JPH05107963A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To assure shutting off of power feeding to a heat source to prevent damage by burning of the device when temperature of a fixing roll is raised abnormally by bringing an excessive temperature rise prevention element into a pressurized contact with a fixing roll. CONSTITUTION:The excessive temperature rise prevention element is constituted with a temperature fuse 4, a plane state heater 5, and a thin film 6 provided with heat resistance and thermal insulation property in this order from inside, and this is brought into a pressurized contact with a fixing roll 1 by a bracket 8 through an insulated layer 7. When the heat source 2 cannot be controlled due to breakdown of a control circuit and the heat source 2 is left lit causing the fixing roll 1 to have its temperature risen abnormally, the temperature of the temperature fuse 4 is risen from the heat of the fixing roll 1 because it is brought into a pressurized contact with the fixing roll 1. Along with that, the temperature fuse 4 is continued to be heated by the plane state heater 5 which is connected in a series with the heat source 2 against the power supply since the heater 5 is left lit along with the heat source 2. Therefore, the response of the temperature fuse 4 is speedy for heat is received from both the fixing roll 1 and the plane state heater 5, and the shutting off of the power supply is assured and carried out speedily at the time of abnormal rising of the temperature of the fixing device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a laser printer, a copying machine or a facsimile which uses an electrophotographic system.

[0002]

2. Description of the Related Art In order to prevent an excessive temperature rise in a fixing device, conventionally, as shown in FIG. 5, a predetermined gap is provided in the vicinity of the surface of a fixing roller 13 which is in pressure contact with a pressure roller 15, and a temperature is maintained. An excessive temperature rise prevention element 16 such as a fuse is arranged. As a result, the heat source 14 of the fixing roller 13 remains lit due to an abnormality in the temperature control circuit, etc.
When 3 is excessively heated, the temperature fuse 16 is blown in response to the abnormal temperature rise in the atmosphere near the fixing roller, and the power supply to the heat source 14 is turned off.

[0003]

However, according to such an excessive temperature rise prevention method, since the excessive temperature rise prevention element is arranged apart from the fixing roller, when the fixing roller has an abnormal temperature rise. , Immediate insensitivity and a delay in response. This is because when the fixing roller has an abnormal temperature rise, the temperature of the atmosphere in the vicinity of the roller first rises, and then heat is transferred to the excessive temperature rise prevention element. The response delay is unstable because there is a time difference between when the ambient temperature is high and when the ambient temperature is low. If the rated operating temperature of the overheat prevention element is lowered in order to reduce such a response delay and a time difference, it is said that the chances of the overheat prevention element erroneously operating increases even in a normal state. There are also problems.

In view of the above-described problem in the conventional excessive temperature rise prevention, the present invention minimizes the response delay to the excessive temperature rise, and reliably supplies power to the heat source when the fixing roller has an abnormal temperature rise. It is an object of the present invention to provide a fixing device that can prevent the device from being burnt out by shutting off.

[0005]

According to the present invention, there is provided a fixing roller which is rotatably supported and has a heat source, a pressure roller which is pressed against the roller and rotates, and a temperature detecting element which detects the temperature of the fixing roller. In the fixing device having the excessive temperature rise prevention element for preventing the excessive temperature rise of the fixing roller, the above problem is solved by pressing the excessive temperature rise prevention element against the fixing roller.

It is preferable to provide a heating heater for the excessive temperature rise prevention element.

It is more preferable to provide a cleaning member on the upstream side of the excessive temperature rise prevention element in the direction of rotation of the fixing roller.

The heater for heating the excessive temperature rise prevention element is controlled to be turned on and off according to the ON / OFF state of the heat source, and the heater for heating the excessive temperature rise prevention element is continuously operated during the warm-up time of the fixing device. Conveniently, the temperature of the overheat prevention element is adjusted to remain below its operating temperature when illuminated.

[0009]

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

The structure of the present invention is shown in FIG. The pressure roller 3 is pressed against the fixing roller 1 having the heat source 2 built therein. At the nip part formed by the contact of these two rollers,
The unfixed image is fixed by passing the recording paper on which the unfixed image is placed. The excessive temperature rise prevention element is composed of a temperature fuse 4, a sheet heater 5, and a heat-resistant and heat-insulating thin film 6 in this order from the inside, and contacts the fixing roller 1 with a bracket 8 via a heat insulating layer 7. Pressed.

A cleaning member 9 is provided on the upstream side in the rotation direction of the fixing roller of the bracket 8 which supports the excessive temperature rise prevention element. This is for preventing the toner fixed on the surface of the fixing roller 1 from being damaged between the excessive temperature rise prevention element and the fixing roller and the damage of the excessive temperature rise prevention element or the roller surface. is there.

Regarding the power supply to the heat source 2 and the planar heater 5, the heat source 2 and the planar heater 5 are connected in series to the power source, as can be understood from FIG.

When the main switch of the main body of the apparatus is turned on, the heat source 2 is turned on and the warm-up of the fixing device is started. Similarly, the planar heater 5 of the excessive temperature rise prevention element
Also lights up and heats the thermal fuse 4. The planar heater 5
Is set to a wattage at which the temperature of the temperature fuse 4 does not exceed the operating temperature of the excessive temperature rise prevention element when the fixing device is continuously turned on until the fixing device is warmed up. Care is taken to prevent malfunction of the protection element.

When the warm-up is completed, a signal is sent to the control circuit 12 based on the temperature detected by the temperature detecting element 10.
The heat source 2 is controlled to be turned on and off, and the temperature of the fixing roller 1 is kept within a certain range.

Further, the planar heater 5 also turns on / off the heat source 2.
It is turned on and off according to F, and the temperature fuse 4 is kept constant below its operating temperature.

FIG. 3 shows the temperature changes of the fixing roller 1 and the thermal fuse 4 during the series of operations described above.

When the control circuit 12 fails and the heat source 2 becomes uncontrollable, the heat source 2 remains lit, and the fixing roller 1 is abnormally heated, the temperature fuse 4 is pressed against the fixing roller 1. In addition, the heat from the fixing roller 1 raises the temperature. At the same time, the planar heater 5, which is connected to the heat source 2 in series with the power source, remains lit in the same manner as the heat source 2, and thus continues to heat the thermal fuse 4. FIG. 4 shows the temperature changes of the fixing roller 1 and the thermal fuse 4 at this time.

As is apparent from FIG. 4, in the prior art,
Since the temperature of the temperature fuse rises via the heat of the warmed ambient temperature in the fixing device, the operation response is slow, whereas in the present invention, the temperature fuse 4 includes both the fixing roller 1 and the planar heater 5. Since the heat is received from the device, the response is quick, and the power supply to the heat source is reliably and quickly shut off when the fixing device has an abnormal temperature rise.

[0019]

In the fixing device of the first aspect, the excessive temperature rise prevention element is pressed against the fixing roller, and in the fixing device of the second aspect, the excessive temperature rise prevention element is further provided with a heating heater. Therefore, when the fixing roller has an abnormal temperature rise, the response delay is small, and the power supply to the heat source can be reliably cut off.

In the fixing device of the third aspect, since the cleaning member is provided on the upstream side in the rotation direction of the fixing roller with respect to the excessive temperature rise prevention element, the surface of the fixing roller and the excessive temperature rise prevention element are prevented from being scratched. be able to.

In the fixing device of claim 4, since the heater for heating the excessive temperature rise prevention element is ON / OFF controlled according to ON / OFF of the heat source, in addition to the effect of claim 1, When the excessive temperature rise prevention element is at a low temperature such as at the time of start-up, it is possible to quickly heat up to a predetermined temperature, and when the fixing device is functioning normally, malfunction of the excessive temperature rise prevention element can be prevented.

In the fixing device of the fifth aspect, when the heater for heating the excessive temperature rise prevention element is continuously turned on during the warm-up time of the fixing device, the temperature of the excessive temperature rise prevention element becomes equal to or lower than its operating temperature. Because it is adjusted to stay,
In addition to the effect of the first aspect, it is possible to prevent malfunction of the excessive temperature rise prevention element when the fixing device is started up.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a fixing device according to an exemplary embodiment of the present invention.

FIG. 2 is a conceptual diagram of an operation flow of the fixing device according to the present invention.

FIG. 3 is a diagram showing temperature changes of a fixing roller and a thermal fuse under normal conditions.

FIG. 4 is a diagram showing temperature changes of a fixing roller and a temperature fuse when the fixing roller is abnormally heated.

FIG. 5 is a schematic sectional view of a conventional fixing device.

[Explanation of symbols]

 1, 13 Fixing roller 2, 14 Heat source 4, 14 Thermal fuse 5 Heater

Claims (5)

[Claims] 1. A fixing roller rotatably supported and provided with a heat source; a pressure roller which is pressed against the roller to rotate;
In a fixing device having a temperature detection element for detecting the temperature of the fixing roller and an excessive temperature rise prevention element for preventing an excessive temperature rise of the fixing roller, the excessive temperature rise prevention element is pressed against the fixing roller. And fixing device. 2. The fixing device according to claim 1, wherein a heater for heating is provided in the excessive temperature rise prevention element. 3. The fixing device according to claim 1, wherein a cleaning member is provided on the upstream side of the excessive temperature rise prevention element in the fixing roller rotation direction. 4. The fixing device according to claim 2, wherein the heater for heating the excessive temperature rise prevention element is ON / OFF controlled according to ON / OFF of the heat source. 5. When the heater for heating the excessive temperature rise prevention element is continuously turned on during the warm-up time of the fixing device, the temperature of the excessive temperature rise prevention element is adjusted to remain below its operating temperature. The fixing device according to claim 2, wherein the fixing device is provided.