JPH04291385A - Fixing device - Google Patents

Abstract

PURPOSE:To improve follow-up ability at the time of rising time, to eliminate malfunction and to surely stop heating when the surface temperature of a fixing roller is abnormal by providing a heat detecting means and a self-temperature control type auxiliary heating means. CONSTITUTION:In the vicinity of the periphery of the fixing roller 1, a second thermostat 9 as a second heat detecting means and a PTC heater 11 as an auxiliary heating means held by a fixing member 10 are disposed. When a thermister 3 is abnormal during the operation and cannot control heating, an infrared-ray heater (RA)2 continues the energizing. Thus, the temperature of the surface of the fixing roller 1 is heated to the temperature of around 180 deg.C exceeding the control temperature. By heating a bracket 12 rather than the surface of the fixing roller 1, the temperature is raised rapidly. Consequently, a first thermostat 13 is activated and detects the malfunction immediately. Thus, the RA2 is turned off, the PTC heater 11 starts the heating of the second thermostat 9 to operate it and the energizing of the infrared-ray heater 2 is interrupted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus that fixes an unfixed toner image on a transfer sheet by applying heat to a transfer sheet using a fixing roller equipped with heating means and whose surface temperature is controlled.

0002

[Prior Art] In a fixing device used in an image forming apparatus such as a copying machine, the temperature of the heat source is controlled so that the surface temperature of the fixing roller is within a certain range, but the temperature usually rises abnormally. A safety device is provided to shut off the heating source when the heating occurs.

In such a safety device, in order to increase the sensitivity of heat detection, a heating means is provided in the heat-sensitive element (thermostat or temperature fuse), and the heating means is made to generate heat at the same time as the fixing roller heater starts heating. An overtemperature rise prevention device has been proposed that speeds up the reaction of the heat-sensitive element in the event of abnormal heating and quickly shuts off the power to the heater (
(See Japanese Unexamined Patent Publication No. 11775/1983).

However, in such a device, in order to make the function effective when the power is turned on, it is necessary to increase the heater capacity to improve the start-up characteristics, and also to prevent malfunction during normal operation. It is difficult to satisfy the contradictory demands of reducing the impact of

That is, if the heating means is constantly operated while the fixing roller is sufficiently heated and the temperature is normally controlled, depending on the capacity of the heating means, the heat-sensitive element may malfunction when the heater is repeatedly turned on and off. there is a possibility. If the temperature of the heating means is controlled to prevent this, the apparatus and system will become complicated.

[0006]

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems in the prior art, and uses a simple method to provide a quick response at startup, etc., and is equipped with a thermal safety device that does not cause malfunctions during normal operation. The present invention aims to provide a fixing device.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present invention fixes the unfixed toner image on the transfer sheet by applying heat to the transfer sheet using a fixing roller equipped with heating means and whose surface temperature is controlled. In the fixing device of the image forming apparatus, a first heat detection means is activated when a first temperature corresponding to the temperature is detected when the surface temperature of the fixing roller becomes equal to or higher than a controlled temperature; a second heat detection means that stops heating the heating means when a second temperature higher than the temperature corresponding to the first temperature is detected; and a second heat detection means that is provided near the second heat detection means and is activated when the first heat detection means is activated. and auxiliary heating means that heats the second heat detection means under self-temperature control until the temperature reaches a predetermined temperature.

[0008]

[Operation] According to the present invention, since the first heat detecting means and the second heat detecting means are provided, they can be installed in separate locations.
The first heat detection means can be installed at a position where it reacts quickly, such as when starting up. Since the first temperature, which corresponds to the surface temperature of the fixing roller when it is abnormal, is set lower than the second temperature, the first heat detection means can quickly detect the abnormal temperature. As a result of this detection, the second heat detection means is heated by the auxiliary heating means that is self-temperature-controlled so as to reach a predetermined temperature, so that the followability of abnormal temperature detection by the second heat detection means is improved, and the second heat detection means operates reliably, ensuring safety during start-up and operation.

On the other hand, during normal operating conditions, the internal temperature of the fixing device has risen sufficiently, so even if the second temperature is higher than the temperature corresponding to the first temperature, the auxiliary heating means does not operate. Regardless of whether it is inactive or not, the second heat detection means is reliably activated in the event of an abnormality. In a normal state, the second heat detection means is not always heated by the auxiliary heating means, so it does not malfunction.

Furthermore, even if the first heat detection means malfunctions due to overshoot or the like and operates for a short period of time, since the heating means is of a self-temperature control type, the temperature does not rise above a predetermined temperature, and the second heat detection means There is no need to immediately shut off the heating means for the fixing roller after heating the fixing roller, thereby preventing malfunctions.

[0011] Furthermore, since the first temperature does not directly stop the heating of the heating means, the capacity can be reduced;
Increased flexibility in installation location.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a fixing device according to an embodiment of the present invention, which is used in an image forming apparatus such as a copying machine. The fixing roller 1 is equipped with an infrared heater 2 as a heating means inside, and a thermistor 3 is disposed on its outer peripheral surface to detect temperature in order to control the temperature of the fixing roller 1 within a predetermined temperature range, and fixes the toner. In order to achieve this, the surface temperature of the fixing roller 1 is controlled to about 180°C to 185°C.

The surface of the fixing roller 1 is treated with a material such as silicone rubber or Teflon that is heat resistant and has excellent mold releasability. 4, a mold release agent such as silicone oil is applied.

A pressure roller 6 is pressed against the fixing roller 1 by a pressure spring 5, and the transfer paper P as a sheet carrying an unfixed toner image is placed in the nip between the fixing roller 1 and the pressure roller 6. While passing through this gap, heat is absorbed from the fixing roller 1, and the toner thereon is melted or the solvent is evaporated and the toner image is fixed.

The transfer paper P on which the toner image has been fixed is separated from the surface of the fixing roller 1 by the separation claw 7, and then discharged by the paper discharge roller 8 to complete the copy image.

Near the outer peripheral surface of the fixing roller 1, there is a second thermostat 9 as a second heat detection means constituting a safety device for preventing abnormal heating of the fixing roller 1, and an auxiliary thermostat held by a mounting member 10. A PTC heater 11 is installed as a heating means. The second thermostat 9 detects the temperature near the surface of the fixing roller 1 and interrupts the energizing circuit of the infrared heater 2 when the temperature is abnormal.

FIG. 2 shows the structure of the side end portion of the fixing roller 1. As shown in FIG. A bracket 12 is attached to a side plate (not shown) of the fixing device, and a first thermostat 13 as a first heat detection means is disposed on the bracket 12 near the side end of the fixing roller 1 through which the infrared heater 2 passes. ing. Since the first thermostat 13 is provided in addition to the second thermostat 9 in this way, the first thermostat 13 can be made small and easily installed near the infrared heater 2 itself. As a result, when the infrared heater 2 is heated and the surface temperature of the fixing roller 1 rises, the temperature of the first thermostat 13 also rises correspondingly or earlier.
Even when the fixing device is started up, the temperature corresponding to the surface temperature of the fixing roller 1 at the time of abnormality can be detected with good followability.

FIG. 3 shows the positional relationship between the second thermostat 9 and the PTC heater 11. The PTC heater 11 is the second
It is attached to a mounting member 10 so that it can be heated near the thermostat 9.

FIG. 4 shows the electrical connections of these instruments. When the power SW 21 is turned on, power is supplied from the DC power supply 22 to the control unit 23, RA1, RA2 and the triac 24 are connected by a signal, the infrared heater 2 is energized, and the PTC heater 11 is not energized, so the fixing roller The surface temperature of 1 is determined by the thermistor 3, for example, 18
Heating is controlled until it reaches 0°C. When the surface of the fixing roller 1 reaches the set temperature (reload state), the triac 24 is turned off.

The normal operation is as described above, but for example, when the thermistor 3 becomes abnormal and heating control becomes impossible (no reload signal is issued), the infrared heater 2 continues to be energized. As a result, the temperature of the surface of the fixing roller 1 exceeds the control temperature of about 180 degrees. In this case, since the bracket 12 is heated more quickly than the surface of the fixing roller 1, the temperature rises faster, and the first thermostat 13 is activated to detect an abnormality earlier.

[0021] As a result, RA2 is turned off, the PTC heater 11 starts heating the second thermostat 9, and the second thermostat 9 is heated.
The thermostat 9 is activated to cut off the power supply to the infrared heater 2.

In this embodiment, the surface of the fixing roller 1 is 18
During normal times, the temperature of the first thermostat 13 is about 0° to 185°C, and when it is abnormally heated, the surface of the fixing roller 1 is around 300 to 350°C. 1 The temperature of thermostat 13 is
The temperature is set to 110°, which is the first temperature. In this way, the first thermostat 13 is set to 3.
It is best to choose one with a temperature higher than 0 to 40°C.

The second thermostat 9 may be set to a temperature that does not cause the transfer paper P to catch fire, and in this example, 160 to 180° C. was used as the second temperature.

Further, the PTC heater 11 is a heater whose temperature is self-controlled until it reaches a predetermined temperature, and in this embodiment, the self-control point (resistance value change temperature ≒ Curie point) is 220°C.
It is assumed that a sufficient amount of heat can be supplied to assist the second thermostat 9 to operate reliably. Such a PTC heater 11 has a large heat capacity when the ambient temperature is low and a small heat capacity when the ambient temperature is high, so there is no need to control the heating temperature, and the system can be simplified.

[0025] With the above configuration, the first thermostat 13 does not directly cut off the power supply to the infrared heater 2, so its capacity can be reduced, and the detection sensitivity can be increased to improve tracking in the event of an abnormality. Can be done. On the other hand, the second
Since the thermostat 9 is not heated by the PTC heater 11 under normal conditions, it will not malfunction. Furthermore, the first thermostat 13 becomes inoperable and the second thermostat 13 becomes inoperable.
Even if the thermostat 9 is not heated by the PTC heater 11, the infrared heater 2 can be shut off by operating only the second thermostat 9, and the provision of the first thermostat 13 reduces safety. There isn't.

Furthermore, it is not necessary to bring the first thermostat 13 and the second thermostat 9 into contact with the fixing roller 1.
Since it is non-contact, it does not damage the fixing roller 1.

Although the first and second heat detection means are thermostats described above, similar temperature detection means may be used such as a thermal fuse or other means.

[0028]

As described above, according to the present invention, by providing the first heat detection means, the second heat detection means, and the self-temperature control type auxiliary heating means, the followability at the time of startup can be improved with a simple configuration. In addition, heating can be reliably stopped when the surface temperature of the fixing roller is abnormal, without malfunctioning during normal operation.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a fixing device according to an embodiment.

FIG. 2 is a perspective view schematically showing a mounting portion of a first thermostat of the fixing device.

FIG. 3 is a schematic diagram showing the positional relationship between a second thermostat and a PTC heater of the fixing device.

FIG. 4 is a wiring diagram of the fixing device.

[Explanation of symbols]

1 Fusing roller 2 Infrared heater (heating means)

Claims (1)

[Claims] 1. A fixing device of an image forming apparatus in which an unfixed toner image is fixed on a transfer sheet by applying heat to a transfer sheet by a fixing roller equipped with a heating means and whose surface temperature is controlled, wherein the surface temperature of the fixing roller is a first heat detection means that operates when a first temperature corresponding to the temperature reaches a controlled temperature or higher; and a first heat detection means that operates when a second temperature corresponding to the first temperature is detected; a second heat detecting means for stopping heating of the heating means; and a second heat detecting means provided near the second heat detecting means, which is activated when the first heat detecting means is activated and performs self-temperature control until a predetermined temperature is reached. A fixing device comprising: auxiliary heating means for heating the fixing device.