JPH06289744A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To prevent a device from being fatally ruptured due to the excessive raising of temperature of a heating roller by supporting the heating roller by a beating made of resin which is softened or melted due to the excessive raising of the temperature of the heating roller, and arranging a circuit applying a power source current when the heating roller is displaced because the bearing is softened or melted in parallel with a heating source. CONSTITUTION:A contact 12 is arranged on the right side of a mandrel 9a, and a contact 13 is arranged on the left side thereof, then the contacts 12 and 13 are connected to a power source D. The heating roller 5 is pivotally supported on side plates 6a and 6b by the bearings 7a and 7b made of resin. When the surface of the roller 5 is excessively heated and the temperature of the bearing 7a rises over its softening point of its melting point, a pressure roller 9 is displaced upward because the roller 5 is biased upward by springs 11a and 11b, so that the projecting part 9d of the mandrel abuts on the contact 13. Then, a circuit including the contact 12, the mandrel 9a and the contact 13 in parallel with a heater 2 is closed, a current flowing in the heater 2 is suddenly reduced and the temperature of the roller 5 is prevented from rising further.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrostatic transfer process such as an electrostatic copying machine and a printer, and more particularly to a fixing device therefor.

[0002]

In the well-known image forming apparatus as described above, in order to fix and fix the toner image on a transfer material carrying an unfixed toner image through a transfer process,
It is necessary to heat and pressurize the transfer material.

Various fixing devices have been proposed, and a typical example thereof will be briefly described below with reference to FIG. FIG. 1 is a front view of a main part of a fixing device including a heating roller having a built-in heat source and a pressure roller in pressure contact with the heating roller. A roller 5 and a pressure roller 9 covered with an elastic material 9b on the outer circumference of a core metal 9a are arranged.

A cover 6 supported in the casing 4
Bearings 7a and 7b made of a resin material are attached to side plates 6a and 6b formed on both sides of the heating roller 5, and the heating roller 5 is axially mounted on the bearings 7a and 7b.
The protruding portions 9c and 9d at both ends of the side plates 6a and 6 of the cover 6 are
The bearings 10a and 10b are provided on the shaft b.

A drive gear 8 connected to a drive source (not shown) is disposed at one end of the heating roller 5, and the both ends of the core of the pressure roller 9 are projected 9d, 9c. The bearings 10a and 10b that pivotally support the cover side plates 6a and 6b
Springs 11a arranged on the cut-and-raised parts 6c and 6d provided on the
The pressure roller 9 is biased toward the heating roller 5 by being supported by the end portion 11b. Therefore, by driving the heating roller 5 by the drive gear 8, the pressure roller 9
Is driven to rotate in a state of contacting the heating roller 5 and forming a pressure contact nip portion as a fixing portion.

A thermo switch 26 is in contact with the heating roller 5 via a spring 27, and a thermistor 15 is in contact with the heating roller 5 via the spring 14 to detect the surface temperature of the heating roller. The temperature of the roller 5 is maintained within a certain range by operating the on / off switch 17 according to a signal from the temperature control circuit 16 depending on the detected temperature. A transfer material (not shown) carrying the unfixed toner image after completing the transfer advances in the direction perpendicular to the paper surface and is fed to the abutting portions of the rollers 5 and 9 where it receives pressure and heat. It is fixed on the toner image transfer material and discharged to the outside of the machine.

In the fixing device having such a structure, the fixed image has streaks due to the contact scratches on the heating roller, and the fixing failure due to the toner and paper dust accumulated and accumulated on the thermistor portion, and the image quality due to the drop There is a possibility that deterioration or the like may occur, and further that the adhesion of these to the thermistor or the thermoswitch may cause its function to be insufficient, resulting in damage to the device due to overheating or failure to fix.

The present invention has been made to cope with such a situation, and in the fixing device as described above, the device is not fatally damaged due to the extreme temperature rise of the overheating roller. It is an object of the present invention to provide such a fixing device.

[0009]

[Constitution of the invention]

To achieve the above object, the present invention comprises a heating roller having a heating source connected to a power source and a pressure roller elastically pressed against the heating roller. In a fixing device configured to allow a transfer material carrying an unfixed toner image to pass through a pressure contact nip portion of both rollers, the heating roller is supported by a resin bearing which is softened or melted by excessive temperature rise of the rollers, and A circuit for supplying a power supply current when the heating roller is displaced by softening or melting of the bearing is arranged in parallel with the heating source, or a parallel circuit formed by the displacement of the heating roller is connected to the pressure roller electrically. Whether to include sex core metal,
Alternatively, the parallel circuit formed by the displacement of the heating roller is a conductive thin layer formed on the heating roller, or a heating roller provided with a heating source connected to a power source and elastically pressed against the heating roller. In a fixing device in which a transfer material carrying an unfixed toner image is allowed to pass through a pressure contact nip portion of both rollers, at least a part of a bearing supporting the heating roller is provided in the roller. A circuit which is formed of a member that softens or melts when heated and has a circuit through which a power supply current flows when the heating roller is displaced by softening or melting the part of the bearing is arranged in parallel with the heating source, or The parallel circuit formed by the displacement of the roller is the conductive core metal of the pressure roller, or the parallel circuit formed by the displacement of the heating roller is formed on the heating roller. It is characterized in that it has a thin conductive layer.

With such a structure, in a fixing device using a heat source, damage to the fixing device due to overheating, fixing failure and contamination of transfer material can be prevented, and a thermoswitch, a thermal fuse, etc. are unnecessary. It also contributes to cost reduction.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS "FIG. 1" is a front view of a fixing device showing an embodiment of the present invention, the basic structure of which is the same as that shown in "FIG. Are denoted by the same reference numerals, and description thereof will be omitted unless necessary.

In the illustrated apparatus, a circuit including a conductive cored bar 9a of a pressure roller is arranged in parallel with a heater 2 in a power source D circuit including a safety fuse 1. That is, the core metal 9
A contact 12 is arranged at the right end of a in the figure, and a contact 13 is arranged at the left end of the a at a distance x from the protruding portion 9d of the core metal. These contacts 12 and 13 are connected to the power supply D. I am doing it.

As described above, the heating roller 5 is pivotally supported on the side plates 6a and 6b by the resin bearings 7a and 7b. In this case, the thickness t of the bearing 7a is t> x. It is set.

With such a structure, when the surface of the heating roller 5 is overheated and proper temperature control is not performed, if the temperature of the bearing 7a exceeds its softening point or melting point and the temperature rises, the roller 5 is heated. Since it is biased upward in the drawing by the springs 11a and 11b, the pressure roller 9 is displaced upward as shown in FIG. 2 and t> x is set as described above. The protrusion 9d contacts the contact 13,
The circuit including the contact 12, the core metal 9a, and the contact 13 is closed in parallel with the heater 2, and the current flowing through the heater is sharply reduced to prevent further temperature rise of the roller 5.

In the above-mentioned apparatus, the pressure roller is used as the member that comes into pressure contact with the overheating roller 5, but the present invention is not limited to this, and for example, a cleaning roller that comes into pressure contact with the heating roller may be used. Further, it is also possible to use a ceramic body as the heating element, and it is of course possible to use a breaker instead of the fuse.

FIG. 3 is a front view of the main part showing another embodiment, and the overall construction is the same as that shown in FIG. In this device, the bearing 2 that supports the heating roller 5
2 (only one of which is shown in the drawing) is attached with a supporting member 23 formed of a material that melts at a high temperature, and this portion is formed so as to abut the side plate 6a.

If the temperature of the heating roller is excessively increased without being controlled, the supporting member 23 is melted, and an electric current flows through the core metal 9a as in the case of the apparatus of the embodiment, so that the temperature of the heating roller 5 is further increased. Can be blocked.

FIG. 4 is a front view of a fixing device showing still another embodiment. In this case, the basic structure of the fixing device portion is the same as that of the above-mentioned embodiment device. The description of it is omitted.

In this apparatus, a conductive thin layer or coating 5a is formed on the inner surface of the heating roller 5,
The contacts 24 and 25 face the thin layer 5a from the side opening of the roller 5, and in the illustrated case, the contact 24 is in contact with the thin layer, and the contact 25 is disposed with a gap x therebetween. There is. The gap x in this case is smaller than the thickness t of the bearing 7a.

With such a structure, as in the case of the above-mentioned respective embodiments, when the heating roller is displaced by melting of its bearing, the contacts 24 and 2 arranged in parallel with the heater 2
5. An electric current flows through the conductive thin layer 5a to prevent the roller 5 from overheating.

In the fixing device having the above-described structure, silicon rubber, fluororubber, etc. are widely used as the pressure roller 9, but this roller is made of a material having a characteristic of melting or softening when an abnormal temperature rise occurs. It can be readily understood that the same effect can be obtained by the configuration.

[0022]

As described above, according to the present invention, temperature detecting members such as a thermoswitch and a thermal fuse are unnecessary, which greatly contributes to cost reduction, and scratches generated on the surface of the heating roller. It is possible to prevent the deterioration of the image quality due to the fall of the toner and the paper powder that adheres and accumulates.

[Brief description of drawings]

FIG. 1 is a sectional view of a fixing device showing an embodiment of the present invention.

FIG. 2 is a diagram showing an operation of the above.

FIG. 3 is a sectional view of an essential part showing another embodiment.

FIG. 4 is a sectional view showing still another embodiment.

FIG. 5 is a sectional view showing a known fixing device.

[Explanation of Codes] 1 Safety fuse 2 Halogen heater 3 Fixing device 5 Heating roller 5a Conductive thin layer 6 Cover 7a, 7b Bearing 8 Drive gear 9 Pressing roller 9a Core bar 10a, 10b Bearing 11a, 11b Spring 12, 13 Contact 15 thermistor 16 temperature control circuit 17 switch 22 bearing 23 support member 24, 25 contacts

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masao Amano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (6)

[Claims] 1. A heating roller provided with a heating source connected to a power source, and a pressure roller elastically pressed against the heating roller, and a transfer material carrying an unfixed toner image is passed through a pressing nip portion of both rollers. In the fixing device, the heating roller is supported by a resin bearing that softens or melts due to excessive temperature rise of the roller, and a power supply current flows when the heating roller is displaced by the softening or melting of the bearing. And a fixing device for an image forming apparatus, wherein the fixing device is arranged in parallel with the heating source. 2. The fixing device according to claim 1, wherein the parallel circuit formed by the displacement of the heating roller includes a conductive cored bar of the pressure roller. 3. The fixing device according to claim 1, wherein the parallel circuit formed by the displacement of the heating roller is a conductive thin layer formed on the heating roller. 4. A heating roller provided with a heating source connected to a power source, and a pressure roller elastically pressed against the heating roller, and a transfer material carrying an unfixed toner image is passed through a pressing nip portion of both rollers. In the fixing device, at least a part of the bearing that supports the heating roller is formed of a member that is softened or melted by excessive temperature rise of the roller, and the heating roller is formed by softening or melting the part of the bearing. A fixing device for an image forming apparatus, wherein a circuit for supplying a power supply current when displaced is arranged in parallel with the heating source. 5. The parallel circuit formed by the displacement of the heating roller is a conductive cored bar of the pressure roller.
The fixing device described. 6. The fixing device according to claim 4, wherein the parallel circuit formed by the displacement of the heating roller is a conductive thin layer formed on the heating roller.