG. 2 is a block diagram illustrating a configuration of a main part of a drive circuit for an inkjet head. The wave form diagram which shows the 1 drop waveform applied to the actuator of an inkjet head. The figure which shows a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform when the drive voltage of 1 drop waveform is applied to the actuator of an inkjet head. The wave form diagram which shows the 2 drop waveform applied to the actuator of an inkjet head. The figure which shows a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform when the drive voltage of 2 drop waveform is applied to the actuator of an inkjet head. The wave form diagram which shows the 3 drop waveform applied to the actuator of an inkjet head. The figure which shows a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform when the drive voltage of 3 drop waveform is applied to the actuator of an inkjet head. The wave form diagram which shows the other 2 drop waveform applied to the actuator of an inkjet head. The figure which shows a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform when the drive voltage of another 2 drop waveform is applied to the actuator of an inkjet head. The 1st waveform diagram for demonstrating how to determine the trailing edge of the contraction pulse of a 2 drop waveform, and the trailing edge of a weak contraction pulse. The equivalent circuit diagram for demonstrating how to determine the trailing edge of a 2-drop waveform contraction pulse and the trailing edge of a weak contraction pulse. The 2nd waveform figure for demonstrating how to determine the trailing edge of the contraction pulse of a 2 drop waveform, and the trailing edge of a weak contraction pulse. FIG. 10 is a third waveform diagram for explaining how to determine the trailing edge of a 2-drop waveform contraction pulse and the trailing edge of a weak contraction pulse. FIG. 3 is a timing diagram illustrating a first example of a connected drive waveform generated by a drive circuit of an inkjet head. FIG. 10 is a timing diagram illustrating a second example of a connected drive waveform generated by a drive circuit of an inkjet head. The timing diagram for demonstrating the multidrop system by the 1st example shown in FIG. The timing diagram for demonstrating the multidrop system by the 2nd example shown in FIG. FIG. 11 is a waveform diagram showing a result of simulating ink pressure and ink flow rate when the time point of the leading edge of the two-drop waveform contraction pulse shown in FIG. 10 is advanced. FIG. 11 is a waveform diagram showing a result of simulating ink pressure and ink flow rate when the time point of the leading edge of the two-drop waveform contraction pulse shown in FIG. 10 is advanced. FIG. 13 is a waveform diagram showing a result of simulating ink pressure and ink flow rate when the time point of the leading edge of the second contraction pulse of the 3-drop waveform shown in FIG. 12 is advanced. FIG. 13 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the time of the leading edge of the first contraction pulse of the 3-drop waveform shown in FIG. 12 is advanced. FIG. 11 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the contraction rate of the weak contraction pulse having the 2-drop waveform shown in FIG. 10 is changed.

Hereinafter, an embodiment of an inkjet head capable of realizing reduction in power consumption and high-speed driving when ink droplets are ejected by a multi-drop method will be described with reference to the drawings.
First, the configuration of the inkjet head 1 will be described with reference to FIGS. 1 to 6.

  FIG. 1 is an exploded perspective view of the inkjet head 1. The inkjet head 1 is, for example, an on-demand inkjet head using a share mode method. The inkjet head 1 is mounted on, for example, an inkjet printer, and ejects ink toward a recording medium.

  The inkjet head 1 includes a base material 100, a frame member 200, a nozzle plate 300, and a housing 400. The inkjet head 1 includes upstream and downstream ink manifolds (not shown), a drive circuit 40, and the like inside the housing 400. The drive circuit 40 operates the inkjet head 1. The upstream and downstream ink manifolds are connected to upstream and downstream ink tanks (not shown) outside the head 1.

  The substrate 100 has a rectangular plate shape, and one surface thereof is used as a mounting surface 121. In the inkjet head 1, two piezoelectric members 118 extending in the longitudinal direction of the substrate 100 are arranged in two rows at the center of the mounting surface 121. Each piezoelectric member 118 has a trapezoidal cross section in the lateral direction, and is arranged in parallel with being spaced apart from each other. The substrate 100 is provided with a plurality of supply ports 125 and a plurality of discharge ports 126 along the longitudinal direction of the piezoelectric member 118.

  The plurality of supply ports 125 are provided between the two piezoelectric members 118, that is, along the central portion of the base material 100, along the longitudinal direction of the base material 100. Each supply port 125 passes through the base material 100 and communicates with an upstream ink manifold (not shown), and the tip is connected to an upstream ink tank (not shown). In other words, the ink supplied from the upstream ink tank to the inkjet head 1 through the upstream ink manifold and the supply port 125 flows into the ink chamber 116 (see FIGS. 5 and 6). The plurality of discharge ports 126 are provided in two rows outside the two piezoelectric members 118 with the supply port 125 interposed therebetween. Each discharge port 126 penetrates the base material 100 and communicates with a downstream ink manifold (not shown), and the tip is connected to a downstream ink tank (not shown). The ink in the ink chamber 116 is discharged to the downstream ink tank through each discharge port 126 and the downstream ink manifold. The ink in the downstream ink tank outside the head 1 is returned to the upstream ink tank by a pump (not shown). Thus, the ink circulates between each ink tank and the ink chamber 116 through the supply port 125 and the discharge port 126.

  The nozzle plate 300 has a rectangular plate shape and includes a plurality of nozzles 301 for ejecting ink droplets. Each nozzle 301 passes through the nozzle plate 300 and is arranged in two rows along the longitudinal direction of the nozzle plate 300. An ink repellent film is formed on the surface 302 of the nozzle plate 300, that is, the surface on the side where ink droplets are ejected from the nozzle 301. The ink repellent film is formed of, for example, a liquid repellent silicon-based liquid repellent material or a fluorine-containing organic material.

  The nozzle plate 300 is disposed so as to face the mounting surface 121 of the substrate 100 with the frame member 200 interposed therebetween. With this arrangement, the inkjet head 1 forms an ink chamber 116 surrounded by the base material 100, the frame member 200, and the nozzle plate 300.

  The frame member 200 is disposed between the mounting surface 121 of the substrate 100 and the nozzle plate 300. The frame member 200 surrounds the two piezoelectric members 118 and has a size that surrounds all the nozzles 301.

The piezoelectric member 118 is made of, for example, lead zirconate titanate (PZT). The piezoelectric member 118 is formed by bonding two plate-like piezoelectric bodies so that their polarization directions are opposed to each other. The piezoelectric member 118 according to the present embodiment has a rod-like outer shape extending in the longitudinal direction. Note that the piezoelectric material is not limited to this. For example, PTO (PbTiO3: lead titanate), PMNT (Pb (Mg1 / 3Nb2 / 3) O3-PbTiO3), PZNT (Pb (Zn1 / 3Nb2 / 3) O3-PbTiO3 ), ZnO, and AlN can be used.
The piezoelectric member 118 is bonded to the mounting surface 121 of the substrate 100. As this adhesive, for example, an epoxy adhesive having thermosetting properties is used.

  FIG. 2 is a partially enlarged perspective view of one of the piezoelectric members 118 arranged in two rows on the substrate 100. In FIG. 2, a part of the nozzle plate 300 is not shown in order to make the internal structure easy to see.

  The piezoelectric member 118 is parallel to the mounting surface 121 of the base material 100 and has an upper surface 118c extending in the short direction of the base material 100, and two slopes inclined so as to spread from both ends of the upper surface 118c toward the mounting surface 121. It has a surface 118b. The piezoelectric member 118 has a plurality of first grooves 131 (hereinafter also referred to as pressure chambers 131) and a plurality of second grooves 132 (hereinafter also referred to as dummy chambers 132) extending on the surface 118 a in the short direction of the substrate 100. And) alternately. That is, the piezoelectric member 118 forms a plurality of partition walls 133 that separate the first groove 131 and the second groove 132. In other words, the partition 133 is a convex portion provided between the first groove 131 and the second groove 132. Both ends of the first groove 131 and the second groove 132 are connected to the inclined surface 118b. In the present embodiment, the first groove 131 and the second groove 132 are grooves formed in the same shape. Note that the shapes of the first groove 131 and the second groove 132 may be different.

  Wall members 117 are provided at both ends of the second groove 132. The wall material 117 seals both ends of the second groove 132. The wall material 117 has an upper surface 117 a that is flush with the upper surface 118 c of the piezoelectric member 118. The upper surface 118 c of the piezoelectric member 118 and the upper surface 117 a of the wall material 117 are bonded to the nozzle plate 300. Thereby, the ink filled in the ink chamber 116 is prevented from entering the second groove 132.

  FIG. 3 is an enlarged cross-sectional view of a portion obtained by cutting the inkjet head 1 shown in FIG. 1 along the line F3-F3 in the longitudinal direction. 4 is a plan view in which one of the piezoelectric members 118 of the inkjet head 1 shown in FIG. 1 is partially enlarged. FIG. 5 is a cross-sectional view of the inkjet head 1 shown in FIG. 4 cut along the line F5-F5. FIG. 6 is a cross-sectional view of the inkjet head 1 shown in FIG. 4 cut along the line F6-F6. Hereinafter, the structure of the ink chamber 116 and how the ink flows will be described in detail with reference to FIGS. 3 to 6.

  First, as shown in FIG. 3, the nozzle 301 of the nozzle plate 300 is provided so that one nozzle 301 communicates with one first groove 131. That is, the nozzle plate 300 has two rows of nozzles 301 corresponding to the first grooves 131 provided in the two rows of piezoelectric members 118, respectively. On the other hand, there is no nozzle corresponding to the second groove 132.

  As shown in FIGS. 5 and 6, the ink chamber 116 is a space surrounded by the mounting surface 121 of the substrate 100, the nozzle plate 300, and the frame member 200. The ink chamber 116 includes a first ink chamber 116a and a second ink chamber 116b. The first ink chamber 116 a is a space between the two piezoelectric members 118. A plurality of supply ports 125 communicate with the first ink chamber 116a. On the other hand, the second ink chamber 116 b is a space on the frame member 200 side (outside) of the two piezoelectric members 118. A plurality of discharge ports 126 communicate with the second ink chamber 116b.

  Ink is supplied from the upstream ink tank outside the head 1 to the first ink chamber 116a via the upstream ink manifold. The ink chamber 116 is gradually filled with the supplied ink. Specifically, the ink that has flowed into the first ink chamber 116a flows out toward the two second ink chambers 116b on the outside through the plurality of first grooves 131 of the piezoelectric member 118 on both sides thereof. As a result, the entire ink chamber 116 surrounded by the frame member 200 is filled with ink. Then, the ink that has flowed into the second ink chamber 116 b flows to the downstream ink tank outside the head 1 through the plurality of discharge ports 126 and the downstream ink manifold.

  As shown in FIGS. 4 and 5, both ends of the plurality of second grooves 132 arranged alternately between the plurality of first grooves 131 are closed by wall materials 117. For this reason, ink does not enter the second groove 132. As described above, the plurality of first grooves 131 function as part of a flow path for circulating ink, while the plurality of second grooves 132 function as a dummy chamber into which ink does not enter.

Next, electrodes and wirings disposed on the base material 100 and the piezoelectric member 118 will be described.
As shown in FIG. 3, the first electrode 134 is formed in the first groove 131, and the second electrode 135 is formed in the second groove 132. In the example of FIG. 3, one first electrode 134 is formed in one first groove 131, and two second electrodes 135 are formed in one second groove 132. The first electrode 134 is formed across a pair of side surfaces 138 and a bottom surface 139 of the first groove 131. The second electrode 135 is formed over each side surface 140 of the second groove 132 and a part of the bottom surface 141.

  As shown in FIGS. 4 to 6, the first wiring 136 extending to the first groove 131 and the second wiring 137 extending to the second groove 132 are provided on the base material 100 of the second ink chamber 116 b. Yes. Specifically, one first wiring 136 is provided for each first groove 131, and two second wirings 137 are provided for each second groove 132. One end of the first wiring 136 is connected to the first electrode 134 formed in the first groove 131, and the other end of the first wiring 136 is connected to the drive circuit 40 shown in FIG. 1 through the flexible wiring board 40a. ing. In addition, one end of each of the two second wirings 137 is connected to each of the two second electrodes 135 formed in the second groove 132, and the other end of the second wiring 137 is connected to the drive circuit 40 via the flexible wiring board 40a. It is connected to the.

  The first electrode 134 and the second electrode 135 provided in the first groove 131 and the second groove 132 are made of, for example, a nickel thin film. For example, the first electrode 134 and the second electrode 135 may be formed of a thin film of Pt (platinum), Al (aluminum), or Ti (titanium). Furthermore, as materials for the first electrode 134 and the second electrode 135, Cu (copper), A1 (aluminum), Ag (silver), Ti (titanium), W (tungsten), Mo (molybdenum), Au (gold), and the like. Other materials can also be used.

  With the above configuration, the piezoelectric member 118 can be deformed by the potential difference between the first electrode 134 and the second electrode 135 facing the first electrode 134 with the piezoelectric member 118 interposed therebetween. That is, the piezoelectric member 118 and the first electrode 134 and the second electrode 135 sandwiching the piezoelectric member 118 constitute an actuator that changes the volume of the first groove 131. The actuator, the first groove 131 filled with ink, and the nozzle 301 corresponding to the first groove 131 constitute one channel for ejecting ink.

  Hereinafter, the first groove 131 in which ink is stored is referred to as a pressure chamber 131, and the second groove 132 in which ink is not stored is referred to as a dummy chamber 132, and the description is continued. First, the drive circuit 40 of the inkjet head 1 will be described with reference to FIG.

  FIG. 7 is a block diagram showing the main configuration of the drive circuit 40 together with an enlarged view of a part of the inkjet head 1 shown in FIG. As for the inkjet head 1, a part of two dummy chambers 132 adjacent to each other with a partition wall 133 interposed therebetween is shown with one pressure chamber 131 communicating with the nozzle 301 of the nozzle plate 300 as the center. As described above, ink is ejected from the nozzle 301 communicating with the pressure chamber 131 by displacing the volume of the pressure chamber 131 containing the ink with the actuator. The actuator shear-deforms the piezoelectric member 118 forming the partition wall 133 of the pressure chamber 131 by a potential difference between the first electrode 134 disposed in the pressure chamber 131 and the second electrode 135 disposed in each of the adjacent dummy chambers 132. Thus, the volume of the pressure chamber 131 is expanded or contracted.

  The drive circuit 40 is a circuit for applying an actuator drive signal to the first electrode 134 and the second electrode 135. The drive circuit 40 includes the waveform generation unit 41, an adjacent waveform generation unit 42, a print data setting unit 43, a waveform unit selection unit 44, a driver unit 45, and a waveform connection control unit 46.

  The waveform generator 31 generates a signal S1 to be applied to the electrode, that is, the first electrode 134 disposed in the pressure chamber 131. The adjacent waveform generation unit 32 generates a signal S <b> 2 to be applied to the adjacent electrode, that is, the second electrode 135 disposed in the two dummy chambers 132 adjacent to the pressure chamber 131.

  The print data setting unit 43 sets print data given from the outside. The waveform unit selector 44 outputs an on / off select signal SL based on the print data set in the print data setting unit 43. The ON time of the select signal SL varies depending on the gradation value of the print data (see FIGS. 22 and 23).

  The driver unit 45 includes a first driver 451 corresponding to the first electrode 134 and a second driver 452 corresponding to the second electrode 135 respectively. The first driver 451 is interposed between the waveform generation unit 41 and the first electrode 134. The first driver 451 applies the signal S <b> 1 generated by the waveform generation unit 41 to the first electrode 134. The second driver 452 is interposed between the adjacent waveform generation unit 42 and the second electrode 135. The second driver 452 has a floating (high impedance) control input, and a select signal SL is input to the floating control input terminal. The second driver 452 applies the signal S2 generated by the adjacent waveform generation unit 42 to the second electrode 135 when the select signal SL is on. When the select signal SL is off, the second driver 452 turns off the output and does not apply the signal S2 generated by the adjacent waveform generation unit 42 to the second electrode 135.

  The waveform generation unit 41 and the adjacent waveform generation unit 42 are each a 1-drop waveform unit setting unit 411, 421, a 2-drop waveform unit setting unit 412, 422, a 3-drop waveform unit setting unit 413, 423, and a drive waveform generation unit 414, 424.

  In the waveform generation unit 41, the 1-drop waveform unit setting unit 411 sets drive waveform data for the first electrode 134 for discharging one drop of ink droplets from the nozzle 301. The 2-drop waveform unit setting unit 412 sets drive waveform data for the first electrode 134 for discharging ink droplets from the nozzle 301 continuously for 2 drops. The 3-drop waveform unit setting unit 413 sets drive waveform data for the first electrode 134 for ejecting ink droplets from the nozzle 301 continuously for 3 drops.

In the adjacent waveform generation unit 42, the 1-drop waveform unit setting unit 421 sets drive waveform data for the second electrode 135 for discharging one drop of ink droplets from the nozzle 301. The 2-drop waveform unit setting unit 422 sets drive waveform data for the second electrode 135 for causing ink droplets to be continuously discharged from the nozzle 301 by two drops. The 3-drop waveform unit setting unit 423 sets drive waveform data for the second electrode 135 for ejecting ink droplets from the nozzle 301 continuously for 3 drops.
Hereinafter, the drive waveform data set in each waveform unit setting unit 411, 421, 412, 422, 413, 423 is referred to as a drive waveform unit.
Here, the 1-drop waveform unit setting units 411 and 421 constitute a first waveform generation unit. The 2-drop waveform unit setting units 412 and 422 and the 3-drop waveform unit setting units 413 and 423 constitute a second waveform generation unit.

  In the waveform generation unit 41, the drive waveform generation unit 414 selects and connects the drive waveform units set in the respective waveform unit setting units 411, 412, and 413 in a predetermined order. Then, the drive waveform generation unit 414 outputs the drive waveform signal S1 for the first electrode 134 to which the plurality of drive waveform units are connected to the first driver 451 of the driver unit 45.

  In the adjacent waveform generation unit 42, the drive waveform generation unit 424 selects and connects the drive waveform units set in the respective waveform unit setting units 421, 422, and 423 in a predetermined order. Then, the drive waveform generation unit 424 outputs the drive waveform signal S2 for the second electrode 135 to which the plurality of drive waveform units are connected to the second driver 452 of the driver unit 45.

  The order in which the drive waveform generation units 414 and 424 select the drive waveform units is controlled by the waveform connection control unit 46. That is, the waveform connection control unit 46 sets the connection order of the waveform unit setting units 411, 421, 412, 422, 413, 423, and connects the waveform units according to the setting, so that the drive waveform generation units 414, 424 are connected. To control.

Here, the drive waveform unit selected by the drive waveform generation unit 414 corresponds to the drive waveform unit selected by the drive waveform generation unit 424 at the same time. That is, when the drive waveform generation unit 414 selects the drive waveform unit of the 1-drop waveform unit setting unit 411, the drive waveform generation unit 424 also selects the drive waveform unit of the 1-drop waveform unit setting unit 421. When the drive waveform generation unit 414 selects the drive waveform unit of the 2-drop waveform unit setting unit 412, the drive waveform generation unit 424 also selects the drive waveform unit of the 2-drop waveform unit setting unit 422. When the drive waveform generation unit 414 selects the drive waveform unit of the 3-drop waveform unit setting unit 413, the drive waveform generation unit 424 also selects the drive waveform unit of the 3-drop waveform unit setting unit 423. The order of connection may be programmable.
Here, the drive waveform generation units 414 and 424 constitute a waveform generation unit.

  As described above, while the select signal SL is on, the drive waveform signal S1 is applied to the first electrode 134, and the drive waveform signal S2 is applied to the second electrode 135. Thus, the actuator is driven by the differential voltage between the drive waveform signal S1 and the drive waveform signal S2. On the other hand, while the select signal SL is OFF, the drive waveform signal S1 is applied to the first electrode 134, but the drive waveform signal S2 is not applied to the second electrode 135, and the second electrode 135 is in a floating state. Therefore, the potential of the second electrode 135 follows the potential of the first electrode 134 that is induced as the capacitance of the actuator. As a result, there is no potential difference between the first electrode 134 and the second electrode 135, so the actuator is not driven.

Next, driving waveform units having a 1-drop waveform, a 2-drop waveform, and a 3-drop waveform used in this embodiment will be described with reference to FIGS.
FIG. 8 shows the difference voltage between the drive waveform unit set in the 1-drop waveform unit setting unit 411 of the waveform generation unit 41 and the drive waveform unit set in the 1-drop waveform unit setting unit 421 of the adjacent waveform generation unit 42. FIG. That is, in the 1-drop waveform unit setting unit 411 and the 1-drop waveform unit setting unit 421, drive waveform units that generate the differential voltage shown in FIG. 8 are set, respectively. This differential voltage becomes the drive voltage of the actuator. By applying this drive voltage to the actuator, only one drop of ink droplet is ejected from the nozzle 301. Such a drive voltage waveform is referred to as a one-drop waveform in the present embodiment.

  FIG. 9 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when a drive voltage having a one-drop waveform is applied to the actuator. In FIG. 9, the drive voltage waveform is indicated by a solid line, the ink pressure waveform is indicated by a one-dot chain line, and the ink flow velocity waveform is indicated by a broken line. The value on the vertical axis is normalized.

  As shown in FIG. 8, the 1-drop waveform is composed of first to seventh waveform elements e11 to e17. The first waveform element e11 expands the volume of the pressure chamber 131 at time t11 and applies a negative pressure to the pressure chamber 131. The second waveform element e12 generates a first waiting time (t12-t11) that starts after the first waveform element e11. The third waveform element e13 restores the volume of the pressure chamber 131 after the first waiting time at the time point t12 has elapsed, and applies a positive pressure to the pressure chamber. The fourth waveform element e14 generates a second waiting time (t13-t12) starting after the third waveform element e13. The fifth waveform element e15 contracts the volume of the pressure chamber 131 after the elapse of the second waiting time at the time point t13, and applies a positive pressure to the pressure chamber 131. The sixth waveform element e16 generates a third waiting time (t14-t13) that starts after the fifth waveform element e15. The seventh waveform element e17 returns the volume of the pressure chamber 131 to the original after the third waiting time at the time point t14 has elapsed.

  Here, the first waveform element e11, the second waveform element e12, and the third waveform element e13 form an expansion pulse P11 that expands the volume of the pressure chamber 131 and then returns to the original volume. That is, the first waveform element e11 is the leading edge of the extension pulse P11, the second waveform element e12 is the pulse width of the extension pulse P11, and the third waveform element e13 is the trailing edge of the extension pulse P11. The fifth waveform element e15, the sixth waveform element e16, and the seventh waveform element e17 form a contraction pulse P12 that contracts the volume of the pressure chamber 131 and then restores the volume. That is, the fifth waveform element e15 is the leading edge of the contraction pulse P12, the sixth waveform element e16 is the pulse width of the contraction pulse P12, and the seventh waveform element e17 is the trailing edge of the contraction pulse P12.

  At time t11 of the leading edge (waveform element e11) of the expansion pulse P11, the partition walls 133 on both sides are displaced so as to expand the volume of the pressure chamber 131. By this displacement, as shown in FIG. 9, negative pressure is instantaneously applied to the ink in the pressure chamber 131. As a result, the ink meniscus in the nozzle 301 moves backward.

  Thereafter, the ink pressure changes from a negative pressure to a positive pressure with the natural vibration. Then, when the first waiting time (waveform element e12) elapses and time t12 of the trailing edge (waveform element e13) of the expansion pulse P11 is reached, the volume of the pressure chamber 131 is restored. At this time, as shown in FIG. 9, positive pressure is instantaneously applied to the ink. As described above, when a positive pressure is instantaneously applied to the ink by a pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301. . That is, the first waiting time is a time for waiting for the ink pressure that has become negative at the leading edge of the expansion pulse P11 to rise to a predetermined value. The predetermined value is a value at which one drop of ink droplet is ejected when a positive pressure is instantaneously applied to the ink at the trailing edge of the expansion pulse P11. In order to eject ink most efficiently, the first waiting time (waveform element e12) is set to ½ of the natural vibration period of ink in the pressure chamber.

  Thereafter, the ink pressure changes from a positive pressure to a negative pressure with the natural vibration. When the ink pressure changes to a negative pressure, the meniscus moves backward with a delay. Then, when the second waiting time (waveform element e14) elapses while the ink pressure is negative and the time t13 of the leading edge (waveform element e15) of the contraction pulse P12 is reached, the volume of the pressure chamber 131 contracts. Thus, the partition walls 133 on both sides are displaced. This displacement momentarily applies a positive pressure to the ink. However, since the ink pressure is negative at time t13 when the positive pressure is applied, ink droplets are not ejected from the nozzle 301.

  When the volume of the pressure chamber 131 is contracted, the third waiting time (waveform element e16) elapses, and when the time t14 of the trailing edge (waveform element e17) of the contraction pulse P12 is reached, the volume of the pressure chamber 131 is reached. Is restored. At this time t14, the amplitude of the ink pressure oscillation is equal to the negative pressure instantaneously applied to the ink by the trailing edge of the contraction pulse P12, and the ink flow rate is zero. Accordingly, the residual vibration in the pressure chamber 131 is canceled thereafter. That is, the second waiting time and the third waiting time are times for generating a timing at which the residual vibration in the pressure chamber 131 is canceled by the trailing edge of the contraction pulse P12.

  In this way, by applying the drive voltage having the one-drop waveform shown in FIG. 8 to the actuator, the pressure chamber 131 operates in the order of expansion, return, contraction, and return. Then, one drop of ink droplet is ejected from the nozzle 301 communicating with the pressure chamber 131 by the expansion and return operations. Further, the residual vibration after ink droplet ejection is canceled by the subsequent contraction and return operations.

  FIG. 10 shows the difference voltage between the drive waveform unit set in the 2-drop waveform unit setting unit 412 of the waveform generation unit 41 and the drive waveform unit set in the 2-drop waveform unit setting unit 422 of the adjacent waveform generation unit 42. FIG. That is, in the 2-drop waveform unit setting unit 412 and the 2-drop waveform unit setting unit 422, drive waveform units that generate the differential voltage shown in FIG. 10 are set. This differential voltage becomes the drive voltage of the actuator. By applying this drive voltage to the actuator, two drops of ink droplets are continuously ejected from the nozzle 301. Such a drive voltage waveform is referred to as a 2-drop waveform in the present embodiment.

  FIG. 11 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when a drive voltage having a 2-drop waveform is applied to the actuator. In FIG. 11, the drive voltage waveform is shown by a solid line, the ink pressure waveform is shown by a one-dot chain line, and the ink flow velocity waveform is shown by a broken line. The value on the vertical axis is normalized.

  As shown in FIG. 10, the 2-drop waveform is composed of first to ninth waveform elements e21 to e29. The first waveform element e21 expands the volume of the pressure chamber 131 at time t21 and applies a negative pressure to the pressure chamber 131. The second waveform element e22 generates a first waiting time (t22-t21) that starts after the first waveform element e21. The third waveform element e23 restores the volume of the pressure chamber 131 after the first waiting time at the time point t22 has elapsed, and applies a positive pressure to the pressure chamber 131. The fourth waveform element e24 generates a second waiting time (t23-t22) that starts after the third waveform element e23. The fifth waveform element e25 contracts the volume of the pressure chamber 131 after the elapse of the second waiting time at the time point t23 and applies a positive pressure to the pressure chamber 131. The sixth waveform element e26 generates a third waiting time (t24-t23) starting after the fifth waveform element e25. The seventh waveform element e27 slightly returns the volume of the pressure chamber 131 after the elapse of the third waiting time at time t24. In the example of FIG. 11, when the shrinkage rate by the waveform element e25 is 100%, the shrinkage rate is returned to 50%. The eighth waveform element e28 generates a fourth waiting time (t25-t24) starting after the seventh waveform element e27. The ninth waveform element e29 returns the volume of the pressure chamber 131 to the original after the fourth waiting time at the time point t25 has elapsed.

  Here, the first waveform element e21, the second waveform element e22, and the third waveform element e23 form an expansion pulse P21 that expands the volume of the pressure chamber 131 and then returns to the original volume. That is, the first waveform element e21 is the leading edge of the expansion pulse P21, the second waveform element e22 is the pulse width of the expansion pulse P21, and the third waveform element e23 is the trailing edge of the expansion pulse P21. The fifth waveform element e25, the sixth waveform element e26, and the seventh waveform element e27 return slightly after the volume of the pressure chamber 131 is contracted, and the contracted state maintained by the sixth waveform element e26. Also, a contraction pulse P22 is formed to make a weak contraction state (weak contraction state). That is, the fifth waveform element e25 is the leading edge of the contraction pulse P22, the sixth waveform element e26 is the pulse width of the contraction pulse P22, and the seventh waveform element e27 is the trailing edge of the contraction pulse P22. The eighth component e28 and the ninth component e29 form a weak contraction pulse P23 for returning to the original state after maintaining the weak contraction state of the pressure chamber 131 for a predetermined time. That is, the eighth waveform element e28 is the pulse width of the weak contraction pulse P23, and the ninth waveform element e29 is the trailing edge of the weak contraction pulse P23.

  At time t21 of the leading edge (waveform element e21) of the expansion pulse P21, the partition walls 133 on both sides are displaced so that the volume of the pressure chamber 131 is expanded. Due to this displacement, a negative pressure is instantaneously applied to the ink in the pressure chamber 131 as shown in FIG. As a result, the ink meniscus in the nozzle 301 moves backward.

  Thereafter, the ink pressure changes from a negative pressure to a positive pressure with the natural vibration. Then, when the first waiting time (waveform element e22) elapses and time t22 of the trailing edge (waveform element e23) of the expansion pulse P21 is reached, the volume of the pressure chamber 131 is restored. At this time, as shown in FIG. 11, a positive pressure is instantaneously applied to the ink. As described above, when a positive pressure is instantaneously applied to the ink by a pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301. (First drop ejection). That is, the first waiting time is a time for waiting for the ink pressure that has become negative pressure at the leading edge of the expansion pulse P21 to rise to a predetermined value. The predetermined value is a value at which one drop of ink droplet is ejected when a positive pressure is instantaneously applied to the ink at the trailing edge of the expansion pulse P21. In the example of FIG. 11, the first waiting time is set to ½ of the natural vibration period of the ink in the pressure chamber.

  Thereafter, the ink pressure changes from a positive pressure to a negative pressure with the natural vibration. When the ink pressure changes to a negative pressure, the meniscus moves backward with a delay. Thereafter, the ink pressure is changed to a positive pressure again. Then, when the second waiting time (waveform element e24) elapses while the ink pressure is positive, and the time t23 of the leading edge (waveform element e25) of the contraction pulse P22 is reached, the volume of the pressure chamber 131 contracts. Thus, the partition walls 133 on both sides are displaced. This displacement momentarily applies positive pressure to the ink. Here, the time point t23 is a time point when the ink pressure becomes substantially the same value as at the time point t22. Accordingly, since the positive pressure is instantaneously applied to the ink by the pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301 (2 Drop eye discharge). That is, the second waiting time is a time to wait for the ink pressure to increase until a positive pressure is instantaneously applied to the ink at the leading edge of the contraction pulse P22 until one drop of ink droplet is ejected. .

  When the volume of the pressure chamber 131 is contracted, the third waiting time (waveform element e26) elapses, and when the time t24 of the trailing edge (waveform element e27) of the contraction pulse P22 is reached, the volume of the pressure chamber 131 is reached. The partition walls 133 on both sides are displaced so that a little returns. By this displacement, the pressure chamber 131 is in a weak contraction state that is weaker than the contraction state. This weak contraction state is maintained until the fourth waiting time (waveform element e28) elapses. Then, when the time point t25 of the trailing edge (waveform element e29) of the weak contraction pulse P23 is reached, the volume of the pressure chamber 131 is restored. At time t25, the amplitude of the ink pressure oscillation is equal to the negative pressure instantaneously applied to the ink by the trailing edge of the weak contraction pulse P23, and the ink flow rate is zero. Accordingly, the residual vibration in the pressure chamber 131 is canceled thereafter. That is, the third waiting time and the fourth waiting time are times for generating a timing at which the residual vibration in the pressure chamber 131 is canceled by the trailing edge of the weak contraction pulse P23.

  In this way, by applying the drive voltage having the 2-drop waveform shown in FIG. 10 to the actuator, the pressure chamber 131 operates in the order of expansion, return, contraction, weak contraction, and return. Then, the first ink droplet is ejected from the nozzle 301 communicating with the pressure chamber 131 by the initial expansion and return operations. Further, the second ink droplet is ejected from the nozzle 301 by the subsequent contraction operation. Then, the residual vibration after the ink droplet discharge is canceled by the subsequent operation of weak contraction and recovery.

  FIG. 12 shows the difference voltage between the drive waveform unit set in the 3-drop waveform unit setting unit 413 of the waveform generation unit 41 and the drive waveform unit set in the 3-drop waveform unit setting unit 423 of the adjacent waveform generation unit 42. FIG. That is, in the 3-drop waveform unit setting unit 413 and the 3-drop waveform unit setting unit 423, drive waveform units that generate the differential voltage shown in FIG. 12 are set. This differential voltage becomes the drive voltage of the actuator. By applying this drive voltage to the actuator, three drops of ink droplets are ejected from the nozzle 301 continuously. Such a drive voltage waveform is referred to as a 3-drop waveform in the present embodiment.

  FIG. 13 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when a driving voltage having a 3-drop waveform is applied to the actuator. In FIG. 13, the drive voltage waveform is shown by a solid line, the ink pressure waveform is shown by a one-dot chain line, and the ink flow velocity waveform is shown by a broken line. The value on the vertical axis is normalized.

  As shown in FIG. 12, the 3-drop waveform includes first to thirteenth waveform elements e31 to e43. The first waveform element e31 expands the volume of the pressure chamber 131 at time t31 and applies a negative pressure to the pressure chamber 131. The second waveform element e32 generates a first waiting time (t32-t31) that starts after the first waveform element e31. The third waveform element e33 returns the volume of the pressure chamber 131 to the original pressure after the first waiting time has elapsed at time t32 and applies a positive pressure to the pressure chamber. The fourth waveform element e34 generates a second waiting time (t33-t32) that starts after the third waveform element e33. The fifth waveform element e <b> 35 contracts the volume of the pressure chamber 131 after the second waiting time has elapsed at time t <b> 33 to apply a positive pressure to the pressure chamber 131. The sixth waveform element e36 generates a third waiting time (t34-t33) that starts after the fifth waveform element e35. The seventh waveform element e37 slightly returns the volume of the pressure chamber 131 after the third waiting time has elapsed at time t34. In the example of FIG. 13, when the shrinkage rate by the waveform element e35 is 100%, the shrinkage rate is returned to 50%. The eighth waveform element e38 generates a fourth waiting time (t35-t34) that starts after the seventh waveform element e37. The ninth waveform element e <b> 39 contracts the volume of the pressure chamber 131 again after the fourth waiting time at time t <b> 35 to apply a positive pressure to the pressure chamber 131. In the example of FIG. 13, when the shrinkage rate by the waveform element e35 is 100%, the shrinkage is performed so that the shrinkage rate is equivalent. The tenth waveform element e40 generates a fifth waiting time (t36-t35) that starts after the ninth waveform element e39. The eleventh waveform element e41 slightly returns the volume of the pressure chamber 131 after the fifth waiting time has elapsed at time t36. In the example of FIG. 13, when the shrinkage rate by the waveform element e39 is 100%, the shrinkage rate is returned to 50%. The twelfth waveform element e42 generates a sixth waiting time (t37-t36) that starts after the eleventh waveform element e41. The thirteenth waveform element e43 returns the volume of the pressure chamber 131 to the original after the sixth waiting time has elapsed at time t37.

  Here, the first waveform element e31, the second waveform element e32, and the third waveform element e33 form an expansion pulse P31 that expands the volume of the pressure chamber 131 and then restores the volume. That is, the first waveform element e31 is the leading edge of the extension pulse P31, the second waveform element e22 is the pulse width of the extension pulse P31, and the third waveform element e23 is the trailing edge of the extension pulse P31. The fifth waveform element e35, the sixth waveform element e36, and the seventh waveform element e37 return slightly after the volume of the pressure chamber 131 is contracted, and the contracted state maintained by the sixth waveform element e36. Also, the first contraction pulse P32 is formed to make the weak contraction state (weak contraction state). That is, the fifth waveform element e35 is the leading edge of the first contraction pulse P32, the sixth waveform element e36 is the pulse width of the first contraction pulse P32, and the seventh waveform element e37 is the first waveform element e37. This is the trailing edge of the contraction pulse P32. The eighth component e38 forms a first weak contraction pulse P33 that maintains the weak contraction state of the pressure chamber 131 by the first contraction pulse P32 for a predetermined time. That is, the eighth waveform element e38 is the pulse width of the first weak contraction pulse P33. The ninth waveform element e39, the tenth waveform element e40, and the eleventh waveform element e41 form a second contraction pulse P34 in which the volume of the pressure chamber 131 is contracted and then returned to a slightly contracted state. . That is, the ninth waveform element e39 is the leading edge of the second contraction pulse P34, the tenth waveform element e40 is the pulse width of the second contraction pulse P34, and the eleventh waveform element e41 is the second waveform pulse e34. This is the trailing edge of the contraction pulse P34. The twelfth component e42 and the thirteenth component e43 form a second weak contraction pulse P35 that returns to the original state after maintaining the weak contraction state of the pressure chamber 131 for a predetermined time. That is, the twelfth waveform element e42 is the pulse width of the second weak contraction pulse P35, and the thirteenth waveform element e43 is the trailing edge of the second weak contraction pulse P35.

  At time t31 of the leading edge (waveform element e31) of the expansion pulse P31, the partition walls 133 on both sides are displaced so that the volume of the pressure chamber 131 is expanded. Due to this displacement, a negative pressure is instantaneously applied to the ink in the pressure chamber 131 as shown in FIG. As a result, the ink meniscus in the nozzle 301 moves backward.

  Thereafter, the ink pressure changes from negative pressure to positive pressure with the natural vibration period. Then, when the first waiting time (waveform element e32) elapses and time t32 of the trailing edge (waveform element e33) of the first expansion pulse P31 is reached, the volume of the pressure chamber 131 is restored. At this time, as shown in FIG. 13, positive pressure is instantaneously applied to the ink. As described above, when a positive pressure is instantaneously applied to the ink by a pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301. (First drop ejection). That is, the first waiting time is a time for waiting for the ink pressure that has become negative at the leading edge of the expansion pulse P31 to rise to a predetermined value. The predetermined value is a value at which one drop of ink droplet is ejected when a positive pressure is instantaneously applied to the ink at the trailing edge of the expansion pulse P31.

  Thereafter, the ink pressure changes from a positive pressure to a negative pressure with the natural vibration. Then, when the second waiting time (waveform element e34) elapses while the ink pressure is positive and the time t33 of the leading edge (waveform element e35) of the first contraction pulse P32 is reached, the pressure chamber 131 The partition walls 133 on both sides are displaced so that the volume contracts. This displacement momentarily applies positive pressure to the ink. Here, the time point t33 is a time point when the ink pressure becomes substantially the same value as at the time point t32. Accordingly, since the positive pressure is instantaneously applied to the ink by the pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301 (2 Drop eye discharge). That is, the second waiting time waits for the ink pressure to rise until a positive pressure is instantaneously applied to the ink at the leading edge of the first contraction pulse P32 so that one drop of ink droplet is discharged. It's time.

  After the volume of the pressure chamber 131 is contracted, the ink pressure turns to a negative pressure. When the third waiting time (waveform element e36) elapses and time t34 of the trailing edge (waveform element e37) of the contraction pulse P32 is reached, the partition walls 133 on both sides are displaced so that the volume of the pressure chamber 131 slightly returns. Let By this displacement, the pressure chamber 131 is in a weak contraction state weaker than the contraction state, and the meniscus is retracted. Here, the time point t34 is during the time when the ink pressure is negative, and in the example of FIG. 13, the time point at which the negative pressure of ink becomes maximum. By making a weak contraction state at this time t34, the vibration amplitude of the ink pressure increases.

  The weakly contracted state is maintained until the fourth waiting time (waveform element e38) elapses, during which the ink pressure changes to a positive pressure. Then, when the time t35 of the trailing edge (waveform element e39) of the weak contraction pulse P33 is reached, the partition walls 133 on both sides are displaced so that the volume of the pressure chamber 131 is contracted again. This displacement momentarily applies positive pressure to the ink. Meniscus then moves forward again. Here, the time point t35 is set to a timing later than the time point when the ink pressure becomes substantially the same value as at the time points t32 and t33. The size of the waveform element e39 that gives a positive pressure to the third drop is only half of the first drop e33 and the second drop e35. Therefore, since it is necessary to wait until the ink pressure becomes larger than in the case of the first drop and the second drop, the timing is delayed. Note that the ink pressure after driving by the waveform element e39 at the time point t35 is substantially the same value as that immediately after the time points t32 and t33. Accordingly, since the positive pressure is instantaneously applied to the ink by the pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, one drop of ink droplet is ejected from the nozzle 301 (third drop ejection). That is, the fourth waiting time waits for the ink pressure to increase until a positive pressure is instantaneously applied to the ink at the leading edge of the second contraction pulse P34 so that one drop of ink droplet is discharged. It's time.

  When the volume of the pressure chamber 131 is contracted, the fifth waiting time (waveform element e40) elapses, and when the time t36 of the trailing edge (waveform element e41) of the second contraction pulse P34 is reached, the pressure chamber The partition walls 133 on both sides are displaced so that the volume of 131 slightly returns. By this displacement, the pressure chamber 131 is in a weak contraction state that is weaker than the contraction state. This weak contraction state is maintained until the sixth waiting time (waveform element e42) elapses. Then, when the time t37 of the trailing edge (waveform element e43) of the second weak contraction pulse P35 is reached, the volume of the pressure chamber 131 is restored. At time t37, the magnitude of the amplitude of the ink pressure oscillation is equal to the negative pressure instantaneously applied to the ink by the trailing edge of the second weak contraction pulse P35, and the ink flow rate is zero. Accordingly, the residual vibration in the pressure chamber 131 is canceled thereafter. That is, the fifth waiting time and the sixth waiting time are times for generating a timing at which the residual vibration in the pressure chamber 131 is canceled by the trailing edge of the second weak contraction pulse P35.

  In this way, by applying the 3-drop waveform driving voltage shown in FIG. 12 to the actuator, the pressure chamber 131 operates in the order of expansion, return, contraction, weak contraction, contraction, weak contraction, and return. Then, the first ink droplet is ejected from the nozzle 301 communicating with the pressure chamber 131 by the initial expansion and return operations. Further, the second ink droplet is ejected from the nozzle 301 by the subsequent contraction operation. Further, the third drop of ink droplets is ejected from the nozzle 301 by the subsequent operation of weak contraction and contraction. Then, the residual vibration after the ink droplet discharge is canceled by the subsequent operation of weak contraction and recovery.

  By the way, in the two-drop waveform described above, a weak contraction pulse P23 is generated at the trailing edge of the contraction pulse P22, and the residual vibration is canceled at the trailing edge of the weak contraction pulse P23. The same applies to a 3-drop waveform. However, when the attenuation of the pressure vibration of the ink in the pressure chamber 131 is relatively small, the residual vibration may be canceled at the trailing edge of the contraction pulse P22 in the 2-drop waveform or the 3-drop waveform as in the 1-drop waveform. Is possible.

  Next, a 2-drop waveform for canceling the residual vibration at the trailing edge of the contraction pulse P22 will be described with reference to FIGS.

  FIG. 14 is a waveform diagram of a 2-drop waveform, and FIG. 15 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the drive voltage of the 2-drop waveform is applied to the actuator. In FIG. 15, the drive voltage waveform is shown by a solid line, the ink pressure waveform is shown by a one-dot chain line, and the ink flow velocity waveform is shown by a broken line. The value on the vertical axis is normalized.

  As shown in FIG. 14, the 2-drop waveform is composed of first to seventh waveform elements e41 to e47. The first waveform element e41 expands the volume of the pressure chamber 131 at time t41 and applies a negative pressure to the pressure chamber 131. The fourth waveform element e42 generates a first waiting time (t42-t41) starting after the first waveform element e41. The third waveform element e43 restores the volume of the pressure chamber 131 after the first waiting time elapses at time t42, and applies a positive pressure to the pressure chamber 131. The fourth waveform element e44 generates a second waiting time (t43-t42) that starts after the third waveform element e43. The fifth waveform element e45 contracts the volume of the pressure chamber 131 after the second waiting time elapses at time t43, and applies a positive pressure to the pressure chamber 131. The sixth waveform element e46 generates a third waiting time (t44-t43) that starts after the fifth waveform element e45. The seventh waveform element e47 returns the volume of the pressure chamber 131 to the original after the third waiting time at the time point t44 has elapsed.

  Here, the first waveform element e41, the second waveform element e42, and the third waveform element e43 form an expansion pulse P41 that expands the volume of the pressure chamber 131 and then returns to the original volume. That is, the first waveform element e41 is the leading edge of the extension pulse P41, the second waveform element e42 is the pulse width of the extension pulse P41, and the third waveform element e43 is the trailing edge of the extension pulse P41. The fifth waveform element e45, the sixth waveform element e46, and the seventh waveform element e47 form a contraction pulse P42 that contracts the volume of the pressure chamber 131 and then restores the volume. That is, the fifth waveform element e45 is the leading edge of the contraction pulse P42, the sixth waveform element e46 is the pulse width of the contraction pulse P42, and the seventh waveform element e47 is the trailing edge of the contraction pulse P42.

  Thereafter, the ink pressure changes from negative pressure to positive pressure with the natural vibration period. Then, when the first waiting time (waveform element e42) elapses and time t42 of the trailing edge (waveform element e43) of the expansion pulse P41 is reached, the volume of the pressure chamber 131 is restored. At this time, as shown in FIG. 15, a positive pressure is instantaneously applied to the ink. As described above, when a positive pressure is instantaneously applied to ink by a pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance. Then, one drop of ink droplet is discharged from the nozzle 301 (discharge of the first drop). That is, the first waiting time is a time for waiting for the ink pressure that has become negative at the leading edge of the expansion pulse P41 to rise to a predetermined value. The predetermined value is a value at which one drop of ink droplet is ejected when a positive pressure is instantaneously applied to the ink at the trailing edge of the expansion pulse P41.

  Thereafter, the ink pressure changes from a positive pressure to a negative pressure with the natural vibration. When the ink pressure changes to a negative pressure, the meniscus moves backward with a delay. Thereafter, the ink pressure is changed to a positive pressure again. Then, when the second waiting time (waveform element e44) elapses and time t43 of the leading edge (waveform element e45) of the contraction pulse P42 is reached, the partition walls 133 on both sides are displaced so that the volume of the pressure chamber 131 contracts. Let This displacement momentarily applies positive pressure to the ink. Here, the time point t43 is a time point when the ink pressure becomes substantially the same value as at the time point t42. Accordingly, since the positive pressure is instantaneously applied to the ink by the pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value, the meniscus starts to advance, and one drop of ink droplet is ejected from the nozzle 301 (2 Drop eye discharge). In other words, the second waiting time is a time to wait for the ink pressure to increase until a positive pressure is instantaneously applied to the ink at the leading edge of the contraction pulse P42 so that one drop of ink droplet is discharged. .

  When the volume of the pressure chamber 131 is contracted, the third waiting time (waveform element e46) elapses, and when the time t44 of the trailing edge of the contraction pulse P42 (waveform element e47) is reached, the volume of the pressure chamber 131 is reached. Is restored. At time t44, the amplitude of the ink pressure oscillation is equal to the negative pressure instantaneously applied to the ink by the trailing edge of the contraction pulse P42, and the ink flow rate is zero. Accordingly, the residual vibration in the pressure chamber 131 is canceled thereafter. That is, the third waiting time is a time for generating a timing at which the residual vibration in the pressure chamber 131 is canceled by the trailing edge of the contraction pulse P42.

  In this way, by applying the 2-drop waveform driving voltage shown in FIG. 14 to the actuator, the pressure chamber 131 operates in the order of expansion, return, contraction, and return. Then, the first ink droplet is ejected from the nozzle 301 communicating with the pressure chamber 131 by the initial expansion and return operations. Further, the second ink droplet is ejected from the nozzle 301 by the subsequent contraction operation. Then, the residual vibration after ejection of the ink droplet is canceled by the subsequent returning operation.

  In the 2-drop waveform shown in FIG. 14, the waveform element that can be used to cancel the residual vibration is limited to the waveform element e47 that is the trailing edge of the contraction pulse P42. Since the output timing of the waveform element e47 is limited to the timing described above, the degree of freedom during cancellation is small. Whether or not the 2-drop waveform shown in FIG. 14 can be used depends on the magnitude of attenuation of the residual vibration of the ink. That is, when the attenuation of the residual vibration of the ink is relatively large, the waveform element e47 may not be canceled well because the pressure change is too large.

  The 2-drop waveform or the 3-drop waveform shown in FIG. 10 or FIG. 12 is provided with a step of setting a weak contraction state at the trailing edge of the contraction pulse P22 or the second contraction pulse P34. If a step of making a weak contraction state is provided at the trailing edge of the contraction pulse, the waveform element e29 or the waveform element e43 for cancellation can be adjusted. For this reason, the freedom degree at the time of cancellation spreads. Next, how to determine the timing of the waveform element for cancellation will be described with reference to FIGS. 16 to 19 by taking a 2-drop waveform as an example.

  FIG. 16 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the pressure chamber 131 is kept in the weak contraction state without terminating the two-drop waveform weak contraction pulse P23 at time t25. In FIG. 16, the drive voltage waveform is shown by a solid line, the ink pressure waveform is shown by a one-dot chain line, and the ink flow velocity waveform is shown by a broken line. The value on the vertical axis is normalized.

  As shown in FIG. 16, when the pressure chamber 131 is continued in the weakly contracted state after the time point t25, the residual vibration is not canceled. Further, if the time point t24 at which the contracted state is shifted to the weakly contracted state is shifted back and forth, the ink pressure and the ink flow speed at that time change, and the magnitude of the subsequent residual vibration changes. In the example of FIG. 16, the residual vibration increases when the weak contraction state is entered before time t24, and the residual vibration decreases when the transition is made to the weak contraction state after time t24. Therefore, the timing of the time point t24 is adjusted, and a time point at which the ink flow velocity is zero and the ink pressure matches the pressure amplitude generated when the pressure chamber 131 is returned from the weakly contracted state to the initial state is searched for by simulation. Then, the time is set as the timing of the trailing edge of the weak contraction pulse P23, that is, the time t25. By doing so, the residual vibration can be canceled as shown in FIG.

  The simulation can be performed using an equivalent circuit shown in FIG. The equivalent circuit is a voltage source V connected to a series circuit of a resistor R, a capacitor C, and an inductor L. In the case of the 2-drop waveform shown in FIG. 10, the resistance R is 0.33Ω, the capacitor C is 0.37 μF, and the inductor L is 0.65 μH. In this case, the first waiting time (t22-t21) is 1.56 μs, the second waiting time (t23-t22) is 2.80 μs, and the third waiting time (t24-t23) is 2. .94 μs, and the fourth waiting time (t25-t24) is 0.66 μs. Such an equivalent circuit is extracted from the residual vibration characteristics of the inkjet head 1, and the values of the resistor R, the capacitor C, and the inductor L are determined by the characteristics.

  Now, the loss of the pressure chamber 131 is represented by the value of the resistance R of the equivalent circuit. When the loss of the pressure chamber 131 is large, that is, when the value of the resistance R is large, the residual vibration is small. Therefore, in that case, the time point t24 at which the contraction state shifts to the weak contraction state is shifted forward. By doing so, it is possible to secure a time point at which the ink pressure matches the pressure amplitude generated when the pressure chamber 131 is returned from the weak contraction state to the initial state. And the time is set as time t25 which ends a weak contraction state.

  For example, when the simulation is performed with the resistance R increased to 0.38Ω and appropriate time points t24 and t25 are selected, the drive voltage waveform, ink pressure waveform and ink flow velocity waveform are as shown in FIG. In FIG. 18, the first waiting time (t22-t21) is 1.56 μs, the second waiting time (t23-t22) is 2.80 μs, and the third waiting time (t24-t23) is 2. .84 μs, and the fourth waiting time (t25−t24) is 0.86 μs.

  On the contrary, when the loss of the pressure chamber 131 is small, that is, when the value of the resistance R is small, the residual vibration becomes large. In this case, the time point t24 at which the contracted state is shifted to the weakly contracted state is shifted later. By doing so, it is possible to secure a time point at which the ink pressure matches the pressure amplitude generated when the pressure chamber 131 is returned from the weak contraction state to the initial state. And the time is set as time t25 which ends a weak contraction state.

For example, if the resistance R is reduced to 0.28Ω and a simulation is performed and appropriate time points t24 and t25 are selected, the drive voltage waveform, ink pressure waveform and ink flow velocity waveform are as shown in FIG. In FIG. 19, the first waiting time (t22-t21) is 1.56 μs, the second waiting time (t23-t22) is 2.80 μs, and the third waiting time (t24-t23) is 3. .14 μs, and the fourth waiting time (t25-t24) is 0.36 μs.
As described above, by providing the step of setting the weak contraction state at the trailing edge of the contraction pulse, the waveform element e29 or the waveform element e43 for cancellation can be adjusted according to the magnitude of the attenuation of the residual vibration of the ink. Therefore, the degree of freedom at the time of cancellation is expanded.

Next, the operation of the drive circuit 40 will be described with reference to FIGS.
In FIG. 20, the drive waveform generation units 414 and 424 select the drive waveform units of the 1-drop waveform unit setting units 411 and 421 twice, and then the drive waveform units of the 2-drop waveform unit setting units 412 and 422 are 2 This is an example in which a drive waveform signal is generated by selecting these times and connecting them. In the figure, a waveform signal S1 is a drive waveform signal S1 that is generated by the drive waveform generator 414 and applied to the first electrode 134 of the pressure chamber 131 via the first driver 451. The waveform signal S2 is a drive waveform signal S2 that is generated by the drive waveform generation unit 424 and applied to the second electrode 135 of the adjacent dummy chamber 132 via the second driver 452. A waveform signal ΔV indicates a differential voltage between the drive waveform signal S1 and the drive waveform signal S2. The first unit U1 shows the waveform of the drive waveform unit first selected by the drive waveform generation units 414 and 424 and the differential voltage thereof. The second unit U2 shows the waveform of the drive waveform unit selected second by the drive waveform generation units 414 and 424 and the differential voltage thereof. The same applies to the third and fourth units U3 and U4, and shows the waveform of the third or fourth selected drive waveform unit and its differential voltage.

  In the example of FIG. 20, when the waveform of the first unit U1 or the second unit U2 is applied to the actuator of the pressure chamber 131, one drop of ink droplet is ejected from the nozzle 301. When the waveform of the third unit U3 or the fourth unit is applied to the actuator of the pressure chamber 131, two drops of ink droplets are continuously ejected from the nozzle 301.

  On the other hand, when the gradation value of the print data is 1, the waveform unit selection unit 44 outputs a select signal that enables the period of the first unit U1. When the gradation value is 2, the waveform unit selection unit 44 outputs a select signal that enables the period of the first unit U1 and the period of the second unit U2. When the gradation value is 4, the waveform unit selector 44 outputs a select signal that enables the period from the first unit U1 to the period of the third unit U3. When the gradation value is 6, the waveform unit selector 44 outputs a select signal that enables the period from the first unit U1 to the period of the fourth unit U4.

  FIG. 22A is an example of a waveform when the waveform unit selection unit 44 outputs a select signal SL that enables the period of the first unit U1. In the period of the first unit U1 in which the select signal SL is on, the drive waveform signal S1 is applied to the first electrode 134, and the drive waveform signal S2 is applied to the second electrode 135. As a result, since the differential voltage ΔV between the drive waveform signal S1 and the drive waveform signal S2 is applied to the actuator of the pressure chamber 131, one drop of ink droplet is ejected from the nozzle 301 communicating with the pressure chamber 131. On the other hand, in the period of the second to fourth units U2, U3, U4 in which the select signal SL is off, the drive waveform signal S1 is applied to the first electrode 134, but the drive waveform signal S2 is applied to the second electrode 135. Is not applied, and the second electrode 135 is in a floating state. For this reason, the potential of the second electrode 135 follows the potential of the first electrode 134. As a result, the differential voltage ΔV becomes zero, so that no ink droplet is ejected. Thus, one drop is ejected in one printing cycle.

  FIG. 22B shows an example of a waveform when the waveform unit selector 44 outputs a select signal SL that enables the period of the first to third units U1, U2, and U3. In the period of the first to third units U1, U2, U3 in which the select signal SL is on, the drive waveform signal S1 is applied to the first electrode 134 and the drive waveform signal S2 is applied to the second electrode 135. As a result, since the differential voltage ΔV between the drive waveform signal S1 and the drive waveform signal S2 is applied to the actuator of the pressure chamber 131, four ink droplets are continuously ejected from the nozzle 301 communicating with the pressure chamber 131. The That is, 1 drop is discharged during the period of the first unit U1, and 1 drop is discharged during the period of the second drop U2. Moreover, 2 drops are discharged in order during the period of the third unit U3. On the other hand, during the period of the fourth unit U4 in which the select signal SL is off, the drive waveform signal S1 is applied to the first electrode 134, but the drive waveform signal S2 is not applied to the second electrode 135. For this reason, the potential of the second electrode 135 follows the potential of the first electrode 134. As a result, the differential voltage ΔV becomes zero, so that no ink droplet is ejected and the second electrode 135 is in a floating state. Thus, 4 drops are ejected in one printing cycle.

  FIG. 22C shows an example of a waveform when the waveform unit selector 44 outputs a select signal SL that enables the period of the first to fourth units U1, U2, U3, U4. In the period of the first to fourth units U1, U2, U3, U4 in which the select signal SL is on, the drive waveform signal S1 is applied to the first electrode 134 and the drive waveform signal S2 is applied to the second electrode 135. The As a result, since the differential voltage ΔV between the drive waveform signal S1 and the drive waveform signal S2 is applied to the actuator of the pressure chamber 131, six drops of ink droplets are continuously ejected from the nozzle 301 communicating with the pressure chamber 131. The That is, 1 drop is discharged during the period of the first unit U1, and 1 drop is discharged during the period of the second drop U2. Further, 2 drops are discharged in order during the period of the third unit U3, and 2 drops are discharged continuously even during the period of the fourth unit U4. Thus, 6 drops are ejected in one printing cycle.

  Although not shown, when the waveform unit selection unit 44 outputs a select signal SL that enables the period of the first unit U1 and the period of the second unit U2, two drops are continuously performed in one printing cycle. Then discharged.

  Therefore, it is possible to realize a multi-drop method in which gradation printing is performed by selectively ejecting 1-drop, 2-drop, 4-drop, or 6-drop ink droplets according to print data.

  Although not shown, when the waveform unit selection unit 44 outputs a select signal SL that enables the period of the second unit U2 and the period of the third unit U3, three drops are continuously performed in one printing cycle. Then discharged.

  Although not shown, when the waveform unit selection unit 44 outputs a selection signal SL that enables the period of the second unit U2 and the periods of the third and fourth units U3 and U4, one printing cycle is performed. 5 drops are continuously discharged.

  If the waveform unit selection unit 44 is configured to be programmable to determine which period the waveform unit selection unit 44 is valid for a predetermined gradation value, any one of U1 to U4 can be set for the gradation value. It is also possible to discharge 0-6 drops in combination.

  In FIG. 21, the drive waveform generation units 414 and 424 select the drive waveform unit of the 1-drop waveform unit setting units 411 and 421 twice, and then the drive waveform unit of the 2-drop waveform unit setting units 412 and 422 is 1 This is an example in which the drive waveform signal is generated by selecting the drive waveform unit of the 3-drop waveform unit setting units 413 and 423 once and selecting the drive waveform signal once. In the figure, reference numerals S1, S2, ΔV, U1, U2, U3, and U4 denote the same components as in FIG.

  In the example of FIG. 21, when the waveform of the first unit U1 or the second unit U2 is applied to the actuator of the pressure chamber 131, one drop of ink droplet is ejected from the nozzle 301. When the waveform of the third unit U3 is applied to the actuator of the pressure chamber 131, two ink droplets are continuously ejected from the nozzle 301. When the waveform of the fourth unit U4 is applied to the actuator of the pressure chamber 131, three drops of ink droplets are continuously ejected from the nozzle 301.

  On the other hand, when the gradation value of the print data is 1, the waveform unit selection unit 44 outputs a select signal that enables the period of the first unit U1. When the gradation value is 2, the waveform unit selection unit 44 outputs a select signal that enables the period of the first unit U1 and the period of the second unit U2. When the gradation value is 4, the waveform unit selector 44 outputs a select signal that enables the period from the first unit U1 to the period of the third unit U3. When the gradation value is 7, the waveform unit selector 44 outputs a select signal that enables the period from the first unit U1 to the period of the fourth unit U4.

  FIG. 23A shows an example of a waveform when the waveform unit selector 44 outputs a select signal SL that enables the period of the first unit U1. FIG. 23B shows an example of a waveform when the waveform unit selector 44 outputs a select signal SL that enables the periods of the first to third units U1, U2, and U3. Since these examples are the same as those described with reference to FIGS. 22A and 22B, description thereof is omitted here.

  FIG. 23C shows an example of a waveform when the waveform unit selector 44 outputs a select signal SL that enables the period of the first to fourth units U1, U2, U3, U4. In the period of the first to fourth units U1, U2, U3, U4 in which the select signal SL is on, the drive waveform signal S1 is applied to the first electrode 134 and the drive waveform signal S2 is applied to the second electrode 135. The As a result, since the differential voltage ΔV between the drive waveform signal S1 and the drive waveform signal S2 is applied to the actuator of the pressure chamber 131, seven drops of ink droplets are continuously ejected from the nozzle 301 communicating with the pressure chamber 131. The That is, 1 drop is discharged during the period of the first unit U1, and 1 drop is discharged during the period of the second drop U2. Further, 2 drops are discharged in order during the period of the third unit U3, and 3 drops are discharged continuously during the period of the fourth unit U4. Thus, 7 drops are ejected in one printing cycle.

  Although not shown, when the waveform unit selection unit 44 outputs a select signal SL that enables the period of the first unit U1 and the period of the second unit U2, two drops are continuously performed in one printing cycle. Then discharged.

  Therefore, it is possible to realize a multi-drop method in which gradation printing is performed by selectively ejecting 1-drop, 2-drop, 4-drop, or 7-drop ink droplets according to print data.

  Although not shown, when the waveform unit selection unit 44 outputs a select signal SL that enables the period of the second unit U2 and the period of the third unit U3, three drops are continuously performed in one printing cycle. Then discharged.

  Although not shown, when the waveform unit selection unit 44 outputs a select signal SL that enables the periods of the third and fourth units U3 and U4, 5 drops are discharged continuously in one printing cycle. Is done.

  If the waveform unit selector 44 is configured to be programmable so that the waveform unit selector 44 is valid for a predetermined gradation value, the period U1 to U4 can be set for the gradation value. It is also possible to discharge 0 to 7 drops as effective in any combination.

  There are a plurality of combinations of periods U1 to U4 for discharging a predetermined number of drops in one printing cycle. For example, in order to discharge 2 drops in one printing cycle, a method of enabling the period of U3 independently may be used in addition to the method of enabling the periods of U1 and U2. For example, in order to discharge 3 drops in one printing cycle, in addition to the method of enabling the periods of U2 and U3, the period of U1 and U3 can also be enabled, and the period of U4 is enabled alone You can also. For example, in order to discharge 5 drops in one printing cycle, the period of U1, U2, and U4 can be validated in addition to the method of validating the period of U3 and U4. Even when the number of drops is the same, the ejection characteristics of the droplets are different, so that the flight characteristics are different. Which combination is used to obtain a predetermined number of drops in one printing cycle can be freely selected so as to obtain desired flight characteristics.

  As described above in detail, according to the inkjet head 1 of the present embodiment, as shown in FIG. 20 or FIG. 21, a drive waveform unit (one drop waveform) for discharging one drop and a plurality of drops are discharged. Therefore, a drive waveform signal can be generated by connecting a drive waveform unit (2-drop waveform or 3-drop waveform). Then, from the drive waveform signals composed of the plurality of drive waveform units, a valid drive waveform unit can be selected according to the print data and applied to the actuator. Therefore, by using, for example, the 2-drop waveform or 3-drop waveform shown in FIG. 10, FIG. 12 or FIG. 14 as the drive waveform unit for ejecting a plurality of drops, the consumption at the time of ejecting ink droplets by the multi-drop method Power reduction and high-speed driving can be realized.

  Specifically, the 2-drop waveform causes 2 drops to be discharged continuously by an example of one operation of expansion, return, and contraction. This series of operations is the same as the one-drop waveform shown in FIG. Accordingly, since double 2 drops can be discharged with the same number of charge / discharge cycles as the 1 drop waveform, power consumption and heat generation per drop can be suppressed. In addition, since the waveform element for canceling the residual vibration is not inserted between the first drop and the second drop, the residual vibration is canceled by the returning operation after the completion of the discharge of the two drops. The time required for discharging is shortened. As a result, high speed driving is possible.

  In addition, the 3-drop waveform discharges 3 drops continuously by a series of operations of expansion, return, contraction, weak contraction, and contraction. In this series of operations, the number of times of charging / discharging is small compared to the case of discharging 3 drops using the 1 drop waveform and the 2 drop waveform shown in FIG. 10 or FIG. Can be suppressed. In addition, since the time until ejection of 3 drops is completed is short, high-speed driving is possible. In addition, when the 3-drop waveform shown in FIG. 12 is used, it is possible to cancel the remaining amount vibration after the 3 drops are continuously ejected from the nozzle 301.

  By the way, when gradation printing is performed, a high resolution is required in order to suppress roughness at the time of a small drop of about 1 drop or 2 drops. On the other hand, for example, high speed and power saving are required at the time of multiple drops of 4 drops or more. In this regard, in this embodiment, as shown in FIG. 20 or FIG. 21, at least two drive waveform units having a 1-drop waveform are connected, and thereafter, drive waveform units having a 2 or 3-drop waveform are connected. Therefore, a 1-drop drive waveform unit is effective when there is a small drop, and a high resolution can be obtained. On the other hand, at the time of multiple drops, a drive waveform unit having a 2-drop waveform or a 3-drop waveform is effective, so that requirements for high speed and power saving can be satisfied.

Hereinafter, modifications of the embodiment will be described.
In the embodiment, the 2-drop waveform unit setting units 412 and 422 and the 3-drop waveform unit setting units 413 and 423 are exemplified as the second waveform generation unit that generates the drive waveform unit for discharging a plurality of drops. The second waveform generator is not limited to this. For example, a drive waveform unit for discharging 4 drops may be generated.

  In the embodiment, as shown in FIGS. 11, 13, and 15, the ink pressures at the time points t23, t33, and t43 when the second drop is ejected are the ink pressures at the time points t22, t32, and t42 when the first drop is ejected. To be almost the same. However, it is not necessarily the same. In short, it is only necessary that the ink pressure becomes positive to the extent that ink can be ejected by the pulse change of the waveform elements e25, e35, e45 for ejecting the second drop.

  FIG. 24 is a waveform diagram showing the result of simulating the ink pressure and the ink flow rate when the time t23 at the leading edge of the contraction pulse P22 having the two-drop waveform shown in FIG. 10 is advanced. In FIG. 24, the drive voltage waveform is indicated by a solid line, the ink pressure waveform is indicated by a one-dot chain line, and the ink flow velocity waveform is indicated by a broken line. The value on the vertical axis is normalized.

  In this example, the time t22 at the trailing edge of the expansion pulse P21 is set when the normalized ink pressure is 0.75, while the time at the leading edge of the contraction pulse P22 is set when the ink pressure is 0.5. t23. With such a waveform, the discharge speed of the second drop is slower than that of the first drop, but even with such a two-drop waveform, two drops can be discharged continuously from the nozzle 301.

  FIG. 25 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the time t23 at the leading edge of the contraction pulse P22 having the two-drop waveform shown in FIG. 10 is further advanced. In FIG. 25, the drive voltage waveform is indicated by a solid line, the ink pressure waveform is indicated by a one-dot chain line, and the ink flow velocity waveform is indicated by a broken line. The value on the vertical axis is normalized.

  In this example, the time t22 at the trailing edge of the expansion pulse P21 is set when the normalized ink pressure is 0.75, whereas the time at the leading edge of the contraction pulse P22 is set when the ink pressure turns positive. t23. With such a waveform, the discharge speed of the second drop is further slower than that of the first drop, but even with such a two-drop waveform, two drops can be discharged continuously from the nozzle 301.

  FIG. 26 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the time t35 at the leading edge of the second contraction pulse P34 having the three-drop waveform shown in FIG. 12 is advanced. In FIG. 26, the drive voltage waveform is indicated by a solid line, the ink pressure waveform is indicated by a one-dot chain line, and the ink flow velocity waveform is indicated by a broken line. The value on the vertical axis is normalized.

  In FIG. 13, the time t32 at the trailing edge of the expansion pulse P31 is when the normalized ink pressure is 0.75, and the time t35 at the leading edge of the second contraction pulse P34 when the ink pressure is 1.3. I was trying. On the other hand, in the modified example of FIG. 26, the time point t32 at the trailing edge of the expansion pulse P31 is when the normalized ink pressure is 0.75, which is the same as in FIG. However, since the time point t35 is advanced, the time point t35 at the leading edge of the second contraction pulse P34 is set when the ink pressure is 1.0, which is lower than that in FIG. Even with such a 3-drop waveform, 3-drop ejection can be continuously performed from the nozzle 301. In such a 3-drop waveform, the flow speed of the third drop is slow.

  FIG. 27 is a waveform diagram showing a result of simulating ink pressure and ink flow velocity when the time t33 at the leading edge of the first contraction pulse P32 having the 3-drop waveform shown in FIG. 12 is advanced. In FIG. 27, the drive voltage waveform is indicated by a solid line, the ink pressure waveform is indicated by a one-dot chain line, and the ink flow velocity waveform is indicated by a broken line. The value on the vertical axis is normalized.

  In this example, the time when the normalized ink pressure is 0.75, which is the same as that in FIG. 13, is set as the time point t32 at the trailing edge of the expansion pulse P31. .5 is the time t33 of the leading edge of the first contraction pulse P32. The peak of the negative pressure is reduced by delaying the time t34 at the trailing edge of the first contraction pulse P32. Accordingly, it is possible to reduce the positive pressure applied to the adjacent channel and prevent bubbles from being generated in the pressure chamber 131 due to the negative pressure. With such a three-drop waveform, the discharge speed of the second drop is slow, but even with such a three-drop waveform, two drops can be discharged continuously from the nozzle 301.

  In the embodiment, as shown in FIGS. 11 and 13, the contraction rates of the weak contraction pulses P23, P33, and P35 are 50% when the contraction rates of the contraction pulses P22, P32, and P34 are 100 &. If the contraction rate of the weak contraction pulses P23, P33, and P35 is 50%, there is an advantage that the drive power supply is simplified. However, it is not limited to the above example.

  FIG. 28 shows an example in which, in the 2-drop waveform shown in FIG. 10, the contraction rate of the weak contraction pulse P23 is 30% when the contraction rate of the contraction pulse P22 is 100 &. Even in such a two-drop waveform, at time points t22 and t23, a positive pressure is instantaneously applied to the ink by a pulse change in a state where the ink pressure is a positive pressure equal to or higher than a predetermined value. One drop is discharged. On the other hand, at the time t25, the magnitude of the amplitude of the ink pressure is equal to the negative pressure instantaneously applied to the ink by the trailing edge of the weak contraction pulse P23, and the ink flow velocity is also zero. Therefore, the residual vibration in the pressure chamber 131 is canceled.

  The configuration of the inkjet head 1 is not limited to that described with reference to FIGS. For example, an inkjet head having one piezoelectric member for each pressure chamber may be used, and an inkjet head that fixes one electrode potential of a pair of electrodes of the piezoelectric member and applies a driving waveform to the other electrode. Also good. Alternatively, each of the first groove 131 and the second groove 132 is a pressure chamber filled with ink, and each pressure chamber is divided into three groups every other two, and is a shared wall type inkjet head. Also good.

  In addition, although several 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 forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet head, 40 ... Drive circuit, 41 ... The said waveform generation part, 42 ... Adjacent waveform generation part, 43 ... Print data setting part, 44 ... Waveform unit selection part, 45 ... Driver part, 46 ... Waveform connection control part, DESCRIPTION OF SYMBOLS 100 ... Base material, 118 ... Piezoelectric member, 131 ... 1st groove | channel (pressure chamber), 132 ... 2nd groove | channel (dummy chamber), 133 ... Partition, 134 ... 1st electrode, 135 ... 2nd electrode, 200 ... Frame member , 300 ... Nozzle plate, 301 ... Nozzle, 400 ... Housing, 411, 421 ... 1 drop waveform unit setting unit, 412, 422 ... 2 drop waveform unit setting unit, 413, 423 ... 3 drop waveform unit setting unit, 414 424 ... Drive waveform generator.

Claims (5)

A pressure chamber containing ink;
A nozzle communicating with the pressure chamber;
An actuator provided corresponding to the pressure chamber and displacing the volume of the pressure chamber;
A drive circuit for driving the actuator;
Comprising
The drive circuit is
A first waveform generator for generating a drive waveform unit for discharging one drop;
A second waveform generator for generating a drive waveform unit for discharging a plurality of drops;
A waveform generator for generating a drive waveform signal by connecting a drive waveform unit generated from the first waveform generator and a drive waveform unit generated from the second waveform generator;
From the drive waveform signal generated by the waveform generator, a waveform unit selector that selects a drive waveform unit that is valid according to print data and applies it to the actuator;
An inkjet head.   The waveform generation unit connects at least two drive waveform units generated from the first waveform generation unit, and then connects the drive waveform units generated from the second waveform generation unit. The inkjet head as described.   The number of times the actuator is charged or discharged by the drive waveform unit generated by the second waveform generator is the drive waveform unit generated from the first waveform generator when the number of the plurality of drops is n. The inkjet head according to claim 1, wherein the number is less than n times the number of times the actuator is charged or discharged.   The required time of the drive waveform unit generated in the second waveform generator is n times the required time of the drive waveform unit generated from the first waveform generator, where n is the number of the plurality of drops. The ink jet head according to claim 1, wherein the number is less.   5. The inkjet head according to claim 1, wherein there are a plurality of the second waveform generation units, and each generates a drive waveform unit for discharging a plurality of different drops.