JP2002072759A - Fixing apparatus with improved safety - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing apparatus which can speedily detect an abnormal temperature rise of a heat roller by a heat sensor and stops supplying electric power to the heat source of a heat roller immediately in the case of an abnor mal temperature rise. SOLUTION: This fixing apparatus comprises the heat roller with a built-in heat source and a pressure roller which faces the heat roller and is energized by a spring to press the heat roller, and fixes a transfer toner image on the surface of transfer paper by passing the transfer paper having the transfer toner image on the surface between the heat roller and pressure roller and is characterized in that the heat roller is held rotatably by a bearing made of thermoplastic resin which has such a fusion point and a softening point that it is neither fused nor softened at fixation time, but fused and softened in the case of an abnormal temperature rise and a heat sensor for prevention against the abnormal temperature rise of the heat roller is provided nearby the surface of the heat roller and opposite it in the direction of depression from the pressure roller.

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 copying machine, a facsimile, a printer, etc., and more particularly, to a fixing device used in a fixing device. The present invention relates to a highly safe fixing device in which abnormal temperature rise of a roller is effectively prevented.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus represented by a copying machine, a toner image is formed on a photoconductor surface by developing an electrostatic latent image formed on the surface of the photoconductor. Is formed on the transfer paper surface to form an image. The transfer paper having the toner image transferred to the surface in this manner is introduced into a fixing device, and the toner image is fixed on the transfer paper surface by heat and pressure. Such a fixing device is composed of a heat roller having a built-in heat source such as a heater, and a pressure roller disposed opposite to the heat roller, and the surface on which the toner image is formed is in contact with the heat roller. In this way, the structure is such that the toner image is fixed on the transfer paper surface by passing the transfer paper between these rollers.

[0003]

In the fixing device having the above structure, a heat roller is used.
It is necessary to prevent abnormal heating of the heat roller. In other words, when an abnormal situation occurs in which the heat roller becomes significantly higher than the temperature required for fixing (fixing temperature), various mechanical parts are seriously damaged, and in some cases, ignition occurs. It is. In order to prevent such an abnormal temperature rise, a conventionally known fixing device arranges a heat sensor such as a thermostat near the roller surface of the heat roller, and when an abnormal temperature rise occurs, an electric signal from the heat sensor is generated. Thus, a measure is taken to cut off the power supply to the heat source built in the heat roller. However, such means as described above still have room for improvement in response to abnormal situations. That is, in the above-described means, the heat sensor does not directly measure the surface temperature of the heat roller, but detects an abnormal temperature rise of the heat roller by measuring the ambient temperature of the heat roller, and sends the heat to the heat source. Is stopped. Therefore, even if the temperature of the heat roller rises abnormally, the abnormal temperature rise is not detected unless the ambient temperature rises accordingly. For example, when the temperature of the heat roller suddenly rises abnormally, such abnormal temperature rise cannot be detected quickly.

Accordingly, it is an object of the present invention to be able to quickly detect an abnormal temperature rise of a heat roller by a heat sensor, and to immediately stop energizing a heat source of the heat roller when an abnormal temperature rise occurs. To provide a simple fixing device.

[0005]

According to the present invention, there is provided a heat roller including a heat source, and a pressure roller facing the heat roller and spring-biased so as to press the heat roller.
In a fixing device in which a transfer paper having a transfer toner image on its surface is passed between a heat roller and a pressure roller, the transfer toner image is fixed on the transfer paper surface. However, it is rotatably held by a bearing made of a thermoplastic resin having a melting point or a softening point such that it melts or softens at an abnormal temperature rise, and is near the roller surface of the heat roller, from the pressure roller. The fixing device is provided with a heat sensor for preventing abnormal temperature rise of the heat roller at a position facing the pressing direction of the fixing roller.

In the present invention, a bearing made of a thermoplastic resin having a melting point or softening point which does not melt or soften during normal fixing, but melts or softens at abnormal temperature rise, is used as the bearing of the heat roller. This is the first feature. In this specification, the melting point or the softening point means the melting point when the melting point is clear, and means the softening point when the melting point is not clear.
That is, the bearing of the heat roller melts or softens due to abnormal temperature rise, and as a result, the holding and fixing force of the rotating shaft of the heat roller is lost. On the other hand, the heat roller is provided with a pressure roller facing the heat roller, and the heat roller is pressed by the pressure roller. Therefore, when the bearing melts or softens, the heat roller moves due to the pressing force from the pressure roller. However, a second feature of the present invention is that the heat sensor is provided near the roller surface of the heat roller and at a position facing the pressing direction from the pressure roller. That is, when an abnormal temperature rise of the heat roller occurs, the bearing of the heat roller melts or softens, so that the heat roller moves by the pressing force from the pressure roller. Therefore, by providing the heat sensor at a position facing the pressing force from the pressure roller, the distance between the sensor surface of the heat sensor and the roller surface of the heat roller is reduced during abnormal temperature rise. As a result, according to the present invention, it is possible to quickly detect the abnormal temperature rise by the heat sensor.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific examples shown in the accompanying drawings. FIG. 1 is a front view showing the structure of the fixing device of the present invention.

In FIG. 1, this fixing device has a heat roller 1 and a pressure roller 2, and a heat sensor 3 such as a thermostat is arranged near the roller surface of the heat roller 1. The heat roller 1 incorporates a heat source (not shown) such as a heater, and the heat source heats the heat roller 1 to a predetermined fixing temperature (generally, about 170 to 200 ° C.). . As shown, the rotating shaft 1a of the heat roller 1 is rotatably supported by a bearing 5 held on a machine frame. On the other hand, the pressure roller 2
The rotating shaft 2 a is arranged so as to face the heat roller 1, the rotating shaft 2 a is held by a bearing 7, and the bearing 7 is urged by a spring 8. That is, the pressure roller 2 is pressed against the heat roller 1 by the pressing force of the spring 8 acting in the direction indicated by the arrow A.

In the fixing device having the above-described structure, the transfer paper having the toner image transferred on the surface thereof in a predetermined image forming process is pressed with the heat roller 1 such that the surface on the toner image side is the heat roller 1 side. The toner image is passed between the heat roller 1 and the pressure roller 2 so that the toner image is fixed on the transfer paper.

In the present invention, the bearing 5 of the heat roller 1 is used.
A thermoplastic resin having a melting point or softening point that does not melt or soften during normal fixing but melts or softens during abnormal temperature rise is used. By using the bearing 5 made of such a thermoplastic resin,
The bearing 5 is melted or softened due to the abnormal temperature rise, and the holding force of the rotating shaft 1a of the heat roller 1 is lost, so that the heat roller 1 moves in the direction opposite to the pressure roller 2 by the pressing force of the pressure roller 2. Will do. If the melting point or softening point of the thermoplastic resin is too high, the melting or softening property in response to abnormal temperature rise becomes worse, and if it is too low, deformation or the like occurs during normal fixing. It is preferable that the temperature is appropriately higher than the above, and it is generally preferable that the temperature be about 250 to 300 ° C. Any thermoplastic resin can be used as long as it has a melting point or softening point in such a range, but generally, a thermoplastic resin having an appropriate rigidity such as a polyolefin resin, a polyester resin, a polyamide resin, and a polycarbonate resin. A plastic resin is used.

In the present invention, the heat sensor 3 such as a thermostat is disposed at a position facing the pressing direction of the pressure roller 2 indicated by an arrow A. That is, the heat sensor 3 is disposed at a position facing the pressure roller 2 with the heat roller 1 interposed therebetween. By arranging the heat sensor 3 at such a position, it is possible to increase the responsiveness of the heat sensor 3 to abnormal temperature rise. That is, when an abnormal temperature rise occurs, the heat roller 1 is pressed by the pressure roller 2 and moves toward the heat sensor 3 due to the melting or softening of the bearing 5 described above. As a result, the heat roller 1 and the heat sensor 3
The distance D from the sensor surface becomes small, and the thermal sensor 3 can immediately detect an abnormal temperature rise of the thermal roller 1. When an abnormal temperature rise is detected by the heat sensor 3, the power supply to the heat source provided inside the heat roller 1 is stopped, thereby minimizing the trouble due to the abnormal temperature rise. Can be reliably prevented. In the present invention, it is preferable that the distance D between the sensor surface of the heat sensor 3 and the heat roller 1 is set to 2 mm or less, particularly in the range of 1.0 to 1.5 mm.
If this interval is too large, the heat roller 1
It is difficult for the thermal sensor 3 to reliably detect abnormal temperature rise even if the thermal sensor 3 moves. On the other hand, if the thermal sensor 3 is too small, the thermal sensor 3 may come into contact with the surface of the thermal roller 1 due to errors in component dimensions or assembly. This causes inconveniences such as inconvenience.

[0012]

According to the present invention, a heat roller bearing made of a thermoplastic resin having a melting point or softening point that melts or softens at an abnormal temperature rise is used, and the pressing force from the pressure roller is used. By arranging the heat sensor near the roller surface of the heat roller at a position facing the above, it has become possible to quickly detect abnormal temperature rise by the heat sensor. Thereby, damage to the apparatus when abnormal temperature rise occurs can be minimized, and trouble such as ignition can be reliably prevented, and the fixing device of the present invention has extremely high safety.

[Brief description of the drawings]

FIG. 1 is a front view showing the structure of a fixing device according to the present invention.

[Explanation of symbols]

 1: Heat roller 2: Pressure roller 3: Heat sensor 5: Bearing of heat roller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Furuya 1-2-28 Tamazo, Chuo-ku, Osaka City Inside Kyocera Mita Corporation (72) Inventor Shinji Yamamoto 1-2-28 Tamazo, Chuo-ku, Osaka City Kyocera Mita Inside (72) Inventor Akira Matayoshi 1-2-28 Tamazo, Chuo-ku, Osaka City Inside Kyocera Mita Corporation (72) Inventor Ryoji Kanematsu 1-2-28 Tamazo, Chuo-ku, Osaka City Inside Kyocera Mita Corporation F Terms (reference) 2H033 AA18 AA42 BA32 BB36

Claims (2)

[Claims] An image forming apparatus comprising: a heat roller having a heat source therein; and a pressure roller facing the heat roller and biased by a spring so as to press the heat roller, and a transfer toner image is provided between the heat roller and the pressure roller. In the fixing device in which the transfer toner image is fixed to the surface of the transfer paper by passing the transfer paper having the surface, the heat roller does not melt or soften at the time of fixing, but melts or softens at the time of abnormal temperature rise. Is rotatably held by a bearing made of a thermoplastic resin having a melting point or a softening point, and is located at a position near the roller surface of the heat roller and opposite to the pressing direction from the pressure roller. A fixing device provided with a heat sensor for preventing abnormal temperature rise of a roller. 2. The fixing device according to claim 1, wherein the sensor surface of the heat sensor and the roller surface of the heat roller are set at an interval of 2 mm or less.