Electrophotography – Machine operation – Job mode
Reexamination Certificate
1998-05-20
2001-02-20
Chen, Sophia S. (Department: 2852)
Electrophotography
Machine operation
Job mode
C399S299000, C399S303000, C399S316000
Reexamination Certificate
active
06192207
ABSTRACT:
This application is based on applications Nos. 9-146064, 9-251809, 9-251810, and 10-112273 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a so-called “tandem-type” image forming apparatus where a plurality of image holding components, such as photosensitive drums, are set along the transportation path of a recording sheet.
(2) Related Art
Tandem-type image forming apparatuses have received much attention in recent years because of their ability to perform color printing at high speed.
A color copying machine, as one example of this type of image forming apparatus, has four photosensitive drums corresponding to four colors set along the transportation path of a recording sheet and a transfer unit. The transfer unit is set under the photosensitive drums and includes a transport belt that runs over a plurality of rollers and transfer chargers respectively facing the photosensitive drums. Toner images of cyan, magenta, yellow, and black separately formed on the photosensitive drums are sequentially transferred by the transfer chargers onto a recording sheet transported by the transport belt. As a result, four color images are superimposed on the recording sheet to form a color image. In general, the photosensitive drum used for forming a black image is set at a rearmost position on the transportation path of the recording sheet for better reproduction of black parts of the color image.
When performing operations aside from full-color image formation, such as when forming a black image formation using this type of image forming apparatus, toner images are not formed on the photosensitive drums for cyan, magenta, and yellow, and a toner image is formed only on the photosensitive drum used for the black image formation.
However, when only one photosensitive drum is used, the recording sheet still comes into contact with the other three photosensitive drums during transportation. For this reason, the three photosensitive drums which are not used for the image formation still need to be rotated. This results in unnecessary wear and tear on the photosensitive drums and cleaning blades that are in contact with the photosensitive drums. Against this backdrop, Japanese Laid-Open Patent Application No. 3-288173 teaches an example of a color image forming apparatus which tilts the whole transfer unit from the horizontal position when black image formation is performed, so that the transport belt does not come into contact with the photosensitive drums for C, M, and Y which are not used for black image formation.
Accordingly, the photosensitive drums of cyan, magenta, and yellow do not need to be rotated when a black image is formed. This prevents unnecessary wear and tear on these photosensitive drums.
Japanese Laid-Open Patent Application No. 3-288173 also teaches that a backup plate may be provided in the transfer unit for each photosensitive drum to improve the transfer of the toner images formed on the photosensitive drums. Each backup plate is an elastic member which presses the transport belt against the photosensitive drum immediately before a transfer position, so that the recording sheet transported by the transport belt is tightly pressed against the surface of the photosensitive drum before the recording sheet enters a transfer area. As a result, each toner image is reliably transferred onto the recording sheet.
With this conventional image forming apparatus, however, the transport belt is separated from the photosensitive drums by the shift of the whole transfer unit which is provided with the transfer chargers. This causes variations in the positions of the transfer chargers relative to the photosensitive drums during the image formation. As a result, image transfer is unstable.
Moreover, with this conventional image forming apparatus, the backup plates of the photosensitive drums of cyan, magenta, and yellow still push up the transport belt when forming a black image. This prevents the transport belt from running smoothly, and accordingly, a satisfactory transferred image cannot be obtained.
In addition, the position at which the photosensitive drum used for black image formation comes into contact with the transport belt, that is, the transfer position, is different when forming a black image than when forming a full-color image. As a result, image transfer is unstable.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide an image forming apparatus which can prevent unnecessary wear and tear of the photosensitive drums and the like without shifting the whole transfer unit.
The second object of the present invention is to provide an image forming apparatus provided with components, such as backup plates, by which a satisfactory transferred image can be obtained even when a single-color image formation is performed.
The third object of the present invention is to provide an image forming apparatus by which the transfer positions of the image holding components used for an image formation do not vary regardless of whether the full-color image formation is performed.
The fourth object of the present invention is to provide an image forming apparatus by which a recording sheet transported to the transport belt is always received with stability even when the part where the recording sheet is received is changed due to the separation of the transport belt.
The first object can be achieved by an image forming apparatus made up of: a transport belt that revolves to transport a recording sheet; a plurality of image forming units which are set along a transportation path of the recording sheet and each include an image holding component; a transport belt moving unit for moving the transport belt between a first state and a second state by changing a form of a revolution of the transport belt, the first state being where the transport belt does not touch at least one of the image holding components and the second state being where the transport belt touches the image holding components not touched in the first state, and also can be achieved by an image forming apparatus including the transportation unit which is a loop-shaped belt.
The second object can be achieved by an image forming apparatus made up of: a transport belt for transporting a recording sheet; a plurality of image forming units which are set along a transportation path of the recording sheet and each include an image holding component; a plurality of members, each member being provided positionally opposite a different one of the image holding components, with the transport belt running between the plurality of members and the image holding components; and a member moving unit for moving a member selectively between a first position where the moved member presses the transport belt against the positionally opposite image holding component and a second position where the moved member is not in contact with the transport belt.
The third object can be achieved by an image forming apparatus which selectively operates in one of a full-color mode and a reduced-color mode, the full-color mode being where an image for a different color is formed on each image holding component and the formed images on the image holding components are successively transferred onto the recording sheet transported by the transportation unit, and the reduced-color mode being where an image is formed on at least one but not all of the image holding components and the formed images are transferred onto the recording sheet transported by the transportation unit, the image forming apparatus being made up of: a separating unit for separating the transportation unit from at least one image holding component that does not have an image formed thereon when the image forming apparatus is operating in the reduced-color mode; and a maintaining unit for maintaining a transportation path of the recording sheet relative to each image holding component used for an image formation regardless of whether an image formation is
Onuki Tetsuya
Yamamoto Koji
Chen Sophia S.
Minolta Co. , Ltd.
Morrison & Foerster / LLP
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