JPH10312131A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of a fixing roller by putting off the time when scratch and wear on the fixing roller occur due to a thermometal cut-out pressing it firmly. SOLUTION: In the fixing device 10 having the fixing roller 3 stored in frame bodies 1 and 2, a halogen heater (heating means) 4 for heating the fixing roller 3, and the thermometal cut-out 6 for cutting off the supply of power to the halogen heater 4 when the temperature of the fixing roller 3 exceeds a specific value, a solenoid 8 (firmly-pressing/separating means) is provided for pressing the thermometal cut-out 6 to the fixing roller 3 firmly or separating it therefrom. When the temperature of the thermometal cut-out 6 is below the specific value, the thermometal cut-out 6 is firmly pressed to the fixing roller 3, and when it its above the specific value, the thermometal cut-out 6 is separated from the fixing roller 3. This shortens the length of time that the thermometal cut-out 6 is firmly pressed to the fixing roller 3, and makes an improvement in the durability of the fixing roller 3, whereby the time when scratch and wear on the fixing roller 3 occur due to the thermometal cut-out 6 firmly pressing it is put off drastically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device having a thermoswitch for cutting off power supply to the heating means when the temperature of a fixing roller becomes a predetermined value or higher.

[0002]

2. Description of the Related Art A fixing device is provided in an image forming apparatus such as a copying machine. An unfixed image transferred onto a transfer material through a predetermined image forming process is heated and pressed by the fixing device to transfer the image. It is fixed as a permanent image on the material.

As shown in FIG. 10, a fixing device 110 has a fixing roller 103 and a pressure roller 105 which rotate in pressure contact with each other, and the fixing roller 103 is heated by a halogen heater 104 incorporated therein. And the power supply to the halogen heater 104 is turned ON / O.
By performing the FF, the temperature is maintained at a predetermined temperature optimal for fixing. If the halogen heater 104 malfunctions and remains ON due to malfunction, the fixing roller 103 may be overheated and generate smoke, and a thermoswitch 106 is provided to prevent this. The thermoswitch 106 turns off the power supply to the halogen heater 104 when detecting a predetermined temperature or higher.

Conventionally, in order to prevent the abrasion of the fixing roller 103 due to the pressure contact of the thermoswitch 106 and the occurrence of scratches due to dust entering between the fixing roller 103 and the thermoswitch 106, the thermoswitch 106 is provided as shown in FIG. It was attached separately from the fixing roller 103.

[0005]

However, when the thermoswitch 106 is mounted at a distance from the fixing roller 103 as described above, when the thermoswitch 106 is operated from a state in which the fixing device 110 is completely cooled, it is difficult to perform the operation. As shown in FIG. 11, the temperature of the fixing roller 103 is equal to the specified temperature t at time a _1.
1 , but the thermo switch 106
In order to spaced apart from 3 times a ₁ to a lower temperature t ₂ than the temperature t ₁ only not increased, the temperature of the thermal switch 106 is increased with increasing temperature around the subsequent thermoswitch 106 , the temperature of the thermoswitch 106 is stabilized becomes t ₃ at time a _2.

Here, if the temperature control of the fixing device 110 becomes impossible and the power supply to the halogen heater 104 is continued in this state, as shown in FIG.
The temperature of 3 rises sharply. Temperature thermoswitch 106 at the time of the temperature maximum desired temperature t ₄ to reach the time a ₁ of the fixing roller 103 is a t _5, the stable temperature t ₃
Lower than, never thermoswitch 106 is turned off, the temperature of the fixing roller 103 at the time of time the operating temperature of the thermoswitch 106 is turned (slightly higher than t ₃₎ t ₆ a ₄ is a t ₇ The fixing roller 103
The surrounding members become high heat, and the surrounding members are required to have high heat resistance and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object thereof is to extend the time required for the fixing roller to be damaged or worn due to the pressure contact of the thermoswitch, thereby increasing the durability of the fixing roller. An object of the present invention is to provide a fixing device capable of improving the performance.

[0008]

According to a first aspect of the present invention, there is provided a fixing roller housed in a frame, a heating unit for heating the fixing roller, and a fixing roller for controlling the temperature of the fixing roller. In a fixing device having a thermo switch that cuts off power supply to the heating unit when the temperature exceeds a predetermined value, a pressure contact / separation unit that presses or separates the thermo switch from or to the fixing roller is provided. I do.

According to a second aspect of the present invention, in the first aspect of the invention, the pressure contact / separation means presses the thermoswitch to a fixing roller when the temperature of the thermoswitch is equal to or lower than a predetermined value. In the above case, the thermoswitch is separated from the fixing roller.

According to a third aspect of the present invention, in the first or second aspect, a temperature detecting means for detecting a temperature of the thermoswitch is provided.

According to a fourth aspect of the present invention, in the first, second, or third aspect, the frame is a mold frame.

Therefore, according to the present invention, the thermoswitch is pressed against the fixing roller only during the initial heating of the fixing roller, and when the temperature of the thermoswitch reaches a predetermined temperature or higher, the thermoswitch is separated from the fixing roller. The time during which the fixing roller is pressed against the fixing roller is shortened, and the time until the fixing roller is scratched or worn due to the pressing of the thermoswitch is extended, so that the durability of the fixing roller can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIGS. 1 and 2 are sectional views of a fixing device according to a first embodiment of the present invention, and FIGS. 3 to 7 are diagrams showing temperature changes of a fixing roller and a thermoswitch.

A fixing device 10 shown in FIGS. 1 and 2 includes a fixing roller 3 and a pressure roller 5 which rotate in a pressed state with each other in frames 1 and 2. Is built-in.

By the way, the thermoswitch support plate 7 is inserted into the frames 1 and 2 from the opening 1a formed on the upper surface of the frame 1.
Is inserted, and an end of the thermoswitch support plate 7 is supported rotatably about a fulcrum 7a. And
A thermoswitch 6 is mounted on a portion of the thermoswitch support plate 7 near the fulcrum 7a.

On the other hand, a solenoid 8 is installed above the frame 1, and the other end of the thermoswitch support plate 7 is connected to a rod 8a of the solenoid 8. The intermediate portion of the thermoswitch support plate 7 is urged by a spring 9 in the clockwise direction in the figure (the direction in which the thermoswitch 6 is separated from the fixing roller 3) around the fulcrum 7a. In addition, a stopper 11 for restricting the rotation of the thermoswitch support plate 7 is attached to a corner portion in the frame 1.

The thermoswitch 6 is a bimetal type thermoswitch.
When the temperature of the bimetal becomes higher than a certain temperature, it deforms, cuts off the electric circuit and cuts off the current to the halogen heater 4 (O
FF).

In the fixing device 10 having the above structure, when the fixing roller 3 is heated to a certain temperature from a state where the fixing device 10 is cooled, the solenoid 8 is turned on, and the rod 8a is moved by the arrow in FIG. Drawn in the direction. Then, as shown in FIG. 1, the thermoswitch support plate 7 rotates counterclockwise around the fulcrum 7 a against the urging force of the spring 9 to press the thermoswitch 6 against the fixing roller 3.

Here, the temperature of the thermoswitch 6 becomes t _{8 by the} time a ₅ shown in FIG. Turned OFF solenoid 8 at the point of this time a _5, thermal switch support plate 7 as shown in FIG. 2 is rotated in the clockwise direction about the fulcrum 7a by the urging force of the spring 9, abuts stop the stopper 11 The thermoswitch 6 is separated from the fixing roller 3 to perform the operation.

[0021] In Thus, the thermo-switch 6 as described above is separated from the fixing roller 3, the temperature of the thermal switch 6 as shown in FIG. 3 is changed to t ₈ ~t ₃ during a ₅ ~a ₁ .

If the halogen heater 4 runs away,
The temperature of the fixing roller 3 temperature t ₂ ~t ₄ as shown in FIG. 4
(Maximum desired temperature). At this time, the temperature of the thermal switch 6 is changed to t ₃ ~t _9, this time, by setting the operating temperature of the thermal switch 6 to t _9, power supply to the halogen heater 4 is cut off (OFF).

Also, when the halogen heater 4 runs away after the fixing roller 3 reaches the temperature t ₂ and the thermo switch 3 reaches the constant value of the temperature t ₃ , as shown in FIG.
Temperature is the temperature of the thermal switch 6 to t ₉ at the point of time a ₈ reaching t _4, the power supply to the halogen heater 4 is cut off (OFF).

Although the temperature rise of the thermoswitch 6 due to the temperature rise around the thermoswitch 6 has not been described above, the temperature rise of the thermoswitch 6 due to the temperature rise around the thermoswitch 6 does not occur. This does not occur if the amount of heat released matches the amount of heat received by the thermoswitch 6 due to a rise in ambient temperature.

However, in some cases, as shown in FIG.
Temperature of the thermo switch 6 under the influence of the ambient temperature from ₅ the time of the drops once, the temperature rises after the temperature reached t _10,
Temperature thermoswitch 6 is t ₃ at time a _9. In such a case, for example, as shown in FIG. 7, delaying the timing of thermo-switch 6 is separated from the fixing roller 3, a high temperature of the thermo switch 6 than t ₃ t ₁₁
It may lower the temperature of the thermal switch 6 to t ₃ by separating the thermoswitch 6 from the fixing roller 3 at time a ₁₀ to reach.

As described above, the temperature change of the thermoswitch 6 can be adjusted by adjusting the timing at which the thermoswitch 6 is separated from the fixing roller 3.

In this embodiment, the fixing roller 3
The thermoswitch 6 is pressed against the fixing roller 3 only at the time of the initial heating, and the thermoswitch 6 is separated from the fixing roller 3 when the temperature of the thermoswitch 6 reaches a predetermined temperature or higher. The time required for the fixing roller 3 to be damaged or worn due to the pressing of the thermoswitch 6 is greatly extended, and the durability of the fixing roller 3 is improved.

If a temperature detecting means is provided directly or in the vicinity of the thermoswitch 6 and the timing of separating the thermoswitch 6 from the fixing roller 3 is adjusted based on the temperature detected by the temperature detecting means, the thermoswitch 6 Can be more accurately adjusted.

In a fixing device of a copying machine, for example, the power supply to the halogen heater is usually started when the power is turned on, but thereafter, the fixing roller is started so that copying can be performed immediately even when the copying operation is not performed. 3 is maintained at a constant temperature, and the temperature around the thermoswitch is also set to a high temperature. Therefore, the operation described above may be performed only when the power is turned on.

The frames 1 and 2 of the fixing device 10 should be formed of a mold frame having a low heat radiation so as to enhance the heat retention around the thermoswitch 6. That is, the frame bodies 1 and 2
Is made of a sheet metal or the like having high heat dissipation, heat inside the frames 1 and 2 escapes to the outside, and it takes a long time for the thermoswitch 6 to reach a certain temperature.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS. 8 and 9 are cross-sectional views of a fixing device according to Embodiment 2 of the present invention. In these drawings, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals. Hereinafter, a repetitive description thereof will be omitted.

In the present embodiment, the shape memory alloy 12 is provided so as to abut against the thermoswitch support plate 7, and the thermoswitch support plate 7 presses the thermoswitch 6 against the fixing roller 3 by a spring 13 (the fulcrum 7 a). Counterclockwise around the center).

As shown in FIG. 8, when the shape memory alloy 12 is heated from the state where the thermoswitch 6 is pressed against the fixing roller 3 and its temperature reaches a certain value, the shape memory alloy 12 Deforms to a pre-stored shape,
As shown in FIG. 9, the thermoswitch support plate 7 is pushed in the direction of the arrow. Then, the thermoswitch support plate 7 rotates clockwise around the fulcrum 7a against the urging force of the spring 13 until it comes into contact with the stopper 11, so that the thermoswitch 6 attached to the thermoswitch support plate 7 is moved. It is separated from the fixing roller 3.

Therefore, according to the present embodiment, since the shape memory alloy 12 is deformed by being heated by the heat from the fixing roller 3, an electric means for operating the solenoid 8 as in the first embodiment is used. Is unnecessary, and there is no need to provide a temperature detecting means directly or in the vicinity of the thermoswitch 6.

Incidentally, instead of the shape memory alloy 12, a bimetal made of two metals having different thermal expansion coefficients can be used.

[0036]

As is apparent from the above description, according to the present invention, the thermoswitch is pressed against the fixing roller only during the initial heating of the fixing roller, and when the thermoswitch reaches a predetermined temperature or higher, the thermoswitch is released from the fixing roller. The distance between the thermoswitch and the fixing roller is shortened due to the separation, and the time until the fixing roller is damaged or worn due to the pressing of the thermoswitch is extended to improve the durability of the fixing roller. Is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fixing device (thermoswitch pressed state) according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the fixing device (thermoswitch separated state) according to the first embodiment of the present invention.

FIG. 3 is a diagram showing temperature changes of a fixing roller and a thermoswitch in the fixing device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing temperature changes of a fixing roller and a thermoswitch in the fixing device according to the first embodiment of the present invention.

FIG. 5 is a diagram showing temperature changes of a fixing roller and a thermoswitch in the fixing device according to the first embodiment of the present invention.

FIG. 6 is a diagram showing temperature changes of a fixing roller and a thermoswitch in the fixing device according to the first embodiment of the present invention.

FIG. 7 is a diagram showing temperature changes of a fixing roller and a thermoswitch in the fixing device according to the first embodiment of the present invention.

FIG. 8 is a cross-sectional view of a fixing device (thermoswitch pressed state) according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view of a fixing device (thermoswitch separated state) according to Embodiment 2 of the present invention.

FIG. 10 is a sectional view of a conventional fixing device.

FIG. 11 is a diagram showing temperature changes of a fixing roller and a thermoswitch in a conventional fixing device.

FIG. 12 is a diagram showing temperature changes of a fixing roller and a thermoswitch in a conventional fixing device.

[Explanation of symbols]

 1, 2 Frame 3 Fixing Roller 4 Halogen Heater (Heating Means) 5 Pressure Roller 6 Thermoswitch 7 Thermoswitch Support Plate 8 Solenoid (Pressing / Separating Means) 9, 13 Spring 10 Fixing Device 11 Stopper 12 Shape Memory Alloy (Pressing Contact)・ Separation means)

Claims (4)

[Claims] 1. A fixing roller housed in a frame, a heating unit for heating the fixing roller, and a thermoswitch for shutting off power supply to the heating unit when the temperature of the fixing roller becomes equal to or higher than a predetermined value. The fixing device according to claim 1, further comprising a pressing / separating unit that presses or separates the thermoswitch with respect to the fixing roller. 2. The pressure contact / separation means presses the thermoswitch to the fixing roller when the temperature of the thermoswitch is equal to or lower than a predetermined value, and separates the thermoswitch from the fixing roller when the temperature of the thermoswitch is equal to or higher than the predetermined value. The fixing device according to claim 1, wherein: 3. The fixing device according to claim 1, further comprising a temperature detection unit that detects a temperature of the thermoswitch. 4. The fixing device according to claim 1, wherein the frame is a mold frame.