Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-02-23
2002-02-12
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S355000, C323S225000, C399S037000
Reexamination Certificate
active
06346800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply device that may be applied to a heating device of electromagnetic inducting heating type, or the like, and also relates to a fixing device that uses the heating device for fixing images in an image forming apparatus.
2. Description of Related Art
Image heating devices (or fixing devices) have been conventionally installed in image forming apparatuses. In a known example that will be discussed below, a fixing device is installed in an image forming apparatus, such as a copying machine or a printer, for the purpose of heating and fixing a toner image on a recording medium.
In image forming apparatuses wherein an unfixed image (toner image) of desired image information is formed by a transfer method or direct method on a recording medium or material (such as a transfer sheet, electrofax sheet, electrostatic recording paper, OHP sheet, printing paper, or format paper), by a suitable image forming process, such as an electrophotographic process, electrostatic recording process, or a magnetic recording process, heat roller type devices were widely used as fixing devices for heating and fixing the unfixed image (toner image) on the surface of the recording medium, to provide a permanent fixed image. More recently, belt heating type fixing devices have been used in practice in view of quick start and energy conservation. Electromagnetic induction heating type devices are also proposed. In the following description, various types of fixing devices used in image forming apparatuses will be explained.
(a) Fixing Device of Heat Roller Type
A fixing device of heat roller type is basically constituted by a pair of rollers, i.e., a fixing roller (heating roller) and a pressure roller that are in pressed contact with each other. With the pair of rollers being rotated, a recording medium that carries an unfixed toner image thereon is nipped and transported by a fixing nip portion at which the rollers are in pressed contact with each other, so that the unfixed toner image is fixed on the surface of the recording medium, utilizing the heat of the fixing roller and the pressing force of the fixing nip portion.
The fixing roller generally has a hollow metal roller made of aluminum, as a base (core), and a halogen lamp as a heat source which is inserted into and placed in the aluminum roller. In operation, the halogen lamp generates heat for heating the fixing roller, and electric power to be supplied to the halogen lamp is controlled so that the outer peripheral surface of the roller is maintained at a certain fixing temperature.
In particular, a fixing device of an image forming apparatus adapted for forming full-color images is required to have an ability to sufficiently heat and fuse a maximum of four layers of toner images to mix different colors. To this end, the core of the fixing roller is made of a material having a large thermal capacity, and a rubber elastic layer is provided on the outer periphery of the core, for surrounding and uniformly fusing a toner image, so that the toner image is heated via the rubber elastic layer. A heat source is placed in a pressure roller as well as in a fixing roller (heating roller), and the pressure roller is heated with its temperature being suitably controlled.
The fixing device of heat roller type as described above, however, has a disadvantage as follows: when the power supply of the image forming apparatus is turned on, and the halogen lamp as the heat source of the fixing device starts being energized at the same time, it requires a considerably long time (waiting time) for the fixing roller having a large thermal capacity and other components to be heated from a totally cold state to a certain temperature that enables fixing. Thus, the fixing device of heat roller type has a poor quick start capability. Also, there is a need to energize the halogen lamp to keep the fixing roller in a certain temperature controlled state while the image forming apparatus is being in the standby state (i.e., while images are not being generated), so that the image forming operations can be carried out at any time. Thus, the fixing device of this type suffers from a large amount of power consumption.
In the case of the fixing device of the above-described full-color image forming apparatus, which uses a fixing roller having a large thermal capacity, an increase in the temperature at the surface of the fixing roller is delayed relative to the desired timing of temperature control, thus causing poor fixing, gloss variations, offset and other problems.
(b) Fixing Device of Film Heating Type
Fixing devices of film heating type have been proposed in, for example, Laid-open Japanese Patent Publications (Kokai) Nos. 63-313182, 2-157878, 4-44075 and 4-204980.
The fixing device of the above type is constructed such that a heat resistant film (fixing film) is sandwiched between a ceramic heater as a heating body and a pressure roller as a pressure member, to thus form a nip portion. A recording medium that carries an unfixed toner image thereon is pinched or nipped between the film and the pressure roller in the nip portion, and fed along with the film. In this manner, heat generated by the ceramic heater is transferred to the recording medium via the film in the nip portion, and the unfixed toner image is thermally fixed onto the surface of the recording medium, using the heat and the pressing force of the nip portion.
The fixing device of film heating type may be constructed as that of on demand type, by using a ceramic heater and a film both having a low thermal capacity. In operation, the ceramic heater as a heat source is energized only during execution of the image forming process of the image forming apparatus, so as to heat the fixing device to a certain fixing temperature. Thus, the fixing device of this type is advantageous in a relatively short waiting time (improved quick start ability) as measured from the turn-on of the power supply of the image forming apparatus until the apparatus is ready to execute the image forming process, and also advantageous in significantly reduced power consumption (power saving) during standby. The fixing device, however, has a difficulty in terms of the thermal capacity when it is used in full-color image forming apparatuses or high-speed machines.
(c) Fixing Device of Electromagnetic Inducting Heating Type
Laid-open Publication No. 51-109739 of Japanese Utility Model Application discloses an induction heating type fixing device in which magnetic flux is used for inducing current in a fixing roller, thereby to generate heat in the form of Joule heat. This type of fixing device makes it possible to directly heat the fixing roller by utilizing induction current, thus achieving a highly efficient fixing process, as compared with the fixing device of heat roller type which uses a halogen lamp as a heat source.
In the fixing device of the induction heating type, however, the energy of alternating magnetic flux generated by an exciting coil serving as magnetic field generating means is used for increasing the temperature of the whole fixing roller, resulting in an increased heat radiation loss, and a reduced ratio of the fixing energy to the energy put into the system, or reduced efficiency.
In view of the above problem, a highly efficient fixing device has been proposed in which the exciting coil is located close to the fixing roller as a heat generating body so as to provide the energy for fixing with a high efficiency, or the distribution of alternating magnetic flux of the exciting coil is concentrated at around the fixing nip portion.
Referring to
FIG. 24
, one example of fixing device of electromagnetic induction heating type will be briefly described wherein the distribution of alternating magnetic flux of the exciting coil is concentrated at around the fixing nip portion so as to improve the efficiency.
In
FIG. 24
, reference numeral
10
denotes a cylindrical fixing film (fixing belt) which serves as a rotator capable of genera
Hayasaki Minoru
Mano Hiroshi
Canon Kabushiki Kaisha
Han Jessica
Rossi & Associates
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