Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
1999-02-22
2001-02-06
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C219S216000, C399S070000, C399S328000
Reexamination Certificate
active
06185388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image heating apparatus for use in an image forming apparatus such as a copying apparatus or a printer, and particularly to an image heating apparatus for sandwiching a recording material carrying an image thereon between a pair of rollers and conveying it and heating the image.
2. Related Background Art
An image heating apparatus, for example, a fixing apparatus, used in an image forming apparatus has merits such as a short warming-up time, a small space and cost saving, and is used in a copying apparatus, a printer or the like.
In the construction of such a fixing apparatus, however, fixation is effected at a relatively high temperature, and this leads to the problem that in a system using a fixing roller (fixing rotatable member) using silicone rubber or fluorine rubber as an elastic layer, the rubber is deteriorated by the high temperature.
Also, there occurs so-called overshooting in which when a set temperature is reached after the closing of a power source switch or immediately after the completion of the copying operation, the roller is excessively heated by the time lag until heat is transferred from heating means to the surface of the roller. By this phenomenon as well, the elastic layer of the fixing roller is deteriorated.
Also, if the fixing operation is performed at a temperature higher than necessary, there is caused so-called high temperature offset which causes a toner to adhere to the fixing roller to thereby cause a bad image.
As means for suppressing overshooting, there has heretofore been proposed a method of stopping power supply to heating by conjecturing the time from the rise of the temperature of the fixing roller till the completion of warming up at the starting time of the image forming apparatus, or stopping power supply to a heating source by the temperature of the fixing roller reaching a predetermined temperature lower than the temperature at the completion of warming up, or decreasing the amount of heat imparted from the heating source to the fixing roller more than immediately after the closing of the power source switch when the temperature of the fixing roller reaches a predetermined temperature lower than the temperature at the completion of warming up.
In any of the above-described methods, however, the warming-up time is not sufficiently short.
Also, in a fixing device having a heating source only on the fixing roller side, the temperature of a pressing roller is needed to be made as high as possible to secure fixativeness, and has a great influence on fixativeness particularly in copying immediately after starting.
On the other hand, as means for suppressing the overshooting immediately after the copying operation, there have been proposed a method in which during continuous copying, power supply to the heating source is cut off depending on a predetermined number of sheets, and a method of decreasing the amount of heat imparted to the fixing roller more than at the start of continuous copying.
In the fixing device having a heating source only on the fixing roller side, however, there arises the problem that the temperature of the pressing roller drops and in the next copying operation, low temperature offset occurs.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-noted problem and an object thereof is to provide an image heating apparatus in which the overshooting of a heating roller during the power supply to a heater is suppressed.
Another object of the present invention is to provide an image heating apparatus having a heater, a heating roller heated by the heater, a back-up roller cooperating with the heating roller to form a nip for holding and conveying a recording material, and power supply control means for controlling the power supply to said heater so that the temperature of said heating roller may maintain a set temperature and wherein when said power supply control means sets the set temperature and changes the temperature of said heating roller, the power supply is cut off before the temperature of said heating roller reaches the set temperature, and a predetermined time later, said heating roller and said back-up roller stop their rotation.
Still another object of the present invention is to provide an image heating apparatus having a heater, a heating roller heated by the heater, a back-up roller cooperating with said heating roller to form a nip for holding and conveying a recording material, power supply control means for controlling the power supply to said heater so that the temperature of said heating roller may maintain a set temperature, and rotation control means for controlling the rotation of said heating roller and said back-up roller in conformity with the temperature of said back-up roller when the temperature of said heating roller is maintained at the set temperature.
Further objects of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5708920 (1998-01-01), Ohnishi et al.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grimley Arthur T.
Ngo Hoang
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