Patent ID: 12257851

DESCRIPTION OF THE EMBODIMENTS

A preferred embodiment of the present disclosure will be specifically described with reference to the accompanying drawings. Note that the following embodiment does not limit the contents of the present disclosure, and not all of the combinations of the features described in these embodiments are necessarily essential for the solving means of the present disclosure. Note that identical constituent elements are denoted by the same reference numeral. The present embodiment will be described using an example in which a thermal type ejection element that ejects a liquid by generating a bubble with an electrothermal conversion element is employed as each ejection element that ejects a liquid, but is not limited to this example. The present embodiment is applicable also to liquid ejection heads employing an ejection method in which a liquid is ejected using a piezoelectric element as well as liquid ejection heads employing other ejection methods. Moreover, the pumps, pressure adjustment units, and so on to be described below are not limited to the configurations described in the embodiment and illustrated in the drawings. In the following description, a basic configuration of the present disclosure will be discussed first, and then characteristic features of the present disclosure will be described.

<Liquid Ejection Apparatus>

FIG.1Ais a view for describing a liquid ejection apparatus, and is an enlarged view of a liquid ejection head of the liquid ejection apparatus and its vicinity. First, a schematic configuration of a liquid ejection apparatus50in the present embodiment will be described with reference toFIGS.1A and1B.FIG.1Ais a perspective view schematically illustrating the liquid ejection apparatus using the liquid ejection head1. The liquid ejection apparatus50in the present embodiment is configured as a serial inkjet printing apparatus that performs printing on a print medium P by ejecting inks as liquids while scanning the liquid ejection head1.

The liquid ejection head1is mounted on a carriage60. The carriage60reciprocally moves in a main scanning direction (X direction) along a guide shaft51. The print medium P is conveyed in a sub scanning direction (Y direction) crossing (in this example, perpendicularly crossing) the main scanning direction by conveyance rollers55,56,57, and58. Note that, in drawings to be referred to below, the Z direction represents a vertical direction and crosses (in this example, perpendicularly crosses) an X-Y plane defined by the X direction and the Y direction. The liquid ejection head1is configured to be attachable to and detachable from the carriage60by a user.

The liquid ejection head1includes circulation units54and a later-described ejection unit3(seeFIGS.2A and2B). While a specific configuration will be described later, the ejection unit3includes a plurality of ejection ports and energy generation elements (hereinafter referred to as “ejection elements”) that generate ejection energy for ejecting liquids from the respective ejection ports.

The liquid ejection apparatus50also includes ink tanks2serving as ink supply sources and external pumps21. The inks stored in the ink tanks2are supplied to the circulation units54through ink supply tubes59by driving forces of the external pumps21.

The liquid ejection apparatus50forms a predetermined image on the print medium P by repeating a printing scan involving performing printing by causing the liquid ejection head1mounted on the carriage60to eject the inks while moving in the main scanning direction, and a conveyance operation involving conveying the print medium P in the sub scanning direction. Note that the liquid ejection head1in the present embodiment is capable of ejecting four types of inks, namely black (B), cyan (C), magenta (M), and yellow (Y) inks, and printing full-color images with these inks. Here, the inks ejectable from the liquid ejection head1are not limited to the above four types of inks. The present disclosure is also applicable to liquid ejection heads for ejecting other types of inks. In short, the types and number of inks to be ejected from the liquid ejection head are not limited.

Also, in the liquid ejection apparatus50, a cap member (not illustrated) capable of covering the ejection port surface of the liquid ejection head1in which its ejection ports are formed is provided at a position separated from the conveyance path for the print medium P in the X direction. The cap member covers the ejection port surface of the liquid ejection head1during a non-print operation, and is used for prevention of drying of the ejection ports, protection of the ejection ports, an ink suction operation from the ejection ports, and so on.

Note that the liquid ejection head1illustrated inFIG.1Arepresents an example where four circulation units54corresponding to the four types of inks are included in the liquid ejection head1, but it suffices that the circulation units54included correspond to the types of liquids to be ejected. Also, a plurality of circulation units54may be included for the same type of liquid. In sum, the liquid ejection head1can have a configuration including one or more circulation units. The liquid ejection head1may be configured not to circulate all of the four types of inks but only circulate at least one of the inks.

FIG.1Bis a block diagram illustrating a control system of the liquid ejection apparatus50. A CPU103functions as a control unit that controls the operation of each unit of the liquid ejection apparatus50based on a program such as a process procedure stored in a ROM101. A RAM102is used as a work area or the like for the CPU103to execute processes. The CPU103receives image data from a host apparatus400outside the liquid ejection apparatus50and controls a head driver1A to control the driving of the ejection elements provided in the ejection unit3. The CPU103also controls drivers for various actuators provided in the liquid ejection apparatus. For example, the CPU103controls a motor driver105A for a carriage motor105for moving the carriage60, a motor driver104A for a conveyance motor104for conveying the print medium P, and the like. Moreover, the CPU103controls a pump driver500A for later-described circulation pumps500, a pump driver21A for the external pumps21, and the like. Note thatFIG.1Billustrates a configuration in which the image data is received from the host apparatus400and processes are performed, but the liquid ejection apparatus50may perform the processes regardless of whether data is given from the host apparatus400.

<Basic Configuration of Liquid Ejection Head>

FIG.2is an exploded perspective view of the liquid ejection head1in the present embodiment.FIGS.3A and3Bare cross-sectional views of the liquid ejection head1illustrated inFIG.2along the IIIA-IIIA line.FIG.3Ais a vertical cross-sectional view of the entire liquid ejection head1, andFIG.3Bis an enlarged view of an ejection module illustrated inFIG.3A. A basic configuration of the liquid ejection head1in the present embodiment will be described below with reference mainly toFIGS.2to3Band toFIG.1Aas appropriate.

As illustrated inFIG.2, the liquid ejection head1includes the circulation units54and the ejection unit3for ejecting the inks supplied from the circulation units54onto the print medium P. The liquid ejection head1in the present embodiment is fixedly supported on the carriage60of the liquid ejection apparatus50by a positioning unit and electric contacts (not illustrated) which are provided to the carriage60. The liquid ejection head1performs printing on the print medium P by ejecting the inks while moving along with the carriage60in the main scanning direction (X direction) illustrated inFIG.1A.

The external pumps21connected to the ink tanks2serving as ink supply sources include the ink supply tubes59(seeFIG.1A). A liquid connector (not illustrated) is provided at the tip of each of these ink supply tubes59. In the state where the liquid ejection head1is mounted to the liquid ejection apparatus50, the liquid connectors which are provided at the tips of the ink supply tubes59and are inlets through which the liquids are introduced are hermetically connected to liquid connector insertion slots53athat are provided on a head housing53of the liquid ejection head1. As a result, ink supply paths extending from the ink tanks2to the liquid ejection head1through the external pumps21are formed. In the present embodiment, four types of inks are used. Hence, four sets each including an ink tank2, an external pump21, an ink supply tube59, and a circulation unit54are provided for the respective inks, and four ink supply paths corresponding to the respective inks are formed independently of each other. As described above, the liquid ejection apparatus50in the present embodiment includes ink supply systems to which the inks are supplied from the ink tanks2provided outside the liquid ejection head1. Note that the liquid ejection apparatus50in the present embodiment does not include ink collection systems that collect the inks in the liquid ejection head1into the ink tanks2. Accordingly, the liquid ejection head1includes the liquid connector insertion slots53ato connect the ink supply tubes59of the ink tanks2but does not include connector insertion slots to connect tubes for collecting the inks in the liquid ejection head1into the ink tanks2. Note that a liquid connector insertion slot53ais provided for each ink.

InFIG.3A, reference signs54B,54C,54M, and54Y denote the circulation units for the black, cyan, magenta, and yellow inks, respectively. The circulation units have substantially the same configuration, and each circulation unit will be denoted as “circulation unit54” in the present embodiment unless otherwise distinguished.

InFIGS.2and3A, the ejection unit3includes two ejection modules300, the first support member4, the second support member7, an electric wiring member (electric wiring tape)5, and an electric contact substrate6. As illustrated inFIG.3B, each ejection module300includes a silicon substrate310with a thickness of 0.5 mm to 1 mm and a plurality of ejection elements15provided in one surface of the silicon substrate310. The ejection elements15in the present embodiment each includes an electrothermal conversion element (heater) that generates thermal energy as ejection energy for ejecting the liquid. Electric power through an electric wiring formed on the silicon substrate310by a film forming technique is supplied to each of the ejection elements15.

Also, a discharge port forming member320is formed on a surface of the silicon substrate310(the lower surface inFIG.3B). In the discharge port forming member320, a plurality of pressure chambers12corresponding to the plurality of ejection elements15and a plurality of ejection ports13to eject the inks are formed by a photolithographic technique. Moreover, common supply channels18and common collection channels19are formed in the silicon substrate310. Furthermore, in the silicon substrate310, there are formed supply connection channels323through which the common supply channels18and the pressure chambers12communicate with one another, and collection connection channels324through which the common collection channels19and the pressure chambers12communicate with one another. In the present embodiment, one ejection module300is configured to eject two types of inks. Specifically, in the two ejection modules illustrated inFIG.3A, the ejection module300located on the left side inFIG.3Aejects the black and cyan inks, and the ejection module300located on the right side inFIG.3Aejects the magenta and yellow inks. Note that this combination is a mere example, and any combination of inks may be employed. The configuration may be such that one ejection module ejects one type of ink or ejects three or more types of inks. The two ejection modules300do not have to eject the same number of types of inks. The configuration may be such that only one ejection module300is included, or three or more ejection modules300are included. Moreover, in the example illustrated inFIGS.3A and3B, two ejection port arrays extending in the Y direction are formed for an ink of one color. A pressure chamber12, a common supply channel18, and a common collection channel19are formed for each of the plurality of ejection ports13forming each ejection port array.

Later-described ink supply ports and ink collection ports are formed on the back surface (the upper surface inFIG.3B) side of the silicon substrate310. Through the ink supply ports, the inks are supplied into the plurality of common supply channels18from ink supply channels48. Through the ink collection ports, the inks are collected into ink collection channels49from the plurality of common collection channels19.

Note that the ink supply ports and the ink collection ports correspond to openings for supplying and collecting the inks during later-described forward ink circulation, respectively. Specifically, during the forward ink circulation, the inks are supplied from the ink supply ports into the common supply channels18, and the inks are collected from the common collection channels19into the ink collection ports. Note that ink circulation in which the inks are caused to flow in the opposite direction may also be performed. In this case, the inks are supplied from the above-described ink collection ports into the common collection channels19, and the inks are collected from the common supply channels18into the ink supply ports.

As illustrated inFIG.3A, the back surfaces (the upper surfaces inFIG.3A) of the ejection modules300are adhesively fixed to one surface of the first support member4(the lower surface inFIG.3A). The ink supply channels48and the ink collection channels49, which penetrate from one surface of the first support member4to the opposite surface of the first support member4, are formed in the first support member4. The openings of the ink supply channels48on one side communicate with the above-mentioned ink supply ports in the silicon substrate310. The openings of the ink collection channels49on the one side communicate with the above-mentioned ink collection ports in the silicon substrate310. Note that the ink supply channels48and the ink collection channels49are provided independently for each type of ink.

Also, the second support member7having openings7a(seeFIG.2) to insert the ejection modules300are adhesively fixed to one surface (the lower surface inFIG.3A) of the first support member4. The electric wiring member5to be electrically connected to the ejection modules300is held on the second support member7. The electric wiring member5is a member for applying electric signals for ink ejection to the ejection modules300. The electric connection parts of the ejection modules300and the electric wiring member5are sealed with a sealant (not illustrated) to be protected from corrosion by the inks and external impacts.

Also, the electric contact substrate6is joined to an end portion5aof the electric wiring member5(seeFIG.2) by thermocompression bonding with an anisotropic conductive film (not illustrated), and the electric wiring member5and the electric contact substrate6are electrically connected to each other. The electric contact substrate6has external signal input terminals (not illustrated) for receiving electric signals from the liquid ejection apparatus50.

Moreover, a joint member8(FIG.3A) is provided between the first support member4and the circulation units54. In the joint member8, a supply port88and a collection port89are formed for each type of ink. Through the supply ports88and the collection ports89, the ink supply channels48and the ink collection channels49in the first support member4and channels formed in the circulation units54communicate with each other. Incidentally, inFIG.3A, a supply port88B and a collection port89B are for the black ink, and a supply port88C and a collection port89C are for the cyan ink. Moreover, a supply port88M and a collection port89M are for the magenta ink, and a supply port88Y and a collection port89Y are for the yellow ink.

Note that the openings at one end of the ink supply channels48and the ink collection channels49in the first support member4have small opening areas matching the ink supply ports and the ink collection ports in the silicon substrate310. On the other hand, the openings at the other end of the ink supply channels48and the ink collection channels49in the first support member4have a large shape whose opening area is the same opening area formed in the joint member8to match the channels in the circulation units54. Employing such a configuration can suppress an increase in channel resistance on the ink collected from each collection channel. Note that the shapes of the openings at one end and the other end of the ink supply channels48and the ink collection channels49are not limited to the above example.

In the liquid ejection head1having the above configuration, the inks supplied to the circulation units54pass through the supply ports88in the joint member8and the ink supply channels48in the first support member4and flow into the common supply channels18from the ink supply ports in the ejection modules300. Thereafter, the inks flow from the common supply channels18into the pressure chambers12through the supply connection channels323. Part of the inks flowing into the pressure chambers is ejected from the ejection ports13as the ejection elements15are driven. The remaining inks not ejected pass through the collection connection channels324and the common collection channels19from the pressure chambers12, and flow from the ink collection ports into the ink collection channels49in the first support member4. Then, the inks flowing into the ink collection channels49flow into the circulation units54through the collection ports89in the joint member8and are collected.

<Constituent Elements of Circulation Units>

FIG.4is a schematic external view of one circulation unit54for one type of ink used in a printing apparatus in the present embodiment. A filter110, the first pressure adjustment unit120, the second pressure adjustment unit150, and a circulation pump500are disposed in the circulation unit54. As illustrated inFIGS.5and6, these constituent elements are connected by channels to form a circulation path for supplying and collecting the ink to and from the ejection module300in the liquid ejection head1.

<Circulation Path in Liquid Ejection Head>

FIG.5is a vertical cross-sectional view schematically illustrating the circulation path for one type of ink (ink of one color) formed in the liquid ejection head1. The relative positions of the components inFIG.5(such as the first pressure adjustment unit120, the second pressure adjustment unit150, and the circulation pump500) are simplified for a clearer description of the circulation path. Thus, the relative positions of the components are different from those of the components inFIG.19to be mentioned later. Incidentally,FIG.6is a block diagram schematically illustrating the circulation path illustrated inFIG.5. As illustrated inFIGS.5and6, the first pressure adjustment unit120includes the first valve chamber121and the first pressure control chamber122. The second pressure adjustment unit150includes the second valve chamber151and the second pressure control chamber152. The first pressure adjustment unit120is configured such that the controlled pressure therein is higher than that in the second pressure adjustment unit150. In the present embodiment, these two pressure adjustment units120and150are used to implement circulation within a certain pressure range inside the circulation path. Also, the configuration is such that the ink flows through the pressure chambers12(ejection elements15) at a flow rate corresponding to the pressure difference between the first pressure adjustment unit120and the second pressure adjustment unit150. A circulation path in the liquid ejection head1and a flow of the ink in the circulation path will be described below with reference toFIGS.5and6. Note that the arrows inFIGS.5and6indicate the flow direction of the ink.

First, how the constituent elements in the liquid ejection head1are connected will be described.

The external pump21, which sends the ink stored in the ink tank2(FIG.6) disposed outside the liquid ejection head1to the liquid ejection head1, is connected to the circulation unit54through the ink supply tube59(FIG.1). The filter110is disposed in the ink channel located on an upstream side of the circulation unit54. The ink supply path located downstream of the filter110is connected to the first valve chamber121of the first pressure adjustment unit120. The first valve chamber121communicates with the first pressure control chamber122through a communication port191A openable and closable by a valve190A illustrated inFIG.5.

The first pressure control chamber122is connected to a supply channel130, a bypass channel160, and a pump outlet channel180of the circulation pump500. The supply channel130is connected to the common supply channels18through the above-mentioned ink supply ports provided in the ejection module300. Also, the bypass channel160is connected to the second valve chamber151provided in the second pressure adjustment unit150. The second valve chamber151communicates with the second pressure control chamber152through a communication port191B that is opened and closed by a valve190B illustrated inFIG.5. Note thatFIGS.5and6illustrate an example where one end of the bypass channel160is connected to the first pressure control chamber122of the first pressure adjustment unit120, and the other end of the bypass channel160is connected to the second valve chamber151of the second pressure adjustment unit150. However, the one end of the bypass channel160may be connected to the supply channel130, and the other end of the bypass channel may be connected to the second valve chamber151.

The second pressure control chamber152is connected to a collection channel140. The collection channel140is connected to the common collection channels19through the above-mentioned ink collection ports provided in the ejection module300. Moreover, the second pressure control chamber152is connected to the circulation pump500through a pump inlet channel170. Note that reference sign170ainFIG.5denotes an inlet port of the pump inlet channel170.

Next, the flow of the ink in the liquid ejection head1having the above configuration will be described. As illustrated inFIG.6, the ink stored in the ink tank2is pressurized by the external pump21provided in the liquid ejection apparatus50, becomes an ink flow at a positive pressure, and is supplied to the circulation unit54of the liquid ejection head1.

The ink supplied to the circulation unit54passes through the filter110so that foreign substances such as dust and bubbles are removed. The ink then flows into the first valve chamber121provided in the first pressure adjustment unit120. The pressure on the ink decreases due to the pressure loss in a case where the ink passes through the filter110, but the pressure on the ink is still positive at this point. Thereafter, in a case where the valve190A is open, the ink flowing into the first valve chamber121passes through the communication port191A and flows into the first pressure control chamber122. Due to the pressure loss in a case where the ink passes through the communication port191A, the pressure on the ink flowing into the first pressure control chamber122switches from the positive pressure to a negative pressure.

Next, the flow of the ink in the circulation path will be described. The circulation pump500operates such that the ink sucked from the pump inlet channel170located upstream of the circulation pump500is sent to the pump outlet channel180located downstream of the circulation pump500. Thus, as the pump is driven, the ink supplied to the first pressure control chamber122flows into the supply channel130and the bypass channel160along with the ink sent from the pump outlet channel180. In the present embodiment, while details will be described later, a piezoelectric diaphragm pump using a piezoelectric element attached to a diaphragm as a driving source is used as a circulation pump capable of sending the liquid. The piezoelectric diaphragm pump is a pump that sends a liquid by inputting a driving voltage to a piezoelectric element to change the volume of a pump chamber and alternatively moving two check valves in response to the changes in pressure.

The ink flowing into the supply channel130flows from the ink supply ports in the ejection module300into the pressure chambers12through the common supply channels18. Part of the ink is ejected from the ejection ports13as the ejection elements15are driven (generate heat). Also, the remaining ink not used in the ejection flows through the pressure chambers12and passes through the common collection channels19. Thereafter, the ink flows into the collection channel140connected to the ejection module300. The ink flowing into the collection channel140flows into the second pressure control chamber152of the second pressure adjustment unit150.

On the other hand, the ink flowing from the first pressure control chamber122into the bypass channel160flows into the second valve chamber151, passes through the communication port191B, and then flows into the second pressure control chamber152. The ink flowing into the second pressure control chamber152through the bypass channel160and the ink collected from the collection channel140are sucked into the circulation pump500through the pump inlet channel170as the circulation pump500is driven. Then, the inks sucked into the circulation pump500are sent to the pump outlet channel180and flow into the first pressure control chamber122again. Thereafter, the ink flowing from the first pressure control chamber122into the second pressure control chamber152through the supply channel130and the ejection module300and the ink flowing into the second pressure control chamber152through the bypass channel160flow into the circulation pump500. Then, the inks are sent from the circulation pump500to the first pressure control chamber122. The ink circulation is performed within the circulation path in this manner.

As described above, in the present embodiment, the liquids can be circulated through the respective circulation paths formed in the liquid ejection head1with the circulation pump500. This makes it possible to suppress thickening of the inks and deposition of precipitating components of the inks of the color materials in the ejection modules300. Accordingly, the excellent fluidity of the inks in the ejection modules300and excellent ejection characteristics at the ejection ports can be maintained.

Also, the circulation paths in the present embodiment are configured to complete within the liquid ejection head1. Thus, the length of the circulation paths is significantly short as compared to a case where the inks are circulated between the ink tanks2disposed outside the liquid ejection head1and the liquid ejection head1. Accordingly, the inks can be circulated with small circulation pumps.

Moreover, the configuration is such that only channels for supplying the inks are included as the channels connecting between the liquid ejection head1and the ink tanks2. In other words, a configuration that does not require channels for collecting the inks from the liquid ejection head1into the ink tanks2is employed. Accordingly, only ink supply tubes connecting between the ink tanks2and the liquid ejection head1are needed, and no ink collection tube is required. The inside of the liquid ejection apparatus50therefore has a simpler configuration having less tubes. This can downsize the entire apparatus. Moreover, the reduction in the number of tubes reduces the fluctuations in ink pressure due to the swinging of the tubes caused by main scanning of the liquid ejection head1. Also, the swinging of the tubes during main scanning of the liquid ejection head1increases a driving load on the carriage motor driving the carriage60. Hence, the reduction of the number of tubes reduces the driving load of the carriage motor, which makes it possible to simplify the main scanning mechanism including the carriage motor and the like. Furthermore, since the inks do not need to be collected into the ink tanks from the liquid ejection head1, the external pumps21can be downsized as well. As described above, according to the present embodiment, it is possible to downsize the liquid ejection apparatus50and reduce costs.

<Pressure Adjustment Units>

FIGS.7A to7Care views illustrating an example of the pressure adjustment units. Configurations and operation of the pressure adjustment units incorporated in the above-described liquid ejection head1(first pressure adjustment unit120and second pressure adjustment unit150) will be described in more detail with reference toFIGS.7A to7C. Note that the first pressure adjustment unit120and the second pressure adjustment unit150have substantially the same configuration. Thus, the following description will be given by taking the first pressure adjustment unit120as an example. As for the second pressure adjustment unit150, only the reference signs of its portions corresponding to those of the first pressure adjustment unit are presented inFIGS.7A to7C. In a case of the second pressure adjustment unit150, the first valve chamber121and the first pressure control chamber122described below should be read as the second valve chamber151and the second pressure control chamber152, respectively.

The first pressure adjustment unit120has the first valve chamber121and the first pressure control chamber122formed in a cylindrical housing125. The first valve chamber121and the first pressure control chamber122are separated by a partition123provided inside the cylindrical housing125. However, the first valve chamber121communicates with the first pressure control chamber122through a communication port191formed in the partition123. A valve190, which switches between allowing communication between the first valve chamber121and the first pressure control chamber122through the communication port191and blocking the communication, is provided in the first valve chamber121. The valve190is held by a valve spring200at a position opposite to the communication port191, and has a tight contact configuration to the partition123by a biasing force from the valve spring200. The valve190blocks the ink flow through the communication port191by being in tight contact with the partition123. Note that the portion of the valve190to be in contact with the partition123is preferably formed of an elastic member in order to enhance the tightness of the contact with the partition123. Also, a valve shaft190ato be inserted through the communication port191is provided in a protruding manner on a center portion of the valve190. By pressing this valve shaft190aagainst the biasing force from the valve spring200, the valve190gets separated from the partition123, thereby allowing the ink to flow through the communication port191. In the following, the state where the valve190blocks the ink flow through the communication port191will be referred to as “closed state”, and the state where the ink can flow through the communication port191will be referred to as “open state”.

The opening portion of the cylindrical housing125is closed by a flexible member230and a pressing plate210. These flexible member230and pressing plate210, the peripheral wall of the housing125, and the partition123form the first pressure control chamber122. The pressing plate210is configured to be displaceable with displacement of the flexible member230. While the materials of the pressing plate210and the flexible member230are not particularly limited, for example, the pressing plate210can be made as a molded resin component, and the flexible member230can be made from a resin film. In this case, the pressing plate210can be fixed to the flexible member230by thermal welding.

A pressure adjustment spring220(biasing member) is provided between the pressing plate210and the partition123. As illustrated inFIG.7A, the pressing plate210and the flexible member230are biased by a biasing force from the pressure adjustment spring220in a direction in which the inner volume of the first pressure control chamber122increases. Also, as the pressure in the first pressure control chamber122decreases, the pressing plate210and the flexible member230get displaced against the pressure from the pressure adjustment spring220in the direction in which the inner volume of the first pressure control chamber122decreases. Then, in a case where the inner volume of the first pressure control chamber122decreases to a certain volume, the pressing plate210abuts the valve shaft190aof the valve190. As the inner volume of the first pressure control chamber122then decreases further, the valve190moves with the valve shaft190aagainst the biasing force from the valve spring200, thereby being separated from the partition123. As a result, the communication port191shifts to the open state (the state ofFIG.7B).

In the present embodiment, the connections in the circulation path are set such that the pressure in the first valve chamber121in a case where the communication port191shifts to the open state is higher than the pressure in the first pressure control chamber122. In this way, in a case where the communication port191shifts to the open state, the ink flows from the first valve chamber121into the first pressure control chamber122. The inflow of the ink displaces the flexible member230and the pressing plate210in the direction in which the inner volume of the first pressure control chamber122increases. As a result, the pressing plate210gets separated from the valve shaft190aof the valve190, and the valve190is brought into tight contact with the partition123by the biasing force from the valve spring200so that the communication port191shifts to the closed state (the state ofFIG.7C).

As described above, in the first pressure adjustment unit120in the present embodiment, in a case where the pressure in the first pressure control chamber122decreases to a certain pressure or less (e.g., in a case where the negative pressure becomes strong), the ink flows from the first valve chamber121through the communication port191. This configuration limits the pressure in the first pressure control chamber122from decreasing any further. Accordingly, the pressure in the first pressure control chamber122is controlled to be maintained within a certain range. In other words, it can be said that the first pressure adjustment unit120adjusts the pressure in the supply channel130since the first pressure control chamber122is connected to the supply channel130.

Next, the pressure in the first pressure control chamber122will be described in more detail.

Consider a state where the flexible member230and the pressing plate210are displaced according to the pressure in the first pressure control chamber122as described above so that the pressing plate210abuts the valve shaft190aand brings the communication port191into the open state (the state ofFIG.7B). The relation between the forces acting on the pressing plate210at this time is represented by Equation 1 below.
P2×S2+F2+(P1−P2)×S1+F1=0  Equation 1

Moreover, Equation 1 is summarized for P2as below.
P2=−(F1+F2+P1×S1)/(S2−S1)  Equation 2P1: Pressure (gauge pressure) in the first valve chamber121P2: Pressure (gauge pressure) in first pressure control chamber122F1: Spring force of the valve spring200F2: Spring force of the pressure adjustment spring220S1: Pressure reception area of the valve190S2: Pressure reception area of the pressing plate210

Here, as for the spring force F1of the valve spring200and the spring force F2of the pressure adjustment spring220, the direction in which they push the valve190and the pressing plate210is defined as the forward direction (the leftward direction inFIGS.7A to7C). Also, the configuration is such that the pressure P1in the first valve chamber121and the pressure P2in the first pressure control chamber122satisfy a relation of P1≥P2.

The pressure P2in the first pressure control chamber122when the communication port191shifts to the open state is determined by Equation 2 and, since the configuration is such that the relation of P1≥P2is satisfied, the ink flows into the first pressure control chamber122from the first valve chamber121when the communication port191shifts to the open state. As a result, the pressure P2in the first pressure control chamber122does not decrease any further, and the pressure P2is kept at a pressure within a certain range.

On the other hand, as illustrated inFIG.7C, the relation between the forces acting on the pressing plate210in a case where the pressing plate210does not abut on the valve shaft190aand the communication port191shifts to the closed state is represented by Equation 3 below.
P3×S3+F3=0  Equation 3

Here, Equation 3 is summarized for P3as below.
P3=−F3/S3  Equation 4F3: Spring force of the pressure adjustment spring220in a state where the pressing plate210does not abut on the valve shaft190aP3: Pressure (gauge pressure) in the first pressure control chamber122in the state where the pressing plate210does not abut on the valve shaft190aS3: Pressure reception area of the pressing plate210in a state where the pressing plate210does not abut on the valve shaft190a

Here,FIG.7Cillustrates a state where the pressing plate210and the flexible member230are displaced in the leftward direction inFIG.7Cup to the limit to which they can be displaced. The pressure P3in the first pressure control chamber122, the spring force F3of the pressure adjustment spring220, and the pressure reception area S3of the pressing plate210change depending on the amount of displacement of the pressing plate210and the flexible member230in displacement to the state ofFIG.7C. Specifically, in a case where the pressing plate210and the flexible member230are situated on the right side inFIG.7Crelative to themselves inFIG.7C, the pressure reception area S3of the pressing plate210is smaller and the spring force F3of the pressure adjustment spring220is larger. Accordingly, the pressure P3in the first pressure control chamber122is smaller in accordance with the relation in Equation 4. Thus, with Equations 2 and 4, the pressure in the first pressure control chamber122gradually increases (that is, the negative pressure weakens toward a value close to the positive pressure side) in shifting from the state ofFIG.7Bto the state ofFIG.7C. Specifically, the pressure in the first pressure control chamber122gradually increases while the pressing plate210and the flexible member230are gradually displaced in the leftward direction from the state where the communication port191is in the open state to the state where the inner volume of the first pressure control chamber reaches the limit to which the pressing plate210and the flexible member230can be displaced. In other words, the negative pressure weakens.

<Circulation Pumps>

Next, a configuration and operation of each circulation pump500incorporated in the above liquid ejection head1will be described in detail with reference toFIGS.8A and8BandFIG.9.

FIGS.8A and8Bare external perspective views of the circulation pump500.FIG.8Ais an external perspective view illustrating the front side of the circulation pump500, andFIG.8Bis an external perspective view illustrating the back side of the circulation pump500. An outer shell of the circulation pump500includes a pump housing505and a cover507fixed to the pump housing505. The pump housing505includes a housing-part main body505aand a channel connection member505badhesively fixed to the outer surface of the housing-part main body505a. In each of the housing-part main body505aand the channel connection member505b, a pair of through-holes communicating with each other are formed at two different positions. One of the pair of through-holes provided at one position forms a pump supply hole501. The other of the pair of through-holes provided at the other position forms a pump discharge hole502. The pump supply hole501is connected to the pump inlet channel170connected to the second pressure control chamber152. The pump discharge hole502is connected to the pump outlet channel180connected to the first pressure control chamber122. The ink supplied from the pump supply hole501passes through a later-described pump chamber503(seeFIG.9) and is discharged from the pump discharge hole502.

FIG.9is a cross-sectional view of the circulation pump500illustrated inFIG.8Aalong the IX-IX line. A diaphragm506is joined to the inner surface of the pump housing505, and the pump chamber503is formed between this diaphragm506and a recess formed in the inner surface of the pump housing505. The pump chamber503communicates with the pump supply hole501and the pump discharge hole502, which are formed in the pump housing505. Also, a check valve504ais provided at an intermediate portion of the pump supply hole501. A check valve504bis provided at an intermediate portion of the pump discharge hole502. Specifically, the check valve504ais disposed such that a part thereof is movable in the leftward direction inFIG.9within a space512aformed at an intermediate portion of the pump supply hole501. The check valve504ais disposed such that a part thereof is movable in the rightward direction inFIG.9within a space512bformed at an intermediate portion of the pump discharge hole502.

As the diaphragm506is displaced so as to increase the volume of the pump chamber503, the pump chamber503is depressurized. In response to this displacement, the check valve504ais separated from the opening of the pump supply hole501in the space512a(that is, moves in the leftward direction inFIG.9). By being separated from the opening of the pump supply hole501in the space512a, the check valve504ashifts to an open state in which the ink is allowed to flow through the pump supply hole501. As the diaphragm506is displaced so as to reduce the volume of the pump chamber503, the pump chamber503is pressurized. In response to this displacement, the check valve504acomes into tight contact with the wall surface around the opening of the pump supply hole501. The check valve504ais thus in a closed state in which the check valve504ablocks the ink flow through the pump supply hole501.

The check valve504b, on the other hand, comes into tight contact with the wall surface around an opening in the pump housing505as the pump chamber503is depressurized, thereby shifting to a closed state in which the check valve504bblocks the ink flow through the pump discharge hole502. Also, as the pump chamber503is pressurized, the check valve504bis separated from the opening in the pump housing505and moves toward the space512b(that is, moves in the rightward direction inFIG.9), thereby allowing the ink to flow through the pump discharge hole502.

Note that the material of each of the check valves504aand504bonly needs to be one that is deformable according to the pressure in the pump chamber503. For example, the material of each of the check valves504aand504bcan made from an elastic material such as Ethylene-Propylene-Diene Methylene linkage (EPDM) or an elastomer, or a film or thin plate of polypropylene or the like. However, the material is not limited to these.

As described above, the pump chamber503is formed by joining the pump housing505and the diaphragm506. Thus, the pressure in the pump chamber503changes as the diaphragm506is deformed. For example, in a case where the diaphragm506is displaced toward the pump housing505(displaced toward the right side inFIG.9), thereby reducing the volume of the pump chamber503, the pressure in the pump chamber503increases. As a result, the check valve504bdisposed so as to face the pump discharge hole502shifts to the open state so that the ink in the pump chamber503is discharged. At this time, the check valve504adisposed so as to face the pump supply hole501is in tight contact with the wall surface around the pump supply hole501, thereby suppressing backflow of the ink from the pump chamber503into the pump supply hole501.

Conversely, in a case where the diaphragm506is displaced in the direction in which the pump chamber503widens, the pressure in the pump chamber503decreases. As a result, the check valve504adisposed so as to face the pump supply hole501shifts to the open state so that the ink is supplied into the pump chamber503. At this time, the check valve504bdisposed in the pump discharge hole502comes into tight contact with the wall surface around an opening formed in the pump housing505to close this opening. This suppresses backflow of the ink from the pump discharge hole502into the pump chamber503.

As described above, in the circulation pump500, the ink is sucked and discharged as the diaphragm506is deformed and thereby changes the pressure in the pump chamber503. At this time, in a case where bubbles have entered the pump chamber503, the displacement of the diaphragm506changes the pressure in the pump chamber503to a lesser extent due to the expansion or shrinkage of the bubbles. Accordingly, the amount of the liquid to be sent decreases. To resolve this phenomenon, the pump chamber503is disposed in parallel with gravity so that the bubbles having entered the pump chamber503can easily gather in an upper portion of the pump chamber503. In addition, the pump discharge hole502is disposed higher than the center of the pump chamber503. This improves the ease of discharge of bubbles in the pump and thus stabilizes the flow rate.

<Flow of Ink Inside Liquid Ejection Head>

FIGS.10A to10Eare diagrams describing a flow of an ink inside the liquid ejection head. The circulation of the ink performed inside the liquid ejection head1will be described with reference toFIGS.10A to10E. The relative positions of the components inFIGS.10A to10Esuch as the first pressure adjustment unit120, the second pressure adjustment unit150, and the circulation pump500are simplified for a clearer description of the ink circulation path. Thus, the relative positions of the components are different from those of the components inFIG.19to be mentioned later.FIG.10Aschematically illustrates the flow of the ink in a case of performing a print operation of performing printing by ejecting the ink from the ejection ports13. Note that the arrows inFIG.10Aindicate the flow of the ink. In the present embodiment, to perform a print operation, both the external pump21and the circulation pump500start being driven. Incidentally, the external pump21and the circulation pump500may be driven regardless of whether a print operation is to be performed or not. The external pump21and the circulation pump500do not have to be driven in conjunction with each other, and may be driven independently of each other.

During the print operation, the circulation pump500is in an ON state (driven state) so that the ink flowing out of the first pressure control chamber122flows into the supply channel130and the bypass channel160. The ink having flowed into the supply channel130passes through the ejection module300and then flows into the collection channel140. Thereafter, the ink is supplied into the second pressure control chamber152.

On the other hand, the ink flowed into the bypass channel160from the first pressure control chamber122flows into the second pressure control chamber152through the second valve chamber151. The ink flowed into the second pressure control chamber152passes through the pump inlet channel170, the circulation pump500, and the pump outlet channel180and then flows into the first pressure control chamber122again. At this time, based on the relation in Equation 2 mentioned above, the controlled pressure in the first valve chamber121is set higher than the controlled pressure in the first pressure control chamber122. Thus, the ink in the first pressure control chamber122does not flow into the first valve chamber121but is supplied to the ejection module300again through the supply channel130. The ink flowed into the ejection module300flows into the first pressure control chamber122again through the collection channel140, the second pressure control chamber152, the pump inlet channel170, the circulation pump500, and the pump outlet channel180. Ink circulation that completes within the liquid ejection head1is performed as described above.

In the above ink circulation, the differential pressure between the controlled pressure in the first pressure control chamber122and the controlled pressure in the second pressure control chamber152determines the amount of circulation (flow rate) of the ink within the ejection module300. Moreover, this differential pressure is set to obtain an amount of circulation that can suppress thickening of the ink near the ejection ports in the ejection module300. Incidentally, the amount of the ink consumed by the printing is supplied from the ink tank2to the first pressure control chamber122through the filter110and the first valve chamber121. How the consumed ink is supplied will now be described in detail. The ink in the circulation path decreases by the amount of the ink consumed by the printing. Accordingly, the pressure in the first pressure control chamber122decreases, resulting in decreasing the ink in the first pressure control chamber. As the ink in the first pressure control chamber122decreases, the inner volume of the first pressure control chamber122decreases accordingly. As this inner volume of the first pressure control chamber122decreases, the communication port191A shifts to the open state so that the ink is supplied from the first valve chamber121to the first pressure control chamber122. A pressure loss occurs in this supplied ink as this ink supplied from the first valve chamber121passes through the communication port191A. As the ink flows into the first pressure control chamber122, the positive pressure on the ink switches to a negative pressure. As the ink flows from the first valve chamber121into the first pressure control chamber122, the pressure in the first pressure control chamber increases. The communication port191A shifts to the closed state when the inner volume of the first pressure control chamber increases. As described above, the communication port191A repetitively switches between the open state and the closed state according to the ink consumption. Incidentally, the communication port191A is kept in the closed state in a case where the ink is not consumed.

FIG.10Bschematically illustrates the flow of the ink immediately after the print operation is finished and the circulation pump500shifts to an OFF state (stop state). At the point when the print operation is finished and the circulation pump500shifts to the OFF state, the pressure in the first pressure control chamber122and the pressure in the second pressure control chamber152are both the controlled pressures used in the print operation. For this reason, the ink moves as illustrated inFIG.10Baccording to the differential pressure between the pressure in the first pressure control chamber122and the pressure in the second pressure control chamber152. Specifically, the ink flow from the first pressure control chamber122to the ejection module300through the supply channel130and then to the second pressure control chamber152through the collection channel140continues to be generated. Moreover, the ink flow from the first pressure control chamber122to the second pressure control chamber152through the bypass channel160and the second valve chamber151continues to be generated.

The amount of the ink moved from the first pressure control chamber122to the second pressure control chamber152by these ink flows is supplied from the ink tank2to the first pressure control chamber122through the filter110and the first valve chamber121. Accordingly, the inner volume of the first pressure control chamber122is maintained constant. According to the relation in Equation 2 mentioned above, the spring force F1of the valve spring200, the spring force F2of the pressure adjustment spring220, the pressure reception area51of the valve190, and the pressure reception area S2of the pressing plate210are maintained constant in a case where the inner volume of the first pressure control chamber122is constant. Thus, the pressure in the first pressure control chamber122is determined depending on the change of the pressure (gauge pressure) P1in the first valve chamber121. In this way, in a case where the pressure P1in the first valve chamber121does not change, the pressure P2in the first pressure control chamber122is maintained at the same pressure as the controlled pressure in the print operation.

On the other hand, the pressure in the second pressure control chamber152changes with time according to the change in inner volume by the inflow of the ink from the first pressure control chamber122. Specifically, the pressure in the second pressure control chamber152changes according to Equation 2 until the communication port191shifts from the state ofFIG.10Bto the closed state to allow no communication between the second valve chamber151and the second pressure control chamber152as illustrated inFIG.10C. Thereafter, the pressing plate210does not abut on the valve shaft190aso that the communication port191shifts to the closed state. Then, as illustrated inFIG.10D, the ink flows from the collection channel140into the second pressure control chamber152. This inflow of the ink displaces the pressing plate210and the flexible member230. The pressure in the second pressure control chamber152changes according to Equation 4. Specifically, the pressure increases until the inner volume of the second pressure control chamber152reaches the maximum.

Note that, once the state ofFIG.10Cis reached, there is no more ink flow from the first pressure control chamber122into the second pressure control chamber152through the bypass channel160and the second valve chamber151. Thus, the ink flow to the second pressure control chamber152through the collection channel140is only generated after the ink in the first pressure control chamber122is supplied to the ejection module300through the supply channel130. As mentioned above, the ink moves from the first pressure control chamber122to the second pressure control chamber152according to the differential pressure between the pressure in the first pressure control chamber122and the pressure in the second pressure control chamber152. Thus, in a case where the pressure in the second pressure control chamber152becomes equal to the pressure in the first pressure control chamber122, the ink stops moving.

Also, in the state where the pressure in the second pressure control chamber152is equal to the pressure in the first pressure control chamber122, the second pressure control chamber152expands to the state illustrated inFIG.10D. In a case where the second pressure control chamber152expands as illustrated inFIG.10D, a reservoir portion capable of holding the ink is formed in the second pressure control chamber152. Note that the transition to the state ofFIG.10Dafter stopping the circulation pump500takes about 1 minute to 2 minutes. The time may vary depending on the shapes and sizes of the channels and properties of the ink. As the circulation pump500is driven in the state where the ink is held in the reservoir portion as illustrated inFIG.10D, the ink in the reservoir portion is supplied to the first pressure control chamber122by the circulation pump500. Accordingly, as illustrated inFIG.10E, the amount of the ink in the first pressure control chamber122increases so that the flexible member230and the pressing plate210are displaced in the expanding direction. Then, as the circulation pump500continues to be driven, the state inside the circulation path changes to the state illustrated inFIG.10A.

Note that, in the above description,FIG.10Ahas been described as an example of the ink circulation during a print operation. However, the ink may be circulated without a print operation, as mentioned above. Even in this case, the ink flows as illustrated inFIGS.10A to10Ein response to the driving and stopping of the circulation pump500.

Also, as described above, in the present embodiment, an example in which the communication port191B in the second pressure adjustment unit150shifts to the open state in a case where the ink is circulated by driving the circulation pump500, and shifts to the closed state in a case where the ink circulation stops, has been used. However, the present embodiment is not limited to this example. The controlled pressure may be set such that the communication port191B in the second pressure adjustment unit150is in the closed state even in a case where the ink is circulated by driving the circulation pump500. This will be specifically described below along with the function of the bypass channel160.

The bypass channel160connecting between the first pressure adjustment unit120and the second pressure adjustment unit150is provided in order that the ejection module300can avoid the effect of the strong negative pressure, for example, in a case where the negative pressure generated inside the circulation path becomes stronger than a preset value. The bypass channel160is also provided in order to supply the ink to the pressure chambers12from both the supply channel130and the collection channel140.

First, a description will be given of an example of avoiding the effect of the negative pressure becoming stronger than the preset value on the ejection module300by providing the bypass channel160. For example, a change in environmental temperature sometimes changes a property (e.g., viscosity) of the ink. As the viscosity of the ink changes, the pressure loss within the circulation path changes as well. For example, as the viscosity of the ink decreases, the amount of pressure loss within the circulation path decreases. As a result, the flow rate of the circulation pump500driven at a constant driving amount increases, and the flow rate through the ejection module300increases. Here, the ejection module300is kept at a constant temperature by a temperature adjustment mechanism (not illustrated). Hence, the viscosity of the ink inside the ejection module300is maintained constant even if the environmental temperature changes. The viscosity of the ink inside the ejection module300remains unchanged whereas the flow rate of the ink flowing through the ejection module300increases, and therefore the negative pressure in the ejection module300becomes accordingly stronger due to flow resistance. If the negative pressure in the ejection module300becomes stronger than the preset value as described above, there is a possibility that the menisci in the ejection ports13may break and the ambient air may be taken into the circulation path, which may lead to a failure to perform normal ejection. Also, even if the menisci do not break, there is still a possibility that the negative pressure in the pressure chambers12may become stronger than a predetermined level and affect the ejection.

For these reasons, in the present embodiment, the bypass channel160is formed in the circulation path. By providing the bypass channel160, the ink flows through the bypass channel160in a case where the negative pressure is stronger than the preset value. Thus, the pressure in the ejection module300is kept constant. Thus, for example, the controlled pressure may be set such that the communication port191B in the second pressure adjustment unit150is maintained in the closed state even in a case where the circulation pump500is driven. Moreover, the controlled pressure in the second pressure adjustment unit150may be set such that the communication port191B in the second pressure adjustment unit150shifts to the open state in a case where the negative pressure becomes stronger than the preset value. In other words, the communication port191B may be in the closed state in a case where the circulation pump500is driven as long as the menisci do not collapse or a predetermined negative pressure is maintained even if the flow rate of the pump changes due to the change in viscosity caused by an environmental change or the like.

Next, a description will be given of an example where the bypass channel160is provided in order to supply the ink to the pressure chambers12from both the supply channel130and the collection channel140. The pressure in the circulation path may fluctuate due to the ejection operations of the ejection elements15. This is because the ejection operations generate a force that draws the ink into the pressure chambers.

In the following, a description will be given of the fact that the ink to be supplied to the pressure chambers12is supplied from both the supply channel130side and the collection channel140side in a case of continuing high-duty printing. While the definition of “duty” may vary depending on various conditions, in the following, a state where a 1200 dpi grid cell is printed with a single 4 pl ink droplet will be considered 100%. “High-duty printing” is, for example, printing performed at a duty of 100%.

In a case of continuing high-duty printing, the amount of the ink flowing from the pressure chambers12into the second pressure control chamber152through the collection channel140decreases. On the other hand, the circulation pump500causes the ink to flow out in a constant amount. This breaks the balance between the inflow into and the outflow from the second pressure control chamber152. Consequently, the ink inside the second pressure control chamber152decreases and the negative pressure in the second pressure control chamber152becomes stronger so that the second pressure control chamber152shrinks. As the negative pressure in the second pressure control chamber152becomes stronger, the amount of inflow of the ink into the second pressure control chamber152through the bypass channel160increases, and the second pressure control chamber152becomes stable in the state where the outflow and the inflow are balanced. Thus, the negative pressure in the second pressure control chamber152becomes stronger according to the duty. Also, as mentioned above, under the configuration in which the communication port191B is in the closed state in a case where the circulation pump500is driven, the communication port191B shifts to the open state depending on the duty so that the ink flows from the bypass channel160into the second pressure control chamber152.

Moreover, as high-duty printing is continued further, the amount of inflow into the second pressure control chamber152from the pressure chambers12through the collection channel140decreases and conversely the amount of inflow into the second pressure control chamber152from the communication port191B through the bypass channel160increases. As this state progresses further, the amount of the ink flowing into the second pressure control chamber152from the pressure chambers12through the collection channel140reaches zero so that the ink flowing from the communication port191B is the entire ink flowing out into the circulation pump500. As this state progresses further, the ink backs up from the second pressure control chamber152into the pressure chambers12through the collection channel140. In this state, the ink flowing from the second pressure control chamber152into the circulation pump500and the ink flowing from the second pressure control chamber152into the pressure chambers12will flow from the communication port191B into the second pressure control chamber152through the bypass channel160. In this case, the ink from the supply channel130and the ink from the collection channel140are filled into the pressure chambers12and ejected therefrom.

Note that this ink backflow that occurs in a case where the printing duty is high is a phenomenon that occurs due to the installation of the bypass channel160. Also, as described above, an example has been described in which the communication port191B in the second pressure adjustment unit shifts to the open state for the backflow of the ink. However, the backflow of the ink may also occur in the state where the communication port191B in the second pressure adjustment unit is in the open state. Moreover, in a configuration without the second pressure adjustment unit, the above backflow of the ink can also occur by installing the bypass channel160.

<Configuration of Ejection Unit>

FIGS.11A and11Bare schematic views illustrating a circulation path for an ink of one color in the ejection unit3in the present embodiment.FIG.11Ais an exploded perspective view of the ejection unit3as seen from the first support member4side.FIG.11Bis an exploded perspective view of the ejection unit3as seen from the ejection module300side. Note that the arrows denoted as “IN” and “OUT” inFIGS.11A and11Bindicate the ink flow, and the ink flow will be described only for one color, but the inks of the other colors flow similarly. Moreover, inFIGS.11A and11B, illustration of the second support member7and the electric wiring member5is omitted, and description of them is also omitted in the following description of the configuration of the ejection unit. Moreover, as for the first support member4inFIG.11A, a cross section along the line XI-XI inFIG.3Ais illustrated. Each ejection module300includes an ejection element substrate340and an opening plate330.FIG.12is a view illustrating the opening plate330.FIG.13is a view illustrating the ejection element substrate340.

The ejection unit3is supplied with an ink from each circulation unit54through the joint member8(seeFIG.3A). An ink path for an ink to return to the joint member8after passing the joint member8will now be described. Note that illustration of the joint member8is omitted in drawings to be mentioned below.

Each ejection module300includes the ejection element substrate340and the opening plate330, which are the silicon substrate310, and further includes the discharge port forming member320. The ejection element substrate340, the opening plate330, and the discharge port forming member320form the ejection module300by being stacked and joined such that each ink's channels communicate with each other. The ejection module300is supported on the first support member4. The ejection unit3is formed by supporting each ejection module300on the first support member4. The ejection element substrate340includes the discharge port forming member320, and the discharge port forming member320includes a plurality of ejection port arrays each being a plurality of ejection ports13forming a line. Part of the ink supplied through ink channels in the ejection module300is ejected from the ejection ports13. The ink not ejected is collected through ink channels in the ejection module300.

As illustrated inFIGS.11A and11BandFIG.12, the opening plate330includes a plurality of arrayed ink supply ports311and a plurality of arrayed ink collection ports312. As illustrated inFIG.13andFIGS.14A to14C, the ejection element substrate340includes a plurality of arrayed supply connection channels323and a plurality of arrayed collection connection channels324. The ejection element substrate340further includes the common supply channels18communicating with the plurality of supply connection channels323and the common collection channels19communicating with the plurality of collection connection channels324. The ink supply channels48and the ink collection channels49(seeFIGS.3A and3B) disposed in the first support member4and the channels disposed in each ejection module300communicate with each other to form the ink channels inside the ejection unit3. Support member supply ports211are openings in cross section forming the ink supply channels48. Support member collection ports212are openings in cross section forming the ink collection channels49.

The ink to be supplied to the ejection unit3is supplied from the circulation unit54(seeFIG.3A) side to the ink supply channels48(seeFIG.3A) in the first support member4. The ink flowed through the support member supply ports211in the ink supply channels48is supplied to the common supply channels18in the ejection element substrate340through the ink supply channels48(seeFIG.3A) and the ink supply ports311in the opening plate330, and enters the supply connection channels323. The channels up to this point are the supply-side channels. Thereafter, the ink passes through the pressure chambers12(seeFIG.3B) in the discharge port forming member320and flows into the collection connection channels324of the collection-side channels. Details of the ink flow in the pressure chambers12will be described below.

In the collection-side channels, the ink entered the collection connection channels324flows into the common collection channels19. Thereafter, the ink flows from the common collection channels19into the ink collection channels49in the first support member4through the ink collection ports312in the opening plate330, and is collected into the circulation unit54through the support member collection ports212.

Regions of the opening plate330where the ink supply ports311or the ink collection ports312are not present correspond to regions of the first support member4for separating the support member supply ports211and the support member collection ports212. Also, the first support member4does not have openings at these regions. Such regions are used as bonding regions in a case of bonding the ejection module300and the first support member4.

InFIG.12, a plurality of arrays of openings arranged along the X direction are provided side by side in the Y direction in the opening plate330, and the openings for supply (IN) and the openings for collection (OUT) are arranged alternately in the Y direction while being shifted from each other by a half pitch in the X direction. InFIG.13, in the ejection element substrate340, the common supply channels18communicating with the plurality of supply connection channels323arrayed in the Y direction and the common collection channels19communicating with the plurality of collection connection channels324arrayed in the Y direction are arrayed alternately in the X direction. The common supply channels18and the common collection channels19are separated by the ink type. Moreover, the number of ejection port arrays for each color determines the numbers of common supply channels18and common collection channels19to be disposed. Also, the number of the disposed supply connection channels323and the number of the disposed collection connection channels324corresponds to the number of ejection ports13. Note that a one-to-one correspondence is not necessarily essential, and a single supply connection channel323and a single collection connection channel324may correspond to a plurality of ejection ports13.

Each ejection module300is formed by stacking and joining the opening plate330and the ejection element substrate340as above such that each ink's channels communicate with each other, and is supported on the first support member4. As a result, ink channels including the supply channels and the collection channels as above are formed.

FIGS.14A to14Care cross-sectional views illustrating ink flows at different portions of the ejection unit3.FIG.14Ais a cross section taken along the line XIVA-XIVA inFIG.11A, and illustrates a cross section of a portion of the ejection unit3where ink supply channels48and ink supply ports311communicate with each other.FIG.14Bis a cross section taken along the line XIVB-XIVB inFIG.11A, and illustrates a cross section of a portion of the ejection unit3where ink collection channels49and ink collection ports312communicate with each other. Also,FIG.14Cis a cross section taken along the line XIVC-XIVC inFIG.11A, and illustrates a cross section of a portion where the ink supply ports311and the ink collection ports312do not communicate with channels in the first support member4.

As illustrated inFIG.14A, the supply channels for supplying the inks supply the inks from the portions where the ink supply channels48in the first support member4and the ink supply ports311in the opening plate330overlap and communicate with each other. Moreover, as illustrated inFIG.14B, the collection channels for collecting the inks collect the inks from the portions where the ink collection channels49in the first support member4and the ink collection ports312in the opening plate330overlap and communicate with each other. Furthermore, as illustrated inFIG.14C, the ejection unit3locally has regions where no opening is provided in the opening plate330. At such regions, the inks are neither supplied nor collected between the ejection element substrate340and the first support member4. The inks are supplied at the regions where the ink supply ports311are provided, as illustrated inFIG.14A. The inks are collected at regions where the ink collection ports312are provided, as illustrated inFIG.14B. Note that the present embodiment has been described by taking the configuration using the opening plate330as an example, but a configuration not using the opening plate330may be employed. For example, the configuration in which channels corresponding to the ink supply channels48and the ink collection channels49are formed in the first support member4, and the ejection element substrate340is joined to the first support member4may be employed.

FIGS.15A and15Bare cross-sectional views illustrating the vicinity of an ejection port13in an ejection module300.FIGS.16A and16Bare cross-sectional views illustrating an ejection module having a configuration as a comparative example in which the common supply channels18and the common collection channels19are widened in the X direction. Note that the bold arrows illustrated in the common supply channel18and the common collection channel19inFIGS.15A and15BandFIGS.16A and16Bindicate the oscillating movement of an ink which occurs in the configuration using the serial liquid ejection apparatus50. The ink supplied to the pressure chamber12through the common supply channel18and the supply connection channel323is ejected from the ejection port13as the ejection element15is driven. In a case where the ejection element15is not driven, the ink is collected from the pressure chamber12into the common collection channel19through the collection connection channel324, which is a collection channel.

In a case of ejecting the ink circulated as above in the configuration using the serial liquid ejection apparatus50, the ink ejection is affected to no small extent by the oscillating movement of the ink inside the ink channels caused by the main scanning of the liquid ejection head1. Specifically, the influence of the oscillating movement of the ink inside the ink channels appears as a difference in the amount of the ink ejected and a deviation in ejection direction. As illustrated inFIGS.16A and16B, in a case where the common supply channels18and the common collection channels19have cross-sectional shapes which are wide in the X direction, which is the main scanning direction, the inks inside the common supply channels18and the common collection channels19more easily receive inertial forces in the main scanning direction so that the inks oscillate greatly. This leads to a possibility that the oscillating movements of the inks may affect the ejection of the inks from the ejection ports13. Moreover, widening the common supply channels18and the common collection channels19in the X direction widens the distance between the colors. This may lower the printing efficiency.

Hence, each common supply channel18and each common collection channel19in the present embodiment whose cross sections are illustrated inFIGS.15A and15Bhave a configuration that each common supply channel18and each common collection channel19extend in the Y direction and also extend in the Z direction, which is perpendicular to the X direction, which is the main scanning direction. With such a configuration, the common supply channel18and the common collection channel19are given small channel widths in the main scanning direction. By giving the common supply channel18and the common collection channel19small channel widths in the main scanning direction, the oscillating movement of the ink inside the common supply channel18and the common collection channel19by the inertial force acting on the ink and exerted in the direction opposite to the main scanning direction (the black bold arrows inFIGS.15A and15B) during main scanning becomes smaller. This reduces the influence of the oscillating movement of the ink in the ejection of the ink. Moreover, by extending the common supply channel18and the common collection channel19in the Z direction, their cross-sectional areas are increased. This reduces the channel pressure drop.

As described above, each common supply channel18and each common collection channel19are given small channel widths in the main scanning direction. This configuration reduces the oscillating movement of the ink inside the common supply channel18and the common collection channel19during main scanning but does not eliminate the oscillating movement. Thus, in the present embodiment, in order to reduce the difference in ejection between the ink types that may be generated by the reduced oscillating movement, the configuration is such that the common supply channel18and the common collection channel19are disposed at positions overlapping each other in the X direction.

As described above, in the present embodiment, the supply connection channels323and the collection connection channels324are provided so as to correspond to the ejection ports13. Moreover, the correspondence relationship between the supply connection channels323and the collection connection channels324establishes such that the supply connection channels323and the collection connection channels324are arrayed in the X direction with the ejection ports13interposed therebetween. Thus, if the common supply channel18and the common collection channel19have a portion(s) where the common supply channel18and the common collection channel19do not overlap each other in the X direction, the correspondence between the supply connection channels323and the collection connection channels324in the X direction breaks. This lack of correspondence affects the ink flow in the pressure chambers12in the X direction and the ink ejection. If this lack of correspondence is combined with the influence of the oscillating movement of the ink, there is a possibility that it may further affect the ink ejection from each ejection port.

Thus, by disposing the common supply channel18and the common collection channel19at positions overlapping each other in the X direction, the oscillating movement of the ink inside the common supply channel18and the common collection channel19during main scanning is substantially the same at any position in the Y direction, in which the ejection ports13are arrayed. Thus, the pressure differences generated in the pressure chambers12between the common supply channel18side and the common collection channel19side do not greatly vary. These low pressure differences enable stable ejection.

Also, some liquid ejection heads which circulate an ink therein are configured such that the channel for supplying the ink to the liquid ejection head and the channel for collecting the ink are the same channel. However, in the present embodiment, the common supply channel18and the common collection channel19are different channels. Moreover, the supply connection channels323and the pressure chambers12communicate with each other, the pressure chambers12and the collection connection channels324communicate with each other, and the inks are ejected from the ejection ports13in the pressure chambers12. That is, the configuration that the pressure chambers12serving as paths connecting the supply connection channels323and the collection connection channels324include the ejection ports13, is formed. Hence, in each pressure chamber12, an ink flow flowing from the supply connection channel323side to the collection connection channel324side is generated, and the ink inside the pressure chamber12is efficiently circulated. The ink inside the pressure chamber12, which tends to be affected by evaporation of the ink from the ejection port13, is kept fresh by efficiently circulating the ink inside the pressure chamber12.

Also, since the two channels, namely the common supply channel18and the common collection channel19, communicate with the pressure chamber12, the ink can be supplied from both channels in a case where it is necessary to perform ejection with a high flow rate. That is, compared to the configuration in which only a single channel is formed for ink supply and collection, the configuration in the present embodiment has an advantage that not only efficient circulation can be performed but also ejection at a high flow rate can be handled.

Incidentally, the oscillating movement of the ink causes a less effect in a case where the common supply channel18and the common collection channel19are disposed at positions close to each other in the X direction. The common supply channel18and the common collection channel19are desirably disposed such that the gap between the channels is 75 μm to 100 μm.

FIG.17is a view illustrating an ejection element substrate340as a comparative example. Note that illustration of the supply connection channels323and the collection connection channels324is omitted inFIG.17. The inks having received thermal energy from the ejection elements15in the pressure chambers12flow into the common collection channels19. Hence, the temperature of the inks flowing through the common collection channels19is higher than the temperature of the inks in the common supply channels18. Here, in the comparative example, only the common collection channels19are present at one portion of the ejection element substrate340in the X direction, as indicated by a portion a circled with the long dashed short dashed line inFIG.17. In this case, the temperature may locally rise at that portion, thereby causing temperature unevenness within the ejection module300. This temperature unevenness may affect the ejection.

The temperature of the inks flowing through the common supply channels18is lower than that in the common collection channels19. Thus, if the common supply channels18and the common collection channels19are close to each other, the ink in the common supply channels18whose temperature is relatively lower lowers the temperature of the ink in the common collection channels19at the points where both channels are close. This suppresses a temperature rise. For this reason, it is preferable that the common supply channels18and the common collection channels19have substantially the same length, be present at positions overlapping each other in the X direction, and be close to each other.

FIGS.18A and18Bare views illustrating a channel configuration of the liquid ejection head1for the inks of the three colors of cyan (C), magenta (M), and yellow (Y). In the liquid ejection head1, a circulation channel is provided for each ink type as illustrated inFIG.18A. The pressure chambers12are provided along the X direction, which is the main scanning direction of the liquid ejection head1. Also, as illustrated inFIG.18B, the common supply channels18and the common collection channels19are provided along the ejection port arrays, which are arrays of ejection ports13. The common supply channels18and the common collection channels19are provided so as to extend in the Y direction with the ejection port arrays therebetween.

<Connection of Main Body Units and Liquid Ejection Head>

FIG.19is a schematic configuration diagram more specifically illustrating a state where an ink tank2and an external pump21provided as main body units of the liquid ejection apparatus50in the present embodiment and the liquid ejection head1are connected, and an arrangement of a circulation pump and so on. The liquid ejection apparatus50in the present embodiment has such a configuration that only the liquid ejection head1can be easily replaced in a case where a problem occurs in the liquid ejection head1. Specifically, the liquid ejection apparatus50in the present embodiment has the liquid connection parts700, with which the respective ink supply tubes59connected to the respective external pumps21and the liquid ejection head1can be easily connected to and disconnected from each other. This enables only the liquid ejection head1to be easily attached to and detached from the liquid ejection apparatus50.

As illustrated inFIG.19, each liquid connection part700has a liquid connector insertion slot53awhich is provided in a protruding manner on the head housing53of the liquid ejection head1, and a cylindrical liquid connector59ainto which this liquid connector insertion slot53ais insertable. The liquid connector insertion slot53ais fluidly connected to an ink supply channel formed in the liquid ejection head1, and is connected to the first pressure adjustment unit120through the filter110mentioned earlier. The liquid connector59ais provided at the tip of the ink supply tube59connected to the external pump21, which supplies the ink in the ink tank2to the liquid ejection head1by pressurization.

As described above, the liquid ejection head1illustrated inFIG.19has the liquid connection part700. This facilitates the work of attaching, detaching, and replacing the liquid ejection head1. However, in a case where the sealing performance between the liquid connector insertion slot53aand the liquid connector59adeteriorates, there is a possibility that the ink supplied by pressurization by the external pump21may leak from the liquid connection part700. The leaked ink may cause a problem in the electrical system if attached to the circulation pump500, for example. To address this, in the present embodiment, the circulation pump, etc., are disposed as below.

<Arrangement of Circulation Pump, etc.>

As illustrated inFIG.19, in the present embodiment, in order to avoid attachment of the ink leaking from the liquid connection part700to the circulation pump500, the circulation pump500is disposed higher than the liquid connection part700in the direction of gravity. Specifically, the circulation pump500is disposed higher than the liquid connector insertion slot53a, which is a liquid inlet in the liquid ejection head1, in the direction of gravity. Moreover, the circulation pump500is disposed at such a position as to be out of contact with the constituent members of the liquid connection part700. In this way, even if the ink leaks from the liquid connection part700, the ink flows in a horizontal direction which is the opening direction of the opening of the liquid connector59aor downward in the direction of gravity. This prevents the ink from reaching the circulation pump500located higher in the direction of gravity. Moreover, disposing the circulation pump500at a position separated from the liquid connection part700also reduces the possibility of the ink reaching the circulation pump500through members.

Furthermore, an electric connection part515electrically connecting the circulation pump500and the electric contact substrate6through a flexible wiring member514is provided higher than the liquid connection part700in the direction of gravity. Thus, the possibility of the ink from the liquid connection part700causing an electrical trouble is reduced.

In addition, in the present embodiment, a wall portion52bof the head housing53is provided. Thus, even if the ink jets out of the liquid connection part700from its opening59b, the wall portion53bblocks that ink and thus reduces the possibility of the ink reaching the circulation pump500or the electric connection part515.

<Pressure Fluctuations in Ejection Module>

Next, pressure fluctuations in the liquid ejection head1in the present embodiment which are associated with a characteristic feature of the present disclosure will be described. In the liquid ejection apparatus50using the serial liquid ejection head1in the present embodiment, the ink supply tubes59are used to supply the inks to the circulation units54of the liquid ejection head1. In the case where the circulation pumps500of the circulation units54are mounted in the liquid ejection head1, the paths from the circulation pumps500to the pressure chambers are short, and the circulation paths for the liquids are therefore short. Thus, there is a possibility that the pressure fluctuations inside the liquid ejection head due to the pump pulsation may become large. Thus, in a case where the liquid ejection head1is scanned in a print operation or the like, the ink supply tubes59are swung. This leads to a possibility that the pressures on the inks inside the ink supply tubes59may fluctuate.

In the present embodiment, components that suppress propagation of the pulsation of the ink within the circulation path are provided on the inlet side and outlet side of the circulation pump500, which is the source of the pulsation. Specifically, the first pressure adjustment unit120is connected to the pump outlet channel180, and the second pressure adjustment unit150is connected to the pump inlet channel170. With this configuration, propagation of the pulsation resulting from the driving of the circulation pump500to the ejection module300can be suppressed from both the inlet side and outlet side of the circulation pump500. In the liquid ejection head1, two pressure adjustment units (first pressure adjustment unit and second pressure adjustment unit) are provided, and pressure fluctuations are handled with the two pressure adjustment units. In this way, it is possible to suppress pressure fluctuations that cannot be suppressed with only a single pressure adjustment unit. More specifically, the pressure adjustment spring220, the pressing plate210, and the flexible member230, which form each pressure adjustment unit, mechanically absorb the pulsation of the ink generated by the circulation pump500, and therefore suppress propagation of the pulsation of the ink to the ejection module300.

Also, as mentioned earlier, the liquid ejection apparatus50in the present embodiment does not include ink collection systems that collect the inks in the liquid ejection head1into the ink tanks2. Specifically, there are no channels for collecting the liquids from the circulation units54. Thus, each ink supply tube59is the only single channel connected to the corresponding circulation unit54. If collection tubes for collecting the inks into the ink tanks2are provided, there will also be a possibility of propagation of pressure fluctuations to the liquid ejection head1from the collection tube side. In the present embodiment, each ink supply tube59is the only single channel connected to the corresponding circulation unit54. Also, each of the inks supplied to the circulation units54from the ink supply tubes59flows into the first valve chamber121of the first pressure adjustment unit120. Then, the opening and closing of the communication port191are controlled with the valve190. In this way, the pressures generated by the swinging of the tubes with scanning of the liquid ejection head1are prevented from affecting the ejection modules300.

Moreover, as mentioned earlier, the supply of the ink to the liquid ejection head1from each ink tank2is preferably supply by pressurization. The supply by pressurization suppresses the pressure fluctuations. A specific description will be given below. As mentioned earlier, the liquid ejection head1is scanned in the main scanning direction. Thus, the ink supply tubes59, which supply the inks from the ink tanks2to the liquid ejection head1, are swung in the main scanning direction, so that the pressure P1in each ink supply tube59fluctuates. Note that the pressure P1is the pressure in the first valve chamber121, as mentioned earlier, and no pressure adjustment mechanism is provided between the first valve chamber121and the ink supply tube59. Thus, the pressure in the ink supply tube59and the pressure in the first valve chamber121will be considered to be the same here. Also, as described in Equation 2, the pressure P2in the first pressure control chamber122of the first pressure adjustment unit120is proportional to the above-described pressure P1. Moreover, as described in Equation 2, the proportionality constant is determined by the ratio between the pressure reception area S1of the valve190and the pressure reception area S2of the pressing plate210(see alsoFIGS.7A to7C). With supply by pressurization, the ratio of the pressure reception area S1of the valve190to the pressure reception area S2of the pressing plate210can be made small. In this way, the fluctuations in the pressure P2due to fluctuations in the pressure P1are made small.

Specifically, the fluctuations in the pressure P2in the first pressure control chamber122due to the fluctuations in the pressure P1in the ink supply tube59caused by scanning are made small. This suppresses the fluctuations in the pressure in the circulation path.

As described above, according to the present embodiment, it is possible to improve the ejection stability. In other words, it is possible to suppress fluctuations in the pressures in the pressure chambers12and thus achieve stable ejection.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2021-204924, filed Dec. 17, 2021, which is hereby incorporated by reference herein in its entirety.