Electrophotography – Document handling – Copy
Reexamination Certificate
2002-02-12
2004-02-03
Brase, Sandra (Department: 2852)
Electrophotography
Document handling
Copy
C271S188000
Reexamination Certificate
active
06687484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet transporting apparatus for guiding a sheet to an aftertreatment apparatus and having a function of correcting a curl of the sheet, and to an image forming apparatus provided with the sheet transporting apparatus.
2. Description of Related Art
An image forming apparatus (such as a copying machine, a printer and the like) employing an electrophotographic process transfers a toner image formed on a photosensitive drum (or an electrophotographic photosensitive member) being an image bearing member to a sheet, and the image forming apparatus passes the sheet, on which the toner image has been transferred, through a fixing device. The image forming apparatus thereby fixes the toner image on the surface of the sheet to be a permanent image. Incidentally, silicone oil is generally applied on the surface of the sheet that is passing through the fixing device in order to prevent the toner of the toner image and the sheet from adhering to a fixing roller.
Moreover, an image forming apparatus equipped with a sheet aftertreatment apparatus for sorting sheets, on which images have been fixed, with a sorter, a finisher or the like is known. Besides, an image forming apparatus equipped with a sheet transporting apparatus (hereinafter referred to as a “buffer unit”) for transporting sheets delivered from the main body of the image forming apparatus to the sheet aftertreatment apparatus is known.
An image forming apparatus employing the electrophotographic process has a full color mode for superimposing four color toners on a sheet as in a full color machine, a monochromatic mode for forming an image only by one color toner, and a two-color and a three-color modes for superimposing two and three color toners on a sheet respectively.
Generally speaking, when a sheet bearing a toner image on one side thereof has been passed through pressure and heating rollers for the fixation of the toner image, the sheet curls to bend to the side of the image surface thereof on which the toner image is borne.
However, when such a curled sheet, which has passed through the fixing device, is contained in a sheet aftertreatment apparatus such as the sorter, the finisher or the like, a delivery tray or the like, a faulty sheet transport such as a sheet jam may often occur, and there is a possibility that the functions of the sheet aftertreatment apparatus such as the sorter, the finisher or the like are not fully performed.
Accordingly, it is generally performed to dispose the buffer unit having a function of correcting the curl formed in a sheet between (the fixing device of) the main body of the image forming apparatus and the sheet aftertreatment apparatus such as the sorter, the finisher or the like or the delivery tray.
Incidentally, the buffer unit may be integrally provided to an image forming apparatus to be one body. Alternatively, the buffer unit may be discretely provided between the main body of the image forming apparatus and the sheet aftertreatment apparatus as a separate body.
Next, FIG.
14
and
FIG. 15
are referred while a related art sheet transporting apparatus and a related art image forming apparatus are described more minutely. Incidentally, for the sake of the convenience of descriptions, the same component as those disclosed in the drawings to be referred in the descriptions of a sheet transporting apparatus and image forming apparatuses according to the embodiments of the present invention that will be described later are designated by the same reference numerals or signs, and the descriptions about the same components are suitably omitted.
As shown in
FIG. 14
, the related art image forming apparatus includes a main body
400
thereof for forming an image on a sheet, a sheet aftertreatment apparatus (hereinafter referred to as a “sorter”)
200
having a function of sorting sheets on which images have already been formed, and a sheet transporting apparatus (hereinafter referred to as a “buffer unit”)
100
disposed between the main body
400
and the sorter
200
.
Incidentally, the shown image forming apparatus has a configuration in which the main body
400
, the buffer unit
100
and the sorter
200
are separately disposed. But an image forming apparatus may be provided with these components formed in one integral body.
The buffer unit
100
has a function of switching the transportation state of a sheet fed from the main body
400
between the transportation of the sheet without the reversing of the surface thereof and the transportation of the sheet with the reversing of the surface thereof.
Moreover, the buffer unit
100
is provided with correcting means
104
and
110
for correcting the curl formed in a transported sheet.
The correcting means
104
corrects an up-curl, or upward bending of a sheet, and the correcting means
110
corrects a down-curl, or downward bending of a sheet.
And, because a sheet ordinarily curls to bend toward one side of the two-side copied sheet in which the image density of a formed image is higher than that on the other side of the sheet, either of the correcting means
104
and
110
is operated on the basis of the information concerning the image densities.
Moreover, the sorter
200
is equipped with a non-sort bin B
0
at the uppermost position and a plurality of sort bins B
1
, B
2
. . . and B
20
at lower positions. The sorter
200
has a function of delivering transported sheets while performing the sorting of the sheets such as the collating and the grouping of the sheets.
As described above, conventionally, when the correcting means
104
and
110
as curl correcting means are provided in the buffer unit
100
, the correcting means
104
and
110
are controlled on the basis of the difference between the image densities of images borne on both sides of a sheet S to be fed into a sheet aftertreatment apparatus such as the sorter
200
regardless of the processing method of the sorter
200
.
However, such a curl correction method being performed on the basis of the difference between the image densities on both sides has a problem of the occurrence of a paper jam (hereinafter simply referred to as a “jam”) owing to the waving of sheets S (see, for example, the sheets S stacked on the sort bin B
7
shown in
FIG. 15
) when the sheets S are delivered on the sort bins B
1
-B
20
of the sorter
200
in a group mode or a stack mode.
The problem is described more minutely in the following.
In the group mode or in the stack mode, the sheets S are delivered on the sort bins B
1
-B
20
.
Hereupon, the curl correction of the sheets S (the up-curl correction of the sheets S by the correcting means
104
in the example in
FIG. 15
) is performed in the buffer unit
100
, and the sheets S are transported through a sort path
205
and delivered by delivery rollers
206
.
Immediately after the correction of a sheet S, the sheet S is slightly curled reversely to the curl in the sheet before the correction. That is, the sheet S in the example shown in
FIG. 15
is slightly down-curled because the sheet S has suffered from the up-curl correction.
Because such sheets S are continuously delivered to the sort bin, a successive sheet S is delivered before the curl (or the up-curl) of a previous sheet S, which has been previously delivered, owing to the toner of an image on the sheet S has grown up. Consequently, the down-curled sheets S continue to be stacked in the sort bin. Then, the height of the stacked delivered sheets S becomes high. Consequently, as shown in
FIG. 15
, a part of the sheets S stacked on the sort bin B
7
is brought into contact with the lower surface of the sort bin B
6
positioned immediately above the sort bin B
7
. Thereby, there is the case where the contact prevents the delivery of a sheet S to be delivered next onto the sort bin B
7
to cause a sheet jam.
Moreover, when the sheets S are continuously delivered on the stacked sheets S having still maintained curls formed by the curl correcting means even if the sheets S are delivered on a tray h
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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