Method for driving liquid ejection head and printer

Abstract

To prevent variation in an amount of ejection of liquid, which is caused by electrical crosstalk between drive elements connected to the same power supply circuit.SOLUTION: A method for driving a head 11 includes inputting, to each of a plurality of driving elements 111 in a predetermined period T, an ejection pulse signal PS1 that changes a volume of a pressure chamber 145 communicating with the nozzle 11a such that a liquid is ejected from a corresponding nozzle 11a, or a non-ejection pulse signal PS2 that changes the volume of the pressure chamber 145 communicating with the nozzle 11a such that the liquid is not ejected from the nozzle 11a. Each of the ejection pulse signal PS1 and the non-ejection pulse signal PS2 includes a volume reduction period in which the volume of the pressure chamber 145 is reduced and a volume expansion period in which the volume of the pressure chamber 145 is expanded. The volume reduction period Tf1 at the ejection pulse signal PS1 and the volume reduction period Tf2 at the non-ejection pulse signal PS2 are overlapped.SELECTED DRAWING: Figure 11

Description

Technical Field

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

Background Art

[0002] Conventionally, in two adjacent ink chambers, it is known that the flying state of ink ejected from a nozzle communicating with one ink chamber changes between the case where ink is ejected from a nozzle communicating with the other ink chamber and the case where ink is not ejected. To suppress this, there is a known prior art in which, even when ink is not ejected from a nozzle communicating with the other ink chamber, the other ink chamber is deformed to such an extent that ink is not ejected from the nozzle communicating with the other ink chamber (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above prior art, when ink is ejected from a nozzle communicating with one ink chamber and no ink is ejected from a nozzle communicating with the other ink chamber, the volume of the other ink chamber is reduced during the period when the volume of one ink chamber is expanded, and the volume of the other ink chamber is expanded during the period when the volume of one ink chamber is reduced. That is, in one ink chamber and the other ink chamber, the volume changes are opposite, and the moving directions of the charges supplied to the actuator provided in one ink chamber and the actuator provided in the other ink chamber are opposite. For this reason, when the actuators provided in one ink chamber and the actuators provided in the other ink chamber are connected to the same power supply, electrical crosstalk occurs between the two actuators. And when electrical crosstalk occurs, the actuator provided in one ink chamber will also be supplied with charges from the actuator provided in the other ink chamber that is closer to the power supply in the electrical path. As a result, the actuator provided in one ink chamber behaves differently when it is supplied with charges only from the power supply and when it is also supplied with charges from the actuator provided in the other ink chamber, and the amount of ink ejected from the nozzle communicating with one ink chamber varies.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a driving method for a liquid ejection head that can suppress variations in the ejection amount of a liquid caused by electrical crosstalk between driving elements connected to the same power supply circuit.

Means for Solving the Problems

[0006] According to a first aspect of the present invention, there is provided a method for driving a liquid ejection head, wherein the liquid ejection head includes a flow path member having a plurality of individual flow paths including a plurality of nozzles and a plurality of pressure chambers respectively communicating with the plurality of nozzles, and a common flow path communicating with the plurality of individual flow paths, A plurality of drive elements fixed to the flow path member so as to correspond to the plurality of nozzles respectively, and electrically connected to a common power supply circuit. Each of the plurality of drive elements applies pressure to the liquid in the pressure chamber by changing the volume of the pressure chamber communicating with the corresponding nozzle. The driving method includes, during a predetermined period, inputting to each of the plurality of drive elements a discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is discharged from the corresponding nozzle, or a non-discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is not discharged from the corresponding nozzle. Each of the discharge pulse signal and the non-discharge pulse signal includes a volume reduction period for reducing the volume of the pressure chamber and a volume expansion period for expanding the volume of the pressure chamber. There is provided a driving method in which the volume reduction period in the discharge pulse signal and the volume reduction period in the non-discharge pulse signal overlap, or the volume expansion period in the discharge pulse signal and the volume expansion period in the non-discharge pulse signal overlap.

[0007] According to a second aspect of the present invention, there is provided a printing apparatus, A flow path member having a plurality of individual flow paths including a plurality of nozzles and a plurality of pressure chambers respectively communicating with the plurality of nozzles, and a common flow path communicating with the plurality of individual flow paths, A plurality of drive elements fixed to the flow path member so as to correspond to the plurality of nozzles respectively, and electrically connected to a common power supply circuit, A controller for controlling the plurality of drive elements, Each of the plurality of drive elements applies pressure to the liquid in the pressure chamber by changing the volume of the pressure chamber communicating with the corresponding nozzle. During a predetermined period, the controller inputs a discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is discharged from the corresponding nozzle to each of the plurality of drive elements, or a non-discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is not discharged from the nozzle. Each of the discharge pulse signal and the non-discharge pulse signal includes a volume reduction period for reducing the volume of the pressure chamber and a volume expansion period for expanding the volume of the pressure chamber. A printing apparatus is provided in which the volume reduction period in the discharge pulse signal and the volume reduction period in the non-discharge pulse signal overlap, or the volume expansion period in the discharge pulse signal and the volume expansion period in the non-discharge pulse signal overlap.

Advantages of the Invention

[0008] According to the first and second aspects of the present invention, the volume reduction period in the discharge pulse signal and the volume reduction period in the non-discharge pulse signal overlap, or the volume expansion period in the discharge pulse signal and the volume expansion period in the non-discharge pulse signal overlap. For this reason, the moving direction of the charge becomes the same among the drive elements connected to the same power supply circuit, and the variation in the discharge amount of the liquid due to the electrical crosstalk among the drive elements connected to the same power supply circuit can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 11

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, a printing apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 9.

[0011] In FIG. 1, the upstream side in the conveyance direction of the medium M is defined as the front of the printing apparatus 1, and the downstream side in the conveyance direction is defined as the rear of the printing apparatus 1. Also, a direction that is parallel to the surface on which the medium M is conveyed (a surface parallel to the paper surface of FIG. 1) and orthogonal to the conveyance direction is defined as the width direction. Note that the left side of the figure is the left side of the printing apparatus 1, and the right side of the figure is the right side of the printing apparatus 1. Further, a direction orthogonal to the conveyance surface of the medium M (a direction orthogonal to the paper surface of FIG. 1) is defined as the vertical direction of the printing apparatus 1. In FIG. 1, the front side of the paper surface is the upper side, and the back side of the paper surface is the lower side. Hereinafter, front, rear, left, right, upper, and lower will be appropriately used for the description.

[0012] As shown in FIG. 1, the printing apparatus 1 includes a platen 3 housed in a housing 2, four line heads 4, two conveying rollers 5A and 5B, and a controller 7.

[0013] On the upper surface of the platen 3, a medium M such as a recording sheet is placed. The four line heads 4 are positioned above the platen 3 so as to face the platen 3. The four line heads 4 are arranged in the front-rear direction. The two conveying rollers 5A and 5B are respectively positioned in front of and behind the platen 3. The two conveying rollers 5A and 5B are respectively driven by a motor (not shown) and convey the medium M on the platen 3 downstream (rearward) in the conveying direction. In the present embodiment, the configuration includes four line heads 4, but the number of line heads 4 is not limited to four. Further, the two conveying rollers 5A and 5B are an example of the conveying mechanism of the present invention.

[0014] As shown in FIG. 3, the controller 7 includes a first substrate 71. The first substrate 71 includes, in addition to an FPGA (Field Programmable Gate Array) 711, a ROM (Read Only Memory) not shown, a RAM (Random Access Memory) not shown, an EEPROM (registered trademark) 712, and the like. The controller 7 can communicate with an external device 9 such as a personal computer. The controller 7 controls the operations of the respective line heads 4 and the conveying rollers 5A and 5B according to a program stored in the ROM in accordance with an instruction from the external device 9 or an operation unit (not shown) provided in the printing apparatus 1. Note that a CPU (Central Processing Unit) or an MPU (Microprocessor Unit) may be used instead of the FPGA 711.

[0015] For example, the controller 7 controls the motors that drive the conveying rollers 5A and 5B to convey the medium M in the conveying direction by the conveying rollers 5A and 5B. Further, the controller 7 controls each line head 4 to eject ink toward the medium M. Thereby, an image is printed on the medium M. Note that the medium M may be a roll-shaped sheet.

[0016] The housing 2 is attached with four head holders 8 corresponding to the four line heads 4. The four head holders 8 are arranged in a row in the front-rear direction above the platen 3 and at a position between the conveying rollers 5A and 5B. Each head holder 8 holds one line head 4.

[0017] The four line heads 4 each discharge four colors of ink: cyan (C), magenta (M), yellow (Y), and black (K). Each line head 4 is supplied with the corresponding one color of ink from an ink tank (not shown).

[0018] As shown in FIG. 2, each line head 4 of the present embodiment includes nine heads 11. The nine heads 11 are arranged in two rows in a staggered pattern along the width direction. Since one color of ink is supplied to one line head 4, the one color of ink is discharged from the nine heads 11 included in the one line head 4. In the present embodiment, the line head 4 is configured to include nine heads 11, but the number of heads 11 is not limited to nine.

[0019] On the bottom surface of each head 11 of the present embodiment, 1680 nozzles 11a are open, and the 1680 nozzles 11a form a plurality of nozzle rows arranged in the width direction. That is, the head 11 has a plurality of nozzles 11a. And each nozzle row is formed by a plurality of nozzles 11a arranged in the conveying direction. In the present embodiment, each head 11 is configured to include 1680 nozzles 11a, but the number of nozzles 11a is not limited to 1680.

[0020] Each head 11 is also provided with the same number of drive elements 111 (see FIG. 7) as the number of nozzles 11a, and the second substrate 50 and the flexible circuit board 60 shown in FIG. 3. The printing apparatus 1 of the present embodiment includes four line heads 4, and each line head 4 includes nine heads 11. Therefore, the printing apparatus 1 includes 36 heads 11. Accordingly, the number of the second substrates 50 is also 36, and the number of the flexible circuit boards 60 connected to the second substrates 50 is also 36. As shown in FIG. 3, the first substrate 71 of the controller 7 is connected to 36 second substrates 50. In FIG. 3, for the sake of convenience, only one second substrate 50 and one flexible circuit board 60 are shown.

[0021] As shown in FIG. 3, the second substrate 50 includes an FPGA 51, a nonvolatile memory 52 such as an EEPROM, a DRAM 53 that temporarily stores raster data received from the controller 7, a D / A converter 20, power supply circuits 21 to 26, and the like. In the present embodiment, the second substrate 50 includes six power supply circuits 21 to 26, but the number of the power supply circuits is not limited to six. The power supply circuits 21 to 25 are an example of the drive power supply circuit of the present invention, and the power supply circuit 26 is an example of the high-potential power supply circuit of the present invention. The flexible circuit board 60 includes a nonvolatile memory 62 such as an EEPROM, a driver IC 27, and the like.

[0022] The FPGA 51 outputs a digital setting signal for setting the output voltage values of the power supply circuits 21 to 26 to the D / A converter 20 under the control of the FPGA 711 provided on the first substrate 71.

[0023] The D / A converter 20 converts the digital setting signal output from the FPGA 51 into an analog setting signal and outputs it to the power supply circuits 21 to 26.

[0024] The power supply circuits 21 to 26 can be, for example, DC / DC converters composed of a plurality of electronic components such as FETs, inductors, resistors, and electrolytic capacitors. Each of the power supply circuits 21 to 26 outputs a voltage (driving voltage) specified by a setting signal to the driver IC 27. That is, the FPGA 51 adjusts the output voltage values of the power supply circuits 21 to 26. In the present embodiment, different output voltage values are preset for the power supply circuits 21 to 26. Details of the configuration of the power supply circuits 21 to 26 will be described later.

[0025] The driver IC 27 is connected to the power supply circuits 21 to 25 via the wirings VDD1 to VDD5, respectively, and is connected to the power supply circuit 26 via the wiring HVDD. Note that the power supply circuit 26 is connected to the drive element 111 (see FIG. 7) described later via the wiring VCOM. The wiring HVDD and the wiring VCOM are such that the wiring drawn from the power supply circuit 26 branches into two wirings in the middle of the path.

[0026] The power supply circuit 26 can be used as the VCOM power supply voltage for the drive element 111 or the HVDD (high-side back gate voltage) of the PMOS transistors 311 to 315 (see FIG. 5) described later.

[0027] The driver IC 27 is connected to n signal lines 34(1) to 34(n) (n is a natural number of 2 or more, and in the present embodiment, is equal to the number of drive elements 111 of the head 11, that is, 1680). The driver IC 27 is connected to n drive elements 111 via the n signal lines 34(1) to 34(n). Each signal line 34 is connected to an individual electrode of the drive element 111.

[0028] The non-volatile memory 52 stores nozzle IDs for identifying each nozzle 11a and the like. Further, the non-volatile memory 52 stores, for example, the correspondence between n nozzles 11a and five power supply circuits 21 to 25. That is, each of the plurality of nozzles 11a is associated with one of the plurality of power supply circuits 21 to 25. Note that these correspondence relationships may be stored not in the non-volatile memory 52 but in a non-volatile memory 62 provided on the flexible circuit board 60.

[0029] The driver IC 27 is also connected to the FPGA 51 via n control lines 33(1) to 33(n) and the control line 40.

[0030] The control lines 33(1) to 33(n) are provided corresponding to n waveform generation circuits 30(1) to 30(n) (see FIG. 4) included in the driver IC 27, which will be described later. A signal for controlling the FET provided in each waveform generation circuit 30 propagates through each control line 33. According to this signal, the waveform generation circuit 30 generates a drive signal for driving the drive element 111 and outputs the generated drive signal to the drive element 111 via the signal line 34.

[0031] Also, a control signal for controlling n selectors 90(1) to 90(n) (see FIG. 4) included in the driver IC 27 is transmitted through the control line 40. The FPGA 51 selects a power supply circuit for generating a drive signal to be output to each signal line 34 by controlling the n selectors 90(1) to 90(n).

[0032] Next, an example of the circuit configuration of the driver IC 27 will be described with reference to FIG. 4. As shown in FIG. 4, the driver IC 27 includes n waveform generation circuits 30(1) to 30(n) and n selectors 90(1) to 90(n).

[0033] The waveform generation circuits 30(1) to 30(n) are provided corresponding to the n drive elements 111 provided in each head 11. That is, the waveform generation circuits 30(1) to 30(n) are provided corresponding to the n nozzles 11a provided in each head 11. Further, the selectors 90(1) to 90(n) are provided corresponding to the waveform generation circuits 30(1) to 30(n). That is, the selectors 90(1) to 90(n) correspond to the n drive elements 111 respectively. Each selector 90 is a hardware component composed of a plurality of FETs formed inside the driver IC 27 and the like.

[0034] The driver IC 27 has n circuit configurations equal to the number of nozzles. Since the n circuit configurations have the same configuration, hereinafter, the circuit configuration provided between the control line 33(1) and the signal line 34(1) will be described. In the driver IC 27, a selector 90(1) and a waveform generation circuit 30(1) are formed between the control line 33(1) and the signal line 34(1).

[0035] The control line 33(1) from the FPGA 51 is connected to the selector 90(1). The control line 33(1) branches in the middle of the path connecting the FPGA 51 and the selector 90(1), and the control line SB(1) branched from the control line 33(1) is connected to the waveform generation circuit 30(1).

[0036] The selector 90(1) and the waveform generation circuit 30(1) are connected by five control lines S1(1) to S5(1). The selector 90(1) connects one of the five control lines S1(1) to S5(1) to the control line 33(1) according to an instruction from the FPGA 51.

[0037] Five wirings connected to the above-mentioned wirings VDD1 to VDD5, a wiring connected to the wiring HVDD, and a wiring connected to the wiring GND are connected to the waveform generation circuit 30(1). That is, the waveform generation circuit 30(1) is connected to the power supply circuits 21 to 25 via the wirings VDD1 to VDD5, and is connected to the power supply circuit 26 via the wiring HVDD.

[0038] Next, an example of the configuration of the waveform generation circuits 30(1) to 30(n) included in the head 11 of the present embodiment will be described with reference to FIG. 5. Since the waveform generation circuits 30(1) to 30(n) have the same configuration, the waveform generation circuit 30(1) will be described below. The waveform generation circuit 30(1) includes five PMOS (P-type Metal Oxide Semiconductor) transistors 311 to 315 (only two are shown in FIG. 5), one NMOS (N-type Metal Oxide Semiconductor) transistor 32, a resistor 35, and the like. The waveform generation circuit 30(1) is connected to the individual electrodes of the drive element 111 via the signal line 34(1).

[0039] Here, as shown in FIG. 7, the drive element 111 of the present embodiment is a piezoelectric element including a first active portion 138 sandwiched between the individual electrode 134 and the high potential electrode 135, and a second active portion 139 sandwiched between the individual electrode 134 and the low potential electrode 136 with respect to one pressure chamber 145. Therefore, as shown in FIGS. 5 and 7, the drive element 111 includes a capacitor 111b' and a capacitor 111b.

[0040] Wiring VDD1 to VDD5 are connected to the five source terminals 311a to 315a of the five PMOS transistors 311 to 315, respectively. The source terminal 32a of the NMOS transistor 32 is connected to the ground. That is, the PMOS transistors 311 to 315 are connected to the power supply circuits 21 to 25 via the wiring VDD1 to VDD5, respectively.

[0041] Control lines S1(1) to S5(1) are connected to the gate terminals 311c to 315c of the PMOS transistors 311 to 315, respectively. Also, a control line SB(1) is connected to the gate terminal 32c of the NMOS transistor 32.

[0042] Further, the drain terminals 311b to 315b of the five PMOS transistors 311 to 315 are connected to one end of the resistor 35. Also, the drain terminal 32b of the NMOS transistor 32 is connected to one end of the resistor 35. The other end of the resistor 35 is connected to the individual electrode 134 of the driving element 111 (the other end of the capacitor 111b' and one end of the capacitor 111b). The high-potential electrode 135 of the driving element 111 (one end of the capacitor 111b') is connected to VCOM, and the low-potential electrode 136 of the driving element 111 (the other end of the capacitor 111b) is connected to ground.

[0043] When the FPGA 51 outputs a low-level ("L") signal to the control line 33(1), any one of the PMOS transistors 311 to 315 connected to the signal line selected by the above-described selector 90(1) becomes on. The capacitor 111b is charged by the voltage supplied from any one of the power supply circuits 21 to 25, and the capacitor 111b' is discharged. On the other hand, when the FPGA 51 outputs a high-level ("H") signal to the control line 33(1), the NMOS transistor 32 becomes on, and the capacitor 111b' is charged by the voltage output from any one of the power supply circuits 21 to 25, and the capacitor 111b is discharged. By alternately charging and discharging the capacitors 111b and 111b', the driving element 111 deforms, and ink is discharged from the discharge port of the nozzle 11a.

[0044] That is, a driving signal for driving the driving element 111 is output to the signal line 34(1). By the selector 90(1) selecting one control line to connect from among the five control lines S1(1) to S5(1), the power supply circuit for generating the driving signal can be selected from among the power supply circuits 21 to 25.

[0045] Next, the structure of the head 11 will be described. As shown in FIG. 6, the head 11 includes a flow path substrate 120 and a piezoelectric actuator 130.

[0046] (Flow path substrate 120) The flow path substrate 120 is formed with a plurality of nozzles 11a, individual flow paths 143 (see FIG. 6) respectively communicating with the plurality of nozzles 11a, and a manifold 142 (see FIG. 6) commonly communicating with the plurality of individual flow paths 143. The flow path substrate 120 is composed of an ink sealing film 121 laminated in the vertical direction and metal plates 122 to 126.

[0047] The plate 122 is formed with through holes defining a plurality of pressure chambers 145. As shown in FIG. 6, the plate 123 is formed with through holes defining communication paths 144 and 146 provided for each pressure chamber 145. The communication paths 144 and 146 overlap vertically with one end and the other end in the front-rear direction of the corresponding pressure chamber 145, respectively. The plate 124 is formed with through holes defining communication paths 147 provided for each communication path 146. The plate 125 is formed with through holes defining communication paths 148 provided for each communication path 147. The communication paths 147 and 148 overlap vertically with the corresponding communication path 146. The nozzle plate 126 is formed with through holes defining the respective nozzles 11a. Each nozzle 11a overlaps vertically with the communication path 148. And each individual flow path 143 is composed of the communication paths 144, the pressure chambers 145, the communication paths 146 to 148, and the nozzles 11a.

[0048] Also, the plate 124 is formed with through holes defining the manifold 142. The communication path 144 of each individual flow path 143 overlaps vertically with the manifold 142. Thereby, each individual flow path 143 communicates with the manifold 142. And an ink supply port (not shown) is formed in a region on the upper surface of the plate 122 where the ink sealing film 121 and the piezoelectric actuator 130 are not formed. The ink supply port communicates with the manifold 142 through a through hole penetrating the plates 122 and 123.

[0049] The ink sealing film 121 is made of a material with low ink permeability such as stainless steel, for example. The ink sealing film 121 is adhered to the upper surface of the plate 122 and seals all the pressure chambers 145 formed in the plate 122.

[0050] In the flow path substrate 120 having the above-described configuration, the ink in an ink tank (not shown) is supplied to the manifold 142 through the ink supply port. The ink supplied to the manifold 142 is supplied to each individual flow path 143. Then, as will be described later, when the piezoelectric actuator 130 is driven, pressure is applied to the ink in each individual flow path 143, and ink droplets are ejected from the nozzles 11a.

[0051] (Piezoelectric actuator 130) The piezoelectric actuator 130 includes a plurality of drive elements 111 each composed of three piezoelectric layers 131 to 133, a plurality of individual electrodes 134, a high-potential electrode 135, and a low-potential electrode 136. The plurality of drive elements 111 respectively correspond to the plurality of individual flow paths 143.

[0052] Each of the three piezoelectric layers 131 to 133 is made of a piezoelectric material mainly composed of lead zirconate titanate or the like. As shown in FIGS. 6 and 7, the three piezoelectric layers 131 to 133 are laminated in the vertical direction. The piezoelectric layer 131 is adhered to the upper surface of the ink sealing film 121 with an adhesive.

[0053] As shown in FIGS. 6 and 7, each of the individual electrodes 134, the high-potential electrode 135, and the low-potential electrode 136 is located on the side opposite to the ink sealing film 121 with respect to the piezoelectric layer 131.

[0054] As shown in FIGS. 6 and 7, each individual electrode 134 is formed on the upper surface of the piezoelectric layer 133 corresponding to the pressure chamber 145. As described above, each individual electrode 134 is connected to the waveform generation circuit 30 of the driver IC 27 via the signal line 34. Either a high potential (VDD potential) or a low potential (GND potential) is selectively applied to each individual electrode 134 via the signal line 34.

[0055] As shown in FIGS. 6 and 7, the high potential electrode 135 is formed on the upper surface of the piezoelectric layer 132. The high potential electrode 135 corresponds to the pressure chamber 145 and the individual electrode 134. The high potential electrode 135 overlaps with the central portion in the left-right direction of the corresponding pressure chamber 145 and the corresponding individual electrode 134 in the up-down direction. And the high potential electrode 135 is connected to the power supply circuit 26 via a through electrode (not shown) that penetrates the piezoelectric layer 133 in the up-down direction, and the wiring VCOM and HVDD described above. A constant potential (VCOM potential) slightly higher than the VDD potential is applied to the high potential electrode 135 from the power supply circuit 26.

[0056] As shown in FIGS. 6 and 7, the low potential electrode 136 is formed on the upper surface of the piezoelectric layer 131. And as shown in FIG. 7, the low potential electrode 136 is located to the left and right of one pressure chamber 145. The right end portion of the left low potential electrode 136 overlaps with the left end portion of the pressure chamber 145 and the left end portion of the individual electrode 134 in the up-down direction. The left end portion of the right low potential electrode 136 overlaps with the right end portion of the pressure chamber 145 and the right end portion of the individual electrode 134 in the up-down direction. As described above, the low potential electrode 136 is connected to the ground.

[0057] As shown in FIG. 7, the portion of the piezoelectric layer 133 sandwiched between the individual electrode 134 and the high potential electrode 135 in the up-down direction is referred to as the first active portion 138. The portion of the piezoelectric layers 132 and 133 sandwiched between the individual electrode 134 and the low potential electrode 136 in the up-down direction is referred to as the second active portion 139. The first active portion 138 is mainly polarized upward, and the second active portion 139 is mainly polarized downward. The piezoelectric actuator 130 includes, for each pressure chamber 145, one first active portion 138 and two second active portions 139 that sandwich the first active portion 138 in the left-right direction.

[0058] Here, referring to FIGS. 8 and 9, taking the case of ejecting an ink droplet from one nozzle 11a as an example, the operation of the drive element 111 corresponding to the nozzle 11a will be described.

[0059] Before the printing device 1 starts printing, as shown in FIG. 8, a low potential (GND potential) is applied to each individual electrode 134. At this time, due to the potential difference between the individual electrode 134 and the high potential electrode 135A2, an upward electric field equal to its polarization direction is generated in the first active part 138, and the first active part 138 contracts in the plane direction (the direction along the left - right direction and the front - back direction). As a result, the portion of the laminate composed of the piezoelectric layers 131 to 133 that overlaps the pressure chamber 145 in the vertical direction bends so as to be convex toward the pressure chamber 145 (downward). At this time, the volume of the pressure chamber 145 is smaller than when the above - mentioned laminate is flat.

[0060] When the printing device 1 starts printing and ejects ink from the nozzle 11a, first, as shown in FIG. 9, the potential of the individual electrode 134 corresponding to the nozzle 11a is switched from a low potential (GND potential) to a high potential (VDD potential). At this time, as the potential difference between the individual electrode 134 and the high potential electrode 135 becomes smaller, the contraction of the first active part 138 becomes smaller. On the other hand, due to the potential difference between the individual electrode 134 and the low potential electrode 136, a downward electric field equal to its polarization direction is generated in the two second active parts 139, and the two second active parts 139 contract in the plane direction. As a result, the portion of the laminate composed of the piezoelectric layers 131 to 133 that overlaps the pressure chamber 145 in the vertical direction bends so as to be convex in the direction away from the pressure chamber 145 (upward). Thereby, the volume of the pressure chamber 145 becomes larger compared to FIG. 8, and ink is drawn into the pressure chamber 145 from the manifold 142.

[0061] Thereafter, as shown in FIG. 8, the potential of the individual electrode 134 corresponding to the nozzle 11a is switched from a high potential (VDD potential) to a low potential (GND potential). At this time, since the potential difference between the individual electrode 134 and the low potential electrode 136 disappears, the contraction of the second active portion 139 is eliminated. On the other hand, due to the potential difference between the individual electrode 134 and the high potential electrode 135, an upward electric field equal to the polarization direction is generated in the first active portion 138, and the first active portion 138 contracts in the plane direction. As a result, the portion of the laminate composed of the piezoelectric layers 131 to 133 that overlaps the pressure chamber 145 in the vertical direction bends so as to be convex (downward) toward the pressure chamber 145. At this time, since the volume of the pressure chamber 145 greatly decreases, a large pressure is applied to the ink in the pressure chamber 145, and the ink drawn from the manifold 142 into the pressure chamber 145 is ejected as ink droplets from the nozzle 11a.

[0062] Next, an example of the printing process using the printing apparatus 1 of the present embodiment will be described with reference to FIG. 10.

[0063] When the printing apparatus 1 receives printing data from the external apparatus 9 (step S1), it analyzes the received printing data (step S2) and executes a printing process (step S3) based on the analysis result.

[0064] In the printing process (step S3), the controller 7 of the printing apparatus 1 controls the motors that drive the transport rollers 5A and 5B to transport the medium M in the transport direction by the transport rollers 5A and 5B. Further, the controller 7 controls each head 11 of each line head 4 to eject ink toward the medium M transported by the transport rollers 5A and 5B.

[0065] Next, the driving method of each head 11 in the printing process (step S3) will be described. During each ejection cycle (the cycle for forming one dot on the medium M) in the printing process (step S3), the controller 7 inputs a ejection pulse signal PS1 as shown in the upper part of the upper row of FIG. 11, or a non-ejection pulse signal PS2 as shown in the upper part of the lower row of FIG. 11, to the individual electrodes 134 of each driving element 111. Note that one ejection cycle is an example of the "predetermined period". Also, the lower part of the upper row of FIG. 11 shows the change in potential at the individual electrode 134 to which the ejection pulse signal PS1 is input, and the lower part of the lower row of FIG. 11 shows the change in potential at the individual electrode 134 to which the non-ejection pulse signal PS2 is input.

[0066] The ejection pulse signal PS1 is a signal for driving the driving element 111 so that ink droplets are ejected from the corresponding nozzle 11a. That is, when the ejection pulse signal PS1 is input to the individual electrode 134 of the driving element 111, the volume of the pressure chamber 145 communicating with the nozzle 11a changes so that ink droplets are ejected from the corresponding nozzle 11a.

[0067] On the other hand, the non-ejection pulse signal PS2 is a signal for driving the driving element 111 so that ink droplets are not ejected from the corresponding nozzle 11a. That is, when the non-ejection pulse signal PS2 is input to the individual electrode 134 of the driving element 111, the volume of the pressure chamber 145 communicating with the nozzle 11a changes so that ink droplets are not ejected from the corresponding nozzle 11a.

[0068] As shown in the upper part of the upper row of FIG. 11, the ejection pulse signal PS1 is maintained at the GND potential from time t0 to time t1 in one ejection cycle T, and is switched to the VDD potential at time t1. Then, it is maintained at the VDD potential from time t1 to time t4, and after being switched from the VDD potential to the GND potential at time t4, it is maintained at the GND potential until time t7.

[0069] When the above-described ejection pulse signal PS1 is input to the individual electrode 134, the potential of the individual electrode 134 changes as shown in the lower part of the upper row of FIG. 11. That is, it is maintained at the GND potential from time t0 to time t1, and rises from the GND potential to the VDD potential from time t1 to time t2. Thereafter, it is maintained at the VDD potential from time t2 to time t4. Then, after falling from the VDD potential to the GND potential from time t4 to time t6, it is maintained at the GND potential until time t7. That is, in order for the potential of the individual electrode 134 to rise from the GND potential to the VDD potential, a period Tr1 from time t1 to time t2 is required. Similarly, in order for the potential of the individual electrode 134 to fall from the VDD potential to the GND potential, a period Tf1 from time t4 to time t6 is required.

[0070] In this embodiment, during the period Tr1 in which the potential of the individual electrode 134 rises from the GND potential to the VDD potential, the driving element 111 deforms so as to be convex upward (see FIG. 9), and the volume of the pressure chamber 145 expands. On the other hand, during the period Tf1 in which the potential of the individual electrode 134 falls from the VDD potential to the GND potential, the driving element 111 deforms so as to be convex downward (see FIG. 8), and the volume of the pressure chamber 145 contracts. That is, in the ejection pulse signal PS1, the period Tr1 is a volume expansion period for expanding the volume of the pressure chamber 145, and the period Tf1 can be said to be a volume contraction period for contracting the volume of the pressure chamber 145.

[0071] On the other hand, as shown in the upper part of the lower row of FIG. 11, the non-ejection pulse signal PS2 is maintained at the GND potential from time t0 to time t3 in one ejection cycle T, and is switched to the VDD potential at time t3. Then, it is maintained at the VDD potential from time t3 to time t4, and after being switched from the VDD potential to the GND potential at time t4, it is maintained at the GND potential until time t7. Note that time t3 is a time after time t1 and before time t4.

[0072] When the above non-ejection pulse signal PS2 is input to the individual electrode 134, the potential of the individual electrode 134 changes as shown in the lower part of the lower row of FIG. 11. That is, it is maintained at the GND potential from time t0 to time t3, and rises from the GND potential to the potential Vc from time t3 to time t4. Note that the potential Vc is lower than the VDD potential. As an example, the potential Vc = 90% of the VDD potential. Then, after falling from the potential Vc to the GND potential from time t4 to time t5, it is maintained at the GND potential until time t7. That is, in order for the potential of the individual electrode 134 to rise from the GND potential to the potential Vc, a period Tr2 from time t3 to time t4 is required. Similarly, in order for the potential of the individual electrode 134 to fall from the potential Vc to the GND potential, a period Tf2 from time t4 to time t5 is required.

[0073] And, similar to the case when the above ejection pulse signal PS1 is input, during the period Tr2 when the potential of the individual electrode 134 rises from the GND potential to the potential Vc, the driving element 111 deforms so as to be convex upward (see FIG. 9), and the volume of the pressure chamber 145 expands. On the other hand, during the period Tf2 when the potential of the individual electrode 134 falls from the potential Vc to the GND potential, the driving element 111 deforms so as to be convex downward (see FIG. 8), and the volume of the pressure chamber 145 shrinks. That is, in the non-ejection pulse signal PS2, the period Tr2 is a volume expansion period for expanding the volume of the pressure chamber 145, and the period Tf2 can be said to be a volume reduction period for reducing the volume of the pressure chamber 145. Note that in the non-ejection pulse signal PS2 of the present embodiment, the volume expansion period Tr2 and the volume reduction period Tf2 are continuous, and there is no time during which the volume of the pressure chamber 145 is maintained in an expanded state like the period from time t2 to time t4 in the ejection pulse signal PS1. Also, as described above, since the potential Vc is lower than the VDD potential, the amount of deformation of the driving element 111 and the amount of change in the volume of the pressure chamber 145 are smaller than when the ejection pulse signal PS1 is input. Therefore, no ink droplets are ejected from the nozzle 11a communicating with the pressure chamber 145.

[0074] And in this embodiment, both the ejection pulse signal PS1 and the non-ejection pulse signal PS2 are switched from the VDD potential to the GND potential at time t4. That is, the timing at which the ejection pulse signal PS1 is switched from the VDD potential to the GND potential is the same as the timing at which the non-ejection pulse signal PS2 is switched from the VDD potential to the GND potential. As a result, the volume reduction period Tf1 in the ejection pulse signal PS1 and the volume reduction period Tf2 in the non-ejection pulse signal PS2 overlap.

[0075] As described above, according to the driving method of the head 11 in this embodiment, in each ejection cycle T, the ejection pulse signal PS1 or the non-ejection pulse signal PS2 is input to the individual electrode 134 of each driving element 111. Thereby, in each ejection cycle T, each driving element 111 is driven regardless of whether or not ink droplets are ejected from the corresponding nozzle 11a. Therefore, compared with the case where the driving element 111 corresponding to the nozzle 11a that does not eject ink droplets is not driven, the fluid crosstalk generated between the plurality of individual flow paths 143 communicating with the same manifold 142 and the mechanical crosstalk generated between the pressure chambers 145 adjacent to each other can be reduced.

[0076] Also, in each ejection cycle T, an ejection pulse signal PS1 is input to the drive element 111 that ejects ink droplets from the corresponding nozzle 11a, and a non-ejection pulse signal PS2 is input to the drive element 111 that does not eject ink droplets from the corresponding nozzle 11a. Then, as shown in FIG. 11, in the same ejection cycle T, the volume reduction period Tf1 in the ejection pulse signal PS1 and the volume reduction period Tf2 in the non-ejection pulse signal PS2 overlap. That is, the drive element 111 corresponding to the nozzle 11a that ejects ink droplets and the drive element 111 corresponding to the nozzle 11a that does not eject ink droplets are deformed in the same direction (convex downward) at the same timing. This means that the potential of the individual electrode 134 of the drive element 111 corresponding to the nozzle 11a that ejects ink droplets and the potential of the individual electrode 134 of the drive element 111 corresponding to the nozzle 11a that does not eject ink droplets are both decreasing toward the GND potential. That is, regardless of whether it corresponds to the nozzle 11a that ejects ink droplets or the nozzle 11a that does not eject ink droplets, the direction of charge movement is the same. And each individual electrode 134 is supplied with charge only from the power supply circuit and is not supplied with some charge from other individual electrodes 134. Therefore, it is possible to suppress variations in the ejection amount of ink droplets caused by electrical crosstalk occurring between the drive elements 111 connected to the same power supply circuit.

[0077] Next, a modification of the above embodiment will be described. In the above embodiment, the timing at which the potential switches from the VDD potential to the GND potential in the ejection pulse signal PS1 and the timing at which the potential switches from the VDD potential to the GND potential in the non-ejection pulse signal PS2 coincided at time t4, but it is not limited to this. As long as the volume reduction period Tf1 in the ejection pulse signal PS1 and the volume reduction period Tf2 in the non-ejection pulse signal PS2 overlap, the timing at which the potential switches from the VDD potential to the GND potential in the non-ejection pulse signal PS2 may be shifted before or after the timing (time t4) at which the potential switches from the VDD potential to the GND potential in the ejection pulse signal PS1.

[0078] Also, in the above embodiment, the volume reduction period Tf1 (the period from time t4 to time t6) in the ejection pulse signal PS1 is longer than the volume reduction period Tf2 (the period from time t4 to time t5) in the non-ejection pulse signal PS2, but it is not limited to this. For example, the volume reduction period Tf1 in the ejection pulse signal PS1 and the volume reduction period Tf2 in the non-ejection pulse signal PS2 may coincide. That is, the start point of the volume reduction period Tf1 in the ejection pulse signal PS1 and the start point of the volume reduction period Tf2 in the non-ejection pulse signal PS2 may coincide, and the end point of the volume reduction period Tf1 in the ejection pulse signal PS1 and the end point of the volume reduction period Tf2 in the non-ejection pulse signal PS2 may also coincide. This can be achieved by expanding the volume expansion period Tr2 in the non-ejection pulse signal PS2 to raise the potential of the individual electrode 134 to VDD instead of Vc. In this case, variations in the ejection amount of ink droplets caused by electrical crosstalk occurring between the drive elements 111 connected to the same power supply circuit can be suppressed.

[0079] In the above embodiment, the volume reduction period Tf1 in the ejection pulse signal PS1 and the volume reduction period Tf2 in the non-ejection pulse signal PS2 overlapped, but it is not limited to this. For example, as shown in FIG. 12, the volume expansion period Tr1 in the ejection pulse signal PS1 and the volume expansion period Tr2 in the non-ejection pulse signal PS2 may overlap. Also in this case, if the volume expansion period Tr1 in the ejection pulse signal PS1 and the volume expansion period Tr2 in the non-ejection pulse signal PS2 overlap, the timing at which the potential switches from the GND potential to the VDD potential in the non-ejection pulse signal PS2 may be shifted before or after the timing (time t1) at which the potential switches from the GND potential to the VDD potential in the ejection pulse signal PS1. Also in this case, variations in the ejection amount of ink droplets caused by electrical crosstalk occurring between the drive elements 111 connected to the same power supply circuit can be suppressed.

[0080] In the above-described embodiment, the ejection pulse signal PS1 included only one pulse for ejecting ink droplets from the nozzle 11a, but this is not restrictive. For example, as shown in the upper part of FIG. 13, the ejection pulse signal PS1A may include, in addition to the main pulse MP for ejecting ink droplets from the nozzle 11a, a prepulse PP input before the main pulse MP and a cancellation pulse CP input after the main pulse MP. Both the prepulse PP and the cancellation pulse CP are pulses for driving the drive element 111 to such an extent that ink droplets are not ejected from the nozzle 11a, and the pulse width of each is shorter than the pulse width of the main pulse MP. The prepulse PP is a pulse for vibrating the meniscus of the ink in the nozzle 11a and can prevent drying of the meniscus of the ink before ejection. On the other hand, the cancellation pulse CP is a pulse for canceling the pressure wave in the pressure chamber 145 generated by the main pulse MP.

[0081] In this case, as shown in the upper part of FIG. 13, the ejection pulse signal PS1A includes, in addition to the volume expansion period Tr1 and the volume reduction period Tf1 by the main pulse MP, the volume expansion period Trp and the volume reduction period Tfp by the prepulse PP, and the volume expansion period Trc and the volume reduction period Tfc by the cancellation pulse CP. Also in this case, as shown in FIG. 13, the volume reduction period Tf2 in the non-ejection pulse signal PS2 only needs to overlap with the volume reduction period by the main pulse MP of the ejection pulse signal PS1A. Also in this case, variations in the ejection amount of ink droplets due to electrical crosstalk occurring between the drive elements 111 connected to the same power supply circuit can be suppressed.

[0082] Also, in each ejection cycle T, any one type of ejection pulse signal among a plurality of types of ejection pulse signals PS1A, PS1B, PS1C having different waveforms, as shown as an example in FIG. 14, or a non-ejection pulse signal PS2 may be input to the individual electrode 134 of each driving element 111. In this case, in one ejection cycle T, for the individual electrode 134 of the driving element 111 corresponding to the nozzle 11a that ejects ink droplets, for example, any one type of ejection pulse signal among a plurality of types of ejection pulse signals PS1A, PS1B, PS1C with different amounts (volumes) of ink droplets to be ejected is input. On the other hand, the non-ejection pulse signal PS2 is input to the individual electrode 134 of the driving element 111 corresponding to the nozzle 11a that does not eject ink droplets, as in the above-described embodiment.

[0083] In this case, the volume reduction period Tf2 in the non-ejection pulse signal PS2 only needs to overlap with the volume reduction period in the ejection pulse signal input to the most driving elements 111 among the plurality of types of ejection pulse signals PS1A, PS1B, PS1C. For example, when among the plurality of types of ejection pulse signals PS1A, PS1B, PS1C, the ejection pulse signal PS1A with the least amount of ink droplets to be ejected and input to the most driving elements 111, as shown in FIG. 14, the volume reduction period Tf2 in the non-ejection pulse signal PS2 only needs to overlap with the volume reduction period Tf1 in the ejection pulse signal PS1A. In this case, in particular, the variation in the ejection amount of ink droplets between the nozzles 11a corresponding to the driving elements 111 to which the ejection pulse signal PS1A is input can be suppressed.

[0084] Furthermore, as shown in FIG. 14, the volume reduction period Tf2 in the non-ejection pulse signal PS2 may overlap with the volume reduction period of the ejection pulse signal PS1B different from the ejection pulse signal PS1A input to the most driving elements 111. Also, the volume expansion period Tr2 in the non-ejection pulse signal PS2 may overlap with the volume reduction period of the ejection pulse signal PS1C different from the ejection pulse signals PS1A and PS1B.

[0085] As described above, the embodiments and modifications of the present invention have been explained, but the present invention is not limited to these, and various design changes are possible as long as they are within the scope described in the claims.

[0086] In the upper part of FIG. 13, the discharge pulse signal PS1A including the prepulse PP, the main pulse MP, and the cancel pulse CP was shown, but it is not limited to this. For example, like the discharge pulse signal PS1C shown at the top in the upper part of FIG. 14, the discharge pulse signal may include the main pulse MP and the cancel pulse CP and may not include the prepulse PP.

[0087] In the above-described embodiments and modifications, each drive element 111 includes three layers of electrodes: an individual electrode 134 to which the VDD potential and the GND potential are selectively applied, a high-potential electrode 135 maintained at a VCOM potential higher than the VDD potential, and a low-potential electrode 136 maintained at the GND potential, but it is not limited to this. For example, each drive element may include two layers of electrodes: an individual electrode to which the VDD potential and the GND potential are selectively applied and a common electrode maintained at the GND potential.

[0088] In the above-described embodiments and modifications, the printing apparatus 1 performs printing on the medium M by a so-called line head method in which ink is discharged from a line head 4 that is long in the width direction and fixed to the printing apparatus 1. However, the printing apparatus 1 may perform printing on the medium M by a so-called serial head method in which the head 11 is moved in the sheet width direction by a carriage.

[0089] In the above-described embodiments and modifications, an example in which the present invention is applied to the head 11 that discharges ink from the nozzle 11a has been described, but it is not limited to this. The present invention can also be applied to heads other than inkjet heads that discharge liquids other than ink from the nozzle 11a.

Explanation of Reference Numerals

[0090] 1 Printing apparatus 4 Line head 5A, 5B Conveyor rollers 7 Controller 11 Head 11a Nozzle 21 - 26 Power Circuit 27 Driver IC 111 Driving Element 120 Flow Substrate 130 Piezoelectric Actuator 142 Manifold 143 Individual Flow Path 145 Pressure Chamber PS1, PS1A, PS1B, PS1C Discharge Pulse Signal PS2 Non - discharge Pulse Signal

Claims

1. A method for driving a liquid ejection head, comprising: The liquid ejection head includes: a flow path member having a plurality of individual flow paths including a plurality of nozzles and a plurality of pressure chambers respectively communicating with the plurality of nozzles, and a common flow path communicating with the plurality of individual flow paths; a plurality of driving elements fixed to the flow path member so as to correspond to the plurality of nozzles respectively and electrically connected to a common power supply circuit; each of the plurality of driving elements applies pressure to the liquid in the pressure chamber by changing the volume of the pressure chamber communicating with the corresponding nozzle; the driving method includes, in a predetermined period, inputting to each of the plurality of driving elements a discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is discharged from the corresponding nozzle, or a non-discharge pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is not discharged from the nozzle; each of the discharge pulse signal and the non-discharge pulse signal includes a volume reduction period for reducing the volume of the pressure chamber and a volume expansion period for expanding the volume of the pressure chamber; a driving method, wherein the volume reduction period in the discharge pulse signal and the volume reduction period in the non-discharge pulse signal overlap, or the volume expansion period in the discharge pulse signal and the volume expansion period in the non-discharge pulse signal overlap.

2. The driving method according to claim 1, wherein in the predetermined period, the volume reduction period in the discharge pulse signal and the volume reduction period in the non-discharge pulse signal overlap.

3. The driving method according to claim 2, wherein a start point of the volume reduction period in the discharge pulse signal coincides with a start point of the volume reduction period in the non-discharge pulse signal, and an end point of the volume reduction period in the discharge pulse signal coincides with an end point of the volume reduction period in the non-discharge pulse signal.

4. In the predetermined period, to each of the plurality of driving elements, one type of discharge pulse signal among a plurality of types of discharge pulse signals having different waveforms, or the non-discharge pulse signal is input, The driving method according to claim 2, wherein the volume reduction period in the first discharge pulse signal input to the most driving elements among the plurality of types of discharge pulse signals and the volume reduction period in the non-discharge pulse signal overlap.

5. During the predetermined period, any one of a plurality of types of ejection pulse signals having different amounts of the liquid to be ejected, or the non-ejection pulse signal, is input to each of the plurality of drive elements. The driving method according to claim 2, wherein a volume reduction period in the first ejection pulse signal, which has the smallest amount of the liquid to be ejected among the plurality of types of ejection pulse signals, overlaps with the volume reduction period in the non-ejection pulse signal.

6. The driving method according to claim 4 or 5, wherein a volume reduction period in a second ejection pulse signal different from the first ejection pulse signal among the plurality of types of ejection pulse signals overlaps with the volume reduction period or the volume expansion period in the non-ejection pulse signal.

7. The driving method according to claim 6, wherein the volume reduction period in the second ejection pulse signal overlaps with the volume expansion period in the non-ejection pulse signal.

8. The ejection pulse signal includes a main pulse for ejecting the liquid and a cancellation pulse that is input after the main pulse and cancels a pressure wave in the pressure chamber generated by the input of the main pulse. The driving method according to claim 2, wherein a volume reduction period by the main pulse included in the ejection pulse signal overlaps with the volume reduction period in the non-ejection pulse signal.

9. A printing apparatus, a flow path member having a plurality of individual flow paths including a plurality of nozzles and a plurality of pressure chambers respectively communicating with the plurality of nozzles, and a common flow path communicating with the plurality of individual flow paths, a plurality of drive elements fixed to the flow path member so as to correspond to the plurality of nozzles respectively and electrically connected to a common power supply circuit, and a controller for controlling the plurality of drive elements. Each of the plurality of drive elements applies pressure to the liquid in the pressure chamber by changing the volume of the pressure chamber communicating with the corresponding nozzle. The controller inputs, during a predetermined period, an ejection pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is ejected from the corresponding nozzle, or a non-ejection pulse signal for changing the volume of the pressure chamber communicating with the nozzle so that the liquid is not ejected from the nozzle, to each of the plurality of drive elements. Each of the ejection pulse signal and the non-ejection pulse signal includes a volume reduction period for reducing the volume of the pressure chamber and a volume expansion period for expanding the volume of the pressure chamber. A printing apparatus in which the volume reduction period in the ejection pulse signal and the volume reduction period in the non-ejection pulse signal overlap, or the volume expansion period in the ejection pulse signal and the volume expansion period in the non-ejection pulse signal overlap. **Claim 10** The printing apparatus according to claim 9, wherein the plurality of drive elements each have a plurality of drive electrodes each electrically connected to the power supply circuit and a plurality of ground electrodes respectively corresponding to the plurality of drive electrodes.

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