JPH0477314B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating device, and particularly to a heating device with a heating prevention function.

Hereinafter, the heating device will be described using a heat fixing device applied to an image forming apparatus such as a copying machine as an example.

A conventional heat fixing device detects the surface temperature of a heating element, such as a fixing roller, heated by a halogen heater as a heat source, using a temperature detection means that is in contact with the fixing roller, and then adjusts the temperature by receiving this detection signal. A circuit connects and disconnects a switch inserted into the heater circuit to control the surface temperature of the fixing roller to be maintained within an allowable range.

By the way, if the switch is not turned on or off due to a malfunction in the temperature control circuit, the fixing roller may be heated to an abnormally high temperature. Therefore, in order to prevent this excessive temperature rise, a temperature fuse as a heat-responsive member is provided close to the fixing roller, and this temperature fuse is inserted in series with the heater circuit, so that the temperature fuse absorbs the heat from the fixing roller. By fusing the fixing roller in response to the heat, the temperature of the fixing roller is prevented from rising excessively.

In this case, placing the temperature fuse close to the fixing roller at a certain distance as described above is
This is due to the following reasons. That is, there is a regular distance-dependent temperature relationship between the fusing roller and the temperature fuse. For example, the surface temperature of the fixing roller is 200
℃, at a position 1mm away from the fixing roller
180℃, 160℃ at a position 2mm away, 180℃ at a position 3mm away, and 90℃ at a position 4mm away.
Therefore, if a temperature fuse with a rated temperature (melting temperature) of 168°C is placed 2 mm apart, it will not blow when the surface temperature of the fixing roller is normally controlled within the allowable range, and will not blow when there is an abnormality. If the temperature of the fixing roller rises excessively due to a malfunction in the temperature control circuit, and the temperature at the location of the temperature fuse reaches 168°C or higher, the temperature fuse will melt and cut off the power to the heating source. It is something that can be done. For this reason, the positional relationship between the temperature fuse and the fixing roller is important, and efforts have been made to minimize changes in the position of the fixing roller due to backlash or thermal expansion on the side where the temperature fuse is located.

However, as mentioned above, if the temperature fuse is located close to the fusing roller but away from the circumferential surface of the fusing roller, a large current will be generated.
When using a temperature fuse that can be turned off, it has a large heat capacity and has a problem of inferior thermal response (reaction time) compared to temperature detection means such as a thermistor.

SUMMARY OF THE INVENTION Therefore, the present invention provides a heating device that solves the above-mentioned problems of the conventional example, improves thermal responsiveness, and can also prevent excessive temperature rise of a heating source whose temperature changes rapidly.

The present invention, which achieves the above object, includes a heating source, a heating roller heated by the heating source, and an overheating prevention element that cuts off power supply to the heating source when the heating roller overheats. In the heating device, the heating roller is fixedly supported on one end side and movably supported on the other end side in the axial direction, and the overtemperature rise prevention element is provided on the movably supported side of the heating roller. , the heating roller thermally expands in the axial direction, thereby shortening the distance between the heating roller and the excessive temperature rise prevention element.

An embodiment of the present invention will be described below.

1 and 2 are longitudinal cross-sectional views of side ends of a heat fixing device and a heat fixing roller of a copying machine to which an embodiment of the present invention is applied.

In the figure, reference numeral 1 denotes a cylindrical fixing roller 1 made of aluminum, which is rotatably held at both ends by bearings 2a and 2b. Note that these bearings 2a, 2b
is attached to a support frame (not shown) of the fixing device. Further, the drive gear 15 is fitted and fixed to the fixing roller 1, and driving force from a drive source (not shown) on the main body side of the copying machine is transmitted via the gear 14 on the main body side. In order to keep the position of the fixing roller 1 constant and prevent it from slipping or coming off from the bearings 2a and 2b, a shaft stopper such as a C-ring is installed in the groove 1a provided only at the driving end of the roller 1. 1
6 is engaged. Further, the pressure roller 19 faces the fixing roller 1 under pressure, and has a stainless steel core 2.
It has a structure in which the circumferential surface of 0 is coated with an elastic layer 18 of silicone rubber. This core metal 20 is the bearing 17a, 1
It is rotatably supported by 7b. A halogen heater 4 is provided inside the fixing roller 1 over substantially its entire width. This halogen heater 4 is supported approximately at the center of the roller 1 by an electrode 3 attached to a frame 7, and is connected to a power source via this electrode 3 to be energized. The thermistor 5 is provided in contact with the surface of the fixing roller 1 and detects the surface temperature of the fixing roller 1. The temperature fuse 6 is located at a position where the heat rays emitted by the halogen heater 4 can be directly sensed, and the fixing roller 1 is located on the side where the drive gear 15 is fixed to the bearing 2 by a shaft stop 16 to prevent "slippage" in the longitudinal direction, that is, on the side of the roller. The roller 1 is provided close to the end face of the roller 1 in this embodiment, on the side where the coefficient of change in thermal expansion is large. The temperature fuse 6 is connected in series between the heater 4 and a power source 11 (FIG. 3) via a lead wire 13 attached to the frame 7.

Here, temperature control of the roller 1 will be explained using FIG. 3.

First, the fixing roller 1 is heated by the heater 4 supported by the electrode 3. Then, depending on the temperature detected by the thermistor 5 as a temperature detection means that is in contact with the surface of the fixing roller 1, a switch 12 is turned on or off by a signal from the temperature control circuit 10 to bring the surface of the roller 1 within an allowable range. control to maintain At this time, the temperature control circuit 10 controls the halogen heater 4 to output the maximum rated output when raising the surface temperature of the roller 1 from room temperature to the temperature necessary for fixing, and once the temperature reaches the temperature necessary for fixing, is controlled to output 1/2 of the output using phase control.

In the unlikely event that the fixing roller 1 generates heat above the rated temperature, the temperature fuse 6 will directly receive the heat above the rated temperature and blow out.
The supply of power to the heater 4 is immediately stopped. At this time, the fixing roller is made of a metal with a large coefficient of thermal expansion, and its movement in the longitudinal direction is restricted by the bearing on the side without the temperature fuse 6.
By shortening the distance between the end face of the fixing roller 1 and the fuse 6 whose position is fixed with the fixing device frame, the fuse 6 can receive heat from the fixing roller 1 more quickly, and the temperature fuse No. 6 is easily fused and the abnormal state can be quickly resolved.

This process will be explained in more detail using FIG. 4. One end of the fixing roller 1 (the left end in FIGS. 1 and 4) is regulated in position with respect to a bearing 2a fixed to a fixing device frame (not shown) by a drive gear 14 and a shaft stopper 16. The positional relationship between the free end of the fixing roller 1 (the right end in FIGS. 1 and 4) and the fixing device frame is uniquely within a minute error range (for example, ±
0.1mm range). That is, when the fixing roller 1 is at room temperature (25 DEG C.), the positional relationship between the free end of the fixing roller and the temperature fuse 6 is 1A-L1. and under normal usage conditions (e.g. 180
℃), the positional relationship is 1B-L1 (1B-L1>1A-) due to thermal expansion in the axial direction of the fixing roller.
L1). In this state, 1D-L1 is determined so that the temperature fuse 6 will not melt or change in quality even if it is affected by temperature under any normal usage conditions.

Now, due to an accident such as a disconnection of the thermistor 5 for temperature control, the halogen heater 4, which is the heating source, lights up continuously.
When the temperature of the fixing roller 1 rises abnormally, the fixing roller thermally expands in the axial direction and extends toward the unfixed free end side, that is, the side where the temperature fuse 6 is disposed. That is, temperatures much higher than normal operating conditions (e.g.
350°C), the positional relationship between the temperature fuse 6 and the end face of the fixing roller 1 is 1C-L1, and the distance between them is close, so that the temperature fuse 6 can receive more of the radiant heat of the fixing roller 1. Become. Therefore, the time T1 until the temperature fuse 6 melts is
It is much shorter than the time T2 until it melts when the thermal expansion of the fixing roller 1 is not considered (T1,
T2) Become.

FIG. 5 is a graph showing the results of a comparative experiment of thermal responsiveness between an example of the present invention and a conventional example. The experiment was conducted using the embodiment shown in FIGS. 1 to 5, which had a fixing roller made of aluminum with a wall thickness of 1.6 mm, an outer diameter of 25 mm, and a length of 260 mm, and a 1.2 Kw halogen heater installed inside. .

First, when we applied AC 100V to the halogen heater mentioned above to heat the fixing roller, the surface temperature of the fixing roller rose over time as shown in graph A in Figure 5, rising to 200°C in about 18 seconds. . On the other hand, we conducted an experiment in which a high-precision temperature fuse with a rating of 226°C ± 1.67°C was connected in series with a halogen heater to continue co-supplying power, assuming an abnormal situation.
Approximately 50 seconds after the abnormality occurred, the fuse fused and the power supply to the halogen heater was cut off. At this time, the distance between the end face of the fixing roller and the fuse is
Although it was 2.6 mm closer than when it was at 200°C, and the surface temperature of the fixing roller momentarily reached about 550°C, the fixing roller did not melt. Furthermore, graph B in Figure 5
shows the relationship between time (seconds) and the ambient temperature around the fuse.

Next, as shown in FIG.
The experiment was conducted using a fixing device which was provided for each of fixing rollers a and 2b so that the positional relationship between the end surface of the fixing roller 1 and the temperature fuse 6 would not change due to thermal expansion of the fixing roller. Similar to last time, we conducted an experiment in which power was continued to be supplied to the heater in the event of an abnormality.
The fuse fused approximately 70 seconds after the abnormality occurred.
Graph C in FIG. 5 shows the relationship between time and the ambient temperature around the fuse.

In the above embodiment, aluminum, which has a large coefficient of linear thermal expansion, is used as the fixing roller material, but metals such as iron, stainless steel, copper, and brass can also be used.

As described above, the embodiments shown in FIGS. 1 to 5 utilize thermal expansion in the axial direction of the fixing roller 1, but due to the thermal expansion in the circumferential direction of the fixing roller 1, that is, the change in the outer diameter, the circumference of the fixing roller It is also possible to utilize the fact that the distance to a temperature fuse provided near the surface changes. In this case, the structure of the bearing allows the fixing roller to expand in a specific radial direction.

Figure 7 shows an example of the above bearing.
The split bearing members 22 and 23 are made of materials having different linear thermal expansion coefficients. A sliding member 24 made of heat-resistant resin mixed with tetrafluoroethylene, for example, a cylindrical resin with good sliding properties made of a mixture of polyimide resin and tetrafluoroethylene, is attached to the inner surfaces of both bearing members 22 and 23. You can also crucify it.
In other words, a resin with good sliding properties expands and contracts sufficiently to follow the material fixing the outside, so if the bearing member 23 is made of a material that thermally expands better than the bearing member 22, it is possible to support the bearing of the fixing roller 1. When the fixing roller 1 is heated, the fixing roller thermally expands into an elliptical cross section as shown in FIG. (The roller 1 actively expands toward the bearing member 23, which is prone to thermal expansion.) Its diameter increases from R1 to R2, and as a result, if a temperature fuse is provided close to the roller surface on the bearing member 23 side, The distance between the fixing roller and the temperature fuse is shortened, the temperature fuse is blown out more quickly, and excessive temperature rise can be reliably prevented.

In an experiment using stainless steel for the bearing member 22 and aluminum for the bearing member 23, a thermal expansion change of R2-R1 = 1.0 mm occurred in a bearing with an inner diameter of 25φ.

FIG. 9 shows another example of the bearing structure, in which the sliding members 27a and 27b are divided into two parts and brought into close contact with the bearing members 25 and 26, respectively.
A frame body 28 that allows 5 and 26 to be moved up and down freely inside.
The spring member 29 is inserted between the frame body 28 and the bearing member 26.

In this example as well, the bearing part of the fixing roller 1 has a large degree of freedom in the vertical direction, and when the fixing roller is heated, it pushes up the bearing member 26 against the spring force of the spring member 29 and forms an elliptical cross section. thermally expands to
The same effects as in the examples shown in FIGS. 7 and 8 can be obtained.

Note that the temperature fuse 6 as a thermally responsive member is
Various types of temperature switches are available, such as temperature switches using bimetals and temperature switches using magnetic materials.

As described above, in the present invention, when the temperature of the fixing roller increases due to the occurrence of an abnormal situation, the fixing roller causes thermal expansion to bring the distance between the fixing roller and the temperature fuse arranged and fixed in the direction of the thermal expansion closer to each other. Therefore, the temperature fuse quickly responds to the excessive heat generation of the fixing roller and blows out, so that the abnormal state can be quickly resolved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the heating device of the present invention, FIG. 2 is an enlarged longitudinal sectional view of a part thereof, FIG. 3 is a block diagram of the temperature control circuit, and FIG. 4 is an explanatory diagram of thermal expansion of the fixing roller.
FIG. 5 is a graph of the heating time versus temperature increase of the fixing roller, FIG. 6 is a vertical cross-sectional view of the fixing roller employing a conventional bearing structure, and FIG. 7 is a diagram showing an example of the bearing structure of the fixing roller. FIG. 8 is the same diagram as above showing a state in which the fixing roller is thermally expanded in the diametrical direction, and FIG. 9 is a diagram showing another example of the bearing structure of the fixing roller. 1 is a fixing roller, 2a and 2b are bearings, 3 is an electrode, 4 is a heater, 5 is a thermistor, 6 is a temperature fuse, and 7 is a frame.

Claims (1)

[Scope of Claims] 1. A heating device comprising a heating source, a heating roller heated by the heating source, and an overheating prevention element that cuts off power supply to the heating source when the heating roller overheats. In the apparatus, the heating roller is fixedly supported at one end and movably supported at the other end in the axial direction, and the excessive temperature rise prevention element is provided on the movably supported side of the heating roller, A heating device characterized in that the distance between the heating roller and the overheating prevention element is shortened by thermal expansion of the roller in the axial direction.