Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-09-20
2001-12-04
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Fixing
C399S328000, C399S330000, C399S329000, C219S619000
Reexamination Certificate
active
06327456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fixing device to be mounted to an image forming apparatus, such as an electrophotographic printer, facsimile machine, or copying machine. More particularly, the present invention relates to a fixing device utilizing an electromagnetic induction heating technique as a fixing technique.
2. Description of the Related Art
A conventional image forming apparatus that uses toner for forming a visible image includes a fixing device that fixes a toner image onto a recording material. Such a fixing device comprises a fixing roller (or a heating roller) for heating and melting a non-fixed toner image, and a pressure roller that presses a recording material against the fixing roller so as to sandwich and transport the recording material with the fixing roller. Conventionally, such a fixing device comprises a halogen lamp as a heater inside the fixing roller. Such a halogen lamp heats the fixing roller to a temperature high enough for toner image fixation.
However, the above heating method utilizing a heater requires a relatively long time to heat the fixing roller to a predetermined temperature, and during the heating, a user cannot use the image forming apparatus and is forced to wait for a long time. Also, since a halogen lamp heater has great heat loss, the energy consumption becomes large in the halogen lamp heating method. Such a problem cannot be overlooked in this time and age of environmental-friendly movement, and there has been an increasing demand for an efficient fixing device with a short rise time.
In view of the above facts, an induction heating fixing device that heats a fixing roller made of a metallic conductor by eddy current caused by electromagnetic wave has been drawing attention, because such a fixing device dramatically shortens the heating time.
FIG. 1
shows the structure of a conventional induction heating fixing device. In this device, an induction coil
1
is inserted into a heating roller
3
that is in pressure-contact with a pressure roller
2
. The induction coil
1
is wound around a bobbin
4
, so that high-frequency current flows through the induction coil
1
in its axis direction via a lead wire attached at either end. The induction coil
1
is held by brackets attached to side plates (not shown), and thus prevented from rotating. In
FIG. 1
, the heating roller
3
rotates clockwise, while the pressure roller
2
rotates counterclockwise. A temperature fuse
5
and a thermistor
6
are disposed on the opposite side of the surface of the heating roller
3
from the pressure roller
2
.
During the fixing operation, high-frequency current flows through the induction coil
1
via the lead wires, generating a high-frequency magnetic field. This high-frequency magnetic field generates induction eddy current in the heating roller
3
made of a metallic conductor, and the fixing roller generates Joule heat due to skin resistance. As shown in
FIG. 1
, a recording sheet S having a toner image T
1
to be fixed thereon is transported from the right in the direction of the arrow. The recording sheet S is then sandwiched by the heating roller
3
and the pressure roller
2
, so that the toner image T
1
is fixed by heat and pressure.
In the above structure, a heating coil for induction-heating the heating roller is inserted into the heating roller so as not to hinder the sheet transportation. Here, the heating roller generally has a cylindrical shape, and the inside of the core bar is not processed. A separation layer is formed outside the core bar, but the separation layer is not directly attached to the core bar, because it is normally difficult for a separation layer to adhere to the surface of the core bar. Therefore, a primer layer is employed to help the bonding between the core bar and t he separation layer.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a fixing device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a fixing device that has a higher thermal conversion efficiency than a conventional induction heating fixing device.
The above objects of the present invention are achieved by a fixing device in which the peripheral surface of a roller facing an induction coil has concavities and convexities with edges.
The above objects of the present invention are also achieved by a fixing device in which a roller facing an induction coil has a core bar, the inner periphery of the core bar has concavities and convexities, and the induction coil is inserted into the core bar. The same effects can be obtained in a case where the outer periphery of the core bar has concavities and convexities, and the induction coil is located outside the roller.
The above objects of the present invention are also achieved by a fixing device provided with a fixing belt wound around at least two rollers. In this fixing device, the fixing belt is made of a magnetic material, an induction coil is located in the vicinity of a pressure contact point between the fixing belt and the pressure roller, and a surface of the fixing belt has concavities and convexities with edges.
The concavities and convexities are formed by a blasting process, an etching process, and a melting and spraying process. In the case of the melting and spraying process, the core bar or the fixing belt should be made of a material selected from the group consisting of titanium, titanium alloys, aluminum, aluminum alloys, copper, and copper alloys, each of which has high thermal conductivity. On the other hand, a material to be melted and sprayed onto the core bar or the fixing belt should be a magnetic material such as stainless steel or iron.
It is preferable that an insulating layer made of fluororesin or silicone rubber is formed on the concavities and convexities. It is more preferable that the insulating layer has a thickness of 0.3 mm or greater. It is even more preferable that the insulating layer also serves as a separation layer.
In accordance with the present invention, the concavities and convexities formed on the surface of the roller facing the induction coil or on the surface of the fixing belt gather the eddy current to the edges of the concavities and convexities, so as to efficiently heat the roller. This technique fundamentally differs from the prior art using the conventional halogen heater technique, in which concavities and convexities are formed on the inner periphery of the heating roller so as to increase the heat reception area to obtain a higher heat absorption rate. In this invention, the locations of the concavities and convexities are determined in accordance with the positional relationship between the roller and the induction coil, thereby ensuring highly efficient heating. More specifically, in a case where the induction coil is inserted into the core bar, the concavities and convexities are formed on the inner surface of the core bar, while in a case where the induction coil is located outside the heating roller, the concavities and convexities are formed on the outer surface of the core bar.
By a blasting process, those concavities and convexities can be formed at low cost. By an etching process, the concavities and convexities are uniformly shaped so as to prevent irregular heat distribution. A melting and spraying process allows a wider variety of materials used for the core bar.
A layer made of resin, more particularly of fluororesin or silicone rubber, can serves as an insulator on the surface with the concavities and convexities, by virtue of its electric insulating characteristics. Even if the coil is brought into contact with the concavities and convexities, such an insulating layer will prevent electric leakage.
Other objects and further features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: Re. 36124 (1999-03-01), Yokoyama et al.
patent: 5300996 (1994-04-01), Yokoyama et
Grimley Arthur T.
Ngo Hoang
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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