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 includes a plurality of pressure chambers each communicating with a nozzle, a plurality of upstream resistance passages and downstream resistance passages each communicating with a pressure chamber, an upstream common liquid chamber, a downstream common liquid chamber, and a bypass passage. The upstream common liquid chamber has one end communicating with an upstream liquid port and extends in the direction of the arrangement of the plurality of pressure chambers while communicating with the plurality of upstream resistance passages. The downstream common liquid chamber has one end communicating with a downstream liquid port and extends in the direction of the arrangement of the plurality of pressure chambers while communicating with the plurality of downstream resistance passages. The bypass passage connects the other ends of the upstream common liquid chamber and the downstream common liquid chamber. The pressure chamber circulation passage formed by the upstream resistance passage, pressure chamber, and downstream resistance passage is inclined to move upstream with respect to the liquid flow in the upstream common liquid chamber and inclined to move downstream with respect to the liquid flow in the downstream common liquid chamber.

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 driving voltage to the actuator of the selected channel to eject the liquid.

[0004] After liquid ejection, a liquid ejection head retains vibrations (meniscus vibrations) determined by the surface tension of the liquid meniscus within the nozzle and the mass of the liquid. For example, high-speed liquid ejection heads need to quickly suppress these vibrations, and for this purpose, resistance channels are provided before and after the pressure chamber. However, when attempting to create a liquid circulation head, these resistance channels hinder liquid circulation. In particular, in multi-nozzle heads with multiple channels, if the upstream-downstream ratio of the resistance channels does not match between channels, a pressure difference will occur between channels, degrading print quality. That is, in channels with relatively low upstream flow resistance, ink tends to spread outwards from the edge of the meniscus, and in channels with relatively low downstream flow resistance, air is more likely to be mixed in. Therefore, it is difficult to maintain a state across all channels where ink does not spread outwards from the edge of the meniscus and air is not mixed in. To avoid these problems, the circulation flow rate must be reduced, but if the circulation flow rate is low, the liquid stirring effect due to the circulation flow is small, and the effect of uniformizing the head temperature due to the circulation flow is also small. Furthermore, while resistance channels are designed to be narrow to provide resistance, if thread-like foreign matter enters the narrow channel due to circulating flow, it can clog the channel and cause a failure to discharge. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-130251 [Patent Document 2] Japanese Patent Publication No. 2016-153240 [Patent Document 3] Japanese Patent Publication No. 2024-31373 [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, a plurality of downstream resistance passages, a downstream common liquid chamber, and a bypass passage. The plurality of pressure chambers each communicate with a nozzle. The plurality of upstream resistance passages each communicate with the pressure chambers. The upstream common liquid chamber has one end communicating with an upstream liquid port and extends in the direction of the arrangement of the plurality of pressure chambers while communicating with the plurality of upstream resistance passages. The plurality of downstream resistance passages each communicate with the pressure chambers. The downstream common liquid chamber has one end communicating with a downstream liquid port and extends in the direction of the arrangement of the plurality of pressure chambers while communicating with the plurality of downstream resistance passages. The bypass passage connects the other end of the upstream common liquid chamber to the other end of the downstream common liquid chamber. The upstream resistance passages, the pressure chambers, and the downstream resistance passages form a pressure chamber circulation passage. The pressure chamber circulation channel is inclined to move upstream with respect to the liquid flow in the upstream common liquid chamber, and to move downstream with respect to the liquid flow in the downstream common liquid chamber. [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 an 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] The above is a plan view of each layer of the head section of the inkjet head. [Figure 7] This is a plan view of each layer of the modified head section. [Figure 8] This is an overall configuration diagram of the ink circulation system for the inkjet head shown above. [Figure 9]This is the drive circuit for the inkjet head described above. [Figure 10] This is the drive waveform applied to the piezoelectric actuator of the inkjet head described above. [Figure 11] This is a diagram illustrating the operation of a piezoelectric actuator given the above drive waveform. [Figure 12] This is a plan view of each layer of the modified head section. [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] As an example of an image forming apparatus equipped with a liquid ejection head of the 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 the sheets S one by one from the cassette 12 to the upstream conveyance path 13. The upstream conveyance path 13 is composed of the feed roller pair 131, 132 and the sheet guide plates 133, 134. The sheet S is sent to the upper surface of the conveyance belt 14 via the upstream conveyance path 13. The arrow 104 in the figure indicates the conveyance path of the sheet S from the cassette 12 to the conveyance belt 14.

[0013] The conveyance belt 14 is a net-like endless belt having a large number of through holes formed on its surface. The three rollers of the drive roller 141, the driven rollers 142, 143 rotatably support the conveyance belt 14. The motor 205 rotates the conveyance belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. The number 105 in the figure indicates the rotation direction of the conveyance belt 14. A negative pressure container 206 is disposed on the back side of the conveyance belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates a negative pressure inside the negative pressure container 206 by the airflow formed, and adsorbs and holds the sheet S on the upper surface of the conveyance belt 14. The number 106 in the figure indicates the flow of the airflow.

[0014] The inkjet heads 100 to 103, which are examples of liquid ejection heads, are arranged to face the sheet S adsorbed and held on the conveyance belt 14 with a slight gap of, for example, 1 mm. 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 colors of the ejected ink are different. The colors of the ink are, for example, cyan, magenta, yellow, and black.

[0015] The supply of ink to each of the inkjet heads 100 to 103 is circulated and supplied by each of the ink circulation devices 341 to 344, respectively. The detailed configuration of the ink circulation devices 341 to 344 will be described later (see FIG. 8). In FIG. 1, for the convenience of drawing, the ink circulation devices 341 to 344 are each illustrated with a broken line frame.

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

[0017] Subsequently, the configurations of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 while referring to FIGS. 2 to 6, but the inkjet heads 101 to 103 also have the same structure as the inkjet head 100.

[0018] As shown in FIG. 2, the inkjet head 100 includes a head portion 2 which is an example of a liquid ejection portion. The head portion 2 is connected to a flexible printed wiring board 21 which is an example of a film wiring board. The flexible printed wiring board 21 is connected to a printed board 22 which is an example of a relay board. The head portion 2 includes a nozzle plate 23 which is an example of a nozzle portion. The ink circulation type head portion 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 for ejecting ink are arranged along, for example, the X direction in the first direction of the nozzle plate 23. The nozzle density is set, for example, within the range of 150 to 1200 dpi. The nozzles 24 are not limited to a single row and may be multiple rows. The detailed configuration of the head portion 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 6 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. In particular, as shown in Figures 5 and 6, the pressure chamber 42 is formed to extend diagonally toward a second direction, for example, the Y direction. That is, the central axis of the pressure chamber 42 is inclined at a predetermined angle with respect to the X direction. As an example, the pressure chamber 42 has a rectangular opening formed in the pressure chamber substrate 4 that penetrates through a third direction, for example, 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. In an ink-circulating head, a pressure chamber circulation flow is formed to circulate and supply ink to the pressure chamber 42. The upstream resistance flow path 43, the pressure chamber 42, and the downstream resistance flow path 46 form the pressure chamber circulation flow path.

[0023] Each pressure chamber 42 has one end (upstream side) on the Y-direction side that communicates with the upstream common liquid chamber 44 via an upstream resistance passage 43. The upstream common liquid chamber 44 is formed to extend along the arrangement direction (X-direction) of the pressure chambers 42, with each upstream resistance passage 43 connected sequentially 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 in the pressure chamber substrate 4 that penetrates in the Z-direction, and then closing the openings on both sides in the Z-direction with a nozzle plate 23 and a diaphragm 41, respectively, to create 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, on 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] Each upstream resistance channel 43 is formed to have a narrower cross-section than, for example, the width of the pressure chamber 42, thereby reducing flow resistance. Each upstream resistance channel 43 is formed in a groove-like shape oblique to the X direction, similar to the pressure chamber 42. In detail, as shown in the plan view of Figure 6, which illustrates the head section 2 divided into layers, the upstream resistance channels 43 are inclined at an acute angle toward the upstream direction relative to the flow of ink circulation in the upstream common liquid chamber 44. That is, the upstream resistance channels 43 are not perpendicular to the upstream common liquid chamber 44, but are inclined toward the upstream ink port 45 and toward the pressure chamber 42. It can also be said that the upstream resistance channels 43 are inclined toward the direction opposite to the direction toward the bypass channel 49. The inclination angle θ1 is, for example, 60°. The direction of ink flow in the upstream common liquid chamber 44 is indicated by an arrow in Figure 6. Thus, at the points where the upstream common liquid chamber 44 branches off to each upstream resistance flow path 43 (upstream branching points), the upstream resistance flow path 43 is inclined in a direction opposite to the ink circulation flow within the upstream common liquid chamber 44. Therefore, even if thread-like foreign matter enters the head section 2, the foreign matter can easily escape to the downstream side of the upstream common liquid chamber 44, making it difficult for the foreign matter to enter the pressure chamber 42.

[0025] Furthermore, the other end (downstream side) of each pressure chamber 42 on the Y-direction side is connected to the downstream common liquid chamber 47 via the downstream resistance passage 46. The downstream common liquid chamber 47 is formed to extend along the arrangement direction (X-direction) of the pressure chambers 42, with each downstream resistance passage 46 connected sequentially 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 then blocking the openings on both sides in the Z-direction with the nozzle plate 23 and the 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 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.

[0026] Each downstream resistance channel 46 is formed to have a narrower cross-section, for example, than the width of the pressure chamber 42, thereby reducing flow resistance. Each downstream resistance channel 46 is formed in a groove shape oblique to the X direction, similar to the pressure chamber 42. In detail, as shown in the plan view of Figure 6, the downstream resistance channel 46 is inclined toward the downstream direction relative to the flow of ink circulation in the downstream common liquid chamber 47. That is, the downstream resistance channel 46 is not perpendicular to the downstream common liquid chamber 47, but is inclined toward the downstream ink port 48 side, moving from the pressure chamber 42 toward the downstream common liquid chamber 47. The inclination angle θ2 is, for example, 60°. The direction of ink flow in the downstream common liquid chamber 47 is indicated by an arrow in Figure 6. Thus, at the points where each downstream resistance channel 46 merges into the downstream common liquid chamber 47 (downstream junctions), the downstream resistance channels 46 are inclined in a direction that aligns with the ink circulation flow within the downstream common liquid chamber 47. Therefore, even if thread-like foreign matter flows in from the upstream side via the bypass channel 49, the foreign matter is easily able to escape to the downstream side and be discharged from the downstream ink port 48.

[0027] Furthermore, the cross-sectional area of ​​the upstream resistance channel 43 and the downstream resistance channel 46 may be reduced by narrowing the width in the Z direction instead of the width in the X direction, or by narrowing both the X and Z directions. In either case, in a plan view, the upstream resistance channel 43 should be inclined such that the pressure chamber circulation flow is obliquely opposed to the ink circulation flow in the upstream common liquid chamber 44, and the downstream resistance channel 46 should be inclined such that the pressure chamber circulation flow is aligned with the ink circulation flow in the downstream common liquid chamber 47. In addition, it is preferable, but not limited to, that the upstream resistance channel 43 and the downstream resistance channel 46 be formed along the central axis of the pressure chamber 42. That is, the cross-sectional area of ​​the ink in the upstream resistance channel 43 and the downstream resistance channel 46 should be smaller than the cross-sectional area of ​​the pressure chamber 42. Therefore, the shape of the cross-sectional area of ​​the upstream resistance channel 43 and the downstream resistance channel 46 is not limited to a rectangle. Furthermore, 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 with respect to the pressure chamber 42, but not limited to that. However, in order to suppress the generation of pressure differences between channels, the upstream-downstream ratio of the resistance channels (43, 46) of each channel should be made to match.

[0028] 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.

[0029] Specifically, the upstream common liquid chamber 44 branches out and connects to each upstream resistance channel 43 sequentially toward the other end in the direction of arrangement of the pressure chambers 42, and connects to one end of the bypass channel 49 beyond the last upstream resistance channel 43. The downstream common liquid chamber 47 connects to the other end of the bypass channel 49, and further merges and connects to each downstream resistance channel 46 sequentially toward the one end in the direction of arrangement of the pressure chambers 42, and connects beyond the last downstream resistance channel 46.

[0030] 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 to provide 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 42 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 deficit is drawn in from the downstream common liquid chamber 47. As shown by the arrows in Figure 6, even when ink flows from the downstream common liquid chamber 47 to the pressure chamber 42 via the downstream resistance channel 46, this flow is directed diagonally against the ink circulation flow in the downstream common liquid chamber 47. Therefore, even if thread-like foreign matter flows in from the upstream side via the bypass channel 49, it is difficult for the foreign matter to enter the pressure chamber 42. This is particularly advantageous when the flow rate of ink ejected from the nozzle 24 is greater than the circulation flow in the pressure chamber.

[0031] 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.

[0032] 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 / 14) times the parallel flow resistance of all channels passing through the pressure chamber 42 so that 1.4 times the discharge flow rate flows through the bypass channel. This setting is achieved, 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, twice the total maximum discharge flow rate, the circulating flow rate when ink is not being discharged will be in a ratio of 3:7 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.

[0033] 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.

[0034] It is even better to provide a pressure damper 8 in the bypass channel 49 to suppress sudden pressure changes. 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 the opening with a flexible material 81 such as a thin polyimide film. The flexible material 81 is an example of a damper 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 and mitigate the sudden pressure changes in the upstream common liquid chamber 44 and the downstream common liquid chamber 47.

[0035] 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, the ink flow rate decreases abruptly. Conversely, when printing a pattern that starts from a blank space and then resumes full duty, the ink flow rate increases abruptly. Such abrupt changes in ink flow rate require the ink, which has mass, to stop or start abruptly, 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.

[0036] 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.

[0037] When a pressure damper 8 is provided, it is preferable that the flow rate of ink flowing through the bypass channel 49 be greater than or equal to the sum of the circulating flow rates of ink flowing 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 channels flowing through the pressure chamber 42. The flow resistance of all the channels flowing through the pressure chamber 42 is the flow resistance of multiple 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 reciprocal of the sum of the reciprocals of the flow resistances of all channels.

[0038] The bypass channel 49 is not limited to having a flattened cross-section; its width in the Z direction and X direction can be adjusted. That is, the cross-sectional area of ​​the bypass channel 49 only needs to 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 can 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. Figure 7 shows an example in which a resistance channel 80 is provided in the bypass channel 49. As an example, the resistance channel 80 is placed at a position that divides the flow length of the bypass channel 49 in half, into upstream and downstream sections. By changing the dimensions of the resistance channel 80 (flow channel cross-sectional area, flow channel length), the ratio of the total flow rate of ink flowing through each pressure chamber 42 to the flow rate of ink flowing through the bypass channel 49 can be adjusted. In this case, the pressure damper 8 may be provided on both sides of the resistance channel.

[0039] Figure 8 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 8, 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.

[0040] 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.

[0041] When the ink circulation device 341 is initially filled with ink, it first 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 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 chambers 42 and bypass passages 49 of each channel. After that, air valve V1 is closed and air valve V2 is opened, and steady circulation occurs at a constant flow rate. At this time, the ink flowing in from the ink supply passage 311 is cleaner ink with fewer foreign matter compared to the ink in the ink discharge passage 331 because it has passed through filter F1. The ink in the ink discharge passage 331 is further from the ink pump 321 than the ink in the ink supply passage 311, and its pressure is stabilized in the ink tank 315, so it is less affected by the pulsation of the ink pump 321 and the pressure is stable. 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 channel 49 are as previously described. The ink ejection operation of each channel is performed while maintaining this ink circulation flow.

[0042] 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 is positioned so that its central axis lies on the central axis of the pressure chamber 42. 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 electrodes 52 are formed to one end face of the piezoelectric actuator 5 in the Y direction and are connected to the 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 electrode 55 formed on this end face.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Figure 9 shows an example of a drive circuit for the inkjet head 100. As shown in Figure 9, 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.

[0047] 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).

[0048] Next, the ink ejection operation will be explained with reference to Figures 10 and 11. 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 10 is an example of a drive waveform provided to the piezoelectric actuator 5.

[0049] When driving the piezoelectric actuator 5, which has a ground potential applied to its common terminal, a voltage V2 is applied to the individual terminals to put it into standby mode, as shown in Figure 10. 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 11(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 10), 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 11(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 drawn in a concave shape towards the pressure chamber 42.

[0050] For example, after a time elapsed that is half the pressure vibration period of the head unit 2, when a voltage V2 is applied to the individual terminals at time t2 in Figure 10, the piezoelectric actuator 5 extends in the stacking direction (Z direction), as shown in Figure 11(c), and the volume of the pressure chamber 42 is relatively reduced, causing ink droplets R to be ejected from the nozzle 24. Then, for example, after a time elapsed that is half the pressure vibration period of the head unit 2, a voltage V1 is applied to the individual terminals at time t3 in Figure 10, and the voltage is returned to V2 at time t4 after a predetermined time. The extension (Figure 11(d)) and return (Figure 11(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, and ink can be ejected. When the series of ink ejections is completed, 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 46.

[0051] As described above, according to the above embodiment, a bypass passage 49 is provided at the other end of the arrangement direction of the multiple pressure chambers 42, connecting the upstream common liquid chamber 44 and the downstream common liquid chamber 47. Furthermore, the pressure chamber circulation passage, which is composed of the upstream resistance passage 43, the pressure chambers 42, and the downstream resistance passage 46, is inclined to move upstream with respect to the ink circulation flow in the upstream common liquid chamber 44, and inclined to move downstream with respect to the ink circulation flow in the downstream common liquid chamber 47. This allows for stable ink ejection in an ink circulation type head.

[0052] Furthermore, as shown in Figure 12, the pressure chamber circulation channel may be configured such that the upstream resistance channel 43 and the downstream resistance channel 46 are inclined, while the pressure chamber 42 is not inclined.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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]

[0057] 10 Inkjet Printers 100-103 Inkjet head 24 nozzles 42 Pressure Chamber 43 Upstream resistance channel 44 Upstream common liquid chamber 46 Downstream resistance channel 47 Downstream common liquid chamber 5. Piezoelectric actuator 8. Pressure damper

Claims

1. Multiple pressure chambers, each connected to a nozzle, Multiple upstream resistance channels communicating with the aforementioned pressure chambers, An upstream common liquid chamber, one end of which communicates with the upstream liquid port and which communicates with the plurality of upstream resistance flow paths and extends in the direction of the arrangement of the plurality of pressure chambers, Multiple downstream resistance channels communicating with each of the aforementioned pressure chambers, A common downstream liquid chamber has one end in communication with a downstream liquid port and extends in the direction of the arrangement of the multiple pressure chambers while communicating with the multiple downstream resistance flow paths, The system includes a bypass channel connecting the other end of the upstream common liquid chamber and the other end of the downstream common liquid chamber, The upstream resistance channel, the pressure chamber, and the downstream resistance channel form a pressure chamber circulation channel. The liquid discharge head is characterized in that the pressure chamber circulation channel is inclined toward the upstream direction with respect to the liquid flow in the upstream common liquid chamber, and toward the downstream direction with respect to the liquid flow in the downstream common liquid chamber.

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

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

4. The liquid discharge head according to any one of claims 1 to 3, characterized in that the total flow rate of the liquid flowing through the bypass channel and the liquid flowing through each pressure chamber circulation channel is equal to or greater than the total maximum discharge flow rate of the liquid discharged from each nozzle.

5. The liquid discharge head according to claim 1, characterized in that the upstream resistance channel is inclined in a direction opposite to the liquid circulation flow in the upstream common liquid chamber, and the downstream resistance channel is inclined in a direction along the liquid circulation flow in the downstream common liquid chamber.

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