Liquid ejecting head

Abstract

The invention provides a liquid ejection head which can stably eject liquid in a liquid circulation mode. A liquid ejection head according to an embodiment includes a plurality of pressure chambers communicating with nozzles, a plurality of upstream-side resistance flow paths, an upstream-side common liquid chamber, an upstream-side liquid port, a plurality of downstream-side resistance flow paths, a downstream-side common liquid chamber, a downstream-side liquid port, and a bypass flow path. A bypass flow path connects the upstream-side common liquid chamber and the downstream-side common liquid chamber on the other end side in the arrangement direction of the plurality of pressure chambers. The total flow rate of the liquid flowing through the bypass flow path and the liquid flowing through a plurality of flow paths from an inlet of each of the upstream-side resistance flow paths to an outlet of each of the downstream-side resistance flow paths is equal to or greater than the total maximum discharge flow rate of the liquid discharged from each of the nozzles.

Description

Technical Field

[0001] Embodiments of the present invention relate to liquid ejection heads. Background Technology

[0002] Liquid ejector heads are known to supply a predetermined amount of liquid to a predetermined location. For example, liquid ejector heads are mounted in inkjet printers, 3D printers, and dispensing devices. Inkjet printers eject droplets of ink from an inkjet head, forming images or the like on the surface of a recording medium. 3D printers eject droplets of modeling material from a modeling material ejector head and solidify the droplets to form a three-dimensional model. Dispensing devices eject droplets of a sample and supply a predetermined amount to multiple containers or the like.

[0003] The liquid ejector head has multiple channels for ejecting liquid. Each channel includes: a nozzle for ejecting liquid, a pressure chamber connected to the nozzle, and an actuator for changing the volume of the pressure chamber. The liquid ejector head selects the channel from the multiple channels for ejecting liquid and applies a drive voltage to the actuator of the selected channel to cause the liquid to be ejected.

[0004] After liquid ejection, residual vibrations (mensity vibrations) remain in the nozzle, determined by the surface tension of the liquid's meniscus and the liquid's mass. For example, in high-speed liquid ejection heads, this vibration needs to be quickly suppressed, thus requiring resistance flow paths before and after the pressure chamber. However, if a liquid circulation head is intended, these resistance flow paths hinder liquid circulation. Particularly in multi-nozzle heads with multiple channels, a mismatch in the upstream / downstream resistance flow path ratio creates pressure differences between channels, leading to degraded print quality. Furthermore, the meniscus is more prone to wetting in upstream channels with lower resistance, and air can easily get trapped in downstream channels with lower resistance. To avoid these problems, the circulation flow rate must be suppressed. However, if the circulation flow rate is less than twice the liquid ejection flow rate, liquid is introduced into the pressure chamber from the downstream side during maximum ejection. This causes older, contaminated liquid from the downstream side to flow back into the pressure chamber.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2007-069127

[0008] Patent Document 2: Japanese Patent Application Publication No. 2023-173168 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The technical problem to be solved by the present invention is to provide a liquid nozzle that can stably eject liquid in a liquid circulation process.

[0011] Solutions for solving technical problems

[0012] The liquid nozzle of this invention comprises: multiple pressure chambers, multiple upstream resistance flow paths, an upstream common liquid chamber, an upstream liquid port, multiple downstream resistance flow paths, a downstream common liquid chamber, a downstream liquid port, and a bypass flow path. The multiple pressure chambers are respectively connected to a nozzle. The multiple upstream resistance flow paths are respectively connected to the pressure chambers. The upstream common liquid chamber is connected to the multiple upstream resistance flow paths. The upstream liquid port is connected to the upstream common liquid chamber at one end of the arrangement direction of the multiple pressure chambers. The multiple downstream resistance flow paths are respectively connected to the pressure chambers. The downstream common liquid chamber is connected to the multiple downstream resistance flow paths. The downstream liquid port is connected to the downstream common liquid chamber at one end of the arrangement direction of the multiple pressure chambers. The bypass flow path connects the upstream common liquid chamber and the downstream common liquid chamber at the other end of the arrangement direction of the multiple pressure chambers. The total flow rate of the liquid flowing through the bypass flow path and the liquid flowing through multiple flow paths from the inlet of each of the upstream resistance flow paths to the outlet of each of the downstream resistance flow paths is greater than or equal to the total maximum ejection flow rate of the liquid ejected from each of the nozzles. Attached Figure Description

[0013] Figure 1 This is an overall configuration diagram of an inkjet printer equipped with the inkjet head of the first embodiment.

[0014] Figure 2 This is a 3D view of the inkjet head mentioned above.

[0015] Figure 3 This is a magnified cross-sectional view of the head of the inkjet head described above.

[0016] Figure 4 This is a magnified cross-sectional view of the head of the inkjet head described above.

[0017] Figure 5 These are magnified perspective and cross-sectional views of the head of the inkjet printhead.

[0018] Figure 6 This is an overall structural diagram of the ink circulation device for the aforementioned inkjet head.

[0019] Figure 7 This is the drive circuit for the inkjet head mentioned above.

[0020] Figure 8 This is the drive waveform provided to the piezoelectric actuator of the aforementioned inkjet head.

[0021] Figure 9 This is an illustration of the operation of a piezoelectric actuator that provides the aforementioned driving waveform.

[0022] Figure 10 These are perspective and cross-sectional views of a portion of the head of the inkjet head in the second embodiment, magnified.

[0023] Figure 11 This is a variation of the inkjet head in the second embodiment.

[0024] Figure 12 These are a perspective view and a cross-sectional view of the head of the inkjet head in the third embodiment, partially enlarged.

[0025] Figure 13 This is a variation of the inkjet head in the third embodiment.

[0026] Explanation of reference numerals in the attached figures

[0027] 10: Inkjet printer; 100-103: Inkjet head; 24: Nozzle; 42: Pressure chamber; 43: Upstream resistance flow path; 44: Upstream common liquid chamber; 45: Upstream ink port; 46: Downstream resistance flow path; 47: Downstream common liquid chamber; 48: Downstream ink port; 49: Bypass flow path; 5: Piezoelectric actuator; 8, 82, 83: Pressure damper. Detailed Implementation

[0028] The following is a detailed description of the liquid ejector head based on the embodiments, with reference to the accompanying drawings. It should be noted that the same reference numerals are used for the same components in each figure.

[0029] (First Implementation)

[0030] As an example of an image forming apparatus equipped with a liquid ejector head according to the first embodiment, an inkjet printer 10 for printing images on a recording medium will be described. Figure 1 The schematic configuration of the inkjet printer 10 is shown. Inside the housing 11, the inkjet printer 10 includes: a cartridge 12 for storing a sheet S, an example of a recording medium; an upstream transport path 13 for the sheet S; a conveyor belt 14 for transporting the sheet S taken from the cartridge 12; multiple inkjet heads 100-103 that eject ink droplets toward the sheet S on the conveyor belt 14; a downstream transport path 15 for the sheet S; an ejection tray 16; and a control board 17. An operation unit 18, serving as a user interface, is located on the upper side of the housing 11.

[0031] Image data printed on sheet S is generated, for example, by computer 200, which is an external connection device. The image data generated by computer 200 is transmitted to control board 17 of inkjet printer 10 via cable 201 and connectors 202 and 203.

[0032] Pick-up roller 204 feeds sheets S one by one from cassette 12 to upstream conveyor path 13. Upstream conveyor path 13 consists of conveyor roller pairs 131 and 132, and sheet guide plates 133 and 134. Sheets S are conveyed through upstream conveyor path 13 to the upper surface of conveyor belt 14. Arrow 104 in the figure shows the conveying path of sheet S from cassette 12 to conveyor belt 14.

[0033] The conveyor belt 14 is a mesh-like annular belt with multiple through holes formed on its surface. Three rollers—drive roller 141, driven rollers 142, and 143—rotate freely, supporting the conveyor belt 14. A motor 205 rotates the conveyor belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. Figure 105 shows the rotation direction of the conveyor belt 14. A negative pressure container 206 is disposed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a pressure-reducing fan 207. The fan 207 creates a negative pressure inside the negative pressure container 206 through the generated airflow, causing the sheet S to adhere and remain on the upper surface of the conveyor belt 14. Figure 106 shows the airflow direction.

[0034] As an example of a liquid ejector head, inkjet heads 100-103 are configured to face the sheet S held on the conveyor belt 14 with a small gap of, for example, 1 mm. Inkjet heads 100-103 eject droplets of ink toward the sheet S respectively. The inkjet heads 100-103 print images as the sheet S passes underneath. Each inkjet head 100-103 has the same structure except for the color of the ejected ink. The ink colors are, for example, cyan, magenta, yellow, and black.

[0035] The ink supply to each inkjet head 100-103 is performed by individual ink circulation devices 341-344. The detailed configuration of the ink circulation devices 341-344 will be described later (see [reference]). Figure 6 ).exist Figure 1 In order to facilitate drawing, ink circulation devices 341 to 344 are shown with dashed boxes respectively.

[0036] After the image is formed, the sheet S is conveyed from conveyor belt 14 to downstream conveyor path 15. Downstream conveyor path 15 consists of conveyor roller pairs 151, 152, 153, and 154, and sheet guide plates 155 and 156 that define the conveying path of the sheet S. The sheet S is conveyed from discharge port 157 to discharge tray 16 via downstream conveyor path 15. Arrow 107 in the figure shows the conveying path of the sheet S.

[0037] Next, the structure of inkjet heads 100-103 will be explained. See below for reference. Figures 2-5 The inkjet head 100 will be described, and the inkjet heads 101 to 103 have the same structure as the inkjet head 100.

[0038] like Figure 2 As shown, the inkjet head 100 includes a head 2, which is an example of a liquid ejection section. The head 2 is connected to a flexible printed wiring board 21, which is an example of a thin-film wiring substrate. The flexible printed wiring board 21 is connected to a printing substrate 22, which is an example of a relay substrate. The head 2 includes a nozzle plate 23, which is an example of a nozzle section. The ink-circulating head 2 is connected to an ink circulation device 341 via an ink supply path 311 and an ink discharge path 331.

[0039] The nozzles 24 of each ink ejection channel are arranged along a first direction, such as the X direction, of the nozzle plate 23. For example, the nozzle density is set in the range of 150 to 1200 dpi. The nozzles 24 are not limited to one row, but can also be in multiple rows. The detailed structure of the head 2 is described later.

[0040] For example, the flexible printed wiring board 21 is a flexible printed wiring substrate using a synthetic resin film such as polyimide. The flexible printed wiring board 21 is equipped with an integrated circuit (IC) 3 (hereinafter referred to as the driver IC) serving as a driver chip. The printing substrate 22 is a rigid through-hole substrate consisting of multiple layers of epoxy resin containing glass fiber and copper wiring layers. The driver IC 3, serving as the control unit of the inkjet head 100, temporarily stores printing data and provides drive signals to each channel to eject ink at predetermined timings. This printing data is transmitted via the printing substrate 22 from a control board 17 equipped with a CPU, which serves as the control unit of the inkjet printer 10.

[0041] Figures 3-5 This is a partial cross-sectional view of the head 2. The nozzle plate 23 is joined to one side of the pressure chamber substrate 4. For example, the nozzle plate 23 is a rectangular plate formed of a resin such as polyimide or a metal such as stainless steel. The vibrating plate 41 is joined to one side of the pressure chamber substrate 4 on the side opposite to the nozzle plate 23. The vibrating plate 41 has flexibility that allows it to deform when an external force is applied. For example, the vibrating plate 41 is a rectangular plate formed of a flexible polyimide film or a metal.

[0042] Pressure chambers 42 are formed on pressure chamber substrate 4. Multiple pressure chambers 42 are arranged at the positions of each nozzle 24 and are in communication with each nozzle 24. As an example, the pressure chamber 42 is formed by creating a rectangular opening in a second direction, such as the Z direction, on the pressure chamber substrate 4, and by blocking the openings on both sides of the Z direction with the nozzle plate 23 and the vibrating plate 41, respectively, to create a space for filling ink. The pressure chamber 42 is formed in a groove shape along a third direction, such as the Y direction.

[0043] Especially Figure 5As shown, in the ink circulation head, one end (upstream side) of each pressure chamber 42 in the Y direction is connected to the upstream common liquid chamber 44 via the upstream resistance flow path 43. The upstream common liquid chamber 44 is formed in a groove shape along the arrangement direction (X direction) of the pressure chambers 42, and each upstream resistance flow path 43 is sequentially connected to its side. The upstream common liquid chamber 44 is an ink supply manifold that supplies ink to each pressure chamber 42 via each upstream resistance flow path 43. As an example, the upstream common liquid chamber 44 is formed by forming an opening in the Z direction through the pressure chamber substrate 4, and blocking the openings on both sides of the Z direction by the nozzle plate 23 and the vibrating plate 41, respectively, to create a space for ink flow. The upstream ink port 45 that supplies ink to the upstream common liquid chamber 44 is provided on one side of the arrangement direction of the plurality of pressure chambers 42, which is provided on the X direction end side in the example shown in the figure. The upstream ink port 45 is connected to the ink supply path 311 (see reference). Figure 2 The upstream ink port 45 is an example of an upstream liquid port.

[0044] The other end (downstream side) of each pressure chamber 42 in the Y direction is connected to the downstream common liquid chamber 47 via the downstream resistance flow path 46. The downstream common liquid chamber 47 is formed in a groove shape along the arrangement direction (X direction) of the pressure chambers 42, and each downstream resistance flow path 46 is connected to its side in sequence. The downstream common liquid chamber 47 is an ink discharge manifold into which ink discharged from each pressure chamber 42 via each downstream resistance flow path 46 flows. As an example, the downstream common liquid chamber 47 is formed by forming an opening in the Z direction through the pressure chamber substrate 4, and blocking the openings on both sides of the Z direction by the nozzle plate 23 and the vibrating plate 41, respectively, to create a space for ink flow. The downstream ink port 48, which discharges ink from the downstream common liquid chamber 47 to the head 2, is provided at one end in the same X direction as the upstream ink port 45. The downstream ink port 48 is connected to the ink discharge path 331 (see reference). Figure 2 Downstream ink port 48 is an example of a downstream liquid port.

[0045] The upstream resistance flow path 43 and the downstream resistance flow path 46 are respectively formed to be narrower than the width in the X direction of the pressure chamber 42, for example, to reduce the flow path profile and provide flow resistance. Alternatively, the width in the Z direction can be narrowed instead of the X direction, or both the X and Z directions can be narrowed. The upstream resistance flow path 43 and the downstream resistance flow path 46 are preferably formed along the central axis in the Y direction of the pressure chamber 42, but are not limited thereto. That is, in the upstream resistance flow path 43 and the downstream resistance flow path 46, the flow path profile of the ink can be smaller than the flow path profile of the pressure chamber 42. Therefore, the shape of the flow path profile in the upstream resistance flow path 43 and the downstream resistance flow path 46 is not limited to rectangles. It should be noted that each upstream resistance flow path 43 preferably has channels with the same shape as each other, but is not limited thereto. Each downstream resistance flow path 46 also preferably has channels with the same shape as each other, but is not limited thereto. The upstream resistance flow path 43 and the downstream resistance flow path 46 are preferably symmetrical in the Y direction across the pressure chamber 42, but are not limited thereto. In order to suppress the generation of pressure difference between the channels, the resistance flow paths (43, 46) of each channel are formed in a way that the upstream and downstream sides are matched.

[0046] The bypass flow path 49 is provided on one side of the arrangement direction of the plurality of pressure chambers 42, and in the example shown in the figure, it is provided on the other end in the X direction. That is, it is provided on the side opposite to the upstream ink port 45 and the downstream ink port 48. The bypass flow path 49 is a flow path that connects the other ends of the upstream common liquid chamber 44 and the downstream common liquid chamber 47 to each other to allow ink to bypass.

[0047] The bypass flow path 49 is formed with a flow path cross-section smaller than that of the upstream shared liquid chamber 44 and the downstream shared liquid chamber 47, thus giving the bypass flow path 49 flow path resistance. For example, it is designed as a flat shape with a reduced width in the Z direction and an increased width in the X direction. Therefore, the circulating flow of ink can form a flow supplying ink to each pressure chamber 42 in addition to the bypass flow path 49. The ratio of the total flow rate of ink flowing through each pressure chamber 42 to the flow rate of ink flowing through the bypass flow path 49 can be adjusted by the flow path resistance of the bypass flow path 49. For example, when the length of the bypass flow path 49 is set constant, if the cross-sectional area of ​​the bypass flow path 49 is increased, more ink flows through the bypass flow path 49; if the cross-sectional area of ​​the bypass flow path 49 is decreased, more ink flows through each pressure chamber 42. In this case, the flow rate of ink flowing through each pressure chamber 42 is adjusted to be less than the flow rate of ink ejected from each nozzle 24. Preferably, the ink flow rate supplied to the pressure chamber 42 is, for example, 0.6 times the ink flow rate ejected from the nozzle 24. The insufficient portion is introduced from the downstream common liquid chamber 47, as described later.

[0048] To supplement the insufficient portion from the downstream shared liquid chamber 47, the total flow rate of ink flowing through the bypass flow path 49 and the flow path of ink flowing through each channel from the inlet of each upstream resistance flow path 43 to the outlet of each downstream resistance flow path 46 is greater than or equal to the total maximum ejection flow rate of ink ejected from each nozzle 24. This flow rate setting is, for example, performed by the ink circulation device 341. It should be noted that the maximum ink ejection flow rate is the total flow rate when ink is ejected from all ejection channels.

[0049] As an example, as described above, when the circulating flow rate of the ink flowing through the pressure chamber 42 is set to 0.6 times the ejection flow rate, the flow resistance of the bypass flow path 49 is set to (6 / 4) times the parallel resistance of the flow resistance of the entire flow path through the pressure chamber 42, such that 0.4 times the ejection flow rate flows through the bypass flow path. This setting is achieved, for example, by adjusting the cross-sectional area of ​​the bypass flow path 49. Furthermore, if the ink is circulated from the upstream ink port 45 to the downstream ink port 48 at, for example, 1 times the total maximum ejection flow rate, the circulating flow rate during periods when no ink is ejected is in a 6:4 ratio between the circulating path through each pressure chamber 42 and the bypass flow path 49. During maximum ejection, although the ink flows backward from the downstream common liquid chamber 47 towards the pressure chamber 42, this portion of the ink is supplied from the bypass flow path 49 to the downstream common liquid chamber 47, so the ink does not flow backward from a point further downstream than the downstream ink port 48, where there is a risk of contamination by foreign objects or air bubbles.

[0050] The relationship between the flow rate of the ink circulating flow through the pressure chamber 42, i.e. the flow rate into the pressure chamber 42 when no ink is ejected from the nozzle 24, and the flow rate of the ink circulating flow through the bypass path 49 is such that the total ink consumption under the condition of maximum ejection flow rate, i.e. maximum continuous ejection from the full nozzle 24, is set to 1, for example, the relationship a) to d) below.

[0051]

[0052] Compared to a) and c), the combined flow rate of b) and d) is larger, which is beneficial for temperature stability and preventing ink component sedimentation. Compared to b) and d), the combined flow rate of a) and c) is smaller, making ink supply easier. Compared to a) and b), the pressure chamber circulation flow rate of c) and d) is smaller, so the flow path resistance has less impact on the nozzle back pressure, making it easier to stabilize the nozzle back pressure. Compared to c) and d), the pressure chamber circulation flow rate of a) and b) is larger, making it easier to discharge foreign matter and air bubbles mixed into the pressure chamber 42 downstream. In the order of a), b), c), and d), the flow rate ratio of the bypass flow path 49 to the pressure chamber circulation flow rate becomes larger, so even if needle-shaped foreign matter is mixed into the supplied ink, it is difficult for such foreign matter to be mixed into the pressure chamber 42. The combined flow rates of a), b), c), and d) all exceed 1, so even at maximum ejection, it can prevent foreign matter in the ink from being introduced into the head 2 from the downstream ink port 48.

[0053] In the bypass flow path 49, the cross-section is not limited to a flat shape; the width in the Z direction and the width in the X direction can be adjusted. That is, the flow path cross-section of the bypass flow path 49 only needs to be smaller than the flow path cross-section of the upstream shared liquid chamber 44 and the downstream shared liquid chamber 47. Therefore, the shape of the flow path cross-section of the bypass flow path 49 is not limited to a rectangle. Resistance can also be provided in a portion of the bypass flow path 49 to adjust the ratio of the flow rate through the bypass flow path 49 to the total flow rate through the pressure chamber 42. In this case, it is desirable that pressure dampers be provided on both sides of the resistance flow path. One of the pressure dampers can be as follows: Figure 11 As shown in (a), it is installed near the ink nozzle. The configuration of the pressure damper will be described later.

[0054] Figure 6 This is the overall configuration of the ink circulation device 341 that circulates ink to the inkjet head 100. The ink circulation device 341 is an example of a liquid circulation device for a liquid printhead. It should be noted that the ink circulation devices 342-344, which circulate ink to the inkjet heads 101-103, also have the same structure as the ink circulation device 341. For example... Figure 6 As shown, the ink circulation device 341 consists of an ink tank 315, an ink pump 321, an ink filter F1, the head 2 of the inkjet head 100, and an ink supply path 311 and an ink discharge path 331 connecting them. Furthermore, air valves V1 and V2 and air filters F2 and F3 are respectively installed in the ink supply path 311 and the ink discharge path 331.

[0055] The upstream shared liquid chamber 44 controls the ink circulation flow to a predetermined flow rate, while the downstream shared liquid chamber 47 controls it to a predetermined pressure. Therefore, it is preferable that the downstream ink discharge path 331 is wider than the ink supply path 311. The ink supply path 311 is, for example, a pipe with a diameter of 3 mm, and the ink discharge path 331 is, for example, a pipe with a diameter of 6 mm. In this case, the opening of the upstream ink port 45 is set to a diameter of 3 mm, and the opening of the downstream ink port 48 is set to a diameter of 6 mm.

[0056] During initial ink filling, the ink circulation device 341 initially closes air valve V2 and opens air valve V1, allowing ink to be supplied from the upstream side by ink pump 321. Ink flows into the head 2 through the upstream ink port 45 and passes through the upstream common liquid chamber 44. Then, it flows into the downstream common liquid chamber 47 via the pressure chambers 42 of each channel and the bypass flow path 49. The ink flow rates through the upstream common liquid chamber 44, the pressure chambers 42 of each channel, and the bypass flow path 49 are set as described above. The ink ejection operation of each channel maintains this ink circulation flow.

[0057] If the explanation is returned Figure 3 As an example of an actuator, a piezoelectric actuator 5 is disposed on one side of the vibrating plate 41 opposite to the pressure chamber 42. The piezoelectric actuators 5 of each channel are arranged in a position sandwiching the vibrating plate 41 and opposite to the pressure chamber 42. The piezoelectric actuators 5 are bonded to the vibrating plate 41, for example, with adhesive. Each piezoelectric actuator 5 is fixed by bonding its Z-direction side, opposite to the vibrating plate 41, to the support member 7. Specifically, for example... Figure 3 As shown, the piezoelectric actuator 5 is a stacked piezoelectric actuator formed by alternately stacking piezoelectric elements 51, first internal electrodes 52, and second internal electrodes 53. The polarization directions of each piezoelectric element 51 are arranged opposite to each other in the Z direction, deformed in a d33 mode. The first internal electrode 52 and the second internal electrode 53 are conductive films formed on the main surface of the piezoelectric element 51. The first internal electrode 52 is formed on one end face of the piezoelectric actuator 5 in the Y direction and connected to a first external electrode 54 formed on that end face. The second internal electrode 53 is formed on the other end face of the piezoelectric actuator 5 in the Y direction and connected to a second external electrode 55 formed on that end face.

[0058] The dummy layer 58 is made of the same material as the piezoelectric element 51. The dummy layer 58 has no internal electrodes and is not subjected to an electric field, therefore it does not deform. The dummy layer 58 serves as the base for fixing the piezoelectric actuator 5 to the support member 7 (see reference). Figure 4 This can be considered as a grinding allowance, or a grinding allowance used to achieve precision during or after assembly. Especially for example... Figure 4As shown, supports 50 can also be arranged between the piezoelectric actuators 5 of each channel, spaced apart by slots 59. Supports 50 can also be constructed from dummy actuators, similar to the piezoelectric actuators 5 used for driving. Supports 50 are, for example, positioned at a location corresponding to the partition wall 40 between adjacent pressure chambers 42. The internal electrodes 52 and 53 of the supports 50 are not connected to the drive circuit of the drive IC 3 (described later), i.e., they are not driven, thus becoming non-deformable fixed parts. Supports 50 can also be formed from other components instead of dummy actuators.

[0059] In the case of a piezoelectric actuator 5 with multiple piezoelectric elements 51 stacked together, as an example, a first internal electrode 52 and a second internal electrode 53 are formed on the main surface of each piezoelectric element 51, which is processed into a thin plate shape. Then, the piezoelectric elements 51 are stacked together and sintered into one piece. Then, a first external electrode 54 and a second external electrode 55 are formed. Then, the piezoelectric elements 51 are polarized with a polarization voltage. The piezoelectric elements 51 are formed from lead-containing piezoelectric materials such as lead zirconate titanate (PZT) or lead-free piezoelectric materials such as potassium sodium niobate. The first internal electrode 52 and the second internal electrode 53 are formed from conductive materials that can be sintered, such as silver and palladium. The first external electrode 54 and the second external electrode 55 are formed from materials such as Ni, Cr, and Au by known methods such as electroplating and sputtering.

[0060] The first external electrode 54 of each channel is connected to the independent wiring 56 of the flexible printed wiring board 21 (see reference). Figure 3 The flexible printed wiring board 21 has a substrate 26, individual wirings 56, an adhesive layer 27, and an insulating layer 28. The flexible printed wiring board 21 is arranged such that the area where the tin-plated layer 29 is formed faces the first external electrode 54, and the first external electrode 54 of each channel is electrically or mechanically connected to the individual wirings 56 by melting solder. Instead of solder, it can also be fixed by ACF (Anisotropic Conductive Film), ACP (Anisotropic Conductive Paste), NCF (Non-Conductive Film), NCP (Non-Conductive Paste), etc., and anisotropic conductive connection can be made in the thickness direction. On the other hand, the second external electrode 55 of each channel is connected to a common wiring (not shown), for example, connected to ground (GND) via the flexible printed wiring board 21.

[0061] Figure 7 This is an example of the drive circuit for the inkjet head 100. For example... Figure 7As shown, in each channel (#1ch~#nch), the piezoelectric actuator 5 connects the first external electrode 54 to the independent wiring 56 and to the output terminal of the driver D (i.e., the drive circuit) of the driver IC3. The connection point between the first external electrode 54 and the independent wiring 56 is the independent terminal of the piezoelectric actuator 5. The second external electrode 55 is connected to the common wiring 57 and to a common potential. The connection point between the second external electrode 55 and the common wiring 57 is the common terminal of the piezoelectric actuator 5.

[0062] The driver IC3 is connected to power supply 70 for drive voltage V1 and power supply 71 for drive voltage V2 supplied to the piezoelectric actuator 5 during ink ejection. Power supplies 70 and 71 have their positive terminals connected to the driver IC3 and their negative terminals connected to ground (GND). The driver IC3 is connected to the control board 17 (see reference 17), which serves as the control unit of the inkjet printer 10. Figure 1 The signal line connecting the printed data is used to transmit the data. Printed data is an example of a control signal. The common wiring 57 from the common terminal of the piezoelectric actuator 5 is connected to ground (GND).

[0063] Next, refer to Figure 8 as well as Figure 9 The ink ejection operation is explained below. Each driver D of driver IC3 provides a drive waveform to the individual terminals of piezoelectric actuator 5 using drive voltages V1, V2, and ground (GND). Voltage V1 is, for example, 20V. Voltage V2 is, for example, 10V. Ground (GND) is, for example, 0V. Which channel of piezoelectric actuator 5 is driven depends, for example, on the printing data. Figure 8 An example of a drive waveform provided to piezoelectric actuator 5.

[0064] When driving the piezoelectric actuator 5, which provides a ground potential to the common terminal, such as Figure 8 As shown, a voltage V2 is supplied to the independent terminal to set it to standby state. If voltage V2 is supplied, an electric field is applied in the direction of the polarization axis of the piezoelectric element 51. Due to the inverse piezoelectric effect of the piezoelectric element, such as... Figure 9 As shown in (a), the piezoelectric actuator 5 elongates in the stacking direction (Z direction) to reduce the volume of the pressure chamber 42. This process occurs before the ink ejection timing. Then, at the ink ejection timing ( Figure 8 At time t1), the potential of the independent terminal is initially lowered to ground (GND), such as Figure 9 As shown in (b), the elongated piezoelectric actuator 5 returns to its original position, i.e., contracts relatively, and the volume of the pressure chamber 42 expands relatively. If the volume of the pressure chamber 42 expands, the meniscus of the interface between the ink in the nozzle 24 and the external air is introduced concavely toward the pressure chamber 42.

[0065] Furthermore, after, for example, half the time of the pressure vibration cycle of head 2 has elapsed, in Figure 8 At time t2, if voltage V2 is supplied to the independent terminal, then as follows Figure 9 As shown in (c), the piezoelectric actuator 5 elongates in the stacking direction (Z direction), and the volume of the pressure chamber 42 is relatively reduced, thereby ejecting ink droplets R from the nozzle 24. Then, after, for example, half the time of the pressure vibration cycle of the head 2 has elapsed, in Figure 8 At time t3, voltage V1 is supplied to the independent terminal, and at time t4, after a predetermined time, voltage V2 is returned. This is due to the elongation of the piezoelectric actuator 5 at this time (…). Figure 9 (d) and restoration ( Figure 9 (a) reduces and restores the volume of pressure chamber 42, thereby attenuating residual vibration. In this way, the volume of pressure chamber 42 changes in conjunction with the longitudinal vibration of the piezoelectric actuator 5 in the stacking direction, enabling ink ejection. Once a series of ink ejections has ended, the volume of ink in pressure chamber 42 decreases only by the amount ejected, and ink flows into pressure chamber 42 via upstream resistance flow path 43. If the ink flow rate supplied from the upstream side of pressure chamber is low, ink is also introduced into pressure chamber 42 from the downstream side via downstream resistance flow path 45.

[0066] (Second Implementation)

[0067] Next, the inkjet head 100 of the second embodiment will be described. For example... Figure 10 As shown, the inkjet head 100 of the second embodiment has the same configuration as the inkjet head 100 of the first embodiment, except that a pressure damper 8 is provided in the bypass flow path 49.

[0068] like Figure 10 As shown, the pressure damper 8 is formed by opening one side of the bypass flow path 49 opposite to the nozzle plate 23 in the Z direction, and sealing the opening with a soft material 81 such as a thin polyimide film. The soft material 81, such as the polyimide film, is an example of a flexible resin covering the opening of the bypass flow path 49. The pressure damper 8 is an example of a membrane damper. When the ink ejection volume changes drastically, the soft material 81 flexes, which can mitigate the drastic pressure changes in the upstream shared liquid chamber 44 and the downstream shared liquid chamber 47.

[0069] That is, especially in multi-nozzle heads with multiple ink ejection channels, the ink flow rate can sometimes change drastically depending on the printing content. For example, when printing patterns with many blank spaces, such as lines, from full-channel printing at full load, the ink flow rate decreases sharply; conversely, when printing patterns from blank spaces at full load, the ink flow rate increases sharply. If such abrupt changes in ink flow occur, the back pressure of the ejected ink changes because the ink of quality must be stopped or started abruptly. Changes in back pressure affect the behavior of the ejected ink, leading to a deterioration in print quality.

[0070] Pressure dampers are sometimes provided as units that absorb changes in the back pressure of ink, but due to the multiple flow paths in the ink-circulating inkjet head 100, it is difficult to provide a pressure damper with a simple configuration. Therefore, if the pressure damper 8 is provided in the bypass flow path 49 as in this embodiment, the damping effect can be applied to both the upstream common liquid chamber 44 and the downstream common liquid chamber 47. Therefore, only one pressure damper 8 is needed. The film-type pressure damper 8 is thin and has a large area, so it can work efficiently. Therefore, compared to providing pressure dampers on the upstream and downstream sides respectively, providing a common pressure damper 8 on both the upstream and downstream sides can absorb pressure changes more efficiently with a smaller area. In addition, since the pressure damper 8 is located on the bypass flow path 49, it also has the advantage of easy ink filling. To enhance the damping effect of the pressure damper 8, the widths in the Z and X directions can be adjusted to make the bypass flow path 49 more flat, thereby increasing the area of ​​the soft material 81. However, the location where the soft material 81 is configured is not limited to an opening in the Z direction.

[0071] The flow rate of ink flowing through the bypass flow path 49, which is equipped with the pressure damper 8, is, for example, greater than or equal to the total circulating flow rate of ink flowing through each pressure chamber 42. That is, in order for the pressure damper 8 to function efficiently, the dimensions (flow path cross-sectional area, flow path length) of the bypass flow path 49 are designed such that the flow path resistance of the bypass flow path 49 is less than or equal to the parallel flow path resistance of the entire flow path through the pressure chamber 42. The flow path resistance of the entire flow path through the pressure chamber 42 is the flow path resistance of multiple flow paths from the inlet of the upstream resistance flow path 43 to the outlet of the downstream resistance flow path 46. The parallel flow path resistance is the sum of the flow path resistances of all channels. To prevent ink backflow from the downstream side before the downstream ink outlet 48, similar to the first embodiment, it is preferable that the total flow rate of ink flowing through the entire flow path through the pressure chamber 42 and the bypass flow path 49 is greater than or equal to the maximum total flow rate ejected from the nozzle 24.

[0072] like Figure 11As shown, pressure dampers 82 and 83 can also be installed near the upstream ink port 45 and the downstream ink port 48. In this case, they are installed on the upstream and downstream sides, respectively. Like pressure damper 8, pressure dampers 82 and 83 have an opening on one side opposite to the nozzle plate 23 in the Z direction, and this opening is formed by sealing with a soft material 81 such as a thin polyimide film. In this way, by installing pressure dampers 8, 82, and 83 at both ends of the upstream common liquid chamber 44 and the downstream common liquid chamber 47, the absorption effect of pressure changes is improved.

[0073] (Third Implementation)

[0074] Next, the inkjet head 100 of the third embodiment will be described. For example... Figure 12 As shown, the inkjet head 100 of the third embodiment has the same configuration as the inkjet head 100 of the first embodiment, except that the bypass flow path 49 is made into a tubular shape.

[0075] like Figure 12 As shown, the tubular bypass flow path 49 is arranged in an inverted U-shape in the Z direction. By making the bypass flow path 49 tubular and setting its maximum height h (in the Z direction), when ink is filled with residual air in the head 2, it is possible to select whether the ink flows through the bypass flow path 49, for example, by adjusting the pressure of the ink supplied by the ink pump 321. That is, the highest point of the bypass flow path 49 is higher than the height of the upstream common liquid chamber 44. As a specific example, when the pressure difference is maintained at a state smaller than ρgh and the ink flows from the upstream ink port 45 to the downstream ink port 48, the ink will not exceed the maximum height h and therefore will not flow through the bypass flow path 49. It should be noted that ρ is the density of the ink and g is the acceleration due to gravity. In this state, ink can be filled into each pressure chamber 42, and then ink can be filled into the bypass flow path 49 by making the upstream and downstream pressure difference greater than ρgh and further circulating the ink. The highest point of the bypass flow path 49 is preferably higher than the height of the common liquid chamber 44. Figure 6 The highest height of ink supply path 311 in the middle.

[0076] The tubular bypass flow path 49 can be made of soft tubing, such as flexible tubing. Alternatively, it can be formed from rigid tubing. Then, as... Figure 13 As shown, a pressure damper 84, made of a flexible bag or the like, can be installed in the tubular bypass flow path 49. Flexible bags easily have a large surface area, thus achieving a high damping effect.

[0077] As described above, according to any of the above embodiments, by providing a bypass flow path 49 connecting the upstream common liquid chamber 44 and the downstream common liquid chamber 47 at the other end of the arrangement direction of the plurality of pressure chambers 42, an inkjet head 100 that can stably eject ink in an ink circulation head can be provided.

[0078] By providing a bypass flow path 49 to increase the overall ink circulation flow rate of the head 2, it is also advantageous to facilitate heat transfer from the ink to the head 2, thereby bringing the temperature of the head 2 closer to the temperature of the ink. Furthermore, by providing a bypass flow path 49 to increase the overall ink circulation flow rate of the head 2, it is possible to agitate the ink by increasing the circulation flow rate, for example, preventing the sedimentation of sediment-forming inks, including those containing silica.

[0079] It should be noted that the piezoelectric actuator 5 is not limited to a stacked type with multiple piezoelectric elements 51. The piezoelectric element 51 can also be a single-layer piezoelectric actuator. In addition, the actuator's operation when a driving voltage is applied is not limited to longitudinal vibration. Moreover, it is not limited to drop-on-demand / piezoelectric methods, but can also be applied to continuous methods.

[0080] In the above embodiments, the inkjet printer 100 is described as an example of a liquid ejection device, but the liquid ejection device may also be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0081] The embodiments of the present invention are presented by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in a wide variety of other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are included in the scope of the invention as described in the claims and their equivalents.

Claims

1. A liquid ejector head, characterized in that, have: Multiple pressure chambers, each connected to a nozzle; Multiple upstream resistance flow paths are connected to the pressure chamber, respectively; The upstream side shares a liquid chamber, which is connected to multiple upstream side resistance flow paths; The upstream liquid port is connected to the upstream shared liquid chamber at one end of the arrangement direction of the plurality of pressure chambers; Multiple downstream resistance flow paths are connected to the pressure chamber, respectively; The downstream side shares a liquid chamber, which is connected to multiple downstream resistance flow paths; The downstream liquid port is connected to the downstream common liquid chamber at one end of the arrangement direction of the plurality of pressure chambers; as well as A bypass flow path connects the upstream common liquid chamber and the downstream common liquid chamber at the other end of the arrangement direction of the plurality of pressure chambers. The total flow rate of the liquid flowing through the bypass flow path and the liquid flowing through multiple flow paths from the inlet of each of the upstream resistance flow paths to the outlet of each of the downstream resistance flow paths is greater than or equal to the total maximum ejection flow rate of the liquid ejected from each of the nozzles.

2. The liquid ejector head according to claim 1, characterized in that, The flow path resistance of the bypass flow path is less than the parallel flow path resistance of the multiple flow paths from the inlet of each of the upstream resistance flow paths to the outlet of each of the downstream resistance flow paths.

3. The liquid ejector head according to claim 1 or 2, characterized in that, A pressure damper is provided in the bypass flow path.

4. The liquid ejector head according to claim 1 or 2, characterized in that, The highest point of the bypass flow path is higher than the height of the upstream shared liquid chamber.

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