Liquid dispensing head

Abstract

To provide a liquid dispensing head that can stably dispense liquid in a liquid circulation system. [Solution] The liquid discharge head of the embodiment comprises a plurality of pressure chambers communicating with each nozzle, a plurality of upstream resistance passages, an upstream common liquid chamber, an upstream liquid port, a plurality of downstream resistance passages, a downstream common liquid chamber, a downstream liquid port, and a bypass passage. The bypass passage connects the upstream common liquid chamber and the downstream common liquid chamber at the other end of the plurality of pressure chambers in the direction of arrangement. The total flow rate of the liquid flowing through the bypass passage and the liquid flowing through the plurality of passages from the inlet of each upstream resistance passage to the outlet of each downstream resistance passage is equal to or greater than the total maximum discharge flow rate of the liquid discharged from each nozzle.

Description

Technical Field

[0001] Embodiments of the present invention relate to a liquid ejection head.

Background Art

[0002] A liquid ejection head that supplies a predetermined amount of liquid to a predetermined position is known. The liquid ejection head is mounted on, for example, an inkjet printer, a 3D printer, a dispensing device, or the like. An inkjet printer ejects ink droplets from an inkjet head to form an image or the like on the surface of a recording medium. A 3D printer ejects droplets of a modeling material from a modeling material ejection head and cures them to form a three-dimensional object. A dispensing device ejects droplets of a sample and supplies a predetermined amount to a plurality of containers or the like.

[0003] The liquid ejection head has a plurality of channels for ejecting liquid. Each channel includes a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and an actuator for changing the volume of the pressure chamber. The liquid ejection head selects a channel for ejecting liquid from among the plurality of channels, and applies a drive voltage to the actuator of the selected channel to eject the liquid.

[0004] After ejection, vibration (meniscus vibration) determined by the surface tension of the liquid meniscus in the nozzle and the mass of this liquid remains in the liquid ejection head. For example, in a high-speed liquid ejection head, it is necessary to quickly suppress this vibration, and for this purpose, resistance channels are provided before and after the pressure chamber. However, if a liquid circulation type head is attempted, this resistance channel hinders the circulation of the liquid. Particularly in a multi-nozzle head having a plurality of channels, if the upstream and downstream flow ratios of the resistance channels do not match in each channel, a pressure difference occurs between the channels, and the printing quality deteriorates. Also, in a channel with a small upstream channel resistance, the meniscus is likely to get wet, and in a channel with a small downstream channel resistance, air is likely to be mixed in. To avoid these problems, the circulation flow rate must be suppressed, but if the circulation flow rate is less than one time the liquid ejection flow rate, the liquid will be drawn from the downstream side into the pressure chamber at the time of maximum liquid ejection. Then, the old and dirty liquid on the downstream side will return to the pressure chamber. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-069127 [Patent Document 2] Japanese Patent Publication No. 2023-173168 [Overview of the project] [Problems that the invention aims to solve]

[0006] The problem that this invention aims to solve is to provide a liquid discharge head that can stably discharge liquid in a liquid circulation system. [Means for solving the problem]

[0007] The liquid discharge head of an embodiment of the present invention comprises a plurality of pressure chambers, a plurality of upstream resistance passages, an upstream common liquid chamber, an upstream liquid port, a plurality of downstream resistance passages, a downstream common liquid chamber, a downstream liquid port, and a bypass passage. Each of the plurality of pressure chambers communicates with a nozzle. Each of the plurality of upstream resistance passages communicates with the pressure chambers. The upstream common liquid chamber communicates with the plurality of upstream resistance passages. The upstream liquid port communicates with the upstream common liquid chamber at one end in the direction of arrangement of the plurality of pressure chambers. Each of the plurality of downstream resistance passages communicates with a pressure chamber. The downstream common liquid chamber communicates with the plurality of downstream resistance passages. The downstream liquid port communicates with the downstream common liquid chamber at one end in the direction of arrangement of the plurality of pressure chambers. The bypass passage connects the upstream common liquid chamber and the downstream common liquid chamber at the other end in the direction of arrangement of the plurality of pressure chambers. The total flow rate of the liquid flowing through the bypass channel and the liquid flowing through the multiple channels from the inlet of each upstream resistance channel to the outlet of each downstream resistance channel is equal to or greater than the total maximum discharge flow rate of the liquid discharged from each nozzle. [Brief explanation of the drawing]

[0008] [Figure 1]This is an overall configuration diagram of an inkjet printer equipped with an inkjet head according to the first embodiment. [Figure 2] The above is a perspective view of the inkjet head. [Figure 3] This is a partially enlarged cross-sectional view of the head portion of the inkjet head shown above. [Figure 4] This is a partially enlarged cross-sectional view of the head portion of the inkjet head shown above. [Figure 5] These are a perspective view and a cross-sectional view of the head portion of the inkjet head shown above, with some parts enlarged. [Figure 6] This is an overall configuration diagram of the ink circulation system for the inkjet head shown above. [Figure 7] This is the drive circuit for the inkjet head described above. [Figure 8] This is the drive waveform applied to the piezoelectric actuator of the inkjet head described above. [Figure 9] This is a diagram illustrating the operation of a piezoelectric actuator given the above drive waveform. [Figure 10] These are a partially enlarged perspective view and a cross-sectional view of the head portion of the inkjet head of the second embodiment. [Figure 11] This is a modified example of the inkjet head of the second embodiment. [Figure 12] These are a partially enlarged perspective view and a cross-sectional view of the head portion of the inkjet head of the third embodiment. [Figure 13] This is a modified example of the inkjet head of the third embodiment. [Modes for carrying out the invention]

[0009] The liquid discharge head according to the embodiment will be described in detail below with reference to the attached drawings. In each drawing, identical components are denoted by the same reference numerals.

[0010] (First Embodiment) As an example of an image forming apparatus equipped with a liquid ejection head of the first embodiment, an inkjet printer 10 for printing images on a recording medium will be described. Figure 1 shows a schematic configuration of the inkjet printer 10. The inkjet printer 10 has a cassette 12 for storing a sheet S, which is an example of a recording medium, an upstream transport path 13 for the sheet S, a transport belt 14 for transporting the sheet S taken out of the cassette 12, a plurality of inkjet heads 100-103 for ejecting ink droplets toward the sheet S on the transport belt 14, a downstream transport path 15 for the sheet S, an output tray 16, and a control board 17 arranged inside the housing 11. The operation unit 18, which is the user interface, is located on the upper side of the housing 11.

[0011] The image data to be printed on sheet S is generated, for example, by an externally connected device, such as a computer 200. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 via cable 201 and connectors 202 and 203.

[0012] The pickup roller 204 supplies sheets S one by one from the cassette 12 to the upstream transport path 13. The upstream transport path 13 consists of feed roller pairs 131 and 132 and sheet guide plates 133 and 134. The sheets S are sent to the upper surface of the transport belt 14 via the upstream transport path 13. The arrow 104 in the figure indicates the transport path of the sheets S from the cassette 12 to the transport belt 14.

[0013] The conveyor belt 14 is a mesh-like endless belt with numerous through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, rotatably support 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. In the figure, 105 indicates the direction of rotation of the conveyor belt 14. A negative pressure container 206 is placed 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 negative pressure inside the negative pressure container 206 with the airflow it generates, causing the sheet S to adhere to and hold on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

[0014] Examples of liquid ejection heads, inkjet heads 100 to 103, are arranged to face a sheet S adsorbed and held on a conveyance belt 14 with a slight gap of, for example, 1 mm therebetween. The inkjet heads 100 to 103 eject ink droplets toward the sheet S, respectively. The inkjet heads 100 to 103 print an image when the sheet S passes below. Each of the inkjet heads 100 to 103 has the same structure except that the color of the ejected ink is different. The colors of the ink are, for example, cyan, magenta, yellow, and black.

[0015] Ink is supplied to each of the inkjet heads 100 to 103 by each of ink circulation devices 341 to 344 in a circulating manner. The detailed configuration of the ink circulation devices 341 to 344 will be described later (see FIG. 6). In FIG. 1, for the convenience of drawing, the ink circulation devices 341 to 344 are each illustrated with a dashed line frame.

[0016] After image formation, the sheet S is sent from the conveyance belt 14 to a downstream conveyance path 15. The downstream conveyance path 15 includes a pair of feed rollers 151, 152, 153, 154 and sheet guide plates 155, 156 that define the conveyance path of the sheet S. The sheet S is sent from the downstream conveyance path 15 to a discharge tray 16 through a discharge port 157. An arrow 107 in the figure indicates the conveyance path of the sheet S.

[0017] Subsequently, the configuration of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 while referring to FIGS. 2 to 5, but the inkjet heads 101 to 103 also have the same structure as the inkjet head 100.

[0018] As shown in Figure 2, the inkjet head 100 includes a head unit 2, which is an example of a liquid ejection unit. The head unit 2 is connected to a flexible printed circuit board 21, which is an example of a film wiring board. The flexible printed circuit board 21 is connected to a printed circuit board 22, which is an example of a relay board. The head unit 2 includes a nozzle plate 23, which is an example of a nozzle unit. The ink-circulating head unit 2 is connected to an ink circulation device 341 via an ink supply path 311 and an ink discharge path 331.

[0019] The nozzles 24 of each channel that eject ink are arranged along the first direction of the nozzle plate 23, for example, the X direction. The nozzle density is set to a range of, for example, 150 to 1200 dpi. The nozzles 24 are not limited to a single row, but may be arranged in multiple rows. The detailed configuration of the head unit 2 will be described later.

[0020] The flexible printed circuit board 21 is a flexible printed circuit board made of a synthetic resin film such as polyimide. The flexible printed circuit board 21 is equipped with a driver chip, which is an integrated circuit (IC) 3 (hereinafter referred to as the driver IC). The printed circuit board 22 is a rigid through-hole board made of multiple layers of glass fiber-reinforced epoxy resin and copper wiring layers. The driver IC 3, which acts as the control unit for the inkjet head 100, temporarily stores the print data sent from the control board 17, which is equipped with a CPU that acts as the control unit for the inkjet printer 10, via the printed circuit board 22, and provides drive signals to each channel to eject ink at predetermined timings.

[0021] Figures 3 to 5 are partial cross-sectional views of the head section 2. The nozzle plate 23 is bonded to one surface of the pressure chamber substrate 4. The nozzle plate 23 is a rectangular plate formed from, for example, a resin such as polyimide or a metal such as stainless steel. The diaphragm 41 is bonded to one surface of the pressure chamber substrate 4 opposite to the nozzle plate 23. The diaphragm 41 is flexible and deforms when an external force is applied. The diaphragm 41 is a rectangular plate formed from, for example, a flexible polyimide film or metal.

[0022] The pressure chamber 42 is formed in the pressure chamber substrate 4. Multiple pressure chambers 42 are arranged at the position of each nozzle 24 and communicate with each nozzle 24. As an example, the pressure chamber 42 has a rectangular opening formed in the pressure chamber substrate 4 that penetrates in a second direction, for example in the Z direction, and the openings on both sides in the Z direction are closed by the nozzle plate 23 and the diaphragm 41, respectively, to form a space for filling with ink. The pressure chamber 42 is formed in a groove shape along a third direction, for example in the Y direction.

[0023] In particular, as shown in Figure 5, in the ink-circulating head, one end (upstream side) of each pressure chamber 42 in the Y direction is connected to the upstream common liquid chamber 44 via an upstream resistance passage 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 passage 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 passage 43. As an example, the upstream common liquid chamber 44 is formed by creating an opening that penetrates in the Z direction in the pressure chamber substrate 4, and blocking the openings on both sides in the Z direction with a nozzle plate 23 and a diaphragm 41, respectively, to form a space through which ink flows. 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 multiple pressure chambers 42, one end in the X direction in the example shown in the figure. The upstream ink port 45 is connected to the ink supply passage 311 (see Figure 2). The upstream ink port 45 is an example of an upstream liquid port.

[0024] The other end (downstream side) of each pressure chamber 42 in the Y direction is connected to a downstream common liquid chamber 47 via a downstream resistance passage 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 passage 46 is connected to its side. The downstream common liquid chamber 47 is an ink discharge manifold through which the ink discharged from each pressure chamber 42 via each downstream resistance passage 46 flows in common. As an example, the downstream common liquid chamber 47 is formed by creating an opening that penetrates in the Z direction in the pressure chamber substrate 4, and blocking the openings on both sides in the Z direction with a nozzle plate 23 and a diaphragm 41, respectively, to form a space through which the ink flows. The downstream ink port 48, which discharges ink from the downstream common liquid chamber 47 to the outside of the head unit 2, is provided on one end in the same X direction as the upstream ink port 45. The downstream ink port 48 is connected to the ink discharge passage 331 (see Figure 2). The downstream ink port 48 is an example of a downstream liquid port.

[0025] The upstream resistance channel 43 and the downstream resistance channel 46 are formed to have a smaller channel cross-section and thus provide flow resistance, for example, by being narrower than the width of the pressure chamber 42 in the X direction. The width may be narrowed in the Z direction instead of the X direction, or both the X and Z directions may be narrowed. The upstream resistance channel 43 and the downstream resistance channel 46 are preferably formed along the central axis in the Y direction of the pressure chamber 42, but are not limited to this. That is, the upstream resistance channel 43 and the downstream resistance channel 46 only need to have a channel cross-section for the ink that is smaller than the channel cross-section of the pressure chamber 42. Therefore, the shape of the channel cross-section of the upstream resistance channel 43 and the downstream resistance channel 46 is not limited to a rectangle. It is preferable, but not limited to, that each upstream resistance channel 43 has the same shape as the other channels. Similarly, it is preferable, but not limited to, that each downstream resistance channel 46 has the same shape as the other channels. The upstream resistance channel 43 and the downstream resistance channel 46 are preferably symmetrical in the Y direction via the pressure chamber 42, but are not limited to this. However, in order to suppress the occurrence of pressure differences between channels, the upstream-downstream ratio of the resistance channels (43, 46) of each channel should be matched.

[0026] The bypass channel 49 is located on one side of the arrangement direction of the multiple pressure chambers 42, on the other end in the X direction in the example shown in the figure. That is, it is located on the opposite side from the upstream ink port 45 and the downstream ink port 48. The bypass channel 49 is a channel that bypasses ink by connecting the other ends of the upstream common liquid chamber 44 and the downstream common liquid chamber 47.

[0027] The bypass channel 49 is formed with a smaller cross-sectional area than the upstream common liquid chamber 44 and the downstream common liquid chamber 47, thereby providing flow resistance. As an example, it is made into a flattened shape with a smaller width in the Z direction and a larger width in the X direction. This allows the ink circulation flow to form not only in the bypass channel 49 but also in the flow supplying ink to each pressure chamber 42. The ratio of the total ink flow rate through each pressure chamber 5 to the ink flow rate through the bypass channel 49 can be adjusted by the flow resistance of the bypass channel 49. For example, when the length of the bypass channel 49 is constant, increasing the cross-sectional area of ​​the bypass channel 49 will allow more ink to flow through the bypass channel 49, and decreasing the cross-sectional area of ​​the bypass channel 49 will allow more ink to flow through each pressure chamber 42. At this time, the ink flow rate through each pressure chamber 42 is adjusted to be less than the ink flow rate discharged 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 discharged from the nozzle 24. The remaining amount will be drawn in from the downstream common liquid chamber 47, as will be described later.

[0028] To compensate for any deficiency from the downstream common liquid chamber 47, the total flow rate of ink flowing through the bypass channel 49 and the flow rate of ink flowing through each channel from the inlet of each upstream resistance channel 43 to the outlet of each downstream resistance channel 46 is set to be equal to or greater than the total maximum discharge flow rate of ink discharged from each nozzle 24. This flow rate setting is performed, for example, by the ink circulation device 341. The maximum ink discharge flow rate is the total flow rate when ink is discharged from all discharge channels.

[0029] As an example, if the circulating flow rate of ink through the pressure chamber 42 is set to 0.6 times the discharge flow rate as described above, the flow resistance of the bypass channel 49 is set to (6 / 4) times the parallel flow resistance of all channels passing through the pressure chamber 42, so that 0.4 times the discharge flow rate flows through the bypass channel. This setting is done, for example, by adjusting the cross-sectional area of ​​the bypass channel 49. Then, if ink is circulated from the upstream ink port 45 to the downstream ink port 48 at, for example, 1 times the total maximum discharge flow rate, the circulating flow rate when ink is not being discharged will be in a 6:4 ratio between the circulation path through each pressure chamber 42 and the bypass channel 49. At maximum discharge, ink flows backward from the downstream common liquid chamber 47 towards the pressure chamber 42, but since that amount of ink is supplied to the downstream common liquid chamber 47 from the bypass channel 49, ink does not flow backward from the downstream side beyond the downstream ink port 48, which may be contaminated with foreign matter or air bubbles.

[0030] The relationship between the flow rate of the ink circulation flow through the pressure chamber 42, that is, the flow rate that flows into the pressure chamber 42 when no ink is ejected from the nozzles 24, and the flow rate of the ink circulation flow through the bypass channel 49, is defined as the relationship a) to d) below, for example, with the maximum ejection flow rate, that is, the total amount of ink consumed when maximum continuous ejection is performed from all nozzles 24, set to 1. Pressure chamber 42 Bypass channel 49 Total ratio a) 0.6 0.4 1 6:4 b) 0.6 1.4 2 3:7 c) 0.2 0.8 1 1:4 d) 0.2 1.8 2 1:9 In the above cases b) and d), the total flow rate is larger than in a) and c), which is advantageous for temperature stability and preventing ink component sedimentation. In the cases a) and c), the total flow rate is smaller than in b) and d), making ink supply easier. In the cases c) and d), the pressure chamber circulation flow rate is smaller than in a) and b), so the effect of flow path resistance on nozzle back pressure is smaller, making it easier to stabilize nozzle back pressure. In the cases a) and b), the pressure chamber circulation flow rate is larger than in c) and d), making it easier to discharge foreign matter and air bubbles mixed into the pressure chamber 42 to the downstream side. In the order a), b), c), and d), the ratio of the flow rate of the bypass flow path 49 to the pressure chamber circulation flow rate is larger, so even if needle-shaped foreign matter is mixed into the supplied ink, it is difficult for it to be mixed into the pressure chamber 42. In all cases a), b), c), and d), the total flow rate is greater than 1, so even at maximum discharge, it is possible to prevent foreign matter in the ink from being drawn into the head unit 2 from the downstream ink port 48.

[0031] The bypass channel 49 is not limited to having a flattened cross-section; its width in the Z direction and X direction may be adjusted. That is, the cross-sectional area of ​​the bypass channel 49 should be smaller than the cross-sectional areas of the upstream common liquid chamber 44 and the downstream common liquid chamber 47. Therefore, the shape of the cross-sectional area of ​​the bypass channel 49 is not limited to a rectangle. A resistance may be provided in a part of the bypass channel 49 to adjust the ratio of the flow rate through the bypass channel 49 to the total flow rate through the pressure chamber 42. In that case, it is desirable to place pressure dampers on both sides of the resistance channel. One of the pressure dampers may be placed near the ink port as shown in Figure 11(a). The configuration of the pressure damper will be described later.

[0032] Figure 6 shows the overall configuration of the ink circulation device 341 that circulates and supplies ink to the inkjet head 100. The ink circulation device 341 is an example of a liquid circulation device for a liquid ejection head. Note that the ink circulation devices 342 to 344 that circulate and supply ink to the inkjet heads 101 to 103 have the same configuration as the ink circulation device 341. As shown in Figure 6, the ink circulation device 341 consists of an ink tank 315, an ink pump 321, an ink filter F1, the head section 2 of the inkjet head 100, and an ink supply passage 311 and an ink discharge passage 331 connecting them. Furthermore, air valves V1 and V2 and air filters F2 and F3 are provided in the ink supply passage 311 and the ink discharge passage 331, respectively.

[0033] The upstream common liquid chamber 44 controls the ink circulation flow to a predetermined flow rate, while the downstream common liquid chamber 47 controls it to a predetermined pressure. For this reason, it is preferable that the downstream ink discharge passage 331 be wider than the ink supply passage 311. The ink supply passage 311 is, for example, a 3 mm diameter tube, and the ink discharge passage 331 is, for example, a 6 mm diameter tube. In this case, the opening of the upstream ink port 45 is 3 mm in diameter, and the opening of the downstream ink port 48 is 6 mm in diameter.

[0034] When the ink circulation device 341 is initially filled with ink, it first closes the air valve V2 and opens the air valve V1, and the ink pump 321 supplies ink from the upstream side. The ink flows into the head unit 2 via the upstream ink port 45 and flows through the upstream common liquid chamber 44. Then, it flows into the downstream common liquid chamber 47 via the pressure chamber 42 and bypass passage 49 of each channel. The settings for the ink flow rate through the upstream common liquid chamber 44, the ink flow rate through the pressure chamber 42 of each channel, and the ink flow rate through the bypass passage 49 are as previously described. The ink ejection operation of each channel is performed while maintaining this ink circulation flow.

[0035] Returning to the explanation in Figure 3, a piezoelectric actuator 5, which is an example of an actuator, is positioned on one side of the diaphragm 41 opposite to the pressure chamber 42. Each channel's piezoelectric actuator 5 is arranged in a position facing the pressure chamber 42, with the diaphragm 41 in between. The piezoelectric actuator 5 and the diaphragm 41 are joined together, for example, with an adhesive. Each piezoelectric actuator 5 is fixed by joining one side opposite to the diaphragm 41 in the Z direction to a support member 7. In particular, as shown in Figure 3, the piezoelectric actuator 5 is a laminated piezoelectric actuator formed by alternately stacking piezoelectric elements 51, such as a piezo element, a first internal electrode 52, and a second internal electrode 53 in layers. Each piezoelectric element 51 is positioned with its polarization direction opposite to that of the others in the Z direction, for example, and is deformed in 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, respectively. The first internal electrode 52 is formed to one end face of the piezoelectric actuator 5 in the Y direction and is connected to a first external electrode 54 formed on this end face. The second internal electrodes 53 are formed to the other end face of the piezoelectric actuator 5 in the Y direction and are connected to the second external electrodes 55 formed on this end face.

[0036] The dummy layer 58 is made of the same material as the piezoelectric body 51. The dummy layer 58 does not have internal electrodes and is not subjected to an electric field, so it does not deform. The dummy layer 58 serves as a base for fixing the piezoelectric actuator 5 to the support member 7 (see Figure 4), or as a polishing surface for polishing during or after assembly to achieve accuracy. In particular, as shown in Figure 4, support columns 50 may be placed between the piezoelectric actuators 5 of each channel via grooves 59. The support columns 50 may be made of dummy actuators formed in the same way as the piezoelectric actuators 5 used for driving. The support columns 50 are positioned, for example, at the partition wall 40 between adjacent pressure chambers 42. The internal electrodes 52 and 53 of the support columns 50 are not connected to the drive circuit of the drive IC 3 described later, and are therefore not driven, so they do not deform. The support columns 50 may be made of a different material instead of being made of dummy actuators.

[0037] In the case of a piezoelectric actuator 5 in which multiple piezoelectric elements 51 are stacked, as an example, a first internal electrode 52 and a second internal electrode 53 are deposited on the main surface of each piezoelectric element 51 that has been processed into a thin plate shape. Then the piezoelectric elements 51 are stacked and fired to form a single unit. After that, a first external electrode 54 and a second external electrode 55 are deposited. After that, 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 sodium potassium niobate. The first internal electrode 52 and the second internal electrode 53 are deposited from a sinterable conductive material such as silver palladium. The first external electrode 54 and the second external electrode 55 are deposited from Ni, Cr, Au, etc., by known methods such as plating or sputtering.

[0038] The first external electrode 54 of each channel is connected to the individual wiring 56 of the flexible printed circuit board 21 (see Figure 3). The flexible printed circuit board 21 has a base material 26, individual wiring 56, an adhesive layer 27, and an insulating layer 28. The flexible printed circuit board 21 is arranged so that the area where the solder plating layer 29 is formed faces the first external electrode 54, and the first external electrode 54 of each channel and the individual wiring 56 are electrically and mechanically connected by melting solder. Instead of solder, the connections may be fixed with ACF (Anisotropic Conductive Film), ACP (Anisotropic Conductive Paste), NCF (Non-Conductive Film), NCP (Non-Conductive Paste), etc., and anisotropic conductive connection may 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 ground (GND) via the flexible printed circuit board 21.

[0039] Figure 7 shows an example of the drive circuit for the inkjet head 100. As shown in Figure 7, each piezoelectric actuator 5 for each channel (#1ch to #nch) has its first external electrode 54 connected to individual wiring 56, which is connected to the output terminal of the drive driver D (i.e., drive circuit) of the drive IC 3. The connection point between the first external electrode 54 and the individual wiring 56 is the individual terminal of the piezoelectric actuator 5. The second external electrode 55 is connected to common wiring 57 and connected 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.

[0040] The drive IC 3 is connected to power supplies 70 for drive voltage V1 and 71 for drive voltage V2, which are supplied to the piezoelectric actuator 5 when ejecting ink. Power supplies 70 and 71 have their positive terminals connected to the drive IC 3 and their negative terminals connected to ground (GND). The drive IC 3 is connected to the signal lines of the print data sent from the control board 17 (see Figure 1), which is the control unit of the inkjet printer 10. 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).

[0041] Next, the ink ejection operation will be explained with reference to Figures 8 and 9. Each drive driver D of the drive IC3 uses drive voltages V1, V2 and ground (GND) to provide a drive waveform to the individual terminals of the piezoelectric actuator 5. 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 is based, for example, on the print data. Figure 8 is an example of a drive waveform provided to the piezoelectric actuator 5.

[0042] When driving the piezoelectric actuator 5, which has a ground potential applied to the common terminal, a voltage V2 is applied to the individual terminals to put it into standby mode, as shown in Figure 8. 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, the piezoelectric actuator 5 expands in the stacking direction (Z direction), as shown in Figure 9(a), and the volume of the pressure chamber 42 decreases. This is done prior to the ink ejection timing. Then, at the ink ejection timing (time t1 in Figure 8), the potential of the individual terminals is first lowered to ground (GND), so the expanded piezoelectric actuator 5 returns to its original position, i.e., contracts relatively, as shown in Figure 9(b), and the volume of the pressure chamber 42 expands relatively. When the volume of the pressure chamber 42 expands, the meniscus at the interface between the ink and the outside air in the nozzle 24 is pulled in a concave shape towards the pressure chamber 42.

[0043] For example, after half the pressure vibration period of the head unit 2 has elapsed, at time t2 in Figure 8, when a voltage V2 is applied to the individual terminals, as shown in Figure 9(c), the piezoelectric actuator 5 extends in the stacking direction (Z direction), relatively reducing the volume of the pressure chamber 42, causing ink droplets R to be ejected from the nozzle 24. Then, for example, after half the pressure vibration period of the head unit 2 has elapsed, at time t3 in Figure 8, a voltage V1 is applied to the individual terminals, and the voltage is returned to V2 at time t4 after a predetermined time. The extension (Figure 9(d)) and return (Figure 9(a)) of the piezoelectric actuator 5 at this time reduce and return the volume of the pressure chamber 42, and this operation dampens residual vibrations. In this way, the volume of the pressure chamber 42 changes in accordance with the longitudinal vibration of the piezoelectric actuator 5 in the stacking direction, allowing ink to be ejected. When the series of ink ejections is complete, the volume of ink in the pressure chamber 42 has decreased by the amount ejected, so ink flows into the pressure chamber 42 via the upstream resistance flow path 43. If the ink flow rate supplied from the upstream side of the pressure chamber is low, ink will also be drawn into the pressure chamber 42 from the downstream side via the downstream resistance channel 45.

[0044] (Second Embodiment) Next, the inkjet head 100 of the second embodiment will be described. 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 channel 49, as shown in Figure 10.

[0045] As shown in Figure 10, the pressure damper 8 is formed by opening one side of the bypass channel 49 opposite to the nozzle plate 23 in the Z direction, and sealing this opening with a flexible material 81 such as a thin polyimide film. The flexible material 81 such as a polyimide film is an example of a flexible resin that covers the opening of the bypass channel 49. The pressure damper 8 is an example of a membrane damper. When the amount of ink discharged changes rapidly, this flexible material 81 can flex, mitigating the rapid pressure changes in the upstream common liquid chamber 44 and the downstream common liquid chamber 47.

[0046] In other words, especially with multi-nozzle heads that have multiple channels for ejecting ink, the flow rate of ejected ink can change abruptly depending on the printing content. For example, when printing a pattern like a line drawing with many blank spaces immediately after printing with all channels at full duty cycle, the ink flow rate decreases abruptly. Conversely, when printing a pattern that starts from a blank space and then resumes full duty cycle, the ink flow rate increases abruptly. Such abrupt changes in ink flow rate require the ink, which has mass, to stop or start suddenly, which changes the back pressure of the ejected ink. Changes in back pressure affect the behavior of the ejected ink and lead to a deterioration in print quality.

[0047] While pressure dampers have been used to absorb changes in ink back pressure, the ink-circulating inkjet head 100 has many flow paths, making it difficult to install a pressure damper with a simple configuration. Therefore, by installing 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. For this reason, only one pressure damper 8 is needed. Membrane-type pressure dampers 8 function more efficiently the thinner and larger their surface area. For this reason, using a common pressure damper 8 for both the upstream and downstream sides allows for more efficient absorption of pressure changes with a smaller surface area than installing separate pressure dampers on the upstream and downstream sides. In addition, since the pressure damper 8 is located on the bypass flow path 49, there is the advantage that it is easier to fill with ink. To enhance the damping effect of the pressure damper 8, the bypass flow path 49 can be made flatter by adjusting its width in the Z and X directions, which increases the surface area of ​​the soft material 81. However, the location where the soft material 81 is placed is not limited to the opening in the Z direction.

[0048] The flow rate of ink flowing through the bypass channel 49 equipped with the pressure damper 8 is set to be greater than or equal to the sum of the circulating ink flow rates through each pressure chamber 42. That is, in order for the pressure damper 8 to function effectively, the dimensions (cross-sectional area and length) of the bypass channel 49 are designed such that the flow resistance of the bypass channel 49 is less than or equal to the parallel flow resistance of all the flow channels through the pressure chamber 42. The flow resistance of all the flow channels through the pressure chamber 42 is the flow resistance of multiple flow channels from the inlet of the upstream resistance channel 43 to the outlet of the downstream resistance channel 46. The parallel flow resistance is the sum of the flow resistances of all channels. To prevent ink from flowing back from the downstream side beyond the downstream ink port 48, as in the first embodiment, it is desirable that the total flow rate of ink flowing through all the flow channels through the pressure chamber 42 and the bypass channel 49 is greater than or equal to the maximum total flow rate discharged from the nozzle 24.

[0049] As shown in Figure 11, pressure dampers 82 and 83 may also be provided near the upstream ink port 45 and the downstream ink port 48. In this case, they are placed individually on the upstream and downstream sides. Similar to pressure damper 8, pressure dampers 82 and 83 are formed by opening 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. 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 enhanced.

[0050] (Third embodiment) Next, the inkjet head 100 of the third embodiment will be described. 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 channel 49 is tubular, as shown in Figure 12.

[0051] As shown in Figure 12, the tubular bypass channel 49 is arranged in an inverted U-shape in the Z direction. By making the bypass channel 49 tubular and providing a maximum height h (in the Z direction), when filling ink from a state where air remains in the head unit 2, it is possible to choose whether or not to pass the ink through the bypass channel 49 by adjusting the pressure of the ink supplied by, for example, the ink pump 321. That is, the highest point of the bypass channel 49 is higher than the height of the upstream common liquid chamber 44. As a specific example, if ink is flowed from the upstream ink port 45 to the downstream ink port 48 while maintaining a pressure difference less than ρgh, the ink cannot exceed the maximum height h and therefore does not flow through the bypass channel 49. Here, ρ is the density of the ink and g is the acceleration due to gravity. In this state, ink is filled into each pressure chamber 42, and then the upstream-downstream pressure difference is increased to ρgh or more and further circulation is performed to fill the bypass channel 49 with ink as well. It is desirable that the highest point of the bypass channel 49 be higher than the maximum height of the ink supply path 311 in Figure 6.

[0052] The tubular bypass channel 49 may be made of a flexible tube or other soft material. Alternatively, it may be made of a rigid tube. Furthermore, as shown in Figure 13, a pressure damper 84 made of a flexible bag or the like may be provided in the tubular bypass channel 49. A flexible bag can easily provide a large surface area, thus achieving a high damping effect.

[0053] As described above, according to any of the embodiments described above, by providing a bypass channel 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 multiple pressure chambers 42, an inkjet head 100 capable of stably ejecting liquid in a liquid circulation system can be provided.

[0054] Providing the bypass channel 49 to increase the overall ink circulation flow rate of the print head 2 has the advantage of making it easier for the ink to transfer heat to the print head 2, bringing the temperature of the print head 2 closer to the temperature of the ink. In addition, providing the bypass channel 49 to increase the overall ink circulation flow rate of the print head 2 allows for agitation of the ink, which has the effect of preventing the settling of sedimentary inks, such as those containing silica.

[0055] Furthermore, the piezoelectric actuator 5 is not limited to a laminated type in which multiple piezoelectric elements 51 are stacked. A piezoelectric actuator with a single layer of piezoelectric elements 51 may also be used. In addition, the operation of the actuator when a driving voltage is applied is not limited to longitudinal vibration. Moreover, it may be applied not only to the drop-on-demand piezoelectric method but also to the continuous method.

[0056] In the above-described embodiment, 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 the material ejection head of a 3D printer or the sample ejection head of a dispensing device.

[0057] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be carried out in various other forms, 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, as well as in the claims and their equivalents. [Explanation of Symbols]

[0058] 10 Inkjet Printers 100-103 Inkjet head 24 nozzles 42 Pressure chamber 43 Upstream resistance channel 44 Upstream common liquid chamber 45 Upstream ink port 46 Downstream resistance channel 47 Downstream common liquid chamber 48 Downstream Ink Port 49 Bypass channel 5. Piezoelectric actuator 8,82,83 Pressure damper

Claims

1. Multiple pressure chambers, each connected to a nozzle, Multiple upstream resistance channels communicating with the aforementioned pressure chambers, A common upstream liquid chamber communicating with multiple upstream resistance channels, An upstream liquid port is provided at one end of the arrangement direction of the multiple pressure chambers, communicating with the upstream common liquid chamber. Multiple downstream resistance channels communicating with each of the aforementioned pressure chambers, A common downstream liquid chamber communicating with multiple downstream resistance channels, A downstream liquid port is provided at one end of the arrangement direction of the multiple pressure chambers, communicating with the downstream common liquid chamber. The system includes a bypass channel connecting the upstream common liquid chamber and the downstream common liquid chamber at the other end of the arrangement direction of the multiple pressure chambers, A liquid discharge head characterized in that the total flow rate of the liquid flowing through the bypass channel and the liquid flowing through the multiple channels from the inlet of each upstream resistance channel to the outlet of each downstream resistance channel is equal to or greater than the total maximum discharge flow rate of the liquid discharged from each nozzle.

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

3. The liquid discharge head according to claim 1 or 2, characterized in that a pressure damper is provided in the bypass channel.

4. The liquid discharge head according to claim 1 or 2, characterized in that the highest point of the bypass channel is higher than the height of the upstream common liquid chamber.

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