Liquid ejection head

Abstract

To provide a liquid discharge head capable of preventing liquid from leaking from a dummy nozzle and air from being suctioned into the dummy nozzle.SOLUTION: A liquid discharge head comprises discharge nozzles and dummy nozzles. A discharge nozzle communicates with a pressure chamber, and an outer opening diameter is smaller than an inner opening diameter. A dummy nozzle is disposed at a position where pressure variation of liquid is smaller than in the discharge nozzle, and an outer opening diameter is equal to or larger than an inner opening diameter, and the outer opening diameter is equal to or smaller than the outer opening diameter of the discharge nozzle.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a liquid ejection head. [Background technology]

[0002] Liquid ejection heads that supply a predetermined amount of liquid to a predetermined position are known. Liquid ejection heads are mounted on, for example, inkjet printers, 3D printers, and dispensing devices. Inkjet printers eject ink droplets from an inkjet head to form images or the like on the surface of a recording medium. 3D printers eject modeling material droplets from a modeling material ejection head, harden them, and form three-dimensional objects. Dispensing devices eject sample droplets and supply them in predetermined amounts to multiple containers or the like.

[0003] A liquid ejection head has multiple channels for ejecting liquid. Each channel has an ejection nozzle that ejects liquid, a pressure chamber that communicates with the ejection nozzle, and an actuator that changes the volume of the pressure chamber. The liquid ejection head selects a channel from the multiple channels that will eject liquid and drives the actuator by providing a drive signal. When the actuator is driven, the volume of the pressure chamber filled with liquid changes, causing the liquid to be ejected from the ejection nozzle. Liquid ejection heads may be equipped with dummy nozzles that do not eject liquid. However, pressure changes that occur when the actuator is driven can cause liquid to leak from the dummy nozzle or, conversely, air to be sucked in. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-23241 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-80923 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-195959 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-6646 [Patent Document 5] Patent Publication No. 2021-41577 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a liquid ejection head that can prevent liquid from leaking from the dummy nozzles or air from being sucked in. [Means for solving the problem]

[0006] The liquid ejection head according to the embodiment of the present invention comprises: pressure chamber, It has a discharge nozzle and a dummy nozzle. At least one end of the pressure chamber in the longitudinal direction is an open end. The discharge nozzle communicates with the pressure chamber, and has an outer opening diameter smaller than an inner opening diameter. The discharge nozzle is provided at a position where a pressure change within the pressure chamber becomes large due to liquid column resonance of 1 / 4 wavelength or 1 / 2 wavelength in the longitudinal direction within the pressure chamber that occurs when the actuator is driven. The dummy nozzle is disposed at a position where the pressure change of the liquid is smaller than that of the discharge nozzle, and the outer opening diameter is equal to or larger than the inner opening diameter and equal to or smaller than the outer opening diameter of the discharge nozzle. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating the overall configuration of an inkjet printer equipped with an inkjet head according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of the inkjet head. [Figure 3] FIG. 2 is a partially enlarged perspective view of a head portion of the inkjet head. [Figure 4] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 5] This is a driving waveform applied to the actuator of the inkjet head. [Figure 6] 10A and 10B are diagrams illustrating the operation of an actuator driven by the above drive waveform. [Figure 7] FIG. 2 is a diagram illustrating the arrangement of ejection nozzles and dummy nozzles of the inkjet head. [Figure 8]5A and 5B are diagrams illustrating liquid column resonance occurring in a pressure chamber of the inkjet head. [Figure 9] 3A and 3B are diagrams showing cross-sectional shapes of the discharge nozzle and the dummy nozzle. [Figure 10] 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. [Figure 11] 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. [Figure 12] 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. [Figure 13] FIG. 10 is a perspective view of an inkjet head according to a second embodiment. [Figure 14] FIG. 2 is a partially enlarged plan view of a head portion of the inkjet head. [Figure 15] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 16] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 17] FIG. 2 is an enlarged cross-sectional view of a pressure chamber and an air chamber of the inkjet head. [Figure 18] 3A to 3C are explanatory diagrams illustrating the operation of the actuator of the inkjet head. [Figure 19] 5A and 5B are explanatory diagrams of liquid column resonance occurring in a pressure chamber of the inkjet head. [Figure 20] 3A and 3B are diagrams showing cross-sectional shapes of ejection nozzles and dummy nozzles of the inkjet head. [Figure 21] FIG. 10 is a partially enlarged plan view of a head portion of an inkjet head according to a third embodiment. [Figure 22] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 23] FIG. 10 is a perspective view of an inkjet head according to a fourth embodiment. [Figure 24] FIG. 2 is a partially enlarged plan view of a head portion of the inkjet head. [Figure 25] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 26] FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. [Figure 27] 5A and 5B are explanatory diagrams of liquid column resonance occurring in a pressure chamber of the inkjet head. [Figure 28] 3A and 3B are diagrams showing cross-sectional shapes of ejection nozzles and dummy nozzles of the inkjet head. [Figure 29] FIG. 2 is an explanatory diagram schematically illustrating how the inkjet head is filled with ink. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a liquid ejection head according to an embodiment will be described in detail with reference to the accompanying drawings, in which the same components are denoted by the same reference numerals.

[0009] (First embodiment) An inkjet printer 10 that prints an image on a recording medium will be described as an example of an image forming apparatus equipped with a liquid ejection head according to the first embodiment. Fig. 1 shows a schematic configuration of the inkjet printer 10. Inside a housing 11, the inkjet printer 10 has arranged therein: a cassette 12 that stores sheets S, which are an example of a recording medium; an upstream transport path 13 for the sheets S; a transport belt 14 that transports the sheets S removed from the cassette 12; a plurality of inkjet heads 100-103 that eject ink droplets toward the sheets S on the transport belt 14; a downstream transport path 15 for the sheets S; an ejection tray 16; and a control board 17. An operation unit 18 that serves as a user interface is located on the upper side of the housing 11.

[0010] Image data to be printed on the sheet S is generated by, for example, a computer 200, which is an externally connected device. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 via a cable 201 and connectors 202 and 203.

[0011] A pickup roller 204 supplies sheets S one by one from the cassette 12 to the upstream conveying path 13. The upstream conveying path 13 is composed of a pair of feed rollers 131 and 132 and sheet guide plates 133 and 134. The sheets S are fed via the upstream conveying path 13 onto the upper surface of the conveying belt 14. An arrow 104 in the figure indicates the conveying path of the sheets S from the cassette 12 to the conveying belt 14.

[0012] The conveyor belt 14 is a mesh-like endless belt with many through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, support the conveyor belt 14 so that it can rotate freely. A motor 205 rotates the drive roller 141 to rotate the conveyor belt 14. The motor 205 is an example of a drive device. In the figure, 105 indicates the direction of rotation of the conveyor belt 14. A negative pressure container 206 is disposed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates an airflow that creates a negative pressure inside the negative pressure container 206, causing the sheet S to be attracted and held on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

[0013] Inkjet heads 100-103, which are an example of liquid ejection heads, are arranged to face sheet S, which is held by suction on conveyor belt 14, with a small gap of, for example, 1 mm between them. Each of inkjet heads 100-103 ejects ink droplets toward sheet S. As sheet S passes below inkjet heads 100-103, they print an image. Each of inkjet heads 100-103 has the same structure except for the color of ink they eject. The ink colors are, for example, cyan, magenta, yellow, and black.

[0014] The inkjet heads 100-103 are connected to ink tanks 315-318 and ink supply pressure adjusters 321-324 via ink flow paths 311-314, respectively. Each ink tank 315-318 is disposed above the corresponding inkjet head 100-103. During standby, each ink supply pressure adjuster 321-324 adjusts the pressure inside each inkjet head 100-103 to a negative pressure, e.g., -1.2 kPa, relative to atmospheric pressure, to prevent ink from leaking from the ejection nozzles 3 (see FIG. 2) of the inkjet heads 100-103. During image formation, ink from each ink tank 315-318 is supplied to each inkjet head 100-103 by the ink supply pressure adjusters 321-324.

[0015] After the image is formed, the sheet S is sent from the conveyor belt 14 to a downstream conveying path 15. The downstream conveying path 15 is made up of pairs of feed rollers 151, 152, 153, and 154, and sheet guide plates 155 and 156 that define the conveying path of the sheet S. The sheet S passes through the downstream conveying path 15 and is sent from a discharge port 157 to a discharge tray 16. An arrow 107 in the figure indicates the conveying path of the sheet S.

[0016] Next, we will explain the configuration of the inkjet heads 100 to 103. Below, we will explain the inkjet head 100 with reference to Figures 2 to 4, but the inkjet heads 101 to 103 have the same structure as the inkjet head 100.

[0017] As shown in Fig. 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 wiring board 21. The head unit 2 includes a plurality of channels for ejecting ink. The head unit 2 includes a nozzle plate 22, an actuator substrate 23, and an ink supply unit 24, which is an example of a liquid supply unit. The ink supply unit 24 is connected to the ink supply pressure adjustment device 321 shown in Fig. 1 via an ink flow path 311.

[0018] The flexible printed wiring board 21 is equipped with a driver chip, a driving integrated circuit (IC) 25 (hereinafter referred to as the driving IC). The driving IC 25, which is an example of a control unit, temporarily stores print data sent from the control board 17 of the inkjet printer 10 and sends driving signals to each channel to eject ink at a predetermined timing.

[0019] The nozzle plate 22, which is an example of a nozzle section, is a rectangular plate made of, for example, a resin such as polyimide or a metal such as stainless steel. Nozzles (ejection nozzles) 3 that eject ink are arranged on the surface of the nozzle plate 22, for example, along the longitudinal direction (X direction) of the nozzle plate 22. The nozzle density is set, for example, within a range of 150 to 1200 dpi. Dummy nozzles 31 are arranged on both sides of the ejection nozzles 3, for example, along the lateral direction (Y direction) of the nozzle plate 22. The dummy nozzles 31 are nozzles that do not eject ink. In other words, each channel that ejects ink has one ejection nozzle 3 and two dummy nozzles 31. Note that in FIG. 2, the ejection nozzles 3 are arranged in two rows in the lateral direction (Y direction) of the nozzle plate 22, but this is not limited to this. The ejection nozzles 3 may be arranged in a single row, for example.

[0020] As shown in particular in Figures 3 and 4, the nozzle plate 22 is attached to the actuator substrate 23 via a frame-shaped member 26. The actuator substrate 23 is a rectangular substrate made of, for example, insulating ceramics. A plurality of pressure chambers 4 for each channel are formed in the space surrounded by the nozzle plate 22, frame-shaped member 26, and actuator substrate 23. A plurality of pressure chambers 4 are arranged in the actuator substrate 23, for example, along the longitudinal direction of the substrate. The pressure chamber 4 for each channel communicates with the discharge nozzle 3 for that channel.

[0021] The pressure chambers 4 are formed, for example, by cutting out two piezoelectric members 41, which are stacked on the surface of the actuator substrate 23 with their polarization directions in opposite directions (for example, facing directions), into rectangular groove shapes (FIG. 4(b)). That is, the piezoelectric members 41 are formed so that their longitudinal direction extends, for example, in the short direction of the actuator substrate 23. The piezoelectric members 41 are formed so that they have a trapezoidal shape when viewed from the side, for example, but the shape when viewed from the side is not limited to a trapezoid.

[0022] Adjacent pressure chambers 4 are separated by side walls of the piezoelectric members 41. That is, each pressure chamber 4 has side walls of the piezoelectric members 41 erected on both sides of its short side, and both ends of its long side are open. One opening at the end of the pressure chamber 4 communicates with a central common ink chamber 42, which is an example of a common liquid chamber, and the other opening communicates with an outer common ink chamber 43, which is also an example of a common liquid chamber. The central common ink chamber 42 communicates with the ink supply groove 27 of the ink supply unit 24 via an ink supply hole 44 formed in the actuator substrate 23. The outer common ink chamber 43 communicates with the ink discharge path 28 of the ink supply unit 24 via an ink discharge hole 45 formed in the actuator substrate 23. With this configuration, ink is circulated and supplied to the pressure chambers 4 of each channel. However, ink supply does not have to be by a circulation system.

[0023] The electrodes 46 are integrally formed on the bottom and both side surfaces of the pressure chamber 4. The electrodes 46 of each pressure chamber 4 are connected to wiring electrodes 47. The piezoelectric member 41 and the electrodes 46 constitute the actuator 5 that changes the volume of the pressure chamber 4. The wiring electrodes 47 extend to the outside of the frame member 26. The surfaces of the electrodes 46 and the wiring electrodes 47 inside the frame member 26 may be covered with a protective film (not shown) to prevent them from coming into contact with ink. The electrodes 46 and wiring electrodes 47 are formed, for example, with a nickel thin film formed by electroless plating or the like. The wiring electrodes 47 are connected to the flexible wiring board 21 at the end of the actuator substrate 23 and are connected to a driver (i.e., a drive circuit) of the drive IC 25. The driver for each channel applies, for example, a drive voltage as a drive signal to the actuator 5 of each channel. With this configuration, when a drive voltage is applied to the actuator 5, an electric field is applied in a direction that intersects (preferably perpendicular to) the polarization axis of the piezoelectric element 41, and the piezoelectric element 41, which forms the side walls on both sides of the pressure chamber 4, deforms in shear mode.

[0024] That is, the ink pressure chamber 4 is formed by being sandwiched between a pair of pillar-shaped actuators 5 that use piezoelectric members 41. A potential difference is applied to both walls of the pillar-shaped actuator 5, i.e., the inner wall and outer wall of the pressure chamber 4, and the actuator 5 is charged, thereby deforming the actuator 5. This changes the volume of the pressure chamber 4, and as a result, the ink pressure inside the pressure chamber 4 changes. Ink is ejected from the ejection nozzle 3 by adjusting the magnitude and timing of this change.

[0025] FIG. 5 shows a drive waveform (DRP waveform) as an example of a drive waveform for driving the actuator 5. FIG. 5 also shows changes in the ink pressure and ink flow velocity within the pressure chamber 4 during drive. The drive waveform sequentially applies a negative voltage (-V) to the actuator 5 during period t1, a ground voltage (GND) during period t2, and a positive voltage (+V) during period t3. Period t1 is set to, for example, half the pressure oscillation period of the head unit 2. When the pressure oscillation period is, for example, 4.8 μs, period t1 is set to 2.4 μs. Period t2 is set to, for example, 3.25 μs, and period t3 is set to 0.7 μs, which is shorter than period t2. In this case, the center interval between periods t1 and t3 is t1 / 2 + t2 + t3 / 2 = (pressure oscillation period).

[0026] The actuator 5 can be driven, for example, by dividing the pressure chambers 4 into three groups, every two of which are driven, in a so-called three-division drive. FIG. 6(a) shows a state in which the electrodes 46 of adjacent groups of three pressure chambers 4 are all at ground potential (GND). In this state, the piezoelectric elements 41 that form the partitions between the pressure chambers 4 are not distorted. FIG. 6(b) shows a state in which a negative voltage (-V) is applied to the electrode 46 of the central pressure chamber 4 during period t1 of the drive waveform in FIG. 5. In this state, an electric field acts on the piezoelectric elements 41 on both sides of the central pressure chamber 4 to which the voltage (-V) is applied, in a direction perpendicular to the polarization direction of the piezoelectric elements 41. As a result, the piezoelectric elements 41 deform outward, expanding the volume of the central pressure chamber 4.

[0027] During the following period t2, the potential of the electrode 46 of the central pressure chamber 4 is set to ground potential (GND), causing the expanded volume of the central pressure chamber 4 to contract to the state shown in Figure 6(a). By contracting the volume of the pressure chamber 4 in this way at the end of period t1, which is set to half the time of the pressure oscillation period, the pressure of the ink inside the pressure chamber 4 increases, as shown in Figure 5, and ink droplets are ejected from the ejection nozzle 3.

[0028] During the following period t3, a positive voltage (+V) is applied to the electrode 46 of the central pressure chamber 4. In this state, as shown in FIG. 6(c), an electric field acts on the piezoelectric elements 41 on both sides of the central pressure chamber 4 in the opposite direction to that in FIG. 6(b), causing the piezoelectric elements 41 to deform inward, thereby contracting the volume of the central pressure chamber 4. After the period t3 has elapsed, the potential of the electrode 46 of the central pressure chamber 4 is set to ground potential (GND), causing the contracted volume of the central pressure chamber 4 to return to the state shown in FIG. 6(a). This contraction and restoration cancels out any residual vibration.

[0029] Next, the shapes and arrangements of the ejection nozzle 3 and the dummy nozzle 31 will be described with reference to FIGS. 7 to 9. As mentioned above, ink is ejected by driving the actuator 5 to change the volume of the pressure chamber 4 and thereby control the pressure within the pressure chamber 4. In the case of a pressure chamber 4 in which one or both longitudinal ends are open and communicate with the common ink chamber 42 (43), liquid column resonance in the longitudinal direction of the pressure chamber 4, which occurs when the actuator 5 is driven, is utilized for ink ejection. In the case of liquid column resonance, the wavelength is the value obtained by multiplying the pressure oscillation period described above by the speed of sound of the ink within the pressure chamber 4. In the case of a pressure chamber 4 that is open at both longitudinal ends as shown in FIG. 7(a), it becomes a 1 / 2 wavelength resonance tube of this wavelength. On the other hand, in the case of a pressure chamber 4 that is open at one longitudinal end and closed at the other as shown in FIG. 7(b), it becomes a 1 / 4 wavelength resonance tube. This differs from inkjet heads that utilize Helmholtz resonance.

[0030] In the case of a half-wavelength resonance tube, if the pressure amplitude and flow velocity amplitude are expressed as standing waves as shown in Figure 8, the pressure amplitude is maximum and the flow velocity amplitude is minimum at the longitudinal center of the pressure chamber 4. On the other hand, the pressure amplitude is minimum and the flow velocity amplitude is maximum at the open end of the standing wave. The discharge nozzle 3 is positioned at a location where the pressure change due to liquid column resonance is greatest. In the case of the half-wavelength resonance tube shown in Figure 7(a), a preferred example is to place the discharge nozzle 3 at the longitudinal center where the pressure amplitude is maximum. In the case of the quarter-wavelength resonance tube shown in Figure 7(b), a preferred example is to place the discharge nozzle 3 at the longitudinal back where the pressure amplitude is maximum. However, as described above, for example, if the pressure chambers 4 are divided into three groups, every two chambers, and the actuator 5 is driven in three divisions, the discharge nozzle 3 should be staggered in position relative to the other groups (see Figures 7, 10-12). The amount of positional shift is determined depending on, for example, the conveyance speed of the sheet S. As such, the position of the discharge nozzle 3 is not strictly limited to the position where the pressure amplitude is maximum, but may be in the vicinity of that position. An example of that vicinity is within 1 / 10 wavelength.

[0031] As shown in FIG. 9, the discharge nozzle 3 has a shape in which the outer opening diameter D1 is smaller than the inner opening diameter D2. As a preferred example, the discharge nozzle 3 has a tapered shape in which the diameter decreases toward the outer tip. The outer opening diameter D1 of the discharge nozzle 3 is, for example, 20 to 30 μm. The inner opening diameter D2 of the discharge nozzle 3 is, for example, 40 to 55 μm. The length L of the discharge nozzle 3 is, for example, 50 μm. The length L of the discharge nozzle 3 is, for example, the same as the thickness of the nozzle plate 22. The outer opening diameter is the opening diameter of the nozzle on the discharge surface side of the nozzle plate 22. On the other hand, the inner opening diameter is the opening diameter of the nozzle on the pressure chamber 4 side of the nozzle plate 22.

[0032] The ejection nozzle 3 forms an ink meniscus M near its opening, and ejects ink by introducing pressure changes into the nozzle due to liquid column resonance that occurs when the actuator 5 is driven. The tapered ejection nozzle 3 increases the ink flow rate by narrowing the outer opening diameter D1, and applies load to the pressure chamber 4 by widening the inner opening diameter D2. When the ejection nozzle 3 is stationary and not ejecting ink, a negative pressure is applied to the pressure chamber 4 to maintain the meniscus M in a concave shape. In other words, the pressure inside the inkjet head 100 is adjusted to a negative pressure relative to atmospheric pressure by the ink supply pressure adjustment device 321. The same applies to the dummy nozzle 31.

[0033] As mentioned above, the pressure chamber 4 and the common ink chambers 42, 43 communicate at the position where the pressure change due to liquid column resonance is smallest and the change in flow velocity is greatest. However, in reality, when the actuator 5 is driven, pressure changes also occur at both ends of the pressure chamber 4 due to the flow of ink in and out between the common ink chambers 42, 43 and the pressure chamber 4. This can have a negative effect on ejection characteristics. The pressure change also propagates via the communication path to the pressure chambers 4 of other surrounding channels. Therefore, dummy nozzles 31 are provided.

[0034] The dummy nozzles 31 are positioned at locations where the pressure amplitude of the liquid column resonance is smaller than that of the ejection nozzles 3, and do not eject ink. In the example of the 1 / 2 wavelength resonance tube shown in FIG. 7(a), a preferred example is to position the dummy nozzles 31 at both longitudinal ends, where the pressure amplitude is smallest. In the example of the 1 / 4 wavelength resonance tube shown in FIG. 7(b), a preferred example is to position the dummy nozzles 31 at the longitudinal end on the opening side, where the pressure amplitude is smallest. Note that the location where the pressure amplitude of the liquid column resonance is smallest is outside the boundary between the pressure chamber 4 and the common ink chamber 42 (43), for example, when considering the opening correction of the liquid column resonance. Therefore, the dummy nozzles 31 may be positioned at this location. The location where the pressure amplitude of the liquid column resonance is smallest can be confirmed, for example, by actual testing or simulation. Of course, the location is not strictly limited to the location where the pressure amplitude is smallest, and may be located near that boundary. In other words, the dummy nozzles 31 do not have to be outside the boundary between the pressure chamber 4 and the common ink chamber 42 (43), but may be positioned inside the boundary or straddling the boundary. As an example, as shown in FIG. 7(c), it is arranged at a position 1 / 10 wavelength inward from the end of the pressure chamber 4 or at a position closer to the common ink chamber 42 (43).

[0035] As shown in FIG. 9, the dummy nozzle 31 has an outer opening diameter D3 that is equal to or larger than the inner opening diameter D4 and is equal to or smaller than the outer opening diameter D1 of the discharge nozzle 3. Preferably, the dummy nozzle 31 has a cylindrical shape as shown in FIG. 9(a) or an inverse tapered shape in which the diameter increases toward the outer tip as shown in FIG. 9(b). The outer opening diameter D3 of the dummy nozzle 31 is, for example, 20 to 30 μm. The inner opening diameter D4 of the dummy nozzle 31 is, for example, 20 to 30 μm in the case of a cylindrical shape, and is, for example, 10 to 20 μm in the case of an inverse tapered shape. The length L of the dummy nozzle 31 is, for example, 50 μm. The length L of the discharge nozzle 3 is, for example, the same as the thickness of the nozzle plate 22.

[0036] The dummy nozzle 31 does not eject ink when positioned where the pressure amplitude of the liquid column resonance is small. However, the position and shape of the meniscus M inside the nozzle change, thereby suppressing pressure changes. In other words, the dummy nozzle 31 functions as a pressure relief nozzle. However, if the dummy nozzle 31 is tapered like the ejection nozzle 3, the meniscus force weakens as the negative pressure in the pressure chamber 4 increases and the meniscus M retreats inward, making it easier for external air to enter through the nozzle, resulting in a low pressure relief capability. For this reason, a cylindrical or inverted tapered shape is preferred for the dummy nozzle 31. With a cylindrical shape, the meniscus force does not change even if the meniscus M retreats inward as indicated by the dashed line in Figure 9 when the negative pressure in the ink chamber of the common ink chamber 42 (43) increases. A cylindrical shape also has the advantage of not applying a load to the common ink chamber 42 (43), making it even more difficult to eject ink from the dummy nozzle 31. Furthermore, if the dummy nozzles 31 are made inversely tapered, the further the meniscus M recedes inward as shown by the dashed lines in Figure 9, the greater the curvature of the meniscus M and the stronger the meniscus force. Multiple dummy nozzles 31 may be provided, for example, adjacent to each other. Increasing the number of dummy nozzles 31 allows for a larger range of volume change in the common ink chamber 42 (43), which in turn increases the pressure relaxation capability.

[0037] That is, as shown in Figure 9(c), if the nozzle taper angle is θ1, the contact angle between the nozzle and the ink is θ2, the nozzle radius of the outer opening diameter is R, the meniscus curvature is r = R / cosθ, and the ink surface tension is δ, then by calculating the pressure difference ΔP between the inside and outside of the meniscus M using the Young-Laplace equation below, we can determine how much negative pressure the nozzle can withstand. ΔP=2δ / r=[2cosθ / R]δ However, θ=θ2-θ1 Similarly to the discharge nozzle 3, when the dummy nozzle 31 is formed in a tapered shape as shown in FIG. 9(c), θ1=10°, θ2=10°, R=15 μm (D1=30 μm), δ=30×10 -3When the discharge pressure is N / m, the nozzle can withstand a negative pressure of -4 kPa. However, when the meniscus M retracts to the inner diameter as shown by the dashed line in Figure 9 (L = 50 μm, R = 23.8 μm (D2 = 47.6 μm)), the nozzle can only withstand a negative pressure of -2.5 kPa. Even if the outer diameter of the dummy nozzle 31 is the same as that of the discharge nozzle 3, if the taper angle θ1 of the dummy nozzle 31 is reduced to 5 degrees, the inner diameter will be reduced to 38.7 μm, and when the meniscus M retracts to the nozzle inner diameter, the nozzle can withstand a negative pressure of -3 kPa. In other words, the dummy nozzle 31 may have a tapered shape with a smaller taper angle than the discharge nozzle 3. Furthermore, if the dummy nozzle 31 has a cylindrical shape, when R = 10 μm (D3 = 20 μm), the nozzle can withstand a negative pressure of -5.9 kPa, and the meniscus force does not change even when the meniscus M retracts. Furthermore, the inversely tapered dummy nozzle 31 can withstand a negative pressure of -5.8 kPa when θ1 = -3°, θ2 = 10°, and R = 10 μm (D3 = 20 μm). When the meniscus M recedes to the inner diameter (L = 50 μm, R = 7.4 μm (D4 = 14.8 μm)), it can withstand a negative pressure of -8.1 kPa. For a cylindrical dummy nozzle 31, θ1 = 0, and for a reversely tapered dummy nozzle 31, θ1 < 0. Therefore, it can be said that the cylindrical or reversely tapered dummy nozzle 31 has a smaller taper than the tapered discharge nozzle 3. It can also be said that the ratio of the inner opening diameter to the outer opening diameter (= inner opening diameter / outer opening diameter) of the dummy nozzle 31 is smaller than the ratio of the inner opening diameter to the outer opening diameter of the discharge nozzle 3.

[0038] As shown in Figure 10, the dummy nozzle 31 is located on the communication path 300 between one channel and the adjacent channel. If the dummy nozzle 31 is located too far from the end of the pressure chamber 4, a pressure difference will occur between that location and the end of the pressure chamber 4; therefore, it is desirable to locate the dummy nozzle 31 near the end of the pressure chamber 4. The dummy nozzle 31 absorbs local pressure changes, thereby reducing pressure propagation through the communication path 300. This action prevents degradation of print quality due to crosstalk, in which the operation of one channel affects the operation of the other channel. The crosstalk reduction effect can be achieved by locating the dummy nozzle 31 in a common ink chamber 42 (43) that is located on the communication path between a pressure chamber 4 and another pressure chamber 4 adjacent to that pressure chamber 4. For this purpose, the dummy nozzle 31 does not necessarily have to be located for each channel as shown in Figure 7. For example, as shown in Figure 11, crosstalk reduction can be expected by locating the dummy nozzle 31 near the end of each piezoelectric element 41 in the common ink chamber 42 (43). Alternatively, for example, as shown in Fig. 12, the crosstalk can be reduced by arranging dummy nozzles 31 on the end side of every other piezoelectric member 41. Note that the arrows 300 in the figure are schematic arrows that indicate pressure propagation along the communication path between channels, as in Fig. 10.

[0039] Furthermore, the dummy nozzles 31 on the common ink chamber 43 side not only have the above-mentioned pressure relief effect, but also have the effect of preventing a dead end in the flow path and making it easier to fill the common ink chamber 43 with ink. In other words, the dummy nozzles 31 function as discharge holes when filling the ink. Alternatively, the dummy nozzles 31 may also be used as suction holes to suck out excess ink.

[0040] Furthermore, by providing the ejection nozzles 3 and the dummy nozzles 31 on the same surface of the nozzle plate 22 of the head section 2, purging of ink and cleaning after purging become easier.

[0041] (Second embodiment) Next, an inkjet head 100 according to a second embodiment will be described with reference to Figs. 13 to 20. Note that the same components as those in the first embodiment are denoted by the same reference numerals. As shown in Fig. 13, the inkjet head 100 has discharge nozzles 3 and dummy nozzles 31 arranged, for example, along the longitudinal direction (X direction) of the nozzle plate 22. The dummy nozzles 31 are arranged along the Y direction relative to each discharge nozzle 3. The discharge nozzles 3 and the two sets of three dummy nozzles 31 on both sides may be formed in multiple rows in the Y direction of the nozzle plate 22.

[0042] As shown in particular in Figures 14 to 16, the nozzle plate 22, in which the ejection nozzles 3 and dummy nozzles 31 are formed, is attached to the actuator substrate 23 via, for example, a frame-shaped member 26. The actuator substrate 23 is a substrate made of, for example, insulating ceramics. The frame-shaped member 26 is made of, for example, resin. The ink pressure chambers 4 of each channel are arranged alternately with the air chambers 40 in, for example, the longitudinal direction (X direction) of the nozzle plate 22 within the space surrounded by the nozzle plate 22, the frame-shaped member 26, and the actuator substrate 23. The pressure chambers 4 of each channel that ejects ink are respectively connected to the ejection nozzles 3 of each channel.

[0043] The pressure chambers 4 are formed, for example, by cutting out, in the shape of a rectangular groove, two piezoelectric members 41 stacked on the surface of the actuator substrate 23 with their polarization directions in opposite directions (for example, facing directions) (see FIG. 17). That is, the piezoelectric members 41 are formed so that their longitudinal direction extends, for example, in the lateral direction (Y direction) of the actuator substrate 23. The piezoelectric members 41 are formed at a height that makes contact with the surface of the nozzle plate 22. Therefore, the pressure chambers 4 have side walls of the piezoelectric members 41 standing on both sides in the lateral direction, and are, for example, elongated spaces with both ends in the longitudinal direction open. Note that the piezoelectric members 41 are formed so that they are trapezoidal in side view, for example, but the shape in side view is not limited to a trapezoid.

[0044] The air chambers 40 are disposed on both sides of the pressure chamber 4, with piezoelectric members 41 interposed therebetween. Similar to the pressure chamber 4, the air chambers 40 are formed by cutting out the piezoelectric member 41 in the shape of, for example, a rectangular groove, and the openings at both ends in the longitudinal direction are closed by, for example, convex wall members 29 extending inward from the frame-shaped member 26, to form an airtight space into which ink is not introduced. The wall members 29 are, for example, resin walls.

[0045] The openings at both ends of the pressure chamber 4 in the longitudinal direction are connected to the ink waiting chamber 6. The ink waiting chamber 6 is an example of a liquid waiting chamber. Each ink waiting chamber 6 is separated from the ink waiting chamber 6 of the adjacent channel by, for example, a convex wall member 29 extending from the frame member 26. In other words, the ink waiting chamber 6 is separated for each channel that ejects ink. When the pressure chamber 4 has openings at both ends, an ink waiting chamber 6 is provided at each end. In a plan view, the ink waiting chamber 6 has a space that is wider in the horizontal direction than the width of the opening of the pressure chamber 4 by the width of the piezoelectric members 41 on both sides. Furthermore, in a vertical cross section, the space is expanded vertically, for example, along the extension of the inclined surface of the piezoelectric member 41. In this way, by making the space of the ink waiting chamber 6 larger than the opening at the end of the pressure chamber 4, both ends of the pressure chamber 4 become open ends where pressure changes due to liquid column resonance are small. However, the space of the ink waiting chamber 6 does not necessarily have to be expanded both horizontally and vertically; it can be expanded in either direction. In addition, although the wall member 29 separating the ink standby chamber 6 of the adjacent channel is used as the wall member 29 that closes the opening of the air chamber 40 in the example described above, they may be formed separately. Furthermore, the wall member 29 may be formed of another material such as a plate.

[0046] The ink standby chambers 6 on both sides of the pressure chamber 4 are connected to the ink supply manifold 62 via narrowed portions 61. That is, a narrowed portion 61 is provided for each ink standby chamber 6 of each channel. The narrowed portion 61 is, for example, a rectangular ink passage. As an example, the narrowed portion 61 is formed so as to penetrate the actuator substrate 23 in the height direction from the bottom surface of the outwardly convex portion of the ink standby chamber 6. As an example, the ink supply manifold 62 is formed in the surface of the ink supply unit 24 in the shape of a groove along the arrangement direction of the narrowed portions 61 (X direction). Then, by stacking the actuator substrate 23 and the ink supply unit 24, the narrowed portion 61 of each channel is connected to the ink supply manifold 62. The opening area of ​​the narrowed portion 61 is set to be at least smaller than the cross-sectional area of ​​the ink standby chamber 6. Furthermore, it is usually set to be even smaller than the opening area of ​​the pressure chamber 4. That is, the cross-sectional area through which ink passes through the narrowed portion 61 is preferably smaller than the cross-sectional area through which ink passes through the ink standby chamber 6 and also smaller than the cross-sectional area through which ink passes through the pressure chamber 4. The length of the narrowed portion 61 is the thickness of the actuator substrate 23. The resistance to ink passing through the narrowed portion 61 is determined by the opening area and length of the narrowed portion 61; the smaller the opening area and the longer the length, the greater the resistance. Note that although FIGS. 14 to 16 show a configuration in which ink is supplied from both ink supply manifolds 62, one of them may be an ink discharge manifold, and ink may be circulated and supplied to the pressure chamber 4. The ink supply manifold 62 and the ink discharge manifold are examples of manifolds that communicate with the narrowed portion 61.

[0047] Although not shown in FIGS. 14 to 16, as shown in FIG. 17, the electrodes 46 are integrally formed on, for example, the bottom and both side surfaces of the pressure chamber 4. The electrodes 46 of each pressure chamber 4 are connected to wiring electrodes 47 as individual electrodes. The electrodes 48 are integrally formed on, for example, the bottom and both side surfaces of the air chamber 40. The electrodes 48 of each air chamber 40 are connected to wiring electrodes 49 as a common electrode. The piezoelectric member 41 and the electrodes 46 and 48 sandwiching the piezoelectric member 41 constitute the actuator 5, which changes the volume of the pressure chamber 4 by shear mode deformation. The electrodes 46 and 48 and the wiring electrodes 47 and 49 are formed of, for example, a nickel thin film formed by electroless plating. In particular, the electrode 46 of the pressure chamber 4 may be covered with a protective film (not shown) to prevent it from coming into contact with ink. The wiring electrodes 47 from the pressure chamber 4 are connected to, for example, the flexible printed wiring board 21 at the end of the actuator substrate 23 and then connected to a driver (i.e., drive circuit) of the drive IC 25. The driver for each channel applies, for example, a drive voltage as a drive signal to the actuator 5 of each channel. Meanwhile, the wiring electrode 49 from the air chamber 40 is connected, for example, to ground (GND). With this configuration, when a drive voltage is applied to the actuator 5, an electric field is applied in a direction that intersects (preferably perpendicular to) the polarization axis of the piezoelectric member 41, and the piezoelectric members 41 that form the side walls on both sides of the pressure chamber 4 deform in shear mode.

[0048] The actuator 5 is driven by applying, for example, the drive waveform (DRP waveform) shown in FIG. 5. FIG. 18(a) shows a state in which the potentials of the electrodes 46, 48 of the adjacent pressure chamber 4 and air chamber 40 are both at ground potential (GND). In this state, the piezoelectric elements 41 on both sides of the pressure chamber 4 are not subjected to any distortion. FIG. 18(b) shows a state in which a negative voltage (-V) is applied to the electrode 46 of the pressure chamber 4 during period t1 of the drive waveform in FIG. 6. In this state, an electric field acts on the piezoelectric elements 41 on both sides of the pressure chamber 4 in a direction perpendicular to their polarization direction, causing the piezoelectric elements 41 to deform outward in a shear mode, thereby expanding the volume of the pressure chamber 4.

[0049] In the following period t2, the potential of the electrode 46 of the pressure chamber 4 is set to ground potential (GND), thereby returning the expanded volume of the pressure chamber 4 to the state shown in Figure 18(a). By returning the volume of the pressure chamber 4 to its original state at the end of period t1, which is set to half the pressure vibration period, the pressure of the ink in the pressure chamber 4 increases as shown in Figure 5, and ink droplets are ejected from the ejection nozzle 3.

[0050] During the following period t3, a positive voltage (+V) is applied to the electrode 46 of the pressure chamber 4. In this state, as shown in FIG. 18(c), an electric field acts on the piezoelectric elements 41 on both sides of the pressure chamber 4 in the opposite direction to that in FIG. 18(b), causing the piezoelectric elements 41 to deform inward, thereby contracting the volume of the pressure chamber 4. After the period t3 has elapsed, the potential of the electrode 46 of the pressure chamber 4 is set to ground potential (GND), causing the contracted volume of the pressure chamber 4 to return to the state shown in FIG. 18(a). This contraction and recovery damps residual vibration.

[0051] The ink ejection described above also utilizes the liquid column resonance in the longitudinal direction of the pressure chamber 4, which occurs when the actuator 5 is driven, because the longitudinal ends of the pressure chamber 4 are open ends. In other words, as shown in Figure 19, it is a 1 / 2 wavelength resonance tube. Therefore, the ejection nozzle 3 is positioned in the longitudinal center where the pressure amplitude is greatest. It does not have to be strictly at the position where the pressure amplitude is greatest, but can be located in the vicinity thereof. An example of the vicinity is within the range of 1 / 10 wavelength.

[0052] As shown in FIG. 20, the discharge nozzle 3 has a shape in which the outer opening diameter D1 is smaller than the inner opening diameter D2. As a preferred example, the discharge nozzle 3 has a tapered shape in which the diameter decreases toward the outer tip. The outer opening diameter D1 of the discharge nozzle 3 is, for example, 20 to 30 μm. The inner opening diameter D2 of the discharge nozzle 3 is, for example, 40 to 55 μm. The length L of the discharge nozzle 3 is, for example, 50 μm. The length L of the discharge nozzle 3 is, for example, the same as the thickness of the nozzle plate 22.

[0053] The dummy nozzle 31 is positioned so as to communicate with the ink standby chamber 6. Pressure changes due to liquid column resonance are suppressed by opening the ends of the pressure chamber 4, so ink is not ejected from the dummy nozzle 31 even when the actuator 5 is driven. As shown in FIG. 20, the dummy nozzle 31 has an outer opening diameter D3 that is equal to or larger than the inner opening diameter D4 and equal to or smaller than the outer opening diameter D1 of the ejection nozzle 3. Preferably, the dummy nozzle 31 has a cylindrical shape as shown in FIG. 20(b) or an inverted tapered shape in which the diameter increases toward the outer tip as shown in FIG. 20(c). The outer opening diameter D3 of the dummy nozzle 31 is, for example, 20 to 30 μm. The inner opening diameter D4 of the dummy nozzle 31 is, for example, 20 to 30 μm in the case of a cylindrical shape, and is, for example, 10 to 20 μm in the case of an inverted tapered shape. The length L of the dummy nozzle 31 is, for example, 50 μm. The length L of the discharge nozzle 3 is the same as the thickness of the nozzle plate 22, for example.

[0054] The dummy nozzles 31 change the position and shape of the meniscus M within the nozzle, even though they do not eject ink, thereby suppressing pressure changes. In other words, the dummy nozzles 31 function as pressure relief nozzles. If the dummy nozzles 31 are located too far from the end of the pressure chamber 4, a pressure difference will occur between that location and the end of the pressure chamber 4. Therefore, it is preferable to locate the dummy nozzles 31 near the end of the pressure chamber 4. Furthermore, the number of dummy nozzles 31 is not limited to one. In the illustrated example, three dummy nozzles 31 are arranged in series, for example, facing the narrowed portion 43. In this way, by providing dummy nozzles 31 in the portion of the nozzle plate 22 corresponding to the ink standby chamber 6, the meniscus M formed within the nozzle suppresses pressure changes in the ink standby chamber 6, thereby stabilizing the pressure in the ink standby chamber 6. The dummy nozzles 31 absorb pressure changes due to changes in the position of the meniscus M. However, the greater the number of dummy nozzles 31, the greater the volume change when the position of the meniscus M changes. Therefore, the greater the number of dummy nozzles 31, the greater the pressure relief ability to absorb pressure changes. The dummy nozzles 31 may be used for purposes other than pressure relief, such as a discharge hole when filling ink, or a suction hole for excess ink.

[0055] Even in the configuration of this embodiment, in reality, pressure changes can occur at both ends of the pressure chamber 4 due to the flow of ink in and out between the pressure chamber 4 and the ink standby chamber 6 when the actuator 5 is driven. If pressure vibrations caused by these pressure changes propagate to surrounding channels, crosstalk problems can occur, but by providing separate ink standby chambers 6 for each channel, the propagation of pressure vibrations to surrounding channels is suppressed. Furthermore, because the ink standby chambers 6 of each channel are connected via the ink supply manifold 62, a constriction section 61 is provided between the ink standby chamber 6 and the ink supply manifold 62 to suppress the propagation of pressure vibrations via the ink supply manifold 62.

[0056] Furthermore, when ejecting ink continuously at high speed, such as in a multi-droplet process, it is preferable to wait until the state of the ink meniscus M inside the ejection nozzle 3 stabilizes after ejecting a droplet of ink before ejecting the next droplet. This is to stabilize the ejection state, such as the amount of ink ejected. If the constriction 61 were not provided, the meniscus M would vibrate due to a resonance other than the liquid column resonance described above, due to the restoring force of the meniscus M returning to its original state after ejection and the mass of ink inside the head resisting this force, resulting in an unstable state of the meniscus M. Immediately after ink ejection, the meniscus M would convexly bulge outward from the ejection nozzle 3, slowing the speed of the next ink ejection and potentially reducing print quality at high drive frequencies. By adjusting the cross-sectional area and length of the constriction 61 located between the ink standby chamber 6 and the ink supply manifold 62 to appropriately set the resistance when the ink passes through, unnecessary vibration of the meniscus M is suppressed, suppressing the swelling of the meniscus M, and quickly stabilizing the meniscus M, enabling high-quality, high-speed printing. Therefore, even if high-speed continuous ejection is performed at a frequency of, for example, 50 kHz, the ink ejection state is stabilized.

[0057] (Third embodiment) Next, an inkjet head 100 according to a third embodiment will be described. The inkjet head 100 according to the third embodiment has the same configuration as the inkjet head 100 of the second embodiment, except that the open end of the pressure chamber 4 is on only one side, forming a quarter-wave resonance tube. Therefore, the same components as those in the inkjet head 100 of the second embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0058] As shown in FIGS. 21 and 22, the pressure chamber 4 of the inkjet head 100 has one open end in the longitudinal direction and the other closed by, for example, a frame-shaped member 26. The open end communicates with the ink standby chamber 6. A pressure chamber 4 with only one open end in the longitudinal direction is a quarter-wave resonance tube. In the case of a quarter-wave resonance tube, if the pressure amplitude and flow velocity amplitude are expressed as standing waves as shown in FIG. 22, the innermost end of the pressure chamber in the longitudinal direction, which is closed by the frame-shaped member 26, becomes the fixed end, where the pressure amplitude is maximum and the flow velocity amplitude is minimum. On the other hand, the open end of the standing wave has the minimum pressure amplitude and the maximum flow velocity amplitude. The ejection nozzle 3 is located at the innermost end in the longitudinal direction where the pressure amplitude is large. Of course, it may be located near that end. An example of the vicinity is within the range of 1 / 10 wavelength. The dummy nozzle 31 is formed at a position communicating with the ink standby chamber 6. In this way, by providing the dummy nozzles 31 that do not eject ink in the portion of the nozzle plate 22 that corresponds to the ink standby chamber 6, the pressure in the ink standby chamber 6 can be stabilized.

[0059] (Fourth embodiment) Next, an inkjet head 100 according to a fourth embodiment will be described with reference to Figs. 23 to 29. Note that the same components as those in the second embodiment are denoted by the same reference numerals. As shown in Fig. 23, the inkjet head 100 has discharge nozzles 3 and dummy nozzles 31 arranged, for example, along the longitudinal direction (X direction) of the nozzle plate 22. The dummy nozzles 31 are arranged along the Y direction relative to each discharge nozzle 3. The discharge nozzles 3 and sets of three dummy nozzles 31 may be formed in multiple rows in the Y direction of the nozzle plate 22.

[0060] As shown in FIGS. 24 to 26, one of the openings at both ends of the pressure chamber 4 in the longitudinal direction communicates with the ink standby chamber 6, and the other communicates with an individual negative pressure ink chamber 7. Each individual negative pressure ink chamber 7 is separated from the individual negative pressure ink chamber 7 of the adjacent channel by, for example, a convex wall member 71 extending from the frame-shaped member 26. In other words, the individual negative pressure ink chambers 7 are separated for each channel that ejects ink. In a plan view, the individual negative pressure ink chamber 7 has a space that is wider in the horizontal direction than the width of the opening of the pressure chamber 4 by the width of the piezoelectric members 41 on both sides. Furthermore, in a longitudinal cross section, the space is expanded vertically, for example, along the extension of the inclined surface of the piezoelectric member 41. By making the space of the individual negative pressure ink chamber 7 larger than the opening at the end of the pressure chamber 4 in this way, the other opening in the longitudinal direction of the pressure chamber 4 becomes an open end where pressure changes due to liquid column resonance, which will be described later, are small. However, the space of the individual negative pressure ink chamber 7 does not necessarily have to be expanded in both the horizontal and vertical directions, and can be expanded in either one direction. Also, although one example has been given in which the wall member 71 separating the individual negative pressure ink chamber 7 of the adjacent channel is also used as the wall member 71 closing the opening of the air chamber 40, they may be formed separately. Furthermore, the wall member 71 may be formed from another member, such as a plate.

[0061] The individual negative pressure ink chamber 7 is a dead end, with no ink flowing in or out except through the opening of the pressure chamber 4. The dummy nozzle 31 is used, for example, as a discharge port when filling the inkjet head 100 with ink, but no ink flows in or out through this dummy nozzle 31 during printing. That is, because the individual negative pressure ink chamber 7 is connected to the open end of the pressure chamber 4, the ink pressure does not rise as it does within the pressure chamber 4, and ink is not ejected from the dummy nozzle 31. Furthermore, since the individual negative pressure ink chamber 7 aims to create a negative pressure within the chamber, it prevents air from being sucked in through the dummy nozzle 31. As shown in FIG. 28, the dummy nozzle 31 has an outer opening diameter D3 that is equal to or larger than the inner opening diameter D4 and equal to or smaller than the outer opening diameter D1 of the ejection nozzle 3. Preferably, the dummy nozzle 31 has a cylindrical shape as shown in FIG. 28(b) or an inverted tapered shape, with the diameter increasing toward the outer tip as shown in FIG. 28(c). The outer opening diameter D3 of the dummy nozzle 31 is, for example, 20 to 30 μm. The inner opening diameter D4 of the dummy nozzle 31 is, for example, 20 to 30 μm in the case of a cylindrical shape and 10 to 20 μm in the case of a reverse tapered shape. The length L of the dummy nozzle 31 is, for example, 50 μm. The length L of the ejection nozzle 3 is, for example, the same as the thickness of the nozzle plate 22. The dummy nozzle 31 has a hole shape and size that prevents air from being sucked in when the individual negative pressure ink chamber 7 becomes negative pressure, while the number of holes is increased to facilitate air discharge when filling the ink. Of course, the number of dummy nozzles 31 formed in one individual negative pressure ink chamber 7 is not limited to three and may be increased or decreased. Furthermore, it is preferable to arrange the dummy nozzles 31 along an extension line of the longitudinal direction (Y direction) of the pressure chamber 4, but the arrangement direction may be changed. The dummy nozzle 31 may be used for purposes other than as a discharge port during ink filling, such as a pressure relief nozzle or a suction port for excess ink.

[0062] Each individual negative pressure ink chamber 7 has a concave air reservoir 72 formed at a position facing the dummy nozzle 31, for example. When the inkjet head 100 is used with the ejection nozzle 3 positioned on the bottom side as shown in FIG. 1, the air reservoir 72 is located above the dummy nozzle 31. That is, the air reservoir 72 is formed on one surface (in this case, the ceiling surface) in the chamber of the individual negative pressure ink chamber 7 that faces away from the direction of gravity, allowing any air remaining in the chamber to accumulate. As a preferred example, the shape of the air reservoir 72 is elliptical in plan view. Furthermore, when viewed in cross section, the outer periphery of the air reservoir 72 is preferably inclined without any steps.

[0063] As described above, when liquid column resonance is used to eject ink, the ink waiting chamber 6 and the individual negative-pressure ink chamber 7 function as open ends during the time domain of the pressure oscillation. However, when the ejection operation is viewed over a longer time span, in the channel repeatedly ejecting ink, the ink meniscus M formed in the ejection nozzle 3 gradually bulges outward in a convex shape as shown by the dashed line in Figure 28. At the same time, the average pressure in the pressure chamber 4, ink waiting chamber 6, and individual negative-pressure ink chamber 7 decreases. When the ink waiting chamber 6 reaches negative pressure, it is replenished with ink from the ink supply manifold 62, thereby eliminating the negative pressure. In contrast, the individual negative-pressure ink chamber 7, which is a dead end, maintains its negative pressure state for a longer period of time than the ink waiting chamber 6 because it is not replenished with ink. This negative pressure then pulls back the ink meniscus M in the ejection nozzle 3, thereby preventing the meniscus M from swelling after ejection.

[0064] The shape of the dummy nozzle 31 is a hole smaller than the ejection nozzle 3, and is preferably a cylindrical or reverse tapered shape rather than tapered like the ejection nozzle 3, because this is suitable for maintaining a negative pressure state in the individual negative pressure ink chamber 7. In other words, when the individual negative pressure ink chamber 7 becomes negative pressure and the meniscus M of the dummy nozzle 31 retreats as shown by the dashed lines (b) and (c) in Figure 28, if the dummy nozzle 31 is cylindrical as in Figure 28(b), the meniscus force will not change, but if the dummy nozzle has a reverse tapered shape as in Figure 28(c), the meniscus force will increase the further it retreats. The level of negative pressure that can be withstood was calculated with reference to Figure 9(c).

[0065] The ink meniscus M of the ejection nozzle 3 does not rise in channels that are not ejecting ink, but does rise in channels that are ejecting ink. This is particularly likely to occur in channels that repeatedly eject ink. Therefore, by separating the individual negative pressure ink chambers 7 for each pressure chamber 4, it is possible to both quickly restore the meniscus M that has risen to its original state and suppress the crosstalk between the channels mentioned above. If the state of the ink meniscus M in the ejection nozzle 3 is stable, stable, high-quality, high-speed printing becomes possible. Therefore, the ink ejection state is stable even when high-speed continuous ejection is performed at a frequency of, for example, 50 kHz.

[0066] Next, filling of the ink into the inkjet head 100 will be described. FIG. 29 is a schematic diagram showing how ink fills the pressure chambers 4, ink standby chambers 6, and individual negative pressure ink chambers 7 when the inkjet head 100 is positioned with the ejection nozzles 3 positioned on the bottom side, as shown in FIG. 1. Ink is filled by supplying ink from the ink supply pressure adjusting device 321 of FIG. 1, for example. As shown in FIG. 29(a), ink from the ink supply manifold 62 flows into the ink standby chamber 6 through the narrowed portion 61 and fills the chamber of the ink standby chamber 6. Furthermore, as shown in FIG. 29(b), ink fills the chambers of each pressure chamber 4, and an ink meniscus M is formed inside the ejection nozzle 3. Furthermore, as shown in FIG. 29(c), ink fills the individual negative pressure ink chambers 7, but air remaining in the chambers when, for example, the dummy nozzles 31 are wet with ink is subsequently released into the concave air reservoirs 7. 2 It accumulates.

[0067] That is, even if air remains in the individual negative pressure ink chamber 7 when ink is filled, it can be accumulated in the air reservoir 72. As a result, it is possible to prevent air from entering the pressure chamber 4, for example, and affecting the ink ejection operation. Furthermore, it is expected that the air in the individual negative pressure ink chamber 7 will function as a buffer to suppress residual vibrations when ink is ejected. It is preferable to form the air reservoir 72 in a position as far away as possible from the open end of the pressure chamber 4.

[0068] In this way, it is possible to return the ink meniscus M inside the ejection nozzle 3, which has bulged outward due to ejection, to its original state. The ink standby chamber 6 does not necessarily have to be separated for each channel, and may be a common ink chamber that communicates with the channels. In this case, the narrowed portion 61 and the ink supply manifold 62 may also be omitted, and the common ink chamber may be communicated with the ink flow path 311.

[0069] The inkjet head 100 is not limited to a configuration in which the ejection nozzles 3 are positioned on the bottom side as shown in FIG. 1 . The inkjet head 100 may be used with the ejection nozzles 3 facing horizontally, or in a direction other than horizontally. If the ejection nozzles 3 do not face vertically downward, in order to minimize the volume of gas remaining in the individual negative pressure ink chambers 7 after filling, it is desirable to position the dummy nozzles 31 as far away from the pressure chambers 4 as possible and as high as possible on the opposite side of the direction of gravity, and to eliminate the air reservoirs 72 or position them even higher than the dummy nozzles 31. The positions and presence or absence of the dummy nozzles 31 and air reservoirs 72 can be determined taking into consideration the orientation of the inkjet head 100 during use and the direction of gravity.

[0070] According to any of the above-described embodiments, the dummy nozzle 31 is provided at a position where the pressure change due to liquid column resonance is smaller than that of the ejection nozzle 3, and the outer opening diameter D3 of the dummy nozzle 31 is equal to or larger than the inner opening diameter D4 and equal to or smaller than the outer opening diameter D1 of the ejection nozzle 3, thereby preventing liquid from leaking or air from being sucked in from the dummy nozzle 31. As described above, the dummy nozzle 31 can be used for purposes such as filling with ink, relieving pressure, or sucking excess ink.

[0071] The inkjet head 100 is not limited to a shear mode type actuator 6 in which a plurality of pressure chambers 4 are arranged. It may also be a drop-on-demand piezoelectric type actuator.

[0072] In the above embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection head, but the liquid ejection head may also be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0073] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0074] 10. Inkjet printer 100~103 Inkjet head 2 Head 22 Nozzle plate 23 Actuator board 3 Discharge nozzle 31 Dummy nozzle 4. Pressure Chamber 41 Piezoelectric element 42 Common ink chamber 43 Common ink chamber 5 Actuators 6 Ink waiting room 61 Stenosis 62 Ink supply manifold 7 Individual negative pressure ink chamber 72 Air reservoir

Claims

1. A pressure chamber having at least one end in the longitudinal direction that is an open end; an ejection nozzle communicating with the pressure chamber and provided at a position where a pressure change in the pressure chamber becomes large due to liquid column resonance of ¼ wavelength or ½ wavelength in the longitudinal direction in the pressure chamber that occurs when the actuator is driven, the ejection nozzle having an outer opening diameter smaller than an inner opening diameter; a dummy nozzle that does not eject liquid, which is positioned at a position where the pressure change due to the liquid column resonance is smaller than that of the ejection nozzle, and has an outer opening diameter that is equal to or larger than the inner opening diameter and is equal to or smaller than the outer opening diameter of the ejection nozzle.

2. 2. The liquid ejection head according to claim 1, wherein the number of the dummy nozzles is greater than the number of the ejection nozzles.

3. 3. The liquid ejection head according to claim 1, wherein the dummy nozzle has a cylindrical shape in which the outer opening diameter and the inner opening diameter are equal.

4. 4. The liquid ejection head according to claim 1, wherein the ejection nozzles and the dummy nozzles are arranged on the same surface of a nozzle portion.

5. a tapered discharge nozzle that communicates with the pressure chamber and has an outer opening diameter smaller than an inner opening diameter; a dummy nozzle that does not eject liquid, which is arranged at a position where the pressure change of the liquid is smaller than that of the ejection nozzle, has an outer opening diameter equal to or smaller than that of the ejection nozzle, and has a tapered, cylindrical, or reverse tapered shape with a smaller taper angle than that of the ejection nozzle; an air reservoir portion disposed above the dummy nozzle in a direction opposite to the direction in which gravity acts.

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