JP7802585B2 - Liquid ejection head - Google Patents

Description

An embodiment of the present invention relates to a liquid ejection head.

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

A liquid ejection head has multiple channels that eject 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 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.

JP 2010-23241 A JP 2015-80923 A Japanese Patent Application Laid-Open No. 2004-195959 Japanese Patent Application Laid-Open No. 2008-6646 Japanese Patent Application Laid-Open No. 2021-41577

The problem that this invention aims to solve is to provide a liquid ejection head that can prevent liquid from leaking or air from being sucked in from dummy nozzles.

A liquid ejection head according to an embodiment of the present invention includes a pressure chamber, an ejection nozzle, and a dummy nozzle. The pressure chamber has at least one longitudinal end that is open. The ejection nozzle communicates with the pressure chamber, and has an outer opening diameter that is smaller than the inner opening diameter. The ejection nozzle is provided at a position where pressure change within the pressure chamber increases due to liquid column resonance of ¼ wavelength or ½ wavelength in the longitudinal direction within the pressure chamber that occurs when the actuator is driven. The dummy nozzle is provided at a position where liquid pressure change 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.

1 is a diagram illustrating the overall configuration of an inkjet printer equipped with an inkjet head according to a first embodiment. FIG. 2 is a perspective view of the inkjet head. FIG. 2 is a partially enlarged perspective view of a head portion of the inkjet head. FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. This is a driving waveform applied to the actuator of the inkjet head. 10A and 10B are diagrams illustrating the operation of an actuator driven by the above drive waveform. FIG. 2 is a diagram illustrating the arrangement of ejection nozzles and dummy nozzles of the inkjet head. 5A and 5B are diagrams illustrating liquid column resonance occurring in a pressure chamber of the inkjet head. 3A and 3B are diagrams showing cross-sectional shapes of the discharge nozzle and the dummy nozzle. 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. 3A and 3B are explanatory diagrams of the arrangement of ejection nozzles and dummy nozzles of the inkjet head and pressure propagation. FIG. 10 is a perspective view of an inkjet head according to a second embodiment. FIG. 2 is a partially enlarged plan view of a head portion of the inkjet head. FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. FIG. 2 is an enlarged cross-sectional view of a pressure chamber and an air chamber of the inkjet head. 3A to 3C are explanatory diagrams illustrating the operation of the actuator of the inkjet head. 5A and 5B are explanatory diagrams of liquid column resonance occurring in a pressure chamber of the inkjet head. 3A and 3B are diagrams showing cross-sectional shapes of ejection nozzles and dummy nozzles of the inkjet head. FIG. 10 is a partially enlarged plan view of a head portion of an inkjet head according to a third embodiment; FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. FIG. 10 is a perspective view of an inkjet head according to a fourth embodiment. FIG. 2 is a partially enlarged plan view of a head portion of the inkjet head. FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. FIG. 2 is a partially enlarged cross-sectional view of a head portion of the inkjet head. 5A and 5B are explanatory diagrams of liquid column resonance occurring in a pressure chamber of the inkjet head. 3A and 3B are diagrams showing cross-sectional shapes of ejection nozzles and dummy nozzles of the inkjet head. FIG. 2 is an explanatory diagram schematically illustrating how the inkjet head is filled with ink.

The liquid ejection head according to the embodiment will be described in detail below with reference to the accompanying drawings. Note that the same components are designated by the same reference numerals in each drawing.

(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. The inkjet printer 10 includes, inside a housing 11, 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, which serves as a user interface, is located on the upper side of the housing 11.

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

The 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. The arrow 104 in the figure indicates the conveying path of the sheets S from the cassette 12 to the conveying belt 14.

The conveyor belt 14 is a mesh-like endless belt with numerous through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, support the conveyor belt 14 for free rotation. 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.

Inkjet heads 100-103, which are an example of liquid ejection heads, are positioned facing sheet S, which is held by suction on conveyor belt 14, with a small gap of, for example, 1 mm between them. Inkjet heads 100-103 each eject ink droplets toward sheet S. Inkjet heads 100-103 print images as sheet S passes underneath. Each inkjet head 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.

The inkjet heads 100-103 are connected to ink tanks 315-318 and ink supply pressure regulators 321-324 via ink flow paths 311-314, respectively. Each ink tank 315-318 is located above the corresponding inkjet head 100-103. During standby, each ink supply pressure regulator 321-324 regulates the pressure inside each inkjet head 100-103 to a negative pressure relative to atmospheric pressure, for example, -1.2 kPa, to prevent ink from leaking from the ejection nozzles 3 (see Figure 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 regulators 321-324.

After image formation, the sheet S is sent from the conveyor belt 14 to the downstream conveying path 15. The downstream conveying path 15 is composed 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 the discharge outlet 157 to the discharge tray 16. The arrow 107 in the figure indicates the conveying path of the sheet S.

Next, the configuration of inkjet heads 100-103 will be described. Below, inkjet head 100 will be described with reference to Figures 2-4, but inkjet heads 101-103 have the same structure as inkjet head 100.

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 has multiple 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.

The flexible printed wiring board 21 is equipped with a driver chip, a driving IC (Integrated Circuit) 25 (hereafter 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 the specified timing.

The nozzle plate 22, an example of a nozzle section, is a rectangular plate made of resin such as polyimide or 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 the 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 Figure 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 also be arranged in a single row, for example.

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. Multiple pressure chambers 4 for each channel are formed within the space surrounded by the nozzle plate 22, frame-shaped member 26, and actuator substrate 23. Multiple pressure chambers 4 are arranged on the actuator substrate 23, for example, along the longitudinal direction of the substrate. The pressure chambers 4 for each channel are connected to the discharge nozzles 3 for each channel.

The pressure chambers 4 are formed on the surface of the actuator substrate 23 by cutting out, for example, rectangular grooves into two piezoelectric members 41 that are stacked with their polarization directions in opposite directions (for example, facing directions) (Figure 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.

Adjacent pressure chambers 4 are separated by side walls made of piezoelectric members 41. That is, each pressure chamber 4 has side walls made of piezoelectric members 41 standing on both sides of its short side, and both ends of its length 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 to the pressure chambers 4 of each channel. However, ink supply does not have to be by a circulation method.

The electrodes 46 are integrally formed on the bottom and both side surfaces of the pressure chamber 4. The electrode 46 of each pressure chamber 4 is connected to a wiring electrode 47. The piezoelectric member 41 and electrode 46 constitute the actuator 5 that changes the volume of the pressure chamber 4. The wiring electrode 47 extends to the outside of the frame member 26. The surfaces of the electrodes 46 and the wiring electrode 47 inside the frame member 26 may be covered with a protective film (not shown) to prevent contact with ink. The electrodes 46 and wiring electrode 47 are formed, for example, with a thin nickel film formed by electroless plating. The wiring electrode 47 is connected to the flexible wiring board 21 at the end of the actuator substrate 23 and is connected to the driver (i.e., drive circuit) of the drive IC 25. The driver for each channel provides a drive signal, for example a drive voltage, 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 member 41, causing the piezoelectric members 41, which form the side walls on both sides of the pressure chamber 4, to deform in shear mode.

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 and outer walls of the pressure chamber 4, and the actuator 5 is charged, causing it to deform. 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.

Figure 5 shows a drive waveform (DRP waveform) as an example of a drive waveform for driving the actuator 5. Figure 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 potential (GND) during period t2, and a positive voltage (+V) during period t3. Period t1 is set to, for example, half the pressure vibration period of the head unit 2. When the pressure vibration 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, shorter than period t2. In this case, the center interval between periods t1 and t3 is t1/2 + t2 + t3/2 = (pressure vibration period).

The actuator 5 can be driven, for example, by dividing the pressure chambers 4 into three groups of two each, known as three-part drive. Figure 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. Figure 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 Figure 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 their polarization direction. This causes the piezoelectric elements 41 to deform outward, thereby expanding the volume of the central pressure chamber 4.

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 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.

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 Figure 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 Figure 6(b), causing the piezoelectric elements 41 to deform inward, thereby contracting the volume of the central pressure chamber 4. After 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 Figure 6(a). This contraction and restoration cancels out any residual vibration.

Next, the shape and arrangement of the ejection nozzle 3 and dummy nozzle 31 will be described with reference to Figures 7 to 9. As previously mentioned, ink is ejected by driving the actuator 5 to change the volume of the pressure chamber 4 and 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 to eject ink. 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 Figure 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 in which one longitudinal end is open and the other end is closed, as shown in Figure 7(b), it becomes a 1/4 wavelength resonance tube. This differs from inkjet heads that utilize Helmholtz resonance.

In the case of a 1/2 wavelength resonance tube, if the pressure amplitude and flow velocity amplitude are represented by a standing wave 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 1/2 wavelength resonance tube of Figure 7(a), a preferred example is to place it in the longitudinal center where the pressure amplitude is maximum. In the case of the 1/4 wavelength resonance tube of Figure 7(b), a preferred example is to place it at the back of the longitudinal center where the pressure amplitude is maximum. However, as mentioned 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 is positioned in a staggered arrangement, offset from the other groups (see Figures 7, 10-12). The amount of positional offset is determined depending on, for example, the transport speed of the sheet S. In this way, the position of the discharge nozzle 3 does not have to be strictly limited to the position where the pressure amplitude is greatest, but may be in the vicinity thereof. An example of the vicinity thereof is within 1/10 of the wavelength.

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 nozzle opening diameter on the discharge surface side of the nozzle plate 22. On the other hand, the inner opening diameter is the nozzle opening diameter on the pressure chamber 4 side of the nozzle plate 22.

The ejection nozzle 3 forms an ink meniscus M near its opening, and ejects ink by introducing pressure changes caused by liquid column resonance that occurs when the actuator 5 is driven into the nozzle. 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 with the wide inner opening diameter D2. When the nozzle is stationary and not ejecting ink, negative pressure is applied to the pressure chamber 4 to maintain the meniscus M in a concave shape. In other words, the ink supply pressure adjustment device 321 adjusts the pressure inside the inkjet head 100 to a negative pressure relative to atmospheric pressure. The same applies to the dummy nozzle 31.

As mentioned above, the pressure chamber 4 and the common ink chambers 42, 43 are connected at the position where the pressure change due to liquid column resonance is smallest and the flow velocity change 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 impact on ejection characteristics. The pressure change also propagates via the connecting passage to the pressure chambers 4 of other surrounding channels. This is why dummy nozzles 31 are provided.

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 place them 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 place them 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 does not have to be strictly 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 Figure 7(c), it is placed 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).

As shown in FIG. 9, the dummy nozzle 31 has an outer opening diameter D3 that is equal to or greater 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 inverted 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 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, for example, the same as the thickness of the nozzle plate 22.

By positioning the dummy nozzle 31 in a location where the pressure amplitude of the liquid column resonance is small, ink is not ejected. 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, as the negative pressure in the pressure chamber 4 increases and the meniscus M retreats inward, the meniscus force weakens, making it easier for external air to enter through the nozzle, resulting in low pressure relief capabilities. For this reason, a cylindrical or inverted tapered shape is preferred for the dummy nozzle 31. With a cylindrical shape, the meniscus force remains unchanged 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 placing a load on 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 adjacent to each other, for example. Increasing the number of dummy nozzles 31 allows for a larger range of volume change in the common ink chamber 42 (43), thereby improving pressure relaxation capabilities.

That is, as shown in FIG. 9(c), if the taper angle of the nozzle 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/cos θ, 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, it is possible to determine how much negative pressure the nozzle can withstand.
ΔP=2δ/r=[2cosθ/R]δ However, θ=θ2−θ1
If the dummy nozzle 31 is formed with a tapered shape as shown in FIG. 9C , similar to the discharge nozzle 3, when θ1 = 10°, θ2 = 10°, R = 15 μm (D1 = 30 μm), and δ = 30 × 10 ⁻³ N/m, the nozzle can withstand a negative pressure of −4 kPa. However, when the meniscus M recedes to the inner diameter as shown by the dashed line in FIG. 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 the dummy nozzle 31 will be able to withstand a pressure of −3 kPa when the meniscus M recedes to the nozzle inner diameter. 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 is a cylindrical dummy nozzle, when R = 10 μm (D3 = 20 μm), it can withstand a negative pressure of -5.9 kPa, and the meniscus force does not change even when the meniscus M recedes. Furthermore, if the dummy nozzle 31 is a reverse tapered dummy nozzle, when θ1 = -3°, θ2 = 10°, and R = 10 μm (D3 = 20 μm), it can withstand a negative pressure of -5.8 kPa. 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 up to -8.1 kPa. Note that for a cylindrical dummy nozzle 31, θ1 = 0, and for a reverse tapered dummy nozzle 31, θ1 < 0. Therefore, it can be said that a cylindrical or reverse tapered dummy nozzle 31 has a smaller taper than a tapered discharge nozzle 3. It can also be said that the ratio of the inner opening diameter to the outer opening diameter of the dummy nozzle 31 (=inner opening diameter/outer opening diameter) is smaller than the ratio of the inner opening diameter to the outer opening diameter of the discharge nozzle 3 .

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, so it is preferable to locate it 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, whereby 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, dummy nozzles 31 do 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, as shown in Figure 12, crosstalk can be reduced by placing 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 paths between channels, similar to Figure 10.

Furthermore, in addition to the above-mentioned pressure relief effect, the dummy nozzles 31 on the common ink chamber 43 side also have the effect of preventing dead ends in the flow path, 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 can also be used as suction holes to suck out excess ink.

Furthermore, by arranging the ejection nozzles 3 and 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.

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.

As shown in particular in Figures 14 to 16, the nozzle plate 22, on 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, frame-shaped member 26, and actuator substrate 23. The pressure chambers 4 of each channel that ejects ink are connected to the ejection nozzles 3 of each channel.

The pressure chamber 4 is formed on the surface of the actuator substrate 23 by cutting, for example, a rectangular groove into two piezoelectric members 41 stacked with their polarization directions in opposite directions (for example, facing directions) (see Figure 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 chamber 4 has side walls of the piezoelectric members 41 erected on both sides in the lateral direction, and is, for example, an elongated space with both ends in the longitudinal direction open. Note that the piezoelectric members 41 are formed so that they are trapezoidal when viewed from the side, for example, but the shape when viewed from the side is not limited to a trapezoid.

The air chambers 40 are located on either side of the pressure chamber 4, with piezoelectric members 41 interposed between them. 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, creating an airtight space into which ink cannot be introduced. The wall members 29 are, for example, resin walls.

The openings at both longitudinal ends of the pressure chamber 4 are connected to the ink standby chamber 6. The ink standby chamber 6 is an example of a liquid standby chamber. Each ink standby chamber 6 is separated from the ink standby 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 standby chamber 6 is separated for each channel that ejects ink. When the pressure chamber 4 has openings at both ends, an ink standby chamber 6 is provided at each end. In a plan view, the ink standby chamber 6 has a space that is wider horizontally 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 standby chamber 6 larger compared to 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 standby chamber 6 does not necessarily have to be expanded both horizontally and vertically; either one is sufficient. In addition, while the wall member 29 separating the ink standby chamber 6 of the adjacent channel is shown as an example to be shared with the wall member 29 that closes the opening of the air chamber 40, they may also be formed separately. Furthermore, the wall member 29 may be formed from another material, such as a plate.

The ink standby chambers 6 on both sides of the pressure chamber 4 are each connected to the ink supply manifold 62 via a narrowed portion 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 that it penetrates 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 as a groove along the arrangement direction of the narrowed portion 61 (X direction). 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 at least smaller than the cross-sectional area of the ink standby chamber 6. It is usually also 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 while Figures 14 to 16 show a configuration in which ink is supplied from both ink supply manifolds 62, one of them may also be an ink discharge manifold, and ink may be circulated and supplied to the pressure chamber 4. The ink supply manifold 62 and ink discharge manifold are examples of manifolds that communicate with the narrowed portion 61.

Although not shown in Figures 14 to 16, as shown in Figure 17, the electrodes 46 are integrally formed, for example, 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 as individual electrodes. The electrodes 48 are integrally formed, for example, on 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, 48 sandwiching the piezoelectric member 41 constitute the actuator 5, which changes the volume of the pressure chamber 4 through shear mode deformation. The electrodes 46, 48 and wiring electrodes 47, 49 are formed, for example, from 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 electrode 47 from the pressure chamber 4 is connected, for example, to the flexible printed wiring board 21 at the end of the actuator substrate 23 and then to the drive driver (i.e., drive circuit) of the drive IC 25. The driver for each channel supplies a drive signal, such as a drive voltage, to the actuator 5 for each channel. Meanwhile, the wiring electrode 49 from the air chamber 40 is connected to ground (GND), for example. 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, causing the piezoelectric members 41 forming the side walls on both sides of the pressure chamber 4 to deform in shear mode.

The actuator 5 is driven by applying, for example, the drive waveform (DRP waveform) shown in Figure 5. Figure 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. Figure 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 Figure 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.

During the following period t2, the potential of the electrode 46 of the pressure chamber 4 is set to ground potential (GND), causing the expanded volume of the pressure chamber 4 to return to the state shown in Figure 18(a). By restoring 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 vibration 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.

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 Figure 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 Figure 18(b), causing the piezoelectric elements 41 to deform inward, thereby contracting the volume of the pressure chamber 4. After 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 Figure 18(a). This contraction and restoration damps residual vibration.

The ink ejection described above also utilizes the liquid column resonance in the longitudinal direction of the pressure chamber, 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 nearby. An example of the vicinity is within the range of 1/10 wavelength.

As shown in Figure 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.

The dummy nozzle 31 is positioned so that it communicates with the ink waiting 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, with the diameter increasing 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 for a cylindrical shape and 10 to 20 μm for a 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, for example, the same as the thickness of the nozzle plate 22.

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, so it is preferable to locate them near the end of the pressure chamber 4. Furthermore, the number of dummy nozzles 31 is not limited to one. In the example shown, three dummy nozzles 31 are arranged in series, for example, facing the constricted 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, 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. 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, the greater the pressure relief ability to absorb pressure changes. The dummy nozzles 31 may also be used for purposes other than pressure relief, such as as a discharge hole when filling with ink, or as a suction hole for excess ink.

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. However, 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.

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, including the amount of ink ejected. If the constriction portion 61 were not provided, the restoring force of the meniscus M attempting to return to its original state after ejection and the mass of ink inside the head resisting this force would cause vibration of the meniscus M due to a resonance other than the liquid column resonance described above, destabilizing the 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 portion 61 located between the ink standby chamber 6 and the ink supply manifold 62 to appropriately set the resistance as 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 when high-speed continuous ejection is performed at a frequency of, for example, 50 kHz, the ink ejection state is stabilized.

(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 pressure chamber 4 has only one open end, 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.

As shown in Figures 21 and 22, the pressure chamber 4 of the inkjet head 100 is open at one longitudinal end and closed at the other end by, for example, a frame-shaped member 26. The open end is connected to the ink waiting chamber 6. A pressure chamber 4 with only one longitudinal open end like this serves as 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 Figure 22, the innermost longitudinal end of the pressure chamber, closed by the frame-shaped member 26, becomes the fixed end, with the maximum pressure amplitude and the minimum flow velocity amplitude. Meanwhile, the open end of the standing wave has the minimum pressure amplitude and the maximum flow velocity amplitude. The ejection nozzle 3 is positioned at the innermost longitudinal end where the pressure amplitude is large. Of course, it may be located near that location. An example of the vicinity is within the range of 1/10 of the wavelength. The dummy nozzle 31 is formed at a position that communicates with the ink waiting chamber 6. In this way, by providing dummy nozzles 31 that do not eject ink in the area of the nozzle plate 22 that corresponds to the ink standby chamber 6, the pressure in the ink standby chamber 6 can be stabilized.

(Fourth embodiment)
Next, an inkjet head 100 according to a fourth embodiment will be described with reference to Figures 23 to 29. Note that the same components as those in the second embodiment are denoted by the same reference numerals. As shown in Figure 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.

As shown in Figures 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, when viewed in 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 individual negative pressure ink chamber 7 larger than the opening at the end of the pressure chamber 4, the other longitudinal opening of the pressure chamber 4 becomes an open end where pressure changes due to liquid column resonance, as described below, 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; it can be expanded in either direction. Also, while one example is 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 that closes the opening of the air chamber 40, they may be formed separately. Furthermore, the wall member 71 may be formed from another material, such as a plate.

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. In other words, because the individual negative pressure ink chamber 7 is connected to the open end of the pressure chamber 4, 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 Figure 28, the outer opening diameter D3 of the dummy nozzle 31 is equal to or greater than the inner opening diameter D4 and equal to or less than the outer opening diameter D1 of the ejection nozzle 3. Preferably, the dummy nozzle 31 has a cylindrical shape as shown in Figure 28(b) or an inverted tapered shape, with the diameter increasing toward the outer tip as shown in Figure 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 if the dummy nozzle 31 has a cylindrical shape and is, for example, 10 to 20 μm if the dummy nozzle 31 has 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, while it is preferable to arrange the dummy nozzles along an extension of the longitudinal direction (Y direction) of the pressure chamber 4, the arrangement direction may also 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.

Each individual negative pressure ink chamber 7 has a concave air reservoir 72 formed in 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 Figure 1, the air reservoir 72 is located above the dummy nozzle 31. In other words, the air reservoir 72 is formed on one side of the chamber of the individual negative pressure ink chamber 7 in the direction opposite to the direction in which gravity acts (in this case, the ceiling surface), allowing any air remaining in the chamber to accumulate. A preferred shape for the air reservoir 72 is, for example, elliptical when viewed from above. Furthermore, when viewed in cross section, it is preferable that the outer periphery of the air reservoir 72 is sloped without any steps.

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 within the time domain of the pressure oscillation. However, when the ejection operation is viewed over a longer time span, in a channel that repeatedly ejects 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, 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.

The dummy nozzle 31 is preferably a smaller hole than the ejection nozzle 3, and is preferably cylindrical or reverse tapered rather than tapered like the ejection nozzle 3, because this is more suitable for maintaining the negative pressure state of 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 it is cylindrical as in Figure 28(b), the meniscus force will remain unchanged, but if it is reverse tapered 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).

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. For this reason, by separating the individual negative pressure ink chambers 7 for each pressure chamber 4, it is possible to both quickly restore the meniscus M to its original state and suppress the crosstalk between channels mentioned above. If the state of the ink meniscus M inside 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 50 kHz, for example.

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 chamber 4, ink standby chamber 6, and individual negative pressure ink chamber 7 when the inkjet head 100 is positioned with the ejection nozzle 3 positioned on the bottom side, as shown in FIG. 1. The ink is filled by supplying ink from, for example, the ink supply pressure adjusting device 321 shown in FIG. 1. 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, forming an ink meniscus M within the ejection nozzle 3. Furthermore, as shown in FIG. 29( c), ink fills the individual negative pressure ink chamber 7, but any air remaining in the chamber, for example, when the dummy nozzle 31 becomes wet with ink, subsequently accumulates in the concave air reservoir 72 .

In other words, even if air remains in the individual negative pressure ink chamber 7 when ink is filled, it can be stored 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, the air in the individual negative pressure ink chamber 7 can be expected to function as a buffer to suppress residual vibrations when ink is ejected. It is preferable to form the air reservoir 72 as far away as possible from the open end of the pressure chamber 4.

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 into individual channels, and may be a common ink chamber that communicates between the channels. In this case, the narrowed portion 61 and ink supply manifold 62 may also be omitted, and the common ink chamber may be connected to the ink flow path 311.

The inkjet head 100 is not limited to being used in a position where the discharge nozzles 3 are located on the bottom side, as shown in Figure 1. The inkjet head 100 may also be used in a position where the discharge nozzles 3 face horizontally, or in a direction other than horizontal. If the discharge 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 reservoir 72 or position it even higher than the dummy nozzles 31. The positions and presence or absence of the dummy nozzles 31 and air reservoir 72 can be determined taking into account the orientation of the inkjet head 100 during use and the direction in which gravity acts.

In 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 up excess ink.

The inkjet head 100 is not limited to a shear mode actuator 6 with multiple pressure chambers 4 arranged therein. It may also be a drop-on-demand piezoelectric actuator, etc.

In the above embodiment, the inkjet head 100 of the inkjet printer 10 was 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.

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 a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

10 Inkjet printer 100 to 103 Inkjet head 2 Head section 22 Nozzle plate 23 Actuator substrate 3 Discharge nozzle 31 Dummy nozzle 4 Pressure chamber 41 Piezoelectric member 42 Common ink chamber 43 Common ink chamber 5 Actuator 6 Ink standby chamber 61 Narrowed section 62 Ink supply manifold 7 Individual negative pressure ink chamber 72 Air reservoir section

Claims (5)

a pressure chamber having at least one end in the longitudinal direction that is an open end;
a discharge 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 discharge 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. A liquid ejection head as described in claim 1, wherein the number of dummy nozzles is greater than the number of ejection nozzles. A liquid ejection head according to claim 1 or 2, characterized in that the dummy nozzle has a cylindrical shape in which the outer opening diameter and the inner opening diameter are equal. A liquid ejection head according to any one of claims 1 to 3, characterized in that the ejection nozzle and the dummy nozzle are arranged on the same surface of the nozzle portion. 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, and has an outer opening diameter equal to or smaller than that of the ejection nozzle, and is either tapered, cylindrical, or reverse tapered with a smaller taper angle than the ejection nozzle;
an air reservoir portion disposed above the dummy nozzle in a direction opposite to the direction in which gravity acts .