JPH0756456A - Fixing device - Google Patents

Abstract

PURPOSE:To make it possible to reduce a size and cost, to shorten warming up time and to suppress electric power consumption by changing the diameter of a press roller to a positive crown shape over its longitudinal direction. CONSTITUTION:The press roller 20 formed by coating an arbor with a heat resistant elastic material 18 like, for example, silicone rubber, and forming a release layer on the surface of this elastic material 18 is brought into pressurized contact with a heating roller 14. The press roller 20 rotates according to rotation of the heating roller 14. While the diameter of the heating roller 14 is constant in the longitudinal direction, the press roller 20 is formed to the positive crown shape of the diameter larger at the center in the longitudinal direction than at both ends in the longitudinal direction. The more specific numerical value of the press roller 20 is required to be determined according to the max. deflection quantity. The pressure on the press roller 20 is kept nearly constant over the longitudinal direction by deflection of the heating roller 14 when the press roller 20 is brought into pressurized contact with the heating roller 14 and, therefore, the fixing strength does not change over the longitudinal direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device, and more particularly, to, for example, rotating a heating roller and a pressure roller pressed against the heating roller to transfer the paper to the paper passed between the heating roller and the pressure roller. The present invention relates to a fixing device for fixing a developed developer image.

[0002]

2. Description of the Related Art Conventionally, a heat roller of a fixing device mounted on an image forming apparatus such as a copying machine or a laser printer has a main diameter of 30 mm to 50 mm. With the miniaturization, the diameter of 16 mm to 30 mm has become the mainstream at present.
Of course, with the miniaturization of the heat roller, many pressure rollers having a diameter of about 20 mm have appeared. further,
There is also an increasing demand for reduction of power consumption and reduction of warm-up time as well as miniaturization of the device.

By the way, as a conventional fixing device 1 having a roller diameter of about 20 mm, as shown in FIG. 3, the heating roller 2 has a diameter that changes in an inverted crown shape over the length direction.
In some cases, the pressure roller 3 having a constant diameter in the length direction is brought into pressure contact with the backup roller 4 at the center of the pressure roller 3 in the length direction. Here, the heating roller 2 is formed in an inverted crown shape because the pressure roller 3 is formed.
This is to prevent the fixing failure due to the bending of the heating roller 2 at the center in the lengthwise direction due to the pressure contact with. The backup roller 4 is attached so that the pressure on the heating roller 2 is constant along the lengthwise direction and the fixing strength is constant. Since the heating roller 2 as a driving roller is formed in an inverted crown shape, the rotational speeds at both ends in the length direction are different from those in the center. However, since both ends in the length direction rotate faster than the center, the paper is passed. The paper that is pulled is pulled toward both ends, and paper wrinkles do not occur.

[0004]

However, in the conventional fixing device 1 as described above, the backup roller 4 is required, so that there is a problem that the device becomes large and costly. Further, since both ends of the heating roller 2 need to have a certain thickness, there is a problem that it takes a long time to warm up and extra power consumption is required.

Therefore, a main object of the present invention is to provide a fixing device which is small in size, can reduce the cost, can shorten the warm-up time, and can suppress the power consumption.

[0006]

SUMMARY OF THE INVENTION The present invention rotates a heating roller and a pressure roller pressed against the heating roller to form a toner image transferred onto a sheet of paper passing between the heating roller and the pressure roller. In the fixing device for fixing, the diameter of the pressure roller is changed in a regular crown shape in the length direction thereof.

[0007]

Since the diameter of the heating roller is formed uniformly in the length direction and the pressure roller that rotates together with the heating roller is formed in a regular crown shape, the pressure applied to the heating roller by bending the heating roller is increased. It becomes constant over the length direction.

[0008]

According to the present invention, since the pressure on the heating roller becomes constant by changing the shape of the pressure roller, the apparatus can be downsized and the cost can be reduced. Further, since the diameter of the heating roller is uniform, the warm-up time can be shortened and the power consumption can be suppressed. In addition, since the pressure roller is formed in a regular crown shape, no fixing failure occurs in the center in the length direction, and since the rotation speed of the heating roller is constant over the length direction, paper wrinkles occur on the paper. There is nothing to do.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0010]

EXAMPLE Referring to FIG. 1, a fixing device 10 of this example.
Includes a heating roller 14 having a heat source 12 mounted therein and a release layer (not shown) for preventing toner offset formed on the surface thereof. The toner offset is a phenomenon in which the toner transferred to the paper adheres to the roller surface. Also,
In the heating roller 14, a core metal 16 is covered with a heat-resistant elastic body 18 such as silicon rubber, and the elastic body 18 is provided.
Pressure roller 20 having a release layer (not shown) formed on its surface
Are pressed against each other, and the pressure roller 20 rotates as the heating roller 14 rotates. For this reason, the toner is transferred onto the surface, and the toner is fixed on the paper (not shown) that is passed between the heating roller 14 and the pressure roller 20. The reason why the release layer is formed also on the pressure roller 20 is that toner offset may occur also on the pressure roller 20 side in the case of double-sided copying.

As can be seen from FIG. 2, the diameter of the heating roller 14 is constant along the length, but the pressure roller 20
With respect to, a regular crown shape is formed in which the diameter is larger at the center in the length direction than at both ends in the length direction. The specific numerical value of the diameter of the pressure roller 20 needs to be determined according to the maximum deflection amount shown in Table 1.

[0012]

[Table 1]

Table 1 shows that an aluminum heating roller having a uniform diameter in the length direction and a wall thickness of 1 mm is supported at both ends, and 6
The maximum amount of deflection is calculated under the assumption that a heating roller is pressed by a pressure roller having a uniform diameter and a heating power of 00 W is applied. The width of the pressure roller is 22
It is set to 5.1 mm, and the load on the heating roller (uniform load) is changed according to the diameter of the heating roller. The load is changed because, in the case of a small machine with a small heating roller diameter, the rotation of the roller is slow, so the toner can be fixed sufficiently even if the nip width between the heating roller and the pressure roller is narrowed. This is because the load can be reduced as the diameter of the heating roller becomes smaller. From this, for example, when the outer diameter of the heating roller is 16.0 mm, the maximum amount of deflection is 103.29 μm.
When the outer diameter of both ends of 0 is 16.0 mm, the outer diameter at the center may be 16.103 mm. In this way, the outer diameter of the pressure roller 20 at the center in the length direction may be made larger than both ends in the length direction by the amount of the maximum deflection.

As a result, the pressure roller 20 is replaced by the heating roller 1.
Since the pressure of the pressure roller 20 becomes substantially constant over the length direction by bending the heating roller 20 when it is pressed against 4, the fixing strength does not change over the length direction. Further, since the diameter of the heating roller 14 is not thicker at both ends as in the prior art, it is possible to reduce the power consumption and the warm-up time. Further, since the backup roller as in the conventional example is not required, the device can be downsized. Further, since the rotation speed of the heating roller 14 is constant over the length direction, paper wrinkles do not occur on the paper.

[Brief description of drawings]

FIG. 1 is an external view showing an embodiment of the present invention.

FIG. 2 is a front view showing the embodiment of FIG.

FIG. 3 is a front view showing a conventional technique.

[Explanation of symbols]

 10 ... Fixing device 14 ... Heating roller 20 ... Pressure roller

Claims (1)

[Claims] 1. A fixing device for rotating a heating roller and a pressure roller pressed against the heating roller to fix the toner image transferred on the paper to the paper passing between the heating roller and the pressure roller. A fixing device, characterized in that the diameter of the pressure roller is changed in a regular crown shape over the length direction thereof.