Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2002-12-18
2004-09-07
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S068000, C399S396000, C399S405000
Reexamination Certificate
active
06788905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine and a printer. More particularly, the invention relates to an improvement of an image forming apparatus of the type in which a sheet bearing an image, which is formed by an image forming part of a main body of the image forming apparatus, is discharged to a sheet receiving part by way of a sheet discharging device.
2. Background Art
A Xerography-based copying machine will be described as a typical example of the image forming apparatus of this type. In the copying machine, a toner image is formed on an image bearing member, such as a photoreceptor drum, and the toner image is transferred onto a sheet, such as a printing paper, directly or through an intermediate transfer body. Thereafter, the toner image, not yet fixed, is fixed on the sheet, and is discharged onto a discharging tray as the sheet receiving part.
In the image forming apparatus thus constructed, a sheet discharging device is provided at a position near an output part of a sheet transport path. The sheet discharging device discharges the sheet bearing the fixed image, which has passed a fixing device, into the discharging tray. This type of sheet discharging device usually includes paired discharging rolls, and these rolls nip the sheet there between and transports the sheet in a nipping state.
When a toner image is formed on an OHP sheet at high speed, toner image fusion was found on the OHP sheet having an image formed thereon placed on the discharging tray. It was confirmed that the toner image fusion leads to image defects, such as image irregularity and image peeling.
This kind of technical problem is due to the fact that the OHP sheets are stacked while storing up therein the heat applied to the sheets by the fixing device. Therefore, it is readily understood that the problem can be solved in a manner that the OHP sheets having undergone fixing process are sufficiently cooled and then stacked.
Some approaches to the problem are proposed. In one approach, a cooling device is located downstream of the fixing device. After pass the fixing device, the OHP sheets or the like are forcibly cooled and then discharged. In another approach, the sheet-to-sheet span is increased by thinning out sheets successively transported to secure a sheet cooling time, although the copy productivity is decreased.
In the former approach, a large cooling device is required to secure a large cooling effect. Accordingly, the device cost is considerably increased. In a case where the sheet transport path ranging from the fixing device to exit rolls is curved, when the sheet is cooled by the cooling device, the sheet tends to remain curled to thereby adversely influence the post-processing of sheets.
In the latter approach, the sheets are transported in thinned-out manner. Accordingly, the copy productivity is considerably reduced. A time from the moment that the sheet leaves the fixing device to the moment when it arrives at the discharging tray and stacked therein remains unchanged. Therefore, the solution approach is insufficient in gaining such effects that the amount of heat stored up in the OHP sheets being stacked in the discharging tray is reduced, thereby eliminating image defects.
Such technical problems are found not only in the OHP sheets but also in special sheets, e.g., coated sheets.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image forming apparatus which, with simple construction, is capable of preventing image defects, which arise from the fusing of image forming materials (e.g., toner) of sheets to be stacked on a sheet receiving part, while minimizing the lowering of copy productivity.
The present invention provides an image forming apparatus which includes, as shown in
FIG. 1
, a sheet discharging device
3
located near the output part of a sheet transport path
2
within a main body
1
of the image forming apparatus and discharges a sheet S having an image formed thereon by an image forming part
11
within the main body
1
of the image forming apparatus to a sheet receiving part
4
, wherein the sheet discharging device
3
comprising: a discharging member
5
, disposed near the output part of the sheet transport path
2
, for transporting the sheet in a nipping manner; a drive force transmitting mechanism
6
for driving the discharging member
5
to rotate; and a discharge control unit
7
for controlling the drive force transmitting mechanism
6
when the sheet S passes the discharging member
5
to thereby delay a time taken for sheet discharging by the discharging member
5
.
In the thus implemented technical idea, the image forming part
11
involves various types of image forming systems, if those are capable of forming an image on a sheet S, such as a Xerography-basis image forming system, electrostatic image forming system, and an ink jet image forming system.
The image forming part
11
shown in
FIG. 1
employs the Xerography-basis image forming system. The image forming part
11
includes an image forming engine
8
for forming an image on a sheet S on the sheet transport path
2
, which is supplied from a sheet supplying unit
12
, a transfer member
9
for transferring the image formed by the image forming engine
8
onto the sheet S, and a fixing unit
10
for fusing and fixing the image transferred onto the sheet S.
Particularly, in the embodiment in which the image forming part
11
includes the fixing unit
10
, the fixing unit
10
discharges the sheets S bearing the images fused and fixed. When the sheets S are stacked while storing up heat, the technical problem (image irregularity, the peeling of an image) appears remarkably. In this respect,: the present invention effectively operates in the embodiment.
Even in an image forming part not including the fixing unit
10
, for example, the one based on an ink jet image forming system, when the sheets S are stacked before the ink is dried, the technical problem (image irregularity, the peeling of an image) arises. Therefore, the present invention also effectively operates also in this case.
Where the sheet discharging device
3
is provided near the output part of the sheet transport path
2
in the main body
1
, it may be incorporated into the main body
1
of the image forming apparatus as its constituent part or as a separate unit.
The sheet receiving part
4
may take any form if it is capable of receiving sheets S discharged from the sheet discharging device
3
. The sheet receiving part
4
may directly be installed on the top part of the main body
1
of the image forming apparatus or it may be installed on the side of the main body
1
in the form of a tray member.
Usually, the discharging member
5
is constructed with a pair of rolls
5
a
and
5
b
, and one of the rolls serves as a drive roll and the other, as a follower roll. Further, the discharging member
5
may be constructed with paired belts, or a combination of a roll and a belt.
The drive force transmitting mechanism
6
may take any suitable form if it is capable of transmitting a driving force from a drive source (which may be a drive source dedicatedly provided or another drive source which is used for another driving purpose) at an appropriate reduction ratio or speed increase ratio.
The discharge control unit
7
may include any means capable of controlling the drive force transmitting mechanism
6
so as to temporarily delay a time taken for the discharging member
5
to discharge the sheet S. The discharge control unit
7
may be designed so as to control the coupling/decoupling of the drive source to the drive force transmitting mechanism
6
, or to control a combination of drive force transmitting members.
The control by the discharge control unit
7
may be any control if it is capable of temporarily delaying a time taken for the discharging member
5
to discharge the sheet S. For example, it may set the sheet discharging speed by the discharging member
5
at a slow speed. A p
Fuji 'Xerox Co., Ltd.
Morgan & Lewis & Bockius, LLP
Royer William J.
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