Liquid dispensing device, inspection device, and liquid dispensing head

Abstract

It should be possible to easily test whether a piezoelectric element is properly electrically connected or not. [Solution] The liquid dispensing device includes a liquid dispensing head and a detection means electrically connectable to the liquid dispensing head. The liquid dispensing head includes a circulation channel through which the liquid circulates and a circulation pump having a piezoelectric element that controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal. The detection means detects the electrical connection state of the piezoelectric element based on a discharge signal generated in conjunction with the discharge of the charge stored in the piezoelectric element by an electrical signal.

Description

[Technical Field]

[0001] The present disclosure relates to an inspection technology for liquid discharge heads. [Background Art]

[0002] Conventionally, ink circulation type inkjet heads (hereinafter, also referred to as liquid discharge heads) are known. Patent Document 1 discloses a technology in which ink stored in an ink tank (hereinafter, also referred to as liquid) is supplied to a liquid discharge head, a part of the ink is discharged, and the undischarged ink is returned to the ink tank. [Prior Art Document] [Patent Document]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2018-30350 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] Inside the liquid discharge head described in Patent Document 1, a piezoelectric pump (hereinafter, also referred to as a circulation pump) that conveys ink (hereinafter, also referred to as liquid) is provided. The circulation pump is driven by a drive signal generated by an electric substrate provided inside the liquid discharge head. In the manufacturing process of the liquid discharge head, it is complicated to perform an electrical connection inspection of the circulation pump after the circulation pump is assembled to the liquid discharge head, and therefore there is a demand for a simple configuration for the electrical connection inspection of the circulation pump. [Means for Solving the Problem]

[0005] A liquid dispensing device according to one aspect of the present disclosure comprises a liquid dispensing head and a detection means electrically connectable to the liquid dispensing head, wherein the liquid dispensing head includes a circulation channel through which liquid circulates and a circulation pump having a piezoelectric element that controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, and the detection means is characterized in that it detects the electrical connection state of the piezoelectric element based on a discharge signal that is generated in conjunction with the discharge of the charge stored in the piezoelectric element by the electrical signal. [Effects of the Invention]

[0006] According to this disclosure, it is possible to easily check whether a piezoelectric element is properly electrically connected or not. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows a schematic configuration example of a liquid dispensing device in the first embodiment. [Figure 2] This is an exploded perspective view of the liquid dispensing head in Figure 1 in the first embodiment. [Figure 3] This is a schematic diagram of the external appearance of the ink circulation unit in the first embodiment shown in Figure 2. [Figure 4] This is a schematic diagram of the circulation path in the liquid discharge head shown in Figure 1 in the first embodiment. [Figure 5] This figure shows an example of the wiring of the circulation pump in Figure 4 in the first embodiment. [Figure 6] This is a schematic cross-sectional view of the circulation pump in Figure 5 in the first embodiment. [Figure 7] This figure shows a schematic diagram of the pump drive circuit configuration for driving the circulation pump shown in Figure 6 in the first embodiment. [Figure 8] This figure shows another schematic diagram of the pump drive circuit that drives the circulation pump in Figure 6 in the first embodiment. [Figure 9] This figure shows an example of the circuit configuration of the boost circuit in Figures 7 and 8 in the first embodiment. [Figure 10]This figure shows an example of the circuit configuration of the output switching circuit in the first embodiment, as shown in Figures 7 and 8. [Figure 11] This is a timing chart of the control signals that control the pump drive circuit in Figures 7 and 8 of the first embodiment. [Figure 12] This diagram illustrates the operating principle for detecting the electrical connection state of the circulation pump and the capacitance of the piezoelectric element in the first embodiment. [Figure 13] This figure shows an example of a maximum value output circuit for obtaining the maximum value of the pump inspection signal in Figure 12 in the first embodiment. [Figure 14] This figure shows an example of an integration circuit for obtaining the integrated value of the pump inspection signal in Figure 12 in the first embodiment. [Figure 15] This figure shows a schematic diagram of the pump drive circuit configuration for driving the circulation pump shown in Figure 6 in the second embodiment. [Figure 16] This is a schematic diagram illustrating the configuration examples for each phase of assembly, inspection, and shipping of the liquid dispensing head in the third embodiment. [Modes for carrying out the invention]

[0008] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Note that the following embodiments are not limiting to the scope of this disclosure, and not all combinations of features described in the following embodiments are essential to the solutions of this disclosure. The same reference numerals are used for identical components.

[0009] (overview) Conventionally, printers employing various recording methods have been put into practical use as recording methods for recording images on recording media such as forms and long paper. For example, printers using thermal transfer methods, wire dot methods, thermal methods, inkjet methods and the like have been put into practical use. Among these various recording methods, inkjet printers have attracted attention due to their low running cost and low recording noise, and are used in a wide range of fields. In the following description, a recording medium to be recorded by an inkjet printer will be appropriately referred to as a recording medium.

[0010] An inkjet printer includes a liquid ejection head. The liquid ejection head includes an ejection element substrate. An ink ejection port is provided by a nozzle member on a surface of the ejection element substrate. An ejection energy generating element is disposed at a position corresponding to the ink ejection port. Ink droplets are ejected from the ejection port by driving the ejection energy generating element. An image is formed when the ink droplets land at desired positions on the recording medium.

[0011] In recent years, in the inkjet printer field that uses inkjet printers, even in liquid ejection head scanning printers, ink circulation type printers that can skillfully use special inks adapted to the recording medium have been demanded in order to output high-quality printed matter. In such a printer, for circulating ink, a configuration has been proposed in which an ink supply path and an ink recovery path are provided, and a differential pressure is generated between the ink supply path and the ink recovery path to obtain an ink circulating flow.

[0012] For example, a printer is disclosed that includes, in a liquid ejection head, a storage section that supplies ink to the liquid ejection head, a storage section that refluxes ink from the liquid ejection head, a circulation pump that conveys ink between the two storage sections, a pressure sensor, and a control circuit. In this printer, the control circuit performs control to drive the circulation pump in accordance with the output of the pressure sensor.

[0013] Incidentally, an electric substrate is provided in such a liquid discharge head. The electric substrate generates a drive signal for driving the circulation pump. The generated drive signal is transmitted to the circulation pump via an electrical connection portion electrically connected to the electric substrate in the liquid discharge head. Therefore, it is desirable that an inspection of whether the electrical connection between the electric substrate and the circulation pump is normally established is performed in the manufacturing process of the liquid discharge head.

[0014] However, after assembling the circulation pump to the liquid discharge head, providing an electrical connection point at a position where a signal having the same potential as that of the electrical connection portion can be detected allows direct detection of an electrical signal from the connection point, but inspecting the electrical connection state between the electric substrate and the circulation pump is complicated. Therefore, a simple inspection is desired. Furthermore, it is desirable that the inspection of the electrical connection state between the electric substrate and the circulation pump can be performed even after the liquid discharge head is mounted on a printer.

[0015] Accordingly, in the present disclosure, a liquid discharge apparatus includes a liquid discharge head and detection means electrically connectable to the liquid discharge head. The liquid discharge head includes a circulation flow path and a circulation pump. Liquid circulates through the circulation flow path. The circulation pump has a piezoelectric element, and controls the circulation flow rate of the liquid circulating through the circulation flow path by a shape change of the piezoelectric element in response to an electrical signal. The detection means detects an electrical connection state of the piezoelectric element based on a discharge signal generated when the electric charge stored in the piezoelectric element is discharged by the electrical signal. According to this configuration, the discharge signal generated when the electric charge is discharged from the piezoelectric element can be detected from outside the liquid discharge head. Therefore, whether the piezoelectric element is normally electrically connected can be easily inspected without providing an electrical connection point at a position where a signal having the same potential as that of the electrical connection portion electrically connected to the electric substrate in the liquid discharge head can be detected. In addition, with the above configuration, even after the liquid discharge head is mounted on the liquid discharge apparatus, measurement of the discharge signal and inspection of the electrical connection state of the piezoelectric element can be performed on the main body side of the liquid discharge apparatus.

[0016] Incidentally, a piezoelectric element is placed inside the circulation pump. The piezoelectric element generates a circulation flow of ink by changing shape in response to an electrical signal. Therefore, the circulation flow rate of the ink fluctuates according to the electrical capacitance of the piezoelectric element (hereinafter also referred to as piezoelectric capacitance). However, there may be manufacturing variations between individual piezoelectric elements. Therefore, even if a predetermined electrical signal is applied to the piezoelectric element, the circulation flow rate of the ink generated by the piezoelectric element may vary. It is desirable that the circulation flow rate of the ink be guaranteed to enable the removal of bubbles that form in the circulation channel through which the ink circulates. Alternatively, it is desirable that the circulation flow rate of the ink be guaranteed to enable normal ejection without being affected by ink evaporation, even in nozzles with low ejection frequency. For this purpose, it is desirable to obtain a constant circulation flow rate. Furthermore, if there is a large variation in piezoelectric capacitance, it is preferable to set the center value of the ink circulation flow rate higher. On the other hand, if the circulation flow rate is set uniformly high, in a system that heats the ink to a predetermined temperature, the increased circulation flow rate of the ink will cause the ink to cool down more easily, and it may be possible to consume more power to heat the ink. In other words, since the power consumption of the liquid discharge head increases, there is a concern that costs will rise if a power supply with even greater capacity is installed to cope with this increased power consumption. Therefore, it is sometimes desirable to maintain a constant circulation flow rate regardless of individual variations in piezoelectric capacity.

[0017] This disclosure allows for the measurement of the capacitance of a piezoelectric element by taking the time integral of a pump inspection signal obtained by dividing the potential of the discharge signal. Therefore, by controlling based on the measured capacitance of the piezoelectric element, it becomes possible to maintain a constant circulation flow rate regardless of individual variations in the capacitance of the piezoelectric elements. The disclosure will be explained in detail below.

[0018] (First Embodiment) Figure 1 is a diagram showing a schematic configuration example of a liquid dispensing device 50 in the 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 in Figure 1(a). 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 in Figure 1(a), the liquid dispensing head 1 is mounted on a carriage 53. The carriage 53 reciprocates along the 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 example) the main scanning direction. In other words, the liquid ejection device 50 constitutes a serial-type inkjet liquid ejection device by ejecting liquid from the liquid ejection head 1 onto the ejection medium P being transported in the transport direction Y while scanning the liquid ejection head 1 in direction X. 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 example) the XY plane specified by direction X and transport direction Y. In the following explanation, direction X, transport direction Y, and direction Z will be used with the same meaning as described above.

[0019] 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.

[0020] 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.

[0021] The CPU 400 in Figure 1(b) controls various aspects of 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 programs retrieved from ROM 401, 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 image data retrieved from the host device 500, the CPU 400 controls the head driver 1A. The head driver 1A controls the liquid dispensing 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 medium to be discharged P along the transport direction Y.

[0022] (Liquid dispensing head 1) Figure 2 is an exploded perspective view of the liquid discharge head 1 of Figure 1 in 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.

[0023] 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.

[0024] 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.

[0025] A contact surface is provided on the side of the flow channel member 110 opposite to the side where the joint 200 is located. The head board 210 is connected to the contact surface. 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 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 by ACF (Anisotropic conductive film) crimping. The head board 210 and the electrical wiring board 330 may also 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. The electrical signals received by the head board 210 are sent to the dispensing element board 310 via the electrical wiring board 330.

[0026] Furthermore, this disclosure works favorably even if the ink circulation unit 54 is located within the liquid ejection device but outside the liquid ejection head 1. However, in the configuration where the circulation pump 27 is located within the liquid ejection head 1, the pump capacity is limited due to the size constraints of the circulation pump 27, and therefore the effects of this disclosure are particularly obtained.

[0027] (Circulation channel) Figure 3 is a schematic diagram of the external appearance of the ink circulation unit 54 in Figure 2 in the first embodiment. One ink circulation unit 54 is provided for each color. The ink circulation unit 54 comprises a first regulator 24, a second regulator 28, a filter 23, and a circulation pump 27. Figure 4 is a schematic diagram of the circulation flow path in the liquid ejection head 1 in Figure 1 in the first embodiment. The circulation flow path in Figure 4 is for one color. The liquid ejection head 1 is provided with the circulation flow 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 ejection device 50. The first regulator 24 comprises a first valve chamber 25 and a first pressure control chamber 26. The first valve chamber 25 and the first pressure control chamber 265 are in communication via a valve (not shown). The second regulator 2 comprises a second valve chamber 29 and a second pressure control chamber 30. The second valve chamber 29 and the second pressure control chamber 30 are connected via a valve (not shown). The circulation pump 27 and the first pressure control chamber 26 are connected via a pump outlet passage 78. The first 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 second pressure control chamber 30 are connected via a recovery passage 76. A portion of the flow path member may constitute the recovery passage 76. The second pressure control chamber 30 and the circulation pump 27 are connected via a pump inlet passage 77. In other words, a circulation flow path is formed consisting of the first pressure control chamber 26, the supply passage 75, the flow path member 110, the recovery passage 76, the second pressure control chamber 30, the pump inlet passage 77, the circulation pump 27, and the pump outlet passage 78. Ink can circulate through this circulation flow path. Furthermore, the flow path member 110 and the discharge unit 300 constitute the discharge module 302. Furthermore, a bypass channel 79 is provided between the first pressure control chamber 26 and the second valve chamber 29, which bypasses the ink circulation channel from the first pressure control chamber 26 to the second valve chamber 29. Details of the bypass channel 79 will be described later. Next, the details of the circulation pump 27 will be explained, followed by the flow of ink circulating through the circulation channel.

[0028] (Drive mechanism of circulation pump 27) Figure 5 shows an example of the wiring of the circulation pump 27 in Figure 4 in the first embodiment. The liquid discharge device 50 includes a main board 230, a carriage board 220, and a head board 210. The main board 230 is provided on the body of the liquid discharge device 50. A 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 supplied 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 608, generated based on a pump control signal 605 and a pump drive voltage 607 generated from a pump drive reference voltage 604, is supplied to the circulation pump 27 via the harness 211. The circulation pump 27 is driven based on the pump drive signal 608. The liquid in the liquid discharge head 1 circulates due to the operation of the circulation pump 27. Details of the pump control signal 605, pump drive reference voltage 604, pump drive voltage 607, and pump drive signal 608 will be described later. Note that the head board 210 and the carriage board 220 may be electrically connected by fixing them using ACF crimping. Next, the configuration of the circulation pump 27 will be described.

[0029] (Internal configuration of the circulation pump 27) Figure 6 is a schematic cross-sectional view of the circulation pump of Figure 5 in the first embodiment. The circulation pump 27 comprises a pump housing 271, a diaphragm unit 276, a first electrode 272, a piezoelectric element 273, a second electrode 274, and a vibrating plate 275. The 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. The first wiring 211a is connected to the first electrode 272 via an electrical connection member 277a. The first wiring 211a is a signal medium that transmits the pump control signal 605a and the pump drive signal 608a to the circulation pump 27. The second wiring 211b is connected to the second electrode 274 via an electrical connection member 277b. The second wiring 211b is a signal medium that transmits the pump control signal 605b and the pump drive signal 608b to the circulation pump 27. In this embodiment, the electrical connection members 277a and 277b are solder, but are not limited to this. Conductive materials such as gold bushings may be used for the electrical connection members 277a and 277b. Details of the pump control signals 605a and 605b and the pump drive signals 608a and 608b will be described later with reference to Figures 10 and 11. The second electrode 274 has one surface in contact with the piezoelectric element 273 and the other surface 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. A concave pump housing 271 is provided so as to cover this laminate. Furthermore, a diaphragm unit 276 is provided on the side of the diaphragm 275 opposite to the side on which the 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. In other words, the pressure chamber 276d is positioned in close contact with the diaphragm 275. An inlet and an outlet are provided at the bottom of the diaphragm unit housing 276a. The valve body 276b (also referred to as the outlet valve body 276b) is positioned at the outlet.Valve body 276c (also referred to as inlet valve body 276c) is positioned at the inlet. Valve body 276b functions as a check valve that can move freely in response to the outflow of liquid from the pressure chamber 276d. Valve body 276c functions as a check valve that can move freely in response to the inflow of liquid into the pressure chamber 276d. Opposite valve body 276b, the pump outlet passage 78 shown in Figure 5 is positioned via the outlet. Opposite valve body 276c, the pump inlet passage 77 shown in Figure 5 is positioned via the inlet. Next, the flow of ink will be explained using Figure 5.

[0030] (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 first valve chamber 25. As the ink supplied to the first valve chamber 25 flows into the first pressure control chamber 26, the 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.

[0031] By applying a voltage to the piezoelectric element 273 in Figure 6, a potential difference is generated, causing the piezoelectric element 273 to vibrate. This vibration moves the diaphragm 275, changing the volume inside the pressure chamber 276d and 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, we return to Figure 4. Driven by the circulation pump 27 in Figure 4, the ink whose pressure is controlled inside the first 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. The discharge element substrate 310 is equipped with a discharge element. The 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. The ink that passes through the pressure chamber inside the discharge element and is discharged into the recovery channel 76 is supplied to the second pressure control chamber 30. In addition, ink supplied to the second valve chamber 29 via the bypass channel 79 is supplied to the second pressure control chamber 30, which is connected to the second valve chamber 29 via a valve. Therefore, the second pressure control chamber 30 is supplied with ink from both the recovery channel 76 and the bypass channel 79. The ink supplied to the second 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 first pressure control chamber 26 via the pump outlet passage 78. In this way, the ink circulates through the ejection element formed on the ejection element substrate 310 via the circulation pump 27. In other words, the viscosity of the ink near the ejection element can be suppressed by the configuration of the circulation passage. The circulation passage is not limited to a configuration that passes through the ejection element. For example, the circulation passage may be configured to circulate the ink inside the ejection unit 300, as long as it is within a range that effectively suppresses the viscosity of the ink near the ejection element.

[0032] The ejection unit 300 is equipped with a temperature sensor (not shown) and a heating element. The CPU 400 monitors the output value of the temperature sensor provided in the ejection unit 300 and drives the heating element as appropriate. This operation makes it possible to maintain the temperature of the ejection unit 300 in a state suitable for liquid ejection. Furthermore, although this disclosure works even without a temperature sensor and heating element, when they are present, the power required for maintaining the temperature by the heating element increases as the ink circulation flow rate increases. Therefore, the effects of this disclosure can be particularly realized. Next, the first to third use cases regarding the inflow and outflow of ink will be explained using Figure 6.

[0033] (First use case) Let's describe a first 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.

[0034] (Second use case) A second use case in which ink flows out from the pressure chamber 276d is described. 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 passage 78.

[0035] (Third use case) A third use case will be described in which neither ink flows into nor out of the pressure chamber 276d. Assume that no potential difference is generated between the first electrode 272 and the second electrode 274. In this assumption, the piezoelectric element 273 and the diaphragm 275 are not displaced in either the expansion or contraction direction into the pressure chamber 276d. Therefore, neither ink flows into nor out of the diaphragm unit 276.

[0036] Specifically, by periodically changing the potential difference between the first electrode 272 and the second electrode 274, the circulation pump 27 allows ink to flow in from the pump inlet channel 77 and to flow out from the pump outlet channel 78. In such a circulation pump 27, for example, manufacturing variations in the piezoelectric element 273 may affect the fluid delivery capacity of the circulation pump 27. Specifically, the capacitance of the piezoelectric element 273 may affect the displacement speed of the piezoelectric element 273 when a constant potential difference is applied between the first electrode 272 and the second electrode 274. Therefore, manufacturing variations in the piezoelectric element 273 may affect the fluid delivery capacity of the circulation pump 27. 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.

[0037] (Pump drive circuit) Figure 7 is a schematic diagram of the pump drive circuit configuration for driving the circulation pump 27 shown in Figure 6 in the first embodiment. The main body of the liquid discharge device 50 includes a CPU 400, a power supply 410, and a head output terminal 421, as well as a pump inspection circuit 480. The liquid discharge head 1 includes an ink circulation unit 54, a head input terminal 422, a boost circuit 423, an output switching circuit 424, a pump output terminal 425, as well as a shunt resistor r and a pump-side resistor R. The head output terminal 421 supplies various signals and various voltages to the head input terminal 422. Examples of various signals include a pump control signal 605 and a boost signal 606. Examples of various voltages include a pump drive reference voltage 604. Details of the pump control signal 605, boost signal 606, and pump drive reference voltage 604 will be described later. The head input terminal 422 also supplies a discharge signal 900 to the head output terminal 421. Details of the discharge signal 900 will be described later. Furthermore, among the head input terminal 422, boost circuit 423, output switching circuit 424, pump output terminal 425, shunt resistor r, and pump-side resistor R, the boost circuit 423, output switching circuit 424, shunt resistor r, and pump-side resistor R function as the pump drive circuit.

[0038] A print signal 601, as image data, is input from the host device 500 to the CPU 400 included in the main body of the liquid dispensing device 50. Meanwhile, a power supply voltage 602 is supplied from the external power supply 510 to the power supply unit 410 included in the main body of the liquid dispensing device 50. Upon receiving the print signal 601 from the host device 500, the CPU 400 activates a power control signal 603 to the power supply unit 410. In this embodiment, the power control signal 603 is assumed to be high active. That is, it is assumed that the power supply unit 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 unit 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 24V. Upon receiving a print signal 601 from the host device 500, the CPU 400 outputs a pump control signal 605 and a boost signal 606 to the head output terminal 421.

[0039] (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.

[0040] (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 24V. Specifically, the head output terminal 421 is a terminal provided on the main body side of the liquid discharge device 50. The head output terminal 421 supplies various signals and voltages to the head input terminal 422 provided on the liquid discharge head 1 side. In this embodiment, the highest voltage output from the head output terminal 421 is assumed to be 24V. Therefore, the voltage output from the head output terminal 421 is assumed to be a relatively low voltage. The head output terminal 421 supplies the pump control signal 605, the boost signal 606a, and the pump drive reference voltage 604 to the head input terminal 422. The head input terminal 422 supplies the pump drive reference voltage 604 supplied from the head output terminal 421 to the voltage input terminal 1001 of the boost circuit 423. The voltage input terminal 1001 will be described later with reference to Figure 9. The head input terminal 422 supplies the boost signal 606 supplied from the head output terminal 421 to the signal input terminal 1002 of the boost circuit 423. The signal input terminal 1002 will be described later with reference to Figure 9. The boost circuit 423 converts the 24V pump drive reference voltage 604 to a predetermined voltage necessary for sufficient displacement of the piezoelectric element 273 provided on the circulation pump 27, according to the boost signal 606. For example, the boost circuit 423 converts the 24V pump drive reference voltage 604 to a voltage of 72V. That is, in this embodiment, it is assumed that the set center voltage for boosting is 72V. The boost circuit 423 outputs the voltage converted to 72V as the pump drive voltage 607 to the output switching circuit 424. A specific circuit example of the boost circuit 423 will be described later with reference to Figure 9.

[0041] (Output switching circuit 424) 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 described later with reference to Figure 10.

[0042] (Pump output terminal 425) 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 at the pump drive frequency. 72V is set as the pump drive voltage 607 of the circulation pump 27. The pump drive signals 608a and 608b output from the pump output terminals 425a and 425b, respectively, are input to the pump input terminal 426 provided on the ink circulation unit 54 via harnesses 211a and 211b.

[0043] (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. The driving of the circulation pump 27 will be described later with reference to Figure 11.

[0044] Here, we will describe the features of this disclosure. The features of this disclosure include a configuration that allows for easy inspection of the electrical connection state of the circulation pump 27 and the piezoelectric capacitance of the piezoelectric element 273. In order to easily inspect the electrical connection state of the circulation pump 27 and the piezoelectric capacitance of the piezoelectric element 273, the charge stored in the piezoelectric element 273 is discharged. Next, we will describe the outline of the discharge path for discharging the charge stored in the piezoelectric element 273.

[0045] (Overview of the discharge route) When the circulation pump 27 is driven by the pump drive signal 608, the piezoelectric element 273 is repeatedly charged and discharged. A feature of this disclosure is that the electrical connection state of the circulation pump 27 and the electrical capacity (piezoelectric capacitance) of the piezoelectric element 273 are detected by detecting the current that flows when the charge stored in the piezoelectric element 273 is discharged as a discharge signal 900.

[0046] The charge stored in the piezoelectric element 273 is controlled by the output switching circuit 424 in the pump drive circuit and discharged to the GND side of the liquid discharge device 50 or inspection device 5000 via the electrical connection part 212. Using this discharge signal 900 as the source signal, the pump inspection circuit 480, provided on the liquid discharge device 50 or inspection device 5000 side, detects the electrical connection state of the circulation pump 27 and the electrical capacitance (piezoelectric capacitance) of the piezoelectric element 273. Alternatively, a signal with a potential lower than that of the discharge signal 900 may be supplied to the pump inspection circuit 480. Lowering the potential below that of the discharge signal 900 lowers the potential of the signal supplied to the main body of the liquid discharge device 50, enabling safer operation.

[0047] In other words, the head output terminal 421 and the head input terminal 422 constitute the electrical connection terminal group in this embodiment. This electrical connection terminal group electrically connects the liquid discharge head 1 and the liquid discharge device 50, and also makes the liquid discharge head 1 detachable. Similarly, in the inspection device 5000, this electrical connection terminal group electrically connects the liquid discharge head 1 and the liquid discharge device 50, and also makes the liquid discharge head 1 detachable. Next, an example in which a signal lowered to the potential of the discharge signal 900 is supplied to the pump inspection circuit 480 will be explained using Figure 8.

[0048] Figure 8 shows another schematic diagram of the pump drive circuit that drives the circulation pump 27 shown in Figure 6 in the first embodiment. The differences between Figure 8 and Figure 7 will be explained in detail later using Figure 10, but in the discharge path from the circulation pump 27, a pump-side resistor R is provided on the circulation pump 27 side and a shunt resistor r is provided on the GND side. The pump-side resistor R and the shunt resistor r are connected in series. The voltage signal output from the signal output terminal 1020 (described later in Figure 10) between the pump-side resistor R and the shunt resistor r is output as a pump inspection signal 901. The pump inspection signal 901 is supplied to the pump inspection signal input terminal 481 provided on the main end side of the liquid discharge device 50 via the pump inspection signal output terminal 482 provided on the liquid discharge head 1. The pump inspection signal 901 supplied to the pump inspection signal input terminal 481 is supplied to the pump inspection circuit 480.

[0049] Furthermore, the features of this disclosure are applicable to the liquid dispensing device 50. Alternatively, the features of this disclosure are also applicable to the inspection device 5000 in the manufacturing process of the liquid dispensing head 1. The configuration of the inspection device 5000 is the same as that of the liquid dispensing device 50. In this embodiment, as will be described in detail later, an example is shown in which a pump drive circuit that generates a pump drive signal 608 for the circulation pump 27 is provided in the liquid dispensing head 1, but it is not limited to this. For example, such a pump drive circuit may be provided on the main body side of the liquid dispensing device 50. Alternatively, such a pump drive circuit may be provided in the inspection device.

[0050] (Boost circuit 423) Figure 9 shows an example of the circuit configuration of the boost circuit 423 in Figures 7 and 8 in the first embodiment. In the example in Figure 9, the boost circuit 423 includes a bypass capacitor 705, an inductor 701, a switching element 702, a diode 703, and a capacitor 704. 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 9, 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. Note that the GND side means the side at the same potential as the ground terminal.

[0051] (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 1001 of the boost circuit 423. The pump drive reference voltage 604 is applied to the voltage input terminal 1001 of the boost circuit 423. One terminal of the inductor 701 is also connected to the voltage input terminal 1001 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 1002 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. Additionally, the cathode of diode 703 is connected to the voltage output terminal 1030. The voltage output terminal 1030 of the boost circuit 423 can output the pump drive voltage 607.

[0052] (Operation of boost circuit 423) When the potential of the boost signal 606 transitions from ground potential to the active potential of 24V, the switching element 702 becomes conductive. Therefore, when the pump drive reference voltage 604 is applied to the voltage input terminal 1001 of the boost circuit 423, current flows from the voltage input terminal 1001 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, the boost signal 606 causes the switching element 702 to repeatedly switch between a conductive and non-conductive state, causing charge to flow into the capacitor 704 and be stored. 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 boost signal 606 is input to the switching element 702 so that the pump drive reference voltage 604 becomes 72V. Note that the boost circuit 423 is not limited to the example in Figure 9. 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.

[0053] Figure 10 shows an example of the circuit configuration of the output switching circuit 424 in Figures 7 and 8 in 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 via the signal output terminal 1010 based on the input of a pump control signal 605a via the signal input terminal 1003 when the pump drive voltage 607 is input via the voltage input terminal 1031. 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 via the signal output terminal 1011 based on the input of a pump control signal 605b via the signal input terminal 1004, while the pump drive voltage 607 is input via the voltage input terminal 1031. The second voltage control circuit 424b includes a b signal system corresponding to the second electrode 274. The b signal system controls the output of the 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.

[0054] (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.

[0055] (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 of the pump drive signal 608a. As a result, transistor 802a becomes active, and a voltage at the same potential as 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.

[0056] (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 potential between the emitter of transistor 802a and the emitter of transistor 803a is at ground potential. On the other hand, since the potential of the base of transistor 802a and the potential of the emitter of transistor 802a are at the same potential, transistor 802a becomes open. Based on the above, 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.

[0057] (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 located 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 second voltage control circuit 424b may be FETs.

[0058] (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.

[0059] (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.

[0060] Based on the above, the output switching circuit 424 alternately switches the potential of the pump control signal 605a and the potential of the pump control signal 605b to the active potential and outputs them, thereby alternately outputting the pump drive signal 608a and the pump drive signal 608b. Next, the details of the discharge path will be explained.

[0061] (Details of the discharge route) Transistors 802a, 803a, and 805a alternately control the terminal voltage of the piezoelectric element 273 between a high state and a low state. When the terminal voltage of the circulation pump 27 is reduced to a low state, the charge stored in the piezoelectric element 273 is discharged. That is, the discharge signal 900 flows along the path indicated by the dashed arrow in Figure 10. A pump-side resistor R and a shunt resistor r are arranged in series in the discharge path. A signal output terminal 1020 is provided between the pump-side resistor R and the shunt resistor r. Therefore, the potential of the discharge signal 900 can be divided by the pump-side resistor R and the shunt resistor r and output. Consequently, the potential of the pump inspection signal 901 output from the signal output terminal 1020 is the potential obtained by dividing the potential of the discharge signal 900 and outputting it. Note that there is at least one circuit configuration in the discharge path in which the pump-side resistor R and the shunt resistor r are connected in series. Therefore, multiple sets of circuit configurations in which a pump-side resistor R and a shunt resistor r are connected in series may exist in the discharge path. If multiple sets exist, each set is connected in series. Thus, the more sets of circuit configurations in which a pump-side resistor R and a shunt resistor r are connected in series, the lower the current value of the discharge signal 900 becomes.

[0062] Furthermore, a high-voltage signal is often required for the drive voltage Vp of the pump drive signal 608 input to the piezoelectric element 273. However, in cases where external contact connection is possible, such as with the pump inspection signal 901, it is desirable to set the drive voltage Vp to a threshold voltage of 42.4V or less, taking into consideration the impact on the outside. For this reason, it is desirable that the relationship between the drive voltage Vp, the pump-side resistance R, and the shunt resistance r satisfies the following equation (1).

[0063] r / (R+r)×Vp ≤ 42.4V (1)

[0064] Considering the degree of freedom in selecting elements based on their voltage ratings, it is more desirable for the pump inspection circuit 480 to satisfy the relationship in equation (2) below.

[0065] r / (R+r)×Vp ≤ 5V (2)

[0066] The threshold voltage of 5V can be changed as appropriate depending on the device configuration that implements the pump inspection circuit 480. Next, the operation of the circulation pump 27 will be described.

[0067] (Driving the circulation pump 27) Figure 11 is a timing chart of the control signals that control the pump drive circuits in Figures 7 and 8 in the first embodiment. First, the potential of the pump drive reference voltage 604 transitions from 0V to 24V. This transition applies the pump drive reference voltage 604 to the boost circuit 423. Next, the potential of the boost signal 606 transitions from 0V to 24V, repeating according to a certain rule. For example, the potential of the boost signal 606 repeats between 0V and 24V based on a constant duty cycle. This repetition increases the potential of the pump drive voltage 607 output from the boost circuit 423 from 0V to 72V. The boosted pump drive voltage 607 is applied to the output switching circuit 424. Within the output switching circuit 424, with the application of the pump drive voltage 607, the potentials of the pump drive signals 608a and 608b rise to 72V, becoming the same potential as the pump drive voltage 607.

[0068] In this embodiment, the potentials of the various signals between the liquid discharge head 1 and the liquid discharge device 50 are relatively low. The various voltages between the liquid discharge head 1 and the liquid discharge device 50 are also relatively low. Therefore, if the electrical connection configuration detects the pump inspection signal 901 from the liquid discharge head 1, a configuration for high-voltage countermeasures becomes unnecessary, making it possible to reduce the size and simplify the configuration. Next, the discharge signal 900 and the pump inspection signal 901, which are features of this disclosure, will be specifically explained with reference to Figure 12.

[0069] Figure 12 illustrates the operating principle for detecting the electrical connection state of the circulation pump 27 and the capacitance of the piezoelectric element 273 in the first embodiment. As described above, when the pump drive signals 608a and 608b are input to the circulation pump 27, the terminal voltage of the piezoelectric element 273 is controlled to a Low state and a High state. When the potential of the pump control signal 605b is in the High state and the potential of the pump control signal 605a is in the Low state, one end of the piezoelectric element is suspended by the drive voltage Vp and the other end is connected to ground. That is, it is in a state where it receives charge and discharges to ground.

[0070] On the other hand, when the potentials of the pump control signals 605a and 605b are in a low state, the terminal voltage of the piezoelectric element 273 is suspended by the drive voltage Vp, and charge continues to build up. If this state continues for a certain period of time, the piezoelectric element 904 will reach a charge saturation state, and no further charge will be stored.

[0071] In this way, the potential of the pump control signal 605a is transitioned to a high state and the potential of the pump control signal 605b is transitioned to a low state so that the charge stored in the piezoelectric element 273 moves from a saturated state to a low state at one end (the side connected to the pump-side resistor R). This transition causes the discharge signal 900 to flow through the pump-side resistor R and the shunt resistor r. This generates the pump inspection signal 901. In other words, the CPU 400 controls the system to wait for the potential of the pump control signal 605a to transition to a high state and the potential of the pump control signal 605b to a low state until the charge stored in the piezoelectric element 273 reaches a saturated state.

[0072] The maximum voltage of the pump inspection signal 901, which flows instantaneously when the charge stored in the piezoelectric element 273 is discharged from a saturated state, is constant regardless of the capacitance of the piezoelectric element 273. Therefore, by detecting the maximum value of the voltage of the pump inspection signal 901, it is possible to determine the number of connections of the piezoelectric element 273. In other words, it is possible to perform an electrical connection test of the circulation pump 27. The current of the discharge signal 900 and the voltage of the pump inspection signal 901, which flow instantaneously when the charge stored in the piezoelectric element 273 is discharged from a saturated state, have time constants that change according to the capacitance of the piezoelectric element 904. This is due to the difference in the amount of charge stored inside the piezoelectric element 273. Therefore, by taking the integral value of the current of the pump inspection signal 901, it is possible to detect the capacitance of the piezoelectric element 273.

[0073] Figure 13 shows an example of a maximum value output circuit for obtaining the maximum voltage of the pump inspection signal 901 in Figure 12 in the first embodiment. The maximum value output circuit in Figure 13 is a circuit that detects the maximum voltage of the pump inspection signal 901 input from the signal input terminal 1005 and holds it for a certain period of time. The maximum value output circuit in Figure 13 includes an operational amplifier, a capacitor, and a diode. When the voltage of the pump inspection signal 901 reaches its peak value, the diode conducts in the forward direction and charges the capacitor. At this time, the voltage across the terminals of the capacitor becomes equal to the maximum voltage of the pump inspection signal 901. Subsequently, when the voltage of the pump inspection signal 901 falls below the maximum value, the diode is biased in the reverse direction and stops conducting. As a result, the capacitor continues to hold the charged voltage. By outputting this held voltage, the maximum voltage of the pump inspection signal 901 is detected and the connection of the circulation pump 27 is checked.

[0074] Figure 14 shows an example of an integration circuit for obtaining the integral value of the current of the pump inspection signal 901 in Figure 12 in the first embodiment. The integration circuit in Figure 14 includes an operational amplifier. A capacitor is also placed on the feedback side of the inverting amplifier. With this circuit configuration, the result of the time integration of the input waveform of the current of the pump inspection signal 901 input from the signal input terminal 1006 can be output from the signal output terminal 1022. Furthermore, an inverting amplifier circuit is placed after the integration circuit in Figure 14. This makes it possible to output a positive integral value. By obtaining this integral output, it is possible to obtain an output corresponding to the capacitance of the piezoelectric element 904.

[0075] As described above, the configuration of this disclosure employs an indirect inspection method using a resistor provided in the charge discharge path and a pump inspection circuit 480, without directly making contact between the terminals of the piezoelectric element 273. This makes it possible to easily measure the electrical connection state of the circulation pump 27 and the electrical capacitance of the piezoelectric element 273.

[0076] Furthermore, if this inspection method is introduced to the inspection device 5000 in the manufacturing process of the liquid discharge head 1, electrical assurance at the time of shipment can be easily implemented. In addition, if this inspection method is introduced to the liquid discharge device 50 in the manufacturing process of the liquid discharge head 1, the following becomes possible: Firstly, it becomes possible to detect electrical connection abnormalities after the liquid discharge head 1 has been installed on the liquid discharge device 50 side and stop the device due to the error. Secondly, it becomes possible to detect the electrical capacitance of the piezoelectric element 273 on the liquid discharge device 50 side and control the pump drive according to the electrical capacitance of the piezoelectric element 273 to maintain a constant liquid circulation flow rate. Thirdly, since the electrical capacitance of the piezoelectric element 273 can be detected, it is also possible to control the device while taking into account manufacturing variations of the piezoelectric element 273.

[0077] (Second embodiment) Figure 15 is a schematic diagram of the pump drive circuit configuration for driving the circulation pump 27 shown in Figure 6 in the second embodiment. This embodiment differs from the first embodiment in that the pump drive circuit that generates the pump drive signals 608a and 608b for the circulation pump 27 is provided on the main body side of the liquid discharge device 50 or the main body side of the inspection device 5000. The differences from the first embodiment will be mainly described below.

[0078] Pump drive signals 608a and 608b generated on the main body side of the liquid discharge device 50 or the inspection device 5000 are input to the liquid discharge head 1 via the head output terminal 421 and the head input terminal 422, and are supplied to the circulation pump 27. That is, the head output terminal 421 and the head input terminal 422 constitute the electrical connection terminal group in this embodiment. This electrical connection terminal group electrically connects the liquid discharge head 1 and the liquid discharge device 50, and also makes the liquid discharge head 1 detachable. Similarly in the inspection device 5000, this electrical connection terminal group electrically connects the liquid discharge head 1 and the liquid discharge device 50, and also makes the liquid discharge head 1 detachable.

[0079] The charge stored in the piezoelectric element 904 is discharged to ground via a discharge path, similar to the first embodiment. The discharge path is similar to the first embodiment in that the pump-side resistor R and the shunt resistor r are connected in series. However, in this embodiment, the pump-side resistor R is located inside the liquid discharge head 1. The shunt resistor r, on the other hand, is located on the main body side of the liquid discharge device 50 or the inspection device 5000. The placement of the pump-side resistor R and the shunt resistor r is not limited; they may be located inside the liquid discharge head 1 or on the main body side of the liquid discharge device 50. Alternatively, both the pump-side resistor R and the shunt resistor r may be located on the main body side of the liquid discharge device 50. Furthermore, the placement of the pump inspection circuit 480 is also not limited; the pump-side resistor R, the shunt resistor r, and the pump inspection circuit 480 may all be located inside the liquid discharge head 1.

[0080] (Third embodiment) Figure 16 is a schematic diagram illustrating the configuration examples for each phase of assembly, inspection, and shipment of the liquid dispensing head 1 in the third embodiment. Phase (I) shows the phase in which the liquid dispensing head 1 is manufactured on the production line. Phase (II) shows the phase in which the manufactured liquid dispensing head 1 is mounted on the inspection device 5000 and undergoes electrical connection testing. Phase (III) shows the phase in which the liquid dispensing head 1 that has passed the inspection is incorporated into the liquid dispensing device 50 and shipped. Thus, after the liquid dispensing head 1 is manufactured, an electrical connection test is performed on the inspection device 5000, and those that pass are incorporated into the liquid dispensing device 50. Therefore, the electrical connection test of the liquid dispensing device 50 can be performed in phase (II), and can also be performed on the liquid dispensing device 50 after shipment. It is possible to detect whether or not the electrical connection state of the liquid dispensing head 1 is faulty with a simple configuration before shipment. Furthermore, even after shipment, it is possible to detect whether or not the electrical connection state of the liquid dispensing head 1 is faulty with a simple configuration in the liquid dispensing device 50.

[0081] (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.

[0082] (Variation 1) For example, one example in which the liquid discharge head 1 includes a boost circuit 423 has been described, 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 realize the functions of the boost circuit 423, etc.

[0083] (Modification 2) Furthermore, while the first embodiment described an example in which a discharge path is provided in signal system a, the invention is not limited to this. A discharge path may also be provided in signal system b. In other words, it is sufficient for a discharge path to be provided in either signal system a or signal system b.

[0084] The disclosure of this embodiment includes configurations represented by the following liquid dispensing device, inspection device, and liquid dispensing head.

[0085] <Configuration 1> Liquid dispensing head and A detection means electrically connectable to the liquid discharge head, Equipped with, The aforementioned liquid dispensing head is A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, Includes, The liquid dispensing device is characterized in that the detection means detects the electrical connection state of the piezoelectric element based on a discharge signal generated in conjunction with the discharge of the charge stored in the piezoelectric element by the electrical signal.

[0086] <Configuration 2> The liquid dispensing device according to configuration 1, further comprising a group of electrical connection terminals that electrically connect the liquid dispensing head and the detection means, and that allow the liquid dispensing head to be attached and detached.

[0087] <Structure 3> Liquid dispensing head and A detection means electrically connectable to the liquid discharge head, A group of electrical connection terminals electrically connects the liquid dispensing head and the detection means, and allows the liquid dispensing head to be attached and detached. Equipped with, The aforementioned liquid dispensing head is A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, Includes, The inspection device is characterized in that the detection means detects the electrical connection state of the piezoelectric element based on a discharge signal generated in conjunction with the discharge of the charge stored in the piezoelectric element by the electrical signal.

[0088] <Structure 4> The piezoelectric element further comprises a discharge path for discharging the charge stored in the piezoelectric element, The aforementioned discharge path is Pump side resistance, A shunt resistor connected in series with the aforementioned pump-side resistor, A signal output terminal is provided between the pump-side resistor and the shunt resistor, which divides the potential of the discharge signal flowing through the discharge path and outputs it as a pump inspection signal. Includes, The pump-side resistor has one end connected to the piezoelectric element and the other end connected to the shunt resistor. The inspection apparatus according to configuration 3, characterized in that the shunt resistor has one end connected to the pump-side resistor and the other end connected to ground.

[0089] <Composition 5> The inspection apparatus according to configuration 4, characterized in that the pump-side resistor is provided in the liquid discharge head.

[0090] <Composition 6> The inspection apparatus according to configuration 4, characterized in that the pump-side resistor and the shunt resistor are provided in the liquid discharge head.

[0091] <Composition 7> The inspection apparatus according to configuration 4, characterized in that the pump-side resistor is provided on the liquid discharge head, and the shunt resistor is provided outside the liquid discharge head.

[0092] <Structure 8> The inspection apparatus according to configuration 5, further comprising a boost circuit that increases the drive voltage for driving the circulation pump to a threshold voltage.

[0093] <Composition 9> The inspection apparatus according to configuration 8, characterized in that the threshold voltage is set to 42.4V or less.

[0094] <Composition 10> If the threshold voltage is Vp, the pump-side resistance is R, and the shunt resistance is r, r / (R+r)×Vp ≤ 42.4V The inspection apparatus according to configuration 9, characterized in that it satisfies the conditions.

[0095] <Composition 11> If the threshold voltage is Vp, the pump-side resistance is R, and the shunt resistance is r, r / (R+r)×Vp ≤ 5V The inspection apparatus according to configuration 9, characterized in that it satisfies the conditions.

[0096] <Composition 12> The inspection apparatus according to configuration 4, characterized in that the discharge path includes at least one set of pump-side resistors and shunt resistors.

[0097] <Composition 13> The system further comprises a maximum value detection means for detecting the maximum value of the pump inspection signal, The inspection apparatus according to configuration 4, characterized in that the detection means detects the number of connected piezoelectric elements based on the maximum value.

[0098] <Composition 14> The pump-side resistor and the shunt resistor are arranged between the piezoelectric element and the ground. The inspection device according to configuration 4, further comprising control means for sending the discharge signal from the piezoelectric element to the ground when detecting the pump inspection signal.

[0099] <Composition 15> The inspection apparatus according to configuration 14, characterized in that the control means does not send the discharge signal until the charge stored in the piezoelectric element is saturated.

[0100] <Composition 16> The inspection apparatus according to configuration 14, characterized in that the control means obtains the integral value until the potential of the discharge signal becomes zero.

[0101] <Composition 17> A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, A signal output terminal that outputs a discharge signal generated when the charge stored in the piezoelectric element is discharged by the aforementioned electrical signal, A liquid dispensing head characterized by including [the following]. [Explanation of Symbols]

[0102] 1. Liquid dispensing head 27 Circulation pump

Claims

1. Liquid dispensing head and A detection means electrically connectable to the liquid discharge head, Equipped with, The aforementioned liquid dispensing head is A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, Includes, The liquid dispensing device is characterized in that the detection means detects the electrical connection state of the piezoelectric element based on a discharge signal generated in conjunction with the discharge of the charge stored in the piezoelectric element by the electrical signal.

2. The liquid dispensing device according to claim 1, further comprising a group of electrical connection terminals that electrically connect the liquid dispensing head and the detection means, and that allow the liquid dispensing head to be attached and detached.

3. Liquid dispensing head and A detection means electrically connectable to the liquid discharge head, A group of electrical connection terminals electrically connects the liquid dispensing head and the detection means, and allows the liquid dispensing head to be attached and detached. Equipped with, The aforementioned liquid dispensing head is A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, Includes, The inspection device is characterized in that the detection means detects the electrical connection state of the piezoelectric element based on a discharge signal generated in conjunction with the discharge of the charge stored in the piezoelectric element by the electrical signal.

4. The piezoelectric element further comprises a discharge path for discharging the charge stored in the piezoelectric element, The aforementioned discharge path is Pump side resistance, A shunt resistor connected in series with the aforementioned pump-side resistor, A signal output terminal is provided between the pump-side resistor and the shunt resistor, which divides the potential of the discharge signal flowing through the discharge path and outputs it as a pump inspection signal. Includes, The pump-side resistor has one end connected to the piezoelectric element and the other end connected to the shunt resistor. The inspection apparatus according to claim 3, characterized in that the shunt resistor has one end connected to the pump-side resistor and the other end connected to ground.

5. The inspection apparatus according to claim 4, characterized in that the pump-side resistor is provided in the liquid discharge head.

6. The inspection apparatus according to claim 4, characterized in that the pump-side resistor and the shunt resistor are provided in the liquid discharge head.

7. The inspection apparatus according to claim 4, characterized in that the pump-side resistor is provided on the liquid discharge head, and the shunt resistor is provided outside the liquid discharge head.

8. The inspection apparatus according to claim 5, further comprising a boost circuit for boosting the drive voltage that drives the circulation pump to a threshold voltage.

9. The inspection apparatus according to claim 8, characterized in that the threshold voltage is set to 42.4V or less.

10. If the threshold voltage is Vp, the pump-side resistance is R, and the shunt resistance is r, r / (R+r)×Vp ≦ 42.4V The inspection apparatus according to claim 9, characterized in that it satisfies the conditions.

11. If the threshold voltage is Vp, the pump-side resistance is R, and the shunt resistance is r, r / (R+r)×Vp ≦ 5V The inspection apparatus according to claim 9, characterized in that it satisfies the conditions.

12. The inspection apparatus according to claim 4, characterized in that the discharge path includes at least one set of pump-side resistors and shunt resistors.

13. The system further comprises a maximum value detection means for detecting the maximum value of the pump inspection signal, The inspection apparatus according to claim 4, characterized in that the detection means detects the number of connected piezoelectric elements based on the maximum value.

14. The pump-side resistor and the shunt resistor are arranged between the piezoelectric element and the ground. The inspection device according to claim 4, further comprising control means for sending the discharge signal from the piezoelectric element to the ground when detecting the pump inspection signal.

15. The inspection apparatus according to claim 14, characterized in that the control means does not transmit the discharge signal until the charge stored in the piezoelectric element is saturated.

16. The inspection apparatus according to claim 14, characterized in that the control means obtains the integral value until the potential of the discharge signal becomes zero.

17. A circulation channel through which the liquid circulates, A circulation pump having a piezoelectric element, which controls the circulation flow rate of the liquid circulating in the circulation channel by changing the shape of the piezoelectric element in response to an electrical signal, A signal output terminal that outputs a discharge signal generated when the charge stored in the piezoelectric element is discharged by the aforementioned electrical signal, A liquid dispensing head characterized by including [the following].

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