JPH0213793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device for fixing a powder image in an electrophotographic device or the like.

Generally, in a fixing device, the surface temperature of a heating roller heated by a heater is detected by a temperature detection means that is in contact with, buried in, or close to the roller, and a temperature control circuit that receives this detection signal detects the temperature of the heating roller as described above. The power applied to the heater is controlled to keep the surface temperature of the roller within an allowable range.

However, if the heater is not controlled due to a failure in the temperature control circuit, the heating roller will be heated to an abnormally high temperature, which may cause burnout of the roller itself or surrounding members, or even a fire. Therefore, in order to prevent this excessive temperature rise, a temperature fuse is provided close to the heating roller, this temperature fuse is inserted in series with the heater circuit, and this temperature fuse receives heat from the heating roller and melts. This prevents the fixing roller from becoming excessively heated.

However, conventionally, temperature fuses were placed to receive radiant heat from heating rollers, so
They are easily affected by the air flow around the rollers and fuses, and there may be cases where the fuses do not melt even though the rollers have actually reached a critical temperature, and the amount of radiant heat received is dependent on the distance from the rollers. Even a slight difference can make a big difference, so a high level of precision is required in the placement of the fuses, otherwise the fuses may frequently melt even when there is no abnormal temperature rise, or even if the temperature rises abnormally. The inconvenience of not melting occurs. Furthermore, if only the radiant heat from the rollers is used, due to the heat capacity of the fuses, it will take a long time from when the rollers reach an abnormal temperature until the fuses melt, that is, the response time will be long, and during that time the rollers will not rise. There is an inconvenience that the temperature progresses, and this inconvenience is especially great for rollers that have a thin wall thickness and a small heat capacity.

The purpose of the present invention is to overcome the various disadvantages mentioned above.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front sectional view of one embodiment of the present invention, and FIG.
The figure is a plan sectional view of the end portion of the heating roller.
A heating roller 1 and a pressure roller 18 sandwich and convey a toner image supporting paper (not shown), at which time the toner image is heated and fixed on the paper. The heating roller 1 is a thin cylindrical roller made of aluminum, and both ends thereof are rotatably held by bearings 2a and 2b. It is preferable to apply a thin layer of tetrafluoroethylene resin, silicone rubber, or the like to the peripheral surface area of the roller 1 that comes into pressure contact with the pressure roller 18 to prevent offset. Furthermore, this bearing 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. The pressure roller 18 rotates as a result of the heating roller 1. And this heating roller 1
The pressure roller 19 facing the pressure roller 19 has a structure in which the circumferential surface of a core metal 20 made of stainless steel is coated with an elastic layer 18 of silicone rubber. This core metal 20 is rotatably supported by bearings 17a and 17b. 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 central shaft portion 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. As a result, the roller 1 is heated from within by the heat rays emitted from the filament 4' of the heater 4.

Reference numeral 5 denotes a temperature sensing element such as a thermistor, which is brought into contact with or in close proximity to the surface of the roller 1 to control the temperature of the heating roller 1 to maintain it within an appropriate temperature range capable of fixing the toner image. Detect. 6 is a temperature fuse. This 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 a frame 7.

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 fix the toner image on the surface of the roller 1. Control to maintain the required temperature within the appropriate range. At this time, the temperature control circuit 10 controls the output voltage changing circuit 9 from the power supply 11 to raise the surface temperature of the roller 1 from room temperature to the temperature required for fixing by increasing the voltage applied to the halogen heater 4. The heater 4 is controlled to output the maximum rated output, and once the temperature necessary for fixing is reached, the voltage applied to the heater 4 is lowered and controlled to output 1/2 of the above output. .

In the unlikely event that the fixing roller 1 is heated to a temperature higher than the rated temperature, the temperature fuse 6 will directly receive heat higher than the rated temperature and melt.
The supply of power to the heater 4 is immediately stopped.

Now, as is clear from Figure 1, fuse 6
is among the radiant heat rays of filament 4' of heater 4,
It is arranged close to the roller end so as to directly receive the heat rays 16 emitted from the opening 1' at one end of the roller 1. A reflector plate 8 is arranged behind the fuse 6 to reflect the heat rays passing by the fuse 6 and direct them toward the fuse 6. This reflector plate 8 may be removed, but its provision has the effect of increasing the amount of heat rays from the heater 4 given to the fuse 6, thereby further shortening the response time of the fuse 6 in the event of an abnormality. In any case, since the fuse 6 is heated by the radiant heat rays of the heater 4, the influence of the surrounding air flow is smaller and the placement accuracy is less, compared to conventional devices that are heated only by the radiant heat of the roller 1. , the response time is also shortened, and the system responds faithfully to abnormal conditions.

Meanwhile, the roller 1 is mainly made of a metal material having a large coefficient of thermal expansion, such as aluminum. Therefore, when heated by the heater 4, the roller 1 extends in its axial direction due to thermal expansion. At that time, as the position of the opening end of the roller facing the fuse 6 moves to the right in FIGS. Responsiveness to conditions becomes slow. Therefore, as shown in FIGS. 1 and 2, the roller 1
A groove 1 is provided at the end on the side where the fuse 6 is disposed.
a, 1b are provided, and C rings 21a, 1b are provided in these grooves.
21b, and these C rings 21a, 21b.
The bearing 2b is sandwiched between the bearings 2b from both sides. Therefore, the roller end portion hardly moves in the axial direction of the roller. (This amount of movement is determined by the distance between the bearing 2b and the C-rings 21a and 21b, but it is usually easy to keep this within ±0.1 mm.) On the other hand, the other end of the roller 1 is The supporting bearing 2a is a sliding bearing that rotatably supports the roller 1 and also supports the roller 1 movably in the axial direction. Therefore, after the roller 1 starts thermal expansion, the end of the roller 1 on the side where the fuse 6 is not provided, that is, the end on the side where the gear 15 is fixed, is displaced to the left in FIG. However, the end on the opening 1' side hardly moves to the right. Therefore, even if the roller 1 expands thermally and its length increases, there will be no inconvenience such as an increase in the amount of heat rays radiated from the heater 4 being kicked by the end of the roller against the fuse 6. Accurate operation is thus possible.

In addition, since the gear 15 side end moves to the left due to thermal expansion, the width of the gear 14 that meshes with the gear 15 is
It is desirable that the gear 15 has a width sufficient to maintain sufficient meshing even when the gear 15 moves in this manner.

Further, in the above embodiment, the end on the opening 1' side was fixedly supported in the roller axial direction by using C rings 21a and 21b, but the C ring was abolished and a sliding bearing 21b was installed between the inner ring and the outer ring. By interposing a ball between the inner ring and the outer ring, replacing it with a ball bearing with almost no axial play between the inner ring and outer ring, press-fitting and fixing the roller 1 into the inner ring, and fixing the outer ring to the frame of the main body of the fixing device, Preventing the opening 1' side end from moving in the roller axial direction,
In other words, it may be fixedly supported. On the other hand, the end of the roller opposite to the opening 1' is freely supported in the axial direction of the roller by a sliding bearing 2a, that is, supported movably in the axial direction of the roller. However, any of the above ball bearings can be used as the bearing 2a. In this case, the inner ring and roller 1 are fixed to each other in the roller rotational direction by a key, and by providing a keyway in the roller axial direction, the roller end can be made movable in the roller axial direction with respect to the inner ring. do it. The outer ring may be fixed to the main body frame of the fixing device.

In addition, as mentioned above, the voltage applied to the heater 4 is
In an apparatus in which the roller 1 is raised from room temperature to an appropriate temperature for fixing, and then again maintained at an appropriate temperature for fixing, and the former is made higher than the latter, the radiant heat rays of the heater 4 are heated as described above. By arranging the fuse so that it receives light directly, it is possible to quickly respond to abnormal conditions. The reason is that when the temperature control circuit malfunctions, normally in such devices, the high voltage mentioned above is applied to the heater and then it is left unattended, and at this time the heater emits high heat, so the heater is directly exposed to the hot wire of the heater. This is because fuses can be quickly fused and abnormal conditions can be dealt with quickly.

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.

Note that instead of the heat-melting temperature fuse 6, various types such as a temperature switch using a bimetal or a temperature switch using a magnetic material can be used.

As described above, when the temperature of the heating roller and its surrounding members rises abnormally due to the occurrence of an abnormal situation, the present invention can quickly respond to the situation and cut off the power supply to the heat source in a safe manner. It is something that enhances sexuality.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of the fixing device of the present invention, FIG. 2 is a cross-sectional view of a part thereof, and FIG. 3 is a block diagram of a temperature control circuit. 1 is a fixing roller, 2a and 2b are bearings, 4 is a heater, 6 is a temperature fuse, and 21a and 21b are C rings.

Claims (1)

[Claims] 1. A fixing device having a cylindrical roller, a heat source disposed in the roller, and a heat-sensitive member disposed near the roller that cuts off power supply to the heat source in response to an abnormal temperature rise. The member is arranged at a position to receive the radiant heat rays of the power source emitted from one open end of the cylindrical roller, and the end of the cylindrical roller on the one open end side is fixedly supported in the roller axial direction. A fixing device characterized in that an end on the other open end side is freely supported in the axial direction of the roller.