Electrophotography – Image formation – Fixing
Reexamination Certificate
1999-09-14
2002-07-30
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S045000
Reexamination Certificate
active
06427060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of the kind using an electrophotographic method or an electrostatic recording method, such as an electrophotographic copying machine, a facsimile set, a printer or the like, and more particularly, to the method for cleaning a fixing device used for such an image forming apparatus.
2. Description of Related Art
Image forming apparatuses such as electrophotographic copying machines are generally provided with a web cleaning device having a cleaning web which is made of a nonwoven cloth or the like for cleaning and removing a residual toner left on an object to be cleaned such as a fixing roller.
FIG. 6
shows, by way of example, a conventional fixing device arranged to fix, by heating, a toner image T formed by the electrophotographic method to a transfer member P which is employed as a recording member. The fixing device shown in
FIG. 6
is provided with a fixing roller
101
which is a fixing rotary body having a heating heater
103
such as a halogen heater disposed inside thereof. The fixing roller
101
is arranged to be rotated in the direction of an arrow by a driving force of a driving motor (not shown).
A pressure roller
102
, which is supported by a bearing (not shown) below the fixing roller
101
, is caused by some known pressing means to be in pressed contact with the fixing roller
101
at least in carrying out a fixing process. The rollers
101
and
102
are thus arranged to rotate in a state of being in pressed contact with each other.
A thermo-sensitive element
104
such as a thermistor or a thermocouple is disposed in contact with the outer circumferential surface of the fixing roller
101
. The thermo-sensitive element
104
is thus arranged to detect the temperature of the fixing roller
101
and to send a detection signal to some known control means. The control means is arranged to control the output of the heater
103
or a voltage applied to the heater
103
on the basis of the detection signal of the thermo-sensitive element
104
, so that the outer circumferential surface of the fixing roller
101
is kept at a toner-image fusing temperature.
Separation claws
151
and
152
are disposed in contact respectively with the fixing roller
101
and the pressure roller
102
and are arranged to reliably separate the transfer member P from the rollers
101
and
102
after a fixing process. The separation claws
151
and
152
are made of a heat resisting resin, such as a polyimide or polyamide resin, coated with a fluororesin.
Meanwhile, a cleaning device
106
is disposed above the fixing roller
101
to remove an offset toner and a foreign matter such as paper powder or the like sticking to the surface of the fixing roller
101
. The cleaning device
106
uses a cleaning web (hereinafter referred to simply as the web)
160
which is a band-shaped element made of a heat resisting nonwoven cloth, such as Nomex (trade name), Himelon (trade name), etc.
Further, a web pressing roller
165
is rotatably supported by a bearing
172
at each of its two ends. The offset toner and foreign matter such as paper powder or the like sticking to the surface of the fixing roller
101
are removed from the surface of the fixing roller
101
and are thus effectively prevented from offsetting, with the web pressing roller
165
arranged to be in pressed contact with the fixing roller
101
.
Generally, the web
160
is arranged to be wound, or taken up, as much as a predetermined amount per sheet of copy by a driving means (not shown), irrespective as to whether the image forming apparatus is in the mode of copying (printing) a single sheet or in the mode of continuously copying a plurality of sheets.
The above-stated fixing device has almost no offset caused by slipping-off of an offset toner from the web
160
while copying (printing) is in process. This is because only a very small amount of toner slips off being not captured by the web
160
in the process of copying. Besides, the slip-off toner, coming into contact with both the fixing roller
101
and the pressure roller
102
, is dispersed on the surfaces of both the fixing roller
101
and the pressure roller
102
to evenly flow out little by little to the surface and back sides of the transfer member P during the copying process. The slip-off toner is, therefore, hardly notable while copying is in process.
On the other hand, when the rollers
101
and
102
are caused to rotate immediately after the start of the image forming apparatus, or when copying is resumed after a pause, however, some residual toner is not completely captured by the web
160
and is allowed to slip off. The slip-off toner then might come out in lumps to stick to the recording member, i.e., the transfer member P, to conspicuously smudge the recording member. Further, if the slip-off toner on the fixing roller
101
comes into contact with the pressure roller
102
, the slip-off toner becomes solid on the pressure roller
102
to stick to the pressure roller
102
, because the temperature of the pressure roller
102
is relatively low at this time. A major portion of the slip-off toner is thus transferred from the fixing roller
101
to the pressure roller
102
.
When the transfer member P is fed under this condition, the majority of the slip-off toner on the pressure roller
102
is re-transferred to the back side of the transfer member P, which is inferior in parting property than the pressure roller
102
. Therefore, a back-side smudged state of the transfer member P tends to stand out.
The smudge which results from offsetting becomes salient particularly when copying is restarted after a pause after completion of continuous copying, due to the following reason.
The fixing roller
101
is controlled and adjusted to be at a predetermined fixing temperature. However, in the case of continuous copying, the process of adjusting the temperature of the fixing roller
101
to the fixing temperature might gradually become too slow, depending on the number of sheets in continuous copying. The temperature of the fixing roller
101
then drops to deteriorate the fixing power of the fixing roller
101
. As a result, the amount of toner offsetting on the surface of the fixing roller
101
comes to increase.
Further, in carrying out continuous copying to obtain a great number of copies of one and the same image, the offset toner concentrates in a position corresponding to the image. This also causes the offsetting smudge to become conspicuous after continuous copying.
The above phenomenon becomes conspicuous also in a case where the operation of the image forming apparatus is restarted after using such transfer members that are inferior in fixing property and thus tend to increase the amount of residual toner.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide an image forming apparatus which is capable of preventing a recording member from being smudged by some offset toner when an image forming operation is performed after a pause after completion of a continuous image forming operation.
It is another object of the invention to provide an image forming apparatus in which, in a case where the number of recording members during a continuous image forming mode is not less than a predetermined number, a cleaning member moves by a second amount larger than a first amount after completion of a continuous image forming operation.
It is a further object of the invention to provide an image forming apparatus in which, after completion of an image forming operation, a cleaning member moves by an amount not less than the width of a part where a rotary member and the cleaning member are in contact with each other in a moving direction of the cleaning member.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4926218 (1990-05-01), Fukao
patent: 5049943
Arakawa Hiroyuki
Nami Yasuo
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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