JP3940525B2 - Induction heating type fixing device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and more particularly to an induction heating type fixing device that performs heating using electromagnetic induction.
[0002]
[Prior art]
In an image forming apparatus that uses toner for forming a visible image, in order to fix the toner image on the recording material, the toner image is conveyed while being sandwiched and conveyed by a heating roller (also referred to as a fixing roller) and a pressure roller. In general, a heat and pressure type fixing device for fixing the image on the recording material is used.
[0003]
In a conventional fixing device in which a halogen lamp heater is built in a heating roller, it takes a long time to heat the heating roller to a predetermined temperature, and the loss of the lamp heater itself is large. As the environmental problems are closed up and a fixing device with high efficiency and quick rise time is required, an induction heating type fixing device has been attracting attention.
[0004]
This induction heating type fixing device is shown in FIGS. 4 and 5 on the front side cut along the axis and on the plane perpendicular to the axis. The heating roller 3 in pressure contact with the pressure roller 2 rotates clockwise on the surface shown in FIG. 5, and the recording sheet S having the toner image T to be fixed is sandwiched between the heating roller 3 and the pressure roller 2. The toner image T is pressed and conveyed in the direction of the arrow, and the toner image T is fixed by heat and pressure. As shown in FIG. 4, the rotation of the heating roller 3 supported by the bearings 101A and 101B is such that the gear 104 fitted and fixed to one end of the roller meshes with a driving gear (not shown), and the driving gear rotates. Made by doing. The core of the heating roller 3 is made of a magnetic material such as stainless steel or iron, and a release layer made of a fluororesin is provided on the outside thereof. A thermal fuse 5 and a thermistor 6 are disposed on the surface of the heating roller 3 opposite to the pressure roller 2.
[0005]
An induction coil 1 of an induction heating device is disposed inside the heating roller 3. The induction coil 1 made of litz wire or the like is wound around a cylindrical bobbin 4 made of an insulator, and has lead wires (not shown) at both ends. These lead wires allow the induction coil 1 to pass high-frequency current from both ends. The bobbin 4 is held so as not to rotate by brackets 103A and 103B provided on the side plates 102A and 102B of the toner image fixing device. A cooling fan 106 is disposed on the outside of the bobbin 4 in the longitudinal direction, and cooling air is sent into the bobbin 4 to cool the induction coil 1 through the bobbin 4. Ferrite members 105A and 105B are provided on both outer sides in the axial direction of the wound induction coil 1, and the leakage magnetic flux from both ends is fed back to the core metal (heating roller).
[0006]
During the fixing operation, a high-frequency current is passed through the induction coil 1, an induced eddy current is generated in the metal core as the metal conductor of the heating roller 3 by the high-frequency magnetic field generated thereby, and the heating roller itself is Joule heat by the skin resistance of the heating roller itself. To generate a desired temperature on the roller surface.
[0007]
[Problems to be solved by the invention]
In the induction heating type fixing device having the above-described configuration, the induction coil is disposed substantially at the center of the heating roller mandrel, and heats the heating roller uniformly and rapidly from the inner peripheral surface. Generally, a fixing device is provided with a thermistor as a temperature control device, and normally, the surface of the heating roller is maintained at a constant temperature by the thermistor. As a safety device, a temperature fuse, a thermostat or the like is provided in the vicinity of the heating roller, and the circuit is forcibly cut off when temperature control by the thermistor becomes impossible.
[0008]
It is known that when the temperature of the heating roller becomes uncontrollable and the roller temperature rises abnormally, the silicone rubber of the pressure roller in contact with the heating roller is deformed or emits smoke. An object of the present invention is to minimize deformation and smoke generation that may occur in a pressure roller or the like even when the temperature of the heating roller becomes uncontrollable.
[0009]
[Means for Solving the Problems]
The above-described problem is to form a nip portion by pressure-contacting two rollers, and to generate a induced magnetic flux in at least one of the two rollers in the fixing device that fixes the toner image to the recording material at the nip portion. In a fixing device configured with a coil unit, a thermal fuse is disposed at a position opposite to the nip portion of one roller, and the coil unit is disposed away from the nip portion and close to the thermal fuse. Is solved.
[0010]
Regarding the distance between the coil portion of the coil unit and the roller metal core, the above-described problem can also be solved by making the nip portion away from other regions. It is preferable that the gap between the coil portion of the coil unit and the inner peripheral surface of the roller core metal is maximized at approximately the center in a region corresponding to the contact range of the two rollers.
[0011]
The fixing device is configured by forming a nip portion by pressing the roller and the belt and fixing a toner image on the recording material at the nip portion, and a coil unit for generating an induced magnetic flux is provided inside the roller. In the apparatus, the thermal fuse is disposed at a position on the opposite side of the nip portion around the roller, and the coil unit is disposed away from the nip portion and close to the thermal fuse, thereby solving the above-described problem.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described based on examples shown in the drawings.
FIG. 1 shows a fixing device according to the first embodiment in a plane whose axis is cut vertically corresponding to FIG. 5 showing a conventional example. As in the example of FIG. 5, the heating roller 3 in pressure contact with the pressure roller 2 rotates clockwise, and a toner image is fixed by pressing a recording sheet (not shown) at a nip formed by the pressure roller 2. . A coil unit 20 formed by winding an induction coil 21 around a cylindrical bobbin 22 (which is held by a bracket and does not rotate in the same manner as the conventional example shown in FIG. 5) is shifted from the center of the metal core in a direction away from the nip portion. Yes. A thermal fuse 5 and a thermistor 6 are disposed around the heating roller 3 and in the vicinity of the coil unit 20.
[0013]
In this case, since the nip part is located away from the induction coil 21, the temperature rise on the nip part region side seems to be delayed, but the heating roller 3 rotates to increase the core metal temperature in the nip part range and record. By the time the sheet reaches, it is brought to a temperature that does not hinder fixing.
[0014]
FIG. 2 shows another configuration example. In the case of this example, the induction coil 11 is basically disposed concentrically with the heating roller 3 except for the range corresponding to the nip portion, and the cored bar is efficiently heated outside the nip portion. In the range corresponding to the nip portion, the induction coil 11 is wound around the bobbin 12 with an interval H so as to be substantially parallel to the recording sheet conveyance direction. Therefore, the bobbin 12 has a cross section in which a portion facing the nip portion has a flat portion as shown in the drawing. As a result, the induction coil 11 is located farthest from the center of the nip.
[0015]
In such a configuration, when the thermistor 6 becomes uncontrollable, and the current continues to flow through the induction coil 11 and the temperature of the surface of the heating roller excessively rises, the thermal fuse 5 is blown to cut off the energization. At that time, since the induction coil 11 is located away from the nip side, the temperature rise is delayed as compared with other regions, and thermal damage to the pressure roller 2 can be reduced. In particular, since the pressure at the center of the nip portion is generally the highest and the temperature of the heating roller 3 is most easily transmitted to the pressure roller 2, the portion, that is, the center of the nip portion is farthest away, Can be suppressed.
[0016]
FIG. 3 shows an example in which a pressure device that presses against the heating roller 3 to form a nip portion is a belt instead of the pressure roller. When the belt-shaped pressurizing device 33 is used, the time for the recording sheet S to contact the heating roller 3 is generally longer than that in the case of the pressure roller. The material of the pressure belt 33 is generally made of silicone rubber like the pressure roller, and it is known that the physical properties are deteriorated and smoke is generated when the heating roller 3 reaches a certain temperature. For this reason, as in the case of the pressure roller, the temperature control by the thermistor becomes impossible, and in a situation where the current continues to flow through the induction coil and it is necessary to cut off the current, the heating roller becomes considerably hot and contacts the belt 33. It is preferable to suppress the temperature rise at the part as much as possible. In this example, the induction coil 31 is located on the same circle in the vicinity of the core of the heating roller 3 in the portion corresponding to the range other than the contact range of the heating roller 3 with the belt 33, while corresponding to the contact range with the belt. In the portion where it is located, it is located on a substantially concentric circle farther from the core than the above positional relationship. Therefore, as shown in the figure, the bobbin 32 is a combination deformed circle in which the angle range surrounded by a dotted line corresponding to the contact range of the heating roller 3 with the belt 33 is a small-diameter circle and the remaining angle range is a large-diameter circle. It has a cross section. In such a configuration, in a normal case, the heating roller 3 is efficiently heated in a range where the induction coil 31 and the metal core are close to each other, and in a range where the induction coil 31 is separated, the temperature rise tends to be delayed, and the thermistor 6 cannot be controlled. When the current continues to flow through the induction coil 31 and the temperature of the surface of the heating roller excessively rises, the thermal fuse 5 provided in the range where the induction coil 31 and the cored bar are close to each other quickly melts to cut off the energization. To do. In the region where the pressure belt 33 and the heating roller 3 are in contact with each other, the temperature rise is delayed as compared with the other regions as described above, and thermal damage to the belt 33 can be reduced.
[0017]
【The invention's effect】
According to the present invention, the thermal fuse is disposed at a position opposite to the nip portion of one roller, and the coil unit is disposed away from the nip portion and close to the thermal fuse, or the coil unit. With regard to the distance between the coil portion of the roller and the metal core, the temperature of the nip portion can be delayed by making the location of the nip portion away from other regions, and the roller surface temperature is excessively increased due to an abnormality. In such a case, it is possible to cut off the energization by fusing the thermal fuse to suppress damage on the pressure roller side.
[0018]
If the gap between the coil part of the coil unit and the inner peripheral surface of the roller core is maximized at the approximate center in the area corresponding to the roller nip, the temperature rise will be delayed most slowly at the point where the applied pressure is highest. This is convenient for preventing damage on the pressure roller side.
[0019]
In the fixing device configured to sandwich and convey the recording material between the roller and the belt, the coil unit is located on the side opposite to the nip portion around the roller so as to be separated from the roller core in a region corresponding to the contact range of the roller and the belt . By placing a thermal fuse at the position, and disposing the coil unit away from the nip part and approaching the thermal fuse, the temperature rise at the nip part can be delayed and seemingly relieved. In such a case, it is possible to cut off the energization by fusing the thermal fuse to suppress damage on the pressure belt side.
[Brief description of the drawings]
FIG. 1 is a schematic side view of an induction heating type fixing device according to a first embodiment of the present invention.
FIG. 2 is a schematic side view of an induction heating type fixing device according to a second embodiment of the present invention.
FIG. 3 is a schematic side view of an induction heating type fixing device according to a third embodiment of the present invention.
FIG. 4 is a schematic front view of a conventionally known induction heating type fixing device.
FIG. 5 is a schematic side view of the fixing device of FIG. 4;
[Explanation of symbols]
2 Pressure roller 3 Heating roller 5 Thermal fuse 6 Thermistor 20 Coil unit 21 Induction coil 22 Bobbin

Claims (5)

A coil unit that generates an induced magnetic flux is provided in at least one of the two rollers to form a nip portion by pressing the two rollers and fix the toner image on the recording material at the nip portion. In the fixing device configured as described above,
A fixing device, wherein a thermal fuse is disposed at a position opposite to the nip portion of one of the rollers, and the coil unit is disposed away from the nip portion and close to the thermal fuse. A coil unit that generates an induced magnetic flux is provided in at least one of the two rollers to form a nip portion by pressing the two rollers and fix the toner image on the recording material at the nip portion. In the fixing device configured as described above,
A thermal fuse is disposed at a position opposite to the nip portion of one of the rollers, and the nip portion is separated from other regions with respect to the distance between the coil portion of the coil unit and the roller metal core. A fixing device.   3. The fixing device according to claim 1, wherein a gap between a coil portion of the coil unit and an inner peripheral surface of the roller core is maximized at a substantially center of the nip portion. The fixing device is configured by forming a nip portion by pressing the roller and the belt and fixing a toner image on the recording material at the nip portion, and a coil unit for generating an induced magnetic flux is provided inside the roller. In the device
A fixing device, wherein a thermal fuse is disposed at a position opposite to the nip portion around the roller, and the coil unit is disposed so as to be away from the nip portion and approach the thermal fuse. An image forming apparatus comprising the fixing device according to claim 1.

Images