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 pressure chamber communicating with a nozzle, an upstream-side resistance flow path, an upstream-side common liquid chamber, an upstream-side liquid port, a downstream-side resistance flow path, a downstream-side common liquid chamber, a downstream-side liquid port, a bypass flow path, and a pressure damper. A plurality of upstream-side resistance flow paths communicate with each of the pressure chambers. An upstream-side common liquid chamber communicates with the plurality of upstream-side resistance flow paths. The plurality of downstream-side resistance flow paths communicate with the pressure chambers, respectively. A downstream-side common liquid chamber communicates with the plurality of downstream-side resistance flow paths. The upstream-side liquid port and the downstream-side liquid port are disposed on one end side in the arrangement direction of the plurality of pressure chambers. The 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. A pressure damper is provided in the bypass flow path.

Description

Technical Field

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

[0002] A liquid ejector head is known to supply a predetermined amount of liquid to a predetermined location. The liquid ejector head is, for example, mounted on an inkjet printer, a 3D printer, or a dispensing device. An inkjet printer ejects droplets of ink from an inkjet head to form images on the surface of a recording medium. A 3D printer ejects droplets of modeling material from a modeling material ejector head and solidifies them to form a three-dimensional model. A dispensing device ejects droplets of a sample and supplies them in a predetermined amount to multiple containers.

[0003] The liquid ejector head has multiple channels for ejecting liquid. Each channel has 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 driving voltage to the actuator of the selected channel to cause the liquid to be ejected.

[0004] After ejection, liquid nozzles retain vibrations (mensill vibrations) determined by the surface tension of the meniscus and the mass of the liquid within the nozzle. For example, in high-speed liquid nozzles, this vibration needs to be suppressed as early as possible, thus resistance flow paths are placed before and after the pressure chamber. However, if a liquid circulation nozzle is desired, these resistance flow paths hinder liquid circulation. In particular, in multi-nozzle nozzles with multiple channels, a mismatch in the upstream / downstream ratio of the resistance flow paths in each channel creates a pressure difference between channels, resulting in poor print quality. Furthermore, the meniscus is easily wetted in channels with low upstream resistance, and air is easily incorporated in channels with low downstream 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 will be drawn into the pressure chamber from the downstream side during maximum ejection. This causes old, dirty liquid from the downstream side to return to 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. 2019-059047 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, a bypass flow path, and a pressure damper. 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 pressure damper is disposed in the bypass flow path. Attached Figure Description

[0013] Figure 1 This is an overall structural 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 driving waveform applied to the piezoelectric actuator of the inkjet head.

[0021] Figure 9 This is an illustration of the operation of a piezoelectric actuator with 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. Detailed Implementation

[0026] The liquid ejector head according to the embodiment will now be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals are used to denote the same structure in each figure.

[0027] (First Implementation)

[0028] As an example of an image forming apparatus equipped with a liquid ejector head according to the first embodiment, an inkjet printer 10 that prints images on a recording medium will be described. Figure 1 A simplified structure 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 for ejecting 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.

[0029] 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 sent to control board 17 of inkjet printer 10 via cable 201, connectors 202 and 203.

[0030] Pick-up roller 204 feeds sheets S one by one from cassette 12 to upstream conveyor path 13. Upstream conveyor path 13 consists of feed roller pairs 131 and 132 and sheet guide plates 133 and 134. Sheets S are delivered to the upper surface of conveyor belt 14 via upstream conveyor path 13. Arrow 104 in the figure indicates the conveying path of sheet S from cassette 12 to conveyor belt 14.

[0031] The conveyor belt 14 is a mesh-like annular belt with numerous through holes formed on its surface. Three rollers, drive roller 141, driven rollers 142 and 143, support the conveyor belt 14 for free rotation. A motor 205 rotates the conveyor belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. In the figure, 105 indicates the direction of rotation 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 airflow, causing the sheet S to adhere and remain on the upper surface of the conveyor belt 14. In the figure, 106 indicates the airflow.

[0032] As an example of a liquid ejector head, inkjet heads 100-103 are configured to face a 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 towards the sheet S. 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.

[0033] The ink supply to each inkjet head 100-103 is circulated through each ink circulation device 341-344. The detailed configuration of the ink circulation devices 341-344 will be described later (see [reference]). Figure 6 ).exist Figure 1 In the diagram, for ease of drawing, ink circulation devices 341 to 344 are shown with dashed boxes.

[0034] After the image is formed, the sheet S is conveyed from the conveyor belt 14 to the downstream conveyor path 15. The downstream conveyor path 15 consists of feed 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 the discharge port 157 to the discharge tray 16 via the downstream conveyor path 15. Arrow 107 in the figure indicates the conveying path of the sheet S.

[0035] Next, the structure of inkjet heads 100-103 will be explained. (Refer to the following...) Figures 2-5 The inkjet head 100 will be described, but inkjet heads 101 to 103 also have the same structure as inkjet head 100.

[0036] 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 membrane 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.

[0037] The nozzles 24 of each ink ejection channel are arranged along a first direction, such as the X direction, of the nozzle plate 23. The nozzle density is set, for example, in the range of 150 to 1200 dpi. The nozzles 24 are not limited to a single row, but can also be in multiple rows. The detailed configuration of the head 2 will be described later.

[0038] The flexible printed wiring board 21 is, for example, a flexible printed wiring substrate using a synthetic resin film such as polyimide. The flexible printed wiring board 21 houses 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 formed by multiple layers of epoxy resin with glass fiber and copper wiring layers. The driver IC 3, serving as the control unit of the inkjet head 100, temporarily stores printing data sent from the control board 17, which is equipped with a CPU serving as the control unit of the inkjet printer 10, via the printing substrate 22, and provides drive signals to each channel at predetermined timings to eject ink.

[0039] 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. The nozzle plate 23 is, for example, a rectangular plate formed from 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 is flexible enough to deform when an external force is applied. The vibrating plate 41 is, for example, a rectangular plate formed from a flexible polyimide film or a metal.

[0040] 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 respectively connected to the nozzle 24. As an example, the pressure chamber 42 forms a space for filling ink by forming a rectangular opening extending along a second direction, such as the Z direction, in the pressure chamber substrate 4, and by using a nozzle plate 23 and a vibrating plate 41 to block the openings on both sides of the Z direction. The pressure chamber 42 is formed in a groove shape along a third direction, such as the Y direction.

[0041] In particular, such as 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 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 forms an ink flow space 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. 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, and in the example shown, it is provided on the X direction end side. 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.

[0042] The other end (downstream side) of each pressure chamber 42 in the Y direction is connected to the downstream common liquid chamber 47 via a 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. The downstream common liquid chamber 47 is an ink discharge manifold through which ink discharged from each pressure chamber 42 via each downstream resistance flow path 46 flows together. 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 the same as the upstream ink port 45 and is provided on one end side in the X direction. 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.

[0043] For example, the upstream resistance flow path 43 and the downstream resistance flow path 46 are formed with narrower cross-sections than the X-direction width of the pressure chamber 42, thereby providing 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 of the pressure chamber 42 in the Y-direction, but are not limited thereto. That is, the flow path cross-section of the ink in the upstream resistance flow path 43 and the downstream resistance flow path 46 only needs to be smaller than the flow path cross-section of the pressure chamber 42. Therefore, the shape of the flow path cross-section of the upstream resistance flow path 43 and the downstream resistance flow path 46 is not limited to rectangles. It should be noted that the channels of each upstream resistance flow path 43 are preferably identical in shape, but are not limited thereto. Similarly, the channels of each downstream resistance flow path 46 are preferably identical in shape, but are not limited thereto. The upstream resistance flow path 43 and the downstream resistance flow path 46 are preferably symmetrical in the Y direction, separated by the pressure chamber 42, but are not limited thereto. However, in order to suppress the generation of pressure difference between the channels, the upstream and downstream ratios of the resistance flow paths (43, 46) of each channel are matched.

[0044] 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.

[0045] The bypass flow path 49 has a flow path profile smaller than that of the upstream common liquid chamber 44 and the downstream common liquid chamber 47, thus incorporating flow path resistance. For example, it is designed as a flattened shape with a narrower width in the Z direction and a wider width in the X direction. This allows the circulating flow of ink to supply ink to each pressure chamber 42, not just the bypass flow path 49. The ratio of the total flow rate of ink flowing in each pressure chamber 42 to the flow rate of ink flowing in 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 constant, increasing the cross-sectional area of ​​the bypass flow path 49 results in more ink flowing in the bypass flow path 49, while decreasing the cross-sectional area of ​​the bypass flow path 49 results in more ink flowing in each pressure chamber 42. In this case, the adjustment ensures that the flow rate of ink flowing in each pressure chamber 42 is less than the flow rate of ink ejected from each nozzle 24. Preferably, the ink flow rate supplied to the pressure chamber 42 is set to, for example, 0.6 times the ink flow rate ejected from the nozzle 24. Any shortfall is introduced from the downstream common liquid chamber 47, as described later.

[0046] To replenish the insufficient amount from the downstream common liquid chamber 47, the total flow rate of ink flowing in the bypass flow path 49 and the flow path of ink flowing in each channel from the inlet of each upstream resistance flow path 43 to the outlet of each downstream resistance flow path 46 is set to be 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.

[0047] As an example, if the circulating flow rate of the ink flowing in the pressure chamber 42 is set to 0.6 times the ejection flow rate, as described above, the flow path resistance of the bypass flow path 49 is set to be (6 / 4) times the parallel flow path resistance relative to the flow path resistance of the entire flow path through the pressure chamber 42, so that 0.4 times the ejection flow rate flows in 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, a total of one time the 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, because this amount of ink is supplied from the bypass flow path 49 to the downstream common liquid chamber 47, the ink will not flow backward from a position further downstream than the downstream ink port 48 where it may be contaminated by foreign objects or air bubbles.

[0048] The maximum ejection flow rate, i.e. the total ink consumption under the condition of maximum continuous ejection from the full nozzle 24, is set to 1. The relationship between the flow rate of the ink circulation flow in the pressure chamber 42, i.e. the flow rate of the ink circulation flow in the pressure chamber 42 when ink is not ejected from the nozzle 24, and the flow rate of the ink circulation flow in the bypass flow path 49, is, for example, the following relationship a) to d).

[0049]

[0050] Because the combined flow rates of b) and d) are larger than those of a) and c), it is beneficial for temperature stability and prevents ink component sedimentation. Because the combined flow rates of a) and c) are smaller than those of b) and d), ink supply is easier. Because the pressure chamber circulation flow rates of c) and d) are smaller than those of a) and b), the flow path resistance has less impact on nozzle back pressure, making it easier to stabilize the nozzle back pressure. Because the pressure chamber circulation flow rates of a) and b) are larger than those of c) and d), it is easier to discharge foreign matter and air bubbles mixed into the pressure chamber 42 downstream. Because the ratio of the bypass flow path 49 flow rate to the pressure chamber circulation flow rate is larger in the order of a), b), c), and d), even if needle-shaped foreign matter is mixed into the supplied ink, it is difficult for it to mix into the pressure chamber 42. Because the combined flow rate of any one of a), b), c), and d) exceeds 1, even at maximum ejection, it is possible to prevent foreign matter in the ink from being introduced into the head 2 from the downstream ink port 48.

[0051] The cross-section of the bypass flow path 49 is not limited to a flat shape; its width in the Z direction and the width in the X direction can also be adjusted. That is, the flow path cross-section of the bypass flow path 49 can be smaller than the flow path cross-sections of the upstream common liquid chamber 44 and the downstream common 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 to a portion of the bypass flow path 49 to adjust the ratio of the flow rate flowing in the bypass flow path 49 to the total flow rate flowing in the pressure chamber 42. In this case, it is desirable to configure pressure dampers on both sides of the resistance flow path. Alternatively, a pressure damper on one side can be... Figure 11 The pressure damper is positioned near the ink port as shown in (a). The configuration of the pressure damper will be described later.

[0052] Figure 6 This refers to the overall structure of the ink circulation device 341, which 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 configuration as the ink circulation device 341. Figure 6 As shown, the ink circulation device 341 is composed 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 provided in the ink supply path 311 and the ink discharge path 331.

[0053] The upstream common liquid chamber 44 controls the ink circulation flow to a predetermined flow rate, while the downstream common liquid chamber 47 controls the ink circulation flow 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.

[0054] During initial ink filling, the ink circulation device 341 initially closes air valve V2 and opens air valve V1, supplying ink from the upstream side via ink pump 321. The ink flows into the head 2 through the upstream ink port 45 and flows in 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 in 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.

[0055] If returned Figure 3 To illustrate, a piezoelectric actuator 5, as an example of an actuator, is disposed on one side of the vibrating plate 41 opposite to the pressure chamber 42. The piezoelectric actuator 5 of each channel is disposed in a position sandwiching the vibrating plate 41 and facing the pressure chamber 42. The piezoelectric actuator 5 and the vibrating plate 41 are joined, for example, by adhesive. Each piezoelectric actuator 5 is fixed by engaging its Z-direction side opposite to the vibrating plate 41 with a support member 7. In particular, as... Figure 3 As shown, the piezoelectric actuator 5 is, for example, a stacked piezoelectric actuator formed by alternately stacking piezoelectric elements such as piezoelectric bodies 51, a first internal electrode 52, and a second internal electrode 53. The polarization directions of each piezoelectric body 51 are arranged opposite to each other in the Z direction, for example, and are deformed in the d33 mode. The first internal electrode 52 and the second internal electrode 53 are conductive films formed on the main surface of the piezoelectric body 51, respectively. The first internal electrode 52 is formed on one end face of the piezoelectric actuator 5 in the Y direction and is 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 is connected to a second external electrode 55 formed on that end face.

[0056] The dummy layer 58 and the piezoelectric element 51 are made of the same material. Since the dummy layer 58 has no internal electrodes and is not subjected to an electric field, 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 7). Figure 4 This refers to the grinding allowance used during or after assembly to achieve precision. Specifically, such as... Figure 4 As shown, support pillars 50 can also be arranged with slots 59 spaced apart from each other in the piezoelectric actuators 5 of each channel. Support pillars 50 can be constructed using dummy actuators, similar to those formed for driving piezoelectric actuators 5. Support pillars 50 are, for example, positioned corresponding to the partition wall 40 between adjacent pressure chambers 42. The internal electrodes 52 and 53 of the support pillars 50 are not connected to the drive circuit of the drive IC 3 (described later) and are therefore not driven, thus becoming non-deformable fixed parts. Support pillars 50 can also be formed using other components instead of dummy actuators.

[0057] 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. After that, a first external electrode 54 and a second external electrode 55 are formed. After that, the piezoelectric elements 51 are polarized with a polarization voltage. The piezoelectric elements 51 are formed using 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 using conductive materials that can be sintered, such as silver or palladium. The first external electrode 54 and the second external electrode 55 are formed using known methods such as electroplating or sputtering with materials such as Ni, Cr, or Au.

[0058] The first external electrode 54 of each channel is connected to the individual 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, a bonding layer 27, and an insulating layer 28. The flexible printed wiring board 21 is arranged such that the area where the solder-plated layer 29 is formed faces the first external electrode 54, and the first external electrode 54 and the individual wirings 56 of each channel are electrically and mechanically connected by melting solder. Alternatively, instead of solder, it can be fixed by ACF (Anisotropic Conductive Film), ACP (Anisotropic Conductive Paste), NCF (Non-Conductive Film), NCP (Non-Coductive Paste), etc., and anisotropic conductive connections 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) and, for example, to a ground line (GND) via the flexible printed wiring board 21.

[0059] Figure 7 This is an example of the drive circuit for the inkjet head 100. For example... Figure 7As shown, the piezoelectric actuators 5 of each channel (#1ch~#nch) connect the first external electrode 54 to a separate wiring 56 and to the output terminal of the driver D (i.e., the drive circuit) of the driver IC 3. The connection point between the first external electrode 54 and the separate wiring 56 is an independent terminal of the piezoelectric actuator 5. The second external electrode 55 is connected to a common wiring 57 and to a common potential. The connection point between the second external electrode 55 and the common wiring 57 is a common terminal of the piezoelectric actuator 5.

[0060] The driver IC3 is connected to power supply 70, which provides the drive voltage V1 to the piezoelectric actuator 5 when ink is ejected, and power supply 71, which provides the drive voltage V2. 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 unit of the inkjet printer 10, i.e., the control board 17 (see reference 17). Figure 1 The signal line for the incoming print data is connected. Print 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).

[0061] Next, refer to Figure 8 and Figure 9 The ink ejection process is explained below. Each driver D of driver IC3 uses drive voltages V1, V2, and ground (GND) to supply drive waveforms to the individual terminals of piezoelectric actuator 5. Voltage V1 is, for example, 20V. Voltage V2 is, for example, 10V. Ground (GND) is, for example, 0V. The decision of which channel of piezoelectric actuator 5 to drive is based, for example, on the printing data. Figure 8 This is an example of the drive waveform given to piezoelectric actuator 5.

[0062] When the piezoelectric actuator 5, which has been given a ground potential to the common terminal, is driven, such as Figure 8 As shown, a voltage V2 is applied to an independent terminal to set it to standby mode. When voltage V2 is applied, an electric field is applied in the direction of the polarization axis of the piezoelectric element 51, and due to the inverse piezoelectric effect of the piezoelectric element, such as... Figure 9 As shown in (a), the piezoelectric actuator 5 is elongated in the stacking direction (Z direction) and the pressure chamber 42 is in a reduced-volume state. This is pre-emptively performed before the ink ejection timing. After this, the ink ejection timing ( Figure 8 At time t1), the potential of the independent terminal is initially lowered to ground (GND), thus as... Figure 9 As shown in (b), the elongated piezoelectric actuator 5 returns to its original state, i.e., it 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 boundary between the ink in the nozzle 24 and the external air is introduced concavely toward the pressure chamber 42.

[0063] Then, for example, after half the time of the pressure vibration cycle of head 2, if in Figure 8 At time t2, a voltage V2 is applied to the independent terminal, then as follows: Figure 9 As shown in (c), the piezoelectric actuator 5 elongates along the stacking direction (Z direction) and the volume of the pressure chamber 42 relatively decreases, thereby ejecting ink droplets R from the nozzle 24. Then, for example, after half the time of the pressure vibration cycle of the head 2, in Figure 8 At time t3, voltage V1 is applied 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 recovery ( Figure 9 (a) causes the volume of pressure chamber 42 to decrease and then recover, and this action attenuates residual vibration. Thus, the volume of pressure chamber 42 changes according to the longitudinal vibration of the piezoelectric actuator 5 in the stacking direction, enabling ink to be ejected. Once a series of ink ejections ends, the volume of ink in pressure chamber 42 decreases, and the ejected amount is reduced, causing ink to flow into pressure chamber 42 via upstream resistance flow path 43. At this time, if the ink flow rate supplied from the upstream side of pressure chamber is low, ink will also be introduced into pressure chamber 42 from the downstream side via downstream resistance flow path 46.

[0064] (Second Implementation)

[0065] 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 structure as the inkjet head 100 of the first embodiment, except that a pressure damper 8 is provided in the bypass flow path 49.

[0066] like Figure 10 As shown, the pressure damper 8 is formed by opening on one side of the bypass flow path 49 opposite to the nozzle plate 23 in the Z direction, and sealing the opening with a thin, soft material 81 such as a 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 to mitigate the rapid pressure changes in the upstream common liquid chamber 44 and the downstream common liquid chamber 47.

[0067] That is, particularly in multi-nozzle heads with multiple ink ejection channels, the ink flow rate can sometimes change drastically depending on the printing content. For example, after printing at full load across all channels, if printing continues on a pattern with a lot of blank space, such as a line drawing, the ink flow rate decreases sharply. Conversely, in a pattern where printing starts at full load from blank space, the ink flow rate increases sharply. If such a sudden change in ink flow occurs, the quality of ink must be stopped or released urgently, thus causing a change in the back pressure of the ejected ink. This change in back pressure affects the behavior of the ejected ink and leads to a deterioration in print quality.

[0068] While pressure dampers are sometimes used as units to absorb changes in ink back pressure, the numerous flow paths in the ink-circulating inkjet head 100 make it difficult to simply configure a pressure damper. Therefore, by placing the pressure damper 8 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. Thus, one pressure damper 8 is sufficient. The thinner and larger the area of ​​the film-type pressure damper 8, the more efficiently it functions. Therefore, compared to placing pressure dampers separately on the upstream and downstream sides, a common pressure damper 8 for both 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 is also easier to fill with ink. Because the damping effect of the pressure damper 8 is improved, adjusting the width of the bypass flow path 49 in the Z and X directions to make it flatter further increases the area of ​​the soft material 81. The location where the soft material 81 is disposed is not limited to an opening in the Z direction.

[0069] The flow rate of ink flowing in the bypass flow path 49 equipped with the pressure damper 8 is, for example, greater than or equal to the total circulating flow rate of ink flowing in each pressure chamber 42. That is, in order for the pressure damper 8 to function effectively, 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 flowing in the pressure chamber 42. The flow path resistance of the entire flow path flowing in 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. In order to prevent ink from flowing backward from a point further downstream than the downstream ink port 48, it is preferable, similar to the first embodiment, that the total flow rate of ink flowing in the entire flow path in the pressure chamber 42 and the ink flowing in the bypass flow path 49 is greater than or equal to the maximum total flow rate ejected from the nozzle 24.

[0070] like Figure 11As shown, pressure dampers 82 and 83 can also be provided near the upstream ink port 45 and the downstream ink port 48. In this case, they are configured separately on the upstream and downstream sides. Pressure dampers 82 and 83 are formed similarly to pressure damper 8 by opening on one side 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. In this way, by providing pressure dampers 8, 82, and 83 at both ends of the upstream common liquid chamber 44 and the downstream common liquid chamber 47, respectively, the absorption effect of pressure changes is improved.

[0071] (Third Implementation)

[0072] 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 structure as the inkjet head 100 of the first embodiment, except that the bypass flow path 49 is made into a tubular shape.

[0073] like Figure 12 As shown, the tubular bypass flow path 49 is configured in an inverted U-shape in the Z direction. If the bypass flow path 49 is tubular and has a maximum height h (in the Z direction), when filling ink from a state where air remains in the head 2, the pressure of the ink supplied by the ink pump 321 can be adjusted to allow it to pass through or not through the bypass flow path 49. That is, the highest point of the bypass flow path 49 is higher than the height of the upstream common liquid chamber 44. For example, if the pressure difference is maintained less 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 in 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.

[0074] By filling each pressure chamber 42 with ink in this state and then circulating the ink to make the upstream and downstream pressure difference greater than ρgh, ink can also be filled into the bypass flow path 49. The highest point of the bypass flow path 49 is expected to be higher than... Figure 6 The highest height of ink supply path 311 in the middle.

[0075] The tubular bypass flow path 49 can be formed, for example, using a flexible tube or other soft tube. Alternatively, it can be formed using a rigid tube. Furthermore, as... Figure 13 As shown, a pressure damper 84, such as a flexible bag, can be installed in the tubular bypass flow path 49. Because the flexible bag allows for a large surface area, a high damping effect can be achieved.

[0076] As explained 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 liquid in a liquid circulation mode can be provided.

[0077] The advantages of increasing the ink circulation flow rate by providing a bypass flow path 49 to the head 2 as a whole are as follows: the ink can easily transfer heat to the head 2, and the temperature of the head 2 can be made close to the temperature of the ink. In addition, the advantages of increasing the ink circulation flow rate by providing a bypass flow path 49 to the head 2 as a whole are as follows: the ink can be stirred by increasing the circulation flow rate, and the settling of inks containing sedimenting agents such as silica can be prevented.

[0078] 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. Furthermore, it is not limited to drop-on-demand piezoelectric methods, but can also be applied to continuous inkjet methods.

[0079] In the above embodiments, the inkjet head 100 of the inkjet printer 10 was 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.

[0080] 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 can be omitted, substituted, and modified in various ways without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

[0081] Explanation of reference numerals in the attached figures

[0082] 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.

Claims

1. A liquid ejection head, characterized by, Possessing: a plurality of pressure chambers, each communicating with a nozzle; a plurality of upstream-side resistance flow paths, each communicating with the pressure chambers; an upstream-side common liquid chamber, communicating with the plurality of upstream-side resistance flow paths; an upstream-side liquid port, communicating with the upstream-side common liquid chamber on one end side in the arrangement direction of the plurality of pressure chambers; a plurality of downstream-side resistance flow paths, each communicating with the pressure chambers; a downstream-side common liquid chamber, communicating with the plurality of downstream-side resistance flow paths; a downstream-side liquid port, communicating with the downstream-side common liquid chamber on one end side in the arrangement direction of the plurality of pressure chambers; a bypass flow path, connecting 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; and a pressure damper provided in the bypass flow path.

2. The liquid ejection head according to claim 1, wherein a flow path resistance of the bypass flow path is lower than a parallel flow path resistance of 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.

3. The liquid ejection head according to claim 1 or 2, wherein the pressure damper is a film damper in which an opening portion is covered with a flexible resin.

4. The liquid ejection head according to claim 1 or 2, wherein the pressure damper is a flexible bag provided midway in the bypass flow path.

5. The liquid ejection head according to claim 1 or 2, wherein a highest point of the bypass flow path is higher than a height of the upstream-side common liquid chamber. ​

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