The present patent application claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2009-088978, filed on Apr. 1, 2009 in the Japan Patent Office, which is incorporated herein by reference in its entirety.
1. Field of the Invention
Illustrative embodiments of the present invention relate to an inkjet recording apparatus that ejects recording liquid onto a recording medium to form an image on the recording medium.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, multi-functional peripherals having two or more of the foregoing capabilities, or plotters. Such image forming apparatuses may include as an image forming section an inkjet recording device employing a liquid ejection method. The inkjet recording device ejects droplets of recording liquid, e.g., ink (hereinafter referred to as “ink droplets”), from nozzles of a recording head to form an image on a recording medium (sheet or material).
Such an inkjet recording device may include a maintenance unit that maintains good performance of the recording head. For example, a conventional type of maintenance unit includes a suction cap and a suction pump that suctions high-viscosity ink from the nozzles of the recording head covered with the suction cap. Such a conventional inkjet recording device may also include a supply pump that supplies ink from an ink cartridge to a recording head.
To perform cleaning to maintain good performance of the recording head, for example, a conventional type of inkjet recording device like that described in JP-3573059-B employs a so-called tube pump. The tube pump creates negative pressure in a capping unit that suctions ink from the recording head and supplies ink from a main tank to a sub tank through a tube. Such a tube pump has a relatively simple structure, allowing the device as a whole to be made more compact, and prevents ink contamination at a mechanical portion for suctioning and discharging ink. With such a configuration, in which ink is supplied from the main tank to the sub tank with the tube pump, while the pump is stopped, the tube is compressed in the tube pump to block a flow path and prevent ink from spontaneously flowing from the main tank to the sub tank by the negative pressure in the sub tank, thus maintaining pressure in the sub tank.
However, if the tube pump is left for a long time with the flow path of the tube blocked, compressed portions of the inner wall of the tube may stick together. Consequently, even if the pump is restarted to rotate, ink may not be supplied or suctioned. Usually, even if portions of the inner wall of the tube stick together, operating the tube pump pushes enough ink through the tube to resolve the blockage, thus allowing ink supply or suctioning to continue. However, at an approach to a compressed area of the tube, even if the pump is operated, ink may be not supplied to resolve the blockage in the tube, requiring waiting for spontaneously separation of the stuck portions of the inner wall. To prevent such a failure, it is conceivable that a sensor and a stepping motor might be used to prevent the pump from stopping at the approach to the compressed area of the tube. However, such a configuration may increase cost and size.
In an illustrative embodiment, an inkjet recording device includes a liquid-droplet ejection head, a flexible tube member, a tube pump, a rotational press member, and a controller. The liquid-droplet ejection head includes a plurality of nozzles for ejecting droplets of a recording liquid. The flexible tube member is connected to the liquid-droplet ejection head. The tube pump is disposed on the flexible tube member to supply the recording liquid to the liquid-droplet ejection head through the flexible tube member. The rotational press member is disposed in the tube pump and, while rotating in a first rotation direction, sequentially compresses the flexible tube member to supply the recording liquid to the liquid-droplet ejection head. The controller is communicatively connected to the tube pump and causes the rotational press member of the tube pump to rotate in the first rotation direction and a second rotation direction opposite to the first rotation direction. At least one portion of the flexible tube member is compressed with the rotational press member while the tube pump is stopped. The controller, prior to rotation of the rotational press member in either the first rotation direction or the second rotation direction, causes the rotational press member to rotate in reverse with respect to the first rotation direction or the second rotation direction.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily acquired as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The accompanying drawings are intended to depict illustrative embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results.
Although the illustrative embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the present invention and all of the components or elements described in the illustrative embodiments of this disclosure are not necessarily indispensable to the present invention.
In this disclosure, the term “recording medium” may be referred to as “sheet”. It is to be noted that the term “sheet” is not intended to limit the recording medium to a specific material and represents an object to which a recording liquid, e.g., ink adheres. Further, a recording sheet, a recording material, or a transfer material may be also used for a synonym of “recording medium”. The term “image formation” is used herein for a synonym of “image recording” and “image printing”.
Below, an example of an image forming apparatus 1 including an inkjet recording device with a maintenance unit according to an illustrative embodiment of the present disclosure is described with reference to
Next, a mechanical section of the image forming apparatus 1 is described with reference to
In the mechanical section of the image forming apparatus 1, a carriage 33 is slidably held with a guide rod 31 and a stay 32. The guide rod 31 and the stay 32 serving as guide members extend between side plates 21A and 21B constituting a frame 21. The carriage 33 is moved by a main scan motor, not illustrated, for scanning in a main scan direction “MSD” indicated by a double arrow illustrated in
On the carriage 33 are mounted recording heads 34 that are four liquid-droplet ejection heads (inkjet heads) to eject droplets of different color inks of, e.g., yellow (Y), cyan (C), magenta (M), and black (K). The recording heads 34 are mounted on the carriage 33 so that a plurality of nozzles is arranged in a direction perpendicular to the main scan direction and ink droplets are ejected downward from the nozzles. As illustrated in
The recording heads 34 serving as droplet ejection heads include pressure generators that generate pressure to eject liquid droplets. As such a pressure generator, the recording heads 34 may employ, for example, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by film boiling of liquid (ink) using an electro/thermal converting element such as a heat-generation resistant, a shape-memory-alloy actuator that uses a metal phase change caused by a temperature change, or an electrostatic actuator that generates pressure by electrostatic force.
On the carriage 33 is mounted a plurality of sub tanks 35Y, 35M, 35C, and 35K (hereinafter collectively referred to as “sub tanks 35”) that supplies the different color inks to the recording heads 34. The different color inks are supplied (refilled) from the ink cartridges 10 (hereinafter referred to as 10K, 10C, 10M, and 10Y when colors distinguished) mounted to the sub tanks 35 via ink supply tubes 37.
The ink cartridges 10 are mounted in the cartridge mount portion 6. As illustrated in
As illustrated in
To feed the sheet 42 from the sheet feed section to a position below the recording heads 34, the image forming apparatus 1 includes a conveyance belt 51, a counter roller 52, a conveyance guide 53, a press member 54, and a front-end press roller 55. The conveyance belt 51 conveys the sheet 42 with the sheet 42 electrostatically attracted thereon. Receiving the sheet 42 from the sheet feed section via a first guide member 45, the counter roller 52 feeds the sheet 42 while sandwiching the sheet 42 between it and the conveyance belt 51. Receiving the sheet 42 sent in a substantially vertically upward direction, the conveyance guide 53 turns the sheet feed direction of the sheet 42 by substantially 90 degrees to guide the sheet 42 onto the conveyance belt 51. The front-end press roller 55 is biased toward the conveyance belt 51 with the press member 54. A charge roller 56 is provided to charge a surface of the conveyance belt 51. The conveyance belt 51 is an endless belt that is looped between a conveyance roller 57 and a tension roller 58 so as to circulate in a belt circulation direction “BCD” (sub-scanning direction) illustrated in
On the inner circumferential surface of the conveyance belt 51 is disposed a second guide member 61 at a position corresponding to a print area of the recording heads 34. The upper surface of the second guide member 61 protrudes to a position closer to the recording heads 34 than a common tangent line of the conveyance roller 57 and the tension roller 58 that support the conveyance belt 51. Thus, at the print area, the conveyance belt 51 is pushed up along the upper face of the second guide member 61 while keeping a highly accurate planarity.
The image forming apparatus 1 further includes a sheet output section that outputs the sheet 42 on which an image has been formed by the recording heads 34. The sheet output section includes a separation claw 71, a first output roller 72, a second output roller 73, and the sheet output tray 3 described above. The separation claw 71 separates the sheet 42 from the conveyance belt 51. A height from a sandwich point between the first output roller 72 and the second output roller 73 to the sheet output tray 3 is set to enough height to stack a great number of sheets on the sheet output tray 3.
A duplex unit 81 is detachably mounted on a rear portion of the image forming apparatus 1. Receiving the sheet 42 returned by reverse rotation of the conveyance belt 51, the duplex unit 81 turns the sheet 42 upside down to feed the sheet 42 between the front-end press roller 55 and the conveyance belt 51. At the top face of the duplex unit 81 is formed a manual-feed tray 82.
As illustrated in
In the image forming apparatus 1 having the above-described configuration, the sheet 42 is separated sheet by sheet from the sheet feed tray 102, fed in a substantially vertically upward direction, guided along the first guide member 45, and conveyed between the conveyance belt 51 and the counter roller 52. Further, the front tip of the sheet 42 is guided with the conveyance guide 53 and pressed against the conveyance belt 51 by the front-end press roller 55 to turn the conveyance direction of the sheet 42 by substantially 90°.
At this time, a control circuit causes an AC (alternating current) bias supply unit to alternately supply positive and negative voltages to the charge roller 56 so that the conveyance belt 51 is charged with an alternating voltage pattern, that is, an alternating band pattern of positively-charged areas and negatively-charged areas in the sub-scanning direction, i.e., the belt circulation direction. When the sheet 42 is fed onto the conveyance belt 51 alternately charged with positive and negative charges, the sheet 42 is electrostatically attracted on the conveyance belt 51 and conveyed in the sub-scanning direction by circulation of the conveyance belt 51.
By driving the recording heads 34 in response to image signals while moving the carriage 33 in the main scan direction, ink droplets are ejected onto the sheet 42 stopped below the recording heads 34 to form one band of a desired image. Then, the sheet 42 is fed by a certain distance and another band of the image is recorded. Receiving a recording end signal or a signal indicating that the rear end of the sheet 42 has arrived at the recording area, the recording heads 34 finish the recording operation and the sheet 42 is outputted to the sheet output tray 3.
In waiting for the next recording (print) operation, the carriage 33 moves to the maintenance unit 91 and the caps 92 cover the recording heads 34. Accordingly, the moisture of the nozzles of the recording heads 34 is kept, thus preventing an ejection failure caused by ink drying. Then, a suction pump, not illustrated, suctions ink from the nozzles with the recording heads 34 covered with the caps 92, which is called “nozzle suction” or “head suction”. Thus, the recovery operation is performed to remove increased-viscosity ink (recording liquid) or air bubbles. Further, before or during a recording operation, as described above, ink droplets unrelated to a recorded image are discharged for maintenance. Such maintenance operation allows keeping a stable ejection performance of the recording heads 34.
A description is given with reference to
A tube pump serving as a liquid-feed pump switches forward feeding and reverse feeding (supply and suction) of ink by changing the rotation direction of a driving motor.
As illustrated in
The tube pump 100 supplies and suctions ink by a restoration force generated when the compressed portion of the tube 105 restores the original state, and has enough flexibility to prevent an excessive increase in the rotation torque of the driving force of the tube pump 100. The tube 105 may be, e.g., a rubber tube of a hardness of approximately 50 to 65. With such a configuration, when the tube pump 100 is stopped, at least one portion of the tube 105 is compressed to block the flow path of the tube 105, thus preventing ink from spontaneously flowing through the tube 105 by a difference in pressure between portions upstream and downstream from the compressed portion. However, with such a configuration, since the tube 105 remains compressed while the tube pump 100 is stopped, portions of the inner wall of the tube 105 might stick together after a long unused time and keeps blocking the flow path even when the tube pump 100 is restarted to rotate the press roller 104. For example, as illustrated in
The present illustrative embodiment prevents such a failure without adding to the tube pump a complex configuration or an expensive component. One example is described with reference to
The above-described failure does not occur unless the pump is stopped for such a long time that portions of the inner wall of the tube remain sticking together so as not to restore the original shape. Hence, in consideration of the product life, a threshold time (Trevreq: time of reverse-rotation request) may be set for a stop time for which the tube pump is stopped until the reverse rotation of the press roller is needed, and the stop time of the tube pump may be monitored. Then, as illustrated in
Further, the tube pump may perform only supply operation without performing suctioning operation except during an air-release refill sequence illustrated in
The air-release refill is a method of filling ink to the sub tank while releasing air from the sub tank and the supply route. As illustrated in
Further, in view of the product life of the tube pump, as illustrated in
The above-described control method is applicable to inkjet recording employing, for example, an ink that contains water, pigment, polymer, and water-soluble organic solvent. The proportion of pigment in the ink may be, e.g., 6 weight percent or greater, and the viscosity of the ink at 25° C. may be, e.g., in a range of 5 mPa·sec or greater and 20 mPa·sec or less. The surface tension of the ink may be, e.g., 40 dyne/cm or less.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein.
With some embodiments of the present invention having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present invention, and all such modifications are intended to be included within the scope of the present invention.
For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.
Number | Date | Country | Kind |
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2009-088978 | Apr 2009 | JP | national |