JPH0631495Y2 - Abnormality prevention device for fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fixing device used in an image forming apparatus or the like, and more particularly to a device for preventing the fixing device from being in an abnormal temperature state.

<Prior Art> In the fixing device, the fixing heater is also turned on after the power is turned on, and the control unit waits for the fixing temperature to reach the reference temperature and then sets the ready state (image forming operation possible state).

In such a fixing device, as shown in FIG. 5, a thermistor for detecting the temperature in order to keep the temperature of the fixing roller constant and a triac as a control element 41 for controlling the energization amount of the heater 40 are used.

<Problems to be Solved by the Invention> However, as shown in FIG.
In a fixing device whose temperature is controlled by and, if foreign matter (copy paper, toner, etc.) enters the contact surface between the thermistor and the fixing roller, even if the temperature of the fixing roller reaches the reference temperature, that temperature is correctly transmitted to the thermistor. There will be cases where there are no cases. Then, the temperature of the fixing roller is likely to rise abnormally.

Therefore, generally, the primary side circuit 4 that drives the heater 40
A temperature fuse or a thermal protector 43 is connected to the inside of the device 2 to prevent the fixing roller 40 from being energized when the temperature of the fixing roller rises abnormally.

However, since the overheat prevention device 43 is used in the primary side circuit 42, it is necessary to separate it from the surface of the fixing roller by 4 mm or more by the electrical equipment control method. Therefore, the temperature detection becomes inaccurate, and at the time when the overheat prevention device 43 operates, the roller and the bearings around it are deformed and deteriorated by heat, and the entire fixing device is greatly damaged. It often costs money.

Therefore, in view of the above problems, the present invention has an object to provide an abnormality prevention device that can be easily restored even when a trouble occurs in the fixing device.

<Means for Solving Problems> In the fixing device 4 having the fixing heater 14 for heating the fixing roller body 13 as shown in FIGS. A control circuit A for controlling the primary side circuit 15 for controlling the primary side circuit 15 and the primary side circuit 15 for connecting the power source VAC and the fixing heater 14 to each other is provided. In the primary side circuit 15, an excessive temperature rise preventing device 17 that melts and cuts off the energization to the fixing heater 14 when the fixing roller body 13 is overheated, and the fixing is performed by an output signal from the secondary side circuit 16. Roller body 13
The control element 18 for controlling the fixing heater 14 and the relay contacts 20 and 21 which are turned off by demagnetizing the relay coil 19 of the secondary side circuit 16 make the fixing heater 14
Which is connected in series to the secondary side circuit 16 has a contact 23a which is opened in the relay drive circuit 22 for driving the relay coil 19 before the melting temperature of the overheat protection device 17 is exceeded. The detection device 23 is connected,
The abnormal temperature detection device 23 is the fixing roller body 13
It was placed close to.

<Operation> In the above problem solving means, when the fixing heater 14 heats the fixing roller body 13 after the power is turned on and the surface temperature of the roller body 13 reaches the reference temperature, the control element 18 in the primary side circuit 15 Output is controlled, heater 14
Energization is controlled.

At this time, if foreign matter (copy paper, toner, etc.) enters the contact surface between the temperature detecting element 15a and the roller body 13,
Even if the surface temperature of the roller body 13 reaches the reference temperature, the temperature is not properly transmitted to the temperature detecting element 15a.
In addition, if the control element 18 fails and the heater 14 is energized and becomes abnormal, the roller body 13
And the temperature of the heater 14 rises, and the fixing device 4 becomes in a dangerous state.

Then, before the temperature of the roller body 13 exceeds the fusing temperature of the overheat prevention device 17, the contact 23a of the abnormal temperature detection device 23 comes off, the relay coil 19 of the relay drive circuit unit 22 is demagnetized, and the relay contacts 20, 21. Turns off and the heating of the heater 14 is stopped.

Therefore, the heating of the heater 14 is stopped by the time the excessive temperature rise prevention device 17 melts, so that damage to the fixing device 4 can be reduced.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a control circuit diagram of an abnormality prevention device for a fixing device showing an embodiment of the present invention, FIG. 2 is a configuration diagram of a main part of the fixing device, FIG. 3 is a functional block diagram thereof, and FIG. FIG. 1 is a schematic configuration diagram of a copying machine to which the fixing device abnormality prevention device of the present invention is applied.

Generally, in a copying machine, as shown in FIG. 4, a photoconductor drum 2, an optical device 3 for performing image formation exposure on the photoconductor drum 2, and a fixing device 4 for fixing an image are arranged inside a copying machine main body 1. Around the photosensitive drum 2, a main charger 5, a developing device 6, a transfer / separation charger 7 and a cleaner 8 are arranged. Further, a paper feed cassette 9 is attached to the lower portion of the copying machine main body 1 on the paper feed side, and a paper ejection unit 10 is provided on the paper ejection side of the copier main body 1.

The fixing device 4 has a pair of upper and lower fixing rollers 11 and 12 arranged on the photoconductor 2 side, and the upper fixing roller 11 is a hollow fixing member having a Teflon coated surface as shown in FIG. The roller main body 13 and a fixing heater 14 arranged inside the roller main body 13 to heat the roller main body 13 are arranged in the roller axial direction. A thermistor, which is the temperature detecting element 15a, is provided so as to come into contact with or approach the surface of the roller body 13.

In the fixing device 4, the abnormality prevention device of the present invention is provided with a control circuit A for controlling energization of the fixing heater 14 as shown in FIGS. 1 and 2, and the control circuit A is a power supply VAC.
Primary side circuit 15 for connecting the fixing heater 14 with the fixing heater 14.
And a secondary-side circuit 16 for controlling the primary-side circuit 15. The primary-side circuit 15 has a temperature limit for cutting off the energization of the fixing heater 14 when the fixing roller body 13 is overheated. Ascent prevention device 17 and the secondary side circuit 1
A control element 18 for controlling the fixing roller main body 13 to be kept at a constant temperature by an output signal from the control unit 6 and relay contacts 20, 21 which are turned off by demagnetizing a relay coil 19 of the secondary side circuit 16, The secondary side circuit 16 is connected in series to the heater 14, and the secondary side circuit 16 has a relay drive circuit section 22 for driving the relay coil 19 and a contact point 23a which is opened before the melting temperature of the overheat prevention device 17 is exceeded. An abnormal temperature detecting device 23 is connected, and the abnormal temperature detecting device 23 is arranged close to the fixing roller body 13.

The control element 18 in the primary side circuit 15 is a triac that controls the current supplied to the fixing heater 14 by on / off control or phase control.

The overheat prevention device 17 is composed of a temperature fuse, a thermal protector, etc.
When the temperature of No. 3 abnormally rises, the fuse is melted to forcibly shut off the energization of the fixing heater 14, and as shown in FIG. It is installed by a certain distance D (4 mm) or more from the surface of the roller body 13 by the control method.

Relay contacts 20 and 21 are interposed between the AC power supply VAC and the fixing heater 14 as shown in FIG.

As shown in FIG. 1, the secondary side circuit 16 is composed of the relay drive circuit section 22 and a control section 24 for driving and controlling the control element 18 and the like. The relay drive circuit unit 22 is supplied with the DC power supply VDC, and the relay coil 19, the abnormal temperature detection device 23, and the transistor 25 are connected in series. The DC power supply VDC (+ 24V) of the relay drive circuit 22 is supplied via the power supply device 26. Further, an ON / OFF signal of the abnormal temperature detection device 23 is input to the control unit 24 as a voltage at the coil end of the relay coil 19, and based on this, a transistor 25 is supplied.
Is turned on and off.

The abnormal temperature detection device 23 is composed of a thermostat (or an element such as a thermal reed switch (TRS) whose contacts open and close due to temperature rise). At the contact point 23a of the abnormal temperature detecting device 23, the control element 18 fails and the fixing heater 14 is kept energized, and the temperature of the fixing roller body 13 rises abnormally to prevent the excessive temperature rise device 1.
It is opened before the fusing temperature of 7 is exceeded, whereby the relay coil 19 is demagnetized, its contacts 20 and 21 are opened, and the supply of power to the fixing heater 14 is stopped. Then, as shown in FIG. 2, the abnormal temperature detecting device 23 is arranged substantially in the middle of the temperature detecting element 15a and the abnormal temperature detecting device 23, and is installed close to the surface of the roller body 13 close to 1 mm. There is.

The control unit 24 is a general one-chip microcomputer, which is mainly composed of a CPU and is composed of a data RAM, a program ROM, and the like, and performs control according to a control program stored in advance in the ROM. The control unit 2
As shown in FIG. 3, reference numeral 4 indicates a temperature control means 27 for controlling the output of the control element 18 in the primary side circuit 15 by the output signal of the temperature detection element 15a and an abnormal temperature prevention device 23 in the relay drive circuit section 22. The display device 28 of the copying machine body 1 and the abnormal temperature control means 29 for controlling the output of the transistor 25 are provided with the output signal.

The thermostat, which is the abnormal temperature prevention device 23,
The power supply VAC is not supplied to the fixing heater 14 unless the abnormal state is repaired and the thermostat is manually reset once the power is cut off by using the manual reset type.

In the above structure, the heater 14 heats the roller body 13 after the power is turned on. Then, when the surface temperature of the roller body 13 reaches the reference temperature, the temperature detection element 15 a outputs the temperature control means 27 of the controller 24. Thereby, the output of the control element 18 in the primary side circuit 15 is controlled, and the energization of the heater 14 is controlled.

At this time, if foreign matter (copy paper, toner, etc.) enters the contact surface between the temperature detecting element 15a and the roller body 13,
Even if the surface temperature of the roller body 13 reaches the reference temperature, the temperature is not properly transmitted to the temperature detecting element 15a.
In addition, when the control element 18 fails and the heater 14 is energized and becomes abnormal, the roller body 1
3 and the temperature of the heater 14 rise, and the fixing device 4 is in a dangerous state.

Then, the temperature of the roller body 13 prevents the temperature from rising too much.
When the temperature exceeds the fusing temperature of 7, the overheat prevention device 17 blows, and the heater 14 is de-energized.
Heating to 3 is stopped, but at this time, the overheat prevention device 17 is provided in the primary side circuit 15, and the roller body 1
Since the fixing device 4 is installed at a distance D from the fixing device 3, the fixing device 4 is greatly damaged when the overheat prevention device 17 is melted.

Therefore, in the relay drive circuit section 22 of the secondary side circuit 16,
An abnormal temperature detection device 23 and a relay coil 19 connected in series with the primary side circuit 15 are provided. As a result, the contact 23a of the abnormal temperature detection device 23 comes off before the fusing temperature of the overheat prevention device 17 is exceeded, and the relay drive circuit unit 22
The relay coil 19 is demagnetized, the relay contacts 20 and 21 are turned off, and the heating of the heater 14 is stopped.

At this time, by the abnormal temperature control means 29 of the control unit 24,
The abnormality is displayed on the display device 28 to inform the user.

Therefore, the damage to the fixing device when the heater is shut off can be reduced as compared with the conventional device, and even if the fixing device has a trouble, it can be easily restored.

Further, since the abnormal temperature detection device 23 is used in the secondary side circuit 16 of the control circuit A, the abnormal temperature detection device 23 can be brought close to the surface of the roller body 13 close to 1 mm, and accurate temperature detection is possible. Therefore, it is possible to prevent the malfunction that is likely to occur in the conventional device.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, although the manual reset type thermostat is used in the embodiment, the control unit 24 may turn off the transistor 25 by opening the thermostat, that is, by storing an abnormal state.

Further, when using the manual reset type thermostat, the transistor 25 may not be provided in the relay drive circuit section 22, and the triac is used as the control element 18, but a unidirectional thyristor may be used. good.

<Effects of the Invention> As is apparent from the above description, according to the present invention, in the fixing device, the control circuit for controlling the energization of the fixing heater controls the primary side circuit connecting the power source and the fixing heater and the primary side circuit. The secondary circuit consists of a secondary side circuit, and the primary side circuit fuses when the fixing roller body overheats and shuts off the power to the fixing heater.Fixed by the output signal from the secondary side circuit. A control element that controls to keep the roller body at a constant temperature and a relay contact that turns off by demagnetizing the relay coil of the secondary side circuit are connected in series to the fixing heater, and the relay coil is driven in the secondary side circuit. The relay drive circuit is connected to an abnormal temperature detection device that has a contact that opens before the fusing temperature of the overheat prevention device is exceeded, so the control element etc. fails and the fixing heater is energized. When the temperature of the fixing roller body and the fixing heater rises and the fixing device becomes in a dangerous state due to the occurrence of an abnormality that causes the temperature to rise, the fusing temperature of the overheat prevention device is exceeded, that is, the fixing device Before the damage becomes large, the contact of the abnormal temperature detection device comes off, the relay coil of the relay drive circuit section is demagnetized, the relay contact is turned off, and overheating of the fixing heater is stopped.

Therefore, the damage to the fixing device when the heater is shut off can be reduced as compared with the conventional device, and even if the fixing device has a trouble, it can be easily restored.

Further, since the abnormal temperature detection device is used in the secondary side circuit of the control circuit, the abnormal temperature detection device can be brought close to the fixing roller body, and accurate temperature detection can be performed.
If a malfunction that tends to occur in a conventional device can be prevented, an excellent effect can be obtained.

[Brief description of drawings]

FIG. 1 is a control circuit diagram of an abnormality prevention device for a fixing device showing an embodiment of the present invention, FIG. 2 is a configuration diagram of a main part of the fixing device, FIG. 3 is a functional block diagram thereof, and FIG. FIG. 5 is a schematic configuration diagram of a copying machine to which the fixing device abnormality prevention device of the present invention is applied, and FIG. 5 is a control circuit diagram of a conventional fixing device abnormality prevention device. 13: fixing roller body, 14: fixing heater, 15:
Primary side circuit, 16: Secondary side circuit, 17: Overtemperature prevention device, 18: Control element, 19: Relay coil, 20, 2
1: relay contact, 22: relay drive circuit part, 23: abnormal temperature detection device, 23a: contact, A: control circuit.

Continuation of the front page (56) Reference JP-A-54-97047 (JP, A) JP-A-59-226911 (JP, A) JP-A-62-231978 (JP, A) JP-A-59-33481 (JP , A) JP 63-180989 (JP, A) JP 63-161477 (JP, A) JP 62-4715 (JP, B2)

Claims (1)

[Scope of utility model registration request] 1. A fixing device having a fixing heater for heating a fixing roller main body, wherein a control circuit for controlling energization of the fixing heater is provided, and the control circuit is a primary side circuit for connecting a power source and the fixing heater. And a secondary side circuit for controlling the primary side circuit, wherein the primary side circuit is a temperature excessive temperature rise prevention device that melts and cuts off energization to the fixing heater when the fixing roller body is overheated, A control element for controlling the fixing roller body to be maintained at a constant temperature by an output signal from the secondary side circuit, and a relay contact which is turned off by demagnetizing a relay coil of the secondary side circuit are connected in series to the fixing heater. The secondary side circuit has a contact that is opened before the melting temperature of the overheat prevention device is exceeded in the relay drive circuit section that drives the relay coil. That abnormal temperature detecting device is connected, the abnormal temperature detecting device abnormality preventing device of the fixing device, characterized in that is arranged in proximity to the fixing roller body.