Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2001-02-28
2002-05-28
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C219S216000, C399S045000, C399S070000
Reexamination Certificate
active
06397021
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an image-forming apparatus such as a laser printer in which electrophotography is used to form an image on print paper, and more particularly to a temperature-controlling apparatus that controls the temperature of a fixing unit that fixes an image transferred onto the print paper.
With an electrophotographic image-forming apparatus, laser light illuminates a photoconductive drum to form an electrostatic latent image thereon. The electrostatic latent image is then developed with toner into a toner image. Then, the toner image is transferred from the photoconductive drum to print paper. Finally, the toner image on the print paper is fixed at the fixing unit and then the paper is discharged from the fixing unit.
FIG. 30
illustrates a fixing unit and the associated control sections of a conventional image-forming apparatus.
The conventional image-forming apparatus will be described with reference to FIG.
30
.
A fixing unit
100
includes a heat roller
1
, a pressure roller
20
, a heater
2
, two springs
21
, and a temperature detector
30
. The heat roller
1
heats a toner image, transferred to a print medium such as A
5
size paper
70
or A
4
size paper
80
, to fix the toner image. The heater
2
generates heat and supplies the heat to the heat roller
1
. The pressure roller
20
is rotatably supported by a shaft
22
and rotates in pressure contact with the heat roller
1
. The springs
21
are disposed at longitudinal ends of the shaft
22
and urge the shaft
22
against the heat roller
1
such that the pressure roller
20
is in pressure contact with the heat roller
1
. The temperature detector
30
is in contact with the outer circumferential surface of the heat roller
1
to detect the temperature of the heat roller
1
.
In order to uniformly heat the toner image on the print medium
70
or
80
, the heat roller
1
takes the shape of a long, hollow cylinder made of a highly heat conductive metal material. The heat roller
1
has a rubber material formed on an outer circumferential surface of the cylinder with a resin coating on the rubber. The coating is highly heat resistant and has good mold-releasing characteristic. The heat roller
1
and the pressure roller
20
are rotated in directions shown by arrows
90
and
91
of
FIG. 30
, respectively.
The heater
2
takes the form of, for example, a halogen lamp that extends in the longitudinal direction of the heat roller
1
but is not in contact with the heat roller
1
.
The pressure roller
20
is a rubber roller in pressure contact with the heat roller
1
. The pressure roller
20
is rotated such that the print medium
70
or
80
is pulled in between the heat roller
1
and the pressure roller
20
and is advanced in a direction shown by arrow
92
.
The temperature detector
30
takes the form of, for example, a temperature measuring thermistor. The temperature detector
30
is disposed, on the circumferential surface of the heat roller
1
outside of a paper path in which the A4 size paper (medium
80
) passes. In this specification, A4 size paper in portrait orientation is a maximum size of print medium that the fixing unit can accept. Specifically, the temperature detector
30
is a distance L
2
(e.g., 0-10 mm) away from the paper path.
A control block
200
shown in
FIG. 30
will be described.
A main controller
11
controls the supply of electric power to the heater
2
, transport of the print medium
70
or
80
, and drive of the pressure roller
20
. An analog/digital (A/D) converter
12
that converts temperature data in analog form detected by the temperature detector
30
into a digital form that can be processed in the main controller
11
. A power switch
13
that switches on and off the electric power supplied to the heater
2
from a power supply
14
under the control of the main controller
11
. In accordance with the instructions from the main controller
11
, a drive controller
15
drives the drive source
16
in the form of, for example, a motor that drives the pressure roller
20
in rotation. A memory
17
stores a control program for the main controller
11
and control data. The operating panel
18
includes an input section
18
b and a display section
18
a
. The input section
18
b allows the user to set the size of print paper and print density prior to printing. The display section
18
a
displays current settings and messages to the operator.
The warm-up operation of the aforementioned conventional image-forming apparatus is performed as follows:
For example, upon power up, the warm-up operation starts. The main controller
11
causes the power switch
13
to shift from an OFF position to an ON position, so that the power supply
14
supplies electric power to the heater
2
. At the same time, the main controller
11
causes the drive controller
15
to drive the motor
16
into rotation. Thus, the motor
16
drives the pressure roller
20
and heat roller
1
in rotation in the directions shown by arrows
90
and
91
. In the warm-up operation, when the temperature detected by the detector
30
reaches a target temperature (e.g., 170° C.) at which the fixing operation can be adequately carried out, the supply of electric power from the power supply to the heater
2
is interrupted. Thereafter, feedback control is performed through a loop (the detector
30
→A/D converter
12
→main controller
11
→power switch
13
→heater
2
→heat roller
1
), thereby maintaining the detected temperature to the target temperature.
The operation when the image-forming apparatus receives print data from a host apparatus will be described.
Upon receiving the print data from the host apparatus, the main controller
11
provides a command to the power switch
13
so that the power switch
13
directs electric power to the heater
2
as required. The main controller
11
also provides a command to the drive controller
15
, thereby causing the drive controller
15
to drive the motor
16
to drive the pressure roller
20
and heat roller
1
in rotation. Then, the main controller
11
causes the print medium
70
or
80
to be fed to the image-forming section from a paper cassette, not shown. A toner image is transferred onto the print medium
70
or
80
and the print medium is advanced by a registry roller, not shown, in a direction shown by white arrow
92
and abuts the pressure roller
20
. The print medium is pulled in between the rotating heat roller
1
and the pressure roller
20
. When the print medium passes between the heat roller
1
and pressure roller
20
, the toner on the print medium
70
or
80
is melted and permanently adheres to the print medium due to the pressure applied by the pressure roller
20
. The print medium
70
or
80
is then discharged with a transport device, not shown, to the outside of the printer.
As described above, the temperature detector
30
is disposed in contact with an area outside of the surface of the heat roller
1
that contacts the print medium. The electric power supplied to the heater
2
is switched on and of f such that a temperature detected by the temperature detector
30
is maintained at a predetermined value.
When the print medium
70
or
80
passes between the heat roller
1
and pressure roller
20
, the print medium absorbs heat from the heat roller
1
to fuse the toner deposited thereon, thereby causing the temperature of the heat roller
1
to decrease. This creates a temperature difference between an area on the heat roller
1
that contacts the print medium and an area on the heat roller
1
that does not contact the print medium.
For example, when A4 size paper (print medium
80
) passes through an area Lb, the heat roller
1
loses heat to the A4 size paper, creating a temperature difference between the area Lb and a point E. However, the distance L
2
between the area Lb and the point E is very short, e.g., 0-10 mm. Thus, the temperature difference between the area Lb and the point E is not large, so that the temperatu
Hayashi Kuniharu
Murakami Tatsuya
Nagamine Masamitsu
Yajima Hiroyuki
Yamane Tsutomu
Akin Gump Strauss Hauer & Feld L.L.P.
Oki Data Corporation
Pendegrass Joan
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