Electrophotography – Image formation – Fixing
Reexamination Certificate
2003-01-28
2004-03-09
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C219S619000, C399S330000
Reexamination Certificate
active
06704537
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image heating apparatus such as a thermal fixing device mounted in an image forming apparatus such as a copying machine, a printer, or the like. In particular, it relates to an image heating apparatus utilizing an induction heating principle.
An image heating apparatus such as a thermal fixing device makes up a large proportion of energy consumption in an entire image forming apparatus, so that the image heating apparatus is desired to reduce its power consumption. Further, there is also a large demand for a reduction in waiting time for printing.
As an image heating apparatus meeting such demands, an induction heating type image heating apparatus has attracted attention (e.g., Japanese Laid-Open Utility Model Application No. Sho-51-109739).
FIG. 16
shows the general structure of an example of an electromagnetic induction heating type fixing apparatus.
In the drawing, a reference numeral
10
designates a fixing film (which hereinafter will be referred to as a sleeve) comprising an electromagnetic induction type heat generating layer (electrically conductive layer, magnetic layer, electrically resistive layer). The fixing film
10
is cylindrical and flexible, and is used as a rotational heating member.
A reference numeral
16
c
designates a film guiding member (which hereinafter will be referred to as sleeve guiding member) in the form of a trough, which is approximately semicircular in cross section. The sleeve
10
is loosely fitted around the sleeve guiding member
16
c.
A reference numeral
15
designates a magnetic field (flux) generating means disposed within the sleeve guiding member
16
c.
The magnetic field generating means comprises an exciting coil
18
, and a magnetic core
17
having an T-shaped cross section.
Designated by a reference numeral
30
is an elastic pressure roller, which is kept pressed upon the bottom surface of the sleeve guiding member
16
c,
with the interposition of the sleeve
10
, with the application of a predetermined pressure, forming a fixing nip N having a predetermined width.
The magnetic core
17
of the magnetic field generating means
15
is disposed so that its position corresponds to the position of the fixing nip N.
The pressure roller
30
is rotationally driven by a driving means M, in the counterclockwise direction indicated by an arrow in the drawing. As the pressure roller
30
is rotationally driven, friction occurs between the peripheral surface of the pressure roller and the outwardly facing surface of the sleeve
10
, in the fixing nip N. As a result, the sleeve
10
is rotated by the pressure roller
30
, around the sleeve guiding member
16
c,
in the clockwise direction indicated by an arrow in the drawing, at a peripheral velocity substantially equal to the peripheral velocity of the pressure roller
30
, with the inwardly facing surface of the sleeve
10
sliding on the bottom surface of the sleeve guiding member
16
c,
in the fixing nip N (pressure roller-driving method).
The sleeve guiding member
16
c
plays the role of maintaining the fixing pressure in the fixing nip N, the role of supporting the magnetic field generating means
15
comprising the combination of the exciting coil and magnetic core
17
, the role of supporting the sleeve
10
, and the role of keeping the sleeve
10
stable while the sleeve
10
is rotationally driven. The sleeve guiding member
16
c
is formed of such a material that does not prevent the passage of a magnetic flux through the sleeve guiding member
16
c
and that can withstand a large amount of load.
The exciting coil
18
generates an alternating magnetic flux as alternating current is supplied to the exciting coil
18
from an unshown exciting circuit. The alternating magnetic flux generated by the exciting coil
18
is concentrated to the fixing nip N, by the magnetic coil
17
with the T-shaped cross section disposed so that its position corresponds to that of the fixing nip N. The magnetic flux concentrated to the fixing nip N generates eddy current in the electromagnetic induction type heat generating layer of the sleeve
10
. This eddy current and the specific resistance of the electromagnetic induction type heat generating layer generates heat (Joule heat) in the electromagnetic induction type heat generating layer. With the presence of the magnetic core
17
with the T-shaped cross section which concentrates the alternating magnetic field to the fixing nip N, the electromagnetic induction heat generation is concentrated to the portion of the sleeve
10
within the fixing nip N. Therefore, the fixing nip N is highly efficiently heated.
The temperature of the fixing nip N is kept at a predetermined level by a temperature control system, inclusive of an unshown temperature detecting means, which controls the current supply to the exciting coil
18
.
Thus, as the pressure roller
30
is rotationally driven, the sleeve
10
is rotated around the sleeve guiding member
16
, while current is supplied to the exciting coil
18
from the exciting circuit. As a result, heat is generated in the sleeve
10
through electromagnetic induction, increasing the temperature of the fixing nip N to a predetermined level, at which it is kept. In this state, a recording medium P, on which an unfixed toner image t has been formed, is conveyed to the fixing nip N, or the interface between the sleeve
10
and pressure roller
30
, with the image bearing surface of the recording medium P facing upward, in other words, facing the surface of the fixing sleeve. In the fixing nip N, the recording medium P is conveyed with the sleeve
10
, being sandwiched between the sleeve
10
and pressure roller
30
, the image bearing surface of the recording medium P remaining flatly in contact with the outwardly facing surface of the sleeve
10
. While the recording medium P is conveyed through the fixing nip N, the recording medium P and the unfixed toner image t thereon are heated by the heat generated in the sleeve
10
by electromagnetic induction. As a result, the unfixed toner image t is permanently fixed to the recording medium P. After being passed through the fixing nip N, the recording medium P is separated from the peripheral surface of the rotating sleeve
10
, and then, is conveyed further to be discharged from the image forming apparatus.
Incidentally, as described above, the exciting oil
18
is required to approach the fixing sleeve
10
. More specifically, as shown in
FIG. 17
, the exciting coil is, e.g., wound substantially in a planar shape and then transformed into a boat shape by bending it in a direction of arrows in the drawing (e.g., Japanese Laid-Open Patent Application (JP-A) No. 2000-243545).
A dimensional relationship in a longitudinal direction among the thus-prepared coil
18
, the magnetic core
17
, the sleeve
10
, and the recording medium P is shown in FIG.
18
.
Referring to
FIG. 18
, the magnetic core
17
is designed to have a length in its longitudinal direction substantially identical to that of the recording medium P. Further, the coil
18
has a longitudinal length longer than that of the magnetic core
17
, and the sleeve
10
has a longitudinal length longer than that of the coil
18
.
However, as shown in
FIG. 16
, the sleeve guiding member
16
c
functioning as a sliding surface (layer) with respect to the sleeve
10
in the nip N is present between the sleeve
10
and the magnetic core
18
, thus resulting in a gap d≠0. For this reason, at both end portions of the coil
18
in the longitudinal direction, a magnetic flux does not enter perpendicular to the sleeve
10
. As a result, a region of action of the magnetic fluxes is narrowed to cause a temperature-lowering region at both end portions of the sleeve in comparison with a central portion thereof. As a result, as described above, when the longitudinal lengths of the recording medium P and the magnetic core
17
are set to be substantially identical to each other (FIG.
18
), the recording medium P has caused fixation failure a
Shida Tomonori
Suzuki Masahiro
Takeuchi Akihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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