JPH0756460A - Device for preventing temperature of fixing device from excessively rising - Google Patents

Abstract

PURPOSE:To prevent the occurrence of abnormality in a temperature controller, and to especially prevent a fixing roller from being burnt and damaged following the abnormality occurring in the temperature controller in the case of turning on a power source. CONSTITUTION:This device is provided with a means 5 for preventing temperature from being excessively rising which stops energizing to a heating element 2 for the fixing roller by making the temperature of a temperature sensing part 5 rise to a specified operating temperature, and also the temperature sensing part 5 is disposed proximately to the fixing roller 1. Furthermore, the device is provided with a heating element 6 for the temperature sensing part proximately to the temperature sensing part 5 whose temperature rises to equal to or more than the specified operating temperature of the means 5 and also whose heating is controlled by the temperature controller 11 in the case of turning on the power source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for preventing excessive temperature rise of a fixing device in an image forming apparatus such as a copying machine or a facsimile.

[0002]

2. Description of the Related Art Conventionally, as a fixing device in an image forming apparatus such as a copying machine or a facsimile, a heat roller type one in which a transfer sheet having a toner image transferred thereon is pressed by a heated fixing roller has been widely adopted. . Further, these fixing devices are provided with an excessive temperature rise preventing device for preventing the fixing roller from rising above a set temperature and causing a burnout accident or the like. There are various types of such an overheat prevention device, for example, Japanese Patent Laid-Open No. 61-
11775, JP-A-58-159565,
JP-A-59-38778 and JP-A-60-1026
No. 76, JP-A No. 58-159566 and the like.

Here, in the overheat prevention device disclosed in Japanese Patent Laid-Open Nos. 61-11775 and 58-159565, it is detected that the temperature of the fixing roller rises above a set temperature. An operating temperature sensitive element and a temperature fuse are arranged close to the fixing roller, and the energization to the fixing roller heater that heats the fixing roller by the operation of the temperature sensitive element and the temperature fuse is cut off. A heating means for heating the temperature-sensitive element and the temperature fuse when the power is turned on is provided, and the temperature-sensitive element and the temperature fuse are heated by the heating means immediately after the power is turned on so that the temperature-sensitive element and the temperature fuse immediately after the power is turned on. It is designed to improve operating performance.

On the other hand, JP-A-59-38778, JP-A-60-102676, and JP-A-58-1.
In the overheat prevention device disclosed in Japanese Patent No. 59566, a temperature fuse or the like, which operates when detecting that the temperature of the fixing roller has risen above a set temperature, is provided at a position separated from the fixing roller. The operation of the fixing roller heater, which heats the fixing roller by operation, is cut off. In order to operate the temperature fuse and the like, the temperature fuse and the like are heated by a heater that generates heat approximately in proportion to the heater for the fixing roller that heats the fixing roller.

[0005]

However, JP-A-61-161
In the overheat prevention device disclosed in Japanese Patent No. 11775 and Japanese Patent Laid-Open No. 58-159565, the temperature sensitive element and the thermal fuse are heated by the heating means only up to the operating temperature at which the energization is cut off. Therefore, immediately after the power is turned on, when the controller for controlling the heat generation of the fixing roller heater becomes abnormal and the fixing roller is overheated, the temperature fuse and the like are affected by the heat from the fixing roller and rise in temperature to the operating temperature. Therefore, there is a risk that the operation of the temperature fuse or the like tends to be delayed and the fixing roller burns out.

On the other hand, JP-A-59-38778, JP-A-60-102676, and JP-A-58-1.
In the overheat prevention device disclosed in Japanese Patent No. 59566, the heater for the fixing roller and the heater are controlled to generate heat in synchronization with each other, and the heater generates heat even when the temperature of the fixing roller is controlled to be constant. . However, since the temperature of the heater is not controlled, there is a risk that the temperature of the heater becomes unstable and the temperature fuse or the like malfunctions.
In addition, since the heater is constantly generating heat, power consumption is large.

[0007]

The invention according to claim 1 is
A fixing device having a fixing roller for heating and fusing and fixing a toner image transferred onto a transfer sheet, a heating roller for heating the fixing roller, and a temperature controller for controlling heat generation of the heating element for the fixing roller. Providing a temperature oversensing unit for shutting off energization to the fixing roller heating element when the temperature sensing unit rises to a predetermined operating temperature, and disposing the temperature sensing unit in proximity to the fixing roller. A heating element for a temperature sensing portion, which is heated to a temperature equal to or higher than the operating temperature of the overheat prevention means and whose heat generation is controlled by the temperature controller when the power is turned on, is provided close to the temperature sensing portion.

According to a second aspect of the present invention, in the first aspect of the invention, the heating element for the temperature sensing portion is made to generate heat from the time when the power is turned on to the time when the reload signal is generated.

[0009]

According to the first aspect of the invention, the temperature controller controls heat generation of the fixing roller heating element and heat generation of the temperature sensing section by the temperature controller when the power is turned on, and the temperature of the fixing roller and the temperature sensing section rises. To do. Here, if the fixing roller heating element and the temperature sensing element heating element generate heat continuously due to an abnormality in the temperature controller when the power is turned on, the temperature sensing element heating element prevents overheating. Since the temperature is set to rise above the operating temperature of the means, the temperature of the temperature sensing part heated by the heating element for the temperature sensing part rises to the operating temperature of the overheat prevention means in a short time, and Turn off the power to the heating element. Therefore, the energization time to the heating element for the fixing roller is shortened due to the occurrence of an abnormality in the temperature controller, and the energization to the heating element for the fixing roller is cut off before the fixing roller becomes overheated, causing the fixing roller to burn out. Is prevented.

According to the second aspect of the present invention, since the temperature sensing element heating element is set so as to rise in temperature above the operating temperature of the overheat prevention means, the heating value from the temperature sensing element heating element is set. Is large, even if the heat generation control of the temperature sensing element heating element is short after the power is turned on until the reload signal is generated, the temperature sensing element is in a sufficient residual heat state, and the temperature sensing element heating element generates heat. Power consumption is reduced because the energization time for the operation is short.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. First, FIG. 2 is a front view showing a main part of a fixing device according to the present invention. A fixing roller 1 for heating and melting and fixing a toner image transferred onto a transfer paper (not shown) is provided. The fixing roller 1 is provided with a halogen heater 2 which is a heating element for the fixing roller for heating the fixing roller 1, and the fixing roller 1 is provided on the outer phase surface of the fixing roller 1.
Is in contact with the thermistor 3 for measuring the temperature. Also,
A bracket 4 is provided in a position close to the fixing roller 1, and the bracket 4 is a temperature-sensing unit that melts and cuts off electricity to the halogen heater 2 when the temperature rises to a predetermined operating temperature. At the same time, a temperature fuse 5, which is means for preventing excessive temperature rise, and a ceramics heater 6, which is a heating element for the temperature sensing unit, which heats the temperature fuse 5, are supported. The thermal fuse 5 and the ceramic heater 6 are provided close to each other, and the thermal fuse 5 is covered with a protective tube 7. Further, the ceramic heater 6 is set to be able to rise above the operating temperature of the thermal fuse 5.

Next, FIG. 1 shows a circuit diagram of the present invention. The halogen heater 2 and the ceramic heater 6 are connected in parallel to an AC power source 8 to turn the halogen heater 2 on and off. SSR (Solid State Relay)
9 and a switch 10 for turning on / off the ceramic heater 6 are provided. Further, the temperature fuse 5 is connected in series to the halogen heater 2 and the ceramic heater 6. Further, the thermistor 3
Is connected to a CPU 11 which is a temperature controller, and the SSR 9 and the switch 10 are connected to the CPU 11.

In such a structure, when the power switch of the image forming apparatus equipped with this fixing device is turned on, C
The SSR 9 and the switch 10 are turned on by the control of the PU 11, and the halogen heater 2 and the ceramics heater 6 are turned on.
Energization to and is started. In addition, a signal from the thermistor 3 which measures the temperature of the fixing roller 1 is input to the CPU 11.

Here, FIG. 3 is a graph showing the temperature changes of the fixing roller 1, the ceramics heater 6 and the thermal fuse 5 after the power switch is turned on.
The temperature of the fixing roller 1 rises as the halogen heater 2 is energized, the temperature of the ceramic heater 6 rises as the ceramic heater 6 is energized, and the temperature of the thermal fuse 5 heated by the ceramic heater 6 rises. To rise. Then, when the CPU 11 detects from the signal from the thermistor 3 that the temperature of the fixing roller 1 has risen to the fixing roller control temperature (specifically, 185 ° C.), a reload signal (copy enable signal) is output and this reloading is performed. When a signal is present, the switch 10 is turned off and the ceramic heater 6 is de-energized. Further, while the reload signal is present, the SSR 9 is on / off controlled by the signal from the thermistor 3, and the temperature of the fixing roller 1 is maintained at substantially the fixing roller control temperature. When the reload signal is output, the temperature fuse 5 has not risen to the operating temperature at which the energization is cut off.

After the power supply to the ceramics heater 6 is cut off, the temperature of the ceramics heater 6 is lowered and the temperature of the thermal fuse 5 is slightly increased due to the influence of heat from the fixing roller 1. Eventually, the ceramics heater 6 is heated. And the temperature fuse 5 are maintained at a temperature slightly lower than the fixing roller control temperature.

Next, a case where the CPU 11 has an abnormality and a reload signal is not output when the power switch is turned on will be described with reference to FIG. Since the reload signal is not output even if the temperature of the fixing roller 1 rises to the fixing roller control temperature, the switch 10 is maintained in the ON state and the ceramic heater 6 is continuously energized and S
SR9 is maintained in the ON state and the halogen heater 2 continues to be energized. Therefore, the temperature of the fixing roller 1 gradually rises above the fixing roller control temperature, the temperature of the ceramics heater 6 also rises, and the temperature of the thermal fuse 5 heated by the ceramics heater 6 also rises.

When the temperature fuse 5 is blown by raising the temperature of the temperature fuse 5 up to the operating temperature (specifically, about 200 ° C.), the halogen heater 2 and the ceramic heater 6 are de-energized. The temperatures of the fixing roller 1 and the ceramic heater 6 gradually decrease.

Here, since the ceramic heater 6 is set to rise above the operating temperature of the thermal fuse 5, the CPU 11 is turned on when the power switch is turned on.
When an abnormality occurs, the temperature fuse 5 is abruptly heated to the operating temperature by being heated by the ceramics heater 6 and melted. Therefore, the time for heating the fixing roller 1 by the halogen heater 2 is shortened and the fixing roller 1 is heated. Energization to the halogen heater 2 is cut off before the temperature rises too much, and the fixing roller 1 is prevented from being overheated and burned out.

Here, the broken line in FIG. 4 shows the temperature change state between the temperature fuse and the fixing roller when the ceramic heater 6 is not provided. The temperature fuse rises in temperature due to the heat of the fixing roller. Therefore, the rate of increase will be moderate. Then, when the temperature fuse rises to the operating temperature and melts down, the temperature of the fixing roller 1 remarkably rises and a burnout accident occurs. Incidentally, in the overheat prevention device disclosed in Japanese Patent Laid-Open No. 61-11775 and Japanese Patent Laid-Open No. 58-159565, a CPU is used.
Since the temperature rise of the thermal fuse at the time of the occurrence of the abnormality is as shown by the one-dot chain line, the thermal fuse 5 of this embodiment is
It takes a longer time to reach the operating temperature, and the temperature of the fixing roller rises accordingly, which increases the risk of a burnout accident.

Further, since the energization time to the ceramic heater 6 is a short time after the power switch is turned on until the reload signal is output, the power consumption is reduced.
In addition, the amount of heat generated by the ceramics heater 6 is large even in such a short-time energization, and the thermal fuse 5 is in a sufficiently residual heat state. Therefore, even if the CPU 11 causes an abnormality immediately after the switch 10 is turned off and the temperature of the fixing roller 1 rises above the fixing roller control temperature, the temperature fuse 5 that has been sufficiently preheated is discharged from the fixing roller 1. The temperature sensitively rises due to the influence of heat, and the fixing roller 1 reaches the operating temperature and melts before it reaches a temperature causing a burning accident. Therefore, the switch 10 is turned off and the ceramic heater 6
Even if an abnormality of the CPU 11 occurs after the power supply to the fixing roller 1 is cut off, the occurrence of a burnout accident of the fixing roller 1 is prevented.

In this embodiment, the temperature fuse 5 that blows when the temperature rises to the operating temperature has been described as an overheat prevention means, but the energization is cut off when the temperature rises to the operating temperature. A thermostat may be used as the temperature rise prevention means which is also a temperature sensing part.

In the present embodiment, the temperature fuse itself has been described as an example of the temperature fuse 5 which is a means for preventing the temperature from rising, but a temperature sensor is provided as the temperature sensing unit and the detection result from this temperature sensor is provided. It is also possible to provide an energization cutoff control unit for cutting off the energization to the halogen heater 2 based on the above, and to form an overheat prevention unit by these temperature sensors and the energization cutoff unit.

[0023]

As described above, according to the first aspect of the present invention, a fixing roller for heating and fusing a toner image transferred onto a transfer sheet to fix the toner image, a heating roller for the fixing roller for heating the fixing roller, and In a fixing device having a temperature controller for controlling heat generation of a heating roller for a fixing roller, an excessive temperature rise preventing means for shutting off energization to the heating element for the fixing roller when the temperature-sensing portion rises to a predetermined operating temperature. A heating element for the temperature sensing portion, which is provided and the temperature sensing portion is disposed in the vicinity of the fixing roller so that the temperature rises above the operating temperature of the overheat prevention means and the heat generation is controlled by the temperature controller when the power is turned on. Since the temperature sensor is provided close to the temperature-sensing unit, the temperature of the fixing roller and that of the temperature-sensing unit continuously generate heat due to an abnormality in the temperature controller when the power is turned on. If the temperature rises, the temperature of the temperature-sensitive part heated by the temperature-sensitive part heating element rises above the operating temperature of the overheat prevention means, so that the energization to the fixing roller heating element can be cut off. Since the temperature sensing element heating element is set to rise above the operating temperature of the temperature rise prevention means, the temperature sensing element heated by the temperature sensing element heating element is heated to the operating temperature in a short time. Therefore, it is possible to shorten the energization time to the heating roller for the fixing roller due to the occurrence of an abnormality in the temperature controller when the power is turned on, and to energize the heating element for the fixing roller before the fixing roller is heated. It is possible to reliably prevent the occurrence of a burnout accident of the fixing roller by shutting off.

According to the invention of claim 2, as described above, in the invention of claim 1, the heating element for the temperature sensing portion is caused to generate heat from the time the power is turned on to the time the reload signal is generated. It is possible to reduce the power consumption by shortening the time for which the heating element for heat generation is energized for heat generation, and to increase the temperature of the heating element for temperature sensing part above the operating temperature of the overheat prevention means. Since the temperature is set, the amount of heat generated from the temperature sensing element heating element is large, and even if the heat generation control of the temperature sensing element heating element is short after the power is turned on until the reload signal is generated, It is possible to make a sufficient residual heat state.Therefore, even if the temperature controller malfunctions and the temperature of the fixing roller rises during the work after the power is turned on, The temperature is sensitive to the influence of heat from the fixing roller. To reach quickly the operating temperature was raised, an effect such as can be the temperature controller during operation after power-on is reliably prevented the occurrence of burnout accident even fixing roller a case of occurrence of abnormality.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a front view showing a main part.

FIG. 3 is a graph showing a temperature change state of the fixing roller, the ceramics heater, and the temperature fuse after the power switch is turned on.

FIG. 4 is a graph showing a temperature change state of the fixing roller, the ceramics heater, and the temperature fuse when the CPU has an abnormality after the power switch is turned on.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Heating element for fixing roller 5 Temperature sensing part, overheating prevention means 6 Heating element for temperature sensing part 11 Temperature controller

Claims (2)

[Claims] 1. A fixing roller for heating and melting and fixing a toner image transferred on a transfer paper, a heating roller for a fixing roller for heating the fixing roller, and a temperature controller for controlling heat generation of the heating element for the fixing roller. In the fixing device having the above-mentioned, the temperature-sensing portion is provided with an excessive temperature rise preventing means for shutting off energization to the heating element for the fixing roller when the temperature rises to a predetermined operating temperature, and the temperature-sensing portion is close to the fixing roller. And a heating element for a temperature sensing portion, which is heated above the operating temperature of the overheating prevention means and whose heat is controlled by the temperature controller when the power is turned on, is provided close to the temperature sensing portion. A device for preventing excessive temperature rise of the fixing device. 2. The overheat prevention device for a fixing device according to claim 1, wherein the heating element for the temperature sensing section is caused to generate heat from the time the power is turned on to the time the reload signal is generated.