Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2000-02-24
2001-02-06
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S069000, C399S329000, C399S334000, C399S328000, C219S216000
Reexamination Certificate
active
06185383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and the like, and more particularly it relates to an image heating apparatus for heating an image on a recording material.
2. Related Background Art
In the past, in many image forming apparatuses of electrophotographic type such as electrophotographic copying machines, electrophotographic printers and the like, as fixing means, a fixing device of contact heating type having a heat roller and having good thermal efficiency and good safety or a fixing device of film heating type having reduced energy consumption has been used.
The fixing device of heat roller fixing type mainly comprises a fixing roller (heat roller) as a heating rotary member, and an elastic pressure roller as a pressure rotary member urged against the fixing roller and is designed so that, while a recording material (transfer sheet, electrostatic recording paper, electrofax paper, printing paper or the like) on which a non-fixed image (toner image) was formed and born is being passed through a fixing nip (abut nip portion) between the rotating rollers, the non-fixed image is permanently fixed to the recording material by heat from the fixing roller and pressure in the fixing nip.
Further, the fixing device of film heating type is disclosed in Japanese Patent Application Laid-open Nos. 63-313182, 2-157878, 4-44075, 4-44076, 4-44077, 4-44078, 4-44079, 4-44080, 4-44081, 4-44082, 4-44083, 4-204980, 4-204981, 4-204982, 4-204983 and 4-204984, for example, and comprises a heating body (heater) and a heat-resistive fixing film (heating rotary member) slidingly contacted with the heating body by a pressurizing rotary member (elastic roller) and is designed so that, while a recording material on which a non-fixed image was born is being passed together with the fixing film through a fixing nip portion between the heating body and the pressurizing rotary member with the interposition of the fixing film, the non-fixed image is permanently fixed to the recording material by heat from the heating body via the fixing film and pressure in the fixing nip portion.
In the fixing device of film heating type, since a wire-shaped heating body having low heat capacity can be used as the heating body and a thin film having low heat capacity can be used as the fixing film, electric power can be saves, and weight and time reduction (on-demand, quick start) can be achieved.
As the wire-shaped heating body having low heat capacity, a so-called ceramic heater can generally be used. The ceramic heater mainly comprises a ceramic substrate made of alumina, aluminum nitride or the like, and a heating body provided on the substrate and capable of generating heat by energization.
Thus, the fixing device of film heating type has various advantages such as unnecessity of waiting pre-heating and elimination of a waiting time due to high heating efficiency and fast rising-up. Particularly, since a method in which a cylindrical film is driven by a conveying force of a pressurizing roller can be realized with low cost, such a method has been adopted to low speed compact image forming apparatuses and is expected to be introduced into large-sized high speed image forming apparatuses in the future.
In the fixing device of film heating type, it is required that a length of a heating element of the heating body be equal to or greater than a maximum of a sheet size, and temperature control of the heating body is effected by detecting a temperature of the heating body by means of a thermistor (temperature detecting element) disposed in the vicinity of a longitudinal center of the heating body. Thus, when a sheet having maximum size is passed, the heat generated from the heating body is absorbed by the sheet, with the result that the temperature of the entire heating body is decreased.
On the other hand, when a sheet having a size smaller than the maximum size is passed in a center standard, since the temperature of only a central portion of the heating body on which the sheet is passed is decreased, the temperature of non-sheet passing portions of the heating body is increased in comparison with the central portion (non-sheet passing portion temperature increase phenomenon), with the result that portions of the film and the pressurizing roller corresponding to both lateral edge portions of the heating body may be damaged. Further, after the small sized sheet was passed, if a larger sized sheet is passed, offset (adhesion of toner to the film) will occur by the influence of the temperature-increased edge portions.
Conventionally, in order to solve this problem, a method in which through-put is reduced (i.e., print frequency is reduced) to widen sheet passing interval has been utilized.
However, the non-sheet passing portion temperature increase phenomenon has become more severe due to high speed tendency of the on-demand fixing device of film heating type, and, thus, it is very difficult to solve the above problem only by reduction of through-put.
In order to solve such a problem, it is considered that heating elements having different lengths and widths are provided on a substrate of the heating body so that the heating elements are selectively energized in accordance with a sheet size of a recording material to be passed (zone heating).
FIGS. 10A and 10B
shows an example of the zone heating which is background of the present invention. In
FIG. 10A
, there are provided a ceramic heater
100
as a heating body, a heater holder
2
, a heat-resistive fixing film
3
and an elastic pressurizing roller
4
.
The heater
100
is held by the heater holder
2
with a heating surface facing downwardly, and the elastic pressurizing roller
4
is urged against the downwardly facing heating surface of the heater
100
with the interposition of the fixing film
3
, thereby forming a fixing nip portion N.
The heater
100
is heated and temperature-adjusted to a predetermined temperature by energization of heating elements. The fixing film
3
is slid on the downwardly facing heating surface of the heater
100
in the fixing nip portion N and is shifted in a direction shown by the arrow.
In a condition that the heater
100
is heated and temperature-adjusted to the predetermined temperature and the fixing film
3
is shifted in the direction shown by the arrow, when a recording material P on which a non-fixed toner image t was formed and born is introduced between the fixing film
3
and the elastic pressurizing roller
4
at the fixing nip portion N, the recording material P is conveyed together with the fixing film
3
through the fixing nip portion N while being closely contacted with the surface of the fixing film
3
. In the fixing nip portion N, the recording material P and the toner image t are heated by the heater
100
via the fixing film
3
, with the result that the toner image t on the recording material P is thermally fixed to the recording material P. A portion of the recording material passed through the fixing nip portion N is separated from the surface of the fixing film and is conveyed.
FIG. 10B
is a partially sectioned schematic plan view of the ceramic heater
100
as the heating body (showing a back side of the heater). The heater
100
comprises a heater substrate
100
a
having a longitudinal direction perpendicular to a sheet passing direction, two parallel heat generating member for large sized sheet (large sized sheet heating element) h
1
and heat generating member for small sized sheet (small sized sheet heating element) h
2
formed on the back surface of the heater substrate
100
a
along the longitudinal direction thereof, electricity supplying electrode pattern portions a, b, c for the heating elements h
1
, h
2
, and a glass coating layer
100
b
over-coated on the heating element forming surface of the heater substrate.
The heater substrate
100
a
is a ceramic substrate having insulation capacity, good heat transferring ability and low heat capacity and is made of aluminum nitride in thi
Kanari Kenji
Miyamoto Toshio
Suzumi Masahiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grimley Arthur T.
Ngo Hoang
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