JPH0728347A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device provided with a pair of fixing rollers each of which has a simple shape having a diameter of 20mm or less, a thickness of 0.5mm or less and a maximum paper-carry width of 8.5 inch or less, has satisfactory strength, has a satisfactory yield in quantity production, is inexpensive, and prevents the occurrence of a wrinkle at the time of image formation. CONSTITUTION:The image forming device carries out image formation by passing a transfer material 3, on which an unfixed image is transferred, through a nip part 1c between the heat roller 1a and the pressure roller 1b, and heating it under pressure, thereby melting the unfixed image on the transfer material under heat and fixing it onto the transfer material. In the image forming device, the heat roller 1a is in the shape of a straight pipe, has reinforced parts at both its ends in the axial direction for the purpose of increasing strength, and has a thin structure in which, when the transfer material 3 is carried, both the ends of the roller in the nip part 1c is larger than the middle of the roller in thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer and a facsimile, and more particularly to an improvement of a pair of fixing rollers used in the image forming apparatus.

[0002]

2. Description of the Related Art FIG. 5 is a view showing a structure of a fixing device in an image forming section of a conventional electrophotographic image forming apparatus. A fixing roller pair 101 constituting a conventional fixing device is a heating roller 10.
1a and a pressure roller 101b for pressing the heating roller 101a in the direction of arrow B shown in the figure. An unfixed image (not shown) on the transfer material 103 is thermally melted and fixed on the transfer material 103 by pressing and heating the transfer material 103 to which the unfixed image is transferred at the nip portion 101c between the rollers. To do. As the heating roller 101a, there is one that is processed into a drum shape (reverse crown shape) as shown in the figure, and it is common to prevent wrinkles from occurring on the transfer paper during conveyance by configuring such a shape. (See Japanese Utility Model Laid-Open No. 58-93955, Japanese Patent Laid-Open No. 58-16274, etc.).

However, since the shape of the heating roller 101a is a drum shape as shown in the figure, there is a problem that the manufacturing cost for processing the heating roller 101a is high. In particular, the heating roller 101a is
The size is 20 mm or less, the wall thickness is 0.5 mm or less, and the maximum width of the transport paper is 8.5 inches or less.
When such a small heating roller 101a is manufactured, the strength is weak because it is thin and thin, and it is difficult to adjust the outer shape by polishing or the like, and it is not possible to secure the outer shape tolerance of the gear mounting portion and the bearing portion of the end portion. As a result, there arises a problem that the gears and bearings cannot be inserted, and when mass-producing this, the yield is reduced due to the above problems. Therefore, the small fixing roller pair has a drawback that the cost is further increased.

[0004]

The fixing roller pair used in the conventional image forming apparatus, especially in the small fixing apparatus, has a drawback that the cost becomes high.

[0005]

The object of the present invention is to solve such a problem. That is, the diameter is 20 mm or less and the wall thickness is 0.5.
Provided is an image forming apparatus having a fixing roller pair for preventing wrinkles during image formation with a simple shape having a maximum width of conveyance paper of 8.5 mm or less and a maximum width of 8.5 inch or less, high yield, good yield in mass production, and low cost. The purpose is to do.

[0006]

In order to achieve the above object, the present invention is to pass a transfer material on which an unfixed image is transferred to a nip portion between a heating roller and a pressure roller, and press and heat the transfer material. In an image forming apparatus that heat-melts an unfixed image on a transfer material to fix it on the transfer material to form an image, the heating roller has a straight pipe shape and increases strength at both ends in the axial direction. It is characterized in that it has a reinforcing portion, and that the roller shape at the nip portion has a thin-walled structure in which both ends are thicker than the central portion when the transfer material is conveyed, and the reinforcing portion is composed of a bent portion.

[0007]

The image forming apparatus configured as described above has a straight pipe shape with increased strength at the end as a heating roller that constitutes a fixing device, has a small diameter of 20 mm or less, and is thick. Is less than 0.5 mm,
Moreover, the maximum width of the conveyed paper is within 8.5 inches. Therefore, when the pressure roller is pressed against the heating roller, the central portion of the fixing roller pair bends so that the pressure at both ends in the axial direction becomes higher than the pressure at the central portion, and the shape is simple and the strength is strong. The yield in mass production is good and the cost is low, and it becomes possible to prevent wrinkles from occurring during image formation.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an image forming unit to which the present invention is applied. An unfixed image 5 formed on the surface of a photosensitive drum 4 of an electrophotographic copying machine which is an example of an electrophotographic image forming apparatus. Is transferred onto the transfer material 3 at the transfer portion 6, and the transfer material 3 having the unfixed image 5 conveyed from the transfer portion 6 by the conveying means 7 (belt or the like) is guided to the entrance guide plate 8 and the fixing roller. It is transported to the opposite side. The fixing roller pair 1 constituting the fixing device is a heating roller 1 having a built-in heating source 9.
a and a pressure roller 1b pressed against the outer peripheral surface of the heating roller 1a in the direction of arrow B.
The unfixed image 5 is heat-fixed and fixed by pinching the transfer material 3 conveyed at the nip portion 1c formed between 1b. The transfer material 3 after fixing is peeled from the heating roller 1a by the separation claw 10, guided by the paper discharge guide plate 11, and discharged by the paper discharge drive roller 12a and the paper discharge driven roller 12b. When the separation claw 10 is not provided, the transfer material 3 after fixing is heated by configuring so that a minute gap can be maintained between the end of the discharge guide plate 11a and the heating roller 1a. It can be peeled off from the roller 1a. The present invention relates to a compact copying machine in which the maximum usable recording paper size is A4 vertical size.

Next, the fixing roller pair 1 of the fixing device in the image forming apparatus will be described. The fixing roller pair 1 sandwiches the transfer material 3 to be fixed in a nip portion 1c between the fixing roller 1a for heating and the pressure roller 1b for pressing,
The unfixed image 5 transferred onto the transfer material 3 is fixed by applying heat and pressure to the transfer material 3. The heating roller 1a of the fixing roller pair 1 includes a heating source 9 such as a halogen lamp.
Is built in. The surface temperature of the heating roller 1a is detected by a temperature detection means such as a thermistor (not shown), and the detection signal is fed back to a temperature control circuit (not shown) to control the heat generation amount of the heating source 9 so that the heating roller 1a is heated.
The surface temperature is controlled to be constant.

FIG. 2 is a sectional view taken along the line AA in FIG. 1. The heating roller 1a of this embodiment has a straight pipe shape which is not a drum shape (inverted crown shape) and has a diameter of 20 mm or less and a wall thickness of 0. 0.5 mm or less, maximum width of transport paper is 8.5 in
It has a straight and simple shape within ch. The straight pipe-shaped end surface is provided with a bent portion 2a that is bent in the inner diameter direction over the entire circumference. This bent portion 2a
Is a reinforcing portion 2 for increasing the strength of the end portion of the heating roller 1a. The maximum width of the conveyance paper is set to 8.5 inch or less in order to fit the size of the short side of the A4 size recording paper. Therefore, although the heating roller 1a has a straight pipe-like simple shape, the strength of the bearing portion is increased and the heating roller 1a is not deformed. Furthermore, since high outer shape accuracy can be ensured when the heating roller 1a is manufactured, the yield in mass production is good and the cost is low. As the material of the heating roller 1a, iron (Fe), stainless steel (SUS), copper (Cu), aluminum (A
l) is used. As the structure of the reinforcing portion 2, the bending portion 2
The method is not limited to a, and a method such as press-fitting a ring or the like (not shown) at the end may be used as long as the strength of the end of the heating roller 1a can be increased.

FIG. 3 is an explanatory view of the structure of the main part of the fixing device. The heating roller 1a has a straight pipe shape and a small diameter of 20 mm or less and a wall thickness of 0.5 mm or less as shown in FIG. Since the maximum width of the conveyed paper is straight and has a simple shape within 8.5 inches, when the pressure roller 1b having a straight shape is pressed against the heating roller 1a, the central portion of the fixing roller pair 1 bends and pressure is applied. Is higher at both ends as compared with the central portion, and as a result, the nip shape is thicker at both ends than at the central portion as shown in the figure. Therefore, it is possible to obtain the same effect as that of the conventional case in which the heating roller 1a is formed into a drum shape and wrinkles are prevented from occurring in the transfer material 3 described above.

FIG. 4 is a plan view of the transfer material which has been fixed. Since the heating roller 1a has a maximum size capable of being conveyed in the longitudinal direction of the A4 recording paper, the maximum width of the conveyed paper is within 8.5 inches. If a recording sheet of size A row No. 3 (297 mm × 420 mm) is to be conveyed vertically using the heating roller having the structure shown in FIG. 2, it is necessary to lengthen the heating roller 1 a accordingly (297 mm or more). ). If the length is increased in this way, the amount of bending becomes too large, and the wrinkles as shown in the drawing often occur. This is because the difference in nip width between the central portion and both end portions of the nip shape becomes too large as described in FIG.

[0013]

As described above, according to the present invention, as the heating roller, a straight pipe shape having a high end strength and a small diameter of 20 mm or less is used. The thickness of the paper was thinned to 0.5 mm or less, and the maximum width of the conveyed paper was set to 8.5 inches or less. Therefore, when a straight pressure roller is pressed against this heating roller, the center part of the fixing roller pair bends. As a result, the nip pressure at both ends becomes higher than that at the center. Therefore,
In a small image forming apparatus that can use A4 portrait size recording paper, the shape of the heating roller is simple, the strength is high, the yield in mass production is good, and the cost is low, and it is possible to prevent wrinkles from occurring during image formation. Becomes

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an explanatory diagram illustrating a state of a main part of the image forming apparatus according to the embodiment of the present invention.

FIG. 4 is a plan view showing a state of occurrence of horizontal wrinkles when fixing is performed on an A3 size transfer material.

FIG. 5 is a structural explanatory view of a fixing device of an image forming unit of a conventional image forming apparatus.

[Explanation of symbols]

1-fixing roller pair, 1a-heating roller, 1b-
..Pressure rollers, 1c ... Nip portion, 2 ... Reinforcing portion, 2a ... Bending portion, 3 ... Transfer material, 4 ... Photoconductor, 5 ... Unfixed image, 6 ... Transfer unit, 7 ... Transport unit, 8 ... Entrance guide plate, 9 ... Heating source, 10 ...
Separation claws, 11 ... Paper ejection guide plate, 11a ... Above paper ejection guide plate, 11b ... Below paper ejection guide plate, 12a ...
・ Paper drive roller, 12b ... Paper driven roller, 10
1-fixing roller pair, 101a-heating roller, 1
01b ... pressure roller, 101c ... nip portion, 1
03 ... Transfer material.

Claims (2)

[Claims] 1. An unfixed image on a transfer material is thermally melted by passing through a transfer material on which an unfixed image is transferred to a nip portion of a heating roller and a pressure roller and heating the transfer material under pressure. In the image forming apparatus for fixing an image to form an image on the heating roller, the heating roller has a straight pipe shape, and has reinforcing portions at both ends in the axial direction for increasing strength,
An image forming apparatus having a thin-walled configuration so that the rollers at the nip portion are deformed so that both ends are thicker than the center portion when the transfer material is conveyed. 2. The image forming apparatus according to claim 1, wherein the reinforcing portion is a bent portion.