Electrophotography – Image formation – Fixing
Reexamination Certificate
1999-11-18
2001-03-20
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
C271S307000, C399S398000
Reexamination Certificate
active
06205316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fixing unit and more particularly to a paper-separating mechanism for use in the fixing unit.
2. Description of the Related Art
With a conventional electrophotographic printer, a charging roller charges the surface of a photoconductive drum and an exposing unit such as an LED head writes an electrostatic latent image on the charged surface of the photoconductive drum. The electrostatic latent image is then developed with toner into a visible image, i.e., toner image. The toner image is subsequently transferred to a print medium when the print medium passes in a sandwiched relation between the photoconductive drum and a transfer roller.
FIG. 19
is a cross-sectional view of a conventional art fixing apparatus.
FIG. 20
is a top view illustrating a relevant portion of the conventional art paper-separating apparatus for use in the fixing apparatus.
Referring to
FIG. 19
, a fixing section
11
includes a heat roller
12
and a pressure roller
13
. The heat roller
12
is rotatably supported and incorporates a halogen lamp
12
a
that functions as a heat-generating element. The pressure roller
13
is urged by urging means such as a spring, not shown, against the heat roller
12
. The heat roller
12
and pressure roller
13
are accommodated in a casing
14
. A paper-separating mechanism
80
is attached to the casing
14
. The paper-separating mechanism
80
is rotatable with respect to the casing and separates recording paper from the heat roller
12
when the recording paper
15
has intimately wrapped around the heat roller
12
during the fixing operation.
The paper-separating mechanism
80
includes a substantially triangular lug
16
rotatably mounted on a shaft
81
and a guide roller
17
rotatably mounted on the lug
16
. The guide roller
17
rotates freely on a shaft
83
and guides the recording paper
15
downstream therefrom. The lug
16
is urged by a compression spring
18
to rotate in a direction opposite to the direction shown by arrow B so that a tip
82
of the lug
16
is pressed against the heat roller
12
. A paper-discharging mechanism
22
is provided downstream of the fixing section
11
. The paper-discharging mechanism
22
includes a transport roller
19
and a pinch roller
20
. The transport roller
19
is driven in rotation by a drive source, not shown. The pinch roller
20
is urged by a flat spring
21
against the transport roller
19
, and rotates together with the transport roller
19
.
The operation of the fixing apparatus of aforementioned construction will be described.
A toner image formed on the photoconductive drum, not shown, is transferred to the recording paper
15
by the transfer device. Then, as the photoconductive drum rotates, the recording paper having the toner image thereon is advanced substantially horizontally in a direction shown by arrow A. The recording paper
15
reaches the fixing section
11
and is pulled in between the heat roller
12
and pressure roller
13
, so that the recording paper
15
is heated pressurized. As a result, the toner image is fixed and the printing completes.
As the heat roller
12
and pressure roller
13
rotate, the recording paper
15
having an image printed thereon is further advanced to the discharging section
22
where the recording paper is pulled in between the transport roller
19
and pinch roller
20
and discharged outside of the printer.
The operation of the paper-separating mechanism
80
will be described.
Prior to the arrival of the recording paper
15
, the lug
16
is positioned at the dotted line position as shown in
FIG. 19
, i.e., a standby position where the lug
16
is in contact with the heat roller
12
. When the leading end of the recording paper
15
comes into contact with the corner
16
a
of the lug
16
, the recording paper
15
pushes the lug
16
up in a direction shown by arrow B against the urging force of the spring
18
. As a result, the lug
16
moves to the solid line position of
FIG. 19
where the tip
82
of the lug
16
is away from the heat roller
12
. When the stopper
16
b
of the lug
16
abuts the casing
14
(i.e., solid line position), the stopper prevents further rotation of the lug
16
and the distance between the heat roller
12
and the tip
82
of the lug
16
reaches a maximum t.
Then, the transport roller
19
and pinch roller
20
advance the recording paper
15
. When the trailing end of the recording paper
15
passes the corner
16
a
, the lug
16
returns to the dotted line position of
FIG. 19
whether the lug
16
is in its standby state.
With the aforementioned conventional fixing apparatus, the corner
16
a
of the paper-separating lug
16
extends into a plane where the paper path lies. Therefore, when the recording paper
15
is advanced, part of the printed surface of the recording paper
15
rubs the corner
16
a
. When a solid black image is printed on the recording paper
15
, the gloss of the image areas that rub the corner
16
a
is significantly different from that of the image areas that do not rub the corner
16
a
. This impairs the image quality.
SUMMARY OF THE INVENTION
An object of the invention is to solve the aforementioned drawbacks of the conventional fixing apparatus and to provide a fixing apparatus that improves the image quality.
A fixing apparatus comprises a heat roller, paper-separating lug, and guide roller. The lug engages the heat roller to separate a recording medium from the heat roller if the recording medium wraps around the roller. The lug is movable between a first position and a second position. The lug is brought into contact engagement with the roller when the lug is in the first position and being out contact engagement with the roller. The guide roller is rotatably mounted to the lug. The guide roller extends into a plane in which a travel path of the recording medium lies, and guides the recording medium after the recording medium is separated from the heat roller.
The lug is rotatable within a predetermined angular range relative to the heat roller so that the lug is away from the heat roller by a predetermined maximum distance when the lug is in the second position.
The guide roller may be movable relative to the lug so that the guide roller extend into and retract from the plane in which the travel path of the recording medium lies. The guide roller yieldably retracts from the plane when the recording medium pushes the guide roller out of the way.
The fixing apparatus may further comprise a holder that holds the lug such that the lug is rotatable relative to the holder. The lug may have a tip and is freely rotatable such that the tip is movable over the predetermined distance when the lug is in the second position. The lug rotates such that the tip moves into contact engagement with the roller when the recording paper pushes the lug.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4475804 (1984-10-01), Kanno et al.
patent: 4929983 (1990-05-01), Barton et al.
patent: 5151742 (1992-09-01), Yamaguchi
patent: 5517292 (1996-05-01), Yajima et al.
patent: 5608512 (1997-03-01), Endo
patent: 5671471 (1997-09-01), Mizuno et al.
patent: 1-060553 (1989-03-01), None
patent: 8-137322 (1996-05-01), None
Akin Gump Strauss Hauer & Feld L.L.P.
Chen Sophia S.
Oki Data Corporation
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