Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
2000-07-11
2001-11-20
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S662000, C219S672000, C399S330000, C399S335000
Reexamination Certificate
active
06320168
ABSTRACT:
RELATED APPLICATION
This application is based on application No. H11-202022 filed in Japan, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fusion devices for use in, for example, electrophotographic copying machines, printers and facsimile apparatus, and more particularly, to a fusion device adapted to fuse toner images onto a recording medium by utilizing low-frequency induction heating.
2. Description of the Related Art
In an image forming apparatus such as an electrophotographic copying machine, printer or facsimile apparatus, there is provided a fusion device adapted to fuse toner images onto a recording medium such as a paper sheet or a transfer material carrying the same.
Although various types of fusion devices exist, there have been proposed induction-heating type fusion devices which exhibit a higher energy conversion efficiency than fusion devices of the type having a halogen lamp as a heat source, as devices satisfying the recent energy saving demand.
An induction-heating type fusion device as disclosed in, for example, Japanese Unexamined Patent Publication No. HEI 10-207265 includes a fixed or movable electrically conductive member of a hollow configuration, an iron core forming a closed magnetic circuit and having a portion inserted into the hollow portion of the electrically conductive member, and an induction coil wound around the iron core forming the closed magnetic circuit, wherein current is passes through the induction coil to generate a magnetic flux which causes the electrically conductive member to generate an induced current along the circumference of the electrically conductive member, thereby induction-heating the electrically conductive member.
Since an image forming apparatus forms images on sheets of different sizes, a fusion device used therein has to perform fusion with respect to sheets of different sizes.
When a small-size sheet is passed through the aforementioned prior art induction-heating fusion device, a sheet-nonpassing zone results through which the sheet does not pass. Since this sheet-nonpassing zone fails to allow heat to escape through the sheet, the temperature is elevated markedly, which causes the permeability of the iron core to vary, thus resulting in an unstable fusion temperature. In addition, such an excessive temperature rise in the nonpassing zone also facilitates deterioration of the device components such as the induction coil and electrically conductive member in that zone.
The prior art induction-heating fusion device has opposite end portions which are cooled more rapidly than a central portion and hence is designed to heat a wider extent than the maximum sheet width of usable sheets so that even a sheet having the maximum sheet width can entirely be heated uniformly. For this reason, the induction coil is required to have a larger length than the maximum sheet width. Thus, the prior art induction-heating device also involves a problem of an increased device size.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an induction-heating fusion device which is capable of stabilizing the fusing temperature over the entire width of a sheet to be passed therethrough by inhibiting an excessive temperature rise in a sheet-nonpassing zone defined, for example, when a small-size sheet passes through the device.
A second object of the present invention is to provide an induction-heating fusion device which is capable of maintaining a fusion-suited temperature over an extent from a central portion to opposite end portions of the device with the use of an induction coil having a coil length substantially equal to the maximum sheet width of usable sheets.
These and other objects are attained by an induction-heating fusion device comprising: an electrically conductive tube; an endless belt covering the tube; a pressure member pressed toward the heat-generating member to define a nip in cooperation with the endless belt; a permeable closed loop having a portion inserted into the tube; a main coil continuously wound around the inserted portion of the closed loop along a peripheral wall of the tube and extending along the length of the tube; a first sub-coil continuously wound around the inserted portion of the closed loop on an end portion of the tube along the peripheral wall of the tube; and a controller for controlling application of current to the main coil from a power source and application of current to the first sub-coil from the power source.
The aforementioned objects of the present invention can also be attained by the above induction-heating fusion device further comprising a second sub-coil continuously wound around the inserted portion of the closed loop on an end portion of the tube along the peripheral wall of the tube, wherein: the second sub-coil is wound around the main coil in an overlapping fashion to a length corresponding to a sheet-nonpassing zone defined when a third standardized sheet which is smaller than the first standardized sheet and larger than the second standardized sheet in width passes through the nip; and when the first standardized sheet passes through the nip, the controller causes alternating current to pass through the main coil while causing alternating current to pass through the second sub-coil constantly in a same direction as that passing through the main coil, and when the third standardized sheet passes through the nip, the controller causes alternating current to pass through the main coil only.
Alternatively, the aforementioned objects are attained by an induction-heating fusion device comprising: an electrically conductive hollow member; an iron core forming a closed loop and having a portion inserted into a hollow portion of the electrically conductive member; a main coil spirally wound around the inserted portion of the iron core along an internal wall of the electrically conductive member; and a first sub-coil continuously wound around the inserted portion of the iron core along the internal wall of the electrically conductive member, wherein the main coil and the sub-coil cause the electrically conductive member to generate induction heat when applied with alternating current.
The aforementioned objects of the present invention can also be attained by the above induction-heating fusion device further comprising a first switch for switching the direction of current passing through the first sub-coil into a direction as same as or opposite to the direction of current passing through the main coil constantly.
The aforementioned objects of the present invention can also be attained by the above induction-heating fusion device further comprising a second sub-coil spirally wound around the inserted portion of the iron core along the internal wall of the electrically conductive member.
Alternatively, the aforementioned objects of the present invention are attained by a fusion device which generates heat by applying current to a coil to cause an electrically conductive member to generate induction current, comprising: an iron core; an electrically conductive member having an endless configuration in section and covering the iron core; a main coil wound around the iron core within the endless configuration of the electrically conductive member for generating a magnetic flux which causes the electrically conductive member to generate an induction current circumferentially thereof; and a sub-coil wound around an end portion of the iron core within the endless configuration of the electrically conductive member for generating a magnetic flux which causes the electrically conductive member to generate induction current circumferentially thereof.
The aforementioned objects of the present invention can also be attained by the above fusion device further comprising a switch for switching the direction of current passing through the sub-coil so that the sub-coil is excited in a direction as same as or opposite to an excited direction of the main coil.
The
Kimata Akinori
Tsujimoto Takahiro
Leung Philip H.
McDermott & Will & Emery
Minolta Co. , Ltd.
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