Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2003-04-02
2004-05-25
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S401000
Reexamination Certificate
active
06741815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile apparatus, and particularly to an electrophotographic image forming apparatus which can reverse the front side and the back side of copy paper on which an image has been fixed by heat and re-feed the copy paper to an image forming portion.
2. Description of Related Art
FIG. 7
of the accompanying drawings is a cross-sectional view of a digital copying machine as a conventional image forming apparatus.
A digital copying machine main body
1
is comprised of a reader
2
for reading the image of a document, and a printer
3
for forming an image on copy paper, and an auto document feeder
4
for successively feeding documents stacked thereon to a predetermined position on the reader
2
is connected to the reader
2
.
A bundle of documents are stacked on the document stacker
401
of the auto document feeder
4
with the image surface of the head page facing upward, and are fed in succession from the uppermost document by the rotative driving of a document feed roller
402
.
The thus fed document is placed on a document glass plate
201
with its image surface facing downwardly, and image reading by the reader
2
is effected. The image reading by the reader
2
is effected by a well-known technique of irradiating the document by an illuminating lamp
202
, and imaging reflected light from the document on a CCD sensor in an image sensor
207
through the intermediary of reflecting mirrors
203
,
204
,
205
and a lens
206
. As the reading operation at this time, there are two ways, i.e., the operation of reading with a scanner unit
208
comprising the illuminating lamp
202
, the reflecting mirror
203
, etc. moved relative to the documents stationarily placed on the document glass plate
201
(stationary document reading mode), and the operation of reading by the scanner unit
208
stationary relative to the document moving on the document glass plate
201
(flowing document reading mode), and the reading operation is selectively changed over in conformity with the mode, whereby the document reading time is shortened to thereby achieve an improvement in productivity. The documents of which the image reading by the reader
2
has been finished are successively delivered onto a document delivery tray
403
with their image surfaces facing downwardly.
A plurality of image data read by the above-described operation are all stored in a large-capacity memory (hard disc), not shown, and the image data stored in the memory are outputted to the printer
3
in the order conforming to an editing mode designated by the operating portion (not shown) of the digital copying machine
1
.
Copy sheets which are recording mediums for the read images are contained in a right deck
301
, a left deck
302
, an upper cassette
303
, a lower cassette
304
an a manual feed tray
305
. The copy sheets successively fed one by one of feed rollers
306
-
310
being selectively rotatively driven are supplied to an image forming portion while being timed by registration rollers
311
. In the image forming portion, a photosensitive drum
312
is rotated in the direction indicated by the arrow in
FIG. 7
by a motor (not shown) and is charged to desired potential by a primary charger
313
, and thereafter is subjected to the application of a predetermined laser beam based on image data, whereby an electrostatic latent image is formed on the photosensitive drum
312
, and the electrostatic latent image is developed as a toner image by a developing device
315
. As a developing process at this time, there is well known a triboelectrification process comprising agitating and conveying a magnetic toner stored in a developing device
315
, attracting it to a rotary developing sleeve
317
on which a magnetic pole pattern (strength and weakness of a magnetic force) has been formed in the circumferential direction, thinly and uniformly regulating an amount of coat by a developing blade
318
of a magnetic material disposed with a uniform minute gap in the lengthwise direction of the developing sleeve and also, causing the toner to rub in an agitating portion and a minute gap portion to thereby impart predetermined charges thereto. The developed toner image is transferred to the supplied copy paper by a transfer charger
319
, and the photosensitive drum
312
after the termination of the transfer has any residual toner thereon removed by a cleaner
320
, and has any residual charges thereon eliminated by a pre-exposure lamp
321
. The toner collected by the cleaner
320
is conveyed to a waste toner bottle (not shown) by a conveying portion such as a screw
322
. The copy paper after the termination of the transfer is stripped from the photosensitive drum
312
by a stripping charger
323
, is transported to a fixing roller
325
by a transport belt
324
, and is subjected to pressure and heating by the fixing roller
325
, whereby the toner image on the copy paper is fixed as a permanent image.
When a single-sided copy mode is selected by an operating portion (not shown), the copy paper on which the toner image has been fixed is delivered onto a delivery tray
331
by delivery rollers
330
via a straight delivery path
333
.
On the other hand, when a two-sided copy mode is selected by the operating portion (not shown), the copy paper of which the toner image on the first side has been fixed is once drawn into a surface reverse portion
327
via a surface reverse transport path
326
, and thereafter goes via a duplex transport path
332
by the reverse rotation of surface reverse rollers
328
, whereby it is again supplied to the image forming portion with the upper side and the lower side of the copy paper reversed, and an image on the second side is formed. The copy paper of which the toner images on the two sides have been fixed goes via the straight delivery path
333
and is delivered onto the delivery tray
331
by the delivery rollers
330
.
In the above-described image forming apparatus, however, when in the two-sided copy mode, there is a case where copy paper heated by the fixing roller is again supplied to the image forming portion in a state in which it is not sufficiently cooled, there has been the undesirable possibility that the toner in the developing device rises in temperature due to the heat radiation from the copy paper and the chargeability thereof is deteriorated and such abnormal image as thin image density occurs.
Also, in cases where, due to heat radiation from copy paper during two-sided copying, the toner in the developing device rises in temperature beyond a fusing point, there is the undesirable possibility that the fused toner is fused to the developing sleeve or the developing blade and the amount of toner coat on the developing sleeve becomes non-uniform and an abnormal image such as uneven image density or a streaked image occurs.
Further, in cases where the fuse toner is fused and bonds to a toner conveying member such as the agitator of the developer or the screw of the cleaner, there is also the undesirable possibility that the conveyance of the toner is hindered or faulty operation due to the rise of a driving load is caused.
Particularly, with the recent tendency toward higher speed image forming apparatus, the time from when copy paper has passed the fixing roller until it again arrives at the image forming portion becomes shorter, and the time for which the heat of duplex copy paper is diffused in a machine and cooled is decreased, and the quantity of heat imparted to the toner in the developing device and the cleaner per unit time tends to increase more and more.
In order to solve the problem of the temperature rise of the toner in the developing device and the cleaner attributable to the heat of the duplex copy paper, there have heretofore been proposed various techniques of disposing a copy paper cooling portion in a transport route downstream of a fixing roller.
As an example of them, as disclosed in Japanese Pat
Fujita Keiko
Sekiguchi Hajime
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