JPH0683233A - Heat fixing device - Google Patents

Abstract

PURPOSE:To prolong the life of a press roll by deforming a deformable member by the heat from a heating means and relatively pressing a belt-like heat transfer body and the press roll by the deformation pressure thereof. CONSTITUTION:A heating element 3 exists in the position apart from the belt- like heat transfer body 5 while the heating element 3 is below a specified temp., but a coil spring 6 made of a shape memory alloy is reset to an extended state when the heating element 3 is heated. The heating element 3 is thereby lowered to bring the belt-like heat transfer body 5 and a working roll 10 into pressurized contact with each other. Namely, the coil spring 6 installed near the heating element 3 is heated as well when the heating element 3 is overheated by a heater. The soil spring 6 is deformed to the shape previously memorized by a shape memory effect to generate pressing force when the preset temp. is attained. This pressing force is transmitted to the press roll 10 to press the press roll 10 to the belt-like heat transfer body 5. Then, the coil spring 6 is apart from the press roll while the belt-like heat transfer body is at the specified temp. or below and, therefore, the long of the press roll is prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device used in electrophotographic printers, ink jet printers and the like.

[0002]

2. Description of the Related Art A conventional heat fixing device is disclosed in
No. 148161, a spring is used as a means for pressing the pressure roll against the heat fixing surface, or the position of the pressure roll 10 is set to the belt-shaped heat transfer member 5 as shown in FIG. The pressure roller 10 is pressed against the heat fixing surface by using the elastic force of the flexible material on the surface of the pressure roller by pressing and fixing the heat roller 3 through the heat generating element 3. In addition, 1 is a drive roll, 2 is a shaft, 4 is a heating element support member, and 9 is a shaft.

[0003]

The conventional thermal fixing device is
Since the pressure roll is constantly pressed against the heating element via the belt-shaped transmission member by spring force or the like, the flexible material on the surface of the pressure roll is liable to be permanently deformed, and the life of the pressure roll is short. It was Also, in order to extend the life of the pressure roll, it is possible to consider a device that separates the pressure roll from the belt-shaped heat transfer member while the energy supply to the heating element is stopped, but the cost is wide because of the wide variety of components. There was a drawback that became high.

It is an object of the present invention to provide a heat sizing apparatus which can extend the life of the pressure roll with a simple structure.

[0005]

In order to achieve the above-mentioned object, when the heat generating element falls below a certain temperature, the pressure roll and the belt-shaped heat transfer element are separated from each other, and the heat generating element exceeds a certain temperature. (EN) Provided is a thermal fixing device capable of pressing a pressure roll against a heating element via a belt-shaped heating element with a constant force when the sheet is exposed.

More specifically, a heat generating means having a heat generating element inside, a drive roll arranged at a predetermined distance from the heat generating means, and a rotatably wound between the heat generating means and the drive roll. A belt-shaped heat transfer member, and a pressure roll that is arranged at a position facing the heat generating means via the belt-shaped heat transfer member and rotates together with the belt-shaped heat transfer member.
In the heat fixing device for fusing and fixing the unfixed toner image on the image support by passing the image support carrying the unfixed toner image between the belt-shaped heat transfer member and the pressure roll, A deformable member made of a shape memory alloy that deforms due to a temperature rise is disposed near the position of the deformable member, and the deformable member is deformed by the heat from the heat generating means. It is configured so as to relatively press the body and the pressure roll.

[0007]

In the heat fixing device configured as described above, when the heating element is overheated by the heater, the elastic body made of a shape memory alloy installed in the vicinity of the heating element is also heated to a preset temperature. When the temperature reaches, the heated elastic body is deformed by the shape memory effect into a shape stored in advance to generate a pressing force, and the pressing force is transmitted to the pressing roll, and the pressing roll is moved to the belt. Pressed against the heat conductor. Alternatively, the pressing force is transmitted to the belt-shaped heat transfer member, and the belt-shaped heat transfer member is pressed against the pressure roll.

[0008]

The present invention will be described below with reference to examples.

In FIG. 1, the heating element 3 is made of a resistance heating type heater or a positive temperature coefficient thermistor heater, and is supported by a heating element support member 4. The belt-shaped heat transfer member 5 is a thin plate endless belt made of polyimide resin, nickel alloy, or the like. The drive roll 1 has a synthetic rubber lined on the surface of a stainless alloy, has a large coefficient of friction with the belt-shaped heat transfer member 5, and rotates about the shaft 2 in the direction of the arrow (the drive system is Although omitted in FIG. 1, the belt-shaped heat transfer member 5 is driven in the direction of the arrow while sliding on the surfaces of the heat generating member support member 4 and the heat generating member 3 by the frictional force with the drive roll 1.

The pressure roll 10 has a shaft 9 lined with a flexible material such as synthetic rubber or sponge, and both ends of the shaft 9 are rotatably supported by levers 7.
One end of the shape memory alloy coil spring 6 is attached to the opposite side of the lever 7 to the pressure roll 10, and the other end is attached to the heating element support member 4. The center of gravity when the pressure roll 10 is attached to the lever 7 is the fulcrum 8
By deciding the shape of the lever 7 so that it is located on the pressure roll 10 side with respect to, the rotational moment in the counterclockwise direction about the fulcrum 8 and the spring of the shape memory alloy coil spring 6 in FIG. The gap with the belt-shaped heat transfer body 5 is set to g by the rotational moment of the force.

The heating element support member 4 is attached to the heating element support member 4 in the process of keeping the surface temperature of the belt-shaped heat transfer element 5 at about 170 ° C. by heat conduction while energizing the heating element 3 to heat the heating element support member 4. The shape memory alloy coil spring 6 thus heated is also heated at the same time. 80 of this shape memory alloy coil spring 6
L2 (L2> L1) shown in Figure 2 for the set length in ° C
And L2−L1 = ΔL. When the shape memory alloy coil spring 6 is heated to 80 ° C., the lever 7 rotates clockwise about the fulcrum 8 by ΔL. Pressure roll 10
As for the surface of L, the lever length of lever 7 is L as shown in FIG.
3 and L4, the displacement is ΔL × L4 / L3 = g ′.

Here, ΔL, L3, so that g <g '.
If L4 is set and g'-g = Δg, the pressure roll 1
The flexible material on the surface of 0 bends by Δg and generates a pressing force according to the elasticity of the flexible material. When the drive roll 1 is rotated in the direction of the arrow, the belt-shaped heat transfer member 5 is also driven in the direction of the arrow, and the pressure roll 10 is also rotated in the direction of the arrow.

In this state, when the recording medium 12 having the heat-melting toner or heat-melting ink 11 attached thereto is passed in the direction of the arrow, the heat energy of the surface of the belt-shaped heat transfer body 5 and the pressing force of the pressure roll 10 are applied. Thus, the heat-melting toner or the heat-melting ink 11 is fixed on the recording medium 12 and is discharged to the left side of the pressure roll in FIG.

When the energization of the heating element 3 is stopped by a command signal generated when the recording medium 12 does not come in for a long time or when the power source of the apparatus is turned off, the heating element support member 4 is gradually cooled, and When the shape memory alloy coil spring 6 is also gradually cooled and reaches a preset temperature of about 80 ° C., the shape memory alloy returns to the state of FIG. 1 due to the shape memory effect, and the belt-shaped heat transfer body 5 and the pressure roller 10 are returned. The gap between and is g.

In the embodiment shown in FIG. 3, a shape memory alloy plate spring 13 is used in place of the shape memory alloy coil spring 6 of FIG. 1, and when the heating element support member 4 is heated, Similarly, the shape memory alloy leaf spring 13 is also heated,
Using the shape memory effect of the shape memory alloy leaf spring 13, for example, the force generated when restoring the shape shown by the broken line in FIG.
As shown in FIG. 4, when the belt-shaped heat transfer member 5 is pressed against the heating element 3 and the heating element support member 4 and the belt-shaped heat transfer member 5 moves in the direction of the arrow, the pressure roll 10 moves in the direction of the arrow. It follows the direction and rotates.

In the embodiment shown in FIGS. 5 and 6, a shape memory alloy coil spring 6 is interposed between the heating element 3 and the heating element supporting member 4 which can be lowered below the heating element supporting member 4. is there.

In this embodiment, when the heating element 3 is below a certain temperature, the heating element 3 is located away from the belt-shaped heat transfer element 5 as shown in FIG. 6
As shown in, the shape memory alloy coil spring 6 returns to the expanded state, whereby the heating element 3 descends, and the belt-shaped heat transfer element 5 and the pressure roll 10 are brought into pressure contact with each other. 13 is a tension roller.

[0018]

As described above, according to the present invention, the pressure roll is pressed against the belt-shaped heat transfer member while the belt-shaped heat transfer member is heated to a certain temperature or higher, and the belt-shaped heat transfer member is pressed. While the temperature of the body is below a certain temperature, the pressure roll is separated from the belt-shaped heating element, so that the life of the pressure roll can be extended.

Furthermore, since the gap between the pressure roll and the belt-shaped heat transfer member can be easily controlled by the combination of the shape memory alloy spring and the lever, an inexpensive heat fixing device can be provided.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a heat fixing device according to the present invention.

FIG. 2 is a side view showing an operation of an embodiment of the heat fixing device according to the present invention.

FIG. 3 is a side view showing another embodiment of the heat fixing device according to the present invention.

FIG. 4 is a side view showing the operation of another embodiment of the heat fixing device according to the present invention.

FIG. 5 is a side view showing still another embodiment of the heat fixing device according to the present invention.

FIG. 6 is a side view showing the operation of still another embodiment of the heat fixing device according to the present invention.

FIG. 7 is a side view showing a conventional heat fixing device.

[Explanation of symbols]

 3 heating element 4 heating element support member (heating means) 5 belt-shaped heat transfer element 6 shape memory alloy coil spring 7 lever 10 pressure roll 11 heat-melting toner or heat-melting ink 12 recording medium 13 shape-memory alloy plate Spring

Claims (2)

[Claims] 1. A heat generating means having a heat generating element inside, a drive roll disposed at a predetermined distance from the heat generating means, and a belt-shaped transmission rotatably wound between the heat generating means and the drive roll. An image support having a heat body and a pressure roll arranged at a position facing the heat generating means via the belt-shaped heat transfer body and rotating together with the belt-shaped heat transfer body, and carrying an unfixed toner image. A heat-fixing device for melting and fixing an unfixed toner image on an image support by passing between the belt-shaped heat transfer member and a pressure roll. A deformable member made of a shape memory alloy is arranged, the deformable member is deformed by heat from the heat generating means, and the belt-shaped heat transfer body and the pressure roll are relatively moved by the deforming pressing force. Configured to press on Thermal fixing device, characterized in that there. 2. The heat fixing device according to claim 1, wherein the pressure roll is configured to move toward the belt-shaped heat transfer body side by the deformation of the deformable member.