JPH04281487A - Image forming device - Google Patents

Abstract

PURPOSE:To surely prevent a fixing device from being damaged caused by overheating by providing a return type heating interruption means on the outside of the fixing device and providing a non-return type inside interruption means to the inside. CONSTITUTION:A heater 10 is incorporated in the heating and fixing roller 6 of the fixing device 5 as a heating means. An interrupting partition plate 12 is provided on the upper side of the cover 11 of the device 5. An outside heating interruption means 13 is provided on the plate 12. The inside heating interruption means 14 is provided to inside of the cover 11 of the device 5. A temperature detection means 15, a thermistor, for example, is arranged on the roller 6 by being brought into contact with it. Then, since the abnormal heating is detected based on the atmospheric temperature of the device 5 and power supply to the heating means 10 is interrupted by the interruption means 13, the heat generation of the whole of the device 5 can be interrupted. When a control part becomes uncontrollable and the power supply to the heating means 10 cannot be controlled, the power supply is interrupted by the interruption means 14. As a result, the power supply to an electric power control element is surely interrupted and the heat is surely prevented from being abnormally generated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device, such as a copying machine, a facsimile machine, or a printer.

0002

2. Description of the Related Art In a fixing device of a copying machine as an example of an image forming apparatus, an object to be heated, such as a heat fixing roller, is heated to a set temperature by a heating means, such as an infrared heater. Conventionally, the temperature of the fixing roller is maintained at a set temperature by detecting the temperature of the fixing roller using a temperature detecting means such as a thermistor, and controlling the supply of electricity to an infrared heater based on the detected signal. In conventional devices, multiple connection points are required between the temperature detection means and the control section that sends control signals to the power control element that controls the energization of the heating means, and these connection points reduce contact resistance over time. In some cases, the signal transmission may be blocked for some reason, resulting in an uncontrollable situation. At that time, there was a problem in that heated means such as a fixing roller of the fixing device overheated and the fixing device was destroyed.

Conventionally, overheating prevention means based on semiconductor control have been used, but they have not been able to reliably prevent destruction and have not been able to provide a sufficient response to uncontrollable or partial overheating.

0004

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide an image forming apparatus that reliably prevents damage to the fixing device due to overheating.

[0005]

[Means for Solving the Problems] The present invention solves the above problems by providing a fixing device for heating and fixing a transferred image on a recording paper, a temperature detecting means for detecting the heating temperature of the fixing device, and a temperature detecting means for detecting the heating temperature of the fixing device. and a power control element that controls energization to the heating means of the fixing device based on a signal, wherein heating cutoff means for cutting off energization to the heating means are disposed inside and outside of the fixing device, The external heating cutoff means placed outside the fixing device is formed into an automatic return type.
The problem has been solved by an image forming apparatus characterized in that the internal heating cutoff means disposed within the fixing device is of a non-automatic return type.

[0006]

[Operation] According to the present invention, heat cutoff means are disposed inside and outside of the fixing device, and overheating of the overheated member of the fixing device is detected based on the ambient temperature outside the fixing device, and the external heat cutoff means is activated. Cut off the power to the The external heating cutoff means can be reset naturally depending on the temperature like a thermostat, and can be used repeatedly. If the control unit becomes uncontrollable for some reason and the power control element, such as a triac, remains energized and the temperature inside the fixing device becomes overheated to a predetermined temperature or higher, the internal heating cutoff means, such as a thermal fuse, is shut off. to ensure that the power to the power control element is cut off. When the internal heating cutoff means is activated, it is abnormal and must be inspected, so even if the temperature drops, the internal heating cutoff means will not return.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained based on the embodiments shown in the drawings.

In FIG. 1, a copying machine as an example of an image forming apparatus charges a photoreceptor 1 with a charger 2,
An electrostatic latent image is formed by exposure using an image exposure device (not shown), developed by a developing device (not shown) to form a toner image, and the toner image is fed from a paper feeding device (not shown) under the action of a transfer charger 3. The transfer paper after fixed copying is conveyed to a fixing device 5 by a conveyor belt 4, and is fixed by being passed between a heating fixing roller 6 and a pressure roller 7 of the fixing device 5, The paper is ejected to the paper ejection tray 8.

After the transfer, residual toner is removed from the photoreceptor 1 by a cleaning device 9, and the process from the next charging step is repeated.

The overheated fixing roller 6 of the fixing device 5 has a built-in heater 10 as heating means. A heat shielding partition plate 12 is provided above the cover 11 of the fixing device 5 , and an external heat cutoff means 13 is provided on the partition plate 12 .

An internal heating cutoff means 14 is provided inside the cover 11 of the fixing device 5, and a temperature detection means 15, such as a thermistor, is arranged in contact with the heating fixing roller 6.

When the temperature inside the fixing device 5 is measured as a temperature distribution in the cover 11, the results shown in FIG. , curve C shows the respective temperature distributions on the back side. From Figure 2, inside the fixing device, the temperature tends to be higher on the back side than on the front side, and the time T indicates an abnormal overheating state.
1, the temperature rapidly increases after time T
2, parts inside the fixing device will be damaged.

Therefore, the external heating cutoff means 13 is installed on the back side where the ambient temperature is high to improve the temperature detection effect.

As the external heating cutoff means 13, an automatic return type cutoff means such as a thermostat is used so that it automatically returns to operable mode when the overheating temperature drops.

In FIG. 3 showing an example of the sequence, the switch (SW) 16 is turned ON, and the control unit 17, for example, the CPU
The power control element (
The heater 10 built into the heat fixing roller 6 is energized through the triac (TRIAC) 18.

When the surface temperature of the heat fixing roller 6 reaches the set temperature, the controller 1 is activated by a signal from the temperature detecting means 15.
7 to operate the power control element 18 to control the current. The relay 20 is activated by a signal from the control unit 17, and the contact 2
Power supply to the heater 10 is turned on and off by opening and closing 0a and 20b.
Can be FF.

[0017] A state in which the temperature does not drop beyond the set temperature is called abnormal heating. If abnormal heating occurs, various parts of the fixing device 5 will be damaged. As shown in the example in the figure, if there are multiple connection points (3 points x 2 times = 6 points) between the temperature detection means, such as the thermistor 15 and the control unit 17, as shown by the circles in the figure, poor contact may occur. This can easily occur, resulting in abnormal heating. Conventionally, when abnormal overheating occurs, the power control element 18
The energization was controlled by controlling the power supply, but if some abnormality occurs and control becomes impossible, the energization will continue. In this case, the heating cutoff unit 14 disposed in the fixing device, for example, a thermal fuse or a thermostat, is operated to stop the power supply to the heater, but in the case of a thermostat,
When the temperature inside the fixing device decreases over time, it becomes operational again and starts supplying electricity, making it possible to distinguish whether the overheating occurred due to an abnormality in the control unit or whether the supply of electricity was cut off due to the operation of the power control element. In the case of fuses, if you try to cut off the power before parts of the fixing device are damaged, you need to lower the operating temperature, which can cause the fuses to blow out frequently. could have occurred.

A non-returnable heat cutoff section 1 is provided inside the fixing device 5.
4. An automatic return type external heating cutoff means 13 that can be repeatedly used outside the fixing device 5 by disposing, for example, a thermal fuse;
For example, a thermostat is installed to control the temperature between 120 and 130℃.
By operating the external heating cutoff means 13, the power supply to the heater 10 is stopped before damage occurs within the fixing device.

If the control unit 17 becomes uncontrollable due to some reason, such as noise or deterioration, and the TRIAC 18 remains energized when the energization must be cut off, the external heating cutoff means 13 should first be turned on. make it work. If the external overheat cutoff means 13 does not operate reliably for some reason and the temperature inside the fixing device rises, resulting in an abnormal overheating state, the internal overheat cutoff means 14 is activated to prevent parts from being damaged. The power supply to the heater 10 is cut off. In this case, the power will not be restarted even if the temperature drops, so restarting will not be possible unless the internal overheat cutoff means is replaced after checking for abnormalities.

In contrast to the example in FIG. 3, as shown in the example in FIG.
It is also possible to connect an external heating cutoff means 13 to the coil side of the relay 20, detect overheating, turn off the relay 20 during operation, and open the contacts 20a and 20b to cut off the power supply to the heater 10. can.

It is also possible to combine an alarm device with the external heating cutoff means 13 so as to notify even a worker who is away from the image forming apparatus of a heating abnormality.

[0022]

According to the present invention, by providing a heating cutoff means outside the fixing device, it is possible to detect and cut off the heat generated in the entire fixing device, and furthermore, it is possible to restore the fixing device, making control easier. If a resettable heating cutoff means is placed inside the fixing device, it will not be effective in preventing damage due to space limitations, and accurate detection will be difficult due to the temperature range during temperature control.
By placing it on the outside, it becomes easier to select a device that will follow only in the event of an abnormality, and a mechanical shut-off means can be selected.The configuration is simpler than that of a semiconductor-type shut-off means, and reliable control is possible. became.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a part of an image forming apparatus.

FIG. 2 is a diagram showing temperature changes in a fixing device.

FIG. 3 is a control circuit diagram according to the present invention.

FIG. 4 is a diagram showing another embodiment of the control circuit.

[Explanation of symbols]

5 Fusing device 6 Fixing roller 10 Heating means 11 Cover 12 Partition plate 13 External heating cutoff means 14 Internal heating cutoff means 15 Temperature detection means

Claims (2)

[Claims] 1. A fixing device that heats and fixes a transferred image on a recording paper, a temperature detection device that detects the heating temperature of the fixing device, and energization of the heating device of the fixing device based on a signal from the temperature detection device. In the image forming apparatus having a power control element for controlling the heating means, heating cutoff means for cutting off electricity to the heating means are disposed inside and outside of the fixing device,
An image forming apparatus characterized in that an external heat cutoff means disposed outside the fixing device is formed as an automatic return type, and an internal heat cutoff means arranged inside the fixing device is formed as a non-automatic return type. 2. An image forming apparatus, wherein the operating temperature of the external heat cutoff means is set lower than the operating temperature of the internal heat cutoff means.