Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2002-03-28
2003-11-04
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
C399S045000, C399S068000
Reexamination Certificate
active
06643477
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a heating device suitably used for the fixing unit of a dry type electrophotographic apparatus, the drying device of a wet type electrophotographic apparatus, the drying device of an ink-jet printer, a rewritable media erasing device and the like, as well as relating to an image forming apparatus using this heating device.
(2) Description of the Prior Art
In a typical heating device for the electrophotographic process, the toner on the paper surface as a recording medium is fixed on the paper by fusing and solidification. While paper of a smaller width compared to the heating width of the heating element is passed through the heating device, heat energy is supplied from the heat source also to the non-paper feed areas through which paper of a smaller width does not pass. However, since there is no paper to which heat can transfer in the non-paper feed areas, heat builds up in these areas, causing excessive temperature rise therein.
If paper of a greater width than the small-width paper is passed through under this condition, deficiencies as follows will occur due to the temperature imbalance between the paper feed area (at the middle) of the small-width paper and the non-paper feed areas (at both sides).
First, due to temperature imbalance, when paper of greater width is passed through, it becomes wrinkled at the areas corresponding to the non-paper feed areas of small-width paper.
Second, since the non-paper feed areas are overheated, if paper with an unfixed image thereon is passed through, to be fixed, under this condition, image deficiencies such as high-temperature offset will occur.
Third, since the heat roller surface is coated with an non-stick layer of fluororesin or the like in order to improve the separability when fixing, this non-stick layer will be heated to high temperatures in the overheated areas, causing heat deterioration and lowering of its durability.
Generally, in order to assure adhesion between the non-stick layer and the metal core of the heat roller, a primer such as a silicon resin adhesive, undercoating or the like is provided. Therefore, due to degradation of the primer itself and due to degradation of the non-stick layer, the bonding strength between the non-stick layer and the primer or that between the primer and the metal core lowers, as a result the non-stick layer and/or primer may peel off.
To solve the above problems, there have been several conventional methods proposed: examples include a method of lowering the surface temperature by forcibly rotating the heating element after passage of printing paper (e.g., Japanese Patent Application Laid-Open Hei 8 No. 21779), a method of naturally cooling the heating element surface by holding the heating element still after passage of printing paper (e.g., Japanese Patent 2696908) and a method of forcibly cooling the overheated parts or the whole of the heating element using a blower such as a fan etc. Further, in order not to generate inefficient heat in the non-paper feed areas during printing, there has been another approach (Japanese Patent Application Laid-Open Sho 60 No. 22164), with which the heat roller is adapted to incorporate divided, or multiple parts, of heat sources in conformity with the sizes of paper that pass over the heat sources.
Next, these prior art techniques will be described in further detail.
(1) The Method Disclosed in Japanese Patent Application Laid-Open 8 No. 211779:
The method disclosed in Japanese Patent Application Laid-Open 8 No. 211779 is aimed at providing a compact and economic fixing unit in which improvements against fixing defects, offsets and the like attributed to the temperature distribution imbalance across the heat roller are made.
More specifically, the controller for regulating the temperature distribution across the heat roller of the fixing unit, as it is commanded to start a new job, estimates the current temperature distribution across the heat roller based on the information as to the previous job and the elapsed time from the end of the job and judges whether the new job is permitted under the present conditions.
If the controller has determined that the heat roller is not uniform in temperature, the controller performs its control such that the heat roller is idly rotated for a fixed period of time before start of the next job, the set temperature is changed before start of the next job, or all the operations are prohibited for a fixed period.
By effecting such control, the next copy job can be started after the heat roller has become uniform in the temperature distribution, without being affected by the previous copying job.
In the above cooling method, there is a risk that the heating element might be partially reduced in temperature to a temperature lower than the functional fixing temperature range because the heating element which has been uneven in temperature is cooled. To lessen this possibility, there is also a proposed method in which the heating element as a whole is heated after the cooling.
(2) The Method Disclosed in Japanese Patent 2696908:
In the method disclosed in Japanese Patent 2696908, if paper of a smaller size than B5, e.g., postcards or smaller, is detected, the copying operation of the small-sized paper alone is halted for a predetermined period, whereby the non-paper feed areas in the heat roller of the fixing unit are inhibited from being elevated in temperature.
More explicitly, in an image forming apparatus having a roller type fixing unit made up of a heat roller and pressing roller put in pressing contact with each other, continuous copying operations of paper of a size smaller than B5 such as postcards, are allowed until the temperature of the non-paper feed areas on the heat roller of the fixing unit becomes elevated to a predetermined temperature, and then after reaching the predetermined temperature, copying operation of the small-size paper alone is halted over a predetermined period of time so that the non-paper feed areas of the heat roller will not become overheated. This halt is continued until the temperature distribution across the heat roller becomes uniform.
(3) The Method Disclosed in Japanese Patent Application Laid-Open Sho 60 No. 22164:
In the method disclosed in Japanese Patent Application Laid-Open Sho 60 No. 22164, temperature control in conformity with the recording paper size is enabled in order not to generate unnecessary heat in the non-paper feed areas during printing.
More clearly, in conformity with the size of recording paper conveyed through the fixing unit, multiple heater elements arranged in the fixing unit are selectively energized. Further, the power of each heater element is also controlled so as to optimize the temperature distribution.
As stated above, in the method disclosed in Japanese Patent Application Laid-Open Hei 8 No. 211779, when the surface temperature of the heat roller has risen, to decrease the temperature the paired rollers, i.e., heat roller and pressing roller, are idly turned for forcible cooling.
However, in order to decrease the temperature difference between the paper feed area and the non-paper feed areas to a small enough level, it is necessary to idly rotate the heat roller for a long time. Accordingly, extra time is needed until the next copying operation is allowed to start, resulting in reduction in throughput.
In the method disclosed in Japanese Patent 2696908, upon a copying operation using small-sized recording paper, the copying operation of small-sized paper alone is halted for a predetermined period, so that the temperature of the heat roller can fall within the range in which copying operations can be implemented.
Solitary prohibition of the copying operation of small sized paper for the predetermined period of time makes it possible to reduce the temperature difference between the paper feed area and the non-paper feed areas to a certain small level. However, it is necessary to take a long halt in order to reduce the temperature of the non-paper feed areas to
Kagawa Toshiaki
Mitsuoka Tetsunori
Conlin David C.
Edwards & Angell LLP
Grainger Quana M.
Sharp Kabushiki Kaisha
Tucker David A.
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