JPH043324Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial field of application to which the invention belongs) This invention heat-fixes an unfixed image onto a recording material, such as those used in recording devices such as copying machines, laser beam printers, and printers. The present invention relates to a device that prevents excessive temperature rise of the device.

(Prior Art) In recent years, a pair of roller type fixing devices have been adopted in heat fixing devices because of their good thermal efficiency and stability of fixing performance.

In order to form a thermal roller, a heater is provided outside or inside the roller.
The roller surface is then heated to a temperature that allows fixing, but the waiting time required for this cannot be avoided.

Recently, in order to shorten this waiting time, a heating roller 1 having a configuration as shown in FIGS. 4 and 5, that is, a metal cylindrical roller with a thickness of several mm and coated with an anti-offset layer of several tens of microns, is used. a heating source 8 therein;
An elastic pressure roller 2 for forming a nip in the heat fixing section, a known guide 6, separation claws 5, 7, a thermistor 3 for temperature control of the heating roller 1, and a safety device 10 such as a temperature fuse or thermoswitch are provided. The temperature control means 9 maintains the temperature of the heating roller 1 at a predetermined temperature. 4 is a cleaning means. The safety device 10 is normally provided near the thermistor 3, as shown in FIG. 5, in order to reflect the surface temperature of the heating roller 1. At this time, the safety device (thermo switch is used in this figure) and thermistor 3 are both installed within the minimum paper passing width area B so that they are not affected by the temperature difference between the paper passing area and the non-paper passing area. There is.

In addition to the above-mentioned safety device, the heat fixing device described above takes safety measures by measuring the energization time of the heater and checking the temperature rise time, but in the event of an abnormality, the power supply side Triack, SSR, which becomes the switching element 12 of
etc., but it is not useful in cases where the heater continues to be energized due to a failure on the power supply side.

Therefore, the most reliable safety devices are search switches or temperature fuses that break at a predetermined temperature, but as mentioned above, these are installed within the paper passing area, so they are prone to malfunction and have poor response status. It's not appropriate. For example, when the recording material is wrapped around the heating roller 1, the temperature transmitted to the safety device 10 appears to be lower, so the surface of the heating roller 1 is heated and rises significantly. It will burn. This phenomenon is particularly noticeable because the thermal response of the safety device is at its limit due to the rapid rise in heating temperature that has been required in recent years.

(Purpose of the Invention) An object of the present invention is to provide a safety device that can detect temperature abnormalities in a conventional heat fixing device more accurately and with a simple configuration, and can prevent damage to the fixing device at low cost.

(Summary of the present invention) In order to achieve the above object, the present invention provides a fixing device having a heat source and a fixing rotating body that heats and fixes an unfixed toner image onto a recording material using heat generated from the heat source. , characterized in that first and second safety devices that cut off power supply to the heat source when the temperature reaches a predetermined temperature are electrically provided in series in the power supply path to the heat source.

In a configuration that is effective in concrete implementation, the plurality of safety devices described above include a first safety device provided in the paper passing and fixing area of the recording material, and a second safety device provided in the non-paper passing portion of the recording material. and the operating rating of the first safety device is lower than the operating rating of the second safety device.

According to the present invention, it is possible to reliably detect an excessive temperature rise in the heat fixing device, and to ensure overall safety at low cost and with certainty.

(Description of Embodiment) FIG. 1 shows an embodiment of the present invention. heating roller 1
The thermistor 3 is installed in the minimum paper passing area B in the center.
The heating roller 1 is supported by left and right side plates 16a and 16b via bearings. AC power supply 13, switching element 1
2. The thermoswitch 10b connected in series with the thermoswitch 10a to the power supply connection connecting the heater 8 is connected to the side plate 1 from the paper passing area A provided on the outside of the non-paper passing side with respect to the right side plate 16a.
6a. The heating roller 1 is driven by a gear 1 on the non-sheet passing side with respect to the left side plate 16a.
This is done via 7. In this embodiment, the control means 9 turns on and off the switching element 12 based on the output from the thermistor 3, so that the surface temperature of the heating roller 1 is controlled at 170°C, and the overshoot at startup is also 185°C, and after continuous paper feeding. Overshoot is also suppressed to a maximum of 190℃. At this time, the thermoswitch 10a is selected to be one that disconnects at the rated temperature of 215°C, so that excessive temperature rise during abnormal conditions will occur when the thermal response of the thermoswitch 10a is at its worst (for example, unless the recording material wraps around the surface of the heating roller 1). : Even at low temperatures (morning - start-up), the heating roller surface temperature only rises to 290°C. Therefore, if the fixing device is damaged, it is necessary to replace the parts such as the heating roller surface and pressure roller if they are made of resin with a heat-resistant temperature of 300°C or less. (e.g. separation claws, insulation bushings, etc.)
etc., there is no need to replace them.

On the other hand, when paper as a recording material wraps around the heating roller 1, the thermal response of the thermoswitch 10a in the paper passing section becomes very poor.
The surface temperature of heating roller 1 when 0a is disconnected is
The temperature rises to around 400°C, and up to around 500°C depending on the way the paper is wrapped and the operating temperature of the thermoswitch. At this time, the transfer paper wrapped around the heating roller 1 emits smoke and is on the verge of catching fire, which is extremely dangerous.

However, in this embodiment, the above-mentioned excessive temperature rise can be prevented by using the thermoswitch 10b provided in the non-sheet passing area. That is, thermo switch 10
The operating temperature of the thermo switch 10a is set to a rated 265°C, which is higher than the rated 215°C of the thermoswitch 10a. Since the surface of the heating roller where the thermo switch 10b is installed is a non-paper-passing area, the temperature of the surface of the heating roller is not taken away while paper is passing, and heat is radiated from the edges, causing the temperature to rise to a worst-case temperature of 245°C. Warm up. The light distribution of the heater 8 at this time is shown in FIG. The heater 8 has the highest light distribution on the gear 17 side with respect to the roller 1, and the contact area of the thermistor 3 and the thermoswitch 1.
The contact area of thermo switch 10b is lower and more uniform, and the other end, which is not the driving side, has a slightly higher light distribution.At the contact area of thermo switch 10b, the light distribution gradually decreases and becomes slightly lower than the center area. There is. With such a light distribution, the surface temperature of the heating roller 1 in contact with the thermoswitch 10b rises at a maximum temperature of 25 degrees Celsius lower than the contact area of the thermistor 3, and the surface temperature of the heating roller 1 When the temperature is stable, the temperature is 10°C lower than the contact area of thermistor 3.

As mentioned above, when the recording material wraps around the heating roller 1, the thermo switch 10 provided above the paper passing area
Safety is ensured by operating the thermoswitch 10b provided in the non-sheet passing area without raising the temperature of the roller surface to about 400°C, or 500°C in the worst case. Furthermore, in this example, the thermoswitch 10b is completely separated from the paper passing area by the side plate inside the fixing device, so no matter how obliquely the recording material is fed, there is no space between the thermoswitch 10b and the heating roller 1. Since there is no need to worry about jamming, an excessive rise in the surface temperature of the heating roller 1 can be quickly detected even if the jam is wrapped around the heating roller 1 when it occurs. At this time, the thermoswitch 10b operates when the portion of the heating roller 1 in contact with the thermoswitch 10b is at 330° C. even in the worst case.
At this time, the surface temperature of the central part of heating roller 1 is 370
℃, but there is no risk of the temperature reaching 400℃ or higher as mentioned above, so there is no risk of the recording paper emitting smoke or catching fire.

Of course, the positions and ratings of the thermoswitches 10a and 10b may be arbitrarily determined, but safety is ensured by wiring them in series during connection to the heater.

FIG. 3 shows another example of a safety device installed in the non-sheet passing area of FIG.
It uses This temperature fuse 10c is a halogen heater 8 which is a heater inside the heating roller 1.
The structure is such that it operates using radiant heat from the Note that 14 is a heat reflecting plate that surrounds the temperature fuse 10c and the end of the roller. Therefore, since the temperature fuse 10c does not directly detect the surface temperature of the heating roller 1, but is non-contact, it operates according to the length of the continuous energization time of the halogen heater 8, in other words, the temperature increases during the heating time. The operating time may be set to a predetermined value depending on the distance to the halogen heater 8, the reflection efficiency of the reflection plate 14, and the distance. In this embodiment, the temperature fuse 10c is activated when the halogen heater 8 is continuously energized for 60 seconds or more.
At this time, the surface temperature of heating roller 1 is 380℃ at worst.
It rose to In this example, a 600W halogen heater 8 was used and the experiment was conducted at a copying speed of 8 sheets/A4 minutes.At this time, the halogen heater 8 could not be used continuously for more than 40 seconds even when paper was passed continuously at a low temperature of 5 degrees Celsius. There is no need to worry about the temperature fuse 10c blowing out except in abnormal situations.

The above configuration has the advantage that the length of the heating roller 1 is only required to be equal to the maximum paper passing area A, and there is no need to take up extra space. Furthermore, since the light distribution of the heater in the bearing can be lowered, there is also the advantage that the bearing does not require much heat resistance. FIG. 6 shows only the configuration around the safety device in the area on the non-sheet passing side of the embodiment of the present invention, but the other configurations are the same as in the previous example. As shown in FIG. 6, instead of elongating the heating roller 1 in the axial direction, a heat absorbing plate 20 is fixed to the main body of the apparatus so as to cover the heater 8 in the non-sheet passing area, and the heat absorbing plate 20 is fixed to the main body of the apparatus to absorb the heat. The thermoswitch 10b can also be brought into contact with the absorption plate 20. At this time, the heat absorbing plate 20 is fixed to the side plate 16a of the fixing device via a heat insulating material 21, thereby minimizing wasteful escape of heat. This configuration has the same effect as that shown in FIG. 1, and has the advantage that the heat absorbing plate 20 does not rotate, so that the thermoswitch 10b can maintain perfect contact. By providing safety measures in both the paper passing area and non-paper passing area in this way,
When the recording material does not wrap around a heating member such as a roller, any abnormal temperature rise in the heating and fixing device is detected in the paper passing area, and the safety device operates at a relatively low temperature, which reduces damage to the fixing device. , the number of replacement parts can be reduced. Further, when the recording material is wrapped around the recording material, the thermoswitch in the non-sheet passing area is operated reliably to prevent the recording material from emitting smoke or catching fire, thereby preventing danger due to excessive temperature rise due to an abnormality in the fixing device.

In the present invention, overtemperature rise can be detected more reliably by providing multiple safety devices that preferably operate with different ratings in different detection devices, and by wiring these in series to the power supply side connection to the heating source. Safety is further improved.

(Effects of the Invention) The present invention can more reliably, inexpensively, and highly reliably prevent excessive temperature rise in the heat fixing device without requiring complicated control.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the arrangement of safety means on the heating roller in an embodiment of the present invention, Fig. 2 is a diagram showing the light distribution of the heater used in Fig. 1, and Fig. 3 is a diagram showing the arrangement of the safety means on the heating roller in an embodiment of the present invention. FIG. 4 is a sectional view of a fixing device used in the present invention and a conventional example, FIG. 5 is an explanatory diagram of the arrangement of the conventional example, and FIG. FIG. 6 is an explanatory view of the main parts of the attachment part of the safety means in the paper area part. 1 is a heating roller, 3 is a thermistor, 8 is a heater, 10, 10a, 10b are thermoswitches, 1
0c is a temperature fuse, A and B are paper passing areas, 16a,
16b is the side plate.

Claims (1)

[Claims for Utility Model Registration] In a fixing device having a heat source and a fixing rotating body that heats and fixes an unfixed toner image onto a recording material using heat generated from the heat source, when the temperature reaches a predetermined temperature, the above-mentioned A fixing device characterized in that first and second safety devices for cutting off power supply to the heat source are electrically provided in series in the power supply path to the heat source.