1. Field of the Invention
The present invention relates to a sheet conveying device including a sheet reversing mechanism capable of reversing a sheet, and to an image forming apparatus, such as a copy machine, a printer, and a facsimile machine, including the sheet conveying device.
2. Description of the Related Art
In general, a sheet conveying device for an image forming apparatus including a sheet reversing mechanism uses a switch-back method. In the switch-back method, a sheet is pulled into a reversing conveying path and is then extracted in the opposite direction to reverse the sheet. In the sheet conveying device having the sheet reversing mechanism using the switch-back method, the reversing conveying path dedicated to reversing the sheet and a switch for switching conveying paths are required. This leads to an increase in the size of the sheet conveying device and the image forming apparatus.
Accordingly, to reduce the size of the sheet conveying device and the image forming apparatus, a sheet reversing mechanism that reverses a sheet by rotating a pair of planetary rollers while the sheet is nipped therebetween has been suggested. This technique is described in Japanese Patent Laid-Open No. 2001-122479.
The structure of known planetary rollers will be described below with reference to
A pair of planetary rollers 102 and 103 is used to reverse and convey a small, thick sheet, such as a card. The planetary rollers 102 and 103 are provided on a rotating disc 120 having a diameter corresponding to the length of a side of a card-shaped sheet (hereinafter simply called a sheet) 101 in a conveying direction thereof. The planetary rollers 102 and 103 include a sun roller 102 that functions as a driving roller and that is rotated by a driving force, and a satellite roller 103 that functions as a driven roller and that is capable of holding the sheet 101 between the sun roller 102 and the satellite roller 103. Guides 140 for guiding the sheet 101 toward the planetary rollers 102 and 103 are attached to the rotating disc 120. The rotating disc 120 is supported such that the rotating disc 120 can rotate around a drive shaft of the sun roller 102.
A pair of supply rollers 121 for conveying the sheet 101 to the position between the sun roller 102 and the satellite roller 103 and guides 140 for guiding the sheet 101 are disposed around the rotating disc 120. In addition, a card position sensor 131 for detecting the trailing edge of the sheet 101 supplied by the supply rollers 121 and a rotational angle sensor 132 for detecting the rotational angle of the rotating disc 120 are also disposed around the rotating disc 120.
A sheet-reversing operation performed by the known planetary rollers 102 and 103 having the above-described structure will now be described.
The sun roller 102 is rotated at the same surface speed (peripheral speed) as that of the supply rollers 121. When the sheet 101 is supplied, the rotating disc 120 is stopped at the position shown in
When it is detected by the rotational angle sensor 132 that the rotating disc 120 has rotated about 180° and reached the position shown in
In the above-described known technique, the sheet 101 is rotated around the drive shaft of one of the planetary rollers 102 and 103, i.e., the sun roller 102, while the sheet 101 is nipped between the planetary rollers 102 and 103. Therefore, the sheet 101 cannot be conveyed along a straight conveying path before and after the rotation, but is conveyed along paths that are shifted from each other. In other words, the position at which the sheet 101 is received by the planetary rollers 102 and 103 and the position at which the sheet 101 is ejected therefrom are shifted from each other in the vertical direction in
The present invention is directed to a sheet conveying device having a small, simple structure and capable of reversing a sheet such that the sheet can be conveyed on a straight line before and after the reversal, and to an image forming apparatus including the sheet conveying device.
According to an aspect of the present invention, a sheet conveying device includes a sheet reversing unit configured to reverse a sheet. The sheet reversing unit includes a pair of rollers configured to be rotatable while being in pressure contact with each other, a connecting mechanism configured to support the pair of rollers such that the pair of rollers are capable of rotating together, a roller driving mechanism configured to transmit a rotational driving force to at least one of the pair of rollers, and a roller-pair rotating mechanism configured to rotate the pair of rollers supported by the connecting mechanism together. The connecting mechanism supports the pair of rollers such that the pair of rollers is capable of rotating around a nip portion of the pair of rollers that are in pressure contact with each other.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An embodiment of the present invention will be described below with reference to the drawings.
A sheet conveying device according to the embodiment of the present invention will be described in detail below. First, the overall schematic structure of an image forming apparatus including the sheet conveying device according to the present embodiment will be described. Then, the structure and operation of a reversing path unit included in the sheet conveying device according to the present embodiment will be described in detail.
The overall structure of the image forming apparatus will be described with reference to the schematic sectional view shown in
An image forming unit includes a photosensitive drum 12, a charger 13, a developing unit 14, a transfer charger 19, a detach charger 20, and a cleaner 26. The charger 13 is provided to uniformly charge the surface of the photosensitive drum 12. A scanner 8 emits, via a mirror 10, an optical image for forming an electrostatic latent image on the surface of the photosensitive drum 12 charged by the charger 13. The developing unit 14 is provided to develop the electrostatic latent image to form a toner image that is to be transferred onto a sheet S. The transfer charger 19 is provided to transfer the toner image on the surface of the photosensitive drum 12 onto the sheet S. The detach charger 20 is provided to remove the sheet S onto which the toner image is transferred from the photosensitive drum 12. The cleaner 26 is provided to remove the toner remaining on the photosensitive drum 12 after the toner image is transferred. As shown in
A case in which, for example, an image is copied on one side of the sheet S and the sheet S is ejected with the side on which the image is copied facing upward will be described. When a copy start button (not shown) is pressed, a sheet S on a feed tray 32 is fed by a sheet feeding unit 36 including feed rollers 36A, 36B, and 36C, and is conveyed by a plurality of pairs of conveying rollers 38. Then, the tilt of the sheet S is corrected by a pair of registration rollers 45. Alternatively, a sheet S on a feed tray 33 is fed by a sheet feeding unit 37 and is conveyed to the registration rollers 45 by the pairs of conveying rollers 38. A sheet may also be fed from a manual feed tray 40. A sheet S on the manual feed tray 40 is fed by a feed roller 42 and is conveyed to the registration rollers 45 by the pairs of conveying rollers 44.
After the sheet S reaches the registration rollers 45 and the tilt thereof is corrected by the registration rollers 45, the sheet S is conveyed to the image forming unit at a predetermined timing. In the image forming unit, the toner image is transferred onto the sheet S. A belt conveyor unit 21 for conveying the sheet S on which the toner image is transferred and a fixing unit 22 for fixing the image on the sheet S conveyed by the belt conveying unit 21 as a permanent image are disposed on the downstream of the image forming unit. The sheet S having the image fixed thereon by the fixing unit 22 passes through a pair of inner ejection rollers 23, guided by a first switch 51, and is ejected from the main body 1 of the image forming apparatus through an ejection conveying path 49. The ejected sheet S is placed on an ejection tray 25 provided outside the main body 1 of the image forming apparatus.
A reversing roller unit 55, which functions as a sheet reversing unit that characterizes the present invention, will be described with reference to
Reversing rollers 55a and 55b are structured such that rotating shafts of the rollers 55a and 55b are rotatably supported by connecting units 61, which function as a connecting mechanism, provided on the left and right sides such that the rollers 55a and 55b are in pressure contact with each other. Thus, the reversing rollers 55a and 55b are rotatably supported while being in pressure contact with each other.
A roller-pair rotating mechanism for rotating the reversing rollers 55a and 55b together will now be described. A rotating gear 58 is fixed at the center of one of the connecting units 61, and is rotatably supported by a shaft 58a. The other connecting unit 61 is rotatably supported by another shaft 58a. In addition, as shown in
The rotating gear 58 meshes with a rotation drive gear 59 to which a rotational driving force is transmitted from a roller-pair rotating motor M2, which is a stepper motor. A driving force is input to the rotating gear 58 from the rotation drive gear 59 through a clutch (not shown) or the like, and thus the overall body of the reversing rollers 55a and 55b can be rotated.
Next, a roller driving mechanism for rotating each of the reversing rollers 55a and 55b will be described.
The reversing rollers 55a and 55b are coaxially integrated with reversing roller gears 57a and 57b, respectively. The reversing roller gears 57a and 57b are arranged to be capable of selectively meshing with a reversing-roller drive gear 60 to which a rotational driving force is transmitted from a roller driving motor M1, which is a stepper motor. When the reversing-roller drive gear 60 meshes with the reversing roller gear 57a, the reversing rollers 55a are rotated by a driving force transmitted thereto, and the reversing rollers 55b are rotated by the rotation of the reversing rollers 55a.
Similarly, when the reversing-roller drive gear 60 meshes with the reversing roller gear 57b, the reversing rollers 55b are rotated by the driving force and the reversing rollers 55a are rotated by the rotation of the reversing rollers 55b. When the overall body of the reversing rollers 55a and 55b is rotated, the reversing-roller drive gear 60 is separated from both the reversing roller gear 57a and the reversing roller gear 57b. Therefore, rotation of the reversing rollers 55a and 55b is stopped.
A trailing-edge detection sensor 52 (see in
The operation of the reversing roller unit 55 will be described with reference to
In Step 1, the driving force of the roller driving motor M1 is transmitted from the reversing-roller drive gear 60 to the reversing roller gear 57a. Accordingly, as shown in
While the reversing rollers 55a and 55b are rotating (revolving) as shown in
If it is determined that the overall body of the reversing rollers 55a and 55b is rotated by 180° as shown in
In this state, the reversing-roller drive gear 60 meshes with the reversing roller gear 57b so that the driving force is transmitted. Accordingly, each of the reversing rollers 55a and 55b is rotated around the center thereof and the sheet S is conveyed in the same direction as the direction shown in
A sheet guide 54 is disposed on the downstream of the reversing rollers 55a and 55b in the sheet conveying direction. The sheet guide 54 serves to prevent flopping of the sheet S in the reversing process, thereby increasing the conveying stability. The sheet guide 54 may be a roller, a spur roller, or a plate on which a sheet having a high sliding performance is attached.
In addition, the rotating direction of the rotation drive gear 59 can be selectively switched so that the rotating (revolving) direction of the reversing rollers 55a and 55b can be switched between positive and negative directions depending on the direction in which the sheet S is curled. For example, in
An example in which the reversing roller unit 55 is used in an image forming apparatus will be described. Referring to
The ejection reversing rollers 55Y are provided at an intermediate position (position near the fixing unit 22) of an ejection conveying path 49 for ejecting the sheet S having an image formed on one side thereof in such a manner that the image faces downward. Trailing-edge detection sensors 52b and 53b are placed in front of and behind the nip portion of the ejection reversing rollers 55Y in the sheet-conveying direction.
An operation of forming images on both sides of the sheet by the image forming unit (duplex copying) will be described below with reference to
The first switch 51 is rotated by a drive unit (not shown) to a position shown in
Then, when the trailing edge of the sheet S is detected by the trailing-edge detection sensor 53a disposed on the downstream of the duplex reversing rollers 55X, the operation of the motors and the like is stopped so that the next sheet S can be received. The sheet S ejected from the duplex reversing rollers 55X is conveyed toward the image forming unit again by the plurality of pairs of rollers 56 ((5)). The following processes are similar to those in the single-sided image forming operation, and explanations thereof are thus omitted.
Next, an operation of ejecting the sheet S having an image formed on one side thereof such that the image faces downward (reversed ejection) will be described with reference to
The first switch 51 is rotated by a drive unit (not shown) to a position shown in
After the sheet S is rotated by 180° and reversed by the ejection reversing rollers 55Y, the sheet S is ejected to the ejection tray 25 such that the side on which the image is formed faces downward. Then, when the trailing edge of the sheet S is detected by the trailing-edge detection sensor 53b disposed on the downstream of the ejection reversing rollers 55Y, the operation of the motors and the like is stopped so that the next sheet S can be received.
Thus, by using the reversing roller unit according to the present invention, the sheet conveyed to the reversing roller unit can be reversed and ejected along a path that is aligned with (on the same straight line as) the path along which the sheet has been conveyed to the reversing roller unit. Therefore, compared to the known structure, the sheet conveying performance can be increased and the occurrence of jamming can be reduced. In addition, the size of the sheet conveying device and the image forming apparatus can be reduced.
Although gear drive units using stepper motors as drive sources have been described in the present embodiment, the present invention is not limited to this. For example, the reversing roller unit 55 may also be driven using DC motors, belts, etc.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.
This application claims the benefit of Japanese Application No. 2006-339862 filed Dec. 18, 2006, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2006-339862 | Dec 2006 | JP | national |