JPH02131274A - Fixation device - Google Patents

Abstract

PURPOSE:To prevent a defect in the travel of a form and a defect in the fixation of a toner image nearby the center of a press-contacting roller by composing the press-contacting roller of a mandrel which has a reverse crown at the axially outer periphery and an elastic body drum part which coats the entire peripheral surface of the mandrel to the same external diameter axially. CONSTITUTION:The drum part 2b formed of an elastic body by forming the mandrel 2a of the press-contacting roller 2 in a reverse crown shape is thick at the center part of the press-contacting roller 2 and becomes thinner toward both ends. Therefore, the hardness of the drum part 2b increases toward both ends of the press-contacting roller 2 and is smaller nearby the center than at both ends. Consequently, when both ends of the press-contacting roller 2 are applied with pressure by a spring 4 to contact a heat roller 1, the nip width between the heat roller 1 and press-contacting roller 2 becomes constant without reference to the deflection of the mandrel of the press-contacting roller 2. Consequently, the travel of a form between both rollers is stabilized and the defect in the fixation of a toner image nearby the center part of the press-contacting roller 2 is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a fixing device for an electrophotographic printer. [Prior Art] This type of fixing device has a heating roller that has a built-in heat source and a pressure roller that is connected between the heating roller and the pressure roller. The toner image formed on the paper is fixed to the paper by applying heat and pressure to the paper while feeding the paper. Conventionally, the pressure roller has a straight axis or has a crown to prevent warping. A roller with a similar shape was used.

[Problem to be solved by the invention]

Among the pressure rollers of the conventional fuser described above, those with straight shafts bend when pressure is applied to both ends of the pressure roller, so the nip width between the heating roller and the pressure roller is limited in the axial direction. In addition, a pressure roller with a crown on the axis can reduce deflection when pressure is applied, but it has little effect on the nib width, and uneven nib width may cause poor paper running or the pressure roller. The problem was that the toner image would not adhere properly to the paper area near the center of the paper. An object of the present invention is to provide a fixing device that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a heating roller having a built-in heat source and a pressure roller that rotates in pressure contact with the heating roller, and a sheet having a toner image transferred thereon is passed between the heating roller and the pressure roller. In the fixing device of an electrophotographic printer, the toner image is fixed on the recording surface of the paper by heating and pressurizing the toner image while heating and pressing the toner image, and the pressure roller is connected to a shaft core having an inverted crown on the outer periphery in the axial direction, and a circumferential surface of the shaft core. It is composed of an elastic body body that covers the whole tree and forms the same outer diameter in the axial direction.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention. In the figure, a heating roller 1 is rotatably mounted horizontally on a frame 6, and a pressure roller 2 has a shaft core 2a having an inverted crown shape whose diameter is tapered from both ends to the center, and
The body 2b is made of an elastic body that covers the entire outer periphery of the body 2a and has a constant outer diameter over the entire length. The shaft core 2a
Bearings 10, 10 supporting both ends of the body 2b are urged upward by a spring 4.4 attached to the frame 6.
is pressed against heating roller 1. The galley is fixed to the heating roller 1, and the driving force from the main body is transmitted thereto.

The heating roller 1 has a built-in heat source 8 in the axial direction.
are fixed from both sides by supports 7.7 attached to the frame 6. Reference numeral 9 denotes a temperature sensor that detects the temperature of the surface of the fixing roller 1 in order to control the heat generation of the heat source 8.

FIG. 2 is a diagram showing the relationship between the hardness and thickness of the elastic body forming the body portion 2b of the pressure roller 2 shown in FIG. As shown in the figure, when the thickness of a uniform elastic body is large, the hardness decreases, and when it is thin, the hardness increases due to the influence of the axis 2a. By forming the axis 2a of the pressure roller 2 into an inverted crown shape, the body 2b made of an elastic body is thick at the center of the pressure roller 2 and becomes thinner toward both ends. Therefore, the hardness of the body 2b increases as it approaches both ends of the pressure roller 2, and the hardness decreases near the center compared to both ends. In this case, even if the axis of the pressure roller 2 is bent, the nip width between the heating roller 1 and the pressure roller 2 remains constant.

〔Effect of the invention〕

As explained above, according to the present invention, the hardness of the pressure roller can be made high at both ends and low near the center by providing an inverted crown on the shaft core of the pressure roller and covering the outer periphery of the shaft core with an elastic material. Therefore, the nib width between the heating roller and the pressure roller in the fixing device can be made uniform, which in turn stabilizes the running of the paper between both rollers, and has the effect of preventing the occurrence of toner image fixation failure near the center of the pressure roller. have

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the hardness and wall thickness of an elastic body forming the body of the pressure roller. 1... Heating roller 2... Pressure roller 2a.
...Axis core 2b...Body part 4...Spring
8...Heat source 10...Bearing Fig. 1

Claims (1)

[Claims] (1) It has a heating roller with a built-in heat source and a pressure roller that rotates in pressure contact with the heating roller, and the paper on which the toner image has been transferred is passed between the heating roller and the pressure roller, and the toner image is transferred. In a fixing device for an electrophotographic printer that fixes heat and pressure on the recording surface of the paper, the pressure roller is attached to a shaft core having an inverted crown on the outer periphery in the axial direction, and a shaft core that covers the entire circumferential surface of the shaft core. 1. A fixing device comprising: an elastic body body having the same outer diameter in both directions;