JP2727561B2 - Temperature control device protection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device of a heating device such as a fixing device of an electronic copying machine, and more particularly, to a protection device for preventing overheating of a heating device.

[Conventional technology]

For example, in a fixing device of an electronic copying machine, a heating roll and a pressure roll having a built-in heater are provided, and a paper is passed between the heating roll and the pressure roll, and the transferred image is heated and pressed. Has been established. In the fixing step of such a heat fixing device, the surface temperature of the heating roll is controlled to about 190 to 200 ° C. by a temperature control device.

As shown in FIG. 2, the temperature control device 9 includes a temperature sensor 6 provided on the surface of the heating roll 1, an electric circuit board 7 provided with a temperature control circuit, a solid state relay 8, and the like. The solid state relay 8 is connected in series with the heater 2 of the heating roll 1 and the current path of the AC power supply 3, and according to the surface temperature of the heating roll 1 detected by the temperature sensor 6, an electric circuit board 7 is provided. The on / off control of the solid state relay 8 controls the temperature of the heating roll 1. Further, a safety device 4 is provided to prevent the heating roll 1 from becoming abnormally high when the temperature control device 9 fails.

The safety device 4 includes a heating roll 1 as shown in FIG.
, And a thermostat, a temperature fuse, and the like, which are operated by radiant heat and convective heat from the heating roll 1, are connected in series to a current path of the heater 2 of the heating roll 1. Then, when the temperature control device 9 does not operate normally for some reason and the temperature of the heating roll 1 is going to become abnormally high, the increase of the radiant heat and the convective heat is detected, and the current of the heater 2 is detected. Block the passage,
I try to prevent overheating.

[Problems to be solved by the invention]

In the conventional safety device 4 described above, a large current flowing through the heater 2 flows through the thermostat or the thermal fuse as it is. Due to this large current, heat is generated in the safety device 4 or the like. Therefore, it is necessary to set the operating temperature of the safety device 4 in consideration of a temperature rise due to heat generation in the safety device 4 and the like, and it is necessary to set the operating temperature of the safety device 4 to a temperature equal to or higher than the actual control temperature. .

In addition, the amount of heat generated by the safety device 4 and the connection with the other wiring and the resulting temperature rise are greatly affected by changes in the electrical resistance value, current value, conduction time, heat capacity, and the like, and are unstable. For this reason, there is a possibility that a malfunction of the safety device 4 may be caused, and there is a problem that the function as a safety device for the temperature control device 9 cannot be reliably performed.

For example, if the safety device 4 is to be operated when the temperature of the heating roll 1 becomes T ° C., the temperature rise ΔT due to the heat generated by the safety device 4 or the like may be obtained if the set temperature is set to T ° C.
Therefore, the safety device 4 is activated before the temperature of the heating roll 1 reaches T ° C., that is, at (T−ΔT) ° C. Therefore, the operating temperature of the safety device 4 is set to a higher (T + ΔT) ° C. in consideration of the temperature rise ΔT of the safety device 4 and the like, and the safety device 4 is turned off when the temperature of the heating roll 1 reaches T ° C. It works. However, the temperature rise ΔT caused by the safety device 4 or the like is unstable as described above, and in some cases, the temperature rise in the safety device 4 or the like is not so large. In such a case, the safety device 4 does not operate until the temperature of the heating roll 1 becomes (T + ΔT) ° C., and the temperature of the heating roll 1 exceeds the upper limit, and not only the heater 2 itself is damaged, but also other There is a problem that the member is also damaged.

The present invention has been devised to solve the above-described problem, and has as its object to prevent heat generation in a safety device or the like and prevent malfunction of the safety device.

[Means for Solving the Problems] In the protection device for a temperature control device of the present invention, in order to achieve the above object, the temperature of the heating element is equal to or higher than a set temperature in a current path of the heating element to be temperature controlled. At the same time, a safety device that is opened by receiving heat from the heating element is connected in series, and a shunt circuit is connected in parallel to the safety circuit, and the shunt circuit is connected to the safety circuit from a current flowing through the heating element. A characteristic is that an open circuit is not formed with a current having a magnitude obtained by subtracting a current flowing through the device, but an open circuit is formed with a current flowing through the heating element.

Further, a fuse can be used as the shunt circuit.

[Action]

In the normal state, the current flowing through the heating element flows through the safety device and the shunt circuit separately. Therefore, the current flowing through the safety device is smaller than the current flowing through the heating element, and the amount of heat generated in the safety device or the like decreases. As a result, the temperature rise in the safety device is small, and the temperature at which the safety device operates can be set accurately.

Further, for example, when the temperature control device breaks down and the temperature of the heating element is going to be higher than the set temperature, the safety device operates and the current path of the heating element becomes an open circuit. Further, since the current path of the shunt circuit also becomes an open circuit in conjunction with the operation of the safety device, the current flowing through the heating element becomes completely zero, and the temperature of the heating element is prevented from further rising.

For example, if a fuse is used as a shunt circuit,
Due to the operation of the safety device, an excessive current flows into the fuse and the fuse is blown, and the current flowing through the heating element is completely blocked.

〔Example〕

Hereinafter, the features of the present invention will be specifically described based on embodiments with reference to the drawings.

FIG. 1 is an explanatory diagram showing a use state of the temperature control device in the present embodiment. Note that the same reference numerals are given to members and the like corresponding to the conventional temperature control device shown in FIG. 2, and description thereof is omitted.

This embodiment is different from the conventional example shown in FIG. 2 in that a fuse 5 is connected in parallel to the safety device 4.

Basically, similarly to the conventional example, the electric circuit board 7 is provided in accordance with the surface temperature of the heating roll 1 detected by the temperature sensor 6.
The on / off of the solid state relay 8 is controlled by controlling the current flowing through the heater 2 as a heating element to control the temperature of the heating roll 1 so that the surface temperature of the heating roll 1 becomes about 190 to 200 ° C. Temperature controlled.

Further, due to a failure of the temperature control device 9 or the like, the heating roll 1
When the temperature becomes abnormally high, the safety device 4 cuts off the current to the heater 2 to prevent overheating.

Here, in the present embodiment, a shunt circuit 10 having a fuse 5 is connected to the safety device 4 in parallel.

Now, the fusing current I _MAX in the fuse 5 of the shunt circuit 10
Assuming that the current flowing through the heater 2 is I _T and the current flowing through the safety device 4 is I _A , it is set as I _T −I _A <I _MAX <I _T.

Incidentally, when the current flowing through the fuse 5 and I _B, it is _{I A + I B = I T} .

That is, the current I _A flowing to the safety device 4 becomes smaller than the current I _T flows to the heater 2, thus, it is possible to suppress heat generation in the safety device 4. That is, since the amount of heat generated in the safety device 4 is affected by the square of the current, the amount of heat generated can be significantly reduced by slightly reducing the current.

Therefore, when setting the operating temperature of the safety device 4, the operating temperature of the safety device 4 can be accurately set without being affected by the heat generated in the safety device 4 itself and the connection portion. In addition, it is less susceptible to changes in the environment or changes over time in the safety device 4 itself.

When the temperature control device 9 breaks down and the heating roll 1 becomes abnormally high temperature, the safety device 4 is activated and the safety device 4 is activated.
0. The current I _A flowing to. Therefore, the heater 2
All current I _T flowing to flow into the fuse 5. Since the current flowing through the fuse 5 is larger than I _T next fusing current I _MAX, the fuse 5 is also blown, the current path of the heater 2 is completely blocked, abnormal overheating of the heating roll 1 is prevented. When the heater 2 is a tungsten lamp or the like, an inrush current of about 10 times the rated current flows at the start of energization. Therefore, it is necessary to determine the rating of the fuse 5 safety device 4 in consideration of this.

Note that a plurality of shunt circuits 10 may be provided, and all the shunt circuits 10 may be shut off in conjunction with the operation of the safety device 4. When a plurality of shunt circuits 10 are provided as described above, the current flowing through the safety device 4 is further reduced, so that heat generation in the safety device 4 can be further suppressed.

〔The invention's effect〕

As described above, according to the present invention, the current flowing through the heating element is divided and flows through the safety device. Therefore, heat generation in the safety device is significantly reduced, and the operating temperature of the safety device can be set accurately. Therefore, when the heating element is going to reach an abnormally high temperature, the current supply to the heating element can be stopped early, that is, before the temperature becomes too high, and no damage is caused to other parts.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a use mode of a temperature control device according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a use mode of a conventional temperature control device. 1: heating roll, 2: heating heater 3: AC power supply, 4: safety device 5: fuse, 6: temperature sensor 7: electric circuit board 8: solid state relay 9: temperature control device, 10: shunt circuit

Claims (2)

(57) [Claims] 1. A safety device which receives heat from a heating element and becomes an open circuit when the temperature of the heating element becomes equal to or higher than a set temperature is connected in series to a current path of the heating element whose temperature is controlled. At the same time, a shunt circuit is connected in parallel to the safety circuit, and a current having a magnitude obtained by subtracting a current flowing through the safety device from a current flowing through the heating element does not constitute an open circuit, but the heating element does not have an open circuit. A protection device for a temperature control device, characterized in that an open circuit is provided with a current flowing through the temperature control device. 2. The protection device for a temperature control device according to claim 1, wherein said shunt circuit is a fuse.