Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2000-07-24
2002-05-07
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S337000
Reexamination Certificate
active
06385410
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fixing apparatus which has a heating roller having a heating means inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material.
At present, a fixing apparatus of the heat roller type which is used in an image forming apparatus such as a copying machine and a laser beam printer is composed of a heating roller having a halogen heater lamp as a heat source inside and being provided with a coating layer for a better releasing ability, and a pressing roller having a surface layer made of a rubber material.
Incidentally, in an image forming apparatus having a fixing apparatus of the above-described structure, two thirds of the electric power is consumed in the fixing apparatus during image formation.
Further, in order to make it possible to form an image whenever it is required, the heating roller of the fixing apparatus is always kept at a predetermined temperature even in standby hours, and two thirds of the electric power of the standby hours also is consumed in the fixing apparatus.
Incidentally, the electric power consumption of a fixing apparatus during the formation of an image is approximately determined by the product of the heat quantity which is necessary for fixing a sheet of transfer material times the number of sheets having an image formed.
In an image forming apparatus of a class with an image forming speed of 20-30 sheets per minute, the heat quantity required for a unit time is small in proportion to the slow speed of image forming, and it is not necessary to store heat in the heating roller; thus, sufficient heat can be supplied at the time of image forming.
Accordingly, from the point of view to save energy, it has been proposed a heating roller having its heat capacity made small by making the thickness of its metallic sleeve as thin as possible.
However, if a heating roller with a thin sleeve is used, there are problems as follows:.
(1) Because the heat capacity of the heating roller is small, the difference between the required heat quantity during fixing and that in idling hours is large.
Accordingly, in the case where a control, in which the supply of electric current to the heating means is turned on and off at a set temperature, is carried out for the temperature control of the heating roller, when fixing is finished and the driving for the rotation of the heating roller is stopped, if the heating means is still actuated, the heat quantity immediately after the stop becomes excessive because of the large supplied heat quantity before and after the stop of rotation of the heating roller; hence, the temperature of the heating roller becomes abnormally higher than the set temperature owing to the overshoot, which results in a useless consumption of electric power.
(2) In the case where a large number of sheets of transfer material having a small width are continuously fixed, only a part of the heating roller (for example, only the central portion of the heating roller) requires heat.
Especially, in the case where plural sheets of transfer material, like sheets of 5.5×8.5R, having a proportion of the smallest width and a larger length in the flow direction than the sheets of transfer material of A-sizes and B-sizes are continuously fixed, there is also a problem that it occurs that unnecessary area is heated, and the temperature rise of the portion with which no paper sheet comes in contact becomes remarkable in accordance with the small heat capacity of the heating roller, which makes the temperature control difficult.
(3) In the case where a control, in which the supply of electric current to the heating means is turned on and off at a set temperature, is carried out for the temperature control of the heating roller, because the heat capacity of the heating roller is small, the temperature of the heating roller rises and drops with respect to the set temperature, and the frequency of turning on and off of the current supply becomes high.
There is also a problem that, when the heating means is turned on, a noise is produced owing to a rush current.
SUMMARY OF THE INVENTION
Heretofore, it has been known that, in order to suppress the electric power consumption of a fixing apparatus, the sleeve of its heating roller is made thin, as is disclosed in the publications of Tokkaihei H7-64420 and Tokkaihei H9-297486. However, in order to obtain a good fixing result through using a thin-sleeve roller, it is necessary to use an optimum fixing condition which is suitable to it, and if a fixing condition which is the same as that used for a conventional thick-sleeve roller was used, a good fixing result could not be obtained. Therefore, it is an object of this invention to provide a fixing apparatus which gives a good fixing result while suppressing electric power consumption by using a thin-sleeve roller.
It is the second object of the invention to provide a fixing apparatus which eliminates a useless electric power consumption at the time of completion of fixing.
It is the third object of the invention to provide a fixing apparatus which is capable of making a temperature control with a high precision in the case where plural sheets of transfer material having a small width are continuously fixed.
It is the fourth object of the invention to provide a fixing apparatus which reduces the generation of noise.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by a fixing apparatus and an image forming apparatus described as follow.
(1) A fixing apparatus for fixing a toner image onto a transfer material, comprising a heating roller being a hollow cylinder, thickness of which is less than 2.0 mm, made of either aluminum or iron, a heat source positioned interior of the heating roller, a pressing roller, comprised of a silicone rubber having a surface hardness ranging from 35° to 75° (Asker C hardness), being in pressure contact with the heating roller to form a nip between the heating roller and the pressing roller, wherein a nip pressure at the nip is in a range of 0.2-2.0 kgf/cm
2
, and a controller to control a conveyance velocity of the transfer material, so that the transfer material passes through the nip within a nip passing time ranging from 20 msec to 40 msec.
(2) An image forming apparatus, comprising an image bearing element to form a latent image on it, a developing device to form a toner image on the image bearing element, a transferring device to transfer the toner image, formed by the developing device, onto a transfer material a fixing device to fix the toner image, transferred by the transferring device, onto the transfer material, the fixing device comprising, a heating roller being a hollow cylinder made of either aluminum or iron, thickness of which is less than 2.0 mm, a heat source positioned interior of the heating roller, and a pressing roller, comprised of a silicone rubber having a surface hardness ranging from 35° to 75° (Asker C hardness), being in pressure contact with the heating roller to form a nip between the heating roller and the pressing roller, wherein a nip pressure at the nip is in a range of 0.2-2.0 kgf/cm
2
, and a controller to control a conveyance velocity of the transfer material, so that the transfer material passes through the nip within a nip passing time ranging from 20 msec to 40 msec.
Further, to overcome the abovementioned problems, other fixing apparatuses, embodied in the present invention, will be described as follows:
(3) A fixing apparatus which has a heating roller having a heat source inside and a pressing roller being in pressure contact with said heating roller, and makes a transfer material having a toner image transferred on it pass between the above-described heating roller and pressing roller to thermally fix said toner image to said transfer material, wherein said heati
Fujita Shinsuke
Hanyu Naohiko
Nemoto Mitsugu
Braun Fred L
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
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