Liquid discharge device

Abstract

To provide a liquid discharge device that can maintain appropriate discharging of liquid and prevent liquid from being unnecessarily consumed.SOLUTION: A liquid discharge device according to the present invention is provided with: a liquid discharge head that can discharge liquid; a circulating mechanism that circulates liquid to be supplied to the liquid discharge head; a recovering unit that performs processing for recovering the liquid discharge head; and a control part that when dissolved gas densities of liquid in a circulation path for the liquid by the circulating mechanism reaches a threshold density, drives the recovering unit in response to satisfaction of a predetermined condition.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a liquid ejection device. [Background technology]

[0002] Some liquid ejection devices, such as inkjet printers, are capable of performing a process to remove air bubbles (degassing) from the liquid supplied to the liquid ejection head, thereby making it possible to maintain proper ejection of the liquid (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-59133 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration of Patent Document 1, liquid is consumed by the degassing, and so there is room for improvement in terms of preventing unnecessary consumption of liquid.

[0005] An exemplary object of the present invention is to be able to maintain appropriate discharge of liquid and to be able to prevent unnecessary consumption of liquid. [Means for solving the problem]

[0006] One aspect of the present invention relates to a liquid ejection device, the liquid ejection device comprising: A liquid ejection head capable of ejecting liquid; a circulation mechanism for circulating the liquid supplied to the liquid ejection head; a recovery unit for performing recovery processing on the liquid ejection head; a control unit that drives the recovery unit in response to establishment of a predetermined condition when a dissolved gas concentration of the liquid in a circulation path of the liquid by the circulation mechanism reaches a threshold concentration. It is characterized by: Effect of the Invention

[0007] According to the present invention, it is possible to maintain appropriate discharge of liquid and prevent unnecessary consumption of liquid. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a liquid ejection device. [Diagram 2] FIG. 2 illustrates an example of the configuration of a recovery unit. [Diagram 3] FIG. 2 is a schematic plan view of a nozzle surface of the liquid ejection head. [Figure 4] FIG. 2 is an exploded perspective view of the liquid ejection head. [Diagram 5] 1A to 1C are schematic cross-sectional views showing examples of the structure of a liquid ejection head. [Figure 6] FIG. 2 is a schematic view showing the appearance of a circulation unit. [Figure 7] FIG. 4 is a schematic cross-sectional view showing an example of a circulation path. [Figure 8] FIG. 2 is a block diagram showing an ink circulation path. [Figure 9] FIG. 2 is a schematic diagram showing an example of a pressure adjustment unit. [Figure 10] FIG. 2 is an external perspective view of a circulation pump. [Figure 11] FIG. 2 is a cross-sectional schematic view of a circulation pump. [Figure 12] 5A and 5B are schematic diagrams for explaining the flow of ink inside the liquid ejection head. [Figure 13] FIG. 4 is a schematic diagram showing a circulation path in the discharge unit. [Figure 14] FIG. 2 shows an aperture plate. [Figure 15] FIG. 2 is a diagram showing a discharge element substrate. [Figure 16] FIG. 4 is a schematic cross-sectional view showing the flow of ink in the ejection unit. [Figure 17] FIG. 4 is a schematic cross-sectional view showing an example of a structure in the vicinity of a discharge port. [Figure 18]11A and 11B are schematic cross-sectional views showing a comparative example of a structure in the vicinity of a discharge port. [Figure 19] FIG. 13 is a diagram showing a comparative example of an ejection element substrate. [Figure 20] 11A and 11B are schematic cross-sectional views showing the flow of ink of other colors. [Figure 21] 1 is a graph showing changes in dissolved oxygen concentration. [Figure 22] 10 is a flowchart showing the control procedure for degassing ink. [Figure 23] FIG. 13 is a diagram showing an example of a threshold concentration Kth. [Figure 24] FIG. 13 is a diagram illustrating an example of a threshold time Tth. [Diagram 25] 10 is a flowchart showing the control procedure for degassing ink. [Figure 26] FIG. 13 is a diagram illustrating an example of a threshold number of times Dth. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] In the following embodiment, a thermal type liquid ejection device is exemplified, and an electrothermal conversion element (heater) that ejects liquid by generating bubbles using thermal energy is exemplified as an ejection element for ejecting liquid, but the liquid ejection method is not limited to this example. For example, the liquid ejection head of the liquid ejection device may adopt other known ejection methods, such as a method of ejecting liquid using a piezoelectric element, that is, the ejection energy used for ejecting liquid may be in other forms. In addition, the individual units exemplified below (for example, a pressure adjustment unit such as a pump, etc.) may be modified within the scope of the gist of the invention.

[0011] First Embodiment <Liquid discharge device> Fig. 1(a) is a perspective view of a liquid ejection device 50 according to this embodiment. Fig. 1(b) is a block diagram showing the system configuration of the liquid ejection device 50. In FIG. 1(a), for ease of explanation, an X direction corresponding to the left-right or width direction of device 50, a Y direction corresponding to the front-back or depth direction of device 50, and a Z direction corresponding to the up-down or height direction of device 50 are shown.

[0012] Here, the X, Y, and Z directions are also shown in other structural diagrams described later, and expressions such as up, down, left, and right in the following description are intended to indicate the relative positional relationship between elements. Thus, for example, the upper surface (or the lower surface) may be expressed as one surface, and the lower surface (or the upper surface) may be expressed as the other surface.

[0013] The liquid ejection device 50 is equipped with a liquid ejection head 1, and performs printing on a printing medium P by scanning the liquid ejection head 1 in a predetermined direction and ejecting liquid (typically ink, which may be referred to as "ink" in the following explanation) from each of the nozzles arranged on the liquid ejection head 1. Such a liquid ejection head 1 is called a serial head, but a line head capable of performing printing once across the entire width of the recording medium P may also be used. In the case of a serial head, a flexible wiring board is used for wiring to supply a drive signal for ejecting liquid, control vibration for adjusting the temperature of the head 1, and the like, and a controller for controlling the drive of the head 1 can be electrically connected to the flexible wiring board.

[0014] The term "recording" as used herein refers to forming an image by discharging liquid onto the recording medium P, and the concept of an image typically includes characters, symbols, figures, photographs, and the like. From this perspective, the liquid discharge device 50 may also be expressed as a recording device, or in this embodiment where ink is used as the liquid, as an inkjet printer. Similarly, the liquid discharge head 1 may also be expressed as a recording head, or the like. Paper is typically used as the recording medium P, but other sheet-like media may also be used.

[0015] As shown in FIG. 1A, the liquid ejection device 50 further includes a carriage 60, a guide shaft 38, a platen 57, an ink supply tube 59, a spool 106, and an encoder 107. 1(b), the liquid ejection device 50 further includes a CPU (Central Processing Unit) 100, a ROM (Read Only Memory) 101, and a RAM (Random Access Memory) 102. The liquid ejection device 50 further includes a head driver 1A, an external pump 21, a pump driver 21A, a circulation pump 500, a pump driver 500A, a carriage motor 103, a motor driver 103A, a conveyance motor 104, and a motor driver 104A. The liquid ejection device 50 further includes a recovery unit motor 22, a motor driver 22A, a timer 35, a temperature and humidity sensor 36, and a head temperature sensor 37.

[0016] A spool 106 holds the recording medium P and conveys the recording medium P in the Y direction based on a conveying roller that is rotated by the drive of a conveying motor 104. The carriage 60 detachably mounts the liquid ejection head 1 and is movable along a guide shaft 38 extending in the X direction, and is driven by a carriage motor 103 to reciprocate the liquid ejection head 1 in the X direction for scanning. The scanning is performed at a speed of 40 inches per second with a timing at which the ink dots become 600 dpi (dots per inch).

[0017] The recording medium P is conveyed, while being sandwiched between a feed roller and a pinch roller, to a position on the platen 57 corresponding to the scanning area of ​​the liquid ejection head 1, i.e., to the recording position by the liquid ejection head 1. During non-recording operations (a resting state in which no recording operation is actually being performed), the nozzle surface of the liquid ejection head 1 is usually capped by a cap 61 of the recovery unit 23 shown in Fig. 2. Therefore, during recording operations, the capping by the cap 61 is released prior to the start of the operation, and then the liquid ejection head 1 is scanned by the carriage 60.

[0018] During the scanning of the liquid ejection head 1 by the carriage 60, the liquid ejection head 1 performs an ejection operation to eject liquid from each nozzle at a timing according to a position signal obtained from the encoder 107. By performing one such scan, recording is performed on the recording medium P over a width (band width) corresponding to the nozzle arrangement range. By alternately repeating one such scan and the transportation of the recording medium P, recording on one sheet of the recording medium P is completed. If necessary, recording on the next recording medium P can be performed in a similar procedure.

[0019] In other embodiments, printing of the band width may be performed by multiple scans, may be performed on both the forward and return passes of head 1, or may be performed by two or more forward passes and two or more return passes (so-called multi-pass printing).

[0020] Furthermore, the power of the carriage motor 205 can be transmitted to the carriage 60 via a carriage belt, but a known power transmission mechanism may also be adopted, such as a structure including a lead screw connected to the carriage motor 205 and a slider that can engage with the groove of the lead screw.

[0021] Ink is supplied to the liquid ejection head 1 from an ink tank 2 (see FIG. 8) attached to the device 50 via an ink supply tube 59 connected to a carriage 60. The ink may be supplied additionally by a pressurizing unit or the like, or may be supplied by negative pressure of a suction pump while a cap 61 of the recovery unit 23 is capping the nozzle surface of the liquid ejection head 1.

[0022] The liquid ejection device 50 is a printer capable of color printing, and the liquid ejection head 1 is capable of ejecting ink of multiple colors, but may be capable of ejecting ink of a single color. When the liquid ejection head 1 is capable of ejecting ink of multiple colors, a plurality of heads 1 capable of ejecting ink of each color may be mounted on the carriage 60 together, or may be mounted on the carriage 60 individually.

[0023] 4, the liquid ejection head 1 includes an ejection unit 3 and a circulation unit 54. Although details will be described later, the ejection unit 3 is provided with a plurality of ejection ports (nozzle holes) and ejection elements that generate ejection energy for ejecting liquid from each ejection port. Furthermore, the circulation unit 54 is used to circulate the ink, the details of which will be described later. Ink stored in the ink tank 2 is supplied to the circulation unit 54 by the external pump 21 via an ink supply tube 59. A circulation unit 54 can be provided for each type of liquid (ink color), but multiple circulation units 54 may be provided for the same type of liquid.

[0024] 1(b), the CPU 100 controls the driving of each element of the liquid ejection device 50 based on a program stored in the ROM 101. The ROM 101 can also store multi-value gradation data, multi-pass masks, and the like obtained as intermediate products in processing. The RAM 102 can function as a work area when the CPU 100 executes processing.

[0025] For example, the CPU 100 receives image data from an external host device 400 and controls a head driver 1 A, thereby controlling the driving of the liquid ejection head 1 . The CPU 100 also controls the driving of drivers in the individual actuators included in the liquid ejection device 50. For example, the CPU 100 can control the driving of a motor driver 103A of a carriage motor 103 for moving the carriage 60, and control the driving of a motor driver 104A of a conveyance motor 104 for conveying the recording medium P. Similarly, the CPU 100 further controls the driving of a pump driver 21A for driving the circulation pump 500, the driving of a pump driver 21A of the external pump 21, and the driving of a motor driver 22A of the recovery unit motor 22. The recovery unit motor 22 is mounted on the recovery unit 23, and switches the driving targets by a camshaft to operate a wiper guide 223 and a suction pump 213, which will be described later (see FIG. 2).

[0026] The CPU 100 can function as a system control unit that controls the entire system of the liquid ejection device 50 together with the ROM 101 and the RAM 102, or can simply function as a control unit.

[0027] The timer 35 measures time, the details of which will be described later. The temperature and humidity sensor 36 detects the temperature and humidity in the usage environment of the main body of the liquid ejection device 50. Furthermore, the head temperature sensor 37 detects the temperature of the liquid ejection head 1.

[0028] <Recovery Unit> 2 is a schematic diagram showing a configuration example of the recovery unit 23. The cap 61 is supported by a lifting mechanism (not shown) so that it can be raised and lowered (the position when it is raised is the raised position, and the position when it is lowered is the lowered position). At the raised position, the cap 61 comes into contact with the liquid ejection head 1 to cover and cap the nozzle surface of the liquid ejection head 1.

[0029] When not in printing operation, the cap 61 caps the nozzle surface of the liquid ejection head 1. This makes it possible to prevent the ink in the nozzles of the liquid ejection head 1 from drying or evaporating, and also makes it possible to suck ink from the nozzles by driving the suction pump 213. During a recording operation, the cap 61 is located in a lowered position, which makes it possible to avoid interference with the liquid ejection head 1 that moves together with the carriage 60. When the cap 61 is in the lowered position, the liquid ejection head 1 can perform preliminary ejection (an operation of preliminarily ejecting liquid prior to the execution of recording so that recording can be properly performed) onto the cap 61 when the liquid ejection head 1 moves to a position facing the cap 61.

[0030] 2, two wipers 221 for wiping two chips on the nozzle surface, and a wiper 222 for wiping the entire nozzle surface (the entire area of ​​the nozzle row) may be provided on the upper surface of the recovery unit 23. The wipers 221 and 222 may also be referred to as wiper blades.

[0031] The wipers 221 and 222 can be fixed to a wiper holder 220. The wiper holder 220 can move in the W direction (the direction in which the nozzles are arranged, which is a direction substantially parallel to the Y direction) along a wiper guide 223. When the liquid ejection head 1 is positioned at the standby position, the wiper holder 220 moves in the W direction while the wipers 221 and 222 are in contact with the nozzle surface, thereby performing a wiping operation. When the wiping operation is completed, the carriage 60 is retracted, and then the wiper holder 220 is moved, whereby the wipers 221 and 222 return to their original positions (the positions before the wiping operation, the initial position).

[0032] The wipers 221 and 222 may be made of an elastic material such as rubber, but may also be made of a porous material capable of absorbing ink, or may be made of a vacuum wiper capable of sucking the nozzle surface. The wiping operation is performed while the wipers 221 and 222 move in one direction, but may also be performed while they move in both directions. The wiping direction is the nozzle arrangement direction, but may also be a direction intersecting this (substantially perpendicular). The wiping operation may be performed by moving the wipers 221 and 222 relative to the nozzle face, and may be performed by moving the nozzle face relative to the wipers 221 and 222 while the wipers 221 and 222 are fixed. The wipers 221 and 222, or some other wiping members, may be distributed among a plurality of recovery units 23, and may be configured so that their wiping directions are different from each other.

[0033] The suction pump 213 is provided in the recovery unit 23, and is driven with the cap 61 capping the nozzle face of the liquid ejection head 1 and substantially sealing the inside of the nozzle, to perform a suction operation of sucking ink from inside the nozzle by generating negative pressure inside the nozzle. The suction operation can be performed when filling the liquid ejection head 1 with ink from the ink tank 2 (at the time of initial filling) and / or when sucking and removing foreign matter such as dust, stuck matter, and air bubbles inside the nozzle (at the time of suction recovery).

[0034] A tube pump may be used as the suction pump 213 (hereinafter, may be referred to as the tube pump 213). The tube pump 213 includes a curved holding portion that holds (at least a part of) the tube 58 along it, a roller that can press the held tube 58, and a roller support portion that rotatably supports the roller. The tube pump 213 rotates the roller support portion in a predetermined direction to rotate the roller while pressing the tube 58, thereby generating negative pressure in the cap 61 and performing a suction operation. The ink sucked in is discharged via the tube 58 to a waste ink absorber (not shown). When the liquid ejection head 1 performs preliminary ejection onto the cap 61, the suction operation can also be performed to discharge ink received in the cap 61 by the preliminary ejection. That is, when the ink held in the cap 61 by the preliminary ejection reaches a predetermined amount, the ink held in the cap 61 can be discharged to the waste ink absorber via the tube 58 by driving the suction pump 213.

[0035] The wiping operation by the wipers 221 and 222 may be expressed as a wiping recovery operation, and the suction operation by the suction pump 213 may be expressed as a suction recovery operation. The wiping operation and the suction operation may be collectively expressed as a recovery operation.

[0036] <Basic configuration of liquid ejection head> Fig. 3(a) is a schematic plan view of the nozzle surface of the liquid ejection head 1, and shows nozzle rows 106A and 106B corresponding to each color. Fig. 3(b) is an enlarged schematic view of a portion of Fig. 3(a).

[0037] 3(b), for each of the colors of ink, C (cyan), M (magenta), Y (yellow) and Bk (black), nozzle rows 106A and 106B are arranged relative to the common ink liquid chamber 105. First nozzles are arranged in the nozzle row 106A, and second nozzles having a smaller nozzle diameter than the first nozzles are arranged in the nozzle row 106B. In this example, the first nozzle is a nozzle capable of ejecting 5pl droplets (ink droplets), and the second nozzle is a nozzle capable of ejecting 2pl droplets. In the following description, the first nozzle may be referred to as a 5pl nozzle, and the nozzle row 106A may be referred to as a 5pl nozzle row 106A. Similarly, the second nozzle may be referred to as a 2pl nozzle, and the nozzle row 106B may be referred to as a 2pl nozzle row 106B. In this example, from the left side of the drawing, a 5pl nozzle row 106A and a 2pl nozzle row 106B for C, M, Y and Bk color inks are arranged in that order. The ejection opening diameter of the 5pl nozzle is about 16.4 μm, and the ejection opening diameter of the 2pl nozzle is about 9.2 μm.

[0038] 3(b), in the liquid ejection head 1, for each color of ink, the nozzle row 106A is provided with ejection ports 107A of 5 pl nozzles, and the nozzle row 106B is provided with ejection ports 107B of 2 pl nozzles, which share the common ink liquid chamber 105. The nozzle rows 106A and 106B are further provided with a bubbling chamber 108 and an introduction section 109, and ink is introduced from the common ink liquid chamber 105 to the bubbling chamber 108 by the introduction section 109.

[0039] Fig. 4 is an exploded perspective view of the liquid ejection head 1. Figs. 5(a) and 5(b) are cross-sectional views showing the structure of the liquid ejection head 1. Fig. 5(a) is a cross-sectional view of the entire liquid ejection head 1, and Fig. 5(b) is an enlarged cross-sectional view of the ejection module therein.

[0040] As described above, the liquid ejection head 1 includes the circulation unit 54 and the ejection unit 3 for ejecting the ink supplied from the circulation unit 54 onto the recording medium P. In this embodiment, the liquid ejection head 1 can be positioned by a positioning unit that can be provided on the carriage 60, and can be connected and fixed to the carriage 60 by an electrical connection unit. In this manner, the liquid ejection head 1 ejects ink onto the recording medium P while scanning in the X direction by the movement of the carriage 60, thereby performing recording.

[0041] An ink supply tube 59 is connected to the external pump 21 (see FIG. 1). A liquid connector (not shown) may be provided at the tip of the ink supply tube 59. When the liquid ejection head 1 is mounted on the liquid ejection device 50, the liquid connector may be inserted into and connected to a liquid connector insertion port (not shown) provided in a housing 53 of the liquid ejection head 1. This forms an ink supply path that extends from the ink tank 2 through the external pump 21 to the liquid ejection head 1.

[0042] In this embodiment, four types of ink are used: C, M, Y, and Bk. Therefore, four sets of ink tanks 2, external pumps 21, ink supply tubes 59, and circulation units 54 are provided corresponding to the four types of ink, and four ink supply paths corresponding to each ink are formed independently of each other. In this way, the liquid ejection device 50 of this embodiment is provided with an ink supply system to which ink is supplied from the ink tank 2 outside the liquid ejection head 1. In this embodiment, the liquid ejection device 50 is not provided with an ink recovery system for recovering ink in the liquid ejection head 1 into the ink tank 2.

[0043] 5(a), the circulation unit corresponding to the Bk ink is designated as circulating unit 54B, and similarly, the circulation units corresponding to the C, M and Y inks are designated as circulating units 54C, 54M and 54Y, respectively. These circulation units 54B, 54C, 54M and 54Y have substantially the same configuration, and in the following description, when there is no need to distinguish between them, they will simply be referred to as circulation unit 54.

[0044] As shown in Fig. 4 and Fig. 5(a), the discharge unit 3 includes two discharge modules 300, a first support member 4, a second support member 7, an electric wiring member (electric wiring tape) 5, and an electric contact board 6. As shown in Fig. 5(b), the discharge module 300 includes a silicon substrate 310 having a thickness of about 0.5 to 1.0 mm, and a plurality of discharge elements 15 provided on the lower surface of the silicon substrate 310. As described above, the discharge elements 15 are electrothermal conversion elements (heaters), and power can be supplied to them via electric wiring formed on the silicon substrate 310 using a known semiconductor process.

[0045] An ejection port forming member 320 is disposed on the lower surface of the silicon substrate 310. In the ejection port forming member 320, a plurality of pressure chambers 12 corresponding to the plurality of ejection elements 15, and a plurality of ejection ports 13 for ejecting ink can be formed by photolithography technology. Further, individual supply flow paths 18 and individual recovery flow paths 19 communicating with each pressure chamber 12 are formed in the silicon substrate 310. In this embodiment, a single ejection module 300 is configured to be capable of ejecting two types of ink. For example, of the two ejection modules 300 shown in Fig. 5(a), one ejection module 300 shown on the left ejects Bk ink and C ink, and the other ejection module 300 shown on the right ejects M ink and Y ink. Furthermore, in this example, two rows of ejection ports extending in the Y direction are formed for one color of ink, and a pressure chamber 12, an individual supply flow path 18, and an individual recovery flow path 19 are formed for each of the multiple ejection ports 13 forming each row.

[0046] An ink supply port 311 and an ink recovery port 312 (see FIG. 13 and the like), which will be described later, are formed on the upper surface of the silicon substrate 310. The ink supply port 311 supplies ink from the ink supply flow path 48 to the multiple individual supply flow paths 18. The ink recovery port 312 recovers ink from the multiple individual recovery flow paths 19 to the ink recovery flow path 49. The ink supply port 311 and the ink recovery port 312 referred to here are openings that supply and recover ink, respectively, during forward ink circulation. That is, during forward ink circulation, ink is supplied from the ink supply port 311 to the individual supply flow path 18, and at the same time, ink is recovered from the individual recovery flow path 19 to the ink recovery port 312. On the other hand, during ink circulation in which ink flows in the direction opposite to the forward direction, ink is supplied from the ink recovery port 312 to the individual recovery flow path 19, and at the same time, ink is recovered from the individual supply flow path 18 to the ink supply port 311.

[0047] 5(a), the upper surface of such an ejection module 300 can be fixed by adhesion to the lower surface of the first support member 4. An ink supply flow path 48 and an ink recovery flow path 49 can be formed in the first support member 4, penetrating from the upper surface to the lower surface. The ink supply flow path 48 (its lower opening) communicates with an ink supply port 311 (see FIG. 13, etc.), and similarly, the ink recovery flow path 49 communicates with an ink recovery port 312. The ink supply flow path 48 and the ink recovery flow path 49 are provided independently of each other for each type of ink.

[0048] 4, a second support member 7 having an opening 7a through which the ejection module 300 is inserted can be fixed by adhesion to the upper surface of the first support member 4. The second support member 7 holds an electric wiring member 5 electrically connected to the ejection module 300. The electric wiring member 5 supplies an electric signal for ejecting ink to the ejection module 300. The portion that realizes the electric connection between the ejection module 300 and the electric wiring member 5 can be sealed with a predetermined sealant and protected from corrosion by ink and external impacts.

[0049] 4, an electrical contact board 6 having an external signal input terminal for receiving an electrical signal from the liquid ejection device 50 is thermocompression-bonded to the end 5a of the electrical wiring member 5, so that the electrical wiring member 5 and the electrical contact board 6 can be electrically connected to each other. This electrical connection can be made via an anisotropic conductive film (not shown).

[0050] As shown in FIG. 5A, a joint member 8 may be provided between the first support member 4 and the circulation unit 54. A supply port 88 and a recovery port 89 are formed in the joint member 8 for each type of ink. The supply port 88 connects the ink supply flow path 48 to the flow path of the circulation unit 54, and the recovery port 89 connects the ink recovery flow path 49 to the flow path of the circulation unit 54. In the figure, the supply port 88 and recovery port 89 corresponding to Bk ink are indicated as supply port 88B and recovery port 89B, respectively. Similarly, the supply port 88 and recovery port 89 corresponding to C, M, and Y ink are indicated as supply port 88C and recovery port 89C, supply port 88M and recovery port 89M, and supply port 88Y and recovery port 89Y, respectively.

[0051] Here, the opening of the ink supply flow path 48 on the ink supply port 311 side can be set so as to approximately coincide with the opening of the ink supply port 311, and similarly, the opening of the ink recovery flow path 49 on the ink recovery port 312 side can be set so as to approximately coincide with the opening of the ink recovery port 312. Furthermore, the opening of the ink supply flow path 48 on the supply port 88 side can be set so as to approximately coincide with the opening of the supply port 88, and similarly, the opening of the ink recovery flow path 49 on the recovery port 89 side can be set so as to approximately coincide with the recovery port 89. With this configuration, the flow path resistance of the ink can be reduced.

[0052] In such a liquid ejection head 1, ink supplied to the circulation unit 54 flows from the ink supply port 311 of the ejection module 300 into the individual supply flow path 18 via the supply port 88 of the joint member 8 and the supply flow path 48 of the first support member 4. The ink flows from the individual supply flow path 18 into the pressure chamber 12, and a part of the ink is ejected from the ejection port 13 in the pressure chamber 12 by driving the ejection element 15. The other part of the ink (i.e., ink that is not ejected and remains) flows from the pressure chamber 12 through the individual recovery flow path 19 and from the ink recovery port 312 into the recovery flow path 49 of the first support member 4. Thereafter, the ink that has flowed into the recovery flow path 49 flows into the circulation unit 54 via the recovery port 89 of the joint member 8 and is recovered. In this manner, the ink is circulated.

[0053] <Components of the circulation unit> 6 is a schematic external view of a circulation unit 54 corresponding to one type (one color) of ink. The circulation unit 54 includes a filter 110, a first pressure adjustment unit 120, a second pressure adjustment unit 150, and a circulation pump 500. These will be described in detail later, but as shown in FIGS. 7 and 8, these are connected by respective flow paths, and a circulation path for supplying and recovering ink to and from the ejection module 300 is formed in the liquid ejection head 1.

[0054] <Circulation path inside the liquid ejection head> Fig. 7 is a schematic cross-sectional view of the liquid ejection head 1, showing the circulation path for one type of ink, and Fig. 8 is a block diagram showing an example of the configuration of the circulation path in Fig. 7. 7 and 8, the first pressure adjustment unit 120 includes a first valve chamber 121 and a first pressure control chamber 122, and the second pressure adjustment unit 150 includes a second valve chamber 151 and a second pressure control chamber 152. In this embodiment, the use of these two pressure adjustment units 120 and 150 makes it possible to circulate ink within a predetermined pressure range. The first pressure adjustment unit 120 is configured to have a relatively higher control pressure than the second pressure adjustment unit 150, and ink flows near the pressure chamber 12 (or the ejection element 15) at a flow rate according to the pressure difference between them.

[0055] In addition, the arrow in the figure indicates the direction in which the ink flows. In the following description, the side in the direction in which the ink flows may be expressed as the downstream side, and the opposite side may be expressed as the upstream side.

[0056] The external pump 21 is connected to the ink supply tube 59 (see FIG. 1) as described above, and pumps ink from the ink tank 2 to the liquid ejection head 1 and sends it to the circulation unit 54, as shown in FIG. 8. The filter 110 is provided in the ink flow path upstream of the circulation unit 54. The ink supply path downstream of the filter 110 is connected to a first valve chamber 121 of a first pressure adjustment unit 120.

[0057] 7, the first valve chamber 121 communicates with the first pressure control chamber 122 via a communication port 191A that is opened and closed by a valve 190A. The first pressure control chamber 122 is connected to the supply flow path 130, the bypass flow path 160, and the pump outlet flow path 180 of the circulation pump 500. The supply flow path 130 is connected to the individual supply flow paths 18 via the ink supply port 311 provided in the ejection module 300. In addition, the bypass flow path 160 is connected to the second valve chamber 151 of the second pressure adjustment unit 150.

[0058] 7, the second valve chamber 151 communicates with the second pressure control chamber 152 via a communication port 191B that is opened and closed by a valve 190B. The second pressure control chamber 152 is connected to the recovery flow path 140. The recovery flow path 140 is connected to the individual recovery flow path 19 via the ink recovery port 312 provided in the ejection module 300. In addition, the second pressure control chamber 152 is connected to the circulation pump 500 via a pump inlet flow path 170. Note that element 170a in FIG. 7 indicates the inlet of the pump inlet flow path 170.

[0059] The ink is pressurized by the external pump 21 and supplied to the circulation unit 54 of the liquid ejection head 1 as a positive pressure ink flow, passes through the filter 110 to remove foreign matter, and then flows into the first valve chamber 121 of the first pressure adjustment unit 120. At that time, the ink is depressurized from positive pressure to negative pressure. The depressurized ink is supplied to the first pressure control chamber 122 together with ink sucked by the circulation pump 500 from the pump inlet flow path 170 on the upstream side and pumped to the pump outlet flow path 180 on the downstream side, and flows into the supply flow path 130 and the bypass flow path 160.

[0060] Although details will be described later, in this embodiment, a piezoelectric diaphragm pump using a piezoelectric element attached to a diaphragm as a drive source can be used as the circulation pump 500. The piezoelectric diaphragm pump changes the volume of the pump chamber when a drive voltage is applied to the piezoelectric element, and pumps liquid by alternately operating two check valves due to pressure fluctuations.

[0061] The ink that has flowed into the supply flow path 130 flows from the ink supply port 311 in the ejection module 300 through the individual supply flow path 18 into the pressure chamber 12, and a portion of the ink is ejected from the ejection port 13 by driving the ejection element 15. The other portion of the ink (i.e., the ink that remains without being ejected) flows into the recovery flow path 140 through the individual recovery flow path 19. The ink that has flowed into the recovery flow path 140 flows into the second pressure control chamber 152 of the second pressure adjustment unit 150.

[0062] On the other hand, the ink that has flowed into the bypass flow path 160 flows into the second valve chamber 151, and then flows into the second pressure control chamber 152 via the communication port 191B.

[0063] The ink that has flowed into the second pressure control chamber 152, together with the ink recovered from the recovery passage 140, is sucked into the circulation pump 500 via the pump inlet passage 170 by the drive of the circulation pump 500. The ink that has been sucked into the circulation pump 500 is sent to the pump outlet passage 180 and flows into the first pressure control chamber 122 again.

[0064] Thereafter, in a similar manner, the ink that is supplied from the first pressure control chamber 122 to the ejection module 300 via the supply flow path 130 and then flows into the second pressure control chamber 152, and the ink that flows into the second pressure control chamber 152 via the bypass flow path 160, flows into the circulation pump 500. The ink is then sent from the circulation pump 500 to the first pressure control chamber 122. In this manner, the ink is circulated.

[0065] According to this structure, the circulation pump 500 provided in the liquid ejection head 1 can circulate the ink in a circulation path formed together with the ejection module 300. The circulation of the ink makes it possible to suppress thickening of the ink and accumulation of sedimentation components in the ejection module 300, and improves the fluidity of the ink in the ejection module 300 and the ejection characteristics at the ejection port 13. Furthermore, the ink does not need to be circulated outside the liquid ejection head 1, and the use of a relatively small circulation pump 500 is advantageous in reducing the size of the head 1 and the device 50.

[0066] The ink is circulated by flowing substantially in one direction by the above-mentioned pressure adjustment units 120 and 150, and the ink in the second pressure control chamber 152 flows to the first pressure control chamber 122 via the circulation pump 500. If it takes a long time for the pressure difference between the first pressure control chamber 122 and the second pressure control chamber 152 to reach the standard, the circulation flow rate cannot reach the standard, making it difficult to start recording. When the ink in the second pressure control chamber 152 is taken into the circulation pump 500, ink also flows in from the ejection module 300, but if a negative pressure equal to or greater than a reference level is applied to the nozzle, air bubbles will be drawn into the ejection port 13. Therefore, when the negative pressure in the second pressure control chamber 152 exceeds a reference level, a valve opens in the same way as the first pressure control chamber 122, allowing ink to flow into the second pressure control chamber 152 from the first pressure control chamber 122 via the communication port 191B, rather than from the ejection module 300. When ink flows into the second pressure control chamber 152, the pressure difference is eliminated and the communication port 191B closes.

[0067] If air bubbles enter the circulation flow path from the nozzle during recording, or if air bubbles generated by gas contained in the ink in the circulation flow path reach the nozzle, this can cause the ink to be ejected improperly. For this reason, as shown in FIG. 7, a relatively large-capacity chamber corresponding to the individual supply flow path 18 and the individual recovery flow path 19 is formed as a bubble storage chamber 606 between the ejection module 300 and the circulation unit 54. This makes it possible to prevent air bubbles from flowing toward the nozzle. The ink may be either non-degassed ink or degassed ink.

[0068] <Pressure adjustment unit> 9(a) to 9(c) are schematic diagrams showing a configuration example of the pressure adjustment unit 120. Note that the pressure adjustment unit 150 is configured similarly to the pressure adjustment unit 120, and corresponding reference numerals are indicated in the drawings. For example, in the case of the second pressure adjustment unit 150, the first valve chamber 121 is replaced with the second valve chamber 151, and the first pressure control chamber 122 is replaced with the second pressure control chamber 152.

[0069] The first valve chamber 121 and the first pressure control chamber 122 are formed in a cylindrical housing 125 of the first pressure adjustment unit 120. The first valve chamber 121 and the first pressure control chamber 122 are defined and separated by a partition wall 123, and communicate with each other via a communication port 191 formed in the partition wall 123. A valve 190 is provided in the first valve chamber 121, which switches between communication between the first valve chamber 121 and the first pressure control chamber 122 and blocking of said communication. The valve 190 is held in a position facing the communication port 191 by a valve spring 200. The valve 190 can come into close contact with the partition wall 123 due to the biasing force of the valve spring 200, and blocks the flow of ink at the communication port 191 by abutting against the partition wall 123. In order to ensure that the valve 190 and the partition wall 123 can be in proper contact with each other, the portion of the valve 190 that comes into contact with the partition wall 123 may be made of an elastic material.

[0070] Furthermore, a valve shaft 190a protrudes from the center of the valve 190 and is inserted into the communication port 191. By pressing the valve shaft 190a against the biasing force of a valve spring 200, the valve 190 moves away from the partition wall 123, allowing ink to flow through the communication port 191.

[0071] In the following description, the state in which the flow of ink through communication port 191 is blocked may be referred to as a “closed state,” and the state in which the flow is possible may be referred to as an “open state.” Figure 9(a) shows the closed state, Figure 9(b) shows the open state, and Figure 9(c) shows another explanation of the closed state.

[0072] The opening of the cylindrical housing 125 is closed by the pressure plate 210 and the flexible member 230. That is, the first pressure control chamber 122 is formed by the pressure plate 210, the flexible member 230, the partition wall 123, and the peripheral wall of the housing 125. The pressure plate 210 is made displaceable by the flexible member 230. The constituent materials of the pressure plate 210 and the flexible member 230 are not limited to this example, but the pressure plate 210 is made of a resin molded part and the flexible member 230 is made of a resin film, in which case they can be fixed by thermal welding.

[0073] A pressure adjustment spring 220 is provided between the pressure plate 210 and the partition wall 123. The pressure plate 210 and the flexible member 230 are biased by the biasing force of the pressure adjustment spring 220 so as to expand the internal volume of the first pressure control chamber 122.

[0074] When the pressure in the first pressure control chamber 122 decreases, the pressure plate 210 and the flexible member 230 are displaced in the direction opposite to the biasing force of the pressure adjustment spring 220, i.e., in the direction in which the internal volume of the first pressure control chamber 122 decreases. When the internal volume of the first pressure control chamber 122 decreases to a reference value, the pressure plate 210 comes into contact with the valve shaft 190a of the valve 190. Thereafter, when the internal volume of the first pressure control chamber 122 further decreases, the valve 190 moves together with the valve shaft 190a in the direction opposite to the biasing force of the valve spring 200 and moves away from the partition wall 123, whereby the communication port 191 opens (see FIG. 9(b)).

[0075] In this embodiment, when the communication port 191 is in the open state, the pressure in the first valve chamber 121 is higher than the pressure in the first pressure control chamber 122, and ink flows from the first valve chamber 121 to the first pressure control chamber 122 in response to the communication port 191 being in the open state. Accordingly, the flexible member 230 and the pressure plate 210 are displaced in a direction in which the internal volume of the first pressure control chamber 122 increases. As a result, the pressure plate 210 moves away from the valve shaft 190a of the valve 190, and the communication port 191 abuts against the partition wall 123 due to the biasing force of the valve spring 200, and the communication port 191 is in the closed state (see FIG. 9(a) or 9(c)).

[0076] In this way, in the first pressure adjustment unit 120, when the pressure inside the first pressure control chamber 122 falls below the reference pressure (for example, when a relatively large negative pressure is applied), ink flows in from the first valve chamber 121 via the communication port 191. This prevents the pressure inside the first pressure control chamber 122 from decreasing further. Therefore, the pressure inside the first pressure control chamber 122 is controlled to be within the reference range.

[0077] Here, as described above, the flexible member 230 and the pressure plate 210 are displaced in response to the pressure in the first pressure control chamber 122, and the pressure plate 210 comes into contact with the valve shaft 190a, opening the communication port 191 (as shown in FIG. 9(b)). At this time, the relationship of the forces acting on the pressure plate 210 is as follows: P2×S2+F2+(P1-P2)×S1+F1=0 (Formula 1) P1: Pressure (gauge pressure) of the first valve chamber 121 P2: Pressure (gauge pressure) of the first pressure control chamber 122 F1: Valve spring force 200 F2: Spring force of the pressure adjusting spring 220 S1: Pressure receiving area of ​​valve 190 S2: Pressure receiving area of ​​the pressure plate 210 Furthermore, rearranging the above (Equation 1) for P2 gives P2=-(F1+F2+P1×S1) / (S2-S1) (Formula 2) It becomes. Here, the spring force F1 of the valve spring 200 and the spring force F2 of the pressure adjustment spring 220 are positive (rightward in FIG. 9(b) and the like) in the direction pressing the valve 190 and the pressure plate 210. The pressure P1 of the first valve chamber 121 and the pressure P2 of the first pressure control chamber 122 are set so that P1≧P2 is satisfied.

[0078] The pressure P2 in the first pressure control chamber 122 when the communication port 191 is in the open state is determined by the above (Equation 2), and when the communication port 191 is in the open state, P1≧P2 holds, and ink flows from the first valve chamber 121 into the first pressure control chamber 122. As a result, the pressure P2 in the first pressure control chamber 122 does not decrease further, and the pressure P2 is maintained within the reference range.

[0079] On the other hand, as shown in FIG. 9C, when the pressure plate 210 is not in contact with the valve shaft 190a and the communication port 191 is closed, the relationship of the forces acting on the pressure plate 210 is as follows: P3×S3+F3=0 (Formula 3) F3: Spring force of the pressure adjusting spring 220 when the communication port 191 is in a closed state P3: Pressure (gauge pressure) of the first pressure control chamber 122 when the communication port 191 is in a closed state S3: Pressure receiving area of ​​the pressure plate 210 when the communication port 191 is in a closed state The pressure P3 is expressed as follows by the above formula (3): P3 = -F3 / S3 (Equation 4) This can be expressed as:

[0080] Here, Fig. 9(c) shows a state where the pressure plate 210 and the flexible member 230 have been displaced to the limit of their displacement (the position where the amount of displacement to the right in the figure is maximum). Depending on the amount of displacement of the pressure plate 210 and the flexible member 230 until they reach the state of Fig. 9(c), the pressure P3 of the first pressure control chamber 122, the spring force F3 of the pressure adjustment spring 220, and the pressure receiving area S3 of the pressure plate 210 change. Specifically, when the pressure plate 210 and the flexible member 230 are positioned to the left of the state of Fig. 9(c), the pressure receiving area S3 of the pressure plate 210 becomes smaller, and the spring force F3 of the pressure adjustment spring 220 becomes larger. As a result, the pressure P3 of the first pressure control chamber 122 becomes smaller according to the above (Equation 4). Therefore, according to the above (Equation 2) and (Equation 4), the pressure in the first pressure control chamber 122 gradually increases, and the negative pressure weakens and approaches the positive pressure side, during the period from the state of FIG. 9(b) (open state of communication port 191) to the state of FIG. 9(c) (closed state of communication port 191).

[0081] <Circulation pump> Fig. 10(a) is a perspective view of the exterior of the front side of circulating pump 500. Fig. 10(b) is a perspective view of the exterior of circulating pump 500 from the rear side. Fig. 11 is a schematic cross-sectional view of circulating pump 500 taken along line IX-IX in Fig. 10(a). The exterior of circulating pump 500 can be formed by pump housing 505 and cover 507 fixed to pump housing 505.

[0082] The pump housing 505 may be formed by a housing body 505a and a flow path connecting member 505b fixed to the outer surface thereof by adhesive. A pair of through holes that communicates between the housing body 505a and the flow path connecting member 505b is provided at two different positions. One of the through holes forms a pump supply hole 501, and the other through hole forms a pump discharge hole 502. The pump supply hole 501 is connected to the pump inlet flow path 170 connected to the second pressure control chamber 152. The pump discharge hole 502 is connected to the pump outlet flow path 180 connected to the first pressure control chamber 122. The ink supplied from the pump supply hole 501 is discharged from the pump discharge hole 502 via the pump chamber 503, as shown in FIG. 11.

[0083] A diaphragm 506 is joined to the inner wall of the pump housing 505, and a pump chamber 503 is formed between the diaphragm 506 and a recess formed in the inner wall of the pump housing 505. The pump chamber 503 communicates with a pump supply hole 501 and a pump discharge hole 502. A check valve 504a is provided in the middle of the pump supply hole 501, and a check valve 504b is provided in the middle of the pump discharge hole 502. The check valve 504a is disposed in a space 512a formed in the middle of the pump supply hole 501 such that a part of the check valve 504a can move to the left in the figure. The check valve 504b is disposed in a space 512b formed in the middle of the pump discharge hole 502 such that a part of the check valve 504b can move to the right in the figure.

[0084] When diaphragm 506 is displaced to increase the volume of pump chamber 503, thereby reducing the pressure in pump chamber 503, check valve 504a moves away from the opening of pump supply hole 501 in space 512a (moves to the left in the figure). When valve 504a moves away from the opening of pump supply hole 501, the pump chamber 503 enters an open state allowing the flow of ink through pump supply hole 501. When diaphragm 506 is displaced to reduce the volume of pump chamber 503, thereby reducing the pressure in pump chamber 503, check valve 504a comes into contact with the wall surface surrounding the opening of pump supply hole 501, thereby entering a closed state in which it blocks the flow of ink through pump supply hole 501.

[0085] On the other hand, when the pump chamber 503 is depressurized, the check valve 504b comes into contact with the wall surface surrounding the opening of the pump housing 505 and enters a closed state in which it blocks the flow of ink through the pump discharge hole 502. When the pump chamber 503 is pressurized, the check valve 504b moves away from the opening of the pump housing 505 toward the space 512b (to the right in the figure), thereby allowing the flow of ink through the pump discharge hole 502.

[0086] Furthermore, the check valves 504a and 504b may be made of any material that is deformable in response to the pressure in the pump chamber 503, and may be made of, for example, an elastic material such as EPDM or elastomer, or a film or thin plate such as polypropylene, but is not limited to these.

[0087] As described above, the pump chamber 503 is formed by joining the pump housing 505 and the diaphragm 506. Therefore, the pressure in the pump chamber 503 changes when the diaphragm 506 is deformed. For example, when diaphragm 506 is displaced toward pump housing 505 (to the right in the figure) and the volume of pump chamber 503 decreases, the pressure inside pump chamber 503 increases. This causes check valve 504b arranged opposite pump discharge hole 502 to open, and ink is discharged from pump chamber 503. At this time, check valve 504a arranged opposite pump supply hole 501 abuts against the wall surface surrounding pump supply hole 501, and backflow of ink from pump chamber 503 to pump supply hole 501 is suppressed. When diaphragm 506 is displaced in the direction in which pump chamber 503 expands, the pressure in pump chamber 503 decreases. As a result, check valve 504a arranged opposite pump supply hole 501 opens, and ink is supplied to pump chamber 503. At this time, check valve 504b arranged at pump discharge hole 502 abuts against the wall surface surrounding an opening formed in pump casing 505 to close said opening, thereby suppressing the backflow of ink from pump discharge hole 502 to pump chamber 503.

[0088] In this way, in the circulation pump 500, the diaphragm 506 deforms to change the pressure in the pump chamber 503, thereby suctioning and discharging ink. At this time, if air bubbles get into the pump chamber 503, even if the diaphragm 506 is displaced, the pressure change in the pump chamber 503 becomes small due to the expansion and contraction of the air bubbles, and the amount of liquid delivered decreases. Therefore, the pump chamber 503 is arranged to extend in the vertical direction so that air bubbles that get into the pump chamber 503 tend to gather above the pump chamber 503, and the pump discharge hole 502 is arranged above the center of the pump chamber 503. This makes it possible to properly discharge air bubbles in the pump chamber 503, and stabilize the flow rate.

[0089] <Ink flow inside the liquid ejection head> 12(a) to 12(e) are schematic diagrams illustrating the flow of ink inside the liquid ejection head 1. FIG.

[0090] Fig. 12(a) shows the flow of ink during the execution of a recording operation. The arrows in the figure indicate the flow of ink. When the recording operation is executed, both the external pump 21 and the circulation pump 500 start to operate. Note that the external pump 21 and the circulation pump 500 may be operating regardless of the recording operation, or may be operated separately / independently without being linked to each other.

[0091] During the recording operation, the circulation pump 500 is in an operating state, and the ink flowing out from the first pressure control chamber 122 flows into the supply flow path 130 and the bypass flow path 160. The ink that flows into the supply flow path 130 passes through the ejection module 300, then flows into the recovery flow path 140, and is then supplied to the second pressure control chamber 152.

[0092] On the other hand, the ink that has flowed from the first pressure control chamber 122 into the bypass flow path 160 flows into the second pressure control chamber 152 via the second valve chamber 151. The ink that has flowed into the second pressure control chamber 152 passes through the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180, and then flows into the first pressure control chamber 122 again. Here, the control pressure by the first valve chamber 121 is set higher than the control pressure of the first pressure control chamber 122 according to the above (Equation 2). Therefore, the ink in the first pressure control chamber 122 is supplied to the ejection module 300 again via the supply flow path 130 without flowing into the first valve chamber 121. The ink that has flowed into the ejection module 300 flows into the first pressure control chamber 122 again via the recovery flow path 140, the second pressure control chamber 152, the pump inlet flow path 170, the circulation pump 500, and the pump outlet flow path 180. In this manner, the ink circulation is completed within the liquid ejection head 1 .

[0093] In ink circulation, the flow rate or circulation amount of ink in the ejection module 300 is determined by the pressure difference (difference in control pressure) between the first pressure control chamber 122 and the second pressure control chamber 152. This pressure difference is set so as to obtain a flow rate that can suppress thickening of ink near the ejection port 13 in the ejection module 300.

[0094] Furthermore, the ink is supplied from the ink tank 2 to the first pressure control chamber 122 via the filter 110 and the first valve chamber 121 in an amount equal to the amount consumed by the recording. As the ink in the circulation path is consumed by the recording, the ink in the first pressure control chamber 122 decreases, and the internal volume of the first pressure control chamber 122 decreases accordingly. As a result, the communication port 191A opens, and ink is supplied from the first valve chamber 121 to the first pressure control chamber 122. A pressure loss occurs in the supplied ink when passing from the first valve chamber 121 through the communication port 191A, and the ink in a positive pressure state becomes a negative pressure state as it flows into the first pressure control chamber 122. As the ink flows from the first valve chamber 121 into the first pressure control chamber 122, the internal volume of the first pressure control chamber increases, and the communication port 191A closes. In this way, the communication opening 191A alternates between the open state and the closed state depending on the consumption of ink. Also, when ink is not consumed, the communication opening 191A is maintained in the closed state.

[0095] FIG. 12B shows the flow of ink after the recording operation is completed and the circulation pump 500 is stopped. At the time when the circulation pump 500 is stopped, the pressures in the first pressure control chamber 122 and the second pressure control chamber 152 remain at the control pressure during the recording operation. Therefore, the ink moves as shown in FIG. 12B according to the pressure difference between the first pressure control chamber 122 and the second pressure control chamber 152. That is, the ink flows from the first pressure control chamber 122 to the ejection module 300 via the supply flow path 130, and then continues to flow toward the second pressure control chamber 152 via the recovery flow path 140. The ink also continues to flow from the first pressure control chamber 122 to the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151.

[0096] In this way, the amount of ink that has moved from the first pressure control chamber 122 to the second pressure control chamber 152 is supplied to the first pressure control chamber 122 from the ink tank 2 via the filter 110 and the first valve chamber 121. Therefore, the content volume in the first pressure control chamber 122 is maintained. According to the above (Equation 2), when the content volume of the first pressure control chamber 122 is constant, the spring force F1 of the valve spring 200, the spring force F2 of the pressure adjustment spring 220, the pressure receiving area S1 of the valve 190, and the pressure receiving area S2 of the pressure plate 210 are maintained constant. Since the pressure P2 in the first pressure control chamber 122 is determined according to the change in the pressure (gauge pressure) P1 in the first valve chamber 121, when there is no change in the pressure P1, the pressure P2 is maintained at the same pressure as the control pressure during the recording operation.

[0097] On the other hand, the pressure of the second pressure control chamber 152 changes over time due to the change in the content volume caused by the inflow of ink from the first pressure control chamber 122. That is, from the state of FIG. 12(b) until the state where the communication port 191 is closed and the second valve chamber 151 and the second pressure control chamber 152 are not in communication with each other (the state of FIG. 12(c)), the pressure of the second pressure control chamber 152 changes according to the above (Equation 2). After that, the pressure plate 210 and the valve shaft 190a are not in contact with each other and the communication port 191 is closed. Then, as shown in FIG. 12(d), ink flows from the recovery passage 140 into the second pressure control chamber 152. This displaces the pressure plate 210 and the flexible member 230, and the pressure of the second pressure control chamber 152 changes and rises according to the above (Equation 4) until the internal volume of the second pressure control chamber 152 becomes maximum.

[0098] 12(c), no ink flow occurs from the first pressure control chamber 122 toward the second pressure control chamber 152 via the bypass flow path 160 and the second valve chamber 151. Therefore, the only flow that can occur is toward the second pressure control chamber 152 via the recovery flow path 140 after the ink in the first pressure control chamber 122 is supplied to the ejection module 300 via the supply flow path 130. As described above, the movement of ink from the first pressure control chamber 122 to the second pressure control chamber 152 occurs according to the pressure difference between the first pressure control chamber 122 and the second pressure control chamber 152. Therefore, when the pressure in the second pressure control chamber 152 becomes equal to the pressure in the first pressure control chamber 122, the movement of ink stops.

[0099] When the pressure in the second pressure control chamber 152 becomes equal to the pressure in the first pressure control chamber 122, the second pressure control chamber 152 expands to the state shown in Fig. 12(d). When the second pressure control chamber 152 expands, a storage portion capable of storing ink is formed in the second pressure control chamber 152. The time from when the circulation pump 500 stops until the state of Fig. 12(d) is reached is approximately 1 to 2 minutes, although this may vary depending on the shape and size of the flow path and the properties of the ink. 12(d), in which a storage portion is formed in the second pressure control chamber 152 and ink can be stored, the circulation pump 500 supplies the ink in the storage portion to the first pressure control chamber 122. As a result, the amount of ink in the first pressure control chamber 122 increases as shown in Fig. 12(e), and the flexible member 230 and the pressure plate 210 are displaced in the expansion direction. Then, as the circulation pump 500 continues to be driven, the state in the circulation path changes as shown in Fig. 12(a).

[0100] 12(a) has been illustrated as an example of one mode during execution of a recording operation, but as described above, ink may be circulated without accompanying a recording operation. Even in this case, ink flows as shown in FIGS. 12(a) to 12(e) in response to driving and stopping of the circulation pump 500.

[0101] In the present embodiment, the communication port 191B in the second pressure adjustment unit 150 is in an open state when the ink is circulated by driving the circulation pump 500, and is in a closed state when the ink circulation is stopped, but this is not limiting. For example, the control pressure may be set so that the communication port 191B in the second pressure adjustment unit 150 is in a closed state even when the ink is circulated by driving the circulation pump 500.

[0102] The bypass flow path 160 connecting the pressure adjustment units 120 and 150 can be provided so that, for example, when the negative pressure generated in the circulation path becomes stronger than normal / standard, the ejection module 300 is not substantially affected by this. For example, when the ink characteristics (viscosity, etc.) change due to an environmental change such as temperature, the pressure loss in the circulation path also changes, and when the viscosity of the ink decreases, for example, the pressure loss in the circulation path decreases, so that the negative pressure in the circulation path may become stronger than normal. As a result, outside air may be drawn into the circulation path from the ejection port 13, destroying the meniscus of the ejection port 13, and ejection may not be performed properly. For this reason, in this embodiment, the bypass flow path 160 is provided in the circulation path.

[0103] By using such a bypass flow path 160, when the negative pressure becomes stronger than normal, ink also flows through the bypass flow path 160, making it possible to maintain the pressure of the ejection module 300. For example, the communication port 191 in the second pressure adjustment unit 150 can be configured to have a control pressure that allows the communication port 191 to be maintained in a closed state even while the circulation pump 500 is in operation. Also, the control pressure of the second pressure adjustment unit may be set so that the communication port 191 is in an open state when the negative pressure becomes stronger.

[0104] In addition, since a force that draws ink into the pressure chamber is generated due to the ejection operation by the ejection element 15, pressure fluctuations in the circulation path may also occur during the ejection operation. Therefore, for example, even if the communication port 191 in the second pressure adjustment unit 150 is configured to be in a closed state while the circulation pump 500 is driven, the communication port 191 may be in an open state during the ejection operation. For example, when a recording with a relatively high duty ratio is continued, the negative pressure in the pressure chamber may become strong. Accordingly, ink moves from the recovery flow path 140 side to the pressure chamber (ejection port 13), that is, a backflow of ink occurs (note that this backflow may occur due to the provision of the bypass flow path 160). As a result, the ink in the second pressure control chamber 152 decreases and the second pressure control chamber 152 shrinks, and as a result, the communication port 191 in the second pressure adjustment unit 150 may be in an open state. In this case, the pressure chamber is filled with ink from the supply flow path 130 and ink from the recovery flow path 140 and ejected.

[0105] In the above description, the communication port 191 in the second pressure adjustment unit 150 is opened in response to the backflow of ink, but the backflow of ink may also occur when the communication port 191 in the second pressure adjustment unit 150 is in the open state. Also, the backflow of ink may occur even in a configuration in which the second pressure adjustment unit 150 is not provided, by providing the bypass flow path 160.

[0106] <Configuration of the discharge unit> Fig. 13(a) is an exploded perspective view of the discharge unit 3 seen from the first support member 4 side to explain the circulation path for one type of ink, and Fig. 13(b) is an exploded perspective view of the discharge unit 3 seen from the discharge module 300 side. Note that for the first support member 4 in Fig. 13(a), a cross-sectional structure is shown taken along line XI-XI in Fig. 5. Arrows shown together with IN / OUT in the figure indicate the direction of ink flow (inflow / outflow), and the same applies to other types (other colors). Here, the second support member 7 and the electrical wiring member 5 are omitted to make the figure easier to see.

[0107] The ejection module 300 includes an ejection element substrate 340 and an aperture plate 330. Fig. 14 is a schematic plan view of the aperture plate 330, and Fig. 15 is a schematic plan view of the ejection element substrate 340. The ejection module 300 is formed by overlapping and joining an ejection element substrate 340 and an aperture plate 330 so as to communicate the flow paths of each ink, and is supported by a first support member 4, thereby forming an ejection unit 3. Ink is supplied to the ejection unit 3 from a circulation unit 54 via a joint member 8 (see FIG. 5(a)).

[0108] The ejection element substrate 340 includes an ejection port forming member 320, as shown in Figures 13(a), 13(b) and 15. The ejection port forming member 320 has a plurality of ejection port rows formed by arranging a plurality of ejection ports 13, and allows a portion of ink supplied via an ink flow path of the ejection module 300 to be ejected from the ejection port 13. The remaining portion of ink that is not ejected is recovered via the ink flow path of the ejection module 300, as described above. The aperture plate 330 has a plurality of ink supply ports 311 and a plurality of ink recovery ports 312, as shown in Figures 13(a), 13(b) and 14.

[0109] 15, and further shown in FIGS. 16(a) to 16(c), a plurality of supply connection flow paths 323 and a plurality of recovery connection flow paths 324 are arranged on the ejection element substrate 340. The plurality of supply connection flow paths 323 communicate with the individual supply flow paths 18, and the plurality of recovery connection flow paths 324 communicate with the individual recovery flow paths 19. The ink flow paths in the ejection unit 3 are formed by communication between an ink supply flow path 48 and an ink recovery flow path 49 (see FIG. 5(a)) provided in the first support member 4, and flow paths provided in the ejection module 300. In the first support member 4, a plurality of support member supply ports 211 are arranged as cross-sectional openings of the ink supply flow passage 48, and a plurality of support member recovery ports 212 are arranged as cross-sectional openings of the ink recovery flow passage 49.

[0110] The ink supplied to the discharge unit 3 is supplied from the circulation unit 54 toward the discharge module 300 to the ink supply flow path 48 of the first support member 4 (see FIGS. 4, 5(a) and 8). The ink is supplied to the individual supply flow paths 18 of the discharge element substrate 340 via the ink supply port 311 of the opening plate 330, and flows into the supply connection flow path 323. The path up to this point corresponds to the supply side flow path. The ink then flows through the pressure chamber 12 (see FIG. 5(b)) of the ejection port forming member 320 to the recovery connection flow path 324 of the recovery side flow path. The flow of ink in the pressure chamber 12 will be described in detail later. The ink that has flowed into the recovery connection flow path 324 flows into the individual recovery flow path 19, and then flows into the ink recovery flow path 49 of the first support member 4 through the ink recovery port 312 of the opening plate 330, and is recovered into the circulation unit 54 through the support member recovery port 212.

[0111] Note that the areas of the opening plate 330 where the ink supply port 311 and the ink recovery port 312 are not formed correspond to the portions of the first support member 4 that separate the support member supply port 211 and the support member recovery port 212. No openings are provided in the first support member 4 to correspond to these areas, and these areas can be used for bonding when bonding the ejection module 300 and the first support member 4.

[0112] 14, the aperture plate 330 is provided with a plurality of rows of apertures arranged in the Y direction, with each row consisting of a plurality of apertures arranged in the X direction. The rows of apertures are arranged in a staggered pattern such that the supply apertures (IN) and the recovery apertures (OUT) are shifted in the X direction by, for example, half the arrangement pitch.

[0113] 15, on the ejection element substrate 340, individual supply flow paths 18 communicating with a plurality of supply connection flow paths 323 arranged in the Y direction and individual recovery flow paths 19 communicating with a plurality of recovery connection flow paths 324 arranged in the Y direction are alternately arranged in the X direction. The individual supply flow paths 18 and individual recovery flow paths 19 are divided for each type of ink, and the number of individual supply flow paths 18 and individual recovery flow paths 19 arranged is determined according to the number of ejection port rows for each color. Similarly, the supply connection flow paths 323 and recovery connection flow paths 324 are arranged in the same number as the ejection ports 13. Note that the numbers do not necessarily correspond one-to-one, and one supply connection flow path 323 and one recovery connection flow path 324 may correspond to two or more ejection ports 13.

[0114] The aperture plate 330 and the ejection element substrate 340 are overlapped and joined together so that the ink flow paths are connected to each other to form an ejection module 300, which is supported by a first support member 4 to form the ink flow paths of the supply flow path and the recovery flow path described above.

[0115] 16(a) to 16(c) are schematic cross-sectional views showing the ink flow in different parts of the ejection unit 3. FIG.

[0116] Fig. 16(a) shows a cross-sectional view of a portion where the ink supply flow path 48 communicates with the ink supply port 311. In the ink supply flow path, as shown in Fig. 16(a), ink is supplied from a portion where the ink supply flow path 48 of the first support member 4 and the ink supply port 311 of the opening plate 330 overlap and communicate with each other.

[0117] Fig. 16(b) shows a cross-sectional view of a portion where the ink recovery channel 49 communicates with the ink recovery port 312. In the ink recovery channel, as shown in Fig. 16(b), ink is recovered from a portion where the ink recovery channel 49 of the first support member 4 and the ink recovery port 312 of the opening plate 330 overlap and communicate with each other.

[0118] Figure 16(c) shows a cross-sectional view of a portion where the ink supply port 311 and the ink recovery port 312 do not communicate with the flow paths of the first support member 4. As shown in Figure 16(c), the opening plate 330 also has an area where no openings are provided. In such an area, ink is not supplied or recovered; that is, ink is supplied in the area where the ink supply port 311 is provided (see Figure 16(a)), and ink is recovered in the area where the ink recovery port 312 is provided (see Figure 16(b)).

[0119] In the present embodiment, the configuration in which the aperture plate 330 is used has been exemplified, but the configuration may be such that the aperture plate 330 is not used. For example, a configuration in which the flow paths corresponding to the ink supply flow path 48 and the ink recovery flow path 49 are formed in the first support member 4 and the ejection element substrate 340 is joined to such first support member 4 may be employed.

[0120] 17(a) and 17(b) are schematic cross-sectional views of the vicinity of the ejection port 13 in the ejection module 300. The thick arrows shown in the individual supply flow paths 18 and the individual recovery flow paths 19 in the drawings indicate the directions of ink oscillation in a liquid ejection device 50 equipped with a liquid ejection head 1 that is a serial head.

[0121] Ink supplied to the pressure chamber 12 via the individual supply flow path 18 and the supply connection flow path 323 is ejected from the ejection port 13 by driving the ejection element 15. When the ejection element 15 is not driven, the ink is recovered from the pressure chamber 12 to the individual recovery flow path 19 via the recovery connection flow path 324, which is a recovery flow path. When the circulating ink is ejected in this manner, the ejection may cause the ink in the ink flow path to oscillate due to the scanning of the liquid ejection head 1. This may cause the amount of ink ejected to vary and the direction of ink ejection to vary.

[0122] 18 shows a schematic cross-sectional view of a comparative example in which the individual supply flow paths 18 and the individual recovery flow paths 19 are widened in the X direction. When the individual supply flow paths 18 and the individual recovery flow paths 19 have a wide cross-sectional shape in the X direction, which is the scanning direction of the liquid ejection head 1, as shown in FIG. 18, the ink in the individual supply flow paths 18 and the individual recovery flow paths 19 may sway relatively greatly due to inertia in the scanning direction. This may affect the ejection of ink from the ejection ports 13. Furthermore, such a configuration may prevent nozzles from being arranged at a high pitch, which may cause a decrease in printing efficiency.

[0123] In this embodiment, as shown in Figures 17(a) to 17(b), the individual supply flow paths 18 and the individual recovery flow paths 19 are formed to extend from the X direction, which is the scanning direction, to the Y direction and Z direction intersecting the X direction. With this configuration, it is possible to suppress the oscillation of ink in the individual supply flow paths 18 and the individual recovery flow paths 19 during scanning of the liquid ejection head 1. This makes it possible to suppress the influence of ink ejection caused by the oscillation of ink. Furthermore, by having the individual supply flow paths 18 and the individual recovery flow paths 19 extend in the Z direction, their cross-sectional areas can be increased, making it possible to reduce pressure loss.

[0124] Furthermore, in this embodiment, the individual supply flow paths 18 and the individual recovery flow paths 19 can be disposed at positions overlapping each other in the X direction so that the effect of the reduced ink oscillation is equal among a plurality of types of ink (including ink of other colors). This allows all types of ink to be ejected in the same manner. The supply connection flow path 323 and the recovery connection flow path 324 are provided corresponding to the ejection port 13, and are positioned side by side in the X direction on either side of the ejection port 13. If the individual supply flow paths 18 and the individual recovery flow paths 19 do not overlap in the X direction, the above-mentioned positional relationship between the supply connection flow path 323 and the recovery connection flow path 324 will not be satisfied. This may affect the flow of ink in the X direction in the pressure chamber 12, the ejection of the ink, etc. The additional oscillation of the ink may further affect the ejection mode of ink for each ejection port 13. Therefore, by arranging the individual supply flow paths 18 and the individual recovery flow paths 19 at positions where they overlap in the X direction, the ink oscillates substantially similarly in the individual supply flow paths 18 and the individual recovery flow paths 19 during scanning for any of the ejection ports 13 arranged in the Y direction. This suppresses variations in the pressure difference between the individual supply flow paths 18 side and the individual recovery flow paths 19 side that may occur within the pressure chambers 12, making it possible to stabilize the ejection of ink.

[0125] Furthermore, by arranging the individual supply flow paths 18 and the individual recovery flow paths 19 closely to each other in the X direction, the above-mentioned influence due to the fluctuation of the ink can be further suppressed, and the distance therebetween may be set to, for example, 75 μm to 100 μm.

[0126] Among such ink circulation type liquid ejection heads 1, there are some in which the flow path for supplying ink to the liquid ejection head 1 and the flow path for recovering ink are configured as the same flow path, but in this embodiment, the individual supply flow paths 18 and the individual recovery flow paths 19 are formed independently. The supply connection flow path 323 and the pressure chamber 12 communicate with each other, and the pressure chamber 12 communicates with the recovery connection flow path 324. The pressure chamber 12 connecting the supply connection flow path 323 and the recovery connection flow path 324 has an ejection port 13, and ink is ejected from the ejection port 13. Therefore, in the pressure chamber 12, a flow of ink is generated from the supply connection flow path 323 side to the recovery connection flow path 324 side, and the ink in the pressure chamber 12 is circulated. Generally, the ink in the pressure chamber 12 may be affected by evaporation at the ejection port 13, but by appropriately circulating the ink in the pressure chamber 12, such an effect is suppressed, and the quality of the ink in the pressure chamber 12 can be maintained.

[0127] In addition, since the two flow paths, the individual supply flow path 18 and the individual recovery flow path 19, are connected to the pressure chamber 12, it is possible to supply ink from both flow paths when ejecting the ink at a relatively large flow rate. In other words, this configuration not only makes it possible to realize ink circulation, but also makes it possible to eject ink at a relatively large flow rate.

[0128] 19 is a schematic plan view of an ejection element substrate 340 as a comparative example. Note that the supply connection flow path 323 and the recovery connection flow path 324 are omitted in the drawing. In the individual recovery flow paths 19, ink that has received thermal energy from the ejection elements 15 in the pressure chambers 12 flows, and thus the ink flows therethrough at a temperature higher than that in the individual supply flow paths 18. At this time, in the example of Fig. 19 which is a comparative example, as shown in the α portion indicated by the dashed line, of the individual supply flow paths 18 and the individual recovery flow paths 19, substantially only the individual recovery flow paths 19 exist in a portion of the ejection element substrate 340 in the X direction. In such a configuration, the temperature becomes locally high in this portion, causing temperature unevenness in the ejection module 300 and affecting the ejection of ink. In the individual supply flow paths 18, ink flows that is lower in temperature than the ink in the individual recovery flow paths 19. Therefore, when the individual supply flow paths 18 and the individual recovery flow paths 19 are adjacent to each other, it is possible to suppress a temperature rise in the vicinity thereof due to heat exchange between the individual supply flow paths 18 and the individual recovery flow paths 19. Therefore, it is preferable that the individual supply flow paths 18 and the individual recovery flow paths 19 have approximately the same length, are positioned so as to overlap each other in the X direction, and are adjacent to each other.

[0129] 20(a) and 20(b) show flow paths for three colors of ink, C, M, and Y, in the liquid ejection head 1. In the liquid ejection head 1, a circulation flow path is provided for each type of ink, as shown in FIG. 20(a). The pressure chambers 12 are provided along the X direction, which is the scanning direction of the liquid ejection head 1. Furthermore, as shown in FIG. 20(b), the individual supply flow paths 18 and the individual recovery flow paths 19 are provided along the ejection port row in which the ejection ports 13 are arranged, and extend in the Y direction so that the individual supply flow paths 18 and the individual recovery flow paths 19 sandwich the ejection port row therebetween.

[0130] Incidentally, air bubbles may occur in the ink due to the circulation described above, and the occurrence of such air bubbles may hinder proper ejection of the ink.

[0131] 21(a) is a graph showing how the dissolved oxygen concentration increases over time in ink that has been degassed (air bubbles removed) by the suction operation of the suction pump 213. The horizontal axis in the figure shows the time axis, and the vertical axis shows the dissolved oxygen concentration. In the figure, the solid line shows the dissolved oxygen concentration when ink is circulated, and the dashed line shows the dissolved oxygen concentration when the ink is left as it is (when ink is not circulated). FIG. 21(b) is an enlarged view of the initial period (10 minutes after the start) in FIG. 21(a). The dissolved oxygen concentration here corresponds to an oxygen concentration that may increase over time. Although the graph shows the dissolved oxygen concentration, the same applies to gases other than oxygen, and in the following explanation, it may be simply referred to as the dissolved gas concentration.

[0132] As shown in Fig. 21(a), the dissolved oxygen concentration increases over time, but the increase is greater when ink is circulated than when ink is left uncirculated. On the other hand, as shown in Fig. 21(b), in the short period of time of about 1 to 2 minutes, there is no substantial difference in the amount of increase in the dissolved oxygen concentration in either case.

[0133] 22 is a flowchart showing an example of a control method for degassing ink. This flowchart is executed mainly by the CPU 100, and can be started after the liquid ejection apparatus 50 is started (for example, after the power button is turned on). In step S801 (hereinafter simply referred to as "S801"; the same applies to other steps described later), the environmental temperature T E Obtain the environmental temperature T E can be obtained by the temperature and humidity sensor 36 (see FIG. 1(a)).

[0134] In S802, the elapsed time T since the ink tank 2 was installed is obtained. The elapsed time T can be obtained by the timer 35.

[0135] In S803, the dissolved gas concentration K of the ink in the ink flow path of the liquid ejection head 1 is calculated based on the elapsed time T. This calculation is performed based on the graph in Fig. 21, but may also be performed based on a predetermined reference table showing typical values, theoretical values, measured values, etc., or may be performed using an arithmetic expression based on a predetermined model. Therefore, this calculation does not necessarily require arithmetic processing, and may simply be expressed as being specific.

[0136] In S804, it is determined whether or not the dissolved gas concentration K has reached the threshold concentration Kth (whether or not K≧Kth). If the dissolved gas concentration K has reached the threshold concentration Kth, the process proceeds to S805, and if not, the process returns to S803. The threshold concentration Kth may be preset to the saturated dissolved gas concentration at 40°C, which is a typical value for the target temperature. The threshold concentration Kth may be determined by the ink properties determined by the environmental temperature, air pressure, the components contained in the ink, the drive frequency, the time and speed of ink circulation, and other factors. For example, the saturated dissolved oxygen amount dissolved in distilled water at 1 atm and 25°C is 8.11 mg / l. In a normal storage environment (1 atm and 25°C), the dissolved gas may reach a saturated state after the passage of time, for example, about three days. FIG. 23 illustrates the saturated dissolved gas concentration at several temperatures for distilled water as the threshold concentration Kth.

[0137] In S805, the time when the dissolved gas concentration K reaches the threshold concentration Kth (the time when K≧Kth) is acquired as time T0. The time T0 can be acquired by the timer 35.

[0138] In S806, it is determined whether the elapsed time (T-T0) since the dissolved gas concentration K reached the threshold concentration Kth has reached the threshold time Tth (whether T≧Tth). If the elapsed time (T-T0) has reached the threshold time Tth, the process proceeds to S807, and if not, the process returns to S805. The threshold time Tth may be preset to a typical value, a theoretical value, an actual measurement value, or the like, of the time at which air bubbles start to form as neglected bubbles due to being left alone. The threshold time Tth may be determined by the environmental temperature, the target temperature (temperature control temperature), the temperature control time, the time and speed of ink circulation, and other factors. In a normal left-alone environment (1 atm and 25°C), neglected bubbles may form after the passage of time of, for example, about one month. FIG. 24 illustrates typical values ​​of the threshold time Tth at several temperatures.

[0139] In S807, the suction pump 213 performs a suction operation.

[0140] Here, the left bubbles do not occur when the dissolved gas concentration K reaches the threshold concentration Kth, which is the saturated dissolved gas concentration, but rather occur gradually over time. Therefore, in this embodiment, in order to prevent unnecessary consumption of ink by the suction operation, the suction operation is performed when the elapsed time (T-T0) after the dissolved gas concentration K reaches the threshold concentration Kth reaches the threshold time Tth at which the left bubbles start to occur. Note that the threshold concentration Kth and the threshold voltage Tth may differ depending on the ink properties and the material of the print head.

[0141] When the suction pump 213 performs the suction operation, the ink bubbles remaining in the ejection module 300 (mainly the pressure chamber 12) are sucked and removed, which resets the elapsed time T. Since the dissolved gas concentration K of the ink newly flowing into the ejection module 300 (mainly the pressure chamber 12) due to the suction operation has decreased, the dissolved gas concentration K is also recalculated in S803.

[0142] According to this embodiment, the suction operation is performed when the time elapsed since the time when the dissolved gas concentration K of the ink reaches a reference value is reached, which makes it possible to recover the ink ejection state and prevent unnecessary consumption of ink due to the suction operation.

[0143] Second Embodiment The second embodiment differs from the first embodiment in that the suction operation is performed when the number of ink ejections reaches a reference value after the ink-dissolved gas concentration K reaches a reference value. In this embodiment, the suction operation is performed based on the number of ink ejections, since the ink is bubbled by receiving thermal energy from the ejection element 15 when the ink is ejected.

[0144] 25 is a flowchart showing an example of a control method for degassing ink in this embodiment. S1101 to S1102 are the same as S801 to S802, and therefore will not be repeated.

[0145] In S1103, the number of ejections D when the ink tank 2 is attached is obtained. The number of ejections D is measured based on the number of pulses of the drive signal for driving the ejection elements 15, and can be measured by the CPU 100, for example.

[0146] S1104 to S1105 are the same as S803 to S804, and therefore will be omitted.

[0147] In S1106, the number of discharges D0 until the dissolved gas concentration K reaches the threshold concentration Kth is acquired. In S1107, the temperature control temperature T N Obtain as.

[0148] In S1108, it is determined whether the number of discharges (D-D0) after the dissolved gas concentration K reaches the threshold concentration Kth reaches the threshold number of times Dth. If the number of discharges (D-D0) reaches the threshold number of times Dth, proceed to S1109, and if not, return to S1106. The threshold number of times Dth may be preset to a typical value, a theoretical value, an actual measurement value, or the like of the number of times of ejection at which air bubbles generated by ejection start to form as printing bubbles. The threshold number of times Dth may be determined based on the environmental temperature, the target temperature, the temperature adjustment time, the time and speed of ink circulation, and other factors. For example, when ink is ejected in an environment with a temperature of 25°C and a humidity of 10%, printing bubbles may occur when approximately 300 ml of ink is ejected. The threshold number of times Dth may also differ depending on the ink properties and the material of the recording head. FIG. 26 illustrates typical values ​​of the threshold time Dth at several temperatures.

[0149] S1109 is the same as S807 and will therefore be omitted.

[0150] Whether or not the number of ejections (D-D0) has reached the threshold number of ejections Dth may be determined for any of the nozzles in S1108. When the suction pump 213 performs a suction operation, the ink bubbles remaining in the ejection module 300 are sucked and removed, so that the number of ejections D is reset, and accordingly the number of ejections (D-D0) is reset, as in the first embodiment.

[0151] According to this embodiment, the suction operation is performed when the number of ink ejections reaches a reference value after the ink-dissolved gas concentration K reaches a reference value. This embodiment also makes it possible to recover the ink ejection state and prevent unnecessary consumption of ink due to the suction operation.

[0152] <Other> In the embodiments, each element is named based on its main function, but the functions described in the embodiments may be sub-functions and are not strictly limited to those expressions. Furthermore, those expressions can be replaced with similar expressions. In the same spirit, the expression "unit" can be replaced with "means," "tool," "component," "member," "structure," "assembly," etc. Alternatively, those words may be omitted or added.

[0153] Summary of the embodiment [1] A liquid ejection head capable of ejecting liquid; a circulation mechanism for circulating the liquid supplied to the liquid ejection head; a recovery unit for performing recovery processing on the liquid ejection head; a control unit that drives the recovery unit in response to establishment of a predetermined condition when a dissolved gas concentration of the liquid in a circulation path of the liquid by the circulation mechanism reaches a threshold concentration. A liquid ejection device comprising: [2] The control unit drives the recovery unit when an elapsed time since the dissolved gas concentration reached the threshold concentration satisfies a criterion. The liquid ejection device according to [1], [3] The control unit includes a measuring means for measuring the elapsed time, and a resetting means for resetting the measuring means when the recovery unit is driven. The liquid ejection device according to [2]. [4] The control unit includes a setting unit that sets the reference based on an environmental temperature. The liquid ejection device according to [2] or [3], [5] The control unit includes a setting unit that sets the reference based on a speed of circulation of the liquid by the circulation mechanism. The liquid ejection device according to any one of [2] to [4], [6] The control unit drives the recovery unit when the number of times the liquid is discharged by the liquid discharge head after the dissolved gas concentration reaches the threshold concentration meets a standard. The liquid ejection device according to [1], [7] The control unit includes a measuring unit that measures the number of ejections, and a reset unit that resets the measuring unit when the recovery unit is driven. The liquid ejection device according to [6]. [8] The control unit includes a setting unit that sets the reference based on an environmental temperature. The liquid ejection device according to [6] or [7], [9] The control unit includes a setting unit that sets the reference based on a speed of circulation of the liquid by the circulation mechanism. The liquid ejection device according to any one of the items [6] to [8],

[10] The determination of the dissolved gas concentration by the control unit includes calculation using a calculation formula based on a predetermined lookup table or a predetermined model. The liquid ejection device according to any one of [1] to [9],

[11] The recovery unit performs a suction operation to suck liquid from nozzles that eject liquid in the liquid ejection head. The liquid ejection device according to any one of [1] to

[10] ,

[0154] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0155] 50: liquid ejection device, 1: liquid ejection head, 500: circulation pump, 23: recovery unit, 100: CPU.

Claims

1. A liquid ejection head capable of ejecting liquid; a circulation mechanism for circulating the liquid supplied to the liquid ejection head; a recovery unit for performing recovery processing on the liquid ejection head; a control unit that drives the recovery unit in response to establishment of a predetermined condition when a dissolved gas concentration of the liquid in a circulation path of the liquid by the circulation mechanism reaches a threshold concentration. A liquid ejection device comprising:

2. The control unit drives the recovery unit when an elapsed time since the dissolved gas concentration reached the threshold concentration satisfies a criterion.

2. The liquid ejection device according to claim 1.

3. The control unit includes a measuring unit that measures the elapsed time, and a reset unit that resets the measuring unit when the recovery unit is driven.

3. The liquid ejection device according to claim 2.

4. The control unit includes a setting unit that sets the reference based on an environmental temperature.

3. The liquid ejection device according to claim 2.

5. The control unit includes a setting unit that sets the reference based on a speed of circulation of the liquid by the circulation mechanism.

3. The liquid ejection device according to claim 2.

6. The control unit drives the recovery unit when the number of times the liquid is discharged by the liquid discharge head after the dissolved gas concentration reaches the threshold concentration meets a standard.

2. The liquid ejection device according to claim 1.

7. The control unit includes a measuring unit that measures the number of ejections, and a reset unit that resets the measuring unit when the recovery unit is driven.

7. The liquid ejection device according to claim 6.

8. The control unit includes a setting unit that sets the reference based on an environmental temperature.

7. The liquid ejection device according to claim 6.

9. The control unit includes a setting unit that sets the reference based on a speed of circulation of the liquid by the circulation mechanism.

7. The liquid ejection device according to claim 6.

10. The determination of the dissolved gas concentration by the control unit includes calculation using a calculation formula based on a predetermined lookup table or a predetermined model.

2. The liquid ejection device according to claim 1.

11. The recovery unit performs a suction operation to suck liquid from nozzles that eject liquid in the liquid ejection head. The liquid ejection device according to any one of claims 1 to 10.

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