JPH01156786A - Heat fixing device - Google Patents

Abstract

PURPOSE:To prevent the temperature of a heat generating roller from rising abnormally by providing a thermostat which turns off the power source when the surface temperature of the heat generating roller exceeds a prescribed value and further providing a cover which cuts off a flow of air to the thermostat. CONSTITUTION:The fixing heat roller 2 is heated by a halogen lamp 3, the surface temperature is detected by a thermistor 4, and a control circuit 6 controls a TRIAC 5 to hold the surface temperature constant. If the circuit 6 becomes faulty to hold the TRIAC 5 on and the temperature of the roll 2 exceeds a control range, the thermostat 9 operates to stop the power supply. Then the thermostat 9 is provided with the cover 10 which covers the part other than a surface facing the roller 2, so the thermostat is prevented from being cooled with a flow of air at the periphery of the roller 2. Consequently, the temperature of the heat fixing roller is prevented from rising up to dangerous temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a heat fixing device used in an electrophotographic apparatus.

BACKGROUND OF THE INVENTION An example of a conventional heat fixing device will be described below with reference to FIG. In FIG. 4, reference numeral 1 denotes a fixing pressing roll, which presses the fixing heat roll 2.

Reference numeral 3 denotes a halogen lamp having a length approximately equal to the length of the heat fixing roll 2. The halogen lamp 3 is inserted into the heat fixing roll 2 and heats the heat fixing roll 2. 4 is a thermistor, which is provided close to the surface of the fixing heat roll 2. 5 is a triac, which is connected in series with the halogen lamp 3. A control circuit 6 controls the triac 5 in accordance with the output signal of the thermistor 4. 7 is a power cable, and 8 is a power source.

A thermostat 9 is attached so as to be in contact with the surface of the fixing heat roll 2, and is connected in series to the power supply 8 and the triac 5.

In the conventional heat fixing device configured as described above, the heat fixing roll 2 is heated by the halogen lamp 3, and the heated fixing heat roll 2 and the fixing press roll 1 fix the toner on the copy paper. The temperature of the surface of the heat fixing roll 2 is detected by a thermistor 4, and the control circuit 6 controls the triac 5 based on the output signal of the thermistor 4 to maintain the temperature of the surface of the heat fixing roll 2 within a certain range.

In the unlikely event that the control circuit 6 or the like malfunctions and the triac 5 is left on and the temperature of the surface of the heat fixing roll 2 becomes higher than the above control range, the thermostat 9 adjusts the temperature of the heat fixing roll 2. The halogen lamp 3 is turned off and the supply of power to the halogen lamp 3 is stopped. This prevents the temperature of the heat fixing roll 2 from reaching a dangerous temperature.

Problems to be Solved by the Invention Electrophotographic apparatuses generally consume a large amount of power, and are often provided with a blower to cool internal components. Furthermore, even without a forced cooling device such as a blower, it is necessary to provide air holes in the case to cool the inside of the case. As described above, there is a flow of air inside the case of the electrophotographic device. In the conventional heat fusing device as described above, when there is an air flow near the fusing heat roll, the thermostat is cooled by this air flow, and even though the fusing heat roll reaches a dangerous temperature, There was a problem that the thermostat sometimes did not work.

The present invention solves the above problems and provides a heat fixing device having a safety device that ensures reliable operation.

Means for Solving the Problems In order to solve the above problems, the present invention connects a temperature responsive means in series with the heating source, which turns off when the temperature on the surface of the heating roller exceeds a specific value. A cover was provided to cover the surface of the temperature responsive means other than the surface facing the heat generating roller.

Effect: With the above-described means, the heat fixing device of the present invention prevents the temperature responsive means from being cooled by the cover even if there is an air flow near the heat fixing roll.

Embodiment Hereinafter, an embodiment of the heat fixing device of the present invention will be described with reference to FIGS. 1 to 3.

1 is a fixing pressing roll, which presses the fixing heat roll 2. Reference numeral 3 denotes a halogen lamp having a length approximately equal to the length of the heat fixing roll 2. The halogen lamp 3 is inserted into the heat fixing roll 2 and heats the heat fixing roll 2. 4 is a thermistor, which is provided close to the surface of the fixing heat roll 2. 5 is a triac, which is connected in series with the halogen lamp 3. A control circuit 6 controls the triac 5 in accordance with the output signal of the thermistor 4. 7 is a power cable, and 8 is a power source. A thermostat 9 is attached so as to be in contact with the surface of the fixing heat roll 2, and is connected in series to the power supply 8 and the triac 5. 10 is a cover;
The side facing the fixing heat roll 12 is open, and a thermostat 9 is installed inside the opening. Each of the above constituent members is provided in a case 12 having air circulation holes 11.

The operation of the heat fixing device of this embodiment configured as above will be explained.

The fixing heat roll 2 is heated by the halogen lamp 3,
The toner on the copy paper is fixed by the heat fixing heat roll 2 and the fixing press roll 1.

The temperature of the surface of the fixing heat roll 2 is detected by the thermistor 4, and the control circuit 6 is controlled based on the output signal of the thermistor 4.
controls the triac 5 to keep the temperature of the surface of the fixing heat roll 2 within a constant range.

In the unlikely event that the control circuit 6 or the like malfunctions and the triac 5 is left on and the temperature of the surface of the heat fixing roll 2 becomes higher than the above control range, the thermostat 9 adjusts the temperature of the heat fixing roll 2. The halogen lamp 3 is turned off and the supply of power to the halogen lamp 3 is stopped. This prevents the temperature of the heat fixing roll 2 from reaching a dangerous temperature.

At this time, the air near the heat fixing roll 2 is
The heat generated causes convection, and the air that has passed through the air holes 11 of the case 12 passes around the heat fixing roll 2. Even if there is air flow near the fixing heat roll 2 in this way,
The air inside the cover 10 remains stagnant, and the air flow near the fixing heat roll 2 causes the thermostat 9 to
is never cooled. Therefore, if the temperature of the surface of the heat fixing roll 2 becomes higher than the limit range, the thermostat 9 is turned off without too much delay, and the temperature of the heat fixing roll 2 does not rise to a dangerous temperature.

This operating state is shown in FIG. In FIG. 3, the vertical axis represents the temperature of the surface of the heat fixing roll 2, and the horizontal axis represents the time elapsed since the halogen lamp 3 was energized. As is clear from the graph in FIG. 3, in the conventional case, the thermostat 9 was activated 94 seconds after the halogen lamp 3 was energized. At this time, the temperature of the surface of the heat fixing roll 2 was 287 degrees. When the operating state of the present invention was measured using a thermostat with the same characteristics as this, the thermostat 9 was activated 74 seconds after the halogen lamp 3 was energized. Fixing heat roll 2 at this time
The surface temperature was 246 degrees.

As described in detail, the heat fixing device of the present invention includes a temperature responsive means that is turned off when the surface temperature of the heat generating roller exceeds a specific value, which is connected in series with the heat source, and the heat generated by the temperature responsive means is Since the cover is provided to cover the surface other than the surface facing the roller, even if there is an air flow near the heat fixing roll, the cover prevents the temperature response means from being cooled, and the temperature on the surface of the heat fixing roll 2 decreases. If becomes higher than the limit range,
The thermostat turns off without too much delay and the temperature of the thermal fuser roll does not rise to dangerous temperatures.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the heat fixing device of the present invention.
FIG. 2 is a perspective view of the main part, FIG. 3 is a characteristic diagram of the same, and FIG. 4 is a block diagram of a conventional heat fixing device. 1... Fixing pressing roll 2... Fixing heat roll 3... Halogen lamp 4... Thermistor 5... Triac 6... Control circuit 7... Power cable 8.
・・Power source 9・Thermostat 10・
...Name of cover agent Patent attorney Toshio Nakao and 18 others
Chichi [sect 0 Fig. 3 1-i et al.
't t <5ec) Figure 4

Claims (1)

[Claims] A heat generating roller having a heat source, a temperature detecting means for detecting the temperature of the surface of the heat generating roller, and a control means for controlling the current supplied to the heat source according to an output signal of the temperature detecting means are provided, A temperature responsive means that faces the roller and turns off when the temperature of the surface of the heat generating roller exceeds a specific value is connected in series with the heat source, and a surface of the temperature responsive means other than the surface facing the heat generating roller is connected in series with the heat source. A heat fixing device characterized by having a cover that covers the.