Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-03-09
2002-11-05
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S323000, C399S327000
Reexamination Certificate
active
06477350
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fixing unit which fixes a developed image having been transferred onto a recording sheet.
BACKGROUND TECHNIQUE
Electrophotographic image-forming apparatuses are used widely at the moment. The electrophotographic image-forming apparatus is explained below by reference to FIG.
6
.
FIG. 6
illustrates schematically a constitution of a conventional electrophotographic image-forming apparatus.
The image forming apparatus
10
has a photosensitive drum
12
which is rotated in the arrow-A direction by a motor (not shown in the drawing). A primary electrifier
14
is provided in opposition to the photosensitive drum
12
. The primary electrifier
14
electrifies uniformly the photosensitive drum
12
by corona discharge. To the uniformly electrified photosensitive drum
12
, light (document-reflected light)
16
having image information of a document is projected to form an electrostatic latent image on the photosensitive drum
12
.
A development unit
18
is provided after the position irradiated by the document-reflected light
16
along the rotation direction of the photosensitive drum
12
to develop the electrostatic latent image. The development unit
18
has a development sleeve
18
a
which is rotated by a motor (not shown in the drawing) in an arrow-B direction. A toner (developing agent) is fed from the development sleeve
18
a
to the photosensitive drum
12
. The electrostatic latent image on the photosensitive drum
12
is moved with rotation of the drum to the position opposing the development sleeve
18
a
. There, the toner is fed from the development sleeve
18
a
to the electrostatic latent image to form a toner image (developed image) on the photosensitive drum
12
.
At a timing in synchronization with the moving speed of the toner image formed on the photosensitive drum
12
registration rollers
20
,
20
′ rotate in an arrow-C or -C′ direction respectively to deliver a recording sheet (not shown in the drawing) like a recording paper sheet toward an image transfer region
22
. The recording sheet delivered from the registration rollers
20
,
20
′ passes through the space between an upper transfer guide plate
24
and a lower transfer guide plate
26
and reaches the photosensitive drum
12
.
The recording sheet having reached the photosensitive drum
12
is then delivered to the transfer region
22
. In the image transfer region
22
, the toner image on the photosensitive drum
12
is transferred by a transfer electrifier
28
onto the recording sheet. Then the recording sheet is separated by a separation electrifier
30
from the photosensitive drum
12
.
At the position after the transfer region
22
in the direction of rotation of the photosensitive drum
12
, a cleaner
34
is provided which has a blade
32
. The blade
32
scrapes a remaining toner on the photosensitive drum
12
after the image transfer.
At the position after the cleaner
34
in the direction of rotation of the photosensitive drum, an eraser
36
is provided. The eraser
36
removes residual potential remaining on the photosensitive drum
12
. On the other hand, the recording sheet having received the transferred toner image is delivered by a delivery member
38
in the arrow-D direction to a fixation unit
40
. In the fixation unit
40
, the toner image is fixed onto the recording sheet. Thereafter the recording sheet is sent out of the apparatus to complete one copying cycle.
The fixation unit
40
is explained by reference to FIG.
7
.
FIG. 7
illustrates schematically the structure of a conventional fixation unit
40
.
The fixation unit
40
serves to visualize permanently the toner image on the recording sheet. The recording sheet having been delivered in the arrow-D direction by the delivery member
38
(see
FIG. 6
) is guided to a fixation inlet
42
, and is introduced to a nip
48
between a fixation roller
44
and a pressure roller
46
. The fixation roller
44
heats the recording sheet up to the fixation temperature. The fixation roller
44
is usually constituted of a pipe made of steel or aluminum, and a fluororesin coating the surface of the pipe.
The pressure roller
46
presses the recording sheet against the fixation roller
44
at a prescribed pressure. The pressure roller
46
is usually constituted of a metal core and an elastomer such as silicone rubbers and fluoro-rubbers coating the outside surface of the metal core in a prescribed thickness. The pressure roller
46
is pressed against the fixation roller
44
at a prescribed pressure to apply a load for fixing the toner image onto the recording sheet.
At the nip
48
, the toner on the recording sheet is fused, and the fused toner is pressed against the recording sheet to be fixed onto the recording sheet. The recording sheet having the toner image fixed thereon is carried by rotation of the fixation roller
44
and pressure roller
46
through a sheet discharge guide having an upper separation claw
50
and a lower separation claw
52
to sheet discharge roller
54
, and is discharged by the discharge rollers
54
out of the apparatus.
The fixation roller
44
and the pressure roller
46
are placed in a first casing
60
. To the first casing
60
, the fixation inlet or paper inlet guide
42
is attached with interposition of a guide-attaching plate
56
. The upper separation claw
50
, the lower separation claw
52
, and the sheet discharge rollers
54
are placed in a second casing
62
. The first casing
60
and the second casing
62
are separable from each other.
In the fixation process, some toner adhering to the recording sheet can be transferred to adhere to the fixation roller
44
. This toner adhering to the fixation roller
44
may be transferred again to the recording sheet to stain the recording sheet. In one method to prevent this staining of the recording sheet, the toner adhering to the fixation roller
44
is transferred to the pressure roller
46
, and the transferred toner is removed from the pressure roller
46
by a contact roller (cleaning roller)
64
. This cleaning roller
64
may be designed to be driven by pressure contact with the pressure roller
46
.
In continuous image fixation onto small-sized recording sheets, the heat of the fixation roller
44
is taken away by the passing recording sheets at the center portion, whereas at the side portions of the fixation roller
44
the heat is not taken away. With this state continued, only the end portions of the fixation roller
44
will be heated to a higher temperature, which may necessitate intermission of the copying to protect the parts near the end portions from the high temperature. In one method to avoid this, a contact roller (cleaning roller or heat radiation roller)
64
having a high thermal conductivity is brought into pressure contact with the pressure roller
46
to be driven therewith.
For space saving, the image-forming apparatus
10
(
FIG. 6
) may be made smaller (compactification). For this compactification, the fixation unit
40
is desirably made compact. To make compact the fixation unit, the cleaning roller (heat radiation roller)
64
is placed below the paper inlet guide
42
as shown in FIG.
7
.
The aforementioned cleaning roller (heat radiation roller)
64
which becomes soiled by the toner is designed to be detachable for cleaning, or to be exchangeable. When the cleaning roller
64
is placed at the paper feed side, the cleaning roller
64
may be designed to be detachable either from the side of the discharge rollers
54
, or from the side of the paper inlet guide
42
.
The method of detaching the cleaning roller
64
is explained with reference to
FIGS. 8 and 9
.
FIG. 8
illustrates schematically a method of detaching the cleaning roller
64
from the side of the sheet-discharge rollers
54
.
FIG. 9
illustrates schematically a method of detaching the cleaning roller
64
from the side of the paper inlet guide
42
.
To detach the cleaning roller
64
from the side of the sheet discharge rollers
54
, firstly the second casing
62
is separat
Copyer Co. Ltd.
Dellett & Walters
Royer William J.
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