JP2024047751A - Liquid ejection head and method for filling liquid ejection head with liquid - Google Patents

Abstract

[Problem] To provide a liquid ejection head capable of filling a common liquid chamber with liquid. [Solution] The liquid ejection head of the embodiment comprises a plurality of pressure chambers, a common liquid chamber, a liquid supply port, and a liquid exhaust port. The plurality of pressure chambers are arranged in a first direction. The common liquid chamber communicates with each of the plurality of pressure chambers, and has a ceiling surface that becomes higher from one end side of the pressure chamber array to the other end side when the pressure chamber array direction is positioned horizontally. A liquid supply port communicates with the common liquid chamber at the center of the pressure chamber array. A liquid exhaust port communicates with the common liquid chamber at the end where the ceiling surface becomes higher. [Selected Figure] Figure 4

Description

Embodiments of the present invention relate to a liquid ejection head and a method for filling a liquid ejection head with liquid.

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 droplets of ink from an inkjet head to form an image or the like on the surface of a recording medium. 3D printers eject droplets of modeling material from a modeling material ejection head, harden them, and form a three-dimensional object. Dispensing devices eject droplets of a sample and supply a predetermined amount to multiple containers, etc.

The liquid ejection head has multiple channels for ejecting liquid. Each channel has a nozzle for ejecting liquid, a pressure chamber connected to the nozzle, and an actuator for changing the volume of the pressure chamber. Liquid is supplied from a common liquid chamber connected to each pressure chamber. For example, when filling the common liquid chamber with liquid, the liquid ejection head has a liquid inlet and outlet for each. If the liquid inlet and outlet are provided at both ends of the common liquid chamber, filling with liquid becomes easy. However, during normal operation, the temperature difference between the liquid supplied from the inlet and the liquid inside the head can cause a concentration distribution throughout the head. In order to suppress this temperature distribution, it is desirable to provide the inlet near the center of the common liquid chamber, but if the outlet is provided at one end of the common liquid chamber, it is difficult to fill the opposite area where the outlet is not provided with liquid without leaving air bubbles.

JP 2003-311995 A JP 2017-193132 A JP 2002-144576 A Patent Document 1: WO2010-109578

The problem that this invention aims to solve is to provide a liquid ejection head that can fill a common liquid chamber with liquid.

A liquid ejection head according to an embodiment of the present invention includes a plurality of pressure chambers, a common liquid chamber, a liquid supply port, and a liquid discharge port. The plurality of pressure chambers are arranged in a first direction. The common liquid chamber communicates with each of the plurality of pressure chambers, and has a ceiling surface that becomes higher from one end side of the pressure chamber arrangement toward the other end side when the arrangement direction of the pressure chambers is positioned horizontally. The liquid supply port communicates with the common liquid chamber at the center of the pressure chamber arrangement. The liquid discharge port communicates with the common liquid chamber at the end where the ceiling surface becomes higher.

1 is an overall configuration diagram of an inkjet printer equipped with an inkjet head according to a first embodiment. FIG. 2 is a perspective view of the inkjet head. 2 is a side view of the inkjet head and an ink recovery container. FIG. 2 is a development view of a head portion of the inkjet head. 5A to 5C are diagrams illustrating the operation of the actuator of the inkjet head. This is a drive waveform to be applied to the actuator. 6A and 6B are explanatory diagrams of the flow of ink during the initial filling. 6A and 6B are explanatory diagrams of the flow of ink during the initial filling. FIG. 11 is an exploded view of a head portion of an inkjet head according to a second embodiment.

The liquid ejection head and liquid filling method according to the embodiment will be described in detail below with reference to the attached drawings. Note that the same components are given the same reference numerals in each drawing.

First Embodiment
As an example of an image forming apparatus equipped with the liquid ejection head of the first embodiment, an inkjet printer 10 that prints an image on a recording medium will be described. Fig. 1 shows a schematic configuration of the inkjet printer 10. The inkjet printer 10 has a housing 11 and includes a cassette 12 that stores a sheet S, which is an example of a recording medium, an upstream transport path 13 for the sheet S, a transport belt 14 that transports the sheet S taken out of the cassette 12, a plurality of inkjet heads 100-103 that eject ink droplets toward the sheet S on the transport belt 14, a downstream transport path 15 for the sheet S, an ejection tray 16, and a control board 17. An operation unit 18, which is a user interface, is located on the upper side of the housing 11.

The image data to be printed on the sheet S is generated, for example, by 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.

The pickup roller 204 supplies the 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, 132 and sheet guide plates 133, 134. The sheets S are fed via the upstream conveying path 13 to 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 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 conveyor belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive device. In the figure, 105 indicates the direction of rotation of the conveyor belt 14. A negative pressure container 206 is disposed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a fan 207 for reducing pressure. The fan 207 creates a negative pressure inside the negative pressure container 206 by forming an airflow, and adsorbs and holds the sheet S on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

The inkjet heads 100-103, which are an example of liquid ejection heads, are arranged to face the sheet S, which is held by suction on the conveyor belt 14, with a small gap of, for example, 1 mm between them. The inkjet heads 100-103 each eject ink droplets toward the sheet S. The inkjet heads 100-103 print images as the sheet S passes underneath them. Each of the inkjet heads 100-103 has the same structure, except that they eject different colors of ink. 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 supply paths 311-314, respectively. Each ink tank 315-318 is disposed above each 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, e.g., -1.2 kPa, relative to atmospheric pressure, so that ink does not leak from the nozzles 26 (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 regulators 321-324.

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

Next, the configuration of inkjet heads 100 to 103 will be described. Below, inkjet head 100 will be described with reference to Figures 2 to 5, but inkjet heads 101 to 103 have the same structure as inkjet head 100.

As shown in Figures 2 and 3, 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, which is an example of a film wiring board. The flexible printed wiring board 21 is further connected to a printed circuit board 22, which serves as a relay board.

The flexible printed wiring board 21 is equipped with a driver chip, a driving integrated circuit (IC) 23 (hereafter referred to as the driving IC). The driving IC 23, which acts as a control unit, temporarily stores print data sent from the control board 17, which is the control unit of the inkjet printer 10, via the printed circuit board 22, and provides driving signals to each channel so that ink is ejected at a predetermined timing.

The head section 2 comprises a nozzle plate 24, an actuator substrate 25, and a common ink chamber 3. The nozzle plate 24, 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. The nozzles 26 of each channel that ejects ink are arranged, for example, along the longitudinal direction (X direction) of the nozzle plate 24. In the case of a three-division drive, which will be described in detail later, a set of three nozzles 26 arranged in a staggered manner with their positions shifted from each other in the Y direction are arranged in the X direction. The nozzle density is set, for example, within the range of 150 to 1200 dpi.

The common ink chamber 3 is connected to the ink supply pressure adjustment device 321 (FIG. 1) via the ink supply path 311. Not only during normal operation but also, for example, during ink filling, ink is supplied from the ink supply pressure adjustment device 321 to the common ink chamber 3 via the ink supply path 311. The common ink chamber 3 is further connected to the ink discharge path 30. As shown in FIG. 3 as an example, the ink discharge path 30 is connected to an ink recovery container 37. The ink recovery container 37 is disposed, for example, in the inkjet printer 10. The ink discharge path 30 is not used, for example, for normal operation of ejecting ink, but is used when filling the head unit 2 with ink. It is preferable to provide the ink discharge path 30 with a valve 31 that can be opened and closed. Anything other than the valve 31 may be used as long as it can block the flow of ink. The ink discharge path 30 may be used for normal operation, for example, to circulate and supply ink to the head unit 2. When used for normal operation, the ink discharge path 30 is connected to one of the lines on the ink tank 315 side. The ink discharge path 30 may be branched and connected to both the ink recovery container 37 and the line on the ink tank 315 side, allowing the flow path to be switched using a valve (not shown).

As shown in FIG. 4 in particular, the common ink chamber 3 comprises a frame member 32 and a lid member 33. The frame member 32 is positioned so that its opening is covered by one surface of the actuator substrate 25. The lid member 33 covers the opening of the frame member 32 on the opposite side to the actuator substrate 25. As a result, the space surrounded by the lid member 33 and the frame member 32 becomes the interior of the common ink chamber 3. Furthermore, the pressure chambers 4 of each channel formed in the actuator substrate 25 communicate with the common ink chamber 3. The common ink chamber 3 is an example of a common liquid chamber that supplies liquid to the pressure chambers 4 of each channel.

At least a part of the inner circumferential surface of the frame member 32 is inclined. In the example of FIG. 4, the frame member 32 is formed as a square frame, and one surface in the longitudinal direction (X direction) is an inclined surface 34. This inclined surface 34 becomes the ceiling surface when the head unit 2 is filled with ink. In other words, the inclined surface (ceiling surface) 34 is a surface located on the opposite side to the direction in which gravity acts when the inkjet head 100 is in the position shown in FIG. 1 (nozzle 26 facing downward), for example. However, the inkjet head 100 is not necessarily used in the position shown in FIG. 1. The inclined surface 34 may be any surface that becomes the ceiling surface when the head unit 2 is in the position for filling ink, regardless of the position of the inkjet head 100 during normal operation.

Therefore, when the head unit 2 is positioned so that the arrangement direction of the pressure chambers 4 faces the horizontal direction (X direction) and the nozzles 23 face downward (i.e., as an example of the posture when filling with ink), the inclined surface 34 becomes higher from one end side of the arrangement of the pressure chambers 4 to the other end side. It is preferable that the inclined surface 34 has a gradient such that the difference in height from one end to the other end is a predetermined value, for example, a difference in height of 3 mm or more for the length from one end to the other end. As will be described in detail later, this is because air bubbles in the common ink chamber 3 tend to move to the other end side. If the ease of movement of air bubbles changes depending on the viscosity of the ink, etc., it is desirable to set the gradient according to the type of ink. Of course, a linear inclined surface 34 is preferable, but this is not limited to this. For example, it may be a ceiling surface such as a curved surface. In addition, the inclined surface 34 may be made to have a lyophilic property and surface roughness that make it easy for air bubbles to move. For this purpose, a surface treatment may be applied.

The lid member 33 is formed, for example, from a plate-shaped member. The lid member 33 is shaped to correspond to the outer peripheral shape of the frame member 32. The ink supply port 35 and the ink discharge port 36 are each openings that penetrate the lid member 33 and communicate with the interior of the common ink chamber 3. The ink supply port 35 is an example of a liquid supply port, and the ink discharge port 36 is an example of a liquid discharge port. The ink supply port 35 and the ink discharge port 36 are preferably circular opening holes. The direction of the holes is, for example, the thickness direction of the lid member 33. Alternatively, the direction of the holes may be tilted in the opposite direction to the direction in which gravity acts.

The ink supply port 35 and ink discharge port 36 are formed on the main surface of the cover member 33, on the side of the inclined surface 34 of the frame member 32, i.e., on the opposite side to the direction in which gravity acts when the ink is filled. In particular, the ink supply port 35 is located in the center of the inclined surface 34. In other words, it is the center of the arrangement of the pressure chambers 4. On the other hand, the ink discharge port 36 is located at the end where the inclined surface 34 is highest. It is desirable to position the ink discharge port 36 where the inclined surface 34 is at its highest point. The same applies to a ceiling surface other than the linear inclined surface 34.

The ink supply port 35 is connected to the ink flow path 311. The ink discharge port 36 is connected to the ink discharge path 30. It is preferable that the ink flow path 311 and the ink discharge path 30 extend in a direction higher than the inclined surface 34 so that air bubbles can easily escape from the common ink chamber 3. They may be at the same height as the inclined surface 34 as long as they are not lowered below the inclined surface 34.

The actuator substrate 25 is a rectangular substrate made of, for example, insulating ceramics. As described above, the pressure chambers 4 of each channel are arranged on the actuator substrate 25 along a first direction, for example, the X direction. The pressure chambers 4 of each channel are connected to the nozzles 26 of each channel.

The pressure chambers 4 are formed by cutting, for example, two piezoelectric members 41 stacked in opposite polarization directions (for example, facing directions) in the actuator substrate 25 into, for example, a rectangular groove shape in a second direction, for example, the Z direction. The piezoelectric members 41 are, for example, piezo elements. In other words, adjacent pressure chambers 51 are separated by side walls made of two piezoelectric members 41 stacked in a third direction, for example, the Y direction. Each pressure chamber 4 is open on the side communicating with the nozzle 26 and closed at the opposite end in the Z direction.

As shown in FIG. 5 in particular, electrodes 42 are integrally formed on the bottom and both side surfaces of the groove-shaped pressure chamber 4. The electrodes 42 are connected to wiring electrodes 43. The piezoelectric member 41 and the electrodes 42 constitute an actuator 5 that changes the volume of the pressure chamber 4. The electrodes 42 and wiring electrodes 43 are formed, for example, from a nickel thin film formed by electroless plating or the like.

The wiring electrode 43 is connected to the flexible wiring board 21 at the end of the actuator substrate 25, and is connected to the driver (i.e., the drive circuit) of the drive IC 23. The driver of each channel provides the actuator 5 of each channel with a drive signal, for example a drive voltage. With this configuration, when a drive voltage is applied to the actuator 5, an electric field is applied in a direction intersecting (preferably perpendicular to) the polarization axis of the piezoelectric member 41, and the piezoelectric member 41, which forms the side wall of the pressure chamber 4 in the X direction, deforms symmetrically in the X direction in shear mode.

Figure 6 shows a drive waveform (DRP waveform) as an example of a drive voltage applied to the actuator 5. Figure 6 also shows the change in ink pressure and ink flow rate in the pressure chamber 4 during driving. The drive waveform sequentially applies a negative potential voltage (-V) to the actuator 5 during period t1, a ground potential (GND) during period t2, and a positive potential voltage (+V) during period t3. Period t1 is set to, for example, 1/2 the pressure vibration period of the head portion 2.

The actuator 5 can be driven in a so-called three-division drive, in which the pressure chambers 4 are divided into three groups of two and driven separately. FIG. 5(a) shows a state in which the potentials of the electrodes 42 of the three adjacent pressure chambers 4 are all at ground potential (GND). In this state, the piezoelectric members 41 that form the partitions between the pressure chambers 4 are not distorted at all. FIG. 5(b) shows a state in which a negative voltage (-V) is applied to the electrode 42 of the central pressure chamber 4 during period t1 of the drive waveform in FIG. 6. In this state, an electric field acts on the piezoelectric members 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, and the piezoelectric members 41 deform outward, expanding the volume of the central pressure chamber 4.

During the following period t2, the potential of the electrode 42 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 FIG. 5(a). By contracting the volume of the pressure chamber 4 at the end point of period t1, which is set to 1/2 the pressure oscillation period, the ink pressure in the pressure chamber 4 increases as shown in FIG. 6, causing ink droplets to be ejected from the ejection nozzle 3.

During the following period t3, a positive voltage (+V) is applied to the electrode 42 of the central pressure chamber 4. In this state, as shown in FIG. 5(c), an electric field acts on the piezoelectric members 41 on both sides of the central pressure chamber 4 in the opposite direction to that in FIG. 5(b), causing the piezoelectric members 41 to deform inward, contracting the volume of the central pressure chamber 4. After period t3 has elapsed, the potential of the electrode 42 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. 5(a). This contraction and return cancels out residual vibration.

Next, the procedure for filling the head portion 2 with ink will be described with reference to Figures 7 to 8. Figures 7 and 8 are schematic diagrams showing the state inside the common ink chamber 3 during each process.

For example, the inkjet head 100 is mounted on the inkjet printer 10, and ink is supplied from the ink supply pressure adjustment device 321. That is, the head unit 2 is in the position for ink filling. Specifically, the arrangement direction of the pressure chambers 4 faces the horizontal direction (X direction), and the nozzles 23 face downward. Next, as shown in FIG. 7A, ink is supplied from the ink supply port 35 to fill the common ink chamber 3 with ink 7. At this time, the valve 31 is opened so that the ink flows from the ink supply port 35 to the ink discharge port 36. The ink discharged from the ink discharge port 36 is collected in the ink recovery container 37. The ink 7 supplied from the ink supply port 35 also flows into the area on the opposite side of the ink discharge port 36 in the common ink chamber 3, but air bubbles 71 remain. For example, if the surface of the nozzle plate 24 is open, the ink 7 also flows out from the nozzle 26, but since the flow path resistance on the nozzle 26 side is large, most of the ink flows toward the ink discharge port 36. During this period, the surface of the nozzle plate 24 may be capped to stop the ink 7 from flowing out of the nozzles 26.

Then, as shown in FIG. 7(b), the system is left as it is. That is, the supply of ink 7 is stopped, the valve 31 is closed to block the ink outlet 36, and the system is left as it is for a predetermined period of time, for example. This causes the air bubble 71 to rise inside the common ink chamber 3 along the inclined surface (ceiling surface) 43. Even if the filling of ink 7 is stopped in this state and normal operation is performed, the air bubble 71 is outside the flow line from the ink supply port 35 to the pressure chamber 4, and therefore is prevented from interfering with the flow of ink 7 during normal operation. Furthermore, the movement of the air bubble toward the pressure chamber 4 is also prevented.

Next, as shown in FIG. 8(c), after leaving it, the air bubbles 71 are removed. As an example, while supplying ink 7 from the ink supply port 35, the valve 31 is opened, for example, to open the ink outlet 36. Since the air bubbles 71 have moved to the vicinity of the ink outlet 36 by leaving it, the air bubbles 71 are discharged from the ink outlet 36 by flowing ink 7, and the size of the air bubbles 71 in the common ink chamber 3 can be reduced. After flowing ink 7 until all the air bubbles 71 are discharged, it is also possible to close the ink outlet 36 and make the common ink chamber 3 free of air bubbles 71, as shown in FIG. 8(d).

The inkjet head 100 filled with ink 7 can eject ink 7 from the nozzle 26 by applying a drive voltage to the actuator 5 based on print data. The flow of ink 7 from the ink supply port 35 toward the actuator 5 diverges from the center toward both sides, minimizing the temperature difference between the channels of the actuator 5. This allows stable ejection from all nozzles. It also reduces uneven density. Furthermore, even if air is sucked from the nozzle 26 when the actuator 5 is driven to expand the volume of the pressure chamber 4, the air bubble 71 rises to the vicinity of the ink outlet 36. Therefore, since the air bubble 71 is outside the flow line from the ink supply port 36 toward the pressure chamber 4, it does not interfere with the flow from the ink supply port 35 toward the actuator 5.

Second Embodiment
Next, an inkjet head 100 according to a second embodiment will be described with reference to Fig. 9. Note that the same components as those in the first embodiment are given the same reference numerals. As shown in Fig. 9, the ink supply port 35 and the ink discharge port 36 may be formed in the frame member 32 instead of in the cover member 33. In this case, as in the first embodiment, the ink supply port 35 is disposed in the center of the arrangement of the pressure chambers 4. The ink discharge port 36 is disposed at the end where the inclined surface 34 is higher.

As a variant, the ink supply port 35 may be formed in the frame member 32 and the ink discharge port 36 may be formed in the cover member 33, or vice versa.

As a further modification, the inclined surface 43 does not necessarily have to be formed on the frame member 32. For example, if the lid member 33 becomes the ceiling surface when in the ink filling position, the inclined surface 43 is formed on the lid member 33. In other words, the inclined surface 43 may be formed in a location that becomes the ceiling surface when in the ink filling position.

As described above, according to any of the above-mentioned embodiments, it is possible to provide a liquid ejection head that can easily fill the common liquid chamber with liquid.

The inkjet head 100 is not limited to a shear mode actuator 5 with multiple pressure chambers 4. It may also be a drop-on-demand piezoelectric actuator.

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

The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

REFERENCE SIGNS LIST 10 Inkjet printer 100 to 103 Inkjet head 26 Nozzle 3 Common ink chamber 32 Frame member 33 Lid member 34 Inclined surface 35 Ink supply port 36 Ink discharge port 4 Pressure chamber 5 Actuator 7 Ink 71 Air bubble

Claims (5)

A plurality of pressure chambers arranged in a first direction;
a common liquid chamber which is in communication with each of the pressure chambers and has a ceiling surface which becomes higher from one end side of the arrangement of the pressure chambers to the other end side when the arrangement direction of the pressure chambers is positioned horizontally;
a liquid supply port communicating with the common liquid chamber at a center of the arrangement of the pressure chambers;
a liquid discharge port communicating with the common liquid chamber at an end of the liquid discharge head where the ceiling surface is elevated. The liquid ejection head according to claim 1, characterized in that the ceiling surface is an inclined surface that becomes higher from one end side of the array of the pressure chambers toward the other end side. The liquid ejection head according to claim 1 or 2, characterized in that either the liquid supply port or the liquid discharge port is an opening formed in the ceiling surface. The liquid ejection head according to claim 1 or 2, characterized in that either the liquid supply port or the liquid discharge port is an opening formed in a wall surface other than the ceiling surface. A method for filling a liquid ejection head with liquid, the liquid ejection head comprising: a plurality of pressure chambers; a common liquid chamber communicating with each of the plurality of pressure chambers and having a ceiling surface which becomes higher from one end side of an array of the pressure chambers to the other end side when the liquid ejection head is in a position for filling with liquid; a liquid supply port communicating with the common liquid chamber at a center of the array of the pressure chambers; and a liquid discharge port communicating with the common liquid chamber at an end where the ceiling surface becomes higher, the method comprising the steps of:
A method for filling a liquid ejection head with liquid, comprising: flowing liquid from the liquid supply port toward the liquid discharge port, temporarily stopping the flow of the liquid to wait for air bubbles to rise to the surface of the common liquid chamber, and then flowing the liquid again from the liquid supply port toward the liquid discharge port.

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