Liquid dispensing device

Abstract

It is not possible to maintain liquid circulation capacity and suppress migration failures. [Solution] The liquid discharge device includes a piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode; a drive control means that controls the strain generated in the piezoelectric means in a drive cycle including a first period and a second period, while a drive voltage that generates strain in the piezoelectric means is supplied to the first electrode and the second electrode; and a diaphragm means that circulates liquid flowing in and out of the pressure chamber due to the vibration of the diaphragm, having a vibrating plate that vibrates in accordance with the strain generated in the piezoelectric means and a pressure chamber to which the vibration of the vibrating plate is transmitted. The first period includes a period in which the drive voltage supplied to either the first electrode or the second electrode is cut off, and the second period includes a period in which no potential difference is generated between the first electrode and the second electrode.

Description

Technical Field

[0001] The present disclosure relates to a liquid ejection device that performs ejection while circulating a liquid.

Background Art

[0002] Conventionally, in the field of inkjet printers, a technique for circulating a liquid (also referred to as ink) in a circulation flow path communicating with a discharge port is known. Further, Patent Document 1 discloses a technique for obtaining liquid circulation ability by circulating a liquid by a piezoelectric pump.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the liquid circulation ability is maintained by the technique described in Patent Document 1, there is a risk that the occurrence rate of migration failure (details will be described later) increases, and it may not be possible to achieve both the maintenance of the liquid circulation ability and the suppression of migration failure.

Means for Solving the Problems

[0005] A liquid dispensing device according to one aspect of the present disclosure comprises: a piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode; a drive control means for controlling the strain generated in the piezoelectric means in a drive cycle including a first period and a second period, while a drive voltage that generates strain in the piezoelectric means is supplied to the first electrode and the second electrode; and a diaphragm means for circulating liquid flowing in and out of the pressure chamber due to the vibration of the diaphragm, wherein the first period includes a period during which the drive voltage supplied to either the first electrode or the second electrode is interrupted, and the second period includes a period during which no potential difference is generated between the first electrode and the second electrode. [Effects of the Invention]

[0006] According to this disclosure, it is possible to maintain liquid circulation capacity and suppress migration failures. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of the liquid dispensing device of the present disclosure according to the first embodiment. [Figure 2] This is an exploded perspective view of the liquid dispensing head of Figure 1 according to the first embodiment. [Figure 3] This is a schematic diagram of the ink circulation unit shown in Figure 2 according to the first embodiment. [Figure 4] This is a schematic diagram of the ink circulation path in which the liquid is circulated by the circulation pump shown in Figure 3 according to the first embodiment. [Figure 5] This figure shows an example of the wiring of the circulation pump in Figure 4 according to the first embodiment. [Figure 6] This is a schematic cross-sectional view of the circulation pump shown in Figure 5 according to the first embodiment. [Figure 7] This figure shows an example of a pump drive circuit for driving the circulation pump shown in Figure 6 according to the first embodiment. [Figure 8]This figure shows an example of a boost circuit according to the first embodiment. [Figure 9] This figure shows an example of the output switching circuit shown in Figure 7 according to the first embodiment. [Figure 10] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the first embodiment. [Figure 11] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the second embodiment. [Figure 12] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the third embodiment. [Figure 13] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the fourth embodiment. [Figure 14] This figure shows an example of a pump drive circuit for driving the circulation pump shown in Figure 6 according to the fifth embodiment. [Figure 15] This figure shows an example of a step-down circuit according to the fifth embodiment. [Figure 16] This figure shows an example of the output switching circuit in Figure 14 according to the fifth embodiment. [Figure 17] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the fifth embodiment. [Figure 18] This figure shows an example of a pump drive circuit for driving the circulation pump in Figure 6 according to the sixth embodiment. [Figure 19] This figure shows an example of a boost circuit according to the sixth embodiment of Figure 18. [Figure 20] This figure illustrates the timing chart of the control signal for controlling the pump drive circuit according to the sixth embodiment. [Figure 21] This figure shows an example of a pump drive circuit for driving the circulation pump in Figure 6 according to the seventh embodiment. [Figure 22] This figure shows an example of a pump drive circuit for driving the circulation pump in Figure 6 according to the eighth embodiment. [Modes for carrying out the invention]

[0008] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the disclosed matters, and not all combinations of the features described in the following embodiments are essential for the solution means of the present disclosure. The same components are denoted by the same reference numerals.

[0009] (Overview) In recent years, in the field of inkjet printers, a liquid ejection head scanning type liquid ejection device has been used. In this liquid ejection head scanning type liquid ejection device, it is required to output a high-quality printed matter. For example, a special ink may be used according to the recording medium for outputting a high-quality printed matter. As such a liquid ejection head scanning type liquid ejection device that can handle such a special ink, an ink circulation type liquid ejection device is required. Specifically, in order to circulate the ink, an ink supply path and an ink recovery path are provided in the ink circulation type liquid ejection device. By generating a differential pressure between this ink supply path and this ink recovery path, the ink circulation type liquid ejection device obtains a circulating flow of the ink. More specifically, the ink circulation type liquid ejection device has a piezoelectric actuator that functions as a piezoelectric pump and a control circuit in order to generate a differential pressure between the ink supply path and the ink recovery path. The piezoelectric actuator circulates the liquid stored in the supply tank to the inkjet head that functions as a liquid ejection head. The control circuit controls the drive voltage for driving the piezoelectric actuator by controlling the length of the energization time to the piezoelectric actuator.

[0010] However, even during time periods other than charging and discharging, a driving voltage is always applied to the piezoelectric actuator. As a result of intensive research by the inventors of the present disclosure, it has been discovered that the incidence rate of migration failure increases as the application time of the driving voltage applied to the piezoelectric actuator progresses. If the application time of the driving voltage is the cause, it is possible to control the energization time of the piezoelectric actuator so as to lower the driving voltage. On the other hand, reducing the driving voltage may reduce the liquid circulation ability. That is, if the piezoelectric actuator is operated, the migration failure progresses, and if the driving voltage is lowered, the migration failure can be avoided, but the liquid circulation ability of the piezoelectric actuator as a piezoelectric pump decreases. Therefore, it is difficult to achieve both suppression of the progression of migration failure and maintenance of the liquid circulation ability.

[0011] Here, the migration failure will be described. The piezoelectric actuator includes a piezoelectric element, two electrodes disposed on both sides of the piezoelectric element, and a diaphragm disposed on one of the two electrodes. Since the piezoelectric actuator is used as a piezoelectric pump, the diaphragm is disposed at a position in contact with the liquid. Therefore, the usage environment of the piezoelectric actuator is high humidity. In a high-humidity usage environment, evaporated moisture penetrates into the piezoelectric element. Further, when the condition where a voltage is applied to the high-humidity environment is biased by the driving voltage applied between the two electrodes, the piezoelectric element, which is originally an insulator, becomes locally conductive. When the piezoelectric element becomes locally conductive, a sufficient potential difference cannot be applied to the piezoelectric element, so the function of the piezoelectric actuator as a piezoelectric pump deteriorates. That is, under the condition where a voltage is applied to a metal, when the metal is in contact with an insulating material, as the insulating material absorbs moisture, the metal component moves on the insulating material. Thus, the failure caused by the decrease in the insulation resistance value between the electrodes under the condition of a high-humidity environment and with a voltage applied is called a migration failure. Such a migration failure causes a short circuit between the electrodes and thus becomes a cause of failure of an electronic device.

[0012] Therefore, in this disclosure, the strain generated in the piezoelectric pump is controlled in a drive cycle including a first period and a second period, while a drive voltage is supplied between the two electrodes. The first period includes a period during which the drive voltage supplied to one of the two electrodes is interrupted. The second period includes a period during which the drive voltage is supplied to each of the two electrodes simultaneously. With this configuration, in the first period, the interruption of the drive voltage supplied to one of the two electrodes generates a potential difference between the drive voltage potential and the ground potential between the two electrodes. Therefore, in the first period, it is possible to generate strain in the piezoelectric pump. As a result, the liquid circulation capacity is maintained. In the second period, since the drive voltage is supplied to each of the two electrodes simultaneously, no potential difference is generated between the two electrodes. If no potential difference is generated between the two electrodes, it is not as if a voltage has been applied between the two electrodes. Therefore, in the second period, the piezoelectric pump is not under conditions where a voltage has been applied, even in a high-humidity environment. As a result, migration failures can be suppressed. Therefore, by controlling the strain generated in the piezoelectric pump during the drive cycle, which includes the first and second periods, it is possible to maintain liquid circulation capacity and suppress migration failures. In this disclosure, three configuration examples are described as examples of configurations in which no potential difference occurs between the two electrodes. The first configuration example is one in which a drive voltage is supplied to each of the two electrodes simultaneously (Embodiments 1 to 3 and 5). The second configuration example is one in which the drive voltage supplied to each of the two electrodes is simultaneously shut off (Embodiment 4). The third configuration example is one in which the potential of the voltage supplied to each of the two electrodes is controlled to be the same potential (Embodiment 6). Details of this disclosure will be described below.

[0013] (First Embodiment) Figure 1 is a schematic diagram of a liquid dispensing device 50 of the present disclosure according to a first embodiment. Figure 1(a) is a schematic perspective view of the liquid dispensing device 50. Figure 1(b) is a block diagram of the control system of the liquid dispensing device 50. The liquid dispensing device 50 comprises a liquid dispensing head 1 and transport rollers 55, 56, 57, and 58. The liquid dispensing head 1 is scannable in a direction X that intersects the transport direction Y of the medium to be dispensed P. In the example shown in Figure 1(a), the liquid dispensing head 1 is mounted on a carriage 53. The carriage 53 reciprocates along a guide axis 51 in the main scanning direction (also referred to as direction X). The transport rollers 55, 56, 57, and 58 transport the medium to be dispensed P in a sub-scanning direction (also referred to as transport direction Y) that intersects (orthogonal in this embodiment) the main scanning direction. In other words, the liquid ejection device 50 constitutes a serial-type inkjet liquid ejection device by scanning the liquid ejection head 1 in direction X and ejecting liquid from the liquid ejection head 1 onto the ejection medium P being transported in the transport direction Y. However, the application of this disclosure is not limited to serial-type inkjet liquid ejection devices. This disclosure can also be applied to a page-wide type inkjet liquid ejection device that ejects liquid onto the ejection medium P being transported in the transport direction Y by using a line head (page-wide type head) that is long in the page width direction of the ejection medium P. In Figure 1(a), direction Z indicates the vertical direction. That is, direction Z is the direction that intersects (orthogonal in this embodiment) the XY plane specified by direction X and transport direction Y. In the following description, direction X, transport direction Y, and direction Z will be used with the same meaning as described above.

[0014] The liquid ejection head 1 is capable of ejecting four types of ink: black (K), cyan (C), magenta (M), and yellow (Y). The liquid ejection head 1 can eject a full-color image using these four types of ink. However, the inks that can be ejected from the liquid ejection head 1 are not limited to the above four types. For example, this disclosure is also applicable to a liquid ejection head 1 for ejecting other types of ink, such as spot color inks. That is, the type and number of inks ejected from the liquid ejection head 1 are not limited. Furthermore, a cap member may be positioned to cover the face surface of the liquid ejection head 1, away from the transport path of the ejection medium P. When not performing a recording operation, the cap member moves relative to the position that covers the face surface of the liquid ejection head 1. This operation prevents the liquid ejection port of the liquid ejection head 1 from drying out, or allows for suction operations for filling or restoring.

[0015] In the example shown in Figure 1(a), an ink circulation unit 54 is mounted on the liquid ejection head 1. A guide 59 housing four ink supply tubes (liquid passages) is attached to the ink circulation unit 54. In addition to the ink supply tubes, the guide 59 also houses the electrical wiring and air piping necessary for liquid ejection. Furthermore, an ink tank 2 and a pump 21 are provided on the main body (not shown) side of the liquid ejection device 50. The ink tank 2 stores ink. The ink stored in the ink tank 2 is supplied to the ink circulation unit 54 via the four ink supply tubes by the driving force of the pump 21. The liquid ejection head 1 may be provided integrally with the ink circulation unit 54 and configured to be removable or attachable to the carriage 53. Alternatively, the ink circulation unit 54 may be provided integrally with the carriage 53, and only the ink circulation unit 54 may be configured to be removable or attachable. In the following description, an example in which the liquid ejection head 1 includes the ink circulation unit 54 will be described.

[0016] The CPU 400 in Figure 1(b) performs various controls on the liquid dispensing device 50. ROM 401 stores programs such as processing procedures. The CPU 400 retrieves these programs from ROM 401. Based on the retrieved programs, the CPU 400 controls the liquid dispensing device 50. The CPU 400 uses RAM 402 as a work area for executing the programs retrieved from ROM 401. The CPU 400 retrieves image data from a host device 500 located outside the liquid dispensing device 50. Based on the retrieved image data, the CPU 400 controls the head driver 1A. The head driver 1A controls the dispensing of liquid by the liquid dispensing head 1. The CPU 400 also controls the motor driver 403A. The motor driver 403A controls the carriage motor 403. The carriage motor 403 moves the carriage 53 along the X direction. The CPU 400 also controls the motor driver 404A. The motor driver 404A controls the transport motor 404. The transport motor 404 controls the transport rollers 55, 56, 57, and 58. The transport rollers 55, 56, 57, and 58 transport the discharge medium P along the transport direction Y.

[0017] (Liquid dispensing head 1) Figure 2 is an exploded perspective view of the liquid discharge head 1 of Figure 1 according to the first embodiment. The liquid discharge head 1 comprises a flow channel member 110, an ink circulation unit 54, and a discharge unit 300. At least a portion of the ink circulation unit 54 is housed in the flow channel member 110 and connected to the flow channel member 110. The discharge unit 300 is provided at the bottom of the flow channel member 110 and connected to the flow channel member 110. Specifically, the ink circulation unit 54 consists of ink circulation units 54m, 54y, 54k, and 54c, each corresponding to a different ink. When not specifically distinguishing between the ink circulation units 54m, 54y, 54k, and 54c, they are referred to as the ink circulation unit 54. Each ink circulation unit 54 is housed in and connected to the flow channel member 110. Each ink circulation unit 54 and the flow channel member 110 may be connected by screw fastening with a sealing member sandwiched between them. Alternatively, each ink circulation unit 54 and the flow path member 110 may be connected by welding. The flow path member 110 has a surface on which four joints 200 are provided, each connected to one of the four ink supply tubes corresponding to the four types of ink. In other words, a separate ink supply path is provided for each type of ink. Specifically, each of the ink circulation units 54m, 54y, 54k, and 54c is connected to the respective ink supply tubes corresponding to each ink from the main body side of the liquid discharge device 50 via its respective joint 200. Each ink supplied from the respective corresponding ink supply tube is supplied to each ink circulation unit 54 via the joint 200. Each ink supplied to each ink circulation unit 54 is supplied to the discharge unit 300 via the flow path member 110.

[0018] The ejection unit 300 comprises an ejection element substrate 310, a support member 320, an electrical wiring board 330, and a cover member 340. The ejection element substrate 310 and the electrical wiring board 330 are bonded and fixed to the support member 320. The cover member 340 is bonded and joined to cover the surface of the electrical wiring board 330. The portion of the cover member 340 corresponding to the ejection element substrate 310 is open. The ejection element substrate 310 has an actuator for ejecting ink. Therefore, the ejection element substrate 310 can eject liquid into the medium P to be ejected, which passes below the liquid ejection head 1. The ejection unit 300 and the flow path member 110 are bonded together using adhesive. Alternatively, the ejection unit 300 and the flow path member 110 may be fixed together by screwing in a sealing member.

[0019] The ejection element substrate 310 and the electrical wiring board 330 are electrically connected by wire bonding. The electrical wiring board 330 sends various electrical signals to the ejection element substrate 310. The ejection element substrate 310 ejects liquid according to the various electrical signals from the electrical wiring board 330, using the drive voltage supplied from the head driver 1A. Details of the various electrical signals will be described later. Note that the ejection element substrate 310 and the electrical wiring board 330 may also be electrically connected by flying lead bonding or the like.

[0020] A contact surface is provided on the side of the flow channel member 110 opposite to the side where the joint 200 is provided. The head board 210 is connected to the contact surface. The head board 210 receives electrical signals from the main body of the liquid dispensing device 50. The head board 210 and the electrical wiring board 330 are electrically connected. The electrical signals received by the head board 210 are sent to the dispensing element board 310 via the electrical wiring board 330. The head board 210 and the flow channel member 110 may be fixed by crimping, by adhesive, or by double-sided tape. The head board 210 and the carriage board 220 may be electrically connected by ACF (Antisotropic Conductive Film) bonding. Alternatively, the head board 210 and the electrical wiring board 330 may be electrically connected by wire bonding. Alternatively, the head board 210 and the electrical wiring board 330 may be electrically connected by flying lead bonding.

[0021] (Ink circulation path) Figure 3 is a schematic diagram of the ink circulation unit 54 of Figure 2 according to the first embodiment. One ink circulation unit 54 is provided for each color. The ink circulation unit 54 comprises a first pressure control mechanism 24, a second pressure control mechanism 28, a filter 23, and a circulation pump 27. Figure 4 is a schematic diagram of the ink circulation path in which the liquid is circulated by the circulation pump 27 of Figure 3 according to the first embodiment. The ink circulation path in Figure 4 is for one color. The liquid discharge head 1 is provided with the ink circulation path in Figure 4 for each ink. The ink tank 2 and the pump 21 are provided on the main body side of the liquid discharge device 50. The first pressure control mechanism 24 comprises a valve chamber 25 and a pressure control chamber 26. The valve chamber 25 and the pressure control chamber 26 are in communication via a valve (not shown). The second pressure control mechanism 28 comprises a valve chamber 29 and a pressure control chamber 30. The valve chamber 29 and the pressure control chamber 30 are in communication via a valve (not shown). The circulation pump 27 and the pressure control chamber 26 are connected via a pump outlet passage 78. The pressure control chamber 26 and the flow path member 110 are connected via a supply passage 75. A portion of the flow path member 110 may constitute the supply passage 75. The flow path member 110 and the pressure control chamber 30 are connected via a recovery passage 76. The position of the flow path member 110 may constitute the recovery passage 76. The pressure control chamber 30 and the circulation pump 27 are connected via a pump inlet passage 77. In other words, an ink circulation path is formed consisting of the pressure control chamber 26, the supply passage 75, the flow path member 110, the recovery passage 76, the pressure control chamber 30, the pump inlet passage 77, the circulation pump 27, and the pump outlet passage 78. Ink can circulate through this ink circulation path. Next, the details of the circulation pump 27 will be described, and then the flow of ink circulating through the ink circulation path will be described.

[0022] (Drive mechanism of circulation pump 27) Figure 5 shows an example of the wiring of the circulation pump 27 in Figure 4 according to the first embodiment. The main board 230 is provided on the body of the liquid discharge device 50. The CPU 400 is mounted on the main board 230. The carriage board 220 is provided on the carriage 53. The main board 230 and the carriage board 220 are connected via an FFC (Flexible Flat Cable). A drive signal is sent from the CPU 400 to the carriage board 220 via the FFC. The carriage board 220 and the head board 210 are connected via an electrical connection part 212. A pump control signal and a pump drive reference voltage are sent from the carriage board 220 to the head board 210 via the electrical connection part 212. The head board 210 and the circulation pump 27 are connected via a harness 211. The harness 211 consists of a cable assembly including a first wiring 211a and a second wiring 211b. A pump drive signal, generated based on the pump control signal and the pump drive voltage generated from the pump drive reference voltage, is output to the circulation pump 27 via the harness 211. Based on the pump drive signal, the circulation pump 27 is driven and the liquid is circulated.

[0023] (Configuration of circulation pump 27) Figure 6 is a schematic cross-sectional view of the circulation pump 27 of Figure 5 according to the first embodiment. The first electrode 272 is connected to the first wiring 211a via an electrical connecting member 277a. The second electrode 274 is connected to the second wiring 211b via an electrical connecting member 277b. In this embodiment, the electrical connecting members 277a and 277b are solder, but are not limited to this. Conductive materials such as gold bushings may be used for the electrical connecting members 277a and 277b. A piezoelectric element 273 is provided between the first electrode 272 and the second electrode 274. One surface of the piezoelectric element 273 is in contact with the first electrode 272. The other surface of the piezoelectric element 273 is in contact with the second electrode 274. One surface of the second electrode 274 is in contact with the piezoelectric element 273, and the other surface is in contact with the diaphragm 275. In other words, a laminate is formed by stacking the first electrode 272, the piezoelectric element 273, the second electrode 274, and the diaphragm 275 in that order. The pump housing 271 is provided so as to cover this laminate. In addition, a diaphragm unit 276 is provided on the side of the diaphragm 275 opposite to the side on which this laminate is formed. The diaphragm unit 276 comprises a diaphragm unit housing 276a, a valve body 276b, and a valve body 276c. The diaphragm unit housing 276a is made of a concave-shaped housing. A pressure chamber 276d is formed when the concave edge of the diaphragm unit housing 276a and the edge of the diaphragm 275 are fixed in contact with each other. Valve bodies 276b and 276c are each installed at a fixed distance from each other at the bottom of the diaphragm unit housing 276a, so as to be able to move freely in response to the outflow of liquid from the pressure chamber 276d and the inflow of liquid into the pressure chamber 276d, and function as valves. Opposite valve body 276b is the pump outlet passage 78 shown in Figure 4. Opposite valve body 276c is the pump inlet passage 77 shown in Figure 4. Next, the flow of ink will be explained using Figure 4.

[0024] (Ink flow) Returning to Figure 4, the pump 21 in Figure 4 pressurizes and supplies ink stored in the ink tank 2 to the liquid discharge head 1. The filter 23 removes dust contained in the pressurized ink supplied from the pump 21. The ink from which dust has been removed by the filter 23 is supplied to the valve chamber 25 of the first pressure control mechanism 24. As the ink supplied to the valve chamber 25 flows into the pressure control chamber 26, its pressure is controlled by the circulation pump 27. Next, the details of the pressure control by the circulation pump 27 will be explained using Figure 6.

[0025] By generating a potential difference in the piezoelectric element 273 in Figure 6, the volume inside the pressure chamber 276d is changed, causing pressure fluctuations inside the pressure chamber 276d. Due to the pressure fluctuations inside the pressure chamber 276d, the two valve bodies 276b and 276c move alternately, sending ink, and the circulation pump 27 functions as a piezoelectric diaphragm pump. The circulation pump 27 is driven to send ink with the pump inlet passage 77 on the downstream side and the pump outlet passage 78 on the upstream side. Now, let's return to Figure 4. Driven by the circulation pump 27 in Figure 4, the ink whose pressure is controlled inside the pressure control chamber 26 is supplied to the supply passage 75 and the bypass passage 79. The supply passage 75 supplies ink to the flow path member 110. The flow path member 110 supplies the ink supplied from the supply passage 75 to the discharge unit 300. The ink supplied to the discharge unit 300 is supplied to the discharge element substrate 310 inside the discharge unit 300. An ink discharge element is provided on the discharge element substrate 310. Ink supplied to the discharge element substrate 310 passes through the discharge element and is then discharged into the recovery channel 76. The discharge element comprises an energy generating element, a pressure chamber, and a discharge port. Ink that has passed through the pressure chamber inside the discharge element and been discharged into the recovery channel 76 is supplied to the pressure control chamber 30. In addition, ink supplied to the valve chamber 29 via the bypass channel 79 is supplied to the pressure control chamber 30, which is connected to the valve chamber 29 via a valve. Thus, ink is supplied to the pressure control chamber 30 from both the recovery channel 76 and the bypass channel 79. The ink supplied to the pressure control chamber 30 is supplied to the circulation pump 27 via the pump inlet channel 77. The ink supplied to the circulation pump 27 is supplied to the pressure control chamber 26 via the pump outlet channel 78. In this way, the ink is circulated by the circulation pump 27, passing through the discharge element formed on the discharge element substrate 310. This constitutes an ink circulation path in which the ink circulates. With this configuration, it is possible to suppress the thickening of the ink in the ejection element. The ink circulation path is not limited to a configuration that passes through the ejection element. For example, the ink circulation path may be configured to circulate the ink inside the ejection unit 300, as long as it is effective in suppressing the thickening of the ink in the ejection element. Next, the inflow and outflow of ink will be explained using the following three use cases with reference to Figure 6.

[0026] (Use Case 1) This section describes a use case in which ink flows into the pressure chamber 276d. Assume that a potential difference is generated from the second electrode 274 towards the first electrode 272, causing the piezoelectric element 273 and the diaphragm 275 to be displaced in a direction that expands the pressure chamber 276d. In this scenario, the valve body 276c opens, and ink flows into the pressure chamber 276d from the pump inlet passage 77.

[0027] (Use Case 2) This section describes a use case in which ink flows out from the pressure chamber 276d. Assume that a potential difference is generated from the first electrode 272 to the second electrode 274, causing the piezoelectric element 273 and the diaphragm 275 to be displaced in a direction that contracts the pressure chamber 276d. In this scenario, the valve body 276b opens, and ink flows out from the pressure chamber 276d into the pump outlet channel 78.

[0028] (Use Case 3) This section describes a use case in which neither ink flows into nor out of the pressure chamber 276d. We assume that no potential difference is generated between the first electrode 272 and the second electrode 274. In this scenario, the piezoelectric element 273 and the diaphragm 275 are not displaced in either an expanding or contracting direction within the pressure chamber 276d. Therefore, no ink flows into or out of the diaphragm unit 276.

[0029] Specifically, by periodically changing the potential difference between the first electrode 272 and the second electrode 274, the circulation pump 27 causes ink to flow in through the pump inlet channel 77 and to flow out through the pump outlet channel 78. Next, the process of generating a drive signal to drive the circulation pump 27 based on a control signal and a reference voltage will be described.

[0030] (Pump drive circuit in the first embodiment) Figure 7 shows an example of a pump drive circuit for driving the circulation pump shown in Figure 6 according to the first embodiment. The liquid discharge device 50 in Figure 7 includes a CPU 400, a power supply 410, and a head output terminal 421 as components included in the main body of the liquid discharge device 50 in Figure 1. The liquid discharge head 1 includes a head input terminal 422, a boost circuit 423, and an output switching circuit 424, in addition to the ink circulation unit 54 described using Figures 1 to 3. The head output terminal 421 supplies various signals and various voltages to the head input terminal 422. Of the head input terminal 422, boost circuit 423, and output switching circuit 424, the boost circuit 423 and the output switching circuit 424 function as a pump drive circuit.

[0031] A print signal 601, as image data, is input from the host device 500 to the CPU 400 of the liquid dispensing device 50. Meanwhile, a power supply voltage 602 is supplied from the external power supply 510 to the power supply device 410. Upon receiving the print signal 601 from the host device 500, the CPU 400 activates a power control signal 603 to the power supply device 410. In this embodiment, the power control signal 603 is assumed to be high active. That is, it is assumed that the power supply device 410 is set to operate when the power control signal 603 is high. Specifically, when the signal potential of the power control signal 603 transitions from 0V to 3.3V, the power supply device 410 outputs a pump drive reference voltage 604 to the head output terminal 421. In this embodiment, the pump drive reference voltage 604 is assumed to be 5V. The CPU 400 receives a print signal 601 from the host device 500 and outputs a pump control signal 605 and a boost signal 606 to the head output terminal 421.

[0032] (Pump control signal 605) The pump control signal 605 includes pump control signal 605a and pump control signal 605b. Pump control signal 605a and pump control signal 605b correspond to the first electrode 272 and the second electrode 274, respectively. Pump control signals 605a and 605b are sent to the output switching circuit 424 via the head output terminal 421 and the head input terminal 422. The signal potential of pump control signals 605a and 605b transitions from 0V to 3.3V, at which point each of the pump control signals 605a and 605b becomes active. That is, each of the pump control signals 605a and 605b is assumed to be highly active.

[0033] (Boost signal 606) The boost circuit 423 is driven when the signal potential of the boost signal 606 transitions from 0V to the active potential of 5V. Specifically, the pump drive reference voltage 604 output from the head input terminal 422 is input to the voltage input terminal of the boost circuit 423. The boost signal 606 output from the head input terminal 422 is input to the signal input terminal of the boost circuit 423. The boost circuit 423 converts the 5V pump drive reference voltage 604 to a voltage necessary for the piezoelectric element 273 provided on the circulation pump 27 to be sufficiently displaced, according to the boost signal 606. For example, the boost circuit 423 converts the 5V pump drive reference voltage 604 to a voltage of 72V. The boost circuit 423 outputs the converted voltage of 72V as the pump drive voltage 607 to the output switching circuit 424. A specific circuit example of the boost circuit 423 will be explained using Figure 8.

[0034] (Boost circuit 423) Figure 8 shows an example of the boost circuit 423 of Figure 7 according to the first embodiment. In the example in Figure 8, the boost circuit 423 includes a bypass capacitor 705, an inductor 701, a switching element 702, a diode 703, a capacitor 704, a voltage divider resistor 706, and a voltage divider resistor 707. For example, a chip inductor is used for the inductor 701. For example, an n-channel FET is used for the switching element 702. In Figure 8, the ground constitutes the potential that serves as the operating reference for the circuit. The ground is configured by a ground terminal, for example, as a frame ground or a signal ground. Alternatively, the ground may be configured by a ground terminal, for example, as a frame ground or a signal ground.

[0035] (Connection configuration of boost circuit 423) One terminal of the bypass capacitor 705 is connected to the ground terminal. The other terminal of the bypass capacitor 705 is connected to the voltage input terminal of the boost circuit 423. The pump drive reference voltage 604 is applied to the voltage input terminal of the boost circuit 423. One terminal of the inductor 701 is also connected to the input terminal of the boost circuit 423. The other terminal of the inductor 701 is connected to the anode of the diode 703 and the drain of the switching element 702. The source of the switching element 702 is connected to the ground terminal. When the boost signal 606 input from the signal input terminal of the boost circuit 423 is input to the gate of the switching element 702, the drain and source of the switching element 702 become conductive. One terminal of the capacitor 704 is connected to the cathode of the diode 703. The other terminal of the capacitor 704 is connected to the ground terminal. Furthermore, one terminal of the voltage divider resistor 706 and the first voltage output terminal of the boost circuit 423 are connected to the cathode of diode 703. The first voltage output terminal can output the pump drive voltage 607. One terminal of the voltage divider resistor 707 is connected to the other terminal of voltage divider resistor 706. The other terminal of voltage divider resistor 707 is connected to the ground terminal. The connection point between voltage divider resistor 706 and voltage divider resistor 707 is connected to the second voltage output terminal of the boost circuit 423. The second voltage output terminal can output the feedback voltage 609.

[0036] (Operation of the boost circuit 423) When the potential of the boost signal 606 transitions from ground potential to the active potential of 5V, the switching element 702 becomes conductive. Therefore, when the pump drive reference voltage 604 is applied to the voltage input terminal of the boost circuit 423, current flows from the voltage input terminal of the boost circuit 423 to the ground terminal via the inductor 701 and the switching element 702. Here, when the potential of the boost signal 606 transitions from active potential to ground potential, the switching element 702 becomes non-conductive, and a back electromotive force is generated in the inductor 701. Therefore, the current generated by the back electromotive force of the inductor 701 flows to the capacitor 704 via the diode 703. As a result, charge flows into the capacitor 704. The charge that flows into and is stored in the capacitor 704 cannot return to the anode side of the diode 703 due to the diode 703. Therefore, as the switching element 702 repeatedly switches between conductive and non-conductive states due to the boost signal 606, charge flows into and is stored in the capacitor 704. As a result, the pump drive voltage 607 is boosted to a voltage higher than the pump drive reference voltage 604. In this embodiment, the pump drive voltage 607 is divided by two voltage divider resistors 706 and 707. This voltage division causes a feedback voltage 609 to be output from the second voltage output terminal. The feedback voltage 609 is output to the CPU 400. Based on the feedback voltage 609, the CPU 400 controls the on / off duty cycle of the boost signal 606 so that the potential of the pump drive voltage 607 output from the first voltage output terminal becomes 72V. Note that the boost circuit 423 is not limited to the example in Figure 8. For example, the boost circuit 423 may be composed of a charge pump circuit. Alternatively, the boost circuit 423 may be composed of a power supply unit that converts AC input from an external source to 72V DC.

[0037] (Output switching circuit 424) Return to Figure 7. The output switching circuit 424 outputs the pump drive voltage 607 as a pump drive signal 608 to the pump output terminal 425 according to the pump control signal 605 input from the head input terminal 422. The pump drive signal 608 includes pump drive signal 608a and pump drive signal 608b. Details of the output switching circuit 424 will be explained using Figure 9.

[0038] Figure 9 shows an example of the output switching circuit 424 in Figure 7 according to the first embodiment. The output switching circuit 424 includes a first voltage control circuit 424a and a second voltage control circuit 424b. The first voltage control circuit 424a and the second voltage control circuit 424b are provided in parallel. The first voltage control circuit 424a outputs a pump drive signal 608a based on the input of a pump control signal 605a when a pump drive voltage 607 is input. The first voltage control circuit 424a includes an a signal system corresponding to the first electrode 272. The a signal system controls the output of the pump drive signal 608a to the first electrode 272 via the first wiring 211a. Therefore, the a signal system can control the voltage applied to the first electrode 272. The second voltage control circuit 424b outputs a pump drive signal 608b based on the input of a pump control signal 605b when a pump drive voltage 607 is input. The second voltage control circuit 424b includes a b signal system corresponding to the second electrode 274. The b signal system outputs a pump drive signal 608b to the second electrode 274 via the second wiring 211b. Thus, the b signal system can control the voltage applied to the second electrode 274.

[0039] (Connection configuration of the first voltage control circuit 424a) The first voltage control circuit 424a includes a resistor 801a, transistors 802a, 803a, 805a, and capacitor 806a. Transistor 802a is an NPN transistor. Transistor 803a is a PNP transistor. Transistor 805a is an NPN transistor. One terminal of resistor 801a is connected to the collector of transistor 802a. The collector of transistor 802a is connected to the voltage input terminal of the pump drive voltage 607. The other terminal of resistor 801a is connected to the base of transistor 802a. The base of transistor 802a is connected to the base of transistor 803a, one terminal of capacitor 806a, and the collector of transistor 805a. The emitter of transistor 803a is connected to the emitter of transistor 802a. A pump drive signal 608a can be output from a signal output terminal provided between the emitter of transistor 803a and the emitter of transistor 802a. A pump control signal 605a is input to the base of transistor 805a. The emitter of transistor 805a and the other terminal of capacitor 806a are connected to the ground terminal. Note that the switching elements of the first voltage control circuit 424a are not limited to transistors 802a, 803a, and 805a. The switching elements of the first voltage control circuit 424a may be FETs.

[0040] (Operation of the first voltage control circuit 424a) (Position of pump control signal 605a: Ground potential) When the potential of the pump control signal 605a is at ground potential, the emitter and collector of transistor 805a are not conducting. Therefore, transistor 805a is open. When transistor 805a is open, the pump drive voltage 607 is applied to the bases of transistor 802a and transistor 803a. At this time, if the potential of the pump drive signal 608a is at ground potential, the potential of the emitter of transistor 802a is at ground potential. Therefore, the potential of the emitter of transistor 802a is lower than the potential of the base of transistor 802a. Consequently, base current flows from the base of transistor 802a to the output destination of the pump drive signal 608a. As a result, transistor 802a becomes active, and the pump drive voltage 607 is output as the pump drive signal 608a. In this case, the output voltage is 72V. On the other hand, the potential of the emitter of transistor 803a and the potential of the base of transistor 803a are at the same potential. Therefore, transistor 803a is open. From the above, when the potential of the pump control signal 605a is at ground potential, the potential of the pump drive signal 608a is at the potential of the pump drive voltage 607.

[0041] (Potential of pump control signal 605a: Active potential) When the potential of the pump control signal 605a is at the active potential, base current flows from the base of transistor 805a to the emitter of transistor 805a. Therefore, transistor 805a becomes active, and the bases of transistor 802a and transistor 803a are connected to the ground terminal. At this time, if the potential of the pump drive signal 608a is 72V, base current flows from the emitter of transistor 803a to the base of transistor 803a. Therefore, transistor 803a becomes active. When transistor 803a becomes active, the emitter and collector of transistor 803a become conductive, and the collector of transistor 803a is connected to the ground terminal. Therefore, the emitter of transistor 802a and the emitter of transistor 803a are connected to the ground terminal. As a result, the potential of the pump drive signal 608a becomes the ground potential. On the other hand, since the base potential of transistor 802a and the emitter potential of transistor 802a are at the same potential, transistor 802a becomes open. Therefore, when the potential of the pump control signal 605a is at the active potential, the potential of the pump drive signal 608a becomes the ground potential.

[0042] (Connection configuration of the second voltage control circuit 424b) The second voltage control circuit 424b includes a resistor 801b, transistors 802b, 803b, 805b, and capacitor 806b. Transistor 802b is an NPN transistor. Transistor 803b is a PNP transistor. Transistor 805b is an NPN transistor. One terminal of resistor 801b is connected to the collector of transistor 802b. The collector of transistor 802b is connected to the voltage input terminal of the pump drive voltage 607. The other terminal of resistor 801b is connected to the base of transistor 802b. The base of transistor 802b is connected to the base of transistor 803b, one terminal of capacitor 806b, and the collector of transistor 805b. The emitter of transistor 803b is connected to the emitter of transistor 802b. A pump drive signal 608b can be output from a signal output terminal provided between the emitter of transistor 803b and the emitter of transistor 802b. A pump control signal 605b is input to the base of transistor 805b. The emitter of transistor 805b and the other terminal of capacitor 806b are connected to the ground terminal. Note that the switching elements of the second voltage control circuit 424b are not limited to transistors 802b, 803b, and 805b. The switching elements of the first voltage control circuit 424a may be FETs.

[0043] (Operation of the second voltage control circuit 424b) (Position of pump control signal 605b: Ground potential) When the potential of the pump control signal 605b is at ground potential, the emitter and collector of transistor 805b are not conducting. Therefore, transistor 805b is open. When transistor 805b is open, the pump drive voltage 607 is applied to the bases of transistor 802b and transistor 803b. At this time, if the potential of the pump drive signal 608b is at ground potential, the potential of the emitter of transistor 802b is at ground potential. Therefore, the potential of the emitter of transistor 802b is lower than the potential of the base of transistor 802b. Consequently, base current flows from the base of transistor 802b to the output destination of the pump drive signal 608b. As a result, transistor 802b becomes active, and the pump drive voltage 607 is output as the pump drive signal 608b. In this case, the output voltage is 72V. On the other hand, the potential of the emitter of transistor 803b and the potential of the base of transistor 803b are at the same potential. Therefore, transistor 803b is open. From the above, when the potential of the pump control signal 605b is at ground potential, the potential of the pump drive signal 608b is at the potential of the pump drive voltage 607.

[0044] (Potential of pump control signal 605b: Active potential) When the potential of the pump control signal 605b is at the active potential, base current flows from the base of transistor 805b to the emitter of transistor 805b. Therefore, transistor 805b becomes active, and the bases of transistor 802b and transistor 803b are connected to the ground terminal. At this time, if the potential of the pump drive signal 608b is 72V, base current flows from the emitter of transistor 803b to the base of transistor 803b. Therefore, transistor 803b becomes active. When transistor 803b becomes active, the emitter and collector of transistor 803b become conductive, and the collector of transistor 803b is connected to the ground terminal. Therefore, the emitter of transistor 802b and the emitter of transistor 803b are connected to the ground terminal. As a result, the potential of the pump drive signal 608b becomes the ground potential. On the other hand, since the base potential of transistor 802b and the emitter potential of transistor 802b are at the same potential, transistor 802b becomes open. Therefore, when the potential of the pump control signal 605b is at the active potential, the potential of the pump drive signal 608b becomes the ground potential.

[0045] (Pump output terminal 425) Return to Figure 7. The pump output terminal 425 is composed of pump output terminals 425a and 425b, which correspond to the first electrode 272 and the second electrode 274, respectively. The pump output terminal 425 is provided on the head board 210. Of the pump drive signals 608a and 608b, pump drive signal 608a is output to pump output terminal 425a. Of the pump drive signals 608a and 608b, pump drive signal 608b is output to pump output terminal 425b. The potential of the pump drive signals 608a and 608b transitions between 0V and 72V. 72V is set as the pump drive voltage of the circulation pump 27. The pump drive signals 608a and 608b output from pump output terminals 425a and 425b are sent to the ink circulation unit 54.

[0046] (Ink circulation unit 54) The ink circulation unit 54 includes a pump input terminal 426 and a circulation pump 27 as components related to the pump drive signals 608a and 608b. The pump drive signals 608a and 608b sent from the pump output terminals 425a and 425b, respectively, are input to the pump input terminal 426. The pump input terminal 426 outputs the pump drive signals 608a and 608b, respectively, to the circulation pump 27. The circulation pump 27 is driven according to the pump drive signals 608a and 608b, respectively, output from the pump input terminal 426. Next, the driving of the circulation pump 27 will be explained using Figure 10.

[0047] (Driving the circulation pump 27) Figure 10 illustrates the timing chart of the control signals that control the pump drive circuit according to the first embodiment. First, the potential of the pump drive reference voltage 604 transitions from 0V to 5V. As a result, the pump drive reference voltage 604 is applied to the boost circuit 423. Next, the potential of the boost signal 606 transitions from 0V to 5V, repeating according to a certain rule. For example, the potential of the boost signal 606 repeats between 0V and 5V based on a constant duty cycle. As a result, the potential of the pump drive voltage 607 output from the boost circuit 423 is boosted from 0V to 72V. The boosted pump drive voltage 607 is applied to the output switching circuit 424. Within the output switching circuit 424, as the pump drive voltage 607 is applied, the potentials of the pump drive signals 608a and 608b rise to 72V, becoming the same potential as the pump drive voltage 607.

[0048] (Period T12) Next, the potential of the pump control signal 605a transitions from 0V to 3.3V. When the potential of the pump control signal 605a is 3.3V, the potential of the pump control signal 605b is 0V. After the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump control signal 605a is maintained at 3.3V for a period T12. On the other hand, as the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump drive signal 608a decreases from 72V to 0V over a transition time T11. The transition time T11 varies mainly based on the capability of the boost circuit 423 and the capacitance of the piezoelectric element 273. The higher the capability of the boost circuit 423, the longer the transition time T11. The larger the capacitance of the piezoelectric element 273, the longer the transition time T11. In this embodiment, a transition time T11 = 12ms is assumed. Furthermore, in this embodiment, a period T12 = 16 ms is assumed. While the potential of the pump drive signal 608a decreases, the potential of the pump control signal 605b remains at 0V, so the potential of the pump drive signal 608b remains at 72V. After the potential of the pump drive signal 608a reaches 0V, it remains at 0V for the entire period T12 during which the pump control signal 605a continues to maintain 3.3V. Therefore, during period T12, there is a period when the potential difference between the potential of the pump drive signal 608a and the potential of the pump drive signal 608b becomes 72V. During this period, the potential difference between the second electrode 274 and the first electrode 272 is 72V. Due to this potential difference, the volume of the piezoelectric element 273 is displaced, and ink flows from the pump inlet passage 77 into the pressure chamber 276d.

[0049] (Period T13) Next, as the potential of the pump control signal 605a transitions to 0V, the potential of the pump control signal 605b transitions from 0V to 3.3V. After the potential of the pump control signal 605b transitions to 3.3V, the potential of the pump control signal 605b is maintained at 3.3V for the duration of period T13. On the other hand, as the potential of the pump control signal 605b transitions to 3.3V, the potential of the pump drive signal 608b decreases from 72V to 0V. After the potential of the pump drive signal 608b reaches 0V, it remains at 0V for the duration of period T13, during which the pump control signal 605b continues to maintain 3.3V. In this embodiment, as with period T12, period T13 = 16ms is assumed. While the potential of the pump drive signal 608b is decreasing, the potential of the pump control signal 605a remains at 0V, so the potential of the pump drive signal 608a transitions from 0V to 72V. After the potential of the pump drive signal 608a reaches 72V, the pump drive signal 608a maintains 72V while the potential of the pump control signal 605a remains at 0V. Therefore, during period T13, there is a period when the potential difference between the potential of the pump drive signal 608a and the potential of the pump drive signal 608b is -72V. During this period, the potential difference between the second electrode 274 and the first electrode 272 is -72V. Due to this potential difference, the volume of the piezoelectric element 273 is displaced, and ink flows out from the pressure chamber 276d to the pump outlet channel 78.

[0050] (Period T14; Period T15; Period T16; Drive cycle T17) After period T13 has elapsed, the potential of the pump control signal 605b transitions from 3.3V to 0V. Simultaneously with the transition of the pump control signal 605b to 0V, the potential of the pump drive signal 608b transitions from 0V to 72V. After the potential of the pump drive signal 608b reaches 72V, the potential of the pump control signal 605b remains at 0V, so the potential of the pump drive signal 608b remains at 72V. On the other hand, the potential of the pump control signal 605a remains at 0V. Therefore, the potential of the pump drive signal 608a continues to remain at 72V. As a result, no potential difference is generated between the first electrode 272 and the second electrode 274. Consequently, the volume displacement of the piezoelectric element 273 is eliminated. Due to the elimination of the displacement of the shape of the piezoelectric element 273, ink flows from the pump inlet channel 77 into the pressure chamber 276d. Simultaneously with the end of period T13, period T14 begins, and while period T14 continues, the potentials of the pump control signals 605a and 605b are maintained at 0V. In this embodiment, period T14 = 32ms. After the elapsed period T14, the potential of the pump control signal 605a transitions back to 3.3V for the duration of period T12. That is, control is repeatedly performed with periods T12, T13, and T14 forming one drive cycle T17. As described above, the delivery capacity of the circulating pump 27 correlates with the volume displacement of the pressure chamber 276d and the number of deliveries. That is, it correlates with the potential difference applied to the piezoelectric element 273 and the drive cycle T17. According to this disclosure, a period T16 is provided between period T15, when a potential difference is generated in the piezoelectric element 273, and the next drive cycle T17. This makes it possible to suppress the progression of migration failure of the piezoelectric element 273 while the circulating pump 27 is not involved in ink delivery. In other words, one drive cycle T17 includes a period T15 in which a potential difference is generated in the piezoelectric element 273 and a period T16 in which no potential difference is generated in the piezoelectric element 273.

[0051] Furthermore, in order to obtain sufficient driving capacity for the circulation pump 27, that is, sufficient displacement of the volume of the piezoelectric element 273, it is desirable that the period T12 be longer than or equal to the transition time T11. However, if the period T12 is made longer under the condition that the driving cycle T17 is constant, the period T15 will become longer and the period T16 will become shorter. If the period T16 becomes shorter, the period for suppressing migration failure will also become shorter. Therefore, it is desirable that the period T12 be, for example, at least twice the time of the transition time T11. Also, if the period T12 and the transition time T11 are equal, it is possible to obtain a higher effect in balancing the driving capacity of the circulation pump 27 and the reliability of the piezoelectric element 273.

[0052] Furthermore, it is preferable that the wiring path from the boost circuit 423 to the circulation pump 27 be located in a place that is difficult for the user to touch. For example, in the head board 210 of Figures 2 and 5, it is preferable that the boost circuit 423 be located on the flow path member 110 side. With this arrangement, the wiring path from the boost circuit 423 to the circulation pump 27 is covered by the flow path member 110. Also, in Figure 5, the carriage board 220 and the head board 210 may be integrated into one unit. Alternatively, the carriage board 220 and the head board 210 may be configured in a way that prevents the user from removing them. If the carriage board 220 and the head board 210 are configured in a way that prevents the user from removing them, the boost circuit 423 may be provided on the carriage board 220.

[0053] (Effects of the first embodiment) From the above description, the liquid discharge device 50 comprises a piezoelectric means, a drive control means, and a diaphragm means. The piezoelectric means has a first electrode 272, a second electrode 274 facing the first electrode 272, and a piezoelectric element 273 disposed between the first electrode 272 and the second electrode 274. The drive control means controls the strain generated in the piezoelectric means in a drive cycle T17 including a first period (period T12 + period T13) and a second period (period T14), while a drive voltage that generates strain in the piezoelectric means is supplied to the first electrode 272 and the second electrode 274. The first period (period T12 + period T13) includes a period in which the drive voltage (pump drive voltage 607) supplied to either the first electrode 272 or the second electrode 274 is interrupted. On the other hand, the second period (period T14) includes a period during which no potential difference is generated between the first electrode 272 and the second electrode 274. For example, the second period (period T14) includes a period during which a drive voltage (pump drive voltage 607) is simultaneously supplied to both the first electrode 272 and the second electrode 274. With such a configuration, during the first period, the drive voltage supplied to either of the two electrodes is interrupted, creating a potential difference between the drive voltage potential and the ground potential between the two electrodes. Therefore, during the first period, it is possible to generate strain in the piezoelectric pump. As a result, the liquid circulation capacity is maintained. On the other hand, during the second period, no potential difference is generated between the first electrode 272 and the second electrode 274. If no potential difference is generated between the first electrode 272 and the second electrode 274, it does not mean that a voltage has been applied between the two electrodes. Therefore, during the second period, the piezoelectric pump is not under conditions where a voltage has been applied, even in a high-humidity environment. That is, the second period may include a period during which no potential difference occurs between the first electrode 272 and the second electrode 274, and during which the drive voltage is supplied simultaneously to both the first electrode 272 and the second electrode 274. With such a configuration, the potential of the first electrode 272 and the potential of the second electrode 274 are the same, so no potential difference occurs between the first electrode 272 and the second electrode 274. Therefore, migration failures can be suppressed. Thus, by controlling the strain generated in the piezoelectric pump during the drive cycle including the first and second periods, it is possible to maintain liquid circulation capacity and suppress migration failures.

[0054] The drive control means may also include a first voltage control circuit 424a and a second voltage control circuit 424b. The first voltage control circuit 424a controls whether or not to interrupt the drive voltage supplied to the first electrode 272. The second voltage control circuit 424b is electrically connected in parallel with the first voltage control circuit 424a and controls whether or not to interrupt the drive voltage supplied to the second electrode 274. With such a configuration, it is possible to supply the same voltage potential to the first electrode 272 and the second electrode 274 while controlling them separately.

[0055] Furthermore, the drive control means may interrupt the drive voltage supplied to the second electrode 274 by the second voltage control circuit 424b while a drive voltage is supplied to the first electrode 272. Alternatively, the drive control means may interrupt the drive voltage supplied to the first electrode 272 by the first voltage control circuit 424a while a drive voltage is supplied to the second electrode 274. With such a configuration, it is possible to generate a potential difference between the first electrode 272 and the second electrode 274. Therefore, the liquid circulation capability can be maintained.

[0056] Furthermore, the first voltage control circuit 424a and the second voltage control circuit 424b may each be further provided with a boosting means that supplies a boosted drive voltage (pump drive voltage 607) based on the drive reference voltage (pump drive reference voltage 604) at the same potential. With such a configuration, the same potential of the pump drive reference voltage 604 is supplied to both the first voltage control circuit 424a and the second voltage control circuit 424b. Therefore, if there is no potential difference between the first voltage control circuit 424a and the second voltage control circuit 424b, the voltage applied to the piezoelectric element 273 is... This eliminates the potential difference, making it possible to realize the period T14 shown in Figure 10. The boosting means may be implemented by a boosting circuit 423, or by a DC-DC converter.

[0057] Furthermore, the first period may include a first interruption period (period T12) and a second interruption period (period T13). During the first interruption period (period T12), the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is interrupted. During the second interruption period (period T13), the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is interrupted. The drive control means may also control the strain generated in the piezoelectric means in the order of the first interruption period (period T12), the second interruption period (period T13), and the second period (period T14) as the drive cycle T17. With such a configuration, it is possible to provide a period for maintaining liquid circulation capacity and a period for suppressing migration failures within a single drive cycle T17.

[0058] Furthermore, the drive control means may start the second interruption period (period T13) simultaneously with the end of the first interruption period (period T12). With such a configuration, the drive cycle T17 can include a period T15 in which a potential difference is applied to the piezoelectric element 273 and a period T16 in which no potential difference is applied to the piezoelectric element 273, and it is also possible to have period T16 immediately following period T15.

[0059] Furthermore, the first interruption period (period T12) may be set to be longer than the time required for the potential of the drive voltage (pump drive voltage 607) supplied to the first electrode 272 to reach zero potential when the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is interrupted. Similarly, the second interruption period (period T13) may be set to be longer than the time required for the potential of the drive voltage (pump drive voltage 607) supplied to the second electrode 274 to reach zero potential when the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is interrupted. With such a configuration, it is possible to maintain a sufficient potential difference between the first electrode 272 and the second electrode 274.

[0060] (Second embodiment) In the second embodiment, descriptions of the same configuration as in the first embodiment will be omitted as appropriate. The second embodiment differs from the first embodiment in that when the pressure chamber 276d expands or contracts, the piezoelectric element 273 remains in a state of no displacement for a certain period of time. Figure 11 is a diagram illustrating the timing chart of the control signal that controls the pump drive circuit according to the second embodiment. Until the potential of the pump drive voltage 607 is increased from 0V to 72V, the timing chart is the same as that of the pump drive circuit in the first embodiment. The timing charts that differ from the first embodiment will be described below.

[0061] (Period T22) After the potential of the pump drive voltage 60 transitions to 72V, the potential of the pump control signal 605a transitions from 0V to 3.3V. After the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump control signal 605a is maintained at 3.3V for the period T22. When the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump drive signal 608a transitions from 72V to 0V for the transition time T21. In this embodiment, the transition time T21 = 12 ms and the period T22 = 16 ms are assumed. On the other hand, while the potential of the pump control signal 605a is maintained at 3.3V, the potential of the pump control signal 605b is maintained at 0V. Therefore, the potential of the pump drive signal 608b is maintained at 72V. During period T22, the potential difference between the potential of the pump drive signal 608b and the potential of the pump drive signal 608a is 72V. That is, the potential difference between the second electrode 274 and the first electrode 272 becomes 72V. As a result, the volume of the piezoelectric element 273 is displaced, and ink flows from the pump inlet passage 77 into the pressure chamber 276d.

[0062] (Period T24) Next, the potential of the pump control signal 605a transitions from 3.3V to 0V. Therefore, the potential of the pump drive signal 608a transitions from 0V to 72V. After the potential of the pump drive signal 608a transitions to 72V, the potential of the pump drive signal 608b remains at 72V for the duration T24. Therefore, no potential difference occurs between the second electrode 274 and the first electrode 272. Consequently, the volume displacement of the piezoelectric element 273 is eliminated. Due to the elimination of the volume displacement of the piezoelectric element 273, ink flows from the pump inlet channel 77 into the pressure chamber 276d.

[0063] (Period T23) After period T24 has elapsed, the potential of the pump control signal 605b transitions from 0V to 3.3V. After the potential of the pump control signal 605b transitions to 3.3V, the potential of the pump control signal 605b is maintained at 3.3V for the duration of period T23. In this embodiment, as with period T12, period T23 is assumed to be 16ms. During period T23, the potential of the pump drive signal 608b transitions from 72V to 0V and maintains a potential of 0V. On the other hand, the potential of the pump drive signal 608a is maintained at 72V. Therefore, the potential difference between the second electrode 274 and the first electrode 272 becomes -72V. Consequently, due to the displacement of the volume of the piezoelectric element 273, ink flows out from the pressure chamber 276d to the pump outlet channel 78. In this embodiment, period T23 is assumed to be 16ms. A response time of 16ms is expected.

[0064] (Period T28) After period T23 has elapsed, the potential of the pump control signal 605b transitions from 3.3V to 0V. After the potential of the pump control signal 605b transitions to 0V, the potential of the pump control signal 605b remains at 0V throughout period T28, and the potential of the pump control signal 605a also remains at 0V. Therefore, no potential difference occurs between the second electrode 274 and the first electrode 272. Consequently, the volume displacement of the piezoelectric element 273 is eliminated. As a result, ink flows out from the pressure chamber 276d into the pump outlet channel 78 by the amount of the volume displacement of the piezoelectric element 273.

[0065] After period T28 has elapsed, the potential of the pump control signal 605a transitions again from 0V to 3.3V. That is, control is repeatedly performed with periods T22, T24, T23, and T28 forming one drive cycle T27. In this embodiment, period T28 is assumed to be 16ms. In other words, one drive cycle T27 includes periods T25a and T25b in which a potential difference is applied to the piezoelectric element 273, and periods T26a and T26b in which no potential difference is applied to the piezoelectric element 273.

[0066] (Effects of the second embodiment) According to this embodiment, when the pressure chamber 276d expands or contracts, the volume of the piezoelectric element 273 remains unchanged for a certain period of time. Specifically, the drive cycle T27 includes periods T25a and T25b in which a potential difference is applied to the piezoelectric element 273, and periods T26a and T26b in which no potential difference is applied to the piezoelectric element 273. In the example shown in Figure 11, each period occurs in the order of periods 25a, T26a, T25b, and T26b within one drive cycle T27. Each period can be adjusted by adjusting the time intervals between periods T22, T24, T23, and T28. Therefore, the inflow and outflow of ink into and out of the pressure chamber 276d can be controlled relatively precisely.

[0067] Furthermore, the drive control means may control the strain generated in the piezoelectric means in the following order: first sub-cutoff period (period T22), third period (period T24), second sub-cutoff period (period T23), and fourth period (period T28). The first sub-cutoff period (period T22) is the period during which the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is cut off. The second sub-cutoff period (period T23) is the period during which the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is cut off. With such a configuration, it is possible to include multiple periods T25a during which a potential difference is applied to the piezoelectric element 273 and periods T26a during which no potential difference is applied to the piezoelectric element 273 within a single drive cycle T27. Therefore, it becomes possible to finely control the period during which the liquid circulation capacity is maintained and the period during which migration failures are suppressed.

[0068] Furthermore, in each of the third period (period T24) and the fourth period (period T28), if the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is interrupted, the following settings may be made: That is, a time longer than the time required from the time the drive voltage (pump drive voltage 607) supplied to the first electrode 272 reaches a certain potential after the supply of the drive voltage (pump drive voltage 607) is resumed may be set. Furthermore, in each of the third period (period T24) and the fourth period (period T28), if the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is interrupted, the following settings may be made: That is, a time longer than the time required from the time the drive voltage (pump drive voltage 607) supplied to the second electrode 274 reaches a certain potential after the supply of the drive voltage (pump drive voltage 607) is resumed may be set. With such a configuration, it is possible to realize multiple periods for suppressing migration failures within one drive cycle T27.

[0069] Furthermore, the first sub-cutoff period (period T22) may be set to a time longer than the potential of the drive voltage (pump drive voltage 607) supplied to the first electrode 272 reaches zero potential when the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is cut off. The second sub-cutoff period (period T23) may be set to a time longer than the potential of the drive voltage supplied to the second electrode 274 reaches zero potential when the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is cut off. With such a configuration, it is possible to maintain sufficient liquid circulation capacity.

[0070] (Third embodiment) In the third embodiment, descriptions of configurations similar to those in the first and second embodiments will be omitted as appropriate. The third embodiment differs from the first and second embodiments in that the potential difference between the second electrode 274 and the first electrode 272 does not reach 72V. Figure 12 is a diagram illustrating the timing chart of the control signal that controls the pump drive circuit according to the third embodiment. Until the potential of the pump drive voltage 607 is boosted from 0V to 72V, the timing chart is the same as that of the pump drive circuit in the first and second embodiments. The timing charts that differ from those of the first and second embodiments will be described below.

[0071] (Period T32) After the potential of the pump drive voltage 607 transitions to 72V, the potential of the pump control signal 605a transitions from 0V to 3.3V. After the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump control signal 605a is maintained at 3.3V for a period T32. The potential of the pump drive signal 608a was planned to be set from 72V to 0V for a transition time T31 when the potential of the pump control signal 605a transitions to 3.3V, but period T32 is shorter than the transition time T31. Therefore, the potential of the pump drive signal 608a does not transition to 0V. In other words, the transition time T31 is the time it takes for the potential of the pump drive signal 608a to transition from 72V to 0V. However, in the example shown in Figure 12, as will be described in detail later, the potential of the pump drive signal 608a reaches 12V before transitioning to 0V, at which point period T32 ends, and the potential of the pump control signal 605a transitions from 3.3V to 0V. Therefore, the potential of the pump drive signal 608a reverses and transitions again to 72V. Thus, the transition time T31 is not shown in Figure 12. For example, a transition time T31 = 12 ms is assumed, and a period T32 = 10 ms is assumed. On the other hand, while the potential of the pump control signal 605a maintains 3.3V, the potential of the pump control signal 605b maintains 0V. Therefore, the potential of the pump drive signal 608b maintains 72V. During period T32, the potential difference between the potential of the pump drive signal 608b and the potential of the pump drive signal 608a is a maximum of 60V. That is, the potential difference between the second electrode 274 and the first electrode 272 is a maximum of 60V. Therefore, the volume of the piezoelectric element 273 is displaced, and ink flows from the pump inlet passage 77 into the pressure chamber 276d.

[0072] (Period T33) Next, the potential of the pump control signal 605a transitions from 3.3V to 0V. Simultaneously with the transition of the pump control signal 605a to 0V, the potential of the pump control signal 605b transitions from 0V to 3.3V. After the potential of the pump control signal 605b transitions to 3.3V, it is maintained at 3.3V for a period T33. The potential of the pump drive signal 608b was planned to be set from 72V to 0V for a transition time T31 when the potential of the pump control signal 605b transitions to 3.3V, but period T33 is shorter than the transition time T31. Therefore, the potential of the pump drive signal 608b does not transition to 0V. That is, the transition time T31 is the time it takes for the potential of the pump drive signal 608b to transition from 72V to 0V. However, in the example shown in Figure 12, the potential of the pump drive signal 608b reaches 12V before transitioning to 0V, at which point period T33 ends, and the potential of the pump control signal 605b transitions from 3.3V to 0V. Therefore, the potential of the pump drive signal 608b reverses and transitions again to 72V. For example, a transition time T31 = 12ms is assumed, and similar to period T32, period T33 = 10ms is assumed. On the other hand, while the potential of the pump control signal 605b maintains 3.3V, the potential of the pump control signal 605a maintains 0V. Therefore, the potential of the pump drive signal 608a is in the process of transitioning towards 72V. During period T33, the potential difference between the potential of the pump drive signal 608a and the potential of the pump drive signal 608b is a maximum of -60V. That is, the potential difference between the second electrode 274 and the first electrode 272 is a maximum of -60V. Therefore, the volume of the piezoelectric element 273 is displaced, and ink flows out from the pressure chamber 276d to the pump outlet channel 78.

[0073] (Period T34) After period T33 has elapsed, the potential of the pump control signal 605b transitions from 3.3V to 0V. After the potential of the pump control signal 605b transitions to 0V, the potential of the pump control signal 605b remains at 0V throughout period T34, and the potential of the pump control signal 605a also remains at 0V. Therefore, no potential difference occurs between the second electrode 274 and the first electrode 272. Consequently, the volume displacement of the piezoelectric element 273 is eliminated.

[0074] After period T34 has elapsed, the potential of the pump control signal 605a transitions again from 0V to 3.3V. That is, control is repeatedly performed with periods T32, T33, and T34 as one drive cycle T37. In this embodiment, period T34 = 44ms is assumed. In other words, one drive cycle T37 includes a period T35 in which a potential difference is applied to the piezoelectric element 273 and a period T36 in which no potential difference is applied to the piezoelectric element 273.

[0075] (Effects of the third embodiment) According to this embodiment, the pump drive signals 608a and 608b undergo a reversal transition before their potential reaches 0V. Therefore, although the liquid circulation capacity is reduced compared to the first and second embodiments, if the reduced liquid circulation capacity is sufficient, it is possible to maintain the liquid circulation capacity of the circulation pump 27 and suppress migration failures of the piezoelectric element 273.

[0076] Furthermore, the first interruption period (period T32) may be set to be shorter than the time required for the potential of the drive voltage (pump drive voltage 607) supplied to the first electrode 272 to reach zero potential when the drive voltage (pump drive voltage 607) supplied to the first electrode 272 is interrupted. The second interruption period (period T33) may be set to be shorter than the time required for the potential of the drive voltage (pump drive voltage 607) supplied to the second electrode 274 to reach zero potential when the drive voltage (pump drive voltage 607) supplied to the second electrode 274 is interrupted. With such a configuration, it is possible to reduce the proportion of the period T35 in which a potential difference is applied to the piezoelectric element 273 within one drive cycle T37, and to increase the proportion of the period T36 in which no potential difference is applied to the piezoelectric element 273.

[0077] (Fourth embodiment) In the fourth embodiment, descriptions of configurations similar to those in the first to third embodiments will be omitted as appropriate. The fourth embodiment differs from the first to third embodiments, in which the pump control signals 605a and 605b are set to active high (positive logic), in that the pump control signals 605a and 605b are set to active low (negative logic). That is, in the first to third embodiments, an example was described in which the second period, as a period during which no potential difference occurs between the two electrodes, includes a period during which the drive voltage is simultaneously supplied to each of the two electrodes, but is not limited to this. In the fourth embodiment, an example is described using Figure 13 in which the second period, as a period during which no potential difference occurs between the two electrodes, includes a period during which the drive voltage supplied to each of the two electrodes is simultaneously cut off. Figure 13 is a diagram illustrating the timing chart of the control signals that control the pump drive circuit according to the fourth embodiment. In the example in Figure 13, the signal potentials of the pump control signals 605a and 605b are inverted. Therefore, when both pump control signals 605a and 605b are 3.3V, the potentials of pump drive signals 608a and 608b remain at 0V. On the other hand, when both pump control signals 605a and 605b are 0V, the potentials of pump drive signals 608a and 608b transition from 0V to 72V. Thus, in this embodiment, when both pump control signals 605a and 605b are 3.3V, no potential difference is applied to the piezoelectric element 273. Thus, it is possible to obtain the same effect as in the first embodiment. For example, in Figure 13, from period T43 to period T44, the potential of pump control signal 605a transitions from 0V to 3.3V. Thus, the potential of pump drive signal 608a transitions from 72V to 0V. On the other hand, from period T43 to period T44, the potential of pump control signal 605b remains at 3.3V. Thus, the potential of pump drive signal 608b remains at 0V. Therefore, in the second period (period T44), since both pump control signals 605a and 605b are 3.3V, the potentials of the pump drive signals 608a and 608b are 0V. In other words, the pump drive signals 608a and 608b cause the second period (period T44) to include a period in which the pump drive voltage 607 supplied to the first electrode 272 and the second electrode 274 are simultaneously interrupted.

[0078] (Effects of the fourth embodiment) The second period (period T44) may include a period during which no potential difference is generated between the first electrode 272 and the second electrode 274, and during which the drive voltage (pump drive voltage 607) supplied to each of the first electrode 272 and the second electrode 274 is simultaneously cut off. That is, the second period (period T44) includes a period during which no drive voltage (pump drive voltage 607) is simultaneously supplied to each of the first electrode 272 and the second electrode 274. With this configuration, during the second period (period T44), no potential difference is generated between the two electrodes, and therefore no voltage is applied between the two electrodes. Thus, during the second period (period T44), the piezoelectric pump is not under conditions where voltage is applied, even in a high-humidity environment. For this reason, migration failures can be suppressed.

[0079] (Fifth embodiment) In the fifth embodiment, descriptions of configurations similar to those in the first to fourth embodiments will be omitted as appropriate. The fifth embodiment differs from the first to fourth embodiments in that the pump drive circuit further includes a step-down circuit 423b, and the configuration of the output switching circuit 424 is changed due to the inclusion of the step-down circuit 423b. Figure 14 shows an example of a pump drive circuit that drives the circulating pump of Figure 6 according to the fifth embodiment. As shown in Figure 14, a step-down signal 606b and a pump drive reference voltage 604 are input to the step-down circuit 423b. The step-down signal 606b is generated by the CPU 400. The step-down signal 606b generated by the CPU 400 is sent to the step-down circuit 423b via the head output terminal 421 and the head input terminal 422. The pump drive voltage 607a and pump drive voltage 607b are sent to the output switching circuit 424. The pump drive voltage 607a is sent from the boost circuit 423a. The pump drive voltage 607b is supplied from the step-down circuit 423b. Next, the details of the step-down circuit 423b will be explained using Figure 15.

[0080] (Step-down circuit 423b) Figure 15 shows an example of the buck converter circuit 423b of Figure 14 according to a fifth embodiment. The buck converter circuit 423b includes a bypass capacitor 715, an inductor 711, a switching element 712, a diode 713, a capacitor 714, a voltage divider resistor 716, and a voltage divider resistor 717. The inductor 711 of the buck converter circuit 423b is connected in a different position than the inductor 701 of the boost converter circuit 423a in Figure 8. The inductor 711 of the buck converter circuit 423b is connected between the switching element 712 and the ground terminal. The diode 713 of the buck converter circuit 423b is connected with its anode and cathode in a different orientation than the diode 703 of the boost converter circuit 423a in Figure 8. The switching element 712 of the buck converter circuit 423b is a p-channel FET, unlike the n-channel FET of the switching element 702 of the boost converter circuit 423a in Figure 8.

[0081] (Connection configuration of step-down circuit 423b) One terminal of the bypass capacitor 715 is connected to the ground terminal. The other terminal of the bypass capacitor 715 is connected to the voltage input terminal of the step-down circuit 423b. The pump drive reference voltage 604 is applied to the voltage input terminal of the step-down circuit 423b. The input terminals of the step-down circuit 423b are connected to the cathode of the diode 713 and the drain of the switching element 712. An inductor 711 is connected between the source of the switching element 712 and the ground terminal. When the step-down signal 606b input from the signal input terminal of the step-down circuit 423b is input to the gate of the switching element 712, the drain and source of the switching element 712 become conductive. The step-down signal 606b is a negative voltage. One terminal of the capacitor 714 is connected to the anode of the diode 713. The other terminal of the capacitor 714 is connected to the ground terminal. Furthermore, one terminal of the voltage divider resistor 716 and the first voltage output terminal of the step-down circuit 423b are connected to the anode of diode 713. The first voltage output terminal can output the pump drive voltage 607b. One terminal of the voltage divider resistor 717 is connected to the other terminal of the voltage divider resistor 716. The ground terminal is connected to the other terminal of the voltage divider resistor 717. The second voltage output terminal of the step-down circuit 423b is connected to the connection point between the voltage divider resistor 716 and the voltage divider resistor 717. The second voltage output terminal can output the feedback voltage 619.

[0082] (Operation of step-down circuit 423b) When the pump drive reference voltage 604 is applied to the voltage input terminal of the step-down circuit 423b and the switching element 712 is in a non-conducting state, charge is accumulated in the capacitor 714. On the other hand, when the pump drive reference voltage 604 is applied to the voltage input terminal of the step-down circuit 423b and the switching element 712 is in a conducting state, the charge accumulated in the capacitor 714 flows out to the inductor 711, and negative charge is accumulated in the inductor 711. Therefore, by repeatedly switching between the non-conducting and conducting states of the switching element 712, negative charge continues to accumulate in the inductor 711, and the potential of the pump drive voltage 607b output from the step-down circuit 423b becomes a negative potential. Next, the output switching circuit 424 will be explained using Figure 16.

[0083] (Output switching circuit 424) Figure 16 shows an example of the output switching circuit 424 in Figure 14 according to the fifth embodiment. In Figure 16, the output switching circuit 424 is composed of a circuit consisting of a group of elements indicated by a symbol with the suffix 'a' and a circuit consisting of a group of elements indicated by a symbol with the suffix 'b'.

[0084] (Connection configuration of output switching circuit 424) (If the suffix is ​​a) The output switching circuit 424 includes NPN transistors 812a, 813a, 814a, and 815a. The pump drive voltage 607a is applied to the collector of NPN transistor 812a. The collector of NPN transistor 813a is connected to the base of NPN transistor 812a. The emitter of PNP transistor 814a is connected to the emitter of NPN transistor 812a. The pump drive signal 608a is output from the connection point between the emitter of NPN transistor 812a and the emitter of PNP transistor 814a. The ground terminal is connected to the emitter of NPN transistor 813a. The input terminal of the pump control signal 605a and the base of PNP transistor 815a are connected to the base of NPN transistor 813a. The collector of PNP transistor 815a is connected to the base of PNP transistor 814a. The pump drive voltage 607b is applied to the collector of the PNP transistor 814a.

[0085] (Connection configuration of output switching circuit 424) (If the suffix is ​​b) The output switching circuit 424 includes NPN transistors 812b, 813b, 814b, and 815b. The pump drive voltage 607a is applied to the collector of NPN transistor 812b. The collector of NPN transistor 813b is connected to the base of NPN transistor 812b. The emitter of PNP transistor 814b is connected to the emitter of NPN transistor 812b. The pump drive signal 608b is output from the connection point between the emitter of NPN transistor 812b and the emitter of PNP transistor 814b. The ground terminal is connected to the emitter of NPN transistor 813b. The input terminal of the pump control signal 605b and the base of PNP transistor 815b are connected to the base of NPN transistor 813b. The collector of PNP transistor 815b is connected to the base of PNP transistor 814b. The pump drive voltage 607b is applied to the collector of the PNP transistor 814b.

[0086] (Operation of output switching circuit 424) When the potential of the pump control signal 605 is 3.3V, the NPN transistors 812 and 813 become conductive, and the PNP transistors 814 and 815 become non-conductive. In this case, the pump drive voltage 607a is output to the pump drive signal 608. On the other hand, when the potential of the pump control signal 605 is 0V, the NPN transistors 812 and 813 become non-conductive, and the PNP transistors 814 and 815 become conductive. In this case, the pump drive voltage 607b is output to the pump drive signal 608. Next, the driving of the circulation pump 27 will be explained using Figure 17.

[0087] (Driving the circulation pump 27) Figure 17 illustrates the timing chart of the control signals that control the pump drive circuit according to the fifth embodiment. First, the potential of the pump drive reference voltage 604 transitions from 0V to 5V. As a result, the pump drive reference voltage 604 is applied to the boost circuit 423a and the buck circuit 423b, respectively. Next, the potentials of the boost signal 606a and the buck signal 606b transition from 0V to 5V, respectively, and this transition is repeated according to a certain rule. As a result, the potential of the pump drive voltage 607a is boosted from 0V to 36V, and the potential of the pump drive voltage 607b is stepped down from 0V to -36V.

[0088] (Period T52) Next, the potential of the pump control signal 605a transitions from 0V to 3.3V. When the potential of the pump control signal 605a is 3.3V, the potential of the pump control signal 605b is 0V. After the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump control signal 605a is maintained at 3.3V for a period T52. On the other hand, as the potential of the pump control signal 605a transitions to 3.3V, the potential of the pump drive signal 608a decreases from 36V to -36V for a transition time T51. In this embodiment, a period T52 = 16ms is assumed. While the potential of the pump drive signal 608a is decreasing, the potential of the pump control signal 605b remains at 0V, so the potential of the pump drive signal 608b remains at 36V. The potential of the pump drive signal 608a reaches -36V and remains at -36V for the duration T52 during which the pump control signal 605a maintains a voltage of 3.3V. Therefore, during period T52, there is a period when the potential difference between the potential of the pump drive signal 608a and the potential of the pump drive signal 608b becomes 72V. During this period, the potential difference between the second electrode 274 and the first electrode 272 is 72V. This potential difference causes the volume of the piezoelectric element 273 to displace, and ink flows from the pump inlet passage 77 into the pressure chamber 276d.

[0089] (Period T53) Next, as the potential of the pump control signal 605a transitions to 0V, the potential of the pump control signal 605b transitions from 0V to 3.3V. After the potential of the pump control signal 605b transitions to 3.3V, the potential of the pump control signal 605b is maintained at 3.3V for the duration of period T53. On the other hand, as the potential of the pump control signal 605b transitions to 3.3V, the potential of the pump drive signal 608b decreases from 36V to -36V. After the potential of the pump drive signal 608b reaches -36V, it remains at -36V for the duration of period T53, during which the pump control signal 605b continues to maintain 3.3V. Also, in this embodiment, as with period T52, period T53 = 16ms is assumed. While the potential of the pump drive signal 608b is decreasing, the potential of the pump control signal 605a remains at 0V, so the potential of the pump drive signal 608a transitions from -36V to 36V. After the potential of the pump drive signal 608a reaches 36V, the pump drive signal 608a maintains 36V while the potential of the pump control signal 605a remains at 0V. Therefore, during period T53, there is a period when the potential difference between the potential of the pump drive signal 608a and the potential of the pump drive signal 608b becomes -72V. During this period, the potential difference between the second electrode 274 and the first electrode 272 is -72V. Due to this potential difference, the volume of the piezoelectric element 273 is displaced, and ink flows out from the pressure chamber 276d to the pump outlet channel 78.

[0090] (Period T54; Period T55; Period T56; Drive cycle T57) After period T53 has elapsed, the potential of the pump control signal 605b transitions from 3.3V to 0V. Simultaneously with the transition of the pump control signal 605b to 0V, the potential of the pump drive signal 608b transitions from -36V to 36V. After the potential of the pump drive signal 608b reaches 36V, the potential of the pump control signal 605b remains at 0V, so the potential of the pump drive signal 608b remains at 36V. On the other hand, the potential of the pump control signal 605a remains at 0V. Therefore, the potential of the pump drive signal 608a continues to remain at 36V. As a result, no potential difference is generated between the first electrode 272 and the second electrode 274. Consequently, the displacement of the piezoelectric element 273 is eliminated. Due to the elimination of the displacement of the piezoelectric element 273, ink flows from the pump inlet channel 77 into the pressure chamber 276d. Simultaneously with the end of period T53, period T54 begins, and while period T54 continues, the potentials of the pump control signals 605a and 605b are maintained at 0V. In this embodiment, period T54 = 32ms. After the elapsed period T54, the potential of the pump control signal 605a transitions back to 3.3V for the duration of period T52. That is, control is repeatedly performed with periods T52, T53, and T54 forming one drive cycle T57. In other words, one drive cycle T57 includes a period T55 in which a potential difference is applied to the piezoelectric element 273, and a period T56 in which no potential difference is applied to the piezoelectric element 273.

[0091] (Effects of the fifth embodiment) According to this embodiment, the potential difference between the first electrode 272 and the second electrode 274 can be set to twice the absolute value of the pump drive voltage 607. That is, it is possible to make the volume displacement of the piezoelectric element 273 relatively large even with a relatively low pump drive voltage.

[0092] Specifically, the liquid discharge device 50 may include a boosting means and a bucking means. The boosting means supplies a boosted voltage obtained by boosting the drive voltage based on the drive reference voltage. The bucking means supplies a bucked voltage obtained by lowering the drive voltage based on the drive reference voltage. The magnitude of the potential of the boosted voltage and the magnitude of the potential of the bucked voltage may be controlled to be the same, and the direction of the boosted voltage and the direction of the bucked voltage may be controlled in opposite directions. With such operation, it is possible to make the potential difference between the first electrode 272 and the second electrode 274 twice the absolute value of the pump drive voltage 607.

[0093] (Sixth embodiment) In the sixth embodiment, descriptions of configurations similar to those in the first to fifth embodiments will be omitted as appropriate. The sixth embodiment differs from the first to fifth embodiments in that the pump drive circuit sends the pump drive signal 618 output from the boost circuit 433 to the pump output terminal 435 without going through the output switching circuit 424. Figure 18 shows an example of a pump drive circuit that drives the circulating pump 27 of Figure 6 according to the sixth embodiment. The boost circuit 433 in Figure 18 generates a pulsed pump drive signal 618. The pump drive signal 618 is output to the first electrode 272 via the first wiring 211a. In this embodiment, the second electrode 274 is connected to the ground terminal via the second wiring 211b. Next, the configuration of the boost circuit 433 will be described with reference to Figure 19.

[0094] (Outline of the configuration of the boost circuit 433) Figure 19 shows an example of the boost circuit 433 of Figure 18 according to the sixth embodiment. Compared to the boost circuit 423 of the first embodiment, the boost circuit 433 has an additional buck circuit. In this buck circuit, the inductor 722, which is a circuit element that realizes the boost circuit, is used as a common element, while the switching element 721b, diode 723b, and capacitor 724b function as the buck circuit. In other words, the boost circuit 433 has the functions of the boost circuit 423 of Figure 8 and the functions of the buck circuit 423b of Figure 15. Furthermore, the boost circuit 433 incorporates an NPN transistor 728 as a circuit that resets the output of the pump drive signal 618. Next, the operation overview of the boost circuit 433 will be described.

[0095] (Operation overview of boost circuit 433) As the potential of boost signal 616b remains at 0V and the potential of boost signal 616a alternates between 5V and 0V, charge accumulates in capacitor 724a, and the potential of pump drive signal 618 is boosted to 72V. Conversely, as the potential of boost signal 616a remains at 5V and the potential of boost signal 616b alternates between 5V and 0V, charge flows out of capacitor 724b, and the potential of pump drive signal 618 is stepped down to -72V. When the potential of reset signal 629 is 5V, NPN transistor 728 becomes conductive, and the potential of pump drive signal 618 becomes 0V.

[0096] Figure 20 illustrates the timing chart of the control signal for controlling the pump drive circuit according to the sixth embodiment. First, the potential of the pump drive reference voltage 614 transitions from 0V to 5V. As a result, the pump drive reference voltage 614 is applied to the boost circuit 433. Next, the potential of the boost signal 616b remains at 0V, and during period T62, the potential of the boost signal 616a transitions from 0V to 5V, repeating according to a certain rule. For example, the potential of the boost signal 616a repeats between 0V and 5V based on a constant duty cycle. As a result, the potential of the pump drive signal 618 output from the boost circuit 433 is boosted from 0V to 72V. During period T62, the potential of the pump drive signal 618, that is, the potential difference between the first electrode 272 and the second electrode 274 connected to the ground terminal, becomes 72V. This potential difference causes the volume of the piezoelectric element 273 to displace, and ink flows from the pump inlet channel 77 into the pressure chamber 276d. In this embodiment, a transition time T61 = 12 ms is assumed. Also, in this embodiment, a duration T62 = 16 ms is assumed.

[0097] Next, the potential of the boost signal 616a is maintained at 5V, and during period T63, the potential of the boost signal 616b transitions from 0V to 5V repeatedly according to a certain rule. For example, the potential of the boost signal 616b repeats between 0V and 5V based on a constant duty cycle. As a result, the potential of the pump drive signal 618 output from the boost circuit 433 is stepped down from 72V to -72V. During period T63, the potential of the pump drive signal 618, that is, the potential difference between the first electrode 272 and the second electrode 274 connected to the ground terminal, becomes -72V. Due to this potential difference, the volume of the piezoelectric element 273 is displaced, and ink flows out from the pressure chamber 276d to the pump outlet channel 78. In this embodiment, period T63 = 16ms is assumed.

[0098] Subsequently, during period T64, the boost signal 616a remains at 5V, the boost signal 616b remains at 0V, and the potential of the reset signal 629 transitions from 0V to 5V. Due to the reset signal, the pump drive signal 618 transitions from -72V to 0V. During period T64, no potential difference occurs between the first electrode 272 and the second electrode 274. Therefore, the displacement of the piezoelectric element 273 is eliminated. Consequently, ink flows from the pump inlet passage 77 into the pressure chamber 276d by the amount by which the volume displacement of the piezoelectric element 273 is eliminated. In this embodiment, period T64 = 32ms. After the elapsed period T64, the potential of the reset signal 629 transitions to 0V, and the potential of the boost signal 616a transitions from 0V to 5V during period T62, repeating according to a certain rule. In other words, control is repeatedly executed with periods T62, T63, and T64 as a single drive cycle T57.

[0099] (Effects of the sixth embodiment) As in this embodiment, it is also possible to drive the circulation pump 27 by alternately transitioning the potential of one electrode of the circulation pump 27 between a positive voltage and a negative voltage, thereby connecting the other electrode to the ground terminal.

[0100] Furthermore, during the first period, a positive voltage and a negative voltage may be supplied to either the first electrode 272 or the second electrode 274 for a certain period of time, while the voltage to the other electrode 274 may be maintained at zero potential. During the second period, the potential of the voltage supplied to each of the first electrode 272 and the second electrode 274 may be controlled to be the same potential. With this operation, the voltage supplied to either the first electrode 272 or the second electrode 274 is controlled. This makes it possible to realize a drive cycle T67 that includes a period T65 in which a potential difference is applied to the piezoelectric element 273 and a period T66 in which no potential difference is applied to the piezoelectric element 273.

[0101] (Seventh Embodiment) In the seventh embodiment, descriptions of configurations similar to those in the first to sixth embodiments will be omitted as appropriate. The seventh embodiment differs from the first to sixth embodiments in that the main body of the liquid discharge device 50 includes a signal generation unit 457. Figure 21 shows an example of a pump drive circuit that drives the circulation pump 27 of Figure 6 according to the seventh embodiment. The signal generation unit 457 in Figure 21 is composed of an FPGA (Field Programmable Gate Array). As shown in Figure 21, by providing the signal generation unit 457 separately from the CPU 400 that controls the main body of the liquid discharge device 50, the processing load can be distributed, making it possible to control the pump more precisely and relatively easily.

[0102] In other words, in addition to the CPU 400, a signal generation unit 457 may be newly provided to generate a pump control signal 635 and a boost signal 636. With such a configuration, the processing load can be distributed by providing it separately from the CPU 400 that controls the main body of the liquid discharge device 50, making it possible to control the pump more precisely and relatively easily.

[0103] (Eighth embodiment) In the eighth embodiment, descriptions of configurations similar to those in the first to seventh embodiments will be omitted as appropriate. The eighth embodiment differs from the first to seventh embodiments in that the pump drive circuit includes a signal generation unit 447. Figure 22 shows an example of a pump drive circuit that drives the circulation pump 27 of Figure 6 according to the eighth embodiment. As shown in Figure 22, in a system in which the circulation pump 27 is provided on the liquid discharge head 1, the wiring distance of the wiring connecting the signal generation unit 447, the boost circuit 443, and the output switching circuit 444 in Figure 22 can be shortened, and the number of electrical contacts can be reduced. That is, the quality of the pump drive signal can be improved.

[0104] In other words, the signal generation unit 447, which generates a boost signal 626 and a pump control signal 625, may be provided on the same circuit board as the boost circuit 443 and the output switching circuit 444. With such a configuration, the wiring length for electrically connecting the signal generation unit 447, the boost circuit 443, and the output switching circuit 44 can be shortened. Therefore, the wiring impedance can be reduced, and the quality of the pump drive signal can be improved.

[0105] <Other Embodiments> Although various examples and embodiments of this disclosure have been described above, the spirit and scope of this disclosure are not limited to the specific descriptions herein. This disclosure is not limited to the embodiments described above, and various modifications may be made. Furthermore, this disclosure may combine some of the embodiments described above as appropriate.

[0106] (Variation 1) For example, one example has been described in which the liquid discharge head 1 includes a boost circuit 423, or a boost circuit 423a and a buck circuit 423b, or a boost circuit 433, or a boost circuit 443, or a boost circuit 453, but it is not limited to this. For example, the liquid discharge head 1 may include a DC-DC converter. If the DC-DC converter includes a boost function, the DC-DC converter can implement the functions of the boost circuit 423, etc. Also, if the DC-DC converter includes a buck function, the DC-DC converter can implement the functions of the buck circuit 423b.

[0107] The disclosure of this embodiment includes configurations represented by the following liquid dispensing device.

[0108] <Configuration 1> A piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode, A drive control means controls the strain generated in the piezoelectric means in a drive cycle including a first period and a second period, while a drive voltage that generates strain in the piezoelectric means is supplied to the first electrode and the second electrode. A diaphragm means comprising a vibrating plate that vibrates in response to strain generated in the piezoelectric means, and a pressure chamber through which the vibration of the vibrating plate is transmitted, and which circulates the liquid flowing in and out of the pressure chamber due to the vibration of the vibrating plate, Equipped with, The first period includes a period during which the drive voltage supplied to either the first electrode or the second electrode is interrupted. The liquid dispensing device is characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode.

[0109] <Configuration 2> The liquid dispensing device according to configuration 1, characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode, during which the drive voltage is simultaneously supplied to each of the first and second electrodes.

[0110] <Structure 3> The drive control means is A first voltage control circuit that controls whether or not to interrupt the drive voltage supplied to the first electrode, A second voltage control circuit is electrically connected in parallel with the first voltage control circuit and controls whether or not to interrupt the drive voltage supplied to the second electrode, The liquid dispensing device according to configuration 2, characterized by comprising the above.

[0111] <Structure 4> The liquid dispensing device according to configuration 3, characterized in that the drive control means cuts off the drive voltage supplied to the second electrode by the second voltage control circuit while the drive voltage is supplied to the first electrode, and cuts off the drive voltage supplied to the first electrode by the first voltage control circuit while the drive voltage is supplied to the second electrode.

[0112] <Composition 5> The liquid dispensing device according to configuration 3, further comprising a boosting means for supplying the drive voltage, which has been boosted based on the drive reference voltage, at the same potential to both the first voltage control circuit and the second voltage control circuit.

[0113] <Composition 6> The first period includes a first interruption period in which the drive voltage supplied to the first electrode is interrupted, and a second interruption period in which the drive voltage supplied to the second electrode is interrupted. The liquid dispensing device according to configuration 5, characterized in that the drive control means controls the strain generated in the piezoelectric means in the order of a first interruption period, a second interruption period, and the second period as the drive cycle.

[0114] <Composition 7> The liquid dispensing device according to configuration 6, characterized in that the drive control means starts the second shut-off period simultaneously with the end of the first shut-off period.

[0115] <Structure 8> The liquid dispensing device according to configuration 5, characterized in that the drive control means controls the strain generated in the piezoelectric means in the following order: a first sub-cutoff period in which the drive voltage supplied to the first electrode in the first period is cut off; a third period corresponding to the second period; a second sub-cutoff period in which the drive voltage supplied to the second electrode in the first period is cut off; and a fourth period corresponding to the second period.

[0116] <Composition 9> The liquid dispensing device according to configuration 8, characterized in that, in the case of the third period and the fourth period, a time longer than the time required from the time the supply of the drive voltage to the first electrode is resumed until the drive voltage supplied to the first electrode reaches a certain potential when the drive voltage supplied to the second electrode is interrupted, and in the case of the drive voltage supplied to the second electrode, a time longer than the time required from the time the supply of the drive voltage to the second electrode is resumed until the drive voltage supplied to the second electrode reaches a certain potential when the drive voltage supplied to the second electrode is interrupted.

[0117] <Composition 10> The first interruption period is set to be longer than the time it takes for the potential of the drive voltage supplied to the first electrode to reach zero when the drive voltage supplied to the first electrode is interrupted. The liquid dispensing device according to configuration 6, characterized in that the second interruption period is set to be longer than the time it takes for the potential of the drive voltage supplied to the second electrode to reach zero potential when the drive voltage supplied to the second electrode is interrupted.

[0118] <Composition 11> The first sub-cutoff period is set to be longer than the time it takes for the potential of the drive voltage supplied to the first electrode to reach zero when the drive voltage supplied to the first electrode is cut off. The liquid dispensing device according to configuration 8, characterized in that the second sub-cutoff period is set to be longer than the time it takes for the potential of the drive voltage supplied to the second electrode to reach zero potential when the drive voltage supplied to the second electrode is cut off.

[0119] <Composition 12> The first interruption period is set to be a time shorter than the time required for the potential of the drive voltage supplied to the first electrode to reach zero when the drive voltage supplied to the first electrode is interrupted. The liquid dispensing device according to configuration 6, characterized in that the second interruption period is set to be a time shorter than the time during which the potential of the drive voltage supplied to the second electrode reaches zero when the drive voltage supplied to the second electrode is interrupted.

[0120] <Composition 13> The drive control means includes a boosting means that supplies a boosted voltage obtained by increasing the drive voltage based on the drive reference voltage, The drive control means is provided with a step-down means that supplies a step-down voltage obtained by reducing the drive voltage based on the drive reference voltage, Furthermore, The liquid dispensing device according to configuration 2, characterized in that the magnitude of the potential of the boosted voltage and the magnitude of the potential of the bucked voltage are controlled to be the same, and the direction of the boosted voltage and the direction of the bucked voltage are controlled to be opposite to each other.

[0121] <Composition 14> The liquid dispensing apparatus according to configuration 5, further comprising signal generation means for generating a control signal for controlling the drive control means and a boost signal for controlling the boosting means.

[0122] <Composition 15> The circuit board further includes the drive control means and the boosting means. The liquid dispensing device according to configuration 14, characterized in that the circuit board further includes the signal generation means.

[0123] <Composition 16> The liquid dispensing device according to configuration 1, characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode, during which the drive voltage supplied to each of the first and second electrodes is simultaneously cut off.

[0124] <Composition 17> A piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode, A drive control means for controlling the strain generated in the piezoelectric means during a drive cycle that includes a first period and a second period, A diaphragm means comprising a vibrating plate that vibrates in response to strain generated in the piezoelectric means, and a pressure chamber through which the vibration of the vibrating plate is transmitted, and which circulates the liquid flowing in and out of the pressure chamber due to the vibration of the vibrating plate, Equipped with, During the first period, a positive voltage and a negative voltage are supplied to either the first electrode or the second electrode for a certain period of time, while the voltage of the other electrode is maintained at zero potential. The liquid dispensing device is characterized in that no potential difference is generated between the first electrode and the second electrode during the second period.

[0125] <Composition 18> The liquid dispensing device according to configuration 17, characterized in that the potential of the voltage supplied to the first electrode and the second electrode is controlled to the same potential during the second period, during which no potential difference is generated between the first electrode and the second electrode. [Explanation of symbols]

[0126] 1. Liquid dispensing head 27 Circulation pump 53 Carriage 54 Ink circulation unit

Claims

1. A piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode, A drive control means controls the strain generated in the piezoelectric means in a drive cycle including a first period and a second period, while a drive voltage that generates strain in the piezoelectric means is supplied to the first electrode and the second electrode. A diaphragm means comprising a vibrating plate that vibrates in response to strain generated in the piezoelectric means, and a pressure chamber through which the vibration of the vibrating plate is transmitted, and which circulates the liquid flowing in and out of the pressure chamber due to the vibration of the vibrating plate, Equipped with, The first period includes a period during which the drive voltage supplied to either the first electrode or the second electrode is interrupted. The liquid dispensing device is characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode.

2. The liquid dispensing apparatus according to claim 1, characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode, and during which the drive voltage is simultaneously supplied to each of the first electrode and the second electrode.

3. The drive control means is A first voltage control circuit that controls whether or not to interrupt the drive voltage supplied to the first electrode, A second voltage control circuit is electrically connected in parallel with the first voltage control circuit and controls whether or not to interrupt the drive voltage supplied to the second electrode, The liquid dispensing device according to claim 2, characterized by comprising:

4. The liquid dispensing apparatus according to claim 3, characterized in that the drive control means interrupts the drive voltage supplied to the second electrode by the second voltage control circuit while the drive voltage is supplied to the first electrode, and interrupts the drive voltage supplied to the first electrode by the first voltage control circuit while the drive voltage is supplied to the second electrode.

5. The liquid dispensing device according to claim 3, further comprising a boosting means for supplying the drive voltage, which has been boosted based on the drive reference voltage, at the same potential to both the first voltage control circuit and the second voltage control circuit.

6. The first period includes a first interruption period in which the drive voltage supplied to the first electrode is interrupted, and a second interruption period in which the drive voltage supplied to the second electrode is interrupted. The liquid dispensing device according to claim 5, characterized in that the drive control means controls the strain generated in the piezoelectric means in the order of a first interruption period, a second interruption period, and the second period as the drive cycle.

7. The liquid dispensing device according to claim 6, characterized in that the drive control means starts the second shut-off period simultaneously with the end of the first shut-off period.

8. The liquid dispensing device according to claim 5, characterized in that the drive control means controls the strain generated in the piezoelectric means in the following order: a first sub-cutoff period in which the drive voltage supplied to the first electrode in the first period is cut off; a third period corresponding to the second period; a second sub-cutoff period in which the drive voltage supplied to the second electrode in the first period is cut off; and a fourth period corresponding to the second period.

9. The liquid dispensing device according to claim 8, characterized in that each of the third and fourth periods is set to be longer than the time required from the time the supply of the drive voltage to the first electrode is resumed until the drive voltage supplied to the first electrode reaches a certain potential when the drive voltage supplied to the first electrode is interrupted, and longer than the time required from the time the supply of the drive voltage to the second electrode is resumed until the drive voltage supplied to the second electrode reaches a certain potential when the drive voltage supplied to the second electrode is interrupted.

10. The first interruption period is set to be longer than the time it takes for the potential of the drive voltage supplied to the first electrode to reach zero when the drive voltage supplied to the first electrode is interrupted. The liquid dispensing device according to claim 6, characterized in that the second interruption period is set to be longer than the time it takes for the potential of the drive voltage supplied to the second electrode to reach zero potential when the drive voltage supplied to the second electrode is interrupted.

11. The first sub-cutoff period is set to be longer than the time it takes for the potential of the drive voltage supplied to the first electrode to reach zero when the drive voltage supplied to the first electrode is cut off. The liquid dispensing device according to claim 8, characterized in that the second sub-cutoff period is set to be longer than the time it takes for the potential of the drive voltage supplied to the second electrode to reach zero potential when the drive voltage supplied to the second electrode is cut off.

12. The first interruption period is set to be a time shorter than the time required for the potential of the drive voltage supplied to the first electrode to reach zero potential when the drive voltage supplied to the first electrode is interrupted. The liquid dispensing device according to claim 6, characterized in that the second interruption period is set to be a time shorter than the time during which the potential of the drive voltage supplied to the second electrode reaches zero when the drive voltage supplied to the second electrode is interrupted.

13. The drive control means includes a boosting means that supplies a boosted voltage obtained by increasing the drive voltage based on the drive reference voltage, The drive control means is provided with a step-down means that supplies a step-down voltage obtained by reducing the drive voltage based on the drive reference voltage, Furthermore, The liquid dispensing device according to claim 2, characterized in that the magnitude of the potential of the boosted voltage and the magnitude of the potential of the bucked voltage are controlled to be the same, and the direction of the boosted voltage and the direction of the bucked voltage are controlled to be opposite to each other.

14. The liquid dispensing apparatus according to claim 5, further comprising signal generation means for generating a control signal for controlling the drive control means and a boost signal for controlling the boosting means.

15. The circuit board further includes the drive control means and the boosting means. The liquid dispensing device according to claim 14, characterized in that the circuit board further includes the signal generation means.

16. The liquid dispensing apparatus according to claim 1, characterized in that the second period includes a period during which no potential difference is generated between the first electrode and the second electrode, during which the drive voltage supplied to each of the first and second electrodes is simultaneously cut off.

17. A piezoelectric means having a first electrode, a second electrode facing the first electrode, and a piezoelectric element disposed between the first electrode and the second electrode, A drive control means for controlling the strain generated in the piezoelectric means during a drive cycle that includes a first period and a second period, A diaphragm means comprising a vibrating plate that vibrates in response to strain generated in the piezoelectric means, and a pressure chamber through which the vibration of the vibrating plate is transmitted, and which circulates the liquid flowing in and out of the pressure chamber due to the vibration of the vibrating plate, Equipped with, During the first period, a positive voltage and a negative voltage are supplied to either the first electrode or the second electrode for a certain period of time, while the voltage of the other electrode is maintained at zero potential. The liquid dispensing device is characterized in that no potential difference is generated between the first electrode and the second electrode during the second period.

18. The liquid dispensing device according to claim 17, characterized in that the second period is a period during which no potential difference occurs between the first electrode and the second electrode, and the potential of the voltage supplied to the first electrode and the second electrode is controlled to be the same potential.

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