# Patent

## Title
Liquid ejection apparatus

## Abstract

A liquid ejection apparatus including: a liquid ejection head including: an inside channel; and ejection openings; a supply channel; a return channel; a supply device; an adjusting device; and a controller, wherein the controller performs a liquid circulation control for circulating liquid through the supply channel, the inside channel, and the return channel in order by controlling (i) the adjusting device such that a channel resistance value of the return channel is less than a predetermined maximum value and (ii) the supply device to supply the liquid into the inside channel, wherein, when the liquid is circulated by the liquid circulation control, the controller starts a liquid discharge control for discharging the liquid by making the channel resistance value larger than that in the liquid circulation control, and wherein the controller controls the supply device such that an amount of the liquid supplied to the inside channel per unit time in the liquid discharge control is larger than that in the liquid circulation control.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority from Japanese Patent Application No. 2010-172238, which was filed on Jul. 30, 2010, the disclosure of which is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid ejection apparatus configured to eject liquid from ejection openings.
2. Description of the Related Art
There is known an ink-jet head configured to eject ink droplets from a plurality of ejection openings and perform a cleaning for the ejection openings by forcibly supplying the ink into ink channels in the ink-jet head by a pump and to discharge air bubbles and thickened or viscous ink remaining in portions of the ink channels which are located near the ejection openings. For example, after a three-way valve is closed to close and seal a discharging passage, a supply pump is operated to pressurize the ink in the ink channels for a predetermined length of time, thereby discharging the ink from nozzles to perform the cleaning of the nozzles.
SUMMARY OF THE INVENTION
In order to perforin a cleaning of ejection openings by reliably discharging ink from all the ejection openings, an ink pressure applied to ink channels needs to be increased to a desired pressure. However, if a relatively long time is required for the ink pressure in the ink channels to reach the desired pressure after the pump starts to be driven, the ink is discharged from the ejection openings in the order of their ink-discharge resistances or channel resistances, an ejection opening having the lowest ink-discharge resistance first. This makes it impossible to instantaneously discharge the ink from all the ejection openings at the same time. Thus, the ink is needlessly discharged from the ejection openings in the cleaning of the ejection openings. The ink may leak from the ejection openings also by slight ink flow in the ink channels, leading to useless ink discharge.
This invention has been developed in view of the above-described situations, and it is an object of the present invention to provide a liquid ejection apparatus configured to efficiently discharge liquid and air bubbles and the like from ejection openings while preventing unnecessary consumption of the liquid.
The object indicated above may be achieved according to the present invention which provides a liquid ejection apparatus comprising: a liquid ejection head including: an inlet opening into which liquid flows; an outlet opening from which the liquid having flowed into the inlet opening flows; an inside channel communicating the inlet opening and the outlet opening with each other; and a plurality of ejection openings through which is ejected the liquid having flowed through a plurality of individual channels that are branched from the inside channel; a tank storing the liquid to be supplied to the liquid ejection head; an air communication device configured to communicate an inside of the tank with an ambient air or interrupt the communication of the inside of the tank with the ambient air; a supply channel communicating the inside of the tank and the inlet opening with each other; a return channel communicating the inside of the tank and the outlet opening with each other; a supply device configured to supply the liquid in the tank to the inside channel via the supply channel; an adjusting device configured to adjust a channel resistance value of the return channel between a predetermined minimum value and a predetermined maximum value; and a controller configured to control the air communication device, the supply device, and the adjusting device, wherein the controller is configured to perform a liquid circulation control for circulating the liquid through the supply channel, the inside channel, and the return channel in order by controlling (i) the adjusting device such that the channel resistance value is less than the predetermined maximum value and (ii) the supply device to supply the liquid into the inside channel, wherein, when the liquid is circulated by the liquid circulation control, the controller starts a liquid discharge control for discharging the liquid from the plurality of ejection openings by increasing the channel resistance value to a value larger than the channel resistance value in the liquid circulation control, and wherein the controller is configured to control the supply device such that a unit-time supply amount, which is an amount of the liquid supplied to the inside channel per unit time, in the liquid discharge control is larger than the unit-time supply amount in the liquid circulation control.
The object indicated above may be achieved according to the present invention which provides a liquid ejection apparatus comprising: a liquid ejection head including: an inlet opening into which liquid flows; an outlet opening from which the liquid having flowed into the inlet opening flows; an inside channel communicating the inlet opening and the outlet opening with each other; and a plurality of ejection openings through which is ejected the liquid having flowed through a plurality of individual channels that are branched from the inside channel; a tank storing the liquid to be supplied to the liquid ejection head; an air communication device configured to communicate an inside of the tank with an ambient air or interrupt the communication of the inside of the tank with the ambient air; a supply channel communicating the inside of the tank and the inlet opening with each other; a return channel communicating the inside of the tank and the outlet opening with each other; a supply device configured to supply the liquid in the tank to the inside channel via the supply channel; an adjusting device provided at a predetermined area expanding from the outlet opening of the inside channel, and configured to adjust a channel resistance value at the predetermined area between a predetermined minimum value and a predetermined maximum value; and a controller configured to control the air communication device, the supply device, and the adjusting device, wherein the controller is configured to perform a liquid circulation control for circulating the liquid through the supply channel, the inside channel, and the return channel in order by controlling (i) the adjusting device such that the channel resistance value is less than the predetermined maximum value and (ii) the supply device to supply the liquid into the inside channel, wherein, when the liquid is circulated by the liquid circulation control, the controller starts a liquid discharge control for discharging the liquid from the plurality of ejection openings in the liquid circulation control by increasing the channel resistance value to a value larger than the channel resistance value in the liquid circulation control, and wherein the controller is configured to control the supply device such that a unit-time supply amount, which is an amount of the liquid supplied to the inside channel per unit time, in the liquid discharge control is larger than the unit-time supply amount in the liquid circulation control.
In the liquid ejection apparatus constructed as described above, air bubbles, foreign matters, and the like remaining in the inside channel can be discharged into the tank by the circulation while preventing the liquid from leaking from the ejection openings. Further, the channel resistance value is increased by the adjustment of the adjusting device in this state to momentarily increase the pressure in the inside channel, whereby the liquid in the inside channel flows into the individual channels so as to be discharged from the ejection openings. In this operation, a relatively high pressure is applied to all the ejection openings from the start of the liquid discharge to discharge the liquid. Accordingly, it is possible to efficiently discharge thickened liquid in the ejection openings, and the air bubbles and the foreign matters, and it is possible to prevent the liquid from being discharged needlessly. Further, the unit-time supply amount in the liquid discharge control is increased, whereby an internal pressure in the inside channel further increases in the liquid discharge. Thus, it is possible to efficiently discharge the thickened liquid in the ejection openings, the air bubbles and the foreign matters.



BRIEF DESCRIPTION OF THE DRAWINGS
The objects, features, advantages, and technical and industrial significance of the present invention will be better understood by reading the following detailed description of an embodiment of the invention, when considered in connection with the accompanying drawings, in which:
FIG. 1 is a plan view generally showing an ink-jet printer as one embodiment of the present invention;
FIG. 2 is a cross-sectional view showing an ink-jet head and an ink supply unit shown in FIG. 1;
FIG. 3 is a plan view showing a head main body shown in FIG. 2;
FIG. 4 is an enlarged view showing an area enclosed by a one-dot chain line shown in FIG. 3;
FIG. 5 is a partial cross-sectional view showing the ink-jet head shown in FIG. 4;
FIG. 6 is a graph showing operational characteristics of a purging pump shown in FIG. 2;
FIG. 7 is a functional block diagram of a controller shown in FIG. 1;
FIG. 8 is a view showing a flow of ink when the ink is circulated by a circulation-and-purging controller shown in FIG. 7;
FIG. 9 is a view showing an operational sequence of the ink-jet printer shown in FIG. 1;
FIG. 10 is a graph showing changes of an ink-flow amount in a purging operation executed by the circulation-and-purging controller shown in FIG. 7; and
FIG. 11 is a view for explaining a modification.



DETAILED DESCRIPTION OF THE EMBODIMENT
Hereinafter, there will be described an embodiment of the present invention by reference to the drawings.
As shown in FIG. 1, an ink-jet printer 101 as one example of a liquid ejection apparatus includes: (a) a sheet conveyance unit 20 configured to convey a sheet P from an upper side toward a lower side in FIG. 1; (b) four ink-jet heads 1 (each as one example of liquid ejection head) configured to eject droplets of inks of respective four colors, namely, black, magenta, cyan, and yellow onto the sheet P conveyed by the conveyance unit 20; four ink supply units 10 configured to respectively supply the inks to the ink-jet heads 1; a maintenance unit 31 configured to perform a maintenance for ink-jet heads 1; and a controller 16 configured to control entire operations of the ink-jet printer 101. It is noted that, in the present embodiment, a sub-scanning direction is a direction parallel to a conveyance direction in which the conveyance unit 20 conveys the sheet P, and a main scanning direction is a direction perpendicular to the sub-scanning direction and along a horizontal plane.
The conveyance unit 20 includes two belt rollers 6, 7 and an endless sheet conveyance belt 8 wound around the rollers 6, 7. The belt roller 7 is a drive roller that is rotated by a drive power from a conveyance motor, not shown. The belt roller 6 is a driven roller that is rotated in accordance with the running or rotation of the conveyance belt 8 which is caused by the rotation of the belt roller 7. The sheet P placed on an outer circumferential face of the conveyance belt 8 is conveyed toward the lower side in FIG. 1.
The four ink-jet heads 1 each extends in the main scanning direction and are disposed in parallel with one another in the sub-scanning direction. That is, the ink-jet printer 101 is a line-type color ink-jet printer in which a plurality of ejection openings 108 through which the ink droplets are ejected are arranged in the main scanning direction. A lower face of each ink-jet head 1 functions as an ejection face 2a in which the plurality of ejection openings 108 are formed (see FIGS. 2-4).
An outer circumferential face of an upper portion of the conveyance belt 8 and the ejection faces 2a face and parallel with each other. When the sheet P conveyed on the conveyance belt 8 passes through positions just under the four ink-jet heads 1, the ink droplets of four colors are ejected in order from the respective ink-jet heads 1 onto an upper face of the sheet P, whereby a desired color image is formed on the sheet P.
Each of the ink supply units 10 is connected to a left end portion of the lower face of a corresponding one of the ink-jet heads 1 in FIG. 1 so as to supply the ink to the corresponding ink-jet head 1.
The maintenance unit 31 includes four wiper members 32. Each of the wiper members 32 is an elastic member for wiping the ejection face 2a of a corresponding one of the ink-jet heads 1 in a wiping operation of a maintenance operation which will be described below. Each wiper member 32 is reciprocable by an actuator, not shown, in the main scanning direction (indicated by an arrow in FIG. 1).
There will be next explained the ink-jet heads 1 in detail with reference to FIG. 2. As shown in FIG. 2, each ink-jet head 1 includes a reservoir unit 71 and a head main body 2.
The reservoir unit 71 is a channel defining member that is fixed to an upper face of the head main body 2 and supplies the ink to the head main body 2. The reservoir unit 71 has an ink inlet channel 72 (as one example of an inside channel), ten ink outlet channels 75, and a discharge channel 73 (as another example of an inside channel) formed therein. It is noted that only a single ink outlet channel 75 is shown in FIG. 2.
The ink inlet channel 72 is a channel into which the ink from the ink supply unit 10 flows via an inlet opening 72a opened in a lower face of the reservoir unit 71. The ink inlet channel 72 functions as an ink reservoir for temporarily storing the flowed ink. In an inner wall face of the ink inlet channel 72, there is formed a hole 72b formed through an outer wall face of the reservoir unit 71. The hole 72b is sealed by a flexible resin film 76 from a side of the hole 72b which is nearer to the outer wall face of the reservoir unit 71. That is, the resin film 76 partly constitutes the inner wall face of the ink inlet channel 72. The resin film 76 is displaced according to changes of a pressure of the ink in the ink inlet channel 72, functioning as a damper for restraining the changes of the ink pressure. Using the resin film 76 enables to provide the damper at low cost. It is noted that, in a normal recording, the resin film 76 slightly projects toward an inside of the ink inlet channel 72. To the outer wall face of the reservoir unit 71 is fixed a plate-like restraining member 77 so as to cover the hole 72b, thereby restraining the resin film 76 from projecting toward an outside of the reservoir unit 71. As a result, it is possible to prevent the resin film 76 from being broken by being excessively displaced when the ink pressure in the ink inlet channel 72 becomes excessively high. In the restraining member 77 is formed an air communicating hole 77a that always keeps a pressure between the restraining member 77 and the resin film 76 at an atmospheric pressure. This facilitates the displacement of the resin film 76.
The ink outlet channels 75 communicate with the ink inlet channel 72 via a filter 75a and with ink supply openings 105b formed in an upper face of a channel unit 9 (see FIG. 3). The filter 75a extends in a direction in which the ink flows in the ink inlet channel 72 (i.e., in the rightward and leftward direction in FIG. 2). In the normal recording, the ink supplied from the ink supply unit 10 flows into the ink inlet channel 72, then passes through the ink outlet channels 75, and finally is supplied from the ink supply openings 105b to the channel unit 9.
The discharge channel 73 communicates with the ink inlet channel 72 at a portion thereof located on an upstream side of the filter 75a and is connected to the ink supply unit 10 via an outlet opening 73a formed in the lower face of the reservoir unit 71.
In a lower inner wall face of the discharge channel 73, there is formed a hole 73b formed through the outer wall face of the reservoir unit 71. The hole 73b is sealed by a flexible resin film 78 from a lower side of the hole 73b, i.e., from a side of the hole 73b which is nearer to the outer wall face of the reservoir unit 71. That is, the resin film 78 partly constitutes the inner wall face of the discharge channel 73. The resin film 78 is displaced according to changes of a pressure of the ink in the discharge channel 73, functioning as a damper for restraining the changes of the ink pressure. Using the resin film 78 enables to provide the damper at low cost. It is noted that, in the normal recording, the resin film 78 slightly projects toward an inside of the discharge channel 73. To the lower outer wall face of the reservoir unit 71 is fixed a plate-like restraining member 79 so as to cover the hole 73b, thereby restraining the resin film 78 from projecting toward an outside of the reservoir unit 71. As a result, it is possible to prevent the resin film 78 from being broken by being excessively displaced when the ink pressure in the discharge channel 73 becomes excessively high. In the restraining member 79 is formed an air communicating hole 79a that always keeps a pressure between the restraining member 79 and the resin film 78 at the atmospheric pressure. This facilitates the displacement of the resin film 78. In ink circulation which will be described below, the ink supplied from the ink supply unit 10 flows into the ink inlet channel 72 via the inlet opening 72a, then passes from the ink inlet channel 72 through the discharge channel 73, and finally returns to the ink supply unit 10 via the outlet opening 73a (see FIG. 8).
There will be next explained the head main body 2 in more detail with reference to FIGS. 3-5. It is noted that, in FIG. 4, pressure chambers 110, apertures 112, and the ejection openings 108 are illustrated by solid lines for easier understanding purposes though these elements should be illustrated by broken lines because these elements are located under actuator units 21.
As shown in FIGS. 3-5, the head main body 2 includes the channel unit 9 and the four actuator units 21 fixed to the upper face of the channel unit 9. The channel unit 9 has ink channels including the pressure chambers 110 and so on. The actuator units 21 include a plurality of unimorph actuators respectively corresponding to the pressure chambers 110 so as to selectively apply ejection energy to the ink in the pressure chambers 110.
The channel unit 9 is a stacked body constituted by a plurality of metal plates 122-130 formed of stainless steel and positioned and stacked on each other. The upper face of the channel unit 9 has the ten ink supply openings 105b opened therein which communicate respectively with the ink outlet channels 75 of the reservoir unit 71 (see FIG. 2). As shown in FIG. 3, in the channel unit 9 are formed a plurality of manifold channels 105 and a plurality of sub-manifold channels 105a. Each of the ink supply openings 105b communicates with a corresponding one of the manifold channels 105, and each of the sub-manifold channels 105a is included in a corresponding one of the manifold channels 105. Further, as shown in FIG. 5, in the channel unit 9 is formed a plurality of individual ink channels 132 each branched from a corresponding one of the sub-manifold channels 105a and extending to a corresponding one of the ejection openings 108 opened in the ejection face 2a via a corresponding one of the pressure chambers 110. In the ejection face 2a, the ejection openings 108 are formed in matrix.
There will be next explained flow of the ink in the channel unit 9. As shown in FIGS. 3-5, in the normal recording, the ink supplied from the ink outlet channels 75 of the reservoir unit 71 to the ink supply openings 105b is distributed to the sub-manifold channels 105a of the manifold channels 105. The ink in the sub-manifold channels 105a flows into the individual ink channels 132 via the respective apertures 112 and the respective pressure chambers 110 and reaches the ejection openings 108 via the respective pressure chambers 110.
There will be next explained the ink supply unit 10 in detail. As shown in FIG. 2, each ink supply unit 10 includes: (a) a sub-tank 80; (b) an ink replenish tube 81 connected to the sub-tank 80; (c) a replenish pump 91 and a replenish valve 92 provided on the ink replenish tube 81; (d) an ink supply tube 82 and an ink returning tube 83; (e) a purging pump 86 provided on the ink supply tube 82; (f) a circulation valve 87 as one example of an adjusting device provided on the ink returning tube 83; and (g) an air communicating valve 88 as one example of an air communication device connected to the sub-tank 80.
The sub-tank 80 is for storing the ink to be supplied to the ink-jet head 1. When an amount of the ink in the sub-tank 80 becomes small, the replenish valve 92 is opened and the replenish pump 91 is driven, thereby replenishing the ink stored in an ink tank 90 to the sub-tank 80 via the ink replenish tube 81. The air communicating valve 88 communicates, in its open state, an inside of the sub-tank 80 with an ambient air or interrupts, in its closed state, the communication of the sub-tank 80 with the ambient air. In the normal recording, the air communicating valve 88 is open, so that the inside of the sub-tank 80 and the ambient air communicate with each other. As a result, an air pressure in the sub-tank 80 is always kept at an atmospheric pressure regardless of the amount of the ink stored in the sub-tank 80, ensuring stable ink supply.
One end of the ink supply tube 82 is connected to the sub-tank 80, and the other end thereof is connected to the inlet opening 72a of the reservoir unit 71 via a joint 82a. Thus, the ink in the sub-tank 80 is supplied to the ink inlet channel 72 of the reservoir unit 71 via the ink supply tube 82. The purging pump 86 functions as a supply portion which is driven to forcibly supply the ink in the sub-tank 80 to the ink inlet channel 72 via the ink supply tube 82. Further, the purging pump 86 functions as a check valve which prevents the ink from flowing from the joint 82a toward the sub-tank 80 in the ink supply tube 82. It is noted that, even where the purging pump 86 is stopped, the ink in the sub-tank 80 can be supplied to the reservoir unit 71 by flowing through the ink supply tube 82.
The purging pump 86 is a motorized three-phase diaphragm pump as a volume pump, and as shown in FIG. 6, three diaphragms are driven in different phases to discharge the ink, thereby restraining a pressure variation upon the ink supply. Further, by changing an electric power to be applied to the purging pump 86, it is possible to control an amount of the ink to be supplied from the purging pump 86 to the ink inlet channel 72 per unit time (hereinafter may be referred to as “unit-time supply amount”). As will be described below, in the present embodiment, the purging pump 86 is driven in two modes in which the unit-time supply amounts to be supplied are different from each other. One of the two modes in which the unit-time supply amount is smaller may be hereinafter referred to as “LO mode”, and the other of the two modes in which the unit-time supply amount is larger may be hereinafter referred to as “HI mode”.
As shown in FIG. 2, one end of the ink returning tube 83 is connected to the sub-tank 80, and the other end thereof is connected to the outlet opening 73a of the reservoir unit 71 via a joint 83a. The circulation valve 87 is an adjustment portion configured to adjust a channel resistance value of the ink returning tube 83 between a predetermined minimum value (in an open state of the circulation valve 87) and a predetermined maximum value (in a closed state of the circulation valve 87). It is noted that, in the present embodiment, the circulation valve 87 is an open-and-close valve for changing between (a) its open state in which the flow of the ink is not interrupted at all and (b) its closed state in which the flow of the ink is completely interrupted or inhibited, but the circulation valve 87 may be a channel controlling valve capable of adjusting the channel resistance value at any value.
There will be next explained the controller 16 with reference to FIG. 7. The controller 16 includes: a Central Processing Unit (CPU); an Electrically Erasable and Programmable Read Only Memory (EEPROM) that rewritably stores programs to be executed by the CPU and data used for the programs; and a Random Access Memory (RAM) that temporarily stores data when the program is executed. The controller 16 includes various functioning sections which are constituted by cooperation of these hardwares and softwares in the EEPROM with each other. The controller 16 is configured to control entire operations of the ink-jet printer 101 and includes: a conveyance controller 41; an image-data storage portion 42; a head controller 43; a non-ejection-time detecting section 46; a circulation-and-purging controller 44; and a maintenance controller 45.
The conveyance controller 41 controls the conveyance motor of the conveyance unit 20 such that the sheet P is conveyed in the conveyance direction at a predetermined speed. The image-data storage portion 42 stores therein image data relating to an image to be recorded on the sheet P.
In the normal recording, the head controller 43 produces an ejection driving signal on the basis of the image data and supplies the produced ejection driving signal to the actuator units 21 such that ink droplets having desired volumes are ejected from the ejection openings 108 at desired timings on the basis of the image data.
On the basis of an ink ejection history, the non-ejection-time detecting section 46 detects, for each ink-jet head 1, an elapsed time from the last (most recent) ejection of the ink droplet from the ejection opening 108 to a current time.
In the maintenance operation which will be described below, the circulation-and-purging controller 44 controls operations of the purging pump 86, the circulation valve 87, and the air communicating valve 88 of each ink supply unit 10. Specific controls of the circulation-and-purging controller 44 will be described below. It is noted that the circulation-and-purging controller 44 also controls the replenish pump 91 and the replenish valve 92 for the ink replenishing, but these are omitted in FIG. 7.
The maintenance controller 45 controls the maintenance unit 31 in the maintenance operation which will be described below.
There will be next explained the maintenance operation with reference to FIGS. 8-10. The maintenance operation is an operation for performing the maintenance of the ink-jet heads 1 and is started when the ink-jet printer 101 is booted up, when a standby time during which the recording has not been performed has passed a specific length of time, and when a command is inputted by a user, for example. During the standby state and the normal recording, the purging pump 86 is stopped, the circulation valve 87 is closed, the air communicating valve 88 is open, the replenish pump 91 is stopped, and the replenish valve 92 is closed (see FIG. 2).
As shown in FIGS. 8 and 9, when the maintenance operation is started, the circulation-and-purging controller 44 opens the circulation valve 87 at a time t1 and then closes the air communicating valve 88 and drives the purging pump 86 in the LO mode at the same time at a time t2. It is noted that the replenish pump 91 is stopped, and the replenish valve 92 is closed during the maintenance operation.
As a result, the ink in the sub-tank 80 is forcibly supplied to the ink inlet channel 72 via the ink supply tube 82. Since the circulation valve 87 is open at this time, a channel resistance in a passage from the ink inlet channel 72 to the sub-tank 80 via the discharge channel 73 and the ink returning tube 83 is less than that in a passage from the ink inlet channel 72 to the ejection openings 108 via the ink outlet channels 75 and the manifold channels 105. Thus, the ink supplied to the ink inlet channel 72 passes through the discharge channel 73 and the ink returning tube 83 in order and returns to the sub-tank 80 (that is, the ink circulation is performed) without flowing into the ink outlet channels 75. When the ink circulation is performed, the pressure of the ink rises in a channel from the purging pump 86 to the sub-tank 80 in the circulation passage. Thus, by the ink flowing by the ink circulation, air bubbles and foreign matters remaining in the ink inlet channel 72, especially the air bubbles and the foreign matters built up on the filter 75a, are carried through the discharge channel 73 and the ink returning tube 83 in order together with the ink, so that the air bubbles and the foreign matters are trapped in the sub-tank 80.
In order to efficiently move the air bubbles and the foreign matters to the sub-tank 80 by the ink circulation, there is a need to increase the unit-time supply amount in a range not higher than an amount (meniscus-break ink-leakage amount) of the ink at a timing when the ink starts to leak or flow from the ejection oepnings 108 by a break of meniscus (meniscus break) of the ink in the ejection openings 108. That is, the unit-time supply amount from the purging pump 86 during the ink circulation is increased as much as possible in a range in which the meniscus of the ink formed in the ejection openings 108 is not broken and the ink is not discharged from the ejection openings 108. It is noted that the meniscus-break ink-leakage amount is a value obtained by actual measurement or a value calculated from a channel structure of the ink-jet head 1, a height relationship between the ink-jet head 1 and the sub-tank 80 in the ink-jet printer 101, viscosity of the ink, and/or so on.
The unit-time supply amount when the purging pump 86 is driven in the LO mode is set at an amount equal to or smaller than the meniscus-break ink-leakage amount and equal to or larger than an ink amount (recoverable ink-flow amount) that can discharge the air bubbles and the foreign matters remaining in the individual ink channels from the ejection openings 108 together with the ink when the ink is discharged from the ejection openings 108 in a purging operation performed later. The recoverable ink-flow amount is a value obtained by actual measurement. From another point of view, where the driving of the purging pump 86 is started in the state in which the circulation valve 87 is closed such that an ink-flow amount is the recoverable ink-flow amount, an ink amount capable of discharging the air bubbles and the foreign matters remaining in the individual ink channels from all the ejection openings 108 together with the ink can be also referred to as the recoverable ink-flow amount. That is, where the purging pump 86 is driven with the ink whose ink amount is less than the recoverable ink-flow amount, the ink may continue to be discharged only from ejection openings 108 respectively communicating with individual ink channels 132 containing relatively small amounts of air bubbles and thickened or viscous ink. In this case, even if a period for discharging the ink is made longer, the ink may not be discharged from all the ejection openings 108 together with the air and the foreign matters. It is noted that the unit-time supply amount when the purging pump 86 is driven in the LO mode may be any value as long as the unit-time supply amount falls within a range equal to or lower than the meniscus-break ink-leakage amount.
In the period during which the air communicating valve 88 is closed in the ink circulation, a negative pressure is produced in the sub-tank 80. The ink in the ink inlet channel 72 is thus sucked into the sub-tank 80 via the discharge channel 73, making it difficult for the ink to flow into the ink outlet channels 75 when compared with the case where the air communicating valve 88 is open. As a result, the pressure in the ink inlet channel 72 is lowered, causing less meniscus break. Thus, when compared with the case where the air communicating valve 88 is open, the unit-time supply amount can be made larger until the pressure in the ink inlet channel 72 becomes closer to a pressure (meniscus-break pressure) at which the meniscus is broken. That is, assuming that the pressure in the ink inlet channel 72 is constant during the circulation, where the air communicating valve 88 is closed, the ink-flow amount is larger in the case where the air communicating valve 88 is open. Further, where the air communicating valve 88 is closed, the pressure in the ink inlet channel 72 during the purging period can be made larger than in the case where the air communicating valve 88 is open. Accordingly, it is possible to efficiently discharge the air bubbles and the foreign matters remaining in the individual ink channels from the ejection openings 108 together with the ink. The unit-time supply amount in the LO mode in FIG. 9 is larger than the meniscus-break ink-leakage amount in the case where the air communicating valve 88 is open in the ink circulation. That is, the unit-time supply amount in the LO mode in FIG. 9 is set at an ink-flow amount that is near the meniscus-break ink-leakage amount in the case where the air communicating valve 88 is closed and that causes the meniscus break when the air communicating valve 88 is opened in the ink circulation. It is noted that, in FIG. 9, a solid-line waveform and a broken-line waveform indicate pressure changes in the ink inlet channel 72, specifically, the solid-line waveform indicates the pressure changes in the channel where the unit-time supply amount is made larger as described above in the state in which the air communicating valve 88 is closed during the ink circulation (i.e., in the case of the present embodiment), and the broken-line waveform indicates the pressure changes in the channel where the air communicating valve 88 is open during the ink circulation (noted that the unit-time supply amount is not made larger and the purging pump 86 is driven with the ink whose ink amount is less than that in the LO mode).
In the ink circulation, the ink pressures in the ink inlet channel 72 and the discharge channel 73 are relatively high when compared with in the normal recording, and accordingly the resin film 76 in the ink inlet channel 72 is held in close contact with the restraining member 77, and the resin film 78 in the discharge channel 73 is held in close contact with the restraining member 79.
As shown in FIGS. 9 and 10, after a predetermined length of time has passed in a state in which the unit-time supply amount is stable, the circulation and purging controller 44 changes the driving mode of the purging pump 86 from the LO mode to the HI mode at a time t2′. As a result, the unit-time supply amount starts to increase. When the unit-time supply amount has reached the meniscus-break ink-leakage amount, in other words, when the pressure in the channel has reached the meniscus-break pressure, the circulation and purging controller 44 closes the circulation valve 87 and opens the air communicating valve 88 at the same time at a time t3. Thus, the ink flow in the discharge channel 73 is suddenly stopped by the circulation valve 87, whereby the ink pressures in the discharge channel 73 and the ink inlet channel 72 suddenly rise. In this state, the purging operation is started. As a result, the ink supplied to the ink inlet channel 72 flows into the ink outlet channels 75 without flowing into the discharge channel 73, and then the ink passes through the manifold channels 105 and the individual ink channels 132 in order and is discharged from the ejection openings 108. The discharged ink is received by a waste-ink tray, not shown. As described above, the circulation and purging controller 44 changes the driving mode of the purging pump 86 from the LO mode to the HI mode at a timing before a predetermined length of time from the start of the purging operation such that the unit-time supply amount is larger than the meniscus-break ink-leakage amount at the start of the purging operation. As a result, the unit-time supply amount is reliably larger at the start of the purging operation than the meniscus-break ink-leakage amount. It is noted that since the meniscus-break ink-leakage amount is larger than the recoverable ink-flow amount, the unit-time supply amount at the start of the purging operation is larger than the recoverable ink-flow amount.
As thus described, the purging operation is started in the state in which the unit-time supply amount is larger than the meniscus-break ink-leakage amount. Accordingly, the ink pressure in the ink inlet channel 72 is relatively high from a point in time just after the purging operation is started, whereby the thickened ink in the ejection openings 108 and the remaining air bubbles and foreign matters can be efficiently discharged from the ejection openings 108 (noted that this purging operation may be hereinafter referred to as “impact purge”). If the impact purge is not performed, that is, if the purging pump 86 starts to be driven (in the HI mode or the LO mode, for example) in the state in which the circulation valve 87 is closed without circulating the ink, to discharge the ink from the ejection openings 108 (a conventional technique), the ink is needlessly discharged from the ejection openings 108 until the unit-time supply amount reaches the recoverable ink-flow amount.
As shown in FIG. 9, in the purging operation, the air communicating valve 88 is opened. Thus, the pressure in the sub-tank 80 forcibly becomes the atmospheric pressure, thereby preventing the pressure in the sub-tank 80 from lowering in accordance with the discharging of the ink. As a result, the ink supply from the purging pump 86 to the ink outlet channels 75 is not hindered, thereby preventing the ink discharging from the ejection openings 108 from being unstable or stopped.
When a predetermined purging amount of the ink has been discharged from the ejection openings 108, the circulation-and-purging controller 44 stops the driving of the purging pump 86 at a time t3′. After the driving of the purging pump 86 has been stopped, the unit-time supply amount decreases as time passes. When the unit-time supply amount has become smaller than the unit-time supply amount in the ink circulation, i.e., in the LO mode, the circulation-and-purging controller 44 opens the circulation valve 87 and closes the air communicating valve 88 at the same time, and stops the purging operation at a time t4. It is noted that the predetermined purging amount is determined by the unit-time supply amount and a length of the purging period. The ink-flow amount per unit time and the length of the purging period for discharging the predetermined purging amount of the ink are obtained by experiment and stored in advance. The circulation-and-purging controller 44 makes the circulation period longer and the purging amount larger in accordance with increase in a temperature detected by a temperature sensor 35 or increase in a length of the elapsed time detected by the non-ejection-time detecting section 46.
As described above, by performing the ink circulation and the purging operation in order, the air bubbles and the foreign matters remaining in the ink inlet channel 72 can be discharged to an outside of the ink-jet heads 1 without flowing into downstream-side channels (e.g., the manifold channels 105, the individual ink channels 132, and the like).
After the unit-time supply amount has become zero, the circulation-and-purging controller 44 opens the air communicating valve 88 and then closes the circulation valve 87.
Then, when the wiping operation has been started, the maintenance controller 45 moves the four ink-jet heads 1 upward by a moving mechanism, not shown, and then moves the four wiper members 32 in the main scanning direction along the ejection faces 2a respectively facing thereto while holding distal ends of the respective wiper members 32 in contact with the respective ejection faces 2a. This operation removes the excessive ink adhering to the ejection faces 2a by the purging operation and recovers or arranges the state of the ink meniscus formed in the ejection openings 108. After the ejection faces 2a have been wiped, the maintenance controller 45 returns the four wiper members 32 and the ink-jet heads 1 to their respective original positions, and the circulation-and-purging controller 44 opens the circulation valve 87, and the wiping operation is completed.
As described above, according to the ink-jet printer 101 as the present embodiment, the air bubbles, the foreign matters, and the like remaining in the ink inlet channel 72 can be discharged into the sub-tank 80 by the ink circulation while preventing the ink from leaking from the ejection openings 108. Further, the circulation valve 87 is closed in this state to momentarily increase the pressure in the ink inlet channel 72, whereby the ink in the ink inlet channel 72 flows into the ink outlet channels 75 so as to be discharged from the ejection openings 108. In this operation, a relatively high pressure is applied to all the ejection openings 108 from the start of the purging operation to discharge the ink in the ejection openings 108. Accordingly, it is possible to efficiently discharge the thickened ink in the ejection openings 108, and the air bubbles and the foreign matters, and it is possible to prevent the ink from being discharged needlessly. Further, since the purging pump 86 is driven in the HI mode during the purging period, the unit-time supply amount during the purging period is larger than that during the ink circulation. Thus, an internal pressure in the channel further increases in the purging period, thereby efficiently discharging the thickened ink in the ejection openings 108, the air bubbles, and the foreign matters.
Further, the unit-time supply amount is equal to or smaller than the meniscus-break ink-leakage amount in the circulation period, thereby preventing the ink from leaking from the ejection openings 108. Further, the unit-time supply amount is larger than the meniscus-break ink-leakage amount in the purging period, thereby discharging the thickened ink in the ejection openings 108, the air bubbles, and the foreign matters more efficiently.
Further, by taking the time delay of the purging pump 86 into consideration, the circulation and purging controller 44 changes the driving mode of the purging pump 86 from the LO mode to the HI mode at the timing before the predetermined length of time from the start of the purging operation such that the unit-time supply amount is larger than the meniscus-break ink-leakage amount at the start of the purging operation. As a result, from the start of the purging operation, the unit-time supply amount is reliably larger than the meniscus-break ink-leakage amount, and the pressure in the channel can be reliably increased. This makes it possible to discharge the ink from the ejection openings 108 more efficiently.
In addition, when the circulation and purging controller 44 has opened the circulation valve 87 and stopped the purging operation, the circulation and purging controller 44 stops the driving of the purging pump 86 at a timing before a predetermined length of time from the stop of the purging operation such that the unit-time supply amount is smaller than that in the LO mode, by taking a length of time required for the rise of the unit-time supply amount into consideration. As a result, the internal pressure of the channel can be reliably made low at the stop of the purging operation. Thus, even where a meniscus withstanding pressure of the meniscus formed in the ejection openings 108 has been lowered because the ink discharged from the ejection openings 108 in a previous purging operation has adhered to defining portions of the ejection openings 108, it is possible to prevent the ink from leaking from the ejection openings 108 and from being discharged unnecessarily.
Further, since the unit-time supply amount is reduced by stopping the driving of the purging pump 86, the unit-time supply amount can be reduced by a simple control, and the purging operation can be quickly completed. It is noted that the circulation valve 87 is completely closed within 0-0.5 seconds, and preferably, within 0-0.2 seconds after the end of the purging operation.
Further, in the above-described embodiment, the circulation valve 87 is completely closed just after the end of the purging operation. Accordingly, it is possible to prevent the ink having adhered to the ejection face 2a by the purging operation from being sucked into the ejection openings 108 by, e.g., a water head difference between the ink-jet head 1 and the sub-tank 80.
Further, in the above-described embodiment, the wiping operation is performed after the end of the purging operation. Accordingly, it is possible to remove the ink and the foreign matters adhering to the ejection faces 2a and to recover or arrange the state of the ink meniscus of the ejection openings 108.
Further, in the above-described embodiment, the resin film 76 partly constitutes the inner wall face of the ink inlet channel 72, and the resin film 78 partly constitutes the inner wall face of the discharge channel 73. Thus, it is possible to efficiently restrain the changes of the ink pressures in the ink inlet channel 72 and the discharge channel 73. Accordingly, the ink can be supplied to the individual ink channels at a stabilized pressure. Further, when the resin films 76, 78 are deformed in the ink circulation, a volume of the channel increases, lowering the pressure in the sub-tank 80. Accordingly, the ink is less likely to leak from the ejection openings 108.
While the embodiment of the present invention has been described above, it is to be understood that the invention is not limited to the details of the illustrated embodiment, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the invention. For example, in the above-described embodiment, the circulation valve 87 is provided on the ink returning tube 83, but as shown in FIG. 11, a circulation valve 187 may be provided on the discharge channel 73 at a position in a predetermined area from the outlet opening 73a to adjust the channel resistance value of the discharge channel 73. Where the printer is configured in this manner, the circulation valve 187 is positioned near the ejection openings 108, making it possible to quickly start discharging the ink from the ejection openings 108 in the purging operation. It is noted that the term “in the predetermined area from the outlet opening 73a” means an area from the outlet opening 73a to a position at which the discharge channel 73 is branched from the ink inlet channel 72 (i.e., in the discharge channel 73).
Further, in the above-described embodiment, the unit-time supply amount is equal to or smaller than the meniscus-break ink-leakage amount during the circulation period, and the unit-time supply amount is larger than the meniscus-break ink-leakage amount during the purging period, but the unit-time supply amount may be equal to or smaller than the meniscus-break ink-leakage amount for at least a part of the purging period, and the unit-time supply amount may be larger than the meniscus-break ink-leakage amount for at least a part of the circulation period, as long as the unit-time supply amount for a part of the purging period is larger than that during the circulation period. For example, where the ink is leaking from only a small number of the ejection openings, the meniscus break occurs in the ejection openings, but an amount of the leaking ink is so small that effects for preventing the ink from being consumed needlessly can be obtained as a whole.
Further, in the above-described embodiment, the circulation and purging controller 44 changes the driving mode of the purging pump 86 from the LO mode to the HI mode at the timing before the predetermined length of time from the start of the purging operation, but the circulation and purging controller 44 may change the driving mode of the purging pump 86 from the LO mode to the HI mode at the same time as or after the start of the purging operation. Also in this configuration, the unit-time supply amount exceeds the meniscus-break ink-leakage amount in the purging period, thereby taking the state in which the ink pressure in the ink inlet channel 72 is relatively high. Accordingly, it is possible to efficiently discharge the thickened ink in the ejection openings 108, and the remaining air bubbles and foreign matters from the ejection openings 108.
In addition, in the above-described embodiment, the circulation and purging controller 44 stops the driving of the purging pump 86 at the timing before the predetermined length of time from the stop of the purging operation, but the circulation and purging controller 44 may stop the driving of the purging pump 86 at the same time as or after the stop of the purging operation.
Further, in the above-described embodiment, the circulation and purging controller 44 reduces the unit-time supply amount by stopping the driving of the purging pump 86 but may reduce the unit-time supply amount by decreasing a drive power of the purging pump 86 continuously or stepwise.
Further, in the above-described embodiment, the circulation valve 87 is selectively opened or closed, but a channel controlling valve capable of adjusting the channel resistance value at any value may be employed as the circulation valve 87. In this case, the channel controlling valve may change the channel resistance value so as to change the channel resistance value stepwise or continuously. Further, the circulation valve 87 does not need to close the ink channel completely. Further, in the above-described embodiment, the channel resistance value of the ink returning tube 83 is adjusted by controlling the circulation valve so as to reduce a cross-sectional area of the ink channel of the ink returning tube 83, but, in order to adjust the channel resistance value of the ink returning tube 83, an outer circumferential face of the ink returning tube 83 may be pinched by a pinching member to deform the ink returning tube 83 so as to reduce the cross-sectional area of the ink channel of the ink returning tube 83.
Further, in the above-described embodiment, the wiping operation is performed in the maintenance operation, but the wiping operation may be omitted.
In addition, in the above-described embodiment, the resin film 76 partly constitutes the inner wail face of the ink inlet channel 72, and the resin film 78 partly constitutes the inner wall face of the discharge channel 73, but the reservoir unit may not include at least one of the resin films 76, 78.
Further, in the above-described embodiment, each actuator unit 21 is provided by the unimorph piezoelectric actuator, but the actuator unit may be constituted by bimorph piezoelectric actuators. Further, the present invention may be applied to a thermal liquid ejection apparatus including heating elements.
The present invention is applicable to a recording apparatus configured to eject liquid other than the ink. Further, the present invention is applicable to a facsimile machine, a copying machine, and the like, in addition to the printer.

## Claims

1. A liquid ejection apparatus comprising:
a liquid ejection head comprising:
an inlet opening into which liquid flows;
an outlet opening from which the liquid having flowed into the inlet opening flows;
an inside channel communicating the inlet opening and the outlet opening with each other; and
a plurality of ejection openings through which is ejected the liquid having flowed through a plurality of individual channels that are branched from the inside channel;

a tank storing the liquid to be supplied to the liquid ejection head;
a supply channel communicating the inside of the tank and the inlet opening with each other;
a return channel communicating the inside of the tank and the outlet opening with each other;
a controller;
a supply device configured to supply the liquid in the tank to the inside channel via the supply channel, the supply device being coupled to the controller; and
an adjusting device configured to adjust a channel resistance value of the return channel between a predetermined minimum value and a predetermined maximum value, the adjusting device being independently coupled to the controller,
wherein the liquid ejection head further comprises an actuator unit coupled to the controller configured to selectively apply ejection energy to the plurality of individual channels based on image data to eject the liquid through the plurality of ejection openings,
wherein the controller is configured to control the supply device and the adjusting device, independently of each other,
wherein the controller is configured to perform a liquid circulation control for circulating the liquid through the supply channel, the inside channel, and the return channel in order by controlling (i) the adjusting device such that the channel resistance value is less than the predetermined maximum value and (ii) the supply device to supply the liquid from the supply channel into the inside channel of the liquid ejection head,
wherein, when the liquid is circulated by the liquid circulation control, the controller starts a liquid discharge control for discharging the liquid from the plurality of ejection openings by increasing the channel resistance value to a value larger than the channel resistance value in the liquid circulation control,
wherein the controller is configured to control the supply device such that a unit-time supply amount, which is an amount of the liquid supplied to the inside channel per unit time, in the liquid discharge control is larger than the unit-time supply amount in the liquid circulation control,
wherein the controller is configured to perform a first discharge control for discharging the liquid from the plurality of ejection openings by the actuator unit on the basis of the image data,
wherein the controller is configured to perform a second discharge control as the liquid discharge control for discharging the liquid from the plurality of election openings, not by the actuator unit, but by the supplying the liquid by the supplying device, and
wherein the controller is configured to control the supply device such that the unit-time supply amount in the second liquid discharge control is larger than the unit-time supply amount in the liquid circulation control.

2. The liquid ejection apparatus according to claim 1, wherein the controller is configured to control the supply device such that the unit-time supply amount in the liquid circulation control is equal to or less than a predetermined amount in which a pressure of the liquid in the individual channels is a meniscus withstanding pressure that is a pressure of the inside channel when any one of meniscuses formed in the plurality of ejection openings is broken, and such that the unit-time supply amount in the liquid discharge control is larger than the predetermined amount.

3. The liquid ejection apparatus according to claim 1, wherein the controller is configured to control the supply device such that the unit-time supply amount starts to increase before a start of the liquid discharge control.

4. The liquid ejection apparatus according to claim 3, wherein the controller is configured to start the liquid discharge control at a time when the unit-time supply amount has increased to a predetermined amount in which a pressure of the liquid in the individual channels is a meniscus withstanding pressure that is a pressure of the inside channel when any one of meniscuses formed in the plurality of ejection openings is broken.

5. The liquid ejection apparatus according to claim 1,
wherein the controller is configured to stop the discharge of the liquid from the plurality of the ejection openings during the liquid discharge control by decreasing the channel resistance value to a value less than the channel resistance value in the liquid discharge control, and
wherein the controller is configured to control the supply device to reduce the unit-time supply amount before the channel resistance value is decreased, such that a unit-time supply amount at a stop of the discharge of the liquid is less than the unit-time supply amount in the liquid circulation control.

6. The liquid ejection apparatus according to claim 5, wherein, at a timing when a unit-time supply amount in the liquid discharge control becomes less than the unit-time supply amount in the liquid circulation control, the controller makes the channel resistance value less than the channel resistance value in the liquid discharge control.

7. The liquid ejection apparatus according to claim 5, wherein the controller is configured to reduce the unit-time supply amount by controlling the supply device to stop the supply of the liquid.

8. The liquid ejection apparatus according to claim 1,
wherein the predetermined maximum value is a value in which the liquid is inhibited from passing through the return channel, and
wherein the controller controls the supply device and the adjusting device such that the channel resistance value becomes the predetermined maximum value just after the supply device has stopped supplying the liquid.

9. The liquid ejection apparatus according to claim 8,
wherein the liquid ejection head has an ejection face having the plurality of the ejection openings formed therein, and
wherein the liquid ejection apparatus further comprises a wiping device configured to wipe the ejection face in a period in which the channel resistance value is the predetermined maximum value.

10. The liquid ejection apparatus according to claim 1, wherein at least a part of inner wall faces of the inside channel and the supply channel is formed of a flexible material.

11. A liquid ejection apparatus comprising:
a liquid ejection head comprising:
an inlet opening into which liquid flows;
an outlet opening from which the liquid having flowed into the inlet opening flows;
an inside channel communicating the inlet opening and the outlet opening with each other; and
a plurality of ejection openings through which is ejected the liquid having flowed through a plurality of individual channels that are branched from the inside channel;

a tank storing the liquid to be supplied to the liquid ejection head;
a supply channel communicating the inside of the tank and the inlet opening with each other;
a return channel communicating the inside of the tank and the outlet opening with each other;
a controller;
a supply device configured to supply the liquid in the tank to the inside channel via the supply channel, the supply device being coupled to the controller to be controlled; and
an adjusting device provided at a predetermined area expanding from the outlet opening of the inside channel, and configured to adjust a channel resistance value at the predetermined area between a predetermined minimum value and a predetermined maximum value, the adjusting device being independently coupled to the controller to be controlled,
wherein the liquid ejection head further comprises an actuator unit coupled to the controller configured to selectively apply ejection energy to the plurality of individual channels based on image data to eject the liquid through the plurality of ejection openings,
wherein the controller is configured to control the supply device and the adjusting device, independently of each other,
wherein the controller is configured to perform a liquid circulation control for circulating the liquid through the supply channel, the inside channel, and the return channel in order by controlling (i) the adjusting device such that the channel resistance value is less than the predetermined maximum value and (ii) the supply device to supply the liquid from the supply channel into the inside channel of the liquid ejection head,
wherein, when the liquid is circulated by the liquid circulation control, the controller starts a liquid discharge control for discharging the liquid from the plurality of ejection openings in the liquid circulation control by increasing the channel resistance value to a value larger than the channel resistance value in the liquid circulation control,
wherein the controller is configured to control the supply device such that a unit-time supply amount, which is an amount of the liquid supplied to the inside channel per unit time, in the liquid discharge control is larger than the unit-time supply amount in the liquid circulation control,
wherein the controller is configured to perform a first discharge control for discharging the liquid from the plurality of ejection openings by the actuator unit on the basis of the image data,
wherein the controller is configured to perform a second discharge control as the liquid discharge control for discharging the liquid from the plurality of ejection openings, not by the actuator unit, but by the supplying the liquid by the supplying device, and
wherein the controller is configured to control the supply device such that the unit-time supply amount in the second liquid discharge control is larger than the unit-time supply amount in the liquid circulation control.

12. The liquid ejection apparatus according to claim 1, wherein the controller is configured to control the adjusting device to increase the channel resistance of the return channel in a state in which the unit-time supply amount is constant.

13. The liquid ejection apparatus according to claim 1, wherein the controller is configured to control the supply device to increase the unit-time supply amount in a state in which the channel resistance of the return channel is constant.

14. The liquid ejection apparatus according to claim 1, wherein the controller is configured to control the supply device such that the liquid supplied into the inside channel is not discharged in the liquid circulation control.