JP4007487B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides an image forming apparatus capable of forming an image on both sides of a recording medium by forming an image on one side of the recording medium and then conveying the recording medium again to the image forming unit to form an image on the other side. About.
[0002]
[Prior art]
Conventionally, a copying machine that forms an image using a developer on a recording medium such as recording paper, an ink jet printer that forms an image by ejecting ink onto the recording medium, and the like have been widely used. These image forming apparatuses such as copying machines and printers are provided with an image forming unit that forms an image on a recording medium. In the above-described copying machine, the image forming unit includes a transfer unit that transfers the developed image to a recording medium, a fixing unit that fixes the developed image transferred by the transfer unit to the recording medium, and the like. In the above-described ink jet printer, the image forming unit includes an ink discharge unit that discharges ink.
[0003]
The image forming apparatus as described above is generally provided with a paper feeding unit for feeding a recording medium to the image forming unit. As the paper feeding unit, a hopper paper feeding unit and a single manual paper feeding unit are known. The hopper paper feeding unit is a paper feeding unit that stacks a large number of recording media and feeds them one by one. The hopper paper feeding unit is mainly for feeding main paper such as plain paper. On the other hand, the single manual paper feed unit is a paper feed unit that stocks and feeds a single recording medium. This single manual sheet feeder is mainly for feeding special paper such as OHP sheets and postcards.
[0004]
By the way, the image forming apparatus forms an image on both sides of the recording medium by forming an image on one side of the recording medium and then transporting the recording medium again to the image forming unit to form an image on the other side. There is also a type (double-sided image forming apparatus). The double-sided image forming apparatus includes a reversing unit that reverses the recording medium on which an image is formed on one surface, and a circulation conveying unit that re-transports the recording medium reversed by the reversing unit to the image forming unit. Is provided.
[0005]
Among the above-described double-sided image forming apparatuses, there is a type in which the circulation conveyance unit and the single manual sheet feeding unit are arranged close to each other in order to reduce the size and space. A conveyance roller for conveying the recording medium is disposed in the circulation conveyance unit. On the other hand, a paper feed roller for feeding a recording medium is arranged in the single manual paper feed unit.
[0006]
Among the types in which the circulating transport unit and single manual feed unit are placed close to each other, the transport roller and the feed roller are fixed to the same drive shaft (roller shaft) for further miniaturization and space saving. Some of them rotate at the same time. In the type using the same drive shaft, only the function of the conveying roller is exhibited by rotating the drive shaft, for example, and conversely, only the function of the paper feeding roller is exhibited by reversing the drive shaft. Yes.
[0007]
[Problems to be solved by the invention]
However, in the above-described image forming apparatus, the transport roller and the paper feed roller are fixed to the same drive shaft and rotated simultaneously. Therefore, when the transport roller is rotated and the recording medium is transported to the circulation transport unit, the paper feed roller is It rotates in the direction opposite to the paper feeding direction. In this case, when the recording medium is placed on the single manual sheet feeding unit, the leading end of the recording medium in contact with the sheet feeding roller is carelessly turned or soiled.
[0008]
In view of the above circumstances, an object of the present invention is to provide an image forming apparatus in which a leading end portion of a recording medium placed on a single manual sheet feeding portion is not carelessly turned or stained.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention includes a paper feed roller that feeds a recording medium one by one to an image forming unit where an image is formed on the recording medium, and an image formed on one surface. And a transport roller that transports the recording medium to the image forming unit again. After the image forming unit forms an image on one surface of the recording medium, the recording medium is transported to the image forming unit by the transport roller again. In an image forming apparatus that forms an image on both sides of a recording medium by forming an image on the other side,
(1) a transport roller shaft for fixing and rotating the transport roller;
(2) Even if the conveyance roller shaft rotates, the conveyance roller shaft is fixed so as not to be driven by this rotation, and a recording medium is brought into contact with the paper supply roller by contacting the paper supply roller. A sheet feeding roller that is driven and rotated by the sheet feeding roller while being sandwiched is provided.
[0010]
Here, the image forming apparatus described above is
(3) a paper feed roller shaft for fixing and rotating the paper feed roller;
(4) You may provide one drive source which rotates this paper-feed roller axis | shaft and the said conveyance roller axis | shaft.
[0011]
In addition, the image forming apparatus described above
(5) a paper feed gear fixed to the paper feed roller shaft for transmitting the driving force of the drive source to the paper feed roller shaft;
(6) A one-way clutch that rotates the paper feeding roller shaft only in a predetermined paper feeding direction when a driving force is transmitted from the driving source to the paper feeding gear.
[0012]
further,
(7) The drive source rotates the transport roller shaft in a predetermined transport direction opposite to the predetermined paper feed direction by rotating in the forward direction, while rotating the transport roller shaft in the predetermined transport direction by rotating in the reverse direction. It may be rotated in the paper feeding direction.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a schematic diagram showing a schematic configuration of a laser beam printer which is an embodiment of an image forming apparatus of the present invention. A process cartridge 16 incorporating a photosensitive drum 12 and a developing machine 14 is freely attached to and detached from the laser beam printer 10. Further, the lower side in FIG. 1 is the upstream side in the transport direction for transporting the recording medium, and the upper side in FIG. 1 is the downstream side in the transport direction. As the recording medium, special paper such as thick plain paper, envelopes, and OHP films other than paper is used in addition to general plain paper. Here, a case where plain paper is used and a case where special paper is used will be described separately.
[0015]
A paper feed cassette 20 on which a large number of plain papers are stacked is detachably attached to the lower part of the laser beam printer 10. On the other hand, on the upper part of the laser beam printer 10, a paper discharge tray 30 on which a recording medium on which an image has been formed is discharged and stacked is disposed. In the vicinity of the paper feed cassette 20, a paper feed unit 22 that feeds the stacked recording media one by one is disposed. A fixing unit 32 for fixing the developed image on the recording medium is disposed near the paper discharge tray 30.
[0016]
The paper feed cassette 20 and the paper discharge tray 30 are connected by a transport path 40 extending from the upstream side to the downstream side in the transport direction described above. In the conveyance path 40, the paper feed unit 22, the process cartridge 16, the fixing unit 32, and the like are arranged as close as possible. Thereby, the laser beam printer 10 is configured in a small size as a whole.
[0017]
The photosensitive drum 12 of the process cartridge 16 is irradiated with laser light from the scanner 18 of the laser unit, whereby an electrostatic latent image is formed on the photosensitive drum 12. This electrostatic latent image is developed by the developing machine 14 and transferred to a recording medium by the transfer roller 24. The process cartridge 16 includes a primary charger 26 that uniformly charges the photosensitive drum 12 and a cleaning unit 28 that removes the developer remaining on the photosensitive drum 12 after the transfer. The laser beam printer 10 also incorporates a resist correction unit 42 that corrects the skew of the recording medium.
[0018]
When images are formed on both sides of plain paper, a large number of plain papers stacked in the paper feed cassette 20 are separated and fed one by one by the paper feed unit 22. One sheet of plain paper that has been separated and fed is corrected in skew by a registration correction unit 42 and conveyed to a pressure nip portion between the photosensitive drum 12 and the transfer roller 24. In the pressure nip portion, the developed image formed on the photosensitive drum 12 is transferred to plain paper. The plain paper to which the developed image is transferred is conveyed through the conveyance path 40 and reaches the fixing unit 32. In the fixing unit 32, the developed image is fixed on plain paper.
[0019]
When an image is formed only on one side of the plain paper, the plain paper that has passed through the fixing unit 32 is discharged to the paper discharge tray 30. When images are formed on both sides of plain paper, first, the plain paper on which the image is formed is sandwiched between the paper discharge roller 46 and the paper discharge roller 48 of the paper discharge unit 44 and conveyed toward the paper discharge tray 30. To do. In the middle of this conveyance, immediately after the paper discharge sensor (not shown) for detecting the rear edge of the recording medium detects the rear edge of the plain paper, the paper discharge roller 46 is rotated in the reverse direction. As a result, the plain paper is conveyed to the circulation conveyance path 50a. At this time, since the leading edge of the plain paper in the conveyance direction is guided by the paper guide, the plain paper is not fed back toward the fixing unit 32.
[0020]
In the circulation conveyance path 50, a conveyance roller 52 and a conveyance roller 54 for conveying the plain paper conveyed through the circulation conveyance path 50 to the registration correction unit 42 are arranged. The configurations of the transport roller 52 and the transport roller 54 will be described later.
[0021]
The plain paper transported by the transport roller 52 and the transport roller 54 passes through the registration correction unit 42, and thereafter, other than the plain paper at the pressure nip portion, as in the order of forming an image on one surface of the plain paper. The developed image is transferred onto the surface, and the plain paper passes through the fixing unit 32 and is then discharged to the paper discharge tray 30.
[0022]
When an image is formed on special paper such as an OHP sheet by the laser beam printer 10, the special paper is not loaded on the paper feed cassette 20 but is placed on the single manual feed tray 60. Here, the single manual feed tray 60 on which only one special paper is placed has been described, but a manual feed tray on which a plurality of special papers can be stacked may be incorporated in the laser beam printer 10. The single manual feed tray 60 is provided with a paper feed roller 64 and a paper feed roller 66 for feeding the special paper placed on the single manual feed tray 60 to the registration correction unit 42 and the image forming unit. The paper feed roller 64 and the paper feed roller 66 will be described with reference to FIG.
[0023]
The special paper fed by the paper feed roller 64 and the paper feed roller 66 passes through the resist correction unit 42, and the developed image is transferred to the special paper at the pressure nip portion, and the special paper passes through the fixing unit 32. Thereafter, the paper is discharged to the paper discharge tray 30.
[0024]
With reference to FIG. 2, the conveyance roller 52, the conveyance roller 54, the paper feed roller 64, and the like will be described.
[0025]
FIG. 2 is a perspective view showing a transport roller shaft, a paper feed roller shaft, and the like.
[0026]
In order to feed the recording medium placed on the single manual feed tray 60 to the image forming unit, a paper feed roller 64 and a paper feed roller 66 are disposed near the entrance of the single manual feed tray 60. In the vicinity of the paper feed roller 64 and the paper feed roller 66, the transport roller 52 and the transport roller 54 described above are arranged.
[0027]
The conveyance rollers 52 are fixed one by one at both ends in the longitudinal direction of the conveyance roller shaft 70. As the conveyance roller shaft 70 rotates, the conveyance roller 52 also rotates in the same direction. A paper feed roller 66 is rotatably fixed to a central portion of the transport roller shaft 70 (a portion sandwiched between the two transport rollers 52). The phrase “fixed to be freely rotatable” here means that the feeding roller 66 is fixed so as not to rotate (followed rotation) following the rotation of the conveyance roller shaft 70. Say.
[0028]
A conveyance gear 72 for rotating the conveyance roller shaft 70 is fixed to one longitudinal end portion of the conveyance roller shaft 70. The conveying gear 72 is engaged with a driving gear 82 that is rotated by a driving motor 80 (an example of a driving source according to the present invention). Accordingly, when the drive motor 80 is rotated, the drive gear 82 is rotated. As a result, the conveyance roller shaft 70 is rotated together with the conveyance gear 72, and the conveyance roller 52 is also rotated. Each conveyance roller 52 is in contact with a conveyance roller 54, and the conveyance roller shaft 70 rotates in the conveyance direction (arrow B direction), so that the conveyance roller 52 and the conveyance roller 54 are connected to the recording medium in the circulation conveyance path 50. Transport while pinching.
[0029]
In the vicinity of the conveyance roller shaft 70, a paper feed roller shaft 62 is arranged in parallel with the conveyance roller shaft 70. A paper feed roller 64 that rotates together with the paper feed roller shaft 62 is fixed to the paper feed roller shaft 62. A paper feed gear 68 that meshes with the transport gear 72 is fixed to one end portion in the longitudinal direction of the paper feed roller shaft 62 via a one-way clutch 84. The one-way clutch 84 is configured such that when a driving force is transmitted from the transport gear 72 to the paper feed gear 68, the paper feed roller shaft 62 rotates only in the paper feed direction (arrow C direction). Therefore, when the driving force for rotating the transport roller shaft 70 in the transport direction is transmitted from the transport gear 72 to the paper feed gear 68, the paper feed gear 68 rotates, but the paper feed roller shaft 62 and the paper feed roller 64 Does not rotate. In this case, the paper feed roller 66 does not rotate. Therefore, the leading edge of the recording medium placed on the single manual feed tray 60 is not turned or soiled by the reverse rotation of the paper feed roller 64 or the paper feed roller 66 (rotation in the direction opposite to the paper feed direction).
[0030]
Only when the driving force that rotates the transport roller shaft 70 in the direction opposite to the transport direction (the direction of arrow A) is transmitted from the drive motor 80 to the paper feed gear 68 via the transport gear 72 and the like. At the same time, the sheet feeding roller shaft 62 rotates, and the sheet feeding roller 64 and the sheet feeding roller 66 also rotate. As a result, the recording medium placed on the single manual feed tray 60 is fed while being sandwiched between the feed roller 64 and the feed roller 66.
[0031]
As described above, when the drive motor 80 rotates forward, for example, this driving force (rotational force) is transmitted to the transport roller shaft 70 via the drive gear 82 and the transport gear 72, and the transport roller 52 moves in the transport direction. Rotate. However, at this time, the sheet feeding roller 66 does not rotate, and the sheet feeding gear 68 rotates but the sheet feeding roller 64 does not rotate by the one-way clutch 84. Therefore, as described above, the leading edge of the recording medium placed on the single manual feed tray 60 is not turned or soiled by the reverse rotation of the paper feed roller 64 or the paper feed roller 66. Note that when the drive motor 80 rotates in the reverse direction, the paper feed roller shaft 62 and the paper feed roller 64 rotate in the paper feed direction.
[0032]
【The invention's effect】
As described above, in the image forming apparatus of the present invention, the paper feed roller does not rotate when the transport roller shaft rotates. For this reason, the leading end portion of the recording medium placed on the single manual sheet feeding portion provided with the sheet feeding roller and the sheet feeding roller is not inadvertently turned or soiled when the transport roller is rotating.
[0033]
Here, when a paper feed roller shaft for fixing and rotating the paper feed roller and one drive source for rotating the paper feed roller shaft and the transport roller shaft are provided, one drive source is sufficient. The number of parts is small and the cost is low.
[0034]
Further, the driving force of the driving source is conducted to the feeding roller shaft, the feeding gear fixed to the feeding roller shaft, and when the driving force is conducted from the driving source to the feeding gear, When a one-way clutch that rotates the paper feed roller shaft only in a predetermined paper feed direction is provided, the paper feed roller rotates only in the predetermined paper feed direction by the one-way clutch, so that it contacts the paper feed roller or paper feed roller. It is possible to more reliably prevent the leading end of the recording medium being turned off from being accidentally turned or soiled.
[0035]
Further, the drive source rotates the transport roller shaft in a predetermined transport direction opposite to the predetermined paper feed direction by rotating in the forward direction, while rotating the transport roller shaft in the predetermined feed direction by rotating in the reverse direction. In the case of rotating in the paper direction, the transport roller shaft and the paper feed roller shaft can be rotated by forward or reverse rotation of the drive source.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a laser beam printer which is an embodiment of an image forming apparatus of the present invention.
FIG. 2 is a perspective view showing a conveyance roller shaft, a paper feed roller shaft, and the like.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Laser beam printer 52 Conveying roller 54 Conveying roller 62 Feed roller shaft 64 Feed roller 66 Feed roller 70 Conveying roller shaft 80 Drive motor 84 One-way clutch

Claims (4)

A single manual feed unit that places a single recording medium and feeds it to an image forming unit on which an image is formed, a paper feed cassette on which a large number of recording media are stacked, and the single manual feed unit A sheet feeding roller that feeds the recording medium placed on the image forming unit to the image forming unit, and a conveyance roller that transports the recording medium having an image formed on one side thereof to the image forming unit again. After the image is formed on one side of the recording medium by the unit, the recording medium is conveyed again to the image forming unit by the conveyance roller, and the image is formed on the other side by forming an image on the other side. In the image forming apparatus to be formed,
A transport roller shaft for fixing and rotating the transport roller;
When forming the image on both sides, even if the transport roller shaft rotates, it is fixed to the transport roller shaft so as not to be driven by this rotation, and the paper feed roller rotates in contact with the paper feed roller. A paper feeding roller that is driven and rotated only along with
When a single recording medium is fed from the single manual sheet feeding unit, the sheet feeding roller rotates following the rotation of the sheet feeding roller, and between the sheet feeding roller and the sheet feeding roller. An image forming apparatus that feeds paper while sandwiching the one recording medium . A paper feed roller shaft for fixing and rotating the paper feed roller;
The image forming apparatus according to claim 1, further comprising: a drive source that rotates the paper feed roller shaft and the transport roller shaft. A paper feed gear fixed to the paper feed roller shaft for transmitting the driving force of the drive source to the paper feed roller shaft;
3. The image according to claim 2, further comprising a one-way clutch that rotates the paper feed roller shaft only in a predetermined paper feed direction when a driving force is transmitted from the drive source to the paper feed gear. Forming equipment. The drive source is
By rotating in the forward direction, the transport roller shaft is rotated in a predetermined transport direction opposite to the predetermined paper feed direction, and by rotating in the reverse direction, the paper feed roller shaft is rotated in the predetermined paper feed direction. The image forming apparatus according to claim 3, wherein the image forming apparatus is provided.

Images