Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-02-05
2003-01-07
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C399S330000, C430S124300
Reexamination Certificate
active
06505027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image forming apparatus such as copying machine, facsimile, printer, etc. and, in particular, to apparatus in which a color image, images of different colors are superimposed, is formed and borne on a recording material and the recording material is heated and pressurized by an image fixing means so as to fix the color image thereon.
2. Related Background Art
As fixing apparatus (fixing devices) used in image forming apparatus for fixing an unfixed toner image, which is indirectly (by means of transferring) or directly formed and borne on a recording material (paper) by a proper image forming process means such as electrophotographic process, on the surface of the recording material as a permanent fixed image by the application of heat, those adopting the heat roller fixing method have been widely in use.
In recent years, there have been put to practical use apparatus adopting the heater type film heating fixing method from the standpoint of quick start and saving energy. Further, there have been proposed apparatus adopting the electromagnetic induction film heating fixing method which causes a film of metal itself heat generation.
a) Fixing Apparatus adopting the Heater Type Film Heating Fixing Method
There are disclosed fixing apparatus adopting the film heating fixing method in, for example, Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open No. 4-44075, and Japanese Patent Application Laid-Open No. 4-204980.
Specifically, these fixing apparatus are such that they have a pressure contacting nip portion (hereinafter referred to as fixing nip portion) formed therein by sandwiching a heat-resistant film (hereinafter referred to as fixing film) between a ceramic heater as a heating body and a pressurizing roller as a pressurizing member, introduce a recording material having an unfixed toner image formed and borne thereon between the fixing film and the pressurizing roller at the above fixing nip portion, convey the recording material together with the fixing film while allowing the same to be nipped between the ceramic heater and the pressurizing roller so as to apply pressuring force of the fixing nip portion to the recording material while providing the same with heat of the ceramic heater via the fixing film, thereby fix the unfixed toner image on the surface of the recording material.
The fixing apparatus adopting the film heating fixing method offer the advantages that they can constitute an on-demand type fixing apparatus using a member with a low heat capacity for the ceramic heater and the film, they should apply current to the ceramic heater as a heat source only when executing image formation to cause the ceramic heater heat generation at a predetermined temperature, their latency from the instance of turning on them until they are in state where they can execute image formation is short (a quick start characteristic), and that they have a substantially low power consumption when standing by (power saving).
b) Fixing Apparatus adopting the Electromagnetic Induction Film Heating Fixing Method
There is disclosed in Japanese Utility Model Application Laid-Open No. 51-109739 a fixing apparatus adopting the electromagnetic induction film heating fixing method which induces an eddy current in a metal layer (heat generating layer) of the fixing film with magnetic flux and causes the metal layer Joule heat generation. This fixing apparatus enables the direct heat generation of the fixing film utilizing the generation of an induced current and has accomplished a highly efficient fixing process compared with the fixing apparatus adopting the heat roller fixing method which utilizes a halogen lump as a heat source.
Depending on the arrangement of coils and a core, however, since the energy of the alternating magnetic flux generated by excitation coils as magnetic field generating means is used for heating the entire fixing film, the radiation loss is big. As a result, there have been cases where the rate of the making energy applied to the fixing process is low, and hence, an inefficient fixing process.
Thus, there has been provided a highly efficient fixing apparatus in which excitation coils are arranged closer to a fixing film, as a heat generating element, and the alternating magnetic flux distribution of the excitation coils is concentrated on the vicinity of the fixing nip portion, so as to obtain the energy to be applied to the fixing more efficiently.
FIG. 16
is a schematic view of the construction of one example of fixing apparatus adopting the electromagnetic induction film heating fixing method which has increased the fixing efficiency by concentrating the alternating magnetic flux distribution of the excitation coils on the fixing nip portion.
In the same figure, reference numeral 10 denotes a cylindrical fixing film, as a rotary body, including electromagnetic induction heat generating layers (conductive material layer, magnetic material layer, resistor layer).
Reference numeral
16
denotes a gutter-shaped film guide member of which cross section is almost semicircular, and the cylindrical fixing film
10
is loose-fit on the outside of this film guide member
16
.
Reference numeral
15
denotes a magnetic field generating means placed on the inside of the film guide member
16
, which consists of excitation coils
18
and an E-shaped magnetic core (core material)
17
.
Reference numeral
30
denotes an elastic pressurizing roller, which forms a fixing nip portion N having a predetermined width in combination with the bottom of the film guide member
16
with a predetermined pressure contacting force while nipping the fixing film
10
at the fixing nip portion and allowing the same to mutually come in pressure contact with the elastic pressurizing roller and the bottom of the film guide member.
The magnetic core
17
of the above magnetic filed generating means
15
is placed in such a manner as to correspond to the fixing nip portion N.
The pressurizing roller
30
is rotatively driven by a driving means M in the counterclockwise direction shown by an arrow. When rotatively driving the pressurizing roller
30
, torque acts on the fixing film
10
by the friction force generated between the above pressurizing roller
30
and the external surface of the fixing film
10
; consequently, the above fixing film
10
is rotated around the periphery of the film guide member
16
at a peripheral speed almost corresponding to that of the pressurizing roller
30
in the clockwise direction shown by an arrow with its internal surface closely touching and sliding on the bottom of the film guide member
16
at the fixing nip portion N (pressuring roller drive fixing method).
The film guide member
16
serves to pressurize the fixing nip portion N, support the excitation coils
18
and the magnetic core
17
, as a magnetic field generating means
15
, support the fixing film
10
, and stabilize the conveyance of the above film
10
during the rotation thereof. This film guide member
16
is an insulating member which does not interfere with magnetic flux's passing and a material is used for it which can resist heavy loads.
The excitation coils
18
generate alternating magnetic flux with alternating current supplied from an excitation circuit not shown in the figure. The alternating magnetic flux distributes intensively at the fixing nip portion N due to the E-shaped magnetic core
17
placed in such a manner as to correspond to the position of the fixing nip portion N and generates an eddy current in the electromagnetic induction heat generating layers of the fixing film
10
at the fixing nip portion N. This eddy current generates Joule heat due to the resistivity of the electromagnetic induction heat generating layers. The electromagnetic induction heat generation of the fixing film
10
occurs intensively at the fixing nip portion N where alternating magnetic flux is allowed to distribute int
Suzuki Masahiro
Takeuchi Akihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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