Inkjet recording apparatus and method for removing air bubbles in inkjet recording apparatus

An inkjet recording apparatus is capable of an operation of removing air bubbles in a recording head that includes the ink supply step, the ink ejection step, and the refilling step. The ink supply step supplies ink to a common flow-passage in the state in which movement of the ink inside a second ink-flow passage is tolerated with an inflow side valve, and movement of the ink inside a third ink-flow passage is restricted with an outflow side valve. The ink ejection step ejects the ink together with the air bubbles inside the common flow-passage from an outflow port into the third ink-flow passage by tolerating movement of the ink inside the third ink-flow passage with the outflow side valve. The refilling step refills the ink in the state in which movement of the ink inside the second ink-flow passage is restricted with the inflow side valve.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese Unexamined Patent Application Publication No. 2012-017754, filed Jan. 31, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

Field

The present invention relates to an inkjet recording apparatus which, in a piece of recording equipment, such as a facsimile, a copying machine, or a printer, performs recording by discharging ink onto a record medium, such as a paper sheet, and particularly relates to recovery of a recording head, which discharges ink.

Recording apparatuses, such as facsimiles, copying machines, and printers, are configured to record an image on a record medium, such as a paper, cloth, or OHP sheet, and according to method of recording, they can be classified into inkjet type, wire dot type, thermal type, etc. Further, the inkjet recording method is available as, for example, a serial type and a line head type. With the inkjet recording method of serial type, recording is performed while the recording head scans the record medium, for example. With the inkjet recording method of line head type, recording is performed by, for example, the single pass method (one pass method). In the inkjet recording apparatus using the inkjet recording method of line head type, recording heads in the form of a line are for example, fixed in, the apparatus main body.

For example, with the inkjet recording apparatus of line head type, a feeding means, such as a feeding belt provided in the apparatus main body feeds the record medium, such as a paper sheet, while the respective nozzles in the line heads having a recording width larger than the width of the record medium discharge the ink, thereby an image being formed on the record medium. Thus, printing at high speed can be accomplished, as compared to the serial type inkjet recording apparatus, in which the recording head makes a reciprocating operation along the direction of width of the record medium.

With such an inkjet recording apparatus, if an air bubble is generated in the ink-flow passage, and the generated air bubble is introduced into a nozzle in the recording head, discharging ink from the nozzle is made impossible, thereby the printing operation cannot be performed.

Then, as the method for removing air bubbles in the ink, an ink supply apparatus is known which performs an operation of circulating the ink by, prior to supplying the ink from the main tank to the sub-tank, sucking up the ink from the bottom portion of the main tank to circulate the ink back to the main tank through the sub-tank.

Further, a droplet discharge head is known which includes a plurality of droplet discharge portions; a common supply passage for supplying the liquid to the supply passage of the respective droplet discharge portions; and a common recovery passage for recovering the liquid from the recovery passage of the respective droplet discharge portions in which a dead water region is formed, a reserving portion for reserving the air bubbles being provided in the dead water region, whereby a pressure fluctuation generated in the pressure chamber in the droplet discharge portion can be more easily propagated to the common recovery passage.

SUMMARY

An inkjet recording apparatus in accordance with one aspect of the present invention includes a recording head, an ink tank, a pump mechanism, a circulation flow passage, an inflow side valve, an outflow side valve, and a damper portion. The recording head has a common flow-passage having an inflow port at one end and an outflow port at the other end, and a plurality of nozzles communicating with the common flow-passage and discharging ink onto a record medium. The ink tank reserves the ink to be discharged onto the record medium. The pump mechanism sucks the ink inside the ink tank, and supplies the ink to the recording head. The circulation flow passage has a first ink-flow passage connecting between the pump mechanism and the ink tank, a second ink-flow passage connecting between the pump mechanism and the inflow port of the recording head, and a third ink-flow passage connecting between the outflow port of the recording head and the ink tank. The inflow side valve is provided in the second ink-flow passage. The outflow side valve is provided in the third ink-flow passage. The damper portion is formed in the ink-flow passage from the inflow side valve to the outflow side valve, buffering a change in internal pressure caused by an operation of the pump mechanism. And, the inkjet recording apparatus is capable of implementing an operation of removing air bubbles in the recording head, which includes: the ink supply step of supplying the ink to the common flow-passage by using the pump mechanism for pressurizing the ink in the state in which movement of the ink inside the second ink-flow passage is tolerated with the inflow side valve, and movement of the ink inside the third ink-flow passage is restricted with the outflow side valve; the ink ejection step of ejecting, after start of the ink supply step, the ink together with the air bubbles inside the common flow-passage from the outflow port into the third ink-flow passage by tolerating movement of the ink inside the third ink-flow passage with the outflow side valve; and the refilling step of, after termination of the ink ejection step, refilling the ink into the pump mechanism from the ink tank through the first ink-flow passage in the state in which movement of the ink inside the second ink-flow passage is restricted with the inflow side valve.

A method for removing air bubbles in an inkjet recording apparatus in accordance with another aspect of the present invention provides the ink supply step, the ink ejection step, and the refilling step for an inkjet recording apparatus including a recording head, an ink tank, a pump mechanism, a circulation flow passage, an inflow side valve, and an outflow side valve. The recording head has a common flow-passage having an inflow port at one end and an outflow port at the other end, and a plurality of nozzles communicating with the common flow-passage. The pump mechanism supplies ink inside the ink tank to the recording head. The circulation flow passage has a first ink-flow passage connecting between the pump mechanism and the ink tank, a second ink-flow passage connecting between the pump mechanism and the inflow port of the recording head, and a third ink-flow passage connecting between the outflow port of the recording head and the ink tank. The inflow side valve is provided in the second ink-flow passage. The outflow side valve is provided in the third ink-flow passage. The ink supply step supplies the ink to the common flow-passage by using the pump mechanism for pressurizing the ink in the state in which movement of the ink inside the second ink-flow passage is tolerated with the inflow side valve, and movement of the ink inside the third ink-flow passage is restricted with the outflow side valve. The ink ejection step ejects, after start of the ink supply step, the ink inside the common flow-passage together with the air bubbles from the outflow port into the third ink-flow passage by tolerating movement of the ink inside the third ink-flow passage with the outflow side valve. The refilling step refills, after termination of the ink ejection step, the ink from the ink tank into the pump mechanism through the first ink-flow passage in the state in which movement of the ink inside the second ink-flow passage is restricted with the inflow side valve.

An inkjet recording apparatus in accordance with another aspect of the present invention includes a recording head, an ink tank, a pump mechanism, a circulation flow passage, an inflow side valve, and an outflow side valve. The recording head has a common flow-passage having an inflow port at one end and an outflow port at the other end, and a plurality of nozzles communicating with the common flow-passage. The pump mechanism supplies ink inside the ink tank to the recording head. The circulation flow passage has a first ink-flow passage connecting between the pump mechanism and the ink tank, a second ink-flow passage connecting between the pump mechanism and the inflow port of the recording head, and a third ink-flow passage connecting between the outflow port of the recording head and the ink tank. The inflow side valve is provided in the second ink-flow passage. The outflow side valve is provided in the third ink-flow passage. And, the ink supply step of supplying the ink to the common flow-passage by using the pump mechanism for pressurizing the ink in the state in which movement of the ink inside the second ink-flow passage is tolerated with the inflow side valve, and movement of the ink inside the third ink-flow passage is restricted with the outflow side valve, the ink ejection step ejects, after start of the ink supply step, the ink inside the common flow-passage together with the air bubbles from the outflow port into the third ink-flow passage by tolerating movement of the ink inside of the third ink-flow passage with the outflow side valve, and the refilling step of refilling, after termination of the ink ejection step, the ink from the ink tank into the pump mechanism through the first ink-flow passage in the state in which movement of the ink inside the second ink-flow passage is restricted with the inflow side valve can be implemented.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinbelow, an embodiment of the present invention will be explained with reference to the drawings.FIG. 1is a side view schematically showing the structure of an inkjet recording apparatus100in accordance with the present invention, andFIG. 2is a plan view of a first conveyance unit5and a recording unit9of the inkjet recording apparatus100shown inFIG. 1when viewed from the top.

As shown inFIG. 1, in the left side portion of the inkjet recording apparatus100, a pick-up tray2for accommodating paper sheets P (record media) is provided. At one end of this pick-up tray2, there are provided a pick-up roller3for picking up the accommodated paper sheets P one by one sequentially from the top-positioned paper sheet P and feeding it to a first conveyance unit5later described, and a driven roller4which is butted against the pick-up roller3and driven thereby to be rotated.

On the downstream side (the right side inFIG. 1) of the pick-up roller3and driven roller4in the paper sheet conveyance direction, the first conveyance unit5and the recording unit9are disposed. The first conveyance unit5includes a first driving roller6which is disposed on the downstream side in the paper sheet conveyance direction, a first driven roller7which is disposed on the upstream side in the paper sheet conveyance direction, and a first feeding belt8which is installed on the first driving roller6and the first driven roller7. With the first driving roller6being driven to be rotated in a clockwise direction, the paper sheet P held by the first feeding belt8is fed in the paper sheet conveyance direction.

Note that the first driving roller6is disposed on the downstream side in the paper sheet conveyance direction, thereby the feeding surface (the upper surface inFIG. 1) of the first feeding belt8being pulled by the first driving roller6, which allows the tension of the feeding surface of the first feeding belt8to be increased, and thus stable feeding of the paper sheet P to be made. As the first feeding belt8, a sheet made of a dielectric resin may be used, and mainly a belt having no seams (a seamless belt) may be used.

The recording unit9includes a head housing10, and line heads11C,11M,11Y, and11K which are held by the head housing10. These line heads11C to11K are supported at a level where a predetermined spacing (for example, 1 mm) with respect to the feeding surface of the first feeding belt8is given, and as shown inFIG. 2, a plurality of (herein three) recording heads17ato17care arranged zigzag along the paper sheet width direction (in a vertical direction inFIG. 2) which is orthogonal to the paper sheet conveyance direction. The line heads11C to11K have a width larger than the width of the paper sheet P fed, and can discharge the ink from a nozzle18corresponding to a printing position onto the paper sheet P which is fed on the first feeding belt8. Further, the respective recording heads17ato17care disposed such that a part of the nozzles18provided in each of them are duplicated in the feeding direction.

The recording heads17ato17cconstituting the respective line heads11C to11K are supplied with ink having a color specified for the respective line heads11C to11K from one of the tanks (not shown) of inks having four different colors (cyan, magenta, yellow and black).

The respective recording heads17ato17cdischarge the ink from the nozzle18onto the paper sheet P which is fed, being adsorbed to the feeding surface of the first feeding belt8to be held thereby, according to image data received from an external computer, or the like. Thereby, on the paper sheet P on the first feeding belt8, there is formed a color image in which the inks of the four colors of cyan, magenta, yellow, and black are superposed one upon another.

Further, at the time of starting the printing following the downtime over a long period of time, the purging operation, which discharges the ink having an increased viscosity from the nozzle18, is executed for the nozzles18in all the recording heads17ato17c, and at an interval between printing operations, the purging operation is made for any nozzles18in the recording heads17ato17cwith which the amount of ink discharge has been lowered below a predetermined value, thereby the recording heads17ato17cbeing prepared for the subsequent printing operation. Thus, poor discharge of the ink due to, for example, drying or clogging of the recording heads17ato17ccan be suppressed.

On the downstream side (the right side inFIG. 1) of the first conveyance unit5in the paper sheet conveyance direction, a second conveyance unit12is disposed. The second conveyance unit12is configured to include a second driving roller13which is disposed on the downstream side in the paper sheet conveyance direction, a second driven roller14which is disposed on the upstream side in the paper sheet conveyance direction, and a second feeding belt15which is installed on the second driving roller13and the second driven roller14, and with the second driving roller13being driven to be rotated in a clockwise direction, the paper sheet P held by the second feeding belt15is fed in the paper sheet conveyance direction.

The paper sheet P on which an ink image is recorded by the recording unit9is fed to the second conveyance unit12, and while being passed through the second conveyance unit12, the inks discharged on the surface of the paper sheet P are dried. Further, under the second conveyance unit12, a maintenance unit19is disposed. The maintenance unit19is moved to under the recording unit9when the above-mentioned purging operation is executed, and wipes off the inks discharged from the nozzles18in the recording heads17to recover the inks.

On the downstream side of the second conveyance unit12in the paper sheet conveyance direction, there is provided a delivery roller pair16for delivering the paper sheet P on which the image is recorded, to the outside of the apparatus main body, and on the downstream side of the delivery roller pair16, there is provided a delivery tray (not shown) on which the paper sheets P delivered to the outside of the apparatus main body are stacked.

FIG. 3is a drawing schematically showing an ink-flow passage of the inkjet recording apparatus100according to the embodiment of the present invention, andFIG. 4is a sectional view schematically showing the internal structure of the recording head17. Between the main tank20for the respective colors and the recording head17, the ink-flow passage shown inFIG. 3is provided, respectively, however, the ink-flow passage for a particular color will be explained here. In addition, the recording heads17ato17care expressed as the recording head17, the symbols17ato17cbeing abbreviated to17.

As shown inFIG. 3, between the main tank20and the recording head17, a sub-tank21and a syringe pump23are disposed, and the sub-tank21and the syringe pump23are connected to each other by a first ink-flow passage22formed of a tubing member. An inflow port27aof the recording head17and the syringe pump23are connected to each other by a second ink-flow passage24formed of a tubing member, and the second ink-flow passage24is connected to the first ink-flow passage22through an inflow side valve25constituted by a three-way valve.

On the other hand, an outflow port27bof the recording head17and the sub-tank21are connected to each other by a third ink-flow passage32formed of a tubing member, and in the third ink-flow passage32, an outflow side valve33constituted by a three-way valve is provided. In addition, to the third ink-flow passage32, a waste fluid tank35is connected through the outflow side valve33. The first ink-flow passage22, the second ink-flow passage24, and the third ink-flow passage32form a circulation flow passage which connects the recording head17, the sub-tank21, and the syringe pump23to one another.

As shown inFIG. 4, in the recording head17, a common flow-passage29ranging from the inflow port27ato the outflow port27bis provided, and in the portion of the common flow-passage29that is closer to the inflow port27a, a damper portion30is formed. With the damper portion30, a part of the inner wall of the common flow-passage29is formed of a flexible film, and when the internal pressure of the common flow-passage29is raised, the damper portion30is inflated outward, while, when the internal pressure is lowered, the damper portion30becomes dented, thereby an abrupt change in internal pressure of the common flow-passage29can be buffered. In the present embodiment, the damper portion30is provided between the inflow port27aand the outflow port27bof the recording head17, however, the damper portion30may be disposed outside of the recording head17, provided that it is placed between the inflow side valve25and the outflow side valve33.

Further, a branch passage31is provided which is branched downward from the common flow-passage29, being led to the respective nozzles18. For example, in a case where the recording head17is a piezoelectric inkjet head which transmits a pressure change caused by a deformation of a piezoelectric element (not shown) to the ink in the nozzle18to fluctuate the meniscus, thereby generating an ink drop, a voltage having a predetermined driving waveform is applied to the piezoelectric element to thereby discharge a predetermined amount of ink from the nozzle18corresponding to printing data.

FIG. 5is a drawing schematically showing the syringe pump23and a driving apparatus70for the syringe pump23which are used in the present embodiment. As shown inFIG. 5, the syringe pump23includes a cylinder63and a piston65. The piston65has a piston portion65a, which is formed at the lower end of a piston rod65b. Further, the upper end of the piston rod65bis extended to above the top wall of the cylinder63, and in the extended end portion of the piston rod65b, a flange portion65cis formed.

Further, there is protruded downward from the lower end face of the cylinder63a supply/ejection portion67, which is hollow cylindrical, being communicated with the cylinder63. The supply/ejection portion67is connected with the first ink-flow passage22, and the ink inside the sub-tank21(refer toFIG. 3) is caused to flow into the cylinder63through the supply/ejection portion67, while the ink inside the cylinder63is ejected through the supply/ejection portion67, the ejected ink being supplied to the recording head17(refer toFIG. 3) through the second ink-flow passage24.

On the other hand, the piston65of the syringe pump23can be vertically moved by the driving apparatus70. The driving apparatus70has a ball screw71, a nut portion77, and a drive motor79. The ball screw71is disposed substantially in parallel with the cylinder63(in a vertical direction) in the vicinity of the flange portion65cof the piston65. The lower end portion and the upper end portion of the ball screw71are rotatably supported by ball screw supporting members73aand73b.

Further, the upper end portion of the ball screw71is extended to above the ball screw supporting member73b, the extended end portion being provided with a coupling75. The coupling75is connected with a rotating shaft79aof the drive motor79such that the ball screw71is rotated with the drive motor79being run. Further, the drive motor79can be run either forward or backward. The ball screw71is operatively engaged with the nut portion77, and with the ball screw71being rotated, the nut portion77is moved upward or downward depending upon the direction of rotation.

Further, in the nut portion77, there is formed a fixing portion77awhich includes two plate-like members, being protruded toward the piston65, and the fixing portion77asandwiches the flange portion65cof the piston65, thereby being connected to the flange portion65c. Thus, with the drive motor79being run, the piston65is moved upward or downward together with the nut portion77.

The relationship between the direction of running of the drive motor79and the direction of movement of the piston65is not specifically limited, and for example, it can be set such that, if the drive motor79is run in a clockwise direction when viewed from the top inFIG. 5, the piston65is moved downward (refer toFIG. 8), while if the drive motor79is run in a counterclockwise direction when viewed from the top inFIG. 5, the piston65is moved upward (refer toFIG. 10).

The cylinder63is partitioned into a first containing chamber63aon the supply/ejection portion67side and a second containing chamber63bon the piston rod65bside by the piston portion65a. Further, the ink supplied from the sub-tank21is contained in the first containing chamber63a. On the periphery of the piston portion65a, a packing (not shown), such as an O-ring, is loaded in order to prevent the ink from being leaked from the first containing chamber63ato the second containing chamber63b, and permit the piston portion65ato be smoothly slid on the inner wall of the cylinder63.

When the drive motor79is run to move the piston portion65aupward (refer toFIG. 10), a negative pressure is generated in the first containing chamber63aof the cylinder63. Such negative pressure causes the ink in the sub-tank21to be sucked into the cylinder63through the inflow side valve25, thereby a substantially predetermined quantity of ink being introduced into the first containing chamber63athrough the supply/ejection portion67. On the other hand, when the drive motor79is run in a direction reverse to that of the above-mentioned motor running, thereby the piston portion65abeing moved downward, a positive pressure is generated in the first containing chamber63a, and such positive pressure causes the ink to be ejected from the supply/ejection portion67, thereby a substantially fixed quantity of ink being supplied to the recording head17through the inflow side valve25(refer toFIG. 8).

Next, the operation of removing air bubbles in the recording head17will be explained.FIG. 6is a flowchart illustrating a first sequence of steps of operation of removing air bubbles in the recording head17, andFIG. 7toFIG. 10are drawings schematically showing the respective steps to be taken in an operation of removing air bubbles in the recording head17. With reference toFIG. 7toFIG. 10, and as required, toFIG. 1toFIG. 5, the procedure for performing an operation of removing air bubbles in the recording head17will be explained along the flow of the steps inFIG. 6.

At a normal time (a printing waiting time), as shown inFIG. 3, the sub-tank21side of the inflow side valve25and the recording head17side thereof are communicated with each other, and a negative pressure is applied to the damper portion30, resulting from a difference in water head between the sub-tank21and the recording head17.

As shown inFIG. 7, in the event where air bubbles B are generated inside the common flow-passage29of the recording head17, the inflow side valve25is first switched over such that the syringe pump23side and the recording head17side are communicated with each other (step S1). Next, the piston65in the syringe pump23is pressed down to pressurize the ink in the syringe pump23for supplying the ink from the inflow port27aof the recording head17to the inside of the common flow-passage29(step S2). And, as the ink is supplied from the inflow port27a, an ink flow directed toward the outflow port27bis generated inside the common flow-passage29, the air bubbles B being moved toward the outflow port27bby the ink flow generated.

At this time, the outflow side valve33is closed, the outflow of the ink from the outflow port27bbeing restricted, and therefore inside the common flow-passage29, a positive pressure is generated, however, as shown inFIG. 8, the damper portion30is inflated to thereby buffer an abrupt increase in internal pressure inside the common flow-passage29due to the ink supply from the syringe pump23.

Next, when the pressurization of the ink by the syringe pump23has been terminated (step S3), the outflow side valve33is opened (step S4). With this, as shown inFIG. 9, the pressure inside the common flow-passage29is released, the ink kept in the damper portion30being ejected from the outflow port27btogether with the air bubbles B. Next, the outflow side valve33is again closed (step S5), and the inflow side valve25is switched over such that the syringe pump23side and the sub-tank21side are communicated with each other (step S6).

Thereafter, as shown inFIG. 10, the piston65in the syringe pump23is pulled up to refill the syringe pump23with the ink (step S7), and the inflow side valve25is switched over such that the sub-tank21side and the recording head17side are communicated with each other (step S8), thereby the operation of removing air bubbles being completed, and the initial state shown inFIG. 3being restored.

Note that, if, before the outflow side valve33is again closed after the ink supply by the syringe pump23having been terminated, the inflow side valve25were switched over such that the syringe pump23side and the sub-tank side are communicated with each other, a reverse flow of the ink would be generated from the inflow port27atoward the syringe pump23side, the ink kept in the damper portion30being ejected into the common flow-passage29with the pressure inside the common flow-passage29being released and the damper portion30being contracted. And, as a result of this, the air bubbles B which could not have been carried away from the outflow port27bwould also flow upstream from the inflow port27a.

Accordingly, by taking the above procedure for performing an operation of removing air bubbles in the recording head17, there will occur no reverse flow of the ink from the inflow port27atoward the syringe pump23side. Thus, the air bubbles B inside the common flow-passage29can be reliably carried away from the outflow port27b. The ink which has been carried away together with the air bubbles B from the outflow port27bare returned to the sub-tank21through the third ink-flow passage32. While the ink is being reserved in the sub-tank21, the air bubbles B in the ink get out of the liquid surface, and therefore, there is no possibility that the ink including air bubbles is supplied to the recording head17from the sub-tank21through the syringe pump23.

Further, since, after the ink inside the common flow-passage29has been ejected from the outflow port27binto the third ink-flow passage32together with the air bubbles B, the outflow side valve33is closed before the inflow side valve25is switched over such that the syringe pump23side and the sub-tank21side are communicated with each other, reverse flowing of the ink inside the third ink-flow passage32into the common flow-passage29at the time of the inflow side valve25being switched over can be suppressed.

As the timing when the outflow side valve33is to be opened, it may be any time after the ink supply by the syringe pump23is terminated and before the inflow side valve25is switched over, and the outflow side valve33can be opened immediately (in a few seconds) after the pressurization of the ink by the syringe pump23having been terminated. Alternatively, for example, like a second sequence of steps illustrated inFIG. 11, the outflow side valve33can be opened simultaneously with the termination of the pressurization of the ink by the syringe pump23(step S3).

FIG. 12is a flowchart illustrating a third sequence of steps of operation of removing air bubbles in the recording head17. In the procedure illustrated inFIG. 12, after the ink supply by the pressurization of the ink by the syringe pump23having been started (step S2), the outflow side valve33is opened (step S3) before the pressurization by the syringe pump23is terminated (step S4). Since the other controls are the same as those inFIG. 6orFIG. 11, explanation thereof will be omitted.

By using the above procedure for making an operation of removing air bubbles in the recording head17, the outflow side valve33can be positively opened before the ink supply by the syringe pump23is terminated, even if the time period from the start of the opening operation of the outflow side valve33to the termination thereof involves a time lag, and therefore, the control of the opening timing for the outflow side valve33can be easily performed. Further, since the outflow side valve33is opened for ejection of the ink before the pressurization of the ink by the syringe pump23is terminated, the time required for operation of removing air bubbles can be shortened.

FIG. 13is a drawing schematically showing another example of configuration of the ink-flow passage of the inkjet recording apparatus100of the present invention. In the present embodiment, the first ink-flow passage22and the second ink-flow passage24are provided independently of each other, and a first inflow side valve25acomprised of a two-way valve is disposed in the second ink-flow passage24, while a second inflow side valve25bcomprised of a two-way valve is disposed in the first ink-flow passage22. The configuration of the other part is the same as that of the ink-flow passage shown inFIG. 3, and therefore, explanation thereof will be omitted.

Also in the configuration shown inFIG. 13, by making an operation of removing air bubbles with the same sequence of steps as that inFIG. 6,FIG. 11, orFIG. 12, occurrence of a reverse flow of the ink from the inflow port27atoward the syringe pump23side is prevented, whereby the air bubbles B inside the common flow-passage29can be reliably carried away from the outflow port27b.

The operation of removing air bubbles as described above can be performed simultaneously with an operation of recovering (purging) the recording head17by forcedly discharging the viscosity-increased ink, foreign matters, air bubbles, and the like in the nozzles18with the syringe pump23being used to pressurize the ink in the recording head17from the inflow port27aside.

However, in a case where the air bubble removing operation is performed simultaneously with the purging operation, generation of air bubbles always involves a certain quantity of ink being discharged from the nozzles18, and therefore a problem has been presented that the ink consumption in an operation other than the printing operation is increased. In addition, the ink in which air bubbles have been merely generated can be used for printing with substantially no problem if the air bubbles are removed, and therefore it is not always required to make a purging. Then, the air bubble removing mode in which only the air bubbles inside the common flow-passage29are removed without the ink being discharged from the nozzle18can be implemented separately of the purging operation.

Further, when the outflow side valve33is opened at step S4inFIG. 6, and at step S3inFIG. 11andFIG. 12, the outflow side valve33is switched over such that, as shown inFIG. 9, the outflow port27bof the recording head17and the sub-tank21are communicated with each other, whereby the ink carried away from the outflow port27btogether with the air bubbles can be reused, however, instead of this scheme, the outflow side valve33may be switched over such that the outflow port27band the waste fluid tank35are communicated with each other.

For example, in a case where the air bubble removing operation is performed simultaneously with the purging operation, communicating the outflow port27bwith the waste fluid tank35causes the ink inside the common flow-passage29to be recovered into the waste fluid tank35, thereby the possibility being eliminated that the ink containing a viscosity-increased ink, foreign matters, and the like are reused. Accordingly, whether the outflow side valve33is switched over to the sub-tank21side, or to the waste fluid tank35side may be determined depending upon the condition of the ink in the common flow-passage29.

Thus, the present invention is not limited to the above-stated embodiment, and may be variously modified within the scope of the spirit of the present invention. For example, the above-stated embodiment is configured such that the syringe pump23is used to supply the ink to the recording head17, however, the method for supplying the ink at the time of printing is not specifically limited, provided that the ink is suppliable from the sub-tank21to the recording head17. For example, an ink supply passage which connects between the sub-tank21and the recording head17not through the syringe pump23may be provided for supplying the ink from the sub-tank21to the recording head17. In addition, a pump mechanism different from the syringe pump23may be used.

In addition, the main tank20and the waste fluid tank35are not indispensable components, and for example, with a small-sized inkjet recording apparatus, the sub-tank21may be replaced with another one when the ink in the sub-tank21is used up, the main tank20being not provided. In addition, instead of the waste fluid tank35, a recovery tray for recovering the viscosity-increased ink or the ink including foreign matters that has been discharged from the nozzle18by the purging operation may be provided.

In addition, the number of nozzles18in the recording head17, the nozzle-to-nozzle spacing, and the like, may be set as appropriate in accordance with the specifications for the inkjet recording apparatus100. In addition, the number of recording heads17is not particularly limited, and for example, a single recording head17may be disposed for each of the line heads11C to11K.

The present invention is applicable to inkjet recording apparatuses which perform recording by discharging the ink from the recording head. By utilizing the present invention, the time required for recovering the recording head can be shortened, whereby there can be obtained an inkjet recording apparatus with which the user waiting time is shorter, and the usability is more excellent. In addition, an inkjet recording apparatus can be obtained which can suppress clogging of the ink discharge nozzle and poor printing due to sucking back a viscosity-increased ink or foreign matters discharged from the ink discharge nozzle.