Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-11-06
2002-04-16
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C219S216000, C399S334000
Reexamination Certificate
active
06373232
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power supply device and an image forming apparatus using the same and, more particularly, to a belt heating type heating device, a power supply device which can be preferably used for an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus having the heating device as an image heating device, and an image forming apparatus using the same.
BACKGROUND OF THE INVENTION
Conventionally, there is an image heating device mounted in an image forming apparatus or the like. For descriptive convenience, the prior art will exemplify an image heating device which is mounted in an image forming apparatus such as a copying machine or printer, and heats and fixes a toner image to a printing medium.
Image forming apparatuses widely use heated roller type devices as fixing devices for heating and fixing, as permanently fixed images to the surfaces of printing media, unfixed images (toner images) of target image information formed on and carried by the printing media (transfer sheets, electrofax sheets, electrostatic transfer printing paper, OHP sheets, printing paper, format paper, and the like) by a transfer method or direct method with proper image forming process means such as an electrophotographic process, electrostatic transfer printing process, and magnetic transfer printing process. Recently, belt heating type devices are becoming commercially available in terms of quick start and energy saving. Also, electromagnetic induction heating type devices are proposed. Various fixing devices in image forming apparatuses will be explained.
(a) Heated Roller Type Fixing Device
A heated roller type fixing device is basically constituted by a pair of urging rollers, i.e., a fixing roller (heating roller) and press roller. The pair of rollers are rotated, and a printing medium on which an unfixed toner image to be fixed is formed and carried is introduced, clamped, and conveyed at a fixing nip portion as an urging portion between the pair of rollers. The unfixed toner image is fused and fixed to the surface of the printing medium by heat of the fixing roller and the applied pressure at the fixing nip portion.
In general, the fixing roller uses an aluminum hollow metal roller as a base (core metal), and a halogen lamp as a heat source is inserted in the hollow portion. The fixing roller is heated by heat generated by the halogen lamp, and adjusted in temperature by controlling power to the halogen lamp so as to maintain the outer surface at a predetermined fixing temperature.
Particularly in the fixing device of an image forming apparatus for forming a full-color image which has to have an ability of sufficiently heating and fusing a toner image of four layers at maximum and mixing colors, the fixing roller incorporates a core metal having a large thermal capacity, the core metal is covered with an elastic rubber layer for covering a toner image and uniformly fusing it, and a toner image is heated via the elastic rubber layer. In addition, the pressuring roller also incorporates a heat source, and is heated and adjusted in temperature.
In the heated roller type fixing device, however, even if the power supply of the image forming apparatus is turned on to simultaneously start energizing the halogen lamp serving as the heat source of the fixing device, the thermal capacity of the fixing roller is large, and it requires a long wait time to heat the fixing roller or the like from a cold state to a predetermined fixable temperature, which impairs quick start. The halogen lamp must be energized to maintain the fixing roller in a predetermined temperature-adjusted state so as to execute image formation operating at any time even in the standby state (no image output state) of the image forming apparatus, which increases the power consumption amount.
Especially in a fixing device using a fixing roller having a large thermal capacity, such as the fixing device of the full-color image forming apparatus, a delay occurs between temperature adjustment and temperature rise on the surface of the fixing roller. This causes problems such as a fixing failure, gloss nonuniformity, and offset.
(b) Film Heating Type Fixing Device
Film heating type fixing devices are disclosed in, e.g., Japanese Patent Laid-Open Nos. 63-313182, 2-157878, 4-44075, and 4-204980.
More specifically, a nip portion is formed by clamping a heat-resistant film (fixing film) between a ceramic heater serving as a heating member and a press roller serving as a press member. A printing medium on which an unfixed toner image to be fixed is formed and carried is introduced between the film and the press roller at the nip portion, and clamped and conveyed together with the film. At the nip portion, heat of the ceramic heater is applied to the printing medium via the film, and the unfixed toner image is fused and fixed to the surface of the printing medium by a pressure applied to the nip portion.
The film heating type fixing device can constitute an on-demand type apparatus using a ceramic heater and a low-heat-capacity member serving as a film. Only when the image forming apparatus is to execute image formation, the ceramic heater as a heat source is energized to generate a predetermined fixing temperature. The wait time from power-on of the image forming apparatus to an image formation executable state is short (quick start), and the power consumption in a standby state is very low (power saving). However, this type of fixing device is insufficient in heat quantity as a fixing device for a full-color image forming apparatus or high-speed machine which requires a large heat quantity.
(c) Electromagnetic Induction Heating Type Fixing Device
Japanese Utility Model Laid-Open No. 51-109739 discloses an induction heating/fixing device for inducing a current in a fixing roller by a magnetic flux and generating heat by Joule heat. The fixing roller can directly generate heat by using generation of an induced current, and this fixing device achieves a fixing process with higher efficiency than in a heated roller type fixing device using a halogen lamp as a heat source.
However, since the energy of an alternating flux generated by an exciting coil serving as a magnetic field generation means is used by temperature rise of the whole fixing roller, the heat dissipation loss is large, and the fixing energy density with respect to applied energy is low, resulting in low efficiency.
For this reason, a high-efficiency fixing device is devised by arranging an exciting coil near a fixing roller serving as a heat generation member, or concentrating the alternating flux distribution of the exciting coil in the vicinity of a fixing nip portion in order to obtain energy acting for fixing at high density.
A schematic arrangement of an electromagnetic induction heating type fixing device which concentrates the alternating flux distribution of an exciting coil to a fixing nip portion to attain high efficiency will be described with reference to
FIG. 3
used in embodiments of the present invention (to be described later) for descriptive convenience.
In
FIG. 3
, reference numeral
10
denotes a cylindrical fixing film serving as an electromagnetic induction heat generation rotary member having an electromagnetic induction heat generation layer (conductive layer, magnetic layer, and resistive layer); and
16
a
and
16
b
, film guide (belt guide) members whose cross section has an almost arcuated groove shape. The cylindrical fixing film
10
is loosely fitted on the outer surface of the film guide members
16
a
and
16
b
. An exciting coil
18
and E-shaped magnetic core (core member)
17
, each of which is arranged inside the film guide members
16
a
and
16
b
, comprise a magnetic field generation means; and
30
, an elastic press roller which forms a fixing nip portion N having a predetermined width with a predetermined applied pressure together with the lower surface of the film guide members
16
a
and
16
b
via the fixing film
10
, and is urged against the fi
Hayasaki Minoru
Mano Hiroshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Patel Rajnikant B.
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