Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2001-07-23
2003-02-04
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S331000
Reexamination Certificate
active
06516165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system.
2. Related Background Art
Conventionally, in an image forming apparatus adopting an electrophotographic system, a laser printer and the like have been known. Description will be given as to a fixing apparatus provided to a prior art image forming apparatus.
In the fixing apparatus provided to the prior art image forming apparatus, a heat fixing apparatus is often used in order perform fixing processing on transferring paper which is a recording medium for bearing a toner image as an unfixed image. That is because the heat fixing apparatus has many merits. For example, the heat fixing apparatus is superior in the storage stability, capable of supporting various devices from a low-speed device to a high-speed device, and has many options of toner. Further, there has been conventionally known a fixing apparatus configured to heat a pressure roller from the inside in order to prevent the pressure roller as a pressure body from being fouled.
Here, a heat roller fixing apparatus as an example of such a fixing apparatus will be described in detail based on FIG.
7
.
FIG. 7
is a cross-sectional view showing a schematic structure of a heat roller fixing apparatus.
The heat roller fixing apparatus includes: a fixing roller
121
as a fixing body; a pressure roller
122
as a pressure body; a heater
135
(
a
) as fixing body heating means which is a halogen lamp as a heating source for the fixing roller
121
; a heater
135
(
c
) as pressure body heating means which is a halogen lamp as a heating source for the pressure roller
122
; temperature adjusting thermistors
129
and
130
as temperature detecting means for the fixing roller
121
and the pressure roller
122
; a release claw
125
; and a fixing inlet guide
134
. In this example, the both temperature adjusting thermistors
129
and
130
are provided in non-image areas. It is to be noted that the temperature adjusting thermistor
130
is used for a non-printing surface side and it may be hence provided at the center.
The fixing roller
121
is configured to have a primer layer (not shown) as an adhesive layer on a hollow core metal
123
made of aluminium, iron or stainless steel and further a fluorocarbon resin layer
124
on the primer layer. As to a thickness of the primer layer (not shown), 5 to 20 &mgr;m is appropriate, and 30 to 70 &mgr;m is appropriate for a thickness of the fluorocarbon resin layer
124
. This fluorocarbon resin layer
124
may be formed by using a tube consisting of PFA resin or by baking the PFA resin.
Since the fixing roller
121
is constituted attaching a high value on the mold releasing property of the surface, the fluorocarbon resin is constituted by pure PFA resin in which a filler is not mixed. A silicon rubber layer may be provided between the fluorocarbon resin layer
124
and the core metal
123
according to needs.
The pressure roller
122
has a structure that an elastic body layer
127
consisting of silicon rubber having the heat resistance is bonded on a hollow core metal
126
consisting of aluminium, iron or stainless steel through a primer layer (not shown) and a PFA resin tube
128
is applied on the uppermost layer portion. As this PFA resin tube
128
, there is used a material in which carbon is mixed so that the resistance value becomes 10
4
to 10
12
&OHgr;·cm in order to increase the bias effect from the pressure roller.
The heaters
135
(
a
) and
135
(
c
) as heating sources for the fixing roller
121
and the pressure roller
122
are provided inside the fixing roller
121
and the pressure roller
122
, respectively, and the heater
135
(
a
) and the heater
135
(
c
) are configured to be driven by the same power supply circuit as controlling means. By using one drive circuit for the heater
135
(
a
) and the heater
135
(
c
), the heater
135
(
a
) in the fixing roller
121
and the heater
135
(
c
) in the pressure roller
122
can be alternatively energized in accordance with each control unit (in this example 1000 ms) which is a predetermined period in time with a predetermined time length ratio (which will be referred to as a lighting ratio hereinafter), and more power can be supplied to the fixing roller
121
provided on a printing surface side (side carrying the toner
132
) of the transferring material to be subjected to fixation, thereby avoiding the power loss caused due to a switching time of a switching device.
Here,
FIG. 8
shows a heater lighting result when an A4-size landscape sheet and an LGL-size sheet are supplied.
As shown in
FIG. 8
, in case of feeding the A4-size landscape sheet, the heater
135
(
a
) is in the on state with the time length of 80% in the control unit in order to maintain the fixing roller
121
at a fixed temperature. Since the heater
135
(
a
) and the heater
135
(
c
) are alternatively turned on, the heater
135
(
c
) is in the on state only 20%. On the contrary, in case of feeding the LGL-size sheet, the heater
135
(
a
) is in the on state only 40% in order to maintain the fixing roller
121
constant, and the heater
135
(
c
) is in the on state 60%. The paper size and the heater lighting ratio of each roller are as shown in Table 1.
TABLE 1
Lighting ratio
Lighting ratio
(%) of fixing
(%) of pressure
Paper size x (mm)
heater
heater
A4-size landscape
90
10
sheet and others
(x ≧ 297)
LTR-size landscape
80
20
sheet and others
(279 ≦ x < 297)
B4-size landscape
60
40
sheet and others
(257 ≦ x < 279)
LGL/envelope and
40
60
others (x < 257)
When the heater
135
(
a
) is not turned on, the high fixing property can be satisfied by heating the pressure roller
122
from the inside. In the above-described structure, both the hardness and the wall thickness of the pressure roller
122
are restricted in order to maintain a nip width to a fixed value or a higher value.
However, the above-described conventional structure/controller have the following drawbacks.
In the structure mentioned above, since the wall thickness of the pressure roller is large, a considerable difference in temperature is generated between the core metal temperature and the surface temperature of the pressure roller depending on the lighting ratio of the heater for the pressure roller. The heater control is determined based on a temperature of the fixing roller on the printing surface side on which the fixing property greatly depends. Therefore, when the power size is small, excessive power is supplied to the heater for the pressure roller, thereby increasing the temperature of the core metal of the pressure roller. As a result, the primer between the core metal and the rubber is deteriorated, and the pressure roller is damaged.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a fixing apparatus and an image forming apparatus having this fixing apparatus capable of avoiding thermal degradation of a pressure body due to excessive increase in temperature of a core metal of the pressure body.
To achieve this aim, according to the present invention, there is provided a fixing apparatus or an image forming apparatus, comprising: a fixing body and a pressure body which are pressed against each other and rotate; fixing body heating means for heating the fixing body upon receiving supply of power from a power supply; pressure body heating means for heating the pressure body upon receiving supply of power from the power supply; temperature detecting means for detecting a temperature of at least one of the fixing body and the pressure body; and controlling means for controlling power supplied to the fixing body heating means and the pressure body heating means from the power supply in such a manner that a temperature detected by the temperature detecting means becomes a predetermined set temperature, an unfixed image being fixed on a recording medium by heating and pressing the recording medium bearing the unfixed image while pinching and conveying the recording medium,
Kobaru Yasunari
Makihira Tomoyuki
LandOfFree
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