Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2002-02-20
2003-12-30
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C219S216000, C374S153000, C399S320000
Reexamination Certificate
active
06671471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image heating apparatus used in an image forming apparatus such as a laser printer or a facsimile apparatus using the electrophotographic process to fix an unfixed toner image on a recording medium such as a sheet by heat and pressure.
2. Related Background Art
An image forming apparatus using electrophotography according to the prior art is constructed as shown, for example, in
FIG. 5
of the accompanying drawings. In
FIG. 5
, the reference numeral
201
designates a photosensitive drum, the reference numeral
202
denotes a charging roller, the reference numeral
203
designates a laser exposing apparatus, the reference numeral
204
denotes a reflecting mirror, the reference numeral
205
designates a developing sleeve, the reference numeral
206
denotes a toner, the reference numeral
207
designates a toner container, the reference numeral
208
denotes a transferring roller, the letter P designates a sheet as a recording medium, the reference numeral
210
denotes a cleaning blade, the reference numeral
211
designates a waste toner container, the reference numeral
212
denotes a fixing device, the reference numeral
213
designates a paper cassette, the reference numeral
214
denotes a sheet feeding roller, the reference numeral
215
designates a separating pad, and the reference numeral
216
denotes a high voltage source.
The epitome of the operation of the image forming apparatus will now be described. The photosensitive drum
201
is rotated in the direction of arrow, and is uniformly charged by the charging roller
202
supplied with electric power from the high voltage source
216
. A laser beam emitted from the laser exposing apparatus
203
is reflected by the reflecting mirror
204
, and thereafter is applied to the photosensitive drum
201
, whereby an electrostatic latent image is formed on the photosensitive drum
201
. The toner container
207
is filled with the toner
206
, and with the rotation of the developing sleeve
205
, a suitable amount of toner is subjected to moderate charging, and thereafter is supplied onto the photosensitive drum
201
.
The toner
206
on the developing sleeve
205
adheres to the electrostatic latent image on the photosensitive drum
201
, and the latent image is developed and visualized as a toner image. The sheet feeding roller
214
feeds the sheets P one by one from the paper cassette
213
in timed relationship with the formation of the toner image.
The separating pad
215
is disposed in abutting relationship with the sheet feeding roller
214
, and the coefficient of friction, grounding angle and shape of the surface thereof are adjusted so as to feed only a recording medium during each sheet feeding time. The visualized toner image on the photosensitive drum
201
is transferred onto the sheet P by the transferring roller
208
. Any untransferred toner not transferred but residual on the photosensitive drum
201
is collected into the waste toner container
211
by the cleaning blade
210
, and the photosensitive drum
201
having had its surface cleaned enters the next image forming process.
Also, the sheet P now bearing the toner image thereon is heated and pressurized by the fixing device
212
, whereby the toner image is permanently fixed on the sheet P.
The epitome of the fixing device
212
will now be described. A lengthwise schematic view of the fixing device
212
is shown in
FIG. 6
of the accompanying drawings, and a cross-sectional view thereof taken along the line
7
—
7
of
FIG. 6
is shown in
FIG. 7
of the accompanying drawings.
FIG. 8
is a lengthwise schematic view of a temperature detecting portion.
The fixing device
212
, as shown in Japanese Patent Application Laid-Open No. 63-31382, uses a film heating process in which a pattern of a resistance heat generating member is provided on a ceramic substrate to thereby form a heat generating member and the heat generating member is used as a heater, which is caused to generate heat to thereby heat a sheet bearing an unfixed toner image thereon through thin film.
The reference numeral
108
designates a heater having a resistance heat generating member
108
a
formed on a ceramic substrate, and the resistance heat generating member
108
a
is coated with a glass layer
108
b
as a protective layer. The resistance heat generating member
108
a
is supplied with electric power by a power source, not shown, and generates heat. Temperature detecting means
117
abuts against the back of the heater
108
and detects the temperature of the heater
108
. The temperature detecting means
117
is comprised of a temperature detecting element (ex. thermistor)
101
, a heat-resistant elastic member
102
for elastically holding and pressuring the temperature detecting element
101
, a frame
104
supporting the temperature detecting element
101
and the elastic member
102
and having a positioning shape for a heater holder
109
, a metal
105
molded integrally with the frame
104
and electrically connected to the temperature detecting element
101
, and a heat-resistant protective sheet
103
(film) for covering the temperature detecting element
101
and the elastic member
102
and positioned by the metal
105
.
The temperature detecting element
101
is vertically movable by an amount corresponding to the expansion and contraction of the elastic member
102
with the aid of a groove formed in the frame
104
. The temperature detecting means
117
is positioned by the heater holder
109
and is biased toward the heater
108
by a pair of springs
106
. The reference numeral
107
denotes a spring supporting member. The amount of electric power supplied to the heater is controlled by a CPU, not shown, so that the detected temperature by the thermistor may become constant.
The heater holder
109
supports the heater
108
and is molded of heat-resistant resin such as PPS or liquid crystal polymer and serves also as a guide member for expediting the smooth rotation of fixing film
111
.
A heater clip
114
and a heater connector
112
for supplying electricity to the heater nip the end portions of the heater
108
and the heater holder
109
therebetween. The fixing film
111
is cylindrical heat-resistant film of three-layer structure. The innermost layer of the fixing film
111
is a base layer, i.e., a layer bearing mechanical characteristics such as the torsion strength and smoothness of the fixing film
111
, and is formed of resin such as polyimide.
The next layer is an electrically conducting primer layer, i.e., an electrically conducting layer having electrically conductive particles such as carbon black dispersed therein. The electrically conducting primer layer serves also as an adhesive effecting the joint of the third layer and the base layer. The outermost layer is a top layer and is designed to have an optimum resistance value and an optimum film thickness so as not to cause various bad images. The reference numeral
110
designates a fixing stay formed of a metal such as iron or aluminum. The fixing stay
110
serves to suppress the deformation of the heater holder
109
by creeping and enhance the rigidity of the heater holder
109
. The reference numeral
113
denotes flanges mounted on the opposite end portions of the fixing stay
110
.
The heater
108
, the heater holder
109
and the fixing film
111
fitted on the fixing stay
110
are located between the flanges
113
on the axially opposite end portions and are subjected to lengthwise regulation. The above-described assembly is a film unit.
The reference numeral
119
designates a pressure roller. The pressure roller
119
comprises a mandrel
119
a
made of aluminum or cast iron and covered with heat-resistant rubber
119
b
such as silicone rubber. The surface layer of the rubber
119
b
of the pressure roller
119
is provided with film of fluorine resin such as PFA, PTFE or FEP having a releasing property with respect to the toner. The pressure roller
119
has its axially opposite end porti
Nakamura Naoki
Nishitani Hitoshi
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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