Electric heating – Inductive heating – With power supply system
Reexamination Certificate
2000-07-26
2002-03-19
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With power supply system
C219S667000, C219S668000, C219S619000, C399S328000, C399S330000
Reexamination Certificate
active
06359269
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating device, an image forming apparatus, and an electric-power control method. More particularly, the invention relates to a heating device which is suitably applied to an electrophotographic apparatus, an electrostatic recording apparatus or the like which includes a heating device of a belt heating type as an image heating device, to an image forming apparatus, and to an electric-power control method.
2. Description of the Related Art
Conventionally, an image heating device (fixing device) is mounted in an image forming apparatus. A description will now be provided of a conventional image heating device (fixing device) which is mounted in an image forming apparatus, such as a copier, a printer or the like, and heats and fixes a toner image formed on a recording material.
In an image forming apparatus, such as a copier, a printer or the like, a heat-roller-type device has been widely used as a fixing device for heating and fixing an unfixed image (toner image) representing object image information formed and carried on a recording material (a transfer sheet, an Electrofax sheet, electrostatic recording paper, an OHP (overhead projector) sheet, printing paper, format paper or the like) according to image transfer or directly using means for an appropriate image forming process, such as an electrophotographic recording process, an electrostatic recording process, a magnetic recording process or the like, as a permanent fixed image on the surface of the recording material. Recently, heat-roller-type devices have been practically used from the viewpoint of quick starting and energy saving. Electromagnetic-induction-heating-type devices have also been proposed. Various types of fixing devices used in respective image forming apparatuses will now be described.
(a) Heat-roller-type Fixing Device
A heat-roller-type fixing device is basically configured by a pair of pressure-contact rollers, i.e., a fixing roller (heating roller) and a pressing roller. The pair of rollers are rotated, a recording material having an unfixed toner image to be fixed formed and carried thereon is guided into a fixing nip portion where the rollers are in pressure contact with each other and is grasped and conveyed at the fixing nip portion, and the unfixed toner image is fixed on the surface of the recording material by the heat of the fixing roller and the pressure at the fixing nip portion.
In general, the fixing roller includes a hollow metal roller made of aluminum as a base material (core), and a tungsten halogen lamp incorporated therein as a heat source. The fixing roller is heated by the heat of the tungsten halogen lamp, and the outer circumferential surface of the fixing roller is maintained at a predetermined fixing temperature by controlling current supply to the tungsten halogen lamp.
Particularly, a fixing device of an image forming apparatus for forming a full-color image, for which a capability of mixing toner images of four layers at maximum by sufficiently heating and fusing the images is required, includes a core having a high heat capacity, and a rubber elastic layer for uniformly fusing the toner images, provided at the outer circumferential surface of the core. The toner images are heated via the rubber elastic layer. In some fixing devices, a heat source is also provided within the pressing roller, and the pressing roller is heated and the temperature of the pressing roller is controlled.
However, in the heat-roller-type fixing device, even if the power supply of the image forming apparatus is turned on and power supply to the tungsten halogen lamp, serving as the heat source of the fixing device, is simultaneously started, a considerable time (a waiting time) is required until the temperature of the fixing roller reaches a predetermined fixable temperature from a completely cooled state, because the heat capacity of the fixing roller is large, resulting in an inferior quick starting property. In order to execute an image forming operation at any time even in a standby state (a non-image-output state) of the image forming apparatus, it is necessary to maintain the fixing roller at a predetermined temperature-control state by supplying power to the tungsten halogen lamp, resulting in large power consumption.
Particularly, when using a fixing roller having a large heat capacity, such as the fixing device of the above-described full-color image forming apparatus, since there is a delay until the temperature of the surface of the fixing roller reaches the temperature set by temperature control, problems such as insufficient fixing, unevenness in the gloss of the fixed image, offset and the like, arise.
(b) Film-heating-type Fixing Device
Film-heating-type fixing devices have been proposed, for example, in Japanese Patent Application Laid-Open (Kokai) Nos. 63-313182 (1988), 2-157878 (1990), 4-44075 (1992), and 4-204980 (1992).
That is, a nip portion is formed by inserting a heat-resisting film (fixing film) between a ceramic heater, serving as a heating member, and a pressing roller, serving as a pressing member. By introducing a recording material having an unfixed toner image to be fixed formed and carried thereon between the film and the pressing roller at the nip portion and grasping and conveying the recording material together with the film, the heat of the ceramic heater is given to the recording material via the film at the nip portion, and the unfixed toner image is fixed on the surface of the recording material by heat and pressure by the pressing force at the nip portion.
The film-heating-type fixing device has the advantages that, for example, an on-demand-type device can be provided by using low-heat-capacity members as the ceramic heater and the film, a state in which the device is heated to a predetermined fixing temperature may be provided by supplying power to the ceramic heater, serving as the heat source, only during image formation by the image forming apparatus, a waiting time from the turning-on of the power supply of the image forming apparatus to a state in which image formation can be executed is short (a quick starting property), and power consumption in a standby state is very small (power saving). However, the device of this type has a problem from the view point of the quantity of heat as a fixing device for a full-color image forming apparatus or a high-speed image forming apparatus requiring a large quantity of heat.
(c) Electromagnetic-induction-heating-type fixing device
Japanese Utility Model Application Laid-Open (Kokai) No. 51-109739 (1976) has disclosed an induction heating fixing device for heating a fixing roller by Joule heat generated by inducing current by a magnetic flux. This device can directly heat the fixing roller by utilizing the generation of an induction current, so that a fixing process having higher efficiency than the heat-roller-type fixing device using a tungsten halogen lamp as a heat source is achieved.
However, since the energy of an AC magnetic flux generated by an exciting coil, serving as magnetic-field generation means, is used for raising the temperature of the entire fixing roller, radiation loss is large. As a result, the ratio of the fixing energy to the input energy is low, thereby causing low efficiency.
Accordingly, high-efficiency fixing devices have been devised, for example, by reducing the distance between the exciting coil and the fixing roller, serving as a heating member, or concentrating the distribution of AC magnetic fluxes of the exciting coil in the vicinity of the fixing nip portion, in order to obtain high-density energy used for fixing.
A description will now be provided of the schematic configuration of an electromagnetic-induction-heating-type fixing device whose efficiency is improved by concentrating the distribution of AC magnetic fluxes of the exciting coil in the vicinity of the fixing nip, with reference to
FIG. 2
which will be used in a first embodiment of the present invention. In
FIG. 2
, a cylindric
Hayasaki Minoru
Mano Hiroshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leung Philip H.
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