Patent Description:
Circulation-type liquid ejection apparatuses have been known which circulate a liquid between a liquid ejection head and a liquid storage unit to discharge bubbles in channels and to suppress thickening of an ink in the vicinities of ejection ports. The circulation-type liquid ejection apparatuses include ones which circulate a liquid by using a main body-side pump provided outside a liquid ejection head, and ones which circulate a liquid by using a pump provided inside a liquid ejection head.

<CIT> describes a configuration that circulates a liquid by using a main body-side pump. <CIT> discloses a configuration in which ink ejection nozzles are disposed between two pressure control units which are provided in a liquid ejection head and differ in pressure, to maintain the flow rates of an ink flowing through the ink ejection nozzles.

<CIT> discloses a liquid ejection apparatus in which a piezoelectric circulation pump is mounted in a liquid ejection head to circulate an ink inside the liquid ejection head. In the configuration of <CIT>, the ink supplied to a pressure control mechanism from the circulation pump is then supplied to liquid ejection ports through ink supply channels, and the ink not ejected is collected to the circulation pump through ink collection channels.

With a configuration that circulates a liquid by using a main body-side pump, as in <CIT>, in a case of ejecting the liquid while scanning the liquid ejection head, the liquid ejection head is scanned with two channels (e.g., soft tubes or the like) for supply and collection drawn out of the liquid ejection head to the main body side. As the liquid ejection head is scanned, the two channels are swung, which leads to a possibility of causing pressure fluctuations inside the liquid ejection head. Consequently, the pressures in the liquid ejection nozzles may become unstable.

On the other hand, with a configuration that circulates a liquid by using a pump inside a liquid ejection head, as in <CIT>, the ink circulation completes within the liquid ejection head. For this reason, only a single channel of an ink supply system needs to be drawn out of the liquid ejection head to the main body side. Also, the opening and closing of this channel of the ink supply system are controlled with a valve. Thus, the pressure generated by the swinging of the tube with scanning of the liquid ejection head is prevented from affecting the ink ejection nozzles. Here, in the case where a pump is mounted inside a liquid ejection head, as in <CIT>, the path from the pump to each pressure chamber is short. Accordingly, the liquid circulation path is short. Thus, there is a possibility that the pressure fluctuations inside the liquid ejection head due to pump pulsation may become large. If the pressure fluctuations inside the liquid ejection head become large, it will cause an oscillating movement of the liquid in each pressure chamber. This may result in variations in ejection volume. In other words, there arises a possibility that it may be difficult to implement stable ejection.

<CIT> shows a generic liquid ejection head according to the preamble of claim <NUM> for ejecting a liquid while being scanned in a main scanning direction, comprising: an ejection element configured to generate a pressure for ejecting the liquid in a pressure chamber; a supply channel through which the liquid is supplied to the pressure chamber; and a collection channel connected to the supply channel through the pressure chamber and through which the liquid is collected from the pressure chamber.

Further liquid ejection heads according to the prior art are shown in <CIT>, <CIT> and <CIT>.

It is the object of the present invention to further develop a liquid ejection head according to the preamble of claim <NUM> such that stable ejection of liquid can be provided by the liquid ejection head.

The object of the present invention is achieved by a liquid ejection head having the features of claim <NUM>.

In particular, a liquid ejection apparatus having, inter alia, the liquid ejection head according to the present invention is specified in claim <NUM>.

Further features, advantages and effects of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

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.

<FIG> is 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 apparatus <NUM> in the present embodiment will be described with reference to <FIG> is a perspective view schematically illustrating the liquid ejection apparatus using the liquid ejection head <NUM>. The liquid ejection apparatus <NUM> in 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 head <NUM>.

The liquid ejection head <NUM> is mounted on a carriage <NUM>. The carriage <NUM> reciprocally moves in a main scanning direction (X direction) along a guide shaft <NUM>. 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 rollers <NUM>, <NUM>, <NUM>, and <NUM>. Note that, in drawings to be referred to below, the Z direction represents a vertical direction and crosses (in this example, perpendicularly crosses) a X-Y plane defined by the X direction and the Y direction. The liquid ejection head <NUM> is configured to be attachable to and detachable from the carriage <NUM> by a user.

The liquid ejection head <NUM> includes circulation units <NUM> and a later-described ejection unit <NUM> (see Figs. 2A and 2B). While a specific configuration will be described later, the ejection unit <NUM> includes 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 apparatus <NUM> also includes ink tanks <NUM> serving as ink supply sources and external pumps <NUM>. The inks stored in the ink tanks <NUM> are supplied to the circulation units <NUM> through ink supply tubes <NUM> by driving forces of the external pumps <NUM>.

The liquid ejection apparatus <NUM> forms a predetermined image on the print medium P by repeating a printing scan involving performing printing by causing the liquid ejection head <NUM> mounted on the carriage <NUM> to 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 head <NUM> in 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 head <NUM> are 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 apparatus <NUM>, a cap member (not illustrated) capable of covering the ejection port surface of the liquid ejection head <NUM> in 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 head <NUM> during 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 head <NUM> illustrated in <FIG> represents an example where four circulation units <NUM> corresponding to the four types of inks are included in the liquid ejection head <NUM>, but it suffices that the circulation units <NUM> included correspond to the types of liquids to be ejected. Also, a plurality of circulation units <NUM> may be included for the same type of liquid. In sum, the liquid ejection head <NUM> can have a configuration including one or more circulation units. The liquid ejection head <NUM> may be configured not to circulate all of the four types of inks but only circulate at least one of the inks.

<FIG> is a block diagram illustrating a control system of the liquid ejection apparatus <NUM>. A CPU <NUM> functions as a control unit that controls the operation of each unit of the liquid ejection apparatus <NUM> based on a program such as a process procedure stored in a ROM <NUM>. A RAM <NUM> is used as a work area or the like for the CPU <NUM> to execute processes. The CPU <NUM> receives image data from a host apparatus <NUM> outside the liquid ejection apparatus <NUM> and controls a head driver 1A to control the driving of the ejection elements provided in the ejection unit <NUM>. The CPU <NUM> also controls drivers for various actuators provided in the liquid ejection apparatus. For example, the CPU <NUM> controls a motor driver 105A for a carriage motor <NUM> for moving the carriage <NUM>, a motor driver 104A for a conveyance motor <NUM> for conveying the print medium P, and the like. Moreover, the CPU <NUM> controls a pump driver 500A for later-described circulation pumps <NUM>, a pump driver 21A for the external pumps <NUM>, and the like. Note that <FIG> illustrates a configuration in which the image data is received from the host apparatus <NUM> and processes are performed, but the liquid ejection apparatus <NUM> may perform the processes regardless of whether data is given from the host apparatus <NUM>.

<FIG> is an exploded perspective view and a top view of the liquid ejection head <NUM> in the present embodiment. <FIG> are cross-sectional views of the liquid ejection head <NUM> illustrated in <FIG> along the IIIA-IIIA line. <FIG> is a vertical cross-sectional view of the entire liquid ejection head <NUM>, and <FIG> is an enlarged view of an ejection module illustrated in <FIG>. A basic configuration of the liquid ejection head <NUM> in the present embodiment will be described below with reference mainly to <FIG> and to <FIG> as appropriate.

As illustrated in <FIG>, the liquid ejection head <NUM> includes the circulation units <NUM> and the ejection unit <NUM> for ejecting the inks supplied from the circulation units <NUM> onto the print medium P. The liquid ejection head <NUM> in the present embodiment is fixedly supported on the carriage <NUM> of the liquid ejection apparatus <NUM> by a positioning unit and electric contacts (not illustrated) which are provided to the carriage <NUM>. The liquid ejection head <NUM> performs printing on the print medium P by ejecting the inks while moving along with the carriage <NUM> in the main scanning direction (X direction) illustrated in <FIG>.

The external pumps <NUM> connected to the ink tanks <NUM> serving as ink supply sources include the ink supply tubes <NUM> (see <FIG>). A liquid connector (not illustrated) is provided at the tip of each of these ink supply tubes <NUM>. In the state where the liquid ejection head <NUM> is mounted to the liquid ejection apparatus <NUM>, the liquid connectors which are provided at the tips of the ink supply tubes <NUM> and are inlets through which the liquids are introduced are hermetically connected to liquid connector insertion slots 53a that are provided on a head housing <NUM> of the liquid ejection head <NUM>. As a result, ink supply paths extending from the ink tanks <NUM> to the liquid ejection head <NUM> through the external pumps <NUM> are formed. In the present embodiment, four types of inks are used. Hence, four sets each including an ink tank <NUM>, an external pump <NUM>, an ink supply tube <NUM>, and a circulation unit <NUM> are 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 apparatus <NUM> in the present embodiment includes ink supply systems to which the inks are supplied from the ink tanks <NUM> provided outside the liquid ejection head <NUM>. Note that the liquid ejection apparatus <NUM> in the present embodiment does not include ink collection systems that collect the inks in the liquid ejection head <NUM> into the ink tanks <NUM>. Accordingly, the liquid ejection head <NUM> includes the liquid connector insertion slots 53a to connect the ink supply tubes <NUM> of the ink tanks <NUM> but does not include connector insertion slots to connect tubes for collecting the inks in the liquid ejection head <NUM> into the ink tanks <NUM>. Note that a liquid connector insertion slot 53a is provided for each ink.

In <FIG>, reference signs 54B, 54C, <NUM>, and 54Y 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 unit <NUM>" in the present embodiment unless otherwise distinguished.

In <FIG> and <FIG>, the ejection unit <NUM> includes two ejection modules <NUM>, the first support member <NUM>, the second support member <NUM>, an electric wiring member (electric wiring tape) <NUM>, and an electric contact substrate <NUM>. As illustrated in <FIG>, each ejection module <NUM> includes a silicon substrate <NUM> with a thickness of <NUM> to <NUM> and a plurality of ejection elements <NUM> provided in one surface of the silicon substrate <NUM>. The ejection elements <NUM> in 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 substrate <NUM> by a film forming technique is supplied to each of the ejection elements <NUM>.

Also, a discharge port forming member <NUM> is formed on a surface of the silicon substrate <NUM> (the lower surface in <FIG>). In the discharge port forming member <NUM>, a plurality of pressure chambers <NUM> corresponding to the plurality of ejection elements <NUM> and a plurality of ejection ports <NUM> to eject the inks are formed by a photolithographic technique. Moreover, common supply channels <NUM> and common collection channels <NUM> are formed in the silicon substrate <NUM>. Furthermore, in the silicon substrate <NUM>, there are formed supply connection channels <NUM> through which the common supply channels <NUM> and the pressure chambers <NUM> communicate with one another, and collection connection channels <NUM> through which the common collection channels <NUM> and the pressure chambers <NUM> communicate with one another. In the present embodiment, one ejection module <NUM> is configured to eject two types of inks. Specifically, in the two ejection modules illustrated in <FIG>, the ejection module <NUM> located on the left side in <FIG> ejects the black and cyan inks, and the ejection module <NUM> located on the right side in <FIG> ejects 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 modules <NUM> do not have to eject the same number of types of inks. The configuration may be such that only one ejection module <NUM> is included, or three or more ejection modules <NUM> are included. Moreover, in the example illustrated in <FIG>, two ejection port arrays extending in the Y direction are formed for an ink of one color. A pressure chamber <NUM>, a common supply channel <NUM>, and a common collection channel <NUM> are formed for each of the plurality of ejection ports <NUM> forming each ejection port array.

Later-described ink supply ports and ink collection ports are formed on the back surface (the upper surface in <FIG>) side of the silicon substrate <NUM>. Through the ink supply ports, the inks are supplied into the plurality of common supply channels <NUM> from ink supply channels <NUM>. Through the ink collection ports, the inks are collected into ink collection channels <NUM> from the plurality of common collection channels <NUM>.

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 channels <NUM>, and the inks are collected from the common collection channels <NUM> into 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 channels <NUM>, and the inks are collected from the common supply channels <NUM> into the ink supply ports.

As illustrated in <FIG>, the back surfaces (the upper surfaces in <FIG>) of the ejection modules <NUM> are adhesively fixed to one surface of the first support member <NUM> (the lower surface in <FIG>). The ink supply channels <NUM> and the ink collection channels <NUM>, which penetrate from one surface of the first support member <NUM> to the opposite surface of the first support member <NUM>, are formed in the first support member <NUM>. The openings of the ink supply channels <NUM> on one side communicate with the above-mentioned ink supply ports in the silicon substrate <NUM>. The openings of the ink collection channels <NUM> on the one side communicate with the above-mentioned ink collection ports in the silicon substrate <NUM>. Note that the ink supply channels <NUM> and the ink collection channels <NUM> are provided independently for each type of ink.

Also, the second support member <NUM> having openings 7a (see <FIG>) to insert the ejection modules <NUM> are adhesively fixed to one surface (the lower surface in <FIG>) of the first support member <NUM>. The electric wiring member <NUM> to be electrically connected to the ejection modules <NUM> is held on the second support member <NUM>. The electric wiring member <NUM> is a member for applying electric signals for ink ejection to the ejection modules <NUM>. The electric connection parts of the ejection modules <NUM> and the electric wiring member <NUM> are sealed with a sealant (not illustrated) to be protected from corrosion by the inks and external impacts.

Also, the electric contact substrate <NUM> is joined to an end portion 5a of the electric wiring member <NUM> (see <FIG>) by thermocompression bonding with an anisotropic conductive film (not illustrated), and the electric wiring member <NUM> and the electric contact substrate <NUM> are electrically connected to each other. The electric contact substrate <NUM> has external signal input terminals (not illustrated) for receiving electric signals from the liquid ejection apparatus <NUM>.

Moreover, a joint member <NUM> (<FIG>) is provided between the first support member <NUM> and the circulation units <NUM>. In the joint member <NUM>, a supply port <NUM> and a collection port <NUM> are formed for each type of ink. Through the supply ports <NUM> and the collection ports <NUM>, the ink supply channels <NUM> and the ink collection channels <NUM> in the first support member <NUM> and channels formed in the circulation units <NUM> communicate with each other. Incidentally, in <FIG>, a supply port 88B and a collection port 89B are for the black ink, and a supply port 88C and a collection port 89C are for the cyan ink. Moreover, a supply port <NUM> and a collection port <NUM> are for the magenta ink, and a supply port 88Y and a collection port 89Y are for the yellow ink.

Note that the openings at one end of the ink supply channels <NUM> and the ink collection channels <NUM> in the first support member <NUM> have small opening areas matching the ink supply ports and the ink collection ports in the silicon substrate <NUM>. On the other hand, the openings at the other end of the ink supply channels <NUM> and the ink collection channels <NUM> in the first support member <NUM> have a large shape whose opening area is the same opening area formed in the joint member <NUM> to match the channels in the circulation units <NUM>. 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 channels <NUM> and the ink collection channels <NUM> are not limited to the above example.

In the liquid ejection head <NUM> having the above configuration, the inks supplied to the circulation units <NUM> pass through the supply ports <NUM> in the joint member <NUM> and the ink supply channels <NUM> in the first support member <NUM> and flow into the common supply channels <NUM> from the ink supply ports in the ejection modules <NUM>. Thereafter, the inks flow from the common supply channels <NUM> into the pressure chambers <NUM> through the supply connection channels <NUM>. Part of the inks flowing into the pressure chambers is ejected from the ejection ports <NUM> as the ejection elements <NUM> are driven. The remaining inks not ejected pass through the collection connection channels <NUM> and the common collection channels <NUM> from the pressure chambers <NUM>, and flow from the ink collection ports into the ink collection channels <NUM> in the first support member <NUM>. Then, the inks flowing into the ink collection channels <NUM> flow into the circulation units <NUM> through the collection ports <NUM> in the joint member <NUM> and are collected.

<FIG> is a schematic external view of one circulation unit <NUM> for one type of ink used in a printing apparatus in the present embodiment. A filter <NUM>, the first pressure adjustment unit <NUM>, the second pressure adjustment unit <NUM>, and a circulation pump <NUM> are disposed in the circulation unit <NUM>. As illustrated in <FIG> and <FIG>, these constituent elements are connected by channels to form a circulation path for supplying and collecting the ink to and from the ejection module <NUM> in the liquid ejection head <NUM>.

<FIG> is a vertical cross-sectional view schematically illustrating the circulation path for one type of ink (ink of one color) formed in the liquid ejection head <NUM>. The relative positions of the components in <FIG> (such as the first pressure adjustment unit <NUM>, the second pressure adjustment unit <NUM>, and the circulation pump <NUM>) are simplified for a clearer description of the circulation path. Thus, the relative positions of the components are different from those of the components in <FIG> to be mentioned later. Incidentally, <FIG> is a block diagram schematically illustrating the circulation path illustrated in <FIG>. As illustrated in <FIG> and <FIG>, the first pressure adjustment unit <NUM> includes the first valve chamber <NUM> and the first pressure control chamber <NUM>. The second pressure adjustment unit <NUM> includes the second valve chamber <NUM> and the second pressure control chamber <NUM>. The first pressure adjustment unit <NUM> is configured such that the controlled pressure therein is higher than that in the second pressure adjustment unit <NUM>. In the present embodiment, these two pressure adjustment units <NUM> and <NUM> are 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 chambers <NUM> (ejection elements <NUM>) at a flow rate corresponding to the pressure difference between the first pressure adjustment unit <NUM> and the second pressure adjustment unit <NUM>. A circulation path in the liquid ejection head <NUM> and a flow of the ink in the circulation path will be described below with reference to <FIG> and <FIG>. Note that the arrows in <FIG> and <FIG> indicate the flow direction of the ink.

First, how the constituent elements in the liquid ejection head <NUM> are connected will be described.

The external pump <NUM>, which sends the ink stored in the ink tank <NUM> (<FIG>) disposed outside the liquid ejection head <NUM> to the liquid ejection head <NUM>, is connected to the circulation unit <NUM> through the ink supply tube <NUM> (<FIG>). The filter <NUM> is disposed in the ink channel located on an upstream side of the circulation unit <NUM>. The ink supply path located downstream of the filter <NUM> is connected to the first valve chamber <NUM> of the first pressure adjustment unit <NUM>. The first valve chamber <NUM> communicates with the first pressure control chamber <NUM> through a communication port 191A openable and closable by a valve 190A illustrated in <FIG>.

The first pressure control chamber <NUM> is connected to a supply channel <NUM>, a bypass channel <NUM>, and a pump outlet channel <NUM> of the circulation pump <NUM>. The supply channel <NUM> is connected to the common supply channels <NUM> through the above-mentioned ink supply ports provided in the ejection module <NUM>. Also, the bypass channel <NUM> is connected to the second valve chamber <NUM> provided in the second pressure adjustment unit <NUM>. The second valve chamber <NUM> communicates with the second pressure control chamber <NUM> through a communication port 191B that is opened and closed by a valve 190B illustrated in <FIG>. Note that <FIG> and <FIG> illustrate an example where one end of the bypass channel <NUM> is connected to the first pressure control chamber <NUM> of the first pressure adjustment unit <NUM>, and the other end of the bypass channel <NUM> is connected to the second valve chamber <NUM> of the second pressure adjustment unit <NUM>. However, the one end of the bypass channel <NUM> may be connected to the supply channel <NUM>, and the other end of the bypass channel may be connected to the second valve chamber <NUM>.

The second pressure control chamber <NUM> is connected to a collection channel <NUM>. The collection channel <NUM> is connected to the common collection channels <NUM> through the above-mentioned ink collection ports provided in the ejection module <NUM>. Moreover, the second pressure control chamber <NUM> is connected to the circulation pump <NUM> through a pump inlet channel <NUM>. Note that reference sign 170a in <FIG> denotes an inlet port of the pump inlet channel <NUM>.

Next, the flow of the ink in the liquid ejection head <NUM> having the above configuration will be described. As illustrated in <FIG>, the ink stored in the ink tank <NUM> is pressurized by the external pump <NUM> provided in the liquid ejection apparatus <NUM>, becomes an ink flow at a positive pressure, and is supplied to the circulation unit <NUM> of the liquid ejection head <NUM>.

The ink supplied to the circulation unit <NUM> passes through the filter <NUM> so that foreign substances such as dust and bubbles are removed. The ink then flows into the first valve chamber <NUM> provided in the first pressure adjustment unit <NUM>. The pressure on the ink decreases due to the pressure loss in a case where the ink passes through the filter <NUM>, but the pressure on the ink is still positive at this point. Thereafter, in a case where the valve 190A is open, the ink flowing into the first valve chamber <NUM> passes through the communication port 191A and flows into the first pressure control chamber <NUM>. Due to the pressure loss in a case where the ink passes through the communication port 191A, the pressure on the ink flowing into the first pressure control chamber <NUM> switches from the positive pressure to a negative pressure.

Next, the flow of the ink in the circulation path will be described. The circulation pump <NUM> operates such that the ink sucked from the pump inlet channel <NUM> located upstream of the circulation pump <NUM> is sent to the pump outlet channel <NUM> located downstream of the circulation pump <NUM>. Thus, as the pump is driven, the ink supplied to the first pressure control chamber <NUM> flows into the supply channel <NUM> and the bypass channel <NUM> along with the ink sent from the pump outlet channel <NUM>. 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 channel <NUM> flows from the ink supply ports in the ejection module <NUM> into the pressure chambers <NUM> through the common supply channels <NUM>. Part of the ink is ejected from the ejection ports <NUM> as the ejection elements <NUM> are driven (generate heat). Also, the remaining ink not used in the ejection flows through the pressure chambers <NUM> and passes through the common collection channels <NUM>. Thereafter, the ink flows into the collection channel <NUM> connected to the ejection module <NUM>. The ink flowing into the collection channel <NUM> flows into the second pressure control chamber <NUM> of the second pressure adjustment unit <NUM>.

On the other hand, the ink flowing from the first pressure control chamber <NUM> into the bypass channel <NUM> flows into the second valve chamber <NUM>, passes through the communication port 191B, and then flows into the second pressure control chamber <NUM>. The ink flowing into the second pressure control chamber <NUM> through the bypass channel <NUM> and the ink collected from the collection channel <NUM> are sucked into the circulation pump <NUM> through the pump inlet channel <NUM> as the circulation pump <NUM> is driven. Then, the inks sucked into the circulation pump <NUM> are sent to the pump outlet channel <NUM> and flow into the first pressure control chamber <NUM> again. Thereafter, the ink flowing from the first pressure control chamber <NUM> into the second pressure control chamber <NUM> through the supply channel <NUM> and the ejection module <NUM> and the ink flowing into the second pressure control chamber <NUM> through the bypass channel <NUM> flow into the circulation pump <NUM>. Then, the inks are sent from the circulation pump <NUM> to the first pressure control chamber <NUM>. 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 head <NUM> with the circulation pump <NUM>. 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 modules <NUM>. Accordingly, the excellent fluidity of the inks in the ejection modules <NUM> and 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 head <NUM>. Thus, the length of the circulation paths is significantly short as compared to a case where the inks are circulated between the ink tanks <NUM> disposed outside the liquid ejection head <NUM> and the liquid ejection head <NUM>. 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 head <NUM> and the ink tanks <NUM>. In other words, a configuration that does not require channels for collecting the inks from the liquid ejection head <NUM> into the ink tanks <NUM> is employed. Accordingly, only ink supply tubes connecting between the ink tanks <NUM> and the liquid ejection head <NUM> are needed, and no ink collection tube is required. The inside of the liquid ejection apparatus <NUM> therefore 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 head <NUM>. Also, the swinging of the tubes during main scanning of the liquid ejection head <NUM> increases a driving load on the carriage motor driving the carriage <NUM>. 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 head <NUM>, the external pumps <NUM> can be downsized as well. As described above, according to the present embodiment, it is possible to downsize the liquid ejection apparatus <NUM> and reduce costs.

<FIG> are views illustrating an example of the pressure adjustment units. Configurations and operation of the pressure adjustment units incorporated in the above-described liquid ejection head <NUM> (first pressure adjustment unit <NUM> and second pressure adjustment unit <NUM>) will be described in more detail with reference to <FIG>. Note that the first pressure adjustment unit <NUM> and the second pressure adjustment unit <NUM> have substantially the same configuration. Thus, the following description will be given by taking the first pressure adjustment unit <NUM> as an example. As for the second pressure adjustment unit <NUM>, only the reference signs of its portions corresponding to those of the first pressure adjustment unit are presented in <FIG>. In a case of the second pressure adjustment unit <NUM>, the first valve chamber <NUM> and the first pressure control chamber <NUM> described below should be read as the second valve chamber <NUM> and the second pressure control chamber <NUM>, respectively.

The first pressure adjustment unit <NUM> has the first valve chamber <NUM> and the first pressure control chamber <NUM> formed in a cylindrical housing <NUM>. The first valve chamber <NUM> and the first pressure control chamber <NUM> are separated by a partition <NUM> provided inside the cylindrical housing <NUM>. However, the first valve chamber <NUM> communicates with the first pressure control chamber <NUM> through a communication port <NUM> formed in the partition <NUM>. A valve <NUM>, which switches between allowing communication between the first valve chamber <NUM> and the first pressure control chamber <NUM> through the communication port <NUM> and blocking the communication, is provided in the first valve chamber <NUM>. The valve <NUM> is held by a valve spring <NUM> at a position opposite to the communication port <NUM>, and has a tight contact configuration to the partition <NUM> by a biasing force from the valve spring <NUM>. The valve <NUM> blocks the ink flow through the communication port <NUM> by being in tight contact with the partition <NUM>. Note that the portion of the valve <NUM> to be in contact with the partition <NUM> is preferably formed of an elastic member in order to enhance the tightness of the contact with the partition <NUM>. Also, a valve shaft 190a to be inserted through the communication port <NUM> is provided in a protruding manner on a center portion of the valve <NUM>. By pressing this valve shaft 190a against the biasing force from the valve spring <NUM>, the valve <NUM> gets separated from the partition <NUM>, thereby allowing the ink to flow through the communication port <NUM>. In the following, the state where the valve <NUM> blocks the ink flow through the communication port <NUM> will be referred to as "closed state", and the state where the ink can flow through the communication port <NUM> will be referred to as "open state".

The opening portion of the cylindrical housing <NUM> is closed by a flexible member <NUM> and a pressing plate <NUM>. These flexible member <NUM> and pressing plate <NUM>, the peripheral wall of the housing <NUM>, and the partition <NUM> form the first pressure control chamber <NUM>. The pressing plate <NUM> is configured to be displaceable with displacement of the flexible member <NUM>. While the materials of the pressing plate <NUM> and the flexible member <NUM> are not particularly limited, for example, the pressing plate <NUM> can be made as a molded resin component, and the flexible member <NUM> can be made from a resin film. In this case, the pressing plate <NUM> can be fixed to the flexible member <NUM> by thermal welding.

A pressure adjustment spring <NUM> (biasing member) is provided between the pressing plate <NUM> and the partition <NUM>. As illustrated in <FIG>, the pressing plate <NUM> and the flexible member <NUM> are biased by a biasing force from the pressure adjustment spring <NUM> in a direction in which the inner volume of the first pressure control chamber <NUM> increases. Also, as the pressure in the first pressure control chamber <NUM> decreases, the pressing plate <NUM> and the flexible member <NUM> get displaced against the pressure from the pressure adjustment spring <NUM> in the direction in which the inner volume of the first pressure control chamber <NUM> decreases. Then, in a case where the inner volume of the first pressure control chamber <NUM> decreases to a certain volume, the pressing plate <NUM> abuts the valve shaft 190a of the valve <NUM>. As the inner volume of the first pressure control chamber <NUM> then decreases further, the valve <NUM> moves with the valve shaft 190a against the biasing force from the valve spring <NUM>, thereby being separated from the partition <NUM>. As a result, the communication port <NUM> shifts to the open state (the state of <FIG>).

In the present embodiment, the connections in the circulation path are set such that the pressure in the first valve chamber <NUM> in a case where the communication port <NUM> shifts to the open state is higher than the pressure in the first pressure control chamber <NUM>. In this way, in a case where the communication port <NUM> shifts to the open state, the ink flows from the first valve chamber <NUM> into the first pressure control chamber <NUM>. The inflow of the ink displaces the flexible member <NUM> and the pressing plate <NUM> in the direction in which the inner volume of the first pressure control chamber <NUM> increases. As a result, the pressing plate <NUM> gets separated from the valve shaft 190a of the valve <NUM>, and the valve <NUM> is brought into tight contact with the partition <NUM> by the biasing force from the valve spring <NUM> so that the communication port <NUM> shifts to the closed state (the state of <FIG>).

As described above, in the first pressure adjustment unit <NUM> in the present embodiment, in a case where the pressure in the first pressure control chamber <NUM> decreases to a certain pressure or less (e.g., in a case where the negative pressure becomes strong), the ink flows from the first valve chamber <NUM> through the communication port <NUM>. This configuration limits the pressure in the first pressure control chamber <NUM> from decreasing any further. Accordingly, the pressure in the first pressure control chamber <NUM> is controlled to be maintained within a certain range. In other words, it can be said that the first pressure adjustment unit <NUM> adjusts the pressure in the supply channel <NUM> since the first pressure control chamber <NUM> is connected to the supply channel <NUM>.

Next, the pressure in the first pressure control chamber <NUM> will be described in more detail.

Consider a state where the flexible member <NUM> and the pressing plate <NUM> are displaced according to the pressure in the first pressure control chamber <NUM> as described above so that the pressing plate <NUM> abuts the valve shaft 190a and brings the communication port <NUM> into the open state (the state of <FIG>). The relation between the forces acting on the pressing plate <NUM> at this time is represented by Equation <NUM> below.

Moreover, Equation <NUM> is summarized for P2 as below.

Here, as for the spring force F1 of the valve spring <NUM> and the spring force F2 of the pressure adjustment spring <NUM>, the direction in which they push the valve <NUM> and the pressing plate <NUM> is defined as the forward direction (the leftward direction in <FIG>). Also, the configuration is such that the pressure P1 in the first valve chamber <NUM> and the pressure P2 in the first pressure control chamber <NUM> satisfy a relation of P1 ≥ P2.

The pressure P2 in the first pressure control chamber <NUM> when the communication port <NUM> shifts to the open state is determined by Equation <NUM> and, since the configuration is such that the relation of P1 ≥ P2 is satisfied, the ink flows into the first pressure control chamber <NUM> from the first valve chamber <NUM> when the communication port <NUM> shifts to the open state. As a result, the pressure P2 in the first pressure control chamber <NUM> does not decrease any further, and the pressure P2 is kept at a pressure within a certain range.

On the other hand, as illustrated in <FIG>, the relation between the forces acting on the pressing plate <NUM> in a case where the pressing plate <NUM> does not abut on the valve shaft 190a and the communication port <NUM> shifts to the closed state is represented by Equation <NUM> below.

Here, Equation <NUM> is summarized for P3 as below.

Here, <FIG> illustrates a state where the pressing plate <NUM> and the flexible member <NUM> are displaced in the leftward direction in <FIG> up to the limit to which they can be displaced. The pressure P3 in the first pressure control chamber <NUM>, the spring force F3 of the pressure adjustment spring <NUM>, and the pressure reception area S3 of the pressing plate <NUM> change depending on the amount of displacement of the pressing plate <NUM> and the flexible member <NUM> in displacement to the state of <FIG>. Specifically, in a case where the pressing plate <NUM> and the flexible member <NUM> are situated on the right side in <FIG> relative to themselves in <FIG>, the pressure reception area S3 of the pressing plate <NUM> is smaller and the spring force F3 of the pressure adjustment spring <NUM> is larger. Accordingly, the pressure P3 in the first pressure control chamber <NUM> is smaller in accordance with the relation in Equation <NUM>. Thus, with Equations <NUM> and <NUM>, the pressure in the first pressure control chamber <NUM> gradually increases (that is, the negative pressure weakens toward a value close to the positive pressure side) in shifting from the state of <FIG> to the state of <FIG>. Specifically, the pressure in the first pressure control chamber <NUM> gradually increases while the pressing plate <NUM> and the flexible member <NUM> are gradually displaced in the leftward direction from the state where the communication port <NUM> is in the open state to the state where the inner volume of the first pressure control chamber reaches the limit to which the pressing plate <NUM> and the flexible member <NUM> can be displaced. In other words, the negative pressure weakens.

Next, a configuration and operation of each circulation pump <NUM> incorporated in the above liquid ejection head <NUM> will be described in detail with reference to <FIG> and <FIG>.

<FIG> are external perspective views of the circulation pump <NUM>. <FIG> is an external perspective view illustrating the front side of the circulation pump <NUM>, and <FIG> is an external perspective view illustrating the back side of the circulation pump <NUM>. An outer shell of the circulation pump <NUM> includes a pump housing <NUM> and a cover <NUM> fixed to the pump housing <NUM>. The pump housing <NUM> includes a housing-part main body 505a and a channel connection member 505b adhesively fixed to the outer surface of the housing-part main body 505a. In each of the housing-part main body 505a and the channel connection member 505b, 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 hole <NUM>. The other of the pair of through-holes provided at the other position forms a pump discharge hole <NUM>. The pump supply hole <NUM> is connected to the pump inlet channel <NUM> connected to the second pressure control chamber <NUM>. The pump discharge hole <NUM> is connected to the pump outlet channel <NUM> connected to the first pressure control chamber <NUM>. The ink supplied from the pump supply hole <NUM> passes through a later-described pump chamber <NUM> (see <FIG>) and is discharged from the pump discharge hole <NUM>.

<FIG> is a cross-sectional view of the circulation pump <NUM> illustrated in <FIG> along the IX-IX line. A diaphragm <NUM> is joined to the inner surface of the pump housing <NUM>, and the pump chamber <NUM> is formed between this diaphragm <NUM> and a recess formed in the inner surface of the pump housing <NUM>. The pump chamber <NUM> communicates with the pump supply hole <NUM> and the pump discharge hole <NUM>, which are formed in the pump housing <NUM>. Also, a check valve 504a is provided at an intermediate portion of the pump supply hole <NUM>. A check valve 504b is provided at an intermediate portion of the pump discharge hole <NUM>. Specifically, the check valve 504a is disposed such that a part thereof is movable in the leftward direction in <FIG> within a space 512a formed at an intermediate portion of the pump supply hole <NUM>. The check valve 504a is disposed such that a part thereof is movable in the rightward direction in <FIG> within a space 512b formed at an intermediate portion of the pump discharge hole <NUM>.

As the diaphragm <NUM> is displaced so as to increase the volume of the pump chamber <NUM>, the pump chamber <NUM> is depressurized. In response to this displacement, the check valve 504a is separated from the opening of the pump supply hole <NUM> in the space 512a (that is, moves in the leftward direction in <FIG>). By being separated from the opening of the pump supply hole <NUM> in the space 512a, the check valve 504a shifts to an open state in which the ink is allowed to flow through the pump supply hole <NUM>. As the diaphragm <NUM> is displaced so as to reduce the volume of the pump chamber <NUM>, the pump chamber <NUM> is pressurized. In response to this displacement, the check valve 504a comes into tight contact with the wall surface around the opening of the pump supply hole <NUM>. The check valve 504a is thus in a closed state in which the check valve 504a blocks the ink flow through the pump supply hole <NUM>.

The check valve 504b, on the other hand, comes into tight contact with the wall surface around an opening in the pump housing <NUM> as the pump chamber <NUM> is depressurized, thereby shifting to a closed state in which the check valve 504b blocks the ink flow through the pump discharge hole <NUM>. Also, as the pump chamber <NUM> is pressurized, the check valve 504b is separated from the opening in the pump housing <NUM> and moves toward the space 512b (that is, moves in the rightward direction in <FIG>), thereby allowing the ink to flow through the pump discharge hole <NUM>.

Note that the material of each of the check valves 504a and 504b only needs to be one that is deformable according to the pressure in the pump chamber <NUM>. For example, the material of each of the check valves 504a and 504b can 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 chamber <NUM> is formed by joining the pump housing <NUM> and the diaphragm <NUM>. Thus, the pressure in the pump chamber <NUM> changes as the diaphragm <NUM> is deformed. For example, in a case where the diaphragm <NUM> is displaced toward the pump housing <NUM> (displaced toward the right side in <FIG>), thereby reducing the volume of the pump chamber <NUM>, the pressure in the pump chamber <NUM> increases. As a result, the check valve 504b disposed so as to face the pump discharge hole <NUM> shifts to the open state so that the ink in the pump chamber <NUM> is discharged. At this time, the check valve 504a disposed so as to face the pump supply hole <NUM> is in tight contact with the wall surface around the pump supply hole <NUM>, thereby suppressing backflow of the ink from the pump chamber <NUM> into the pump supply hole <NUM>.

Conversely, in a case where the diaphragm <NUM> is displaced in the direction in which the pump chamber <NUM> widens, the pressure in the pump chamber <NUM> decreases. As a result, the check valve 504a disposed so as to face the pump supply hole <NUM> shifts to the open state so that the ink is supplied into the pump chamber <NUM>. At this time, the check valve 504b disposed in the pump discharge hole <NUM> comes into tight contact with the wall surface around an opening formed in the pump housing <NUM> to close this opening. This suppresses backflow of the ink from the pump discharge hole <NUM> into the pump chamber <NUM>.

As described above, in the circulation pump <NUM>, the ink is sucked and discharged as the diaphragm <NUM> is deformed and thereby changes the pressure in the pump chamber <NUM>. At this time, in a case where bubbles have entered the pump chamber <NUM>, the displacement of the diaphragm <NUM> changes the pressure in the pump chamber <NUM> to 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 chamber <NUM> is disposed in parallel with gravity so that the bubbles having entered the pump chamber <NUM> can easily gather in an upper portion of the pump chamber <NUM>. In addition, the pump discharge hole <NUM> is disposed higher than the center of the pump chamber <NUM>. This improves the ease of discharge of bubbles in the pump and thus stabilizes the flow rate.

<FIG> are diagrams describing a flow of an ink inside the liquid ejection head. The circulation of the ink performed inside the liquid ejection head <NUM> will be described with reference to <FIG>. The relative positions of the components in <FIG> such as the first pressure adjustment unit <NUM>, the second pressure adjustment unit <NUM>, and the circulation pump <NUM> are simplified for a clearer description of the ink circulation path. Thus, the relative positions of the components are different from those of the components in <FIG> to be mentioned later. <FIG> schematically illustrates the flow of the ink in a case of performing a print operation of performing printing by ejecting the ink from the ejection ports <NUM>. Note that the arrows in <FIG> indicate the flow of the ink. In the present embodiment, to perform a print operation, both the external pump <NUM> and the circulation pump <NUM> start being driven. Incidentally, the external pump <NUM> and the circulation pump <NUM> may be driven regardless of whether a print operation is to be performed or not. The external pump <NUM> and the circulation pump <NUM> do not have to be driven in conjunction with each other, and may be driven independently of each other.

During the print operation, the circulation pump <NUM> is in an ON state (driven state) so that the ink flowing out of the first pressure control chamber <NUM> flows into the supply channel <NUM> and the bypass channel <NUM>. The ink having flowed into the supply channel <NUM> passes through the ejection module <NUM> and then flows into the collection channel <NUM>. Thereafter, the ink is supplied into the second pressure control chamber <NUM>.

On the other hand, the ink flowed into the bypass channel <NUM> from the first pressure control chamber <NUM> flows into the second pressure control chamber <NUM> through the second valve chamber <NUM>. The ink flowed into the second pressure control chamber <NUM> passes through the pump inlet channel <NUM>, the circulation pump <NUM>, and the pump outlet channel <NUM> and then flows into the first pressure control chamber <NUM> again. At this time, based on the relation in Equation <NUM> mentioned above, the controlled pressure in the first valve chamber <NUM> is set higher than the controlled pressure in the first pressure control chamber <NUM>. Thus, the ink in the first pressure control chamber <NUM> does not flow into the first valve chamber <NUM> but is supplied to the ejection module <NUM> again through the supply channel <NUM>. The ink flowed into the ejection module <NUM> flows into the first pressure control chamber <NUM> again through the collection channel <NUM>, the second pressure control chamber <NUM>, the pump inlet channel <NUM>, the circulation pump <NUM>, and the pump outlet channel <NUM>. Ink circulation that completes within the liquid ejection head <NUM> is performed as described above.

In the above ink circulation, the differential pressure between the controlled pressure in the first pressure control chamber <NUM> and the controlled pressure in the second pressure control chamber <NUM> determines the amount of circulation (flow rate) of the ink within the ejection module <NUM>. 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 module <NUM>. Incidentally, the amount of the ink consumed by the printing is supplied from the ink tank <NUM> to the first pressure control chamber <NUM> through the filter <NUM> and the first valve chamber <NUM>. 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 chamber <NUM> decreases, resulting in decreasing the ink in the first pressure control chamber. As the ink in the first pressure control chamber <NUM> decreases, the inner volume of the first pressure control chamber <NUM> decreases accordingly. As this inner volume of the first pressure control chamber <NUM> decreases, the communication port 191A shifts to the open state so that the ink is supplied from the first valve chamber <NUM> to the first pressure control chamber <NUM>. A pressure loss occurs in this supplied ink as this ink supplied from the first valve chamber <NUM> passes through the communication port 191A. As the ink flows into the first pressure control chamber <NUM>, the positive pressure on the ink switches to a negative pressure. As the ink flows from the first valve chamber <NUM> into the first pressure control chamber <NUM>, the pressure in the first pressure control chamber increases. The communication port 191A shifts to the closed state when the inner volume of the first pressure control chamber increases. As described above, the communication port 191A repetitively switches between the open state and the closed state according to the ink consumption. Incidentally, the communication port 191A is kept in the closed state in a case where the ink is not consumed.

<FIG> schematically illustrates the flow of the ink immediately after the print operation is finished and the circulation pump <NUM> shifts to an OFF state (stop state). At the point when the print operation is finished and the circulation pump <NUM> shifts to the OFF state, the pressure in the first pressure control chamber <NUM> and the pressure in the second pressure control chamber <NUM> are both the controlled pressures used in the print operation. For this reason, the ink moves as illustrated in <FIG> according to the differential pressure between the pressure in the first pressure control chamber <NUM> and the pressure in the second pressure control chamber <NUM>. Specifically, the ink flow from the first pressure control chamber <NUM> to the ejection module <NUM> through the supply channel <NUM> and then to the second pressure control chamber <NUM> through the collection channel <NUM> continues to be generated. Moreover, the ink flow from the first pressure control chamber <NUM> to the second pressure control chamber <NUM> through the bypass channel <NUM> and the second valve chamber <NUM> continues to be generated.

The amount of the ink moved from the first pressure control chamber <NUM> to the second pressure control chamber <NUM> by these ink flows is supplied from the ink tank <NUM> to the first pressure control chamber <NUM> through the filter <NUM> and the first valve chamber <NUM>. Accordingly, the inner volume of the first pressure control chamber <NUM> is maintained constant. According to the relation in Equation <NUM> mentioned above, the spring force F1 of the valve spring <NUM>, the spring force F2 of the pressure adjustment spring <NUM>, the pressure reception area S1 of the valve <NUM>, and the pressure reception area S2 of the pressing plate <NUM> are maintained constant in a case where the inner volume of the first pressure control chamber <NUM> is constant. Thus, the pressure in the first pressure control chamber <NUM> is determined depending on the change of the pressure (gauge pressure) P1 in the first valve chamber <NUM>. In this way, in a case where the pressure P1 in the first valve chamber <NUM> does not change, the pressure P2 in the first pressure control chamber <NUM> is maintained at the same pressure as the controlled pressure in the print operation.

On the other hand, the pressure in the second pressure control chamber <NUM> changes with time according to the change in inner volume by the inflow of the ink from the first pressure control chamber <NUM>. Specifically, the pressure in the second pressure control chamber <NUM> changes according to Equation <NUM> until the communication port <NUM> shifts from the state of <FIG> to the closed state to allow no communication between the second valve chamber <NUM> and the second pressure control chamber <NUM> as illustrated in <FIG>. Thereafter, the pressing plate <NUM> dose not abut on the valve shaft 190a so that the communication port <NUM> shifts to the closed state. Then, as illustrated in <FIG>, the ink flows from the collection channel <NUM> into the second pressure control chamber <NUM>. This inflow of the ink displaces the pressing plate <NUM> and the flexible member <NUM>. The pressure in the second pressure control chamber <NUM> changes according to Equation <NUM>. Specifically, the pressure increases until the inner volume of the second pressure control chamber <NUM> reaches the maximum.

Note that, once the state of <FIG> is reached, there is no more ink flow from the first pressure control chamber <NUM> into the second pressure control chamber <NUM> through the bypass channel <NUM> and the second valve chamber <NUM>. Thus, the ink flow to the second pressure control chamber <NUM> through the collection channel <NUM> is only generated after the ink in the first pressure control chamber <NUM> is supplied to the ejection module <NUM> through the supply channel <NUM>. As mentioned above, the ink moves from the first pressure control chamber <NUM> to the second pressure control chamber <NUM> according to the differential pressure between the pressure in the first pressure control chamber <NUM> and the pressure in the second pressure control chamber <NUM>. Thus, in a case where the pressure in the second pressure control chamber <NUM> becomes equal to the pressure in the first pressure control chamber <NUM>, the ink stops moving.

Also, in the state where the pressure in the second pressure control chamber <NUM> is equal to the pressure in the first pressure control chamber <NUM>, the second pressure control chamber <NUM> expands to the state illustrated in <FIG>. In a case where the second pressure control chamber <NUM> expands as illustrated in <FIG>, a reservoir portion capable of holding the ink is formed in the second pressure control chamber <NUM>. Note that the transition to the state of <FIG> after stopping the circulation pump <NUM> takes about <NUM> minute to <NUM> minutes. The time may vary depending on the shapes and sizes of the channels and properties of the ink. As the circulation pump <NUM> is driven in the state where the ink is held in the reservoir portion as illustrated in <FIG>, the ink in the reservoir portion is supplied to the first pressure control chamber <NUM> by the circulation pump <NUM>. Accordingly, as illustrated in <FIG>, the amount of the ink in the first pressure control chamber <NUM> increases so that the flexible member <NUM> and the pressing plate <NUM> are displaced in the expanding direction. Then, as the circulation pump <NUM> continues to be driven, the state inside the circulation path changes to the state illustrated in <FIG>.

Note that, in the above description, <FIG> has 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 in <FIG> in response to the driving and stopping of the circulation pump <NUM>.

Also, as described above, in the present embodiment, an example in which the communication port 191B in the second pressure adjustment unit <NUM> shifts to the open state in a case where the ink is circulated by driving the circulation pump <NUM>, 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 port 191B in the second pressure adjustment unit <NUM> is in the closed state even in a case where the ink is circulated by driving the circulation pump <NUM>. This will be specifically described below along with the function of the bypass channel <NUM>.

The bypass channel <NUM> connecting between the first pressure adjustment unit <NUM> and the second pressure adjustment unit <NUM> is provided in order that the ejection module <NUM> can 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 channel <NUM> is also provided in order to supply the ink to the pressure chambers <NUM> from both the supply channel <NUM> and the collection channel <NUM>.

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 module <NUM> by providing the bypass channel <NUM>. 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 pump <NUM> driven at a constant driving amount increases, and the flow rate through the ejection module <NUM> increases. Here, the ejection module <NUM> is kept at a constant temperature by a temperature adjustment mechanism (not illustrated). Hence, the viscosity of the ink inside the ejection module <NUM> is maintained constant even if the environmental temperature changes. The viscosity of the ink inside the ejection module <NUM> remains unchanged whereas the flow rate of the ink flowing through the ejection module <NUM> increases, and therefore the negative pressure in the ejection module <NUM> becomes accordingly stronger due to flow resistance. If the negative pressure in the ejection module <NUM> becomes stronger than the preset value as described above, there is a possibility that the menisci in the ejection ports <NUM> may 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 chambers <NUM> may become stronger than a predetermined level and affect the ejection.

For these reasons, in the present embodiment, the bypass channel <NUM> is formed in the circulation path. By providing the bypass channel <NUM>, the ink flows through the bypass channel <NUM> in a case where the negative pressure is stronger than the preset value. Thus, the pressure in the ejection module <NUM> is kept constant. Thus, for example, the controlled pressure may be set such that the communication port 191B in the second pressure adjustment unit <NUM> is maintained in the closed state even in a case where the circulation pump <NUM> is driven. Moreover, the controlled pressure in the second pressure adjustment unit <NUM> may be set such that the communication port 191B in the second pressure adjustment unit <NUM> shifts to the open state in a case where the negative pressure becomes stronger than the preset value. In other words, the communication port 191B may be in the closed state in a case where the circulation pump <NUM> is 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 channel <NUM> is provided in order to supply the ink to the pressure chambers <NUM> from both the supply channel <NUM> and the collection channel <NUM>. The pressure in the circulation path may fluctuate due to the ejection operations of the ejection elements <NUM>. 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 chambers <NUM> is supplied from both the supply channel <NUM> side and the collection channel <NUM> side 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 <NUM> dpi grid cell is printed with a single <NUM> pl ink droplet will be considered <NUM>%. "High-duty printing" is, for example, printing performed at a duty of <NUM>%.

In a case of continuing high-duty printing, the amount of the ink flowing from the pressure chambers <NUM> into the second pressure control chamber <NUM> through the collection channel <NUM> decreases. On the other hand, the circulation pump <NUM> causes 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 chamber <NUM>. Consequently, the ink inside the second pressure control chamber <NUM> decreases and the negative pressure in the second pressure control chamber <NUM> becomes stronger so that the second pressure control chamber <NUM> shrinks. As the negative pressure in the second pressure control chamber <NUM> becomes stronger, the amount of inflow of the ink into the second pressure control chamber <NUM> through the bypass channel <NUM> increases, and the second pressure control chamber <NUM> becomes stable in the state where the outflow and the inflow are balanced. Thus, the negative pressure in the second pressure control chamber <NUM> becomes stronger according to the duty. Also, as mentioned above, under the configuration in which the communication port 191B is in the closed state in a case where the circulation pump <NUM> is driven, the communication port 191B shifts to the open state depending on the duty so that the ink flows from the bypass channel <NUM> into the second pressure control chamber <NUM>.

Moreover, as high-duty printing is continued further, the amount of inflow into the second pressure control chamber <NUM> from the pressure chambers <NUM> through the collection channel <NUM> decreases and conversely the amount of inflow into the second pressure control chamber <NUM> from the communication port 191B through the bypass channel <NUM> increases. As this state progresses further, the amount of the ink flowing into the second pressure control chamber <NUM> from the pressure chambers <NUM> through the collection channel <NUM> reaches zero so that the ink flowing from the communication port 191B is the entire ink flowing out into the circulation pump <NUM>. As this state progresses further, the ink backs up from the second pressure control chamber <NUM> into the pressure chambers <NUM> through the collection channel <NUM>. In this state, the ink flowing from the second pressure control chamber <NUM> into the circulation pump <NUM> and the ink flowing from the second pressure control chamber <NUM> into the pressure chambers <NUM> will flow from the communication port 191B into the second pressure control chamber <NUM> through the bypass channel <NUM>. In this case, the ink from the supply channel <NUM> and the ink from the collection channel <NUM> are filled into the pressure chambers <NUM> and 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 channel <NUM>. Also, as described above, an example has been described in which the communication port 191B 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 port 191B 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 channel <NUM>.

<FIG> are schematic views illustrating a circulation path for an ink of one color in the ejection unit <NUM> in the present embodiment. <FIG> is an exploded perspective view of the ejection unit <NUM> as seen from the first support member <NUM> side. <FIG> is an exploded perspective view of the ejection unit <NUM> as seen from the ejection module <NUM> side. Note that the arrows denoted as "IN" and "OUT" in <FIG> indicate the ink flow, and the ink flow will be described only for one color, but the inks of the other colors flow similarly. Moreover, in <FIG>, illustration of the second support member <NUM> and the electric wiring member <NUM> is 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 member <NUM> in <FIG>, a cross section along the line XI-XI in <FIG> is illustrated. Each ejection module <NUM> includes an ejection element substrate <NUM> and an opening plate <NUM>. <FIG> is a view illustrating the opening plate <NUM>. <FIG> is a view illustrating the ejection element substrate <NUM>.

The ejection unit <NUM> is supplied with an ink from each circulation unit <NUM> through the joint member <NUM> (see <FIG>). An ink path for an ink to return to the joint member <NUM> after passing the joint member <NUM> will now be described. Note that illustration of the joint member <NUM> is omitted in drawings to be mentioned below.

Each ejection module <NUM> includes the ejection element substrate <NUM> and the opening plate <NUM>, which are the silicon substrate <NUM>, and further includes the discharge port forming member <NUM>. The ejection element substrate <NUM>, the opening plate <NUM>, and the discharge port forming member <NUM> form the ejection module <NUM> by being stacked and joined such that each ink's channels communicate with each other. The ejection module <NUM> is supported on the first support member <NUM>. The ejection unit <NUM> is formed by supporting each ejection module <NUM> on the first support member <NUM>. The ejection element substrate <NUM> includes the discharge port forming member <NUM>, and the discharge port forming member <NUM> includes a plurality of ejection port arrays each being a plurality of ejection ports <NUM> forming a line. Part of the ink supplied through ink channels in the ejection module <NUM> is ejected from the ejection ports <NUM>. The ink not ejected is collected through ink channels in the ejection module <NUM>.

As illustrated in <FIG> and <FIG>, the opening plate <NUM> includes a plurality of arrayed ink supply ports <NUM> and a plurality of arrayed ink collection ports <NUM>. As illustrated in <FIG> and <FIG>, the ejection element substrate <NUM> includes a plurality of arrayed supply connection channels <NUM> and a plurality of arrayed collection connection channels <NUM>. The ejection element substrate <NUM> further includes the common supply channels <NUM> communicating with the plurality of supply connection channels <NUM> and the common collection channels <NUM> communicating with the plurality of collection connection channels <NUM>. The ink supply channels <NUM> and the ink collection channels <NUM> (see <FIG>) disposed in the first support member <NUM> and the channels disposed in each ejection module <NUM> communicate with each other to form the ink channels inside the ejection unit <NUM>. Support member supply ports <NUM> are openings in cross section forming the ink supply channels <NUM>. Support member collection ports <NUM> are openings in cross section forming the ink collection channels <NUM>.

The ink to be supplied to the ejection unit <NUM> is supplied from the circulation unit <NUM> (see <FIG>) side to the ink supply channels <NUM> (see <FIG>) in the first support member <NUM>. The ink flowed through the support member supply ports <NUM> in the ink supply channels <NUM> is supplied to the common supply channels <NUM> in the ejection element substrate <NUM> through the ink supply channels <NUM> (see <FIG>) and the ink supply ports <NUM> in the opening plate <NUM>, and enters the supply connection channels <NUM>. The channels up to this point are the supply-side channels. Thereafter, the ink passes through the pressure chambers <NUM> (see <FIG>) in the discharge port forming member <NUM> and flows into the collection connection channels <NUM> of the collection-side channels. Details of the ink flow in the pressure chambers <NUM> will be described below.

In the collection-side channels, the ink entered the collection connection channels <NUM> flows into the common collection channels <NUM>. Thereafter, the ink flows from the common collection channels <NUM> into the ink collection channels <NUM> in the first support member <NUM> through the ink collection ports <NUM> in the opening plate <NUM>, and is collected into the circulation unit <NUM> through the support member collection ports <NUM>.

Regions of the opening plate <NUM> where the ink supply ports <NUM> or the ink collection ports <NUM> are not present correspond to regions of the first support member <NUM> for separating the support member supply ports <NUM> and the support member collection ports <NUM>. Also, the first support member <NUM> does not have openings at these regions. Such regions are used as bonding regions in a case of bonding the ejection module <NUM> and the first support member <NUM>.

In <FIG>, a plurality of arrays of openings arranged along the X direction are provided side by side in the Y direction in the opening plate <NUM>, 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. In <FIG>, in the ejection element substrate <NUM>, the common supply channels <NUM> communicating with the plurality of supply connection channels <NUM> arrayed in the Y direction and the common collection channels <NUM> communicating with the plurality of collection connection channels <NUM> arrayed in the Y direction are arrayed alternately in the X direction. The common supply channels <NUM> and the common collection channels <NUM> are separated by the ink type. Moreover, the number of ejection port arrays for each color determines the numbers of common supply channels <NUM> and common collection channels <NUM> to be disposed. Also, the number of the disposed supply connection channels <NUM> and the number of the disposed collection connection channels <NUM> corresponds to the number of ejection ports <NUM>. Note that a one-to-one correspondence is not necessarily essential, and a single supply connection channel <NUM> and a single collection connection channel <NUM> may correspond to a plurality of ejection ports <NUM>.

Each ejection module <NUM> is formed by stacking and joining the opening plate <NUM> and the ejection element substrate <NUM> as above such that each ink's channels communicate with each other, and is supported on the first support member <NUM>. As a result, ink channels including the supply channels and the collection channels as above are formed.

<FIG> are cross-sectional views illustrating ink flows at different portions of the ejection unit <NUM>. <FIG> is a cross section taken along the line XIVA-XIVA in <FIG>, and illustrates a cross section of a portion of the ejection unit <NUM> where ink supply channels <NUM> and ink supply ports <NUM> communicate with each other. <FIG> is a cross section taken along the line XIVB-XIVB in <FIG>, and illustrates a cross section of a portion of the ejection unit <NUM> where ink collection channels <NUM> and ink collection ports <NUM> communicate with each other. Also, <FIG> is a cross section taken along the line XIVC-XIVC in <FIG>, and illustrates a cross section of a portion where the ink supply ports <NUM> and the ink collection ports <NUM> do not communicate with channels in the first support member <NUM>.

As illustrated in <FIG>, the supply channels for supplying the inks supply the inks from the portions where the ink supply channels <NUM> in the first support member <NUM> and the ink supply ports <NUM> in the opening plate <NUM> overlap and communicate with each other. Moreover, as illustrated in <FIG>, the collection channels for collecting the inks collect the inks from the portions where the ink collection channels <NUM> in the first support member <NUM> and the ink collection ports <NUM> in the opening plate <NUM> overlap and communicate with each other. Furthermore, as illustrated in <FIG>, the ejection unit <NUM> locally has regions where no opening is provided in the opening plate <NUM>. At such regions, the inks are neither supplied or collected between the ejection element substrate <NUM> and the first support member <NUM>. The inks are supplied at the regions where the ink supply ports <NUM> are provided, as illustrated in <FIG>. The inks are collected at regions where the ink collection ports <NUM> are provided, as illustrated in <FIG>. Note that the present embodiment has been described by taking the configuration using the opening plate <NUM> as an example, but a configuration not using the opening plate <NUM> may be employed. For example, the configuration in which channels corresponding to the ink supply channels <NUM> and the ink collection channels <NUM> are formed in the first support member <NUM>, and the ejection element substrate <NUM> is joined to the first support member <NUM> may be employed.

<FIG> are cross-sectional views illustrating the vicinity of an ejection port <NUM> in an ejection module <NUM>. <FIG> are cross-sectional views illustrating an ejection module having a configuration as a comparative example in which the common supply channels <NUM> and the common collection channels <NUM> are widened in the X direction. Note that the bold arrows illustrated in the common supply channel <NUM> and the common collection channel <NUM> in <FIG> and <FIG> indicate the oscillating movement of an ink which occurs in the configuration using the serial liquid ejection apparatus <NUM>. The ink supplied to the pressure chamber <NUM> through the common supply channel <NUM> and the supply connection channel <NUM> is ejected from the ejection port <NUM> as the ejection element <NUM> is driven. In a case where the ejection element <NUM> is not driven, the ink is collected from the pressure chamber <NUM> into the common collection channel <NUM> through the collection connection channel <NUM>, which is a collection channel.

In a case of ejecting the ink circulated as above in the configuration using the serial liquid ejection apparatus <NUM>, 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 head <NUM>. 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 in <FIG>, in a case where the common supply channels <NUM> and the common collection channels <NUM> have cross-sectional shapes which are wide in the X direction, which is the main scanning direction, the inks inside the common supply channels <NUM> and the common collection channels <NUM> more easily receive inertial forces in the main scanning direction so that the inks oscillates greatly. This leads to a possibility that the oscillating movements of the inks may affect the ejection of the inks from the ejection ports <NUM>. Moreover, widening the common supply channels <NUM> and the common collection channels <NUM> in the X direction widens the distance between the colors. This may lower the printing efficiency.

Hence, each common supply channel <NUM> and each common collection channel <NUM> in the present embodiment whose cross sections are illustrated in <FIG> have a configuration that, each common supply channel <NUM> and each common collection channel <NUM> extend 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 channel <NUM> and the common collection channel <NUM> are given small channel widths in the main scanning direction. By giving the common supply channel <NUM> and the common collection channel <NUM> small channel widths in the main scanning direction, the oscillating movement of the ink inside the common supply channel <NUM> and the common collection channel <NUM> by the inertial force acting on the ink and exerted in the direction opposite to the main scanning direction (the black bold arrows in <FIG>) 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 channel <NUM> and the common collection channel <NUM> in the Z direction, their cross-sectional areas are increased. This reduces the channel pressure drop.

As described above, each common supply channel <NUM> and each common collection channel <NUM> are given small channel widths in the main scanning direction. This configuration reduces the oscillating movement of the ink inside the common supply channel <NUM> and the common collection channel <NUM> during 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 channel <NUM> and the common collection channel <NUM> are disposed at positions overlapping each other in the X direction.

As described above, in the present embodiment, the supply connection channels <NUM> and the collection connection channels <NUM> are provided so as to correspond to the ejection ports <NUM>. Moreover, the correspondence relationship between the supply connection channels <NUM> and the collection connection channels <NUM> establishes such that the supply connection channels <NUM> and the collection connection channels <NUM> are arrayed in the X direction with the ejection ports <NUM> interposed therebetween. Thus, if the common supply channel <NUM> and the common collection channel <NUM> have a portion(s) where the common supply channel <NUM> and the common collection channel <NUM> do not overlap each other in the X direction, the correspondence between the supply connection channels <NUM> and the collection connection channels <NUM> in the X direction breaks. This incorrespondence affects the ink flow in the pressure chambers <NUM> in the X direction and the ink ejection. If this incorrespondence is combined with the influence of the oscillating movement of the ink, there is a possibility that it may further affects the ink ejection from each ejection port.

Thus, by disposing the common supply channel <NUM> and the common collection channel <NUM> at positions overlapping each other in the X direction, the oscillating movement of the ink inside the common supply channel <NUM> and the common collection channel <NUM> during main scanning is substantially the same at any position in the Y direction, in which the ejection ports <NUM> are arrayed. Thus, the pressure differences generated in the pressure chambers <NUM> between the common supply channel <NUM> side and the common collection channel <NUM> side 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 channel <NUM> and the common collection channel <NUM> are different channels. Moreover, the supply connection channels <NUM> and the pressure chambers <NUM> communicate with each other, the pressure chambers <NUM> and the collection connection channels <NUM> communicate with each other, and the inks are ejected from the ejection ports <NUM> in the pressure chambers <NUM>. That is, the configuration that the pressure chambers <NUM> serving as paths connecting the supply connection channels <NUM> and the collection connection channels <NUM> include the ejection ports <NUM>, is formed. Hence, in each pressure chamber <NUM>, an ink flow flowing from the supply connection channel <NUM> side to the collection connection channel <NUM> side is generated, and the ink inside the pressure chamber <NUM> is efficiently circulated. The ink inside the pressure chamber <NUM>, which tends to be affected by evaporation of the ink from the ejection port <NUM>, is kept fresh by efficiently circulating the ink inside the pressure chamber <NUM>.

Also, since the two channels, namely the common supply channel <NUM> and the common collection channel <NUM>, communicate with the pressure chamber <NUM>, 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 channel <NUM> and the common collection channel <NUM> are disposed at positions close to each other in the X direction. The common supply channel <NUM> and the common collection channel <NUM> are desirably disposed such that the gap between the channels is <NUM> to <NUM>.

<FIG> is a view illustrating an ejection element substrate <NUM> as a comparative example. Note that illustration of the supply connection channels <NUM> and the collection connection channels <NUM> is omitted in <FIG>. The inks having received thermal energy from the ejection elements <NUM> in the pressure chambers <NUM> flow into the common collection channels <NUM>. Hence, the temperature of the inks flowing through the common collection channels <NUM> is higher than the temperature of the inks in the common supply channels <NUM>. Here, in the comparative example, only the common collection channels <NUM> are present at one portion of the ejection element substrate <NUM> in the X direction, as indicated by a portion α circled with the long dashed short dashed line in <FIG>. In this case, the temperature may locally rise at that portion, thereby causing temperature unevenness within the ejection module <NUM>. This temperature unevenness may affect the ejection.

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

<FIG> are views illustrating a channel configuration of the liquid ejection head <NUM> for the inks of the three colors of cyan (C), magenta (M), and yellow (Y). In the liquid ejection head <NUM>, a circulation channel is provided for each ink type as illustrated in <FIG>. The pressure chambers <NUM> are provided along the X direction, which is the main scanning direction of the liquid ejection head <NUM>. Also, as illustrated in <FIG>, the common supply channels <NUM> and the common collection channels <NUM> are provided along the ejection port arrays, which are arrays of ejection ports <NUM>. The common supply channels <NUM> and the common collection channels <NUM> are provided so as to extend in the Y direction with the ejection port arrays therebetween.

<FIG> is a schematic configuration diagram more specifically illustrating a state where an ink tank <NUM> and an external pump <NUM> provided as main body units of the liquid ejection apparatus <NUM> in the present embodiment and the liquid ejection head <NUM> are connected, and an arrangement of a circulation pump and so on. The liquid ejection apparatus <NUM> in the present embodiment has such a configuration that only the liquid ejection head <NUM> can be easily replaced in a case where a trouble occurs in the liquid ejection head <NUM>. Specifically, the liquid ejection apparatus <NUM> in the present embodiment has the liquid connection parts <NUM>, with which the respective ink supply tubes <NUM> connected to the respective external pumps <NUM> and the liquid ejection head <NUM> can be easily connected to and disconnected from each other. This enables only the liquid ejection head <NUM> to be easily attached to and detached from the liquid ejection apparatus <NUM>.

As illustrated in <FIG>, each liquid connection part <NUM> has a liquid connector insertion slot 53a which is provided in a protruding manner on the head housing <NUM> of the liquid ejection head <NUM>, and a cylindrical liquid connector 59a into which this liquid connector insertion slot 53a is insertable. The liquid connector insertion slot 53a is fluidly connected to an ink supply channel formed in the liquid ejection head <NUM>, and is connected to the first pressure adjustment unit <NUM> through the filter <NUM> mentioned earlier. The liquid connector 59a is provided at the tip of the ink supply tube <NUM> connected to the external pump <NUM>, which supplies the ink in the ink tank <NUM> to the liquid ejection head <NUM> by pressurization.

As described above, the liquid ejection head <NUM> illustrated in <FIG> has the liquid connection part <NUM>. This facilitates the work of attaching, detaching, and replacing the liquid ejection head <NUM>. However, in a case where the sealing performance between the liquid connector insertion slot 53a and the liquid connector 59a deteriorates, there is a possibility that the ink supplied by pressurization by the external pump <NUM> may leak from the liquid connection part <NUM>. The leaked ink may cause a trouble in the electrical system if attached to the circulation pump <NUM>, for example. To address this, in the present embodiment, the circulation pump, etc. are disposed as below.

As illustrated in <FIG>, in the present embodiment, in order to avoid attachment of the ink leaking from the liquid connection part <NUM> to the circulation pump <NUM>, the circulation pump <NUM> is disposed higher than the liquid connection part <NUM> in the direction of gravity. Specifically, the circulation pump <NUM> is disposed higher than the liquid connector insertion slot 53a, which is a liquid inlet in the liquid ejection head <NUM>, in the direction of gravity. Moreover, the circulation pump <NUM> is disposed at such a position as to be out of contact with the constituent members of the liquid connection part <NUM>. In this way, even if the ink leaks from the liquid connection part <NUM>, the ink flows in a horizontal direction which is the opening direction of the opening of the liquid connector 59a or downward in the direction of gravity. This prevents the ink from reaching the circulation pump <NUM> located higher in the direction of gravity. Moreover, disposing the circulation pump <NUM> at a position separated from the liquid connection part <NUM> also reduces the possibility of the ink reaching the circulation pump <NUM> through members.

Furthermore, an electric connection part <NUM> electrically connecting the circulation pump <NUM> and the electric contact substrate <NUM> through a flexible wiring member <NUM> is provided higher than the liquid connection part <NUM> in the direction of gravity. Thus, the possibility of the ink from the liquid connection part <NUM> causing an electrical trouble is reduced.

In addition, in the present embodiment, a wall portion 52b of the head housing <NUM> is provided. Thus, even if the ink jets out of the liquid connection part <NUM> from its opening 59b, the wall portion 53b blocks that ink and thus reduces the possibility of the ink reaching the circulation pump <NUM> or the electric connection part <NUM>.

Next, pressure fluctuations in the liquid ejection head <NUM> in the present embodiment which are associated with a characteristic feature of the present disclosure will be described. In the liquid ejection apparatus <NUM> using the serial liquid ejection head <NUM> in the present embodiment, the ink supply tubes <NUM> are used to supply the inks to the circulation units <NUM> of the liquid ejection head <NUM>. In the case where the circulation pumps <NUM> of the circulation units <NUM> are mounted in the liquid ejection head <NUM>, the paths from the circulation pumps <NUM> to 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 head <NUM> is scanned in a print operation or the like, the ink supply tubes <NUM> are swung. This leads to a possibility that the pressures on the inks inside the ink supply tubes <NUM> may 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 pump <NUM>, which is the source of the pulsation. Specifically, the first pressure adjustment unit <NUM> is connected to the pump outlet channel <NUM>, and the second pressure adjustment unit <NUM> is connected to the pump inlet channel <NUM>. With this configuration, propagation of the pulsation resulting from the driving of the circulation pump <NUM> to the ejection module <NUM> can be suppressed from both the inlet side and outlet side of the circulation pump <NUM>. In the liquid ejection head <NUM>, 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 spring <NUM>, the pressing plate <NUM>, and the flexible member <NUM>, which form each pressure adjustment unit, mechanically absorb the pulsation of the ink generated by the circulation pump <NUM>, and therefore suppress propagation of the pulsation of the ink to the ejection module <NUM>.

Also, as mentioned earlier, the liquid ejection apparatus <NUM> in the present embodiment does not include ink collection systems that collect the inks in the liquid ejection head <NUM> into the ink tanks <NUM>. Specifically, there are no channels for collecting the liquids from the circulation units <NUM>. Thus, each ink supply tube <NUM> is the only single channel connected to the corresponding circulation unit <NUM>. If collection tubes for collecting the inks into the ink tanks <NUM> are provided, there will also be a possibility of propagation of pressure fluctuations to the liquid ejection head <NUM> from the collection tube side. In the present embodiment, each ink supply tube <NUM> is the only single channel connected to the corresponding circulation unit <NUM>. Also, each of the inks supplied to the circulation units <NUM> from the ink supply tubes <NUM> flows into the first valve chamber <NUM> of the first pressure adjustment unit <NUM>. Then, the opening and closing of the communication port <NUM> are controlled with the valve <NUM>. In this way, the pressures generated by the swinging of the tubes with scanning of the liquid ejection head <NUM> is prevented from affecting the ejection modules <NUM>.

Moreover, as mentioned earlier, the supply of the ink to the liquid ejection head <NUM> from each ink tank <NUM> is 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 head <NUM> is scanned in the main scanning direction. Thus, the ink supply tubes <NUM>, which supply the inks from the ink tanks <NUM> to the liquid ejection head <NUM>, is swung in the main scanning direction, so that the pressure P1 in each ink supply tube <NUM> fluctuates. Note that the pressure P1 is the pressure in the first valve chamber <NUM>, as mentioned earlier, and no pressure adjustment mechanism is provided between the first valve chamber <NUM> and the ink supply tube <NUM>. Thus, the pressure in the ink supply tube <NUM> and the pressure in the first valve chamber <NUM> will be considered the same thing here. Also, as described in Equation <NUM>, the pressure P2 in the first pressure control chamber <NUM> of the first pressure adjustment unit <NUM> is proportional to the above-described pressure P1. Moreover, as described in Equation <NUM>, the proportionality constant is determined by the ratio between the pressure reception area S1 of the valve <NUM> and the pressure reception area S2 of the pressing plate <NUM> (see also <FIG>). With supply by pressurization, the ratio of the pressure reception area S1 of the valve <NUM> to the pressure reception area S2 of the pressing plate <NUM> can be made small. In this way, the fluctuations in the pressure P2 due to fluctuations in the pressure P1 are made small. Specifically, the fluctuations in the pressure P2 in the first pressure control chamber <NUM> due to the fluctuations in the pressure P1 in the ink supply tube <NUM> caused 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 chambers <NUM> and thus achieve stable ejection.

Claim 1:
A liquid ejection head (<NUM>) for ejecting a liquid while being scanned in a main scanning direction (X), comprising:
an ejection element (<NUM>) configured to generate a pressure for ejecting the liquid in a pressure chamber (<NUM>);
a supply channel (<NUM>) through which the liquid is supplied to the pressure chamber (<NUM>);
a collection channel (<NUM>) connected to the supply channel (<NUM>) through the pressure chamber (<NUM>) and through which the liquid is collected from the pressure chamber (<NUM>);
a circulation pump (<NUM>) capable of supplying the liquid from the supply channel (<NUM>) into the pressure chamber (<NUM>), and collecting the liquid in the pressure chamber (<NUM>) through the collection channel (<NUM>) and sending the liquid to the supply channel (<NUM>);
a first pressure adjustment unit (<NUM>) disposed between an outlet channel (<NUM>) of the circulation pump (<NUM>) and the supply channel (<NUM>) and configured to adjust a pressure in the supply channel (<NUM>); and
a second pressure adjustment unit (<NUM>) disposed between an inlet channel (<NUM>) of the circulation pump (<NUM>) and the collection channel (<NUM>) and configured to adjust a pressure in the collection channel (<NUM>).