This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2011-058139, filed on Mar. 16, 2011, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting droplets of ink. Such inkjet-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving a carriage mounting the recording head in a main scanning direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
As for the recording heads used in these liquid-ejection-type image forming apparatuses, several different types are known. One example is a piezoelectric recording head that ejects droplets by deforming a diaphragm using, e.g., piezoelectric actuators. When the piezoelectric actuators deform the diaphragm, the volumes of chambers containing the liquid change. As a result, the internal pressures of the chambers increase, thus ejecting droplets from the head. Another example is a thermal recording head that ejects droplets by increasing the internal pressures of chambers using, e.g., heaters disposed in the chambers. The heaters are heated by electric current to generate bubbles in the chambers. As a result, the internal pressures of the chambers increase, thus ejecting droplets from the head.
For such liquid-ejection type image forming apparatuses, there is demand for enhancing throughput, i.e., speed of image formation. One way to increase the throughput is to enhance the efficiency of liquid supply. For example, a tube supply method is proposed in which ink is supplied from a large-volume ink cartridge (main tank) mounted in the image forming apparatus to a head tank (also referred to as a sub tank or buffer tank) mounted in an upper portion of the recording head through a tube.
In this regard, in a case where ink is supplied from the ink cartridge to the head tank via a tube made of, e.g., resin, it is difficult to use the head tank with the head tank constantly full of ink and an air layer is formed in an upper space of the head tank. The amount of air in the head tank is likely to increase over time due to air permeating from wall faces of the resin tube and the head tank or air bubbles entering the tube at the installation and removal of the ink cartridge.
A small amount of air in the head tank is not so problematic. However, if the amount of air in the head tank is too large, the amount of change in the volume of air relative to temperature change increases. As a result, the internal pressure of the head tank may be out of a proper range of negative pressures to be maintained, thus leaking ink from nozzles of the recording head or hampering normal ink ejection. In addition, when the amount of air in the head tank is too large, air may mix into ink, thus hampering normal droplet ejection.
Therefore, it is preferable to control the amount of air in the head tank below a threshold amount while maintaining the internal pressure of the head tank within a proper range.
Hence, for example, JP-2010-120263-A proposes a liquid ejection apparatus that has an exhaust mechanism including an air storage part, a valve, and a flexible member. The air storage part is disposed at a liquid supply channel for supplying liquid to the recording head and temporarily stores air contained in ink. The valve opens and closes an exhaust passage leading from the air storage part to the outside. The flexible member is deformed by negative pressure generated in the exhaust passage to open the valve and exhaust air from the air storage part to the outside through the exhaust passage.
However, in the above-described configuration, by negative pressure (exhaust pressure) generated in the exhaust passage, the flexible member is deformed to open the valve. As a result, when the valve is opened, the exhaust pressure may affect the internal pressure of the head, thus sucking air from the nozzles into the liquid ejection head.
In other words, a large negative pressure need be applied to the exhaust passage to open the valve, and once the valve is opened, the large negative pressure directly acts on the liquid ejection head. In particular, in a case where air is exhausted from a plurality of air storage parts, a larger negative pressure need be applied to the exhaust passage, thus making it difficult to perform exhaust operation with the pressure of the head stably maintained.
In an aspect of this disclosure, there is provided an image forming apparatus including a recording head, a head tank, an exhaust unit, and a suctioning device. The recording head has nozzles to eject droplets of liquid. The head tank has a plurality of liquid chambers to supply the liquid to the recording head. The plurality of liquid chambers has exhaust ports to exhaust air therefrom. The exhaust unit is connected to the head tank to exhaust air from the head tank. The suctioning device is connected to the exhaust unit. The exhaust unit includes an exhaust channel, an exhaust chamber, a valve member, a valve driving chamber, a valve driving member, and a choke channel. The exhaust channel is connected to the suctioning device to exhaust air from the head tank. The exhaust chamber is connected to the exhaust ports of the plurality of liquid chambers. The valve member collectively opens and closes the exhaust ports. The valve driving chamber communicates with the exhaust channel and has a flexible member forming a wall face of the valve driving chamber. The valve driving member is disposed at the flexible member to open and close the valve member. The choke channel communicates the exhaust chamber with the valve driving chamber. When the suctioning device suctions air through the exhaust channel with the liquid being in the choke channel, a volume of the valve driving chamber contracts and the valve member opens the exhaust ports.
The aforementioned and other aspects, features, and advantages of the present disclosure would be 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 exemplary 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 exemplary embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and all of the components or elements described in the exemplary embodiments of this disclosure are not necessarily indispensable to the present invention.
In this disclosure, the term “image forming apparatus” refers to an apparatus (e.g., droplet ejection apparatus or liquid ejection apparatus) that ejects ink or any other liquid on a medium to form an image on the medium. The medium is made of, for example, paper, string, fiber, cloth, leather, metal, plastic, glass, timber, and ceramic. The term “image formation”, which is used herein as a synonym for “image recording” and “image printing”, includes providing not only meaningful images such as characters and figures but meaningless images such as patterns to the medium (in other words, the term “image formation” includes only causing liquid droplets to land on the medium). The term “ink” as used herein is not limited to “ink” in a narrow sense and includes any types of liquid useable for image formation, such as a recording liquid, a fixing solution, a DNA sample, and a pattern material. The term “sheet” used herein is not limited to a sheet of paper and includes anything such as an OHP (overhead projector) sheet or a cloth sheet on which ink droplets are attached. In other words, the term “sheet” is used as a generic term including a recording medium, a recorded medium, or a recording sheet. The term “image” used herein is not limited to a two-dimensional image and includes, for example, an image applied to a three dimensional object and a three dimensional object itself formed as a three-dimensionally molded image.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, exemplary embodiments of the present disclosure are described below.
First, an inkjet recording apparatus is described as an image forming apparatus according to an exemplary embodiment of this disclosure with reference to
In the inkjet recording apparatus 1000, a carriage 120 is supported by a guide rod 122 and a guide rail 124 so as to slide in a main scanning direction (i.e., a long direction of the guide rod 122). The guide rod 122 serving as a guide member extends between a left side plate 123L and a right side plate 123R standing on a main frame 30, and the guide rail 124 is mounted on a rear frame 128 extending to the main frame 30. The carriage 120 is moved in the long direction of the guide rod 122 (the main scanning direction) by a main scanning motor 551 and a timing belt.
On the carriage 120 are mounted recording heads 1 (liquid ejection heads) for ejecting ink droplets of different colors, e.g., black (K), cyan (C), magenta (M), and yellow (Y). The recording heads 1 are mounted on the carriage 120 so that multiple ink-ejection ports (nozzles) are arranged in a direction perpendicular to the main scanning direction and ink droplets are ejected downward from the nozzles.
As illustrated in
It is to be noted that the recording head is not limited to the thermal type head but may be a piezoelectric-type head that obtains ejection pressure by deforming a diaphragm with piezoelectric elements, an electrostatic-type head that obtains ejection pressure by deforming a diaphragm with electrostatic force, or any other suitable type head.
Below the carriage 120, a sheet 8 on which an image is formed by the recording heads 1 is conveyed in a direction (hereinafter “sub-scanning direction”) perpendicular to the main scanning direction. As illustrated in
At this time, the scanning of the carriage 120 in the main scanning direction is properly synchronized with the ejection of ink droplets from the recording heads 1 in accordance with image data to form a first band of a desired image on the sheet 8. After the first band has been formed, the sheet 8 is fed by a certain distance in the sub-scanning direction and the recording heads 1 form a second band of the target image on the sheet 8. By repeating such operations, the whole image is formed on the sheet 8.
To an upper part of the recording heads 1 is integrally connected a head tank (buffer tank or sub tank) 101 including ink chambers 104 that temporarily store ink. The term “integrally” as used herein represents that the recording heads 1 and the head tank 101 are mounted on the carriage 120, and also includes that the recording heads 1 are connected to the head tank 101 via, e.g., tubes or pipes.
Desired color inks are supplied from ink cartridges (main tanks) 76 serving as liquid tanks that separately store the respective color inks, to the head tank 101 via liquid supply tubes 16. The ink cartridges (main tanks) 76 are detachably mounted on, e.g., a cartridge holder disposed at one end of the inkjet recording apparatus 1000 in the main scanning direction.
A suctioning pump 60 serving as a suctioning device is connected to the head tank 101 via an exhaust tube 112.
At the other end of the inkjet recording apparatus 1 in the main scanning direction is disposed a maintenance unit 31 that maintains and recovers conditions of the recording heads 1. The maintenance unit 31 has caps 32 to cover nozzle faces of the recording heads 1 and a aspiration pump 34 to aspirate the interior of the caps 32, and a drain passage 33 through which waste liquid (waste ink) aspirated with the aspiration pump 34 is drained. The waste ink is discharged from the drain passage 33 to a waste tank mounted on the main frame 30. The maintenance unit 31 also has a moving mechanism to move the caps 32 back and forth (in this embodiment, up and down) relative to the nozzle faces of the recording heads 1. The maintenance unit 31 further has a wiping member to wipe the nozzle faces of the recording heads 1 and a wiping unit to hold the wiping member so as to be movable back and forth relative to the nozzle faces of the recording heads 1.
Next, a head tank in a first exemplary embodiment is described with reference to
The head tank 101 has integrally-molded ink chambers 104Y, 104M, 104C, and 104K (collectively referred to as “ink chambers 104” unless colors are distinguished) serving as liquid storage chambers to store yellow (Y), magenta (M), cyan (C), and black (K) inks, respectively. The head tank 101 includes filters 109 adjacent to portions connected to the recording heads 1 to filter ink to remove foreign substances from the ink, and supplies the filtered ink to the recording heads 1 via supply ports 21.
The head tank 101 has film members 107, each of which is a flexible member molded in concave shape to form a wall face of the head tank 101. Each flexible member 107 is urged by a spring 108 in such a direction as to increase the volume of the head tank 101. The head tank 101 has an air-amount sensor 103 to detect the amount of air in the head tank 101.
The air-amount sensor 103 includes paired electrodes to detect a liquid level of ink within each ink chamber 104 based on a change in electric resistance between the electrodes. In other words, the air-amount sensor 103 serves as a liquid level detector to detect the liquid level of ink within each ink chamber 104. As described above, one end of each liquid supply tube 16 is connected to the head tank 101 and the other end is connected to a corresponding one of the ink cartridges 76. The ink cartridges 76 are disposed lower than the nozzle faces of the recording heads 1 to maintain the interiors of the recording heads 1 with in a proper range of negative pressures by liquid head difference.
At an upper portion of the head tank 101 is disposed an exhaust mechanism (exhaust unit) 200 serving as an air exhaust unit to exhaust air from the ink chambers 104 via the exhaust tube 112 serving as an exhaust channel.
Next, the exhaust unit 200 is described with reference to
The exhaust unit 200 has a common exhaust chamber 105 commonly used for the ink chambers 104 and exhaust ports 111 dedicated to the ink chambers 104. Each exhaust port 111 serving as an exhaust opening is disposed at an upper portion of each ink chamber 104 and connected so as to be openable to the common exhaust chamber 105. The upper side of the common exhaust chamber 105 is covered with a cover member 106.
Within the common exhaust chamber 105 is disposed an air release valve 80 serving as a valve member to collectively open and close the exhaust ports 111 of the ink chambers 104. The air release valve 80 has a valve body 80a with seal members 80b and serves as a normally closed valve with each seal member 80b being pressed against an opening side of each exhaust port 111 by a first urging spring 81 serving as a first urging member. When the air release valve 80 is pushed up by an L-shaped driving lever 82 folded downward relative to the air release valve 80, the air release valve 80 opens the exhaust ports 111. The driving lever 82 is pivotably supported by a support shaft 82a.
The common exhaust chamber 105 communicates from a lower opening (exhaust port) 89a with a lower portion of a pin driving chamber 85 serving as a valve driving chamber via a choke channel 89. The choke channel 89 is a narrow tubular channel formed by sealing, with a flexible film 86, an opening of a passage formed in a wall face of the head tank 101.
A driving pin 83 and a second urging spring 84 are disposed in the pin driving chamber 85. The driving pin 83 is a valve driving member movable back and forth relative to the driving lever 82. The second urging spring 84 is a second urging member to urge the driving pin 83 away from the driving lever 82. The flexible film 86 forms a wall face of the pin driving chamber 85, and when the flexible film 86 deforms inward, the driving pin 83 moves in such a direction to push the driving lever 82.
Between the pin driving chamber 85 and the common exhaust chamber 105 is formed a thorough hole through which the driving pin 83 passes. A deformable seal member 87 seals around the thorough hole to communicate the pin driving chamber 85 with the common exhaust chamber 105 only through the choke channel 89.
The pin driving chamber 85 is connected to an exhaust channel 88, thus allowing the suctioning pump 60 to suction and exhaust air from the pin driving chamber 85 via the exhaust tube 112.
The suctioning pump 60 is preferably a gear pump, a diaphragm pump, or any other type of pump capable of opening the channel under suspension. However, even if, like a tube pump, a pump closes the channel under suspension, the pump can be employed provided that air can be released through a branched channel.
Next, exhaust operation of the exhaust unit 200 is described with reference to
As illustrated in
When the suctioning pump 60 starts exhaust operation, as illustrated in
At this time, if the flow amount of exhaust air is too large, the negative pressure in each ink chamber 104 excessively increases, thus undesirably suctioning air from the nozzles of the recording heads 1. Hence, the flow amount of exhaust air is preferably approximately 0.1 to approximately 0.2 cc/s. By contrast, if the flow amount of exhaust air is small, the negative pressure in each ink chamber 104 decreases, thus closing the air release valve 80 (
As described above, in this exemplary embodiment, the head tank 101 has the air-amount sensor 103, thus allowing the suctioning pump 60 to be stopped based on detection results of the air-amount sensor 103.
In this exemplary embodiment, air is exhausted from each of the ink chambers 104 to the suctioning pump 60 through a single exhaust passage (including each exhaust port 111, the common exhaust chamber 105, the choke channel 89, the pin driving chamber 85, the exhaust channel 88, and the exhaust tube 112).
In the exhaust operation, as illustrated in
Next, a second exemplary embodiment of the present disclosure is described with reference to
In this exemplary embodiment, the head tank 101 has a floating valve 110 in each ink chamber 104, instead of the air-amount sensor 103 in the first exemplary embodiment.
In this configuration, as with the above-described first exemplary embodiment, when the suctioning pump 60 drives to perform exhaust operation, air is exhausted from each ink chamber 104 while the states illustrated in
In a case where the flow amount of air exhaust is small, the exhaust ports 111 of the ink chambers 104 might not be partially opened due to the small flow amount. Even in such a case, from one ink chamber 104 having finished exhaust operation, the corresponding exhaust port 111 is closed with the floating valve 110. As a result, each time another ink chamber 104 finishes exhaust operation, the corresponding exhaust port 111 is closed with the floating valve 110, thus increasing the negative pressure in the pin driving chamber 85. Finally, all of the exhaust ports 111 of the ink chambers 104 are opened, thus allowing air to be reliably exhausted from all of the ink chambers 104.
Next, a third exemplary embodiment of the present disclosure is described with reference to
As described above, when air is fully exhausted from all of the ink chambers 104, the exhaust passage is choked. As a result, as illustrated in
Then, as fluid (air and ink) flows back from the suctioning pump 60, the volume of the pin driving chamber 85 restores. As a result, the pushing force of the driving pin 83 against the driving lever 82 decreases, thus closing the air release valve 80.
Accordingly, by detecting the position of the driving pin 83 with the position sensor 91, closing of the air release valve 80 can be confirmed, thus allows smooth shift to a subsequent operation, such as printing operation, without an extra waiting time.
In this exemplary embodiment, the second urging spring 84 is disposed in the pin driving chamber 85 to urge the driving pin 83 in such a direction as to increase the volume of the head tank 101. Thus, when the suctioning pump 60 stops, the driving pin 83 can immediately and reliably return to the original position.
In the above description, the operation and effects of exemplary embodiments are described taking examples in which different color inks are supplied to multiple recording heads. However, it is to be noted that the configuration of the recording heads and ink is not limited to the above-described configuration but, for example, a single color ink may be supplied to multiple recording heads or inks of different compositions may be supplied to multiple recording heads. Alternatively, a configuration in which different types of liquids are ejected from a single head having multiple nozzle rows may be employed in a liquid supply system. The image forming apparatus is not limited to an image forming apparatus that ejects “ink” in strict meaning but may be a liquid ejection apparatus (included in the image forming apparatus in this disclosure) that ejects liquid other than strictly-defined “ink”.
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 present disclosure may be practiced otherwise than as specifically described herein. With some embodiments 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 disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.
Number | Date | Country | Kind |
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2011-058139 | Mar 2011 | JP | national |