Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
1997-03-10
2001-04-24
Heinrich, Samuel M. (Department: 1725)
Electric heating
Heating devices
Combined with diverse-type art device
C219S494000, C219S543000
Reexamination Certificate
active
06222158
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
In recent years, fixing apparatuses comprising a heater in which a heat generating resistor is formed on a thermally conductive ceramic substrate have been proposed, for example, in U.S. Pat. No. 5,148,226; and U.S. Ser. No. 712,532, or the like.
Such a heater has a small thermal capacity; therefore, it can quickly change the apparatus temperature. Also, there is no rush current. Having these characteristics gives an advantage as a heat source for the fixing device in an image recording apparatus, for example, and makes such a heater superior to a halogen heater which constitutes the mainstream of the heat generating source for the thermal fixing devices.
FIG. 1
shows an example of such a heater.
FIG.
1
(
a
) is a partially cutaway plan view of the front surface of the above-mentioned heater
3
, and
FIG.
1
(
b
) is a plan view of the rear surface thereof. A heat generating thick film resistor
5
generates heat as a voltage is applied between power supply electrodes
8
and
9
connected to the opposite ends of the heat generating resistor
5
.
As for the temperature control of the heater
3
, the power supplied to the heat generating thick film resistor
5
is controlled to keep constant the temperature of the heater
3
detected by a thermistor
6
.
FIG. 2
shows a thermal fixing apparatus of the through-film heating type in which the heat generating thick film resistor
5
formed on a ceramic substrate
4
is used as the heat source. This type of thermal fixing apparatus
1
has advantages such that it quickly starts up because of the fast temperature rise of the heater
3
; it can save electricity; and the like. In other words, it is very effective.
However, the small thermal capacity of the heater
3
makes it difficult to control. Generally speaking, the thermal fixing device in an image recording apparatus is controlled to keep a constant temperature; therefore, it is not preferable for the temperature to change suddenly during the image fixing operation.
Thus, when the heat generating thick film resistor
5
is used as the heat source for the thermal fixing apparatus, such a heat generating thick film resistor
5
that has a slightly higher power rating than the actually needed power rating is employed and the power applied to the heat generating thick film resistor
5
is controlled in phase or in wave number to keep constant the temperature.
Therefore, when a temperature sensor
6
of the heater
3
, or the circuit for controlling the driving means of the heat generating thick film resistor
5
malfunctions and the power is continuously supplied to the heat generating thick film resistor
5
, the temperature of the heat generating thick film resistor
5
rapidly increases.
When such an anomaly is left unattended, the thermal fixing device is liable to start smoking or flaming, eventually. Thus, in anticipation of such a situation, the thermal fixing apparatus is provided with a thermal protector
13
(FIG.
4
(
b
)) such as a thermal fuse.
Further, in order not to induce the above-mentioned abnormal condition, a current transformer, photocoupler, or the like may be provided to prepare for the malfunctioning of a triac or the like which controls the power supplied to the heat generating thick film resistor
5
, wherein when it is detected that a current is flowing through the heat generating thick film resistor
5
while no driving signal is sent out from the temperature control circuit, a control system comprising a relay or the like, being independent from the triac, is used to interrupt the power supply.
However, the thermal protector
13
such as the thermal fuse has generally a larger thermal capacity than the heat generating resistor
5
or ceramic substrate
4
which makes up the heater, and responds slower. Therefore, before the thermal protector
13
responds, the heater
3
(ceramic substrate on which the heat generating thick film resistor is formed) breaks because of thermal stress. When such a condition occurs, electrical discharge begins between adjacent broken pieces of the heat generating thick film resistor
5
, corresponding to the fracture lines of the heater. Since the ambient temperature is high, the combustibles in the surrounding areas are easily ignited, causing smoking or flaming.
SUMMARY OF THE INVENTION
Accordingly, a primary object of the present invention is to provide a fixing heater in which the heat generation of the resistor can be reliably stopped when the ceramic substrate fractures.
Another object of the present invention is to provide a fixing heater in which smoking or flaming can be prevented even when the ceramic substrate fractures.
According to an aspect of the present invention, the fixing heater comprises: a ceramic substrate; a heat generating resistive member which is formed on the ceramic substrate in such a manner as to extend in the longitudinal axis of the ceramic substrate; a temperature detecting member for detecting the temperature of the ceramic substrate; and an electrically conductive member formed on the ceramic substrate in such a manner as to extend in the longitudinal axis of the ceramic substrate.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3892947 (1975-07-01), Strengholt
patent: 3916256 (1975-10-01), Kotani
patent: 5083168 (1992-01-01), Kusaka et al.
patent: 5148226 (1992-09-01), Setoriyama et al.
patent: 5376773 (1994-12-01), Masuda et al.
patent: 3028534 (1982-02-01), None
patent: 56-24180 (1981-03-01), None
patent: 58-5772 (1983-01-01), None
patent: 2-143277 (1990-06-01), None
Nakata Yasuhiro
Nashida Yasumasa
Yoshimoto Toshio
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Heinrich Samuel M.
LandOfFree
Fixing heater comprising electrically conductive member... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fixing heater comprising electrically conductive member..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fixing heater comprising electrically conductive member... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2523943