Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2000-09-11
2001-12-25
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C219S469000, C399S069000, C399S330000, C399S334000, C355S117000
Reexamination Certificate
active
06333490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of fixing a toner image to a recording medium by fusing and pressing the toner image to the recording medium in an image forming system such as a copying machine, a printer, a facsimile machine, etc.
2. Description of the Related Art
FIG. 14
of the accompanying drawings shows a conventional recent toner image fixing apparatus for use in electrophotographic machines. As shown in
FIG. 14
, the toner image fixing apparatus has a belt fixing system comprising a fixing roller R
1
, a heating and tensioning roller R
3
, an endless fixing belt B trained around the rollers R
1
, R
3
, and a pressing roller R
2
disposed below and pressed against the fixing roller R
1
with the fixing belt B interposed therebetween. When a recording medium D in the form of a sheet with an unfixed toner image carried thereon is fed into the toner image fixing apparatus by a sheet feeder, the recording medium D is reheated by the heating and tensioning roller R
3
, and then the toner image is fixed to the recording medium D by the fixing belt B in a nipping region between the rollers R
1
, R
2
. Since the recording medium D is preheated, the nipping region may be set to a relatively low temperature. The fixing belt B is of such a small heat capacity that when the recording medium D passes through the nipping region, the temperature of the fixing belt B is quickly lowered to increase the coherent ability of the toner which is separated from the fixing belt B at the outlet of the nipping region, for thereby allowing the toner to be easily separated from the fixing belt B. Even if the fixing belt B is free of oil or coated with a small amount of oil, a clear fixed toner image can be produced on the recording medium D without offsets. The toner image fixing apparatus shown in
FIG. 14
is thus capable of solving the problems of toner separation and oil coating, which have not been eliminated by other toner image fixing apparatus using only a heating roller.
The conventional toner image fixing apparatus shown in
FIG. 14
will be described in greater detail. The pressing roller R
2
is positioned directly beneath the fixing roller R
1
, and the heating and tensioning roller R
3
is disposed upstream of the fixing roller R
1
with respect the direction in which the recording medium D is fed into the toner image fixing apparatus along the fixing belt B that is trained around the rollers R
1
, R
3
.
The toner image fixing apparatus also has an oil coating roller R
4
disposed above an upper run of the fixing belt B. A guide plate G for supporting the recording medium D is disposed below a lower run of the fixing belt B, and a gap between the guide plate G and the lower run of the fixing belt B serves as a preheating passage P for preheating the recording medium D when the recording medium D travels below the heating and tensioning roller R
3
toward the nipping region.
The fixing belt B is tensioned to a desired tension level when the heating and tensioning roller R
3
is pushed away from the fixing roller R
1
by a pressing lever U. The fixing belt B is actuated by the fixing roller R
1
which is coupled to an actuator. Since the fixing belt B is appropriately tensioned, it can stably rotate around the rollers R
1
, R
3
without undesirable slippage and sagging.
A heater H is housed in the heating and tensioning roller R
3
. The heating and tensioning roller R
3
is associated with a thermistor S for measuring the temperature of the surface of the heating and tensioning roller R
3
. The fixing belt B on the heating and tensioning roller R
3
has a sheet-contact area which is contacted by the recording medium D that is fed from the sheet feeder and a non-sheet-contact area which is not contacted by the recording medium D that is fed from the sheet feeder. The thermistor S is kept out of contact with the sheet-contact area of the fixing belt B on the heating and tensioning roller R
3
, but held in contact with the non-sheet-contact area of the fixing belt B on the heating and tensioning roller R
3
.
During the fixing process, based on a signal from the thermistor S, a controller (not shown) connected to the thermistor S controls the amount of heat generated by the heating and tensioning roller R
3
so that the temperature of the surface of the heating and tensioning roller R
3
will be kept at a preset level.
The temperature of the fixing belt B on the fixing roller R
1
varies depending on the period of time in which the fixing belt B has rotated, and is not constant when the recording medium D passes through the nipping region. If the period of time in which the fixing belt B has rotated is short, then the temperature of the fixing belt B on the fixing roller R
1
is low. In order to increase the temperature of the fixing belt B on the fixing roller R
1
, it is necessary to increase a temperature setting for the heating and tensioning roller R
3
for thereby bringing the temperature of the fixing belt B on the fixing roller R
1
into a toner image fixing temperature range at all times.
If the toner image fixing apparatus shown in
FIG. 14
is used to produce successive full-color copies, since the period of time in which the fixing belt B has rotated increases, the temperature of the fixing belt B on the fixing roller R
1
also increases, and so does the temperature of the outlet of the nipping region.
FIG. 15
of the accompanying drawings shows temperature characteristics of the toner image fixing apparatus shown in FIG.
14
.
In
FIG. 15
, the horizontal axis represents the period of time in which the fixing belt B has rotated, and the vertical axis represents the temperature of the fixing belt B on the rollers R
1
, R
3
. First, a temperature characteristic of the toner image fixing apparatus at the time the amount of heat radiated by the heater H is controlled in order to equalize the temperature of the fixing belt B on the heating and tensioning roller R
3
to a preset temperature T2 will be described below. A solid-line wavy curve W1 represents the temperature of the fixing belt B on the heating and tensioning roller R
3
, and a solid-line curve C1 represents the temperature of the fixing belt B on the fixing roller R
1
.
After a standby period, as the period of time in which the fixing belt B has rotated increases, the temperature of the fixing belt B on the fixing roller R
1
increases. When the temperature of the fixing belt B on the fixing roller R
1
exceeds an upper limit temperature T1 of a toner image fixing temperature range, the possibility of hot sheet offsets, i.e., sheet offsets at high temperatures, or sheet jams increases. When the temperature of the fixing belt B on the fixing roller R
1
becomes lower than a lower limit temperature T1′ of the toner image fixing temperature range, the possibility of cold sheet offsets, i.e., sheet offsets at low temperatures, or unfixed toner regions increases. Therefore, the temperature of the fixing belt B on the fixing roller R
1
should be kept in the toner image fixing temperature range which lies between the upper limit temperature T1 and the lower limit temperature T1′.
The above drawback, i.e., sheet offsets and sheet jams, can be avoided when the temperature of the fixing belt B on the heating and tensioning roller R
3
is set to a temperature T2′, lower than the preset temperature T2, such that the temperature of the fixing belt B on the fixing roller R
1
will be equal to or below the upper limit temperature T1 at its maximum, as indicated by broken-line characteristics curves W2, C2. However, it will take a longer period of time for the temperature of the fixing belt B on the fixing roller R
1
to reach the lower limit temperature T1′ of the toner image fixing temperature range, with the result that a fixation readiness time, i.e., a period of time required for the toner image fixing apparatus to become ready for fixing toner images, increases from TS to TS′.
After the toner image on the recordin
Hamada Yasuhide
Higashi Yuichiro
Armstrong Westerman Hattori McLeland & Naughton LLP
Fuqua Shawntina
Nitto Kogyo Co. Ltd.
Walberg Teresa
LandOfFree
Toner image fixing apparatus capable of keeping constant... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Toner image fixing apparatus capable of keeping constant..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Toner image fixing apparatus capable of keeping constant... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2581484