Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-03-06
2004-05-04
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000
Reexamination Certificate
active
06731901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image heating apparatus of an image forming apparatus, which uses an electrophotographic process, such as a copying machine, a laser printer, a facsimile and the like.
2. Related Background Art
Recently, a fixing apparatus has adopted a film heating process. The film heating process, as it is disclosed in Japanese Patent Application Laid-Open No. 63-313182, first produces a heater by forming a pattern of a heating body on a ceramic substrate, and then heats a body to be heated by making the heater generate heat through a cylindrically formed thin film placed between the heater and the body to be heated.
If an endless belt-like film is used in such a film heating process, a large approaching force is produced on the film. As a measure to the approaching force, a method disclosed in Japanese Patent Application Laid-Open Nos. 4-44075 and 4-44077 has been put to practical use. In the method, the film is wound loosely and driven for the reduction of the approaching force of the film and for the decrease of the driving torque therefor.
FIG. 7
shows the configuration of the pressurizing portion of An image heating apparatus being related art of the present invention. In
FIG. 7
, a reference numeral
101
designates a heat-proof film; a reference numeral
103
designates a heater holding member; and a reference numeral
104
designates a metal stay. A reference numeral
127
designates a compression spring, and a reference numeral
105
designates a pressurizing force transmitting member, which is made of a resin member and is provided with a pressurizing portion
105
a
. The lower end portion of the compression spring
127
touches the top surface of the pressurizing portion
105
a
. A reference numeral
106
designates a pressure roller, and a reference numeral
128
designates a spring pressing member, which the upper end portion of the compression spring
127
touches. A reference numeral
131
designates a pressure roller supporting member having a notch portion. The upper portion of the notch portion is formed to be an opening. A pressure roller bearing
132
for supporting the pressure roller
106
by the shaft thereof is fitted to the lower portion of the notch portion.
As shown in
FIG. 7
, the heat fixing apparatus is configured to make it possible to press a heater
102
(see
FIG. 8
) against the pressure roller
106
by pressurizing the pressuring portion
105
a
of the pressuring force transmitting member
105
to the pressure roller
106
with the compression spring
127
, with the metal stay
104
and the heater holding member
103
being put between the pressuring portion
105
a
and the heater
102
.
The spring pressing member
128
has the function of pressing the upper end of the compression spring
127
. However, if the spring pressing member
128
only satisfied the function, the spring pressing member
128
might integrally be formed with the pressure roller supporting member
131
.
However, if the pressure roller supporting member
131
and the spring pressing member
128
were integrally formed, the pressurizing force transmitting member
105
could not inserted into the pressure roller supporting member
131
from the direction of an arrow A shown in
FIG. 7
when the pressurizing force transmitting member
105
would be incorporated into the pressure roller supporting member
131
. Besides, when the compression spring
127
would be assembled, the compression spring
127
should be inserted from aside into the space formed by the integrally configured pressure roller supporting member
131
and the spring pressing member
128
while the compression spring
127
should be being compressed. Accordingly, for avoiding such problems concerning the operability of assembling, the pressure roller supporting member
131
and the spring pressing member
128
are formed as separate parts such that the compressing spring
127
and the spring pressing member
128
can be assembled from the direction of the arrow A shown in
FIG. 7
after the pressurizing force transmitting member
105
has been incorporated into the pressure roller supporting member
131
.
Moreover, it is general that a projection (a paring or a drawing having a height of a degree of the thickness of a sheet metal) is formed on each of the spring pressing member
128
and the pressurizing force transmitting member
105
for locating the compression spring
127
.
However, the heat fixing apparatus shown in
FIG. 7
has the following problems.
A first problem is the inferior efficiency of the assembling of the spring pressing member
128
. The pressurizing force of the compression spring
127
is generally 10 kg or more. And it seems to be inevitable to improve the thermal efficiency of the heat fixing apparatus in consideration of the recent demand of the market of increasing the printing speed of a laser printer and of improving the fixing property thereof. Consequently, the pressurizing force has the tendency of being increasing furthermore afterwards.
Moreover, the spring pressing member
128
is generally incorporated into the pressure roller supporting member
131
as follows. That is, one method is, as shown in
FIG. 8A
, to fit one end side of the spring pressing member
128
to the pressure roller supporting member
131
, and then to rotate the other end side of the spring pressing member
128
against the spring force of the compression spring
127
around the fitted end side thereof while incorporating the spring pressing member
128
to the pressure roller supporting member
131
. Another method is, as shown in
FIG. 8B
, to slide the spring pressing member
128
against the spring force of the compression spring
127
while incorporating the spring pressing member
128
in the pressure roller supporting member
131
. The largeness of the spring load exceeding 5 kg on one side is a factor making the operability at the assembling of the spring pressing member
128
worse.
A second problem of the heat fixing apparatus shown in
FIG. 7
concerns the spring constant of the compression spring
127
. That is, the spring constant cannot be made to be large owing to the assembling method thereof described above.
It is needless to say that the spring constant of the compression spring
127
is desirable to be as small as possible for attaining the stable pressurizing force of the compression spring
127
to make the fixing property of the heat fixing apparatus stable from consideration of the hardness of the pressure roller
106
, the load of the compression spring
127
, and the dispersion of the accuracy of the dimensions of each part at the mass production thereof.
However, if the spring constant is made too small, the free length of the spring before the assembling thereof becomes long as a result. Thereby, the compression spring
127
is buckled in the assembling process thereof. Consequently, the problem concerning the inferiority of the assembling efficiency is further promoted.
Moreover, the loss of the spring force of the compression spring
127
owing to the buckling thereof frequently becomes a problem when the free length thereof becomes long as a result of the reduction of the spring constant.
FIG. 9A
shows the situation. Generally, it is said that the loss of the spring force is easily produced when the rate of the free length of a compression spring to the winding diameter thereof exceeds four. Consequently, the free length is normally set within the range of the condition of the rate, and the minimum spring constant is generally determined on the basis of the set free length.
A method for decreasing the loss of the spring force owing to the buckling, as shown in
FIG. 9B
, provides a guide bar
128
a
in the inner diameter portion of the compression spring
127
to prevent the buckling thereof. However, in the case where the compression spring
127
and the spring pressing member
128
are rotated or slid while being incorporated in the pressure roller supporting member
131
as shown in FIG.
Nakamura Naoki
Nishitani Hitoshi
Beatty Robert
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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