Droplet ejection apparatus and ink-jet recording apparatus

A droplet ejection apparatus is provided of which maintenancibility is improved while liquid stored therein is prevented from being wasted at the time of maintenance. The apparatus includes a main tank storing the liquid, a head unit including a sub-tank that temporarily stores the liquid fed from the main tank and an ejection head that ejects the liquid fed from the sub-tank as droplets, a head unit transfer device that transfers the head unit to a predetermined position, a displacement member disposed to freely move in the liquid in a liquid supply passage from the sub-tank to the ejection head, a continuous pressurizing unit that continuously moves the displacement member to continuously apply pressure to the liquid, and an instantaneous pressurizing unit that instantaneously moves the displacement member to instantaneously apply pressure to the liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2005-242775 filed Aug. 24, 2005 in the Japan Patent Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

This invention relates to a droplet ejection apparatus that ejects liquid supplied from a sub-tank as droplets. This invention is particularly effective when applied to an ink-jet recording apparatus (ink-jet printer).

When there is a bubble or a foreign body choked inside an ejection head of a droplet ejection apparatus, or a solid body or a slurry stuck to the ejection head, the droplet ejection apparatus is no longer able to eject droplets normally. The solid body or slurry here is a transformed body of an ingredient contained in liquid, which viscosity is increased by evaporation of moisture. Accordingly, an ink-jet recording apparatus including a droplet ejection apparatus, for example, is no longer able to obtain a favorable image (recording result).

To solve this problem, for example, an ink-jet recording apparatus includes a recovery function of a positive pressure purge system. In the ink-jet recording apparatus, the air inside the sub-tank is compressed using an air pump to apply pressure (positive pressure) to the ink inside the sub-tank. The pressure washes away the ink to the downstream so as to discharge the ink from the ejection head. In this manner, ink and foreign bodies inside the ejection head are removed.

SUMMARY

In a positive pressure purge system as above, it is difficult to achieve sufficient recovery effects if a discharge speed of ink is less than a predetermined speed (e.g., 0.1 m/s).

The larger the discharge speed is, the larger the difference (hereinafter, referred to as “pressure difference”) between the pressure inside the sub-tank and the atmospheric pressure. Therefore, it is necessary to set the pressure difference to a predetermined value and above in order to set the discharge speed of ink to the predetermined speed or above.

In the above ink-jet recording apparatus, the pressure difference is increased by compression of the air, that is, compressible fluid. inside the sub-tank. Therefore, compared to the case in which incompressible fluid like liquid is compressed, the pressure rising speed (pressure propagation speed) is slow, requiring time until the ink discharge speed reaches the predetermined speed.

On the other hand, the pressure difference required to simply discharge (eject) ink is much lower than the pressure difference (hereinafter, referred to as “necessary pressure difference”) required for the ink discharge speed to reach the predetermined speed. Therefore, in the above ink-jet recording apparatus, a great amount of ink is discharged during a period from when the ink starts to be discharged (ejected) from the ejection head until the ink discharge speed reaches the predetermined speed and above.

Accordingly, the above ink-jet recording apparatus has a problem that much ink is wasted at the time of operation of the recovery function (positive pressure purge).

In a droplet ejection apparatus which temporarily stores liquid fed from a main tank in a sub-tank and then supplies to the ejection head, a bubble and a foreign body may be choked or an ingredient in the liquid in a solid or slurry form may be stuck in a liquid supply passage from the main tank to the sub-tank.

Similar to the above ink-jet recording apparatus, there may be provided a recovery device that increases the difference between the pressure inside the main tank and the air pressure so that the foreign body and slurry ingredient choked in the liquid supply passage from the main tank to the sub-tank can be discharged with ink from the ejection head. However, as noted above, it is most likely that much ink is wasted due to a slow pressure increase.

Also, the length of the liquid supply passage from the main tank to the sub-tank and further to the ejection head is relatively long. Therefore, relatively much time is required to discharge the liquid in the liquid supply passage using a normal air pump. Thus, when there are a lot of bubbles in the liquid supply passage such as at the time of initial startup or liquid refill, a great deal of time is required for the operation of discharging bubbles (maintenance). There is a problem that the maintenancibility is low.

The problem of maintenancibility may be solved by using a large-sized air pump. However, this leads to an increase in size and manufacturing cost of the droplet ejection. apparatus. The problem of wasting much ink still remains.

The present invention is made to solve the above problems. It would be desirable to improve maintenancibility of a droplet ejection apparatus that temporarily stores liquid like ink fed from a main tank in a sub-tank to be fed to the ejection head, preventing the liquid from being wasted during the maintenance such as at the time of recovery function operation and initial startup.

One aspect of the present invention may provide a droplet ejection apparatus that includes a main tank that stores liquid; a head unit that includes a sub-tank that temporarily stores the liquid fed from the main tank and an ejection head that ejects the liquid fed from the sub-tank as droplets; a head unit transfer device that transfers the head unit to a predetermined position; a displacement member that is disposed to freely move in the liquid in a liquid supply passage from the sub-tank to the ejection head; a continuous pressurizing unit that continuously moves the displacement member to continuously apply pressure to the liquid; and an instantaneous pressurizing unit that instantaneously moves the displacement member to instantaneously apply pressure to the liquid.

When removing bubbles and foreign bodies choked in the ejection head, it is sufficient to discharge only the liquid present inside the ejection head. It is only necessary to instantaneously (sporadically) apply pressure to the liquid inside the ejection head.

On the other hand, the liquid existing in the liquid supply passage from the main tank to the sub-tank is much more than the liquid present in the ejection head. Therefore, in order to discharge bubbles and foreign bodies choked in the liquid supply passage from the main tank to the sub-tank, it is necessary to transmit a great deal of liquid to the ejection head side in a short time by continuously applying pressure to the liquid.

The droplet ejection apparatus of the present invention permits generation of an instantaneous pressurized stream that provides instantaneous (sporadic) application of pressure to the liquid inside the ejection head and a continuous pressurized stream that provides continuous application of pressure to the liquid. Therefore, in either case in removing bubbles or foreign bodies choked inside the ejection head or in the liquid supply passage from the main tank to the sub-tank, the liquid to be consumed can be saved. Furthermore, bubbles and foreign bodies choked in the liquid supply passage can be quickly removed.

Another aspect of the present invention may provide a droplet ejection apparatus that includes a main tank that stores liquid; a head unit that includes a sub-tank that temporarily stores the liquid fed from the main tank and an ejection head that ejects the liquid fed from the sub-tank as droplets; a head unit transfer device that transfers the head unit to a predetermined position; a screw pump device; a screw rotation device; and a screw displacement device. The screw pump device is provided with a screw having a rotation shaft displaceably supported in an axial direction and a spiral wing formed at an outer periphery of the rotation shaft. The screw pump device further includes a housing forming a cylindrical storage space for accommodation of the screw and having a discharge opening at an end in a longitudinal direction. The screw pump device delivers the liquid toward the ejection head side. The screw rotation device rotates the screw. The screw displacement device axially displaces the screw to the discharge opening side.

According to the above droplet ejection apparatus, the screw pump device transmits the liquid as incompressible fluid toward the ejection head side, while directly applying pressure to the liquid and not to compressible fluid like the air. Therefore, a difference between the pressure inside the sub-tank and the air pressure can be instantaneously increased to a required pressure difference, thus preventing the liquid from being wasted at the time of the recovery function operation.

In the above droplet ejection apparatus, the screw can be rotated and displaced in an axial direction. Thus, rotation of the screw by the screw rotation device can continuously apply pressure to the liquid and transmit a lot of liquid to the ejection head side, while displacement of the screw to the discharge opening side by the screw displacement device can provide instantaneous (sporadic) application of pressure to the liquid inside the ejection head.

Accordingly, waste of the liquid at the time of maintenance like recovery function operation and initial startup can be reduced in the present droplet ejection apparatus. Maintenancibility can be also improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

1. Description of Multi Function Apparatus1

The present invention is applied to an ink-jet recording apparatus as a so-called multi function apparatus including a printer function, a scanner function, a copying function, and a facsimile function.

Referring toFIG. 1, a multi function apparatus1is provided with a scanner2on the upper part for reading an image, and a casing1aon the lower part. As shown inFIG. 2, an ink-jet recording apparatus7is provided in the upper part inside the casing1a. The ink-jet recording apparatus7records (forms) an image onto a recording sheet20as a recording medium. In the lower part inside the casing1a, a sheet feeding device30is provided which supplies the recording sheet20to the ink-jet recording apparatus7.

A frame5is provided on the rear side inside the casing1aand on the upper side of the sheet feeding device30. The frame5is formed nearly into a rectangular parallelepiped which extends in a right and left direction (direction perpendicular to the surface ofFIG. 2drawing). The ink-jet recording apparatus7is disposed on the frame5. In the rear of the frame5, a conveying path5ais formed which guides the recording sheet20placed on the sheet feeding device30to the ink-jet recording apparatus7.

The ink-jet recording apparatus7includes a conveying roller7aprovided adjacent to an exit of the conveying path5a, and a discharge roller7bprovided where the recording sheet20with an image recorded thereon is discharged. The conveying roller7arotates by receiving a rotational driving force of a sheet conveying motor123(seeFIG. 5). Detailed structure of the ink-jet recording apparatus7will be explained later.

The sheet feeding device30has a feed cassette3attached through an opening1bof the casing1a. The feed cassette3includes a sheet storage3athat stores plural number of recording sheets20.

The topmost recording sheet20out of the recording sheets20stored in the sheet storage3ais transmitted to the ink-jet recording apparatus7via the conveying path5a, given a conveying force from the feeding roller8.

The feeding roller8is rotatably supported to a tip end of an arm10which is rotatably (pivotably) held by a driving shaft9. A rotational force that rotates the feeding roller8is supplied from a sheet feeding motor122(seeFIG. 5) via the driving shaft9.

As shown inFIG. 1, an operation panel6having various operation buttons and a liquid crystal panel is provided at the front on the upper part of the multi function apparatus1. A user can set up various setting items of the multi functional apparatus1, input necessary information such as a facsimile number, and confirm the operation state and communication records by operation of the various operation buttons on the operation panel6.

2.1 Overall Structure of Ink-jet Recording Apparatus7

The ink-jet recording apparatus7is a sort of image forming apparatus which forms an image on the recording sheet20by ejecting ink onto the recording sheet20using a droplet ejection apparatus according to the present invention.FIG. 3is a schematic diagram of the ink-jet recording apparatus7.

A head unit11is mounted on a carriage4. The head unit11moves parallel to (back and forth in) a direction orthogonal to a conveying direction of the recording sheet20(right and left direction on the surface ofFIG. 3drawing). The head unit11includes a plurality of recording heads69and a plurality of sub-tanks31. Detail of the head unit11will be explained later.

A guide bar24extends along a moving direction of the carriage4(head unit11) to guide the transfer of the carriage4. The carriage4is connected to an endless belt25provided along the guide bar24.

The endless belt25extends between a pulley26provided on one end side of the guide bar24(right side inFIG. 3) and an idle pulley27provided on the other end side. The pulley26is rotationally driven by a carriage motor28. Accordingly, as the carriage motor28is driven to rotate the endless belt26, the carriage4, that is, the head unit11, mechanically moves parallel in a right and left direction inFIG. 3.

In the vicinity of the guide bar24, a timing slit29is arranged which extends parallel to the guide bar24. The timing slit29has linear slits of a certain width formed per predetermined interval in a longitudinal direction.

The carriage4has a detector (not shown) constituted of a photo interrupter in which a light-emitting element and a light-receiving element face each other with the timing slit29therebetween. The detector and the timing slit29constitute a linear encoder (carriage feed encoder)118(seeFIG. 5) that detects a moving distance (position) of the carriage4(head unit11).

As shown inFIG. 3, the area where the carriage4moves back and forth along (parallel to) the guide bar24is divided into three sections, i.e., a recording section where recording is performed onto the recording sheet20, a standby section and a gap adjustment section where no recording is performed.

The standby section is provided in the vicinity of an end of the guide bar24on the pulley26side. In the standby section, the carriage4stands by for a period during which neither recording nor maintenance is performed, or later-explained wiping or recovery operation (positive purge) is performed.

The gap adjustment section is for operation of a not shown gap adjustment device. The gap adjustment device adjusts a gap between each nozzle37(seeFIG. 4) of the recording head69and the recording sheet20to an appropriate value.

A cap21is a cover member that covers the nozzles37of the recording head69to prevent the ink retained in the nozzles37from being dried. The cap21operates, driven by a cap driving portion22.

The cap21and the cap driving portion22are arranged at the lower side of the recording head69in the standby section. When the carriage4is stopped at a predetermined position in the standby section, the cap driving portion22ascends the cap21so that the cap21abuts on the under surface of the recording head69to cover the nozzles37. To the contrary, when moving the carriage4such as at the time of recording operation or maintenance, the cap driving portion22descends the cap21to disclose the nozzles37.

Adjacent to the cap21in a moving direction of the carriage4, there are provided a waste ink tray16that receives ink discharged (ejected) from the nozzles37at the time of recovery operation, and a wiper blade18that wipes ink attached on an opening plane of the nozzles37.

A wiper driving portion19moves the wiper blade18. The wiper blade18stands by normally at a distance from the recording head69(nozzles37). However, at the time of recovery operation, the wiper blade18moves as close to the recording head69(nozzles37) as that the edge portion thereof may contact with the nozzles37.

At the upper side of the head unit11in the standby section, a screw driving portion12is provided which axially rotates or displaces a later-explained screw33.

The screw driving portion12is disposed inside the casing1avia a not shown frame. The screw driving portion12is provided so as to be able to move up and down. Detail of the screw driving portion12will be explained later.

2.2 Structure of Head Unit11and Screw Driving Portion12

FIG. 4Ais a schematic diagram showing an ink supply passage including the head unit11, andFIG. 4Bis a top view of the sub-tank31. As shown inFIG. 4A, the recording head69having the plurality of nozzles37that eject ink as droplets (ink drops) is provided at the lower side of the head unit11. The recording head69in the present embodiment is a known type which uses a piezoelectric device.

At the upper side of the recording head69, a sub-tank31is provided which temporarily stores ink supplied from an ink cartridge (main tank)71via a tube72. There are a number of sub-tanks31and cartridges71which correspond to the number of ink colors. In the present embodiment, there are four sub-tanks31and cartridges71, respectively, which correspond to four colors of black, cyan, yellow and magenta.

The sub-tanks31and the cartridges71are different from each other in only stored ink colors. Therefore, only a description for the sub-tank31storing black ink (leftmost side inFIG. 3) is provided hereinafter.

The sub-tank31is formed into a flat cube (seeFIG. 4B) which is divided into two spaces31aand31bby a partition wall32. One of the space31a(hereinafter, referred to as “sub-tank portion31a”) out of the two spaces31aand31bdirectly communicates with the tube72.

On the other hand, the space31b(hereinafter, referred to as “storage space31b”) is formed nearly into a cylinder which extends in a vertical direction. The storage space31bcommunicates with the tube72via a communication path32aprovided in the partition wall32. A check valve32cthat prevents adverse current of ink from the storage space31bto the sub-tank portion31ais provided in the communication path32awhich communicates the sub-tank portion31aand the storage space31b.

The storage space31bstores a screw33including a rotation shaft33aand a spiral wing33bformed on the outer circumference of the rotation shaft33a. The screw33and a member composing the storage space31blike the partition wall32(hereinafter, the member referred to as “housing35”) constitute a screw pump34that delivers ink to the recording head69(nozzles37).

The rotation shaft33aof the screw33can be displaced in an axial direction (up and down direction in the present embodiment). The rotation shaft33ais rotatably supported to the housing35. The rotation shaft33arotates or is axially displaced by a rotational force or an axial displacement force received from the screw driving portion12.

At the lower end in a longitudinal direction of the housing36(storage space31b), a discharge opening35ais provided which communicates with the recording head69, i.e., the plurality of nozzles37. At the upper end in a vertical direction, a lid member33cis provided which closes an end on the upper side in a longitudinal direction of the housing35(storage space31b) when the screw33is axially displaced to the lower end side.

InFIG. 4A, the discharge opening35aappears as if it communicates with only the rightmost nozzle37. However, the discharge opening35acommunicates with all the nozzles37via a not shown dispensing path.

In the present embodiment, the lid member33cis integrally formed with the screw33(rotation shaft33a). Therefore, the lid member33copens/closes the upper end in a longitudinal direction of the housing35(storage space31b) in mechanical conjunction with the axial displacement of the screw33.

A spring33dbiases the screw33to the upper end side in the longitudinal direction of the housing35(storage space31b). In the present embodiment, the spring33dis constituted from a coil-like metal spring or rubber.

A gear33cis connected to the upper end side in the longitudinal direction of the screw33(rotation shaft33a). The gear33etransmits a rotational force given from the screw driving portion12to the screw33. In the present embodiment, the spring33dis arranged between the gear33eand the housing35. Accordingly, a resilient force of the spring33dis transmitted to the screw33via the gear33e.

The screw driving portion12includes a slide pressing portion12athat moves in a direction parallel to a longitudinal direction of the screw33(rotation shaft33a) and presses the upper end side in the longitudinal direction of the screw33toward the lower end side (discharge opening36aside), a connecting gear12bthat moves up and down integrally with the slide pressing portion12ato transmit a rotational force to the gear33e, and a screw driving portion12c(seeFIG. 5) that supplies power to the slide pressing portion12aor the connecting gear12b.

3. Electric Structure of Ink-jet Recording Apparatus7

FIG. 5is a block diagram showing an electric constitution of the ink-jet recording apparatus7. As shown inFIG. 5, the ink-jet recording apparatus7includes a control device110that controls later-explained respective driving circuits120ato120g. The control device110is constituted from a CPU111, a ROM112, a RAM113and an EEPROM114.

The control device110receives outputs from various sensors116such as a known media sensor or resist sensor that can detect presence of the recording sheet20, a front end, a rear end and ends in a width direction of the recording sheet20, a sheet conveying encoder117that detects a conveying distance (position) of the recording sheet20, the operation panel6, and a carriage feeding encoder118.

Outputs from the control device110are inputted to a feed motor driving circuit120athat drives the feed motor122, a conveying motor driving circuit120bthat drives the feed conveying motor123, a carriage motor driving circuit120cthat drives the carriage motor28, a recording head driving circuit120dthat drives the recording head69(piezoelectric element), a screw driving circuit120ethat drives the screw driving portion12c, a cap driving circuit120fthat drives the cap driving portion22, and a wiper driving circuit120gthat drives the wiper driving portion19.

The control device110controls each driving target through the CPU111which controls the respective driving circuits120ato120gaccording to various programs stored in the ROM112and the EEPROM114.

The multi function apparatus1of the present embodiment can communicate with a personal computer (hereinafter, referred to as “PC”)125. According to recording instructions from the PC125, the multi function apparatus1records image data transmitted together with the instructions onto the recording sheet20.

4. Characteristic Operation of Ink-jet Recording Apparatus7of Present Embodiment

The ink-jet recording apparatus7of the present embodiment can generate two types of pressurized streams at the time of maintenance such as at recovery function operation and initial startup. One is an instantaneous pressurized stream which instantaneously (sporadically) pressurizes ink inside the recording head69, and the other is a continuous pressurized stream which continuously pressurizes ink inside the recording head69.

FIGS. 6A to 6Cshow operation of the screw driving portion12in the case of generating an instantaneous pressurized stream. Firstly as shown inFIG. 6A, the carriage4is moved so that the sub-tank31in which generation of an instantaneous pressurized stream is desired, that is, the sub-tank31corresponding to the recording head69(nozzles37) on which recovery operation is to be performed, is positioned directly below the screw driving portion12.

Next, as shown inFIG. 6B, the screw driving portion12is descended to press the upper end side (gear33e) of the screw33with the slide pressing portion12a. Thereby, the ink inside the storage space31(housing35) is pressurized by the screw33(particularly by the wing33b) to the discharge opening35aside. As a result, an instantaneous (sporadic) pressurized stream is generated and the ink is discharged from the recording head69(nozzles37).

It is necessary that the descending speed of the slide pressing portion12ais set to generate the discharge speed which is sufficient to remove the ink with increased viscosity or foreign bodies out of the recording head69. The particular descending speed should be determined considering a hole diameter and the number of the nozzles37and a gap between the screw33(wing33b) and the internal wall of the housing

When the screw driving portion12is ascended, the screw33returns to the upper side (original position) by a resilient force of the spring33d. Thus, if the screw driving portion12is again descended, an instantaneous pressurized stream is regenerated.

When terminating the recovery operation, the screw driving portion12is ascended until the slide pressing portion12ais no longer in contact with the screw33, as shown inFIG. 6C.

4.1.2. Continuous Pressurized Stream

FIGS. 7A to 7Dare diagrams showing operation of the screw driving portion12in the case of generating a continuous pressurized stream. Firstly as shown inFIG. 7A, the carriage4is moved so that the sub-tank31in which generation of a continuous pressurized stream is desired, that is, the sub-tank31corresponding to the recording head69(nozzles37) on which recovery operation is to be performed, is positioned directly below the screw driving portion12.

Next, as shown inFIG. 7B, the screw driving portion12is descended so that the gear33eand the connecting gear12bare engaged. Then, as shown inFIG. 7C, the connecting gear12bis rotated so as to rotate the screw33. Thereby, the ink inside the housing35(storage space31) is continuously pressurized to the discharge opening35aside. In conjunction therewith, the ink continuously flows from the cartridge71to the sub-tank31. In this manner, a continuous pressurized stream is generated and the ink is discharged from the recording head69(nozzles37).

When terminating the recovery operation, the screw driving portion12is ascended until the gear33dis no longer in contact with the connecting gear12b, as shown inFIG. 7D.

The continuous pressurized stream is generated by rotating the screw33while the instantaneous pressurized stream is generated by moving the screw33in parallel to an axial direction. It is preferable that the moving (descending) speed of the screw driving portion12when connecting the screw driving portion12to the screw33in the case of generating the continuous pressurized stream is smaller than the moving speed in the case of generating the instantaneous pressurized stream.

This is because, in the case of the instantaneous pressurized stream, it is necessary to instantaneously move the screw33in parallel to an axial direction, while the continuous pressurized stream has nothing to do with the moving speed of the screw driving portion12. Rather, in the case of continuous pressurized stream, if the moving speed is extremely large, there is a fear that the gear33eand the connection gear12bmay not be engaged at the time of connection.

4.2. Control of Recovery Operation (Pressurized Stream)

FIGS. 8 to 15are flowcharts showing control of the recovery operation. Hereinafter, the control of the recovery operation will be explained by way of the flowcharts.

FIGS. 8 to 13are flowcharts showing automatic recovery control.FIG. 8shows a main control flow of the automatic recovery control.

The main control flow shown inFIG. 8is started once a power switch of the multi function apparatus1is turned on. Firstly, an initial startup process is performed (S1). Detail of the initial startup process will be explained later.

When the initial startup process (S1) is completed, a timer is started (S3). It is then determined whether a predetermined time (192 hours in the present embodiment) has passed since the timer is started (S5). If the predetermined time has passed (S5: YES), a regular purge process is performed (S7). Detail of the regular purge process (S7) will be explained later.

When the regular purge process is completed, the timer is stopped and initialized (S9). Again, the timer is started (S3). S3to SO are repeated until the multi function apparatus1is powered off.

4.2.2. Initial Startup Process

FIG. 9is a flowchart showing a control flow of the initial startup process. Firstly, a startup continuous pressurizing process is performed (S11). The startup continuous pressurizing process is a process of generating a continuous pressurized stream. Detail of the startup continuous pressurizing process will be explained later.

When the startup continuous pressurizing process is completed, an instantaneous pressurizing process1is performed which generates an instantaneous pressurized stream (S13). The instantaneous pressurizing process1is a process, as shown inFIG. 10, of depressing the upper end side of the screw33by means of the slide pressing portion12ato generate an instantaneous pressurized stream (S21) and then raising the slide pressing portion12ato release pressure on the ink (S22).

When the instantaneous pressurized process1is completed, wiping is performed in which the opening plane of the nozzles37is wiped by the wiper blade18(S15) as shown inFIG. 9. Then, a piezoelectric device is driven and the ink is ejected from the recording head69in the same manner as in the case of actual recording onto the recording sheet20to perform flushing (S17).

When flushing is ended, the nozzles37are covered with the cap21(S19) to end the initial startup process. Here, covering the nozzles37with the cap21is called capping.

The reason why flushing is performed after wiping is because wiping causes mixing of a plurality of colors of ink on the opening plane of the nozzles37. If left alone, the mixed ink may enter the nozzles37from the openings and change the color of ink inside the nozzles37.

Therefore, after wiping, the carriage4is once returned to the position facing the waste ink tray16so that flushing is performed, thus preventing a change in color of ink inside the nozzles37due to possible entering of ink from the openings to the inside of the nozzles37.

4.2.3. Startup Continuous Pressurizing Process

FIG. 11is a flowchart showing the startup continuous pressurizing process. Firstly, the carriage4is moved so that the sub-tank31in which a continuous pressurizing stream is generated is positioned directly below the screw driving portion12(S31). Then, the screw driving portion12is descended so that the gear33eis engaged with the connecting gear12b(S33).

When the screw33starts to rotate (S35), it is determined whether an initial volume of ink has been delivered (S37). Here, the “initial volume of ink” corresponds to a volume of the ink supply passage from the cartridge71to the sub-tank portion31a. In the present embodiment, whether or not the initial volume of ink has been delivered is determined by confirming whether a first predetermined time has passed since the screw33starts to rotate or whether the total revolution of the screw33has exceeded a first predetermined revolution.

When it is determined that the initial volume of ink has been delivered (S37: YES), the rotation of the screw33, that is, drive of the screw pump34is stopped (S39) to end the startup continuous pressurizing process.

4.2.4. Regular Purge Process

FIG. 12is a flowchart showing the regular purge process. Firstly, a regular purge continuous pressurizing process is performed (S41) and then the instantaneous pressurizing process1(SeeFIG. 10) is performed (843).

When the instantaneous pressurizing process1is completed (S43), wiping is performed (S45). Thereafter, flushing is performed (S47) and capping is performed (S49).

FIG. 13is a flowchart showing the regular purge continuous pressurizing process. The regular purge continuous pressurizing process (FIG. 13) is different from the startup continuous pressurizing process (FIG. 11) only in the determination step of stopping the rotation of the screw33. The other steps are identical.

That is, firstly, the carriage4is moved so that the sub-tank31in which a continuous pressurizing stream is generated is positioned directly below the screw driving portion12(S51). Then, the screw driving portion12is descended so that the gear33eand the connecting gear12bare engaged (S53).

When the screw33starts to rotate (S55), it is determined whether a regular purge volume of ink has been delivered (S57). Here, the “regular purge volume of ink” corresponds to a less volume of ink than a volume of the ink supply passage from the cartridge71to the sub-tank portion31a. In the present embodiment, whether or not the regular purge volume of ink has been delivered is determined by confirming whether a second predetermined time which is shorter than the first predetermined time has passed since the screw33starts to rotate or whether the total revolution of the screw33has exceeded a second predetermined revolution which is smaller than the first predetermined revolution.

When it is determined that the regular purge volume of ink has been delivered (S57: YES), the rotation of the screw33, that is, drive of the screw pump34is stopped (S59) to end the regular purge continuous pressurizing process.

The automatic purge process (FIG. 8) is a process which automatically performs the continuous pressurizing process and the instantaneous pressurizing process once the power switch is powered on. A manual purge process is a process started when a purge switch (cleaning switch) for the recovery operation is manually operated.

FIG. 14is a flowchart showing the manual purge process. When a user switches on the purge switch (cleaning switch), the manual purge process is started and whether the cartridge71has been exchanged is determined (S61).

In the present embodiment, it is determined that the cartridge71has been exchanged when the cartridge71in a state that the ink therein is less than a predetermined amount is removed and again installed.

When it is determined that the cartridge71has been exchanged (S61: YES), an instantaneous pressurizing process2is performed (S63). The instantaneous pressurizing process2is the process shown inFIG. 15, which outline is the same as the instantaneous pressurizing process1.

That is, the carriage4is firstly moved so that the sub-tank31in which an instantaneous pressurizing stream is to be generated is positioned directly below the screw driving portion12(S91). Then, the screw driving portion12is descended so that the upper end side (gear33e) of the screw33is depressed by the slide pressing portion12aso that an instantaneous pressurized stream is generated (S93)

When the depression by the slide pressing portion12ais ended, the slide pressing portion12a(screw driving portion12) is raised (S95) to perform wiping (S97). After wiping, flushing is performed (S99) and then capping is performed (S100),

As noted above, when the instantaneous pressurizing process2is completed, the manual purge process-is ended as shown inFIG. 14.

When it is determined in S61that the cartridge71has not been exchanged (S61: NO), it is confirmed whether the user has performed a confirming operation to continue the manual purge process, that is, whether the user has operated a manual purge process confirmation switch (not shown) (S65).

When it is confirmed that the user has performed a confirming operation to continue the manual purge process (S65: YES), the instantaneous pressurizing process2is performed (S67). Then, it is determined whether the user has instructed test printing (S69). When it is determined that the user has instructed test printing (S69: YES), test printing is performed and a counter value indicating the number of test printing is incremented (S71). On the other hand, when it is determined that the user has not instructed test printing (S69: NO), the manual purge process is ended.

Subsequently, it is determined that whether the result of the test printing is favorable, that is, whether the user has operated a button or a switch that indicates that the result of the test printing is favorable (S73).

When it is determined that the result of the test printing is favorable (S73: YES), the manual purge process is ended. When it is determined that the result of the test printing is not favorable (S73: NO), it is then determined whether the counter value is not less than a predetermined value N (N=2 in the present embodiment) (S75).

If the counter value is less than the predetermined value N (S75: NO), the process returns to S67and again the instantaneous pressurizing process2is performed. On the other hand, if the counter value is not less than the predetermined value N (S75: YES), the regular purge process (seeFIG. 12) is performed (S77). The timer started in the main control flow (seeFIG. 8) is initialized (S79).

Subsequently, it is again determined whether the user has instructed test printing (S81). When it is determined that the user has instructed test printing (S81: YES), test printing is performed (S83). On the other hand, if it is determined that the user has not instructed test printing (S81: NO), the manual purge process is ended.

After the test printing, it is determined whether the result of the test printing is favorable (S85). When it is determined that the result of the test printing is favorable (S85: YES), the manual purge process is ended. When it is determined that the result of the test printing is not favorable (S85: NO), the initial startup process (seeFIG. 9) is performed (S87). Then, the process returns to S79to again initialize the timer (S79).

5. Feature of Ink-jet Recording Apparatus7of Present Embodiment

In the ink-jet recording apparatus7of the present embodiment, ink is not pressurized via the air present on the upper side of the sub-tank portion31a(sub-tank31). The ink in the sub-tank31is directly pressurized to perform the recovery operation. Thus, compared to the case of pressurizing the ink inside the sub-tank31via the air, a difference between the ink pressure inside the sub-tank31and the air pressure can be instantaneously increased to a required difference. Accordingly, wasteful consumption of ink at the operation of the recovery function can be avoided.

When removing bubbles and foreign bodies choked in the recording head69, discharge (ejection) of ink present inside the recording head69is sufficient. Thus, it is only necessary to instantaneously (sporadically) pressurize the liquid inside the recording head69.

On the other hand, the volume of ink present in the ink supply passage from the cartridge71to the sub-tank31(sub-tank portion31a) is much larger than the volume of ink present in the recording head69. Accordingly, in order to discharge (eject) bubbles and foreign bodies choked in the ink supply passage from the cartridge71to the sub-tank31, it is necessary to continuously pressurize the ink so as to deliver a large volume of ink to the recording head69side.

In the present embodiment, generation of an instantaneous pressurized stream that instantaneously (sporadically) pressurizes the ink inside the recording head69and a continuous pressurized stream that continuously pressurizes the ink can be generated. Therefore, in either case of removing bubbles and foreign bodies choked in the recording head or in the ink supply passage from the cartridge71to the sub-tank31, wasteful consumption of ink can be inhibited and further in the latter case, removal operation of bubbles and foreign bodies can be completed in a short time.

Accordingly, in the present embodiment, waste of ink can be prevented at the time of maintenance like recovery operation and initial startup. At the same time, maintenacibility can be improved.

The wing33bof the screw33is spirally formed along the rotation shaft33a. Therefore, a spiral space formed by the wing33bis a space connecting one end through the other end in a longitudinal direction of the housing35(storage space31b).

Accordingly, when the screw33is displaced to the discharge opening35aside, pressure by an instantaneous pressurized stream may escape to the opposite side of the discharge opening35a. There is a fear that a sufficient pressure difference may not be achieved.

In the present embodiment, there is provided the lid member33cthat closes the upper end part in a longitudinal direction of the housing35(storage space31b) when the screw33is axially displaced. Thus, escape to the opposite side of the discharge opening35aof pressure by the instantaneous pressurized stream which occurs when the screw33is displaced to the discharge opening35aside can be reliably avoided. Accordingly, the pressure by the instantaneous pressurized stream can be certainly applied to the recording head69side.

Also in the present embodiment, the lid member33cis integrally formed with the rotation shaft33a. Thus, as soon as the screw33is axially displaced, the upper end side in a longitudinal direction of the housing35(storage31b) is closed. Accordingly, the pressure by the instantaneous pressurized stream can be certainly applied to the recording head69side.

Furthermore, the communication path32ais provided with the check valve32c. Thus, at the time of generating an instantaneous or continuous pressurized stream, flow of the pressurized stream toward the sub-tank portion31aside can be prevented. Accordingly, the pressure by the instantaneous pressurized stream can be certainly applied to the recording head69side.

As seen from the drawings, in the present embodiment, the communication path32ais provided roughly at the mid-height part of the partition wall32. The reason for this is explained hereinafter.

That is, the screw pump34pressure-feeds to the recording head69side the ink supplied through the communication path32ainto the housing35(storage space31b). Here, the pumping action by the screw pump34operates only within the space from the communication path32ato the discharge opening35a.

Accordingly, in order for the screw pump34to effectively operate, it is preferable that the communication path32ais provided on the upper end side of the partition wall32so as to increase a distance between the communication path32aand the discharge opening35a.

However, if the communication path32ais provided on the upper end side of the partition wall32, there is a fear that the ink may not be supplied from the sub-tank portion31ato the housing35(storage space31b) when the ink inside the sub-tank31(sub-tank portion31a) is consumed to lower the liquid surface.

Therefore, in the present embodiment, the communication path32ais provided at the mid-height part of the partition wall32, so as to prevent the ink from not being supplied from the sub-tank31ato the housing35(storage space31b) while effectively operating the screw pump34.

Also, in the present embodiment, when displacing the screw33in a rotation or axial direction, the carriage4is moved to relocate the head unit11at a position where the screw driving portion12is installed. Thus, without providing as many of the screw driving portion12as the number of the sub-tanks31, an instantaneous or continuous pressurized stream can be generated.

Accordingly, maintenancibility can be improved while preventing an increase in manufacturing cost and size of the ink-jet recording apparatus7and while preventing wasteful consumption of the liquid at the time of maintenance like recovery operation and initial startup.

Furthermore, in the present embodiment, a recovery operation (purge process) is automatically performed per predetermined time. Thus, failure can be avoided due to attachment of the ingredients of ink in the form of a solid body or a slurry inside the recording head69(nozzles37) before happens.

Additionally, in the recovery operation (purge process) automatically performed, the instantaneous pressurizing process is performed after the completion of the continuous pressurizing process. Therefore, after the removal of foreign bodies and the slurry ingredient with increased viscosity which are choked in the ink supply passage from the cartridge71to the sub-tank31, the foreign bodies and the like attached inside the recording head69(nozzles37) are removed. Thus, reliability of the recovery process is ensured.

Also in the manual purge process, the instantaneous pressurized process precedes the continuous pressurized process. Therefore, removal of the foreign bodies and the like attached inside the recording head69(nozzles37) is given priority. Accordingly, the removal can be completed in short time.

Other Embodiments

The screw driving portion12may be separated into two. A screw rotation portion and a screw displacement portion may be independently provided instead of the integrated screw driving portion12.

In the above embodiment, the carriage4is moved so as to select the sub-tank31to which the recovery process is performed. However, the same number of screw driving portion12may be provided as the number of the sub-tanks31, so that the recovery process may be performed without moving the carriage4.

In the above embodiment, the housing35and the sub-tank31integrally constitute the sub-tank31. However, the housing35and the sub-tank31amay be formed separately.

In the above embodiment, the lid member33cand the screw33are integrated. However, the lid member33cmay be separately formed so as to close the upper end side in a longitudinal direction of the housing35(storage31b) in conjunction with the displacement of the screw33.

Additionally, the position of the communication path32ashould not be limited to the substantially middle part in a vertical direction as shown inFIG. 4.

In the above embodiment, an instantaneous pressurized stream is generated once when the screw33is pressed once in the instantaneous pressurizing process. However, the instantaneous pressurized stream may be generated a plural number of times during one cycle of the process.

The present invention may be applied to a soldering machine which ejects melted solder from nozzles onto various printed circuit boards for automatic soldering, an apparatus that ejects high molecule organic material (luminous body) in an ink-jet manner to form organic coating upon manufacturing an organic EL display, or an apparatus that ejects resin in a slurry form from nozzles. The present invention may be applied to various droplet ejection apparatus which are designed to eject liquid stored in a sub-tank as droplets from nozzles.

The present invention should not be limited to the above embodiment and can be practiced in various manners without departing from the technical scope of the invention.