JPH04181978A - Fixing device - Google Patents

Abstract

PURPOSE:To detect the surface temp. of a heat roller without damaging and wearing the roller surface by providing a rotating member which rotates at the circumferential speed approximately equal to the circumferential speed of the heat roller between the heat roller and a means for detecting the surface temp. of the heat roller. CONSTITUTION:A cap 12 is mounted on one side of a cylindrical ring 9 and a shaft 10 is attached to this cap 12. This shaft 10 is supported by a bearing 11. The ring 9 is so disposed as to come into contact with the surface of the roller 4. The ring is, therefore, driven by the roller 4, to rotate in an arrow B direction when the roller rotates. Further, a thermoswitch 1 is disposed in the position where the switch slides in contact with the inner peripheral surface of the ring 9. The temp. of the roller 4 surface is exactly detected in this way without chipping or damaging the surface of the roller 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer, and more particularly to a fixing device for fixing an image on a transfer material.

[Prior Art] Conventionally, a fixing device in an image forming apparatus such as a copying machine is shown in FIG.
, 6. First, a formed toner image is transferred onto a sheet of paper 8 by a photosensitive drum and a developing device (not shown) and is conveyed to a fixing roller (arrow A in the figure).The paper is then transferred to a fixing entrance guide 7.
and is transported to the nip portion between the fixing roller 4 and the pressure roller 6. The fixing roller 4 usually has a hollow interior, and a halogen heater 5 is disposed therein. The fixing roller is heated by this Haloken heater, and the pressure roller 6 is also heated by rotating in contact with the fixing roller. When the paper carrying the toner image is caught in the nip between the pressure roller 6 and the fixing roller 4, the pressure of the roller crushes the toner, and the heat of the roller melts the toner. The toner image is fused to the paper. How well the toner is fixed on the paper largely depends on the surface temperature of the roller.
It is necessary to keep the roller at a constant temperature at all times. Therefore, the thermistor 3 is placed in contact with the roller surface to measure the roller surface temperature. If the temperature is low, the heater 5 is turned on, and if the temperature is too high, it is turned off to keep the roller surface temperature constant. ing. In addition to the thermistor mentioned above, the roller also has
Thermoswitch 1 is also in contact. This happens when the thermistor 3 breaks down and temperature measurement becomes impossible, or when the heater control circuit mentioned above breaks down.
This is to prevent the heater from being left on and causing abnormal heating of the roller. For example, set the roller surface temperature to 180℃.
If the thermo switch is controlled to keep the temperature at 230°C, the temperature of the thermoswitch is set to turn off at a temperature several tens of degrees higher than that temperature, for example, 230°C.

[Problems to be Solved by the Invention] However, in the conventional example described above, the thermistor 3 and the thermoswitch l are constantly in contact with and sliding on the rotating roller 4, so that the surface of the roller 4 does not come into contact with the surface of the roller 4. The parts were worn out, which shortened the roller's durable life. Further, if dust or small dirt adheres to the surface of the thermistor or thermoswitch, the surface of the roller 4 may be scratched and the image transferred onto the paper may be damaged.

In addition, in order to eliminate the above-mentioned drawbacks, if the thermistor and thermoswitch are placed outside the area where the paper passes, that is, closer to the end of the roller, the heat dissipated from the end of the roller will be large.
It was difficult to accurately control the temperature of the entire roller.

[Means for Solving the Problems] According to the present invention, the above-mentioned problems can be solved by providing a rotating member having substantially the same circumferential speed as the heat roller between the heat roller and the temperature detection means for the heat roller. This is the solution.

[Embodiment] Figs. 1 and 2 show schematic diagrams of an embodiment of the present invention. In order to simplify the diagram, the thermistor will be omitted and a thermoswitch will be explained as an example. The paper 8 is conveyed to the nip portion of the rollers 4.6 while being guided by the entrance kite 7, and the process of fixing the toner image on the paper is the same as in the conventional example.

The cylindrical ring 9 has a lid 12 attached to one side thereof, and a shaft 10 is attached to the lid. axis 1
0 is supported by a bearing 11. Therefore, ring 9
is rotatable about an axis 10.

Further, since the ring 9 is arranged so as to come into contact with the surface of the roller 4, when the roller 4 rotates, the ring 9 follows and rotates in the direction of arrow B in the figure. The thermoswitch l is arranged at a position where it abuts and slides on the inner peripheral surface of the ring 9. Therefore, the temperature detected by the thermoswitch 1 is precisely the temperature of the inner peripheral surface of the ring 9.

However, since the ring 9 is thin (and is made of copper and other materials with excellent heat conduction), the inner surface temperature of the ring 9 and the surface temperature of the roller 4 are almost the same. ,
No problems will occur. Since the ring 9 rotates as a result of the roller 4, it does not scrape or damage the surface of the roller. The surface of the ring 9 is coated with Teflon resin to prevent dirt.

Other embodiments of the present invention are shown in FIGS. 3 and 4. The small roller 13 is in contact with the fixing roller 4.

When the fixing roller 4 rotates, the small roller 13 also rotates as a result. The thermo switch l comes into contact with the small roller 13,
The fixing roller 4 is sliding, and the surface temperature of the fixing roller 4 is the same as the small roller 13.
It is transmitted to the thermo switch via.

The small roller I3 is made of a material with excellent heat conductivity, and its diameter is made as small as possible.

Thereby, the thermoswitch can detect a temperature that is approximately the same as the surface temperature of the fixing roller 4.

Although the embodiments described above are all related to thermoswitches, it is also possible to use a similar configuration for a thermistor, and it is also possible to use a plurality of rotating members that rotate in contact with the fixing roller. is also possible.

[Effects of the Invention] As explained above, by providing a rotating member whose circumferential speed is approximately the same as that of the heat roller between the heat roller and the heat roller surface temperature detection means, it is possible to prevent the roller surface from being scratched or It is possible to detect the surface temperature of the heat roller without abrading the surface.

[Brief explanation of drawings]

1 and 2 are perspective views of one embodiment of the present invention, and sectional views. FIGS. 3 and 4 are perspective views of other embodiments of the present invention, and
Cross-sectional views FIGS. 5 and 6 are a perspective view and a sectional view showing a conventional example. ■...Thermoswitch 3...Thermistor 4...Heat roller 6...Pressure roller 8...Paper 9...Ring 13...Small roller

Claims (1)

[Claims] In a fixing device that sandwiches a sheet of paper on which a toner image is formed between a pair of rollers and heats and fixes the toner image on the sheet, a means for detecting the surface temperature of the thermal roller and a thermal roller are installed between the thermal roller and the thermal roller. A fixing device characterized by having a rotating member having substantially the same circumferential speed.