JPH0558544B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In a thermal fixing device that uses a thermistor whose resistance value has a negative temperature characteristic to measure the temperature of a heating roller, the thermistor is structurally connected to the main body by a connector. Since this disconnection of the connector causes thermal runaway of the heater, power is not supplied to the heater when the disconnection of the connector occurs.

[Industrial application field]

The present invention relates to a heat fixing device for fixing toner on paper in electronic printers, copying machines, etc., and in particular, the present invention relates to a heat fixing device for fixing toner on paper such as an electronic printer device or a copying device. Regarding an overheating prevention device.

In electronic printer devices, copying devices, etc., for example, a latent image is created on a photosensitive drum using light, toner is attached to this latent image, and this toner is transferred onto paper and heated by a heating roller or the like to print it on the paper. Printing and copying are performed by fixing this toner.

FIG. 3 is a diagram illustrating an example of a heat fixing device.

FIG. 3a is a cross-sectional view of the heat fixing device, where 1 is a heating roller, 2 is a heater that is the heat source of the heating roller 1,
For example, halogen lamps are used. Reference numeral 3 denotes a temperature detection section that measures the temperature of the heating roller 1, and a thermistor is used, for example.

Reference numeral 4 denotes a pressure roller which pinches the paper between it and the heating roller 1 and presses the paper against the heating roller 1. Reference numeral 5 denotes a feeding roller that feeds out the paper with toner attached between the heating roller 1 and the pressure roller 4. 6 is a cleaner that cleans the heating roller 1, and 7 is a discharge roller that discharges the paper. 8 is a stacker for holding paper.

FIG. 3b is a sectional view of the heating roller 1, in which a heater 2 is housed in the center of the heating roller 1. Power is supplied from a power source 9 so that 1 maintains a constant temperature.

In the thermal fixing device that performs fixing using the heating roller 1 as described above, the temperature of the heating roller 1 is measured and the power source 9 of the heater 2 used as a heat source is controlled. In order to reduce temperature ripples in this temperature detection, a thermistor that has a small heat capacity and a resistance that decreases as the temperature rises, and has a negative temperature characteristic, is usually used.

Therefore, if the apparent resistance of the thermistor is large due to breakage of the thermistor, etc., the heating roller 1
Since the temperature of the heater is determined to be low and power continues to be supplied to the heater, thermal runaway of the heater occurs.

By the way, due to the configuration of the heat fixing device, the temperature detection section 3
is connected to the main body by a connector, and disconnection of the connector also causes thermal runaway of the heater as described above, so it is desirable to detect disconnection of the connector and prevent power supply to the heater.

[Conventional technology]

Conventionally, indirect detection methods have been used to detect disconnection of a thermistor or disconnection of a connector, such as by determining whether or not there is a change in resistance of the thermistor within a certain period of time after power supply to the heater is started.

[Problem that the invention seeks to solve]

As mentioned above, the temperature detection unit 3 is connected to the main body by a connector, so it is often forgotten to attach this connector when assembling the device or during maintenance and inspection. Since it is an indirect method, there is a problem in that thermal runaway of the heater cannot be prevented and a failure occurs in the thermal fixing device.

In view of these problems, the present invention detects only disconnection of the thermistor connector by direct means, and blocks power supply to the heater.

[Means for solving problems]

FIG. 1 is a block diagram of a circuit showing one embodiment of the present invention.

11 is a connector for connecting the thermistor 3, 12
is an operational amplifier whose output becomes "1" when the temperature of thermistor 3 is, for example, 180°C or higher, that is, when the resistance of thermistor 3 is small, 13 is a NOR circuit, and 14 is a NOR circuit.
This is a driver that drives the driver 10 when the circuit 13 sends out "1", and 15 is a connector that connects the driver 10 to the driver 14.

If connector 11 is disconnected, NOR circuit 1
3 is configured such that the driver 14 does not drive the driver 10 by sending "0".

[Effect]

With the above configuration, even if the thermistor connector is disconnected, power is not supplied to the heater, thereby preventing thermal runaway of the heater and preventing human error such as forgetting to attach the connector during maintenance and inspection of the thermal fixing device. It is possible to prevent failures in the heat fixing device.

〔Example〕

In FIG. 1, as the temperature of the thermistor 3 increases, the resistance decreases and the current supplied from the power supply voltage E increases, so the voltage drop across the resistor _R3 increases and the potential at the - terminal of the operational amplifier 12 increases. descend. For example, assuming that the temperature of the heating roller 1 shown in FIG. In this case, “0” is sent.

The power supply voltage E is supplied to the NOR circuit 13 via the resistor _R1 , but since it is grounded via the connector 11, "0" is supplied. Therefore, NOR circuit 1
The output of 3 becomes "1" when the temperature is 180° C. or less, and the driver 14 drives the driver 10, which supplies the AC power source 9 to the halogen lamp 2.

When the temperature exceeds 180° C., the operational amplifier 12 outputs "1", the NOR circuit 13 outputs "0", and the driver 14 stops driving the driver 10.

When the heat fixing device is operated with the connector 11 disconnected, the power supply voltage E becomes "1" due to the resistor _R1 .
The signal is supplied to the NOR circuit 13. Therefore, NOR circuit 1
3, even if the operational amplifier 12 sends out a logical value of "1" or "0", its output remains "0".

Therefore, since the driver 14 does not drive the driver 10, the halogen lamp 2 is not heated and thermal runaway is prevented.

FIG. 2 is a block diagram of a circuit showing another embodiment.

Since the method of detecting the change in the resistance value of the thermistor 3 in Figure 2 is different from that in Figure 1, a NOT circuit 16 is added.
The logical value given to the NOR circuit 13 is inverted.

When the resistance of the thermistor 3 decreases, the voltage generated at the resistor R ₄ increases, and the operational amplifier 12 detects the potential of the + terminal and sends out "1" when the voltage reaches 180° C. or higher, for example. Since the NOT circuit 16 is sending out "0", the NOR circuit 13 is sending out "0".

When the operational amplifier 12 is sending out “0”,
The NOR circuit 13 sends out “1” and the driver 14
drives the driver 10.

If connector 11 is disconnected, NOT circuit 1
6 sends out "1". Therefore, the NOR circuit 13 is independent of the logical value sent out by the operational amplifier 12.
Send “0”.

〔Effect of the invention〕

As explained above, the present invention stops the power supply to the halogen lamp when the connector connecting the thermistor is disconnected, thereby preventing thermal runaway of the heater.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a circuit showing one embodiment of the present invention, Fig. 2 is a block diagram of a circuit showing another embodiment of the invention, and Fig. 3 is a diagram illustrating an example of a heat fixing device. . In the figure, 1 is a heating roller, 2 is a heater, and 3 is a heating roller.
is a temperature detection unit, 4 is a pressure roller, 5 is a feed roller, 6 is a cleaner, 7 is a discharge roller, 8 is a stacker, 9 is a power source, 10, 14 are drivers, 11,
15 is a connector, 12 is an operational amplifier, 13 is a
16 is a NOR circuit, and 16 is a NOT circuit.

Claims (1)

[Claims] 1. It has a first connection end with a first signal line connected to a power source and a second connection end with a second signal line connected to ground, and is heated by a heater 2. a thermistor 3 disposed near the member to be heated so as to detect a temperature change of the member to be heated; a first terminal for separating and connecting the first signal line; and a first terminal for separating and connecting the first signal line; a connector 11 having a second terminal to be separated and connected; a first signal line from the first terminal to the power source; and/or a second signal line from the second terminal to the ground. A heater 2 connected to the signal line of the thermistor 3 and installed on the heated member so that the temperature of the heated member reaches a predetermined temperature according to the detection result. between the first terminal and the first connection end, or between the second terminal and the second connection end,
A third signal line connected via a third terminal of the connector 11 and separated and connected by the connector 11; and a control means 14 controlling the heater 2 according to the potential on the third signal line. What is claimed is: 1. A heater overheat prevention device comprising: a detection means for preventing drive control of the heater;