Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-03-18
2003-11-25
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000, C219S619000, C399S330000
Reexamination Certificate
active
06654585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal fixing device of an image forming device.
2. Description of the Related Art
Image forming devices, such as laser printers, normally have a thermal fixing device for fixing toner that has been transferred onto a sheet. The thermal fixing device includes a thermal roller and a pressing roller. The thermal fixing device thermally fixes the toner onto the sheet while the sheet passes between the thermal roller and the pressing roller.
The thermal roller of the thermal fixing device normally is a tube. A halogen heater is mounted in the tube following the axial direction of the tube. The halogen heater heats up the tube.
Recently, a thermal fixing device has been proposed wherein the tube is heated directly by induction. A plurality of induction coils are disposed on the tube following the axial direction of the tube. An alternating current if passed through each of the induction coils to generate an induced magnetic flux. The induced magnetic flux induces a current at surface portions of the tube that confront one of the induction coils. Joule heat associated with the induced current heats up the surface portions of the tube. As a result, the entire surface of the tube is heated up directly.
However, the Joule heat that heats the tube can heat up and damage the induction coils on the tube. Also, it is expensive to provide the plurality of induction coils following the axial direction of the tube.
One conventional thermal fixing device includes a single induction coil disposed in confrontation with the entire axial length of the tube. Providing a single induction coil instead of a plurality of induction coils reduces costs. However, in this case the magnetic flux is concentrated at the axial ends of the tube and weaker at the central portion of the tube. As a result, the ends of the tube heat up excessively and the center heats up insufficiently. Such a configuration cannot heat up the tube uniformly.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the above-described problems and provide a thermal fixing device that uses induction heating to uniformly heat a thermal region of a thermal member for thermally fixing an image onto a recording medium, the thermal fixing device having a compact and simple configuration, enhanced durability, and reduced cost.
In order to achieve the above-described objectives, a thermal fixing device according to the present invention includes a magnetic circuit configured from an induction coil, a propagation member, and a thermal member. The propagation member is made from a magnetic material that propagates magnetic flux induced by the induction coil. The thermal member has a thermal region made from a magnetic material. The propagation member is magnetically connected to both ends of the thermal region of the thermal member so that the magnetic flux induced by the induction coil heats the thermal region of the thermal member.
With this configuration, when an alternating current is applied to the induction coil, then an induced magnetic flux propagates through the propagation member and an induced current is generated from one end to the other of the thermal region of the heated member. Joule heat associated with the induced current directly heats up the thermal region. For this reason, the entire thermal region can be directly and uniformly heated up across its entire axial length without providing a plurality of induction coils in confrontation with the thermal region across the length of the heated member. Accordingly, the induction coil will not be damaged so that durability can be enhanced. Also, the thermal region of the heated member for thermally fixing the recording medium can be uniformly heated using an induction heating method using only a simple configuration.
It is desirable that the entire thermal region of the thermal member propagate the induced magnetic flux so that magnetic flux is induced across the entire thermal region of the thermal member from one end to the other of the thermal region. As a result, the entire thermal region heats up at the same time. For this reason, the thermal region can be even more uniformly heated up using a simple induction heating configuration.
When the induction coil and the propagation member are stationary and the thermal member is movable, there will be situations when a gap will exist between the thermal member and at least one of the induction coil and the propagation member so that the thermal member can move with respect to the induction coil and the propagation member. The gap will increase the magnetic reluctance between the movable thermal member and the induction coil and the propagation member. In this case, it is desirable to provide a magnetic reluctance reducer for reducing magnetic reluctance between the propagation member and the thermal member so that the induced magnetic flux from the stationary propagation member can be propagated to the thermal region of the movable thermal member. As a result, the magnetic reluctance at the gap can be reduced so that induction heating can be efficiently achieved.
It is desirable that the magnetic reluctance reducer increase the surface area that propagates the induced magnetic flux from the propagation member so that the induced magnetic flux is propagated to the thermal region. As a result, the magnetic reluctance can be reliably reduced and efficient induction heating can be easily and reliably achieved.
It is desirable that the magnetic reluctance reducer serves as a support for the movable thermal member, so that the number of components can be reduced so that induction heating can be performed reliably with a simple configuration.
It is desirable that the induction coil be provided to the outside of the movable thermal member, with respect to the lengthwise direction of the movable thermal member, so that the thermal fixing device can be formed in a more compact shape. Also, with this configuration, the induction coil is less likely to be damaged from heat generated from the thermal region of the thermal member.
When the induction coil is provided around the propagation member at a position external from the movable thermal member in the lengthwise direction of the movable thermal member, it is desirable that the induction coil be installed with respect to the movable thermal member in an integral manner with the connection end portion of the propagation member. With this configuration, during assembly of the thermal fixing device, the induction coil can be provided external from the movable thermal member in the lengthwise direction of the movable thermal member by merely mounting the connection end portion of the propagation member to the movable thermal member. For this reason, the induction coil can be reliably provided to the outside of the movable thermal member in the lengthwise direction of the movable thermal member by a simple assembly process and the thermal fixing device can be made in a more compact shape.
It is desirable that the induction coil be provided around the propagation member at a position external from an axial direction end of the roller so that the thermal fixing device can be made more compact. In this case, it is further desirable that the roller surface have a larger magnetic reluctance than magnetic reluctance of the propagation member so that efficient induction heating can be reliably achieved.
It is desirable that the propagation member be adapted for changing length of a pathway through the thermal region where the propagation member propagates the induced magnetic flux. With this configuration, if the size of the recording medium is changed, then the thermal region can be changed to a size that matches the size of the recording medium by changing the length of the pathway through the thermal region where the propagation member propagates the induced magnetic flux. For this reason, thermal fixing can be appropriately and efficiently performed in accordance with size of the recor
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Pendegrass Joan
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