JPH0772707A - Image forming device - Google Patents

Abstract

PURPOSE:To more improve image quality by allowing even an image forming roller deficient in rigidity to uniformly press-contact with an image carrier. CONSTITUTION:In this image forming device constituted so that a transfer roller 8 as the image forming roller is pressed to contact with a photosensitive body 3, tension springs 22 are provided outside pressurizing compression springs 21. The bending moment M2 is generated by the elasticity of the springs 22 and the central part of the roller 8 is prevented from floating from the photosensitive body 3 by the bending moment M2, to obtain uniform electrification, transfer, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus equipped with an image carrier and an image forming roller arranged around the image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, an electrostatic latent image is formed by charging or exposing an image carrier made of, for example, a drum-shaped photoreceptor, and a toner image is formed on the electrostatic latent image. In order to visualize a toner image and transfer the toner image onto a predetermined transfer paper, various corona dischargers are used for charging and transferring.

When such a corona discharger is used, ozone is easily generated during discharge, but in recent years, an image forming apparatus using a roller instead of the corona discharger is practically used for the purpose of suppressing the generation of ozone. It has come to be realized.

FIG. 13 shows a conventional example of an image forming apparatus in which a roller is used instead of a corona discharger for charging and transferring.

In this figure, a photosensitive member 3 composed of a drum is provided in a substantially central portion of a housing 2 which is a main body of the image forming apparatus 1. The photosensitive member 3 is rotationally driven in the direction of an arrow shown in the drawing. To be done. During this rotation, the surface of the photoconductor 3 is uniformly charged by the charging roller 4 rotating in the direction of the arrow in the figure.

Next, the optical writing device 5 performs optical writing on the charged surface of the photoconductor 3 to form a predetermined electrostatic latent image on the photoconductor. This electrostatic latent image is visualized as a toner image by the toner carried on the developing roller 7 of the developing device 6.

On the other hand, the transfer sheet (recording sheet) 11 is transferred from the registration roller section 9 at a predetermined timing with the photosensitive member 3
And the transfer roller 8 between them.

The transfer roller 8 is adapted to rotate while being driven in the direction of the arrow in the figure, and the toner image on the photoconductor is transferred onto the transfer paper 11 at the transfer portion between the transfer roller 8 and the photoconductor 3. To be done. After this transfer, the transfer paper 11 passes through the fixing roller portion 12 and is discharged from the discharge roller portion 13 to the outside of the machine.

The charging roller 4 and the transfer roller 8 are also called image forming rollers, and in order to perform good charging and transfer, the image forming roller is applied to the photosensitive member at a constant pressure. It is necessary to make contact.

Conventionally, the press-contacting means has a structure as shown in FIG. Here, for convenience, the transfer roller 8 shown in FIG. 13 is applied as the image forming roller, and the pressure contact structure of this roller will be described below.

The transfer roller 8 has a roller shaft 8A serving as a core at the center, and bearings 1 are provided at both ends thereof.
4, 14 are engaged (FIG. 15). Bearing 14
And the substrate 15 of the image forming apparatus main body between the compression spring 1
6, the transfer roller 8 is pressed against the photoconductor 3 via the bearing 14 by this elasticity. Transfer roller 8
Is rotated by pressing force of the compression spring 16 against the photoconductor 13. The bearing 14 is
As shown in FIG. 15, the photoconductor 3 is movable in the vertical direction by the guide member 17 fixed to the substrate 15.
It is held so that it does not move in the axial direction.

Conventionally, as shown in FIG. 14, since the roller shaft is pressed at both ends of the roller shaft, a bending moment of M1 is generated at both ends of the roller shaft, and the roller 8 moves as shown in the drawing. There is a problem in that the contact pressure at the central portion (contact pressure with respect to the photoconductor 3) is weakened, the central portion of the roller is lifted from the photoconductor, or the contact pressure at both ends becomes too strong.

This type of image forming roller is required to make uniform contact with the photosensitive member in the axial direction thereof with a light load. On the other hand, this type of image forming apparatus, particularly a laser printer, is required to be further downsized, and not only the photoconductor 3 but also the image forming roller is required to be further downsized.

Since this type of image forming roller is manufactured by forming an elastic body such as rubber around the roller shaft, the roller shaft (core bar) is considerably thin when the diameter of the roller becomes small. And the rigidity is insufficient.
In the pressure method shown in, the roller shaft is more easily bent,
It is difficult to obtain uniform contact property.

In this case, when the image forming roller is a charging roller, the charging potential is lowered at the central portion in the axial direction of the photosensitive member, which causes an abnormal image.
Further, when the image forming roller is a transfer roller, the transferability is deteriorated at the central portion, white spots are generated on the image, or the image is partially cut off at both end sides, and the image quality is deteriorated. Cause. Further, in the case of any of the rollers, when the contact pressure becomes non-uniform, the roller surface and the photosensitive member surface are easily worn, and the life thereof is shortened.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to improve the image quality further by using an image forming roller having a low rigidity so that the roller can be uniformly pressed against the image carrier. An object of the present invention is to provide an image forming apparatus that can be achieved.

[0017]

To achieve the above object, the present invention comprises an image carrier and a roller shaft at the center, and an image having an elastic surface rotating while being pressed against the image carrier. In an image forming apparatus including a forming roller,
A first elastic member that exerts an elastic force on the roller shaft so that the image forming roller is in pressure contact with the image carrier on both ends of the roller shaft.
Of the first spring material is attached to both end sides of the roller shaft, and the elastic force is weaker than that of the first spring material at positions axially outside of the first spring material. Secondly exerting elastic force on the roller shaft in the direction opposite to the elastic force applying direction
The present invention proposes an image forming apparatus provided with the above spring material.

In order to achieve the above object, the present invention comprises an image carrier, a roller shaft at the center thereof, and an image forming roller which rotates while its elastic surface is in pressure contact with the image carrier. In the image forming apparatus described above, both end sides of the roller shaft are rotatably supported by first and second bearings arranged in an adjacent positional relationship such that they are inside and outside with respect to the axial direction. Are supported by a common bearing support member, and a spring force of a spring material is applied to the bearing support member such that the image forming roller is brought into pressure contact with the image bearing member. The present invention proposes an image forming apparatus which is located at a position further inward in the axial direction than the bearing.

Further, in order to achieve the above object, the present invention further comprises an image carrier and an image forming roller having a roller shaft at the center thereof and having an elastic surface rotating while being pressed against the image carrier. In the image forming apparatus including the above, there is proposed an image forming apparatus in which a magnet body is provided inside the image carrier for uniformly pressing the image forming roller to the outer peripheral surface of the image carrier in the axial direction by magnetic force. It is a thing.

The image forming roller is arranged at a position corresponding to the magnetic pole of the magnet body, and the magnet body is rotated so that the magnetic pole is located at a position not corresponding to the image forming roller during non-image formation. It is effective if it can be displaced.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a pressing component of an image forming roller provided in an image forming apparatus according to an embodiment of the present invention.

Reference numeral 8 is a transfer roller which is an example of an image forming roller, and the other charging roller 4 (FIG. 13) and the like are also included in the image forming roller, and the present invention can be applied. However, here, for convenience, the transfer roller 8 is taken as an application example, and the description of the embodiment will be continued. Since the basic structure and operation of the image forming apparatus having the transfer roller 8 and the charging roller 4 are the same as those described above with reference to FIG. 13, the description thereof will be omitted. The same applies to other embodiments described later.

The transfer roller (hereinafter, simply referred to as "roller") 8 has a roller shaft 8A at its center and rotates while being pressed against the photoconductor 3. The surface of the roller 8 that is pressed against the photoconductor 3 has elasticity.

For example, as shown in FIG. 4, the roller 8 is composed of a metal roller shaft 8A and a cylindrical elastic body 8B integrally formed around the metal roller shaft 8A. The elastic body 8B is made of rubber or sponge having a medium resistance and is conductive, and is deformed by being pressed to be brought into close contact with the photoconductor 3. Note that FIG. 5 is a cross-sectional view of the roller 8.

At both ends of the roller shaft 8A, a first spring member 21 is attached which exerts an elastic force on the roller shaft 8A so that the roller 8 comes into pressure contact with the photosensitive member 3. In this example,
This spring material 21 is a compression coil spring (hereinafter, “compression spring”).
Which is the substrate 1 on the image forming apparatus main body side.
5, and a bearing 18 that engages the roller shaft 8A as shown in FIG.
It is supposed to be interposed between and.

Also, on both end sides of the roller shaft 8A, the first
The elastic force is weaker than the compression spring 21, which is the spring material of the roller shaft, in the axial outer side of the roller shaft, and is elastic to the roller shaft 8A in the direction opposite to the elastic force application direction of the spring. A second spring member 22 that exerts a force is attached. In this example, the spring member 22 is a tension spring, which is interposed between the substrate 15 and the bearing 19 fitted on the roller shaft 8A as shown in FIG.

Here, in FIG. 1, both bearings 18, 19 are shown.
The distance (distance between bearing centers) is L, the pressure applied by the spring 21 is A1, and the tensile force by the spring 22 is B1.

First, the roller 8 is pressed against the photoconductor 3 by the force of the compression spring 21, and the pressing force at this time is the difference between the pressing force A1 by the spring 21 and the tensile force B of the tension spring 22 ( A1-B1). On the other hand, the pulling force B1 generated by the spring 22 causes a bending moment of M2 (B1 × L) on both sides of the roller shaft 8A. To do.

That is, the bending moment M2 is generated, so that the bending of the roller 8 shown in FIG. 14 is eliminated, and the adhesion of the central portion of the roller 8 is maintained. It comes to come into uniform pressure contact (adhesion) in the axial direction.

In any case, the pressure contact force at the center of the roller is not weakened or the center is not lifted from the photosensitive member. As a result, the charging and the transfer are favorably and uniformly performed, and the quality of the obtained image is improved. Then, such a function can be performed even when the rigidity of the image forming roller is insufficient.

The guide member 23 shown in FIG. 2 is fixed to the base plate 15, supports the bearing 18 movably in the vertical direction, and holds it so as not to move in the axial direction and the direction orthogonal thereto. Work. The bearing 19 is also supported by a guide member having the same structure.

Next, another embodiment of the invention will be described. 6 and 7, the roller 8 having the same form as the roller 8 shown in FIGS. 1 and 4 is arranged so that both end sides of the roller shaft 8A are located inside and outside with respect to the axial direction. The first and second bearings 31 and 32 are rotatably supported.

Both bearings 31 and 32 are supported by a common bearing support member 24, which is a roller 8.
Has a protrusion 24a extending toward the central portion of the roller, where a spring force of a spring material acts such that the roller 8 is pressed against the photoconductor 3.

In this example, the spring material is a compression coil spring 25, and this spring 25 is interposed between the substrate 15 and the protrusion 24a. The acting position of the spring 25 is the inner bearing 3
It is defined to be further inside than 1.

Here, the distance from the center of the inner bearing 31 to the center of the spring 25 is L1, and the distance between the centers of both bearings 31 and 32 is L2.

When a pressure A2 is applied to the bearing support member 24 by the spring 25, an upward force B2 acts on the outer bearing 32 with the inner bearing 31 as a fulcrum. That is, in the relation of A2 × L1 = B2 × L2, B
An upward force of 2 is generated. Then, a bending moment of M3 (B2 × L2) is generated in the inner bearing 31.

This bending moment M3 acts to cancel the bending moment M1 (FIG. 14), so that, as in the previous embodiment of the invention, good adhesion is maintained at the center of the roller. Become. In the case of this embodiment, one set of springs is sufficient. The bearing support member 24
Are supported by a guide member corresponding to the guide member 23 (FIG. 2) of the previous embodiment.

Next, another embodiment of the invention will be described.

In FIG. 8, a roller 28 corresponds to the roller 8 shown in FIG. 1, and is formed integrally with a roller shaft 28A having a thickened main shaft portion excluding both end sides and the main shaft portion. It is composed of an elastic body 28B. Roller shaft 2
8A is made of a magnetic material made of metal.

As shown in FIG. 9, the roller shaft 28A is supported by a guide member 26 integrated with the substrate 15,
Although it is movable in the vertical direction, it is held immovably in the direction orthogonal to this direction.

On the other hand, the photosensitive member 33 corresponds to the photosensitive member 3 shown in FIG. 13 and is composed of a drum member 33A having a photosensitive layer formed on the surface thereof. Inside the drum body 33A, roller-shaped magnet bodies 34 having shaft portions 34a at both ends are provided. The magnet body 34 is held so as not to rotate, while the drum body 33A has the bearing 3
It is supported by 5 and can rotate.

With this magnetic force, the magnet body 34 attracts the roller shaft 28A, which is a magnetic body, and brings the elastic body 28B into uniform pressure contact over the entire axial direction. That is, the surface of the roller 8 is brought into close contact with the photoconductor 33 uniformly. As shown in FIG. 8, if the main shaft portion of the roller shaft 28A (the shaft portion on which the elastic body 28B is formed) is made as thick as possible,
The distance from the magnet body 34 is shortened, and the attraction force of the roller 28 (the attraction force due to the magnetic force of the magnet body) can be increased. In addition, as shown in FIG. 9, the roller 28 is placed at a position corresponding to the magnetic pole of the magnet body 34 (N pole in the illustrated example), and is effectively attracted toward the photoconductor 33.

With such a structure, the entire roller 28 is attracted to the side of the photoconductor 33 by the magnet body 34, so that there is no fear of bending the roller body, and the entire area in the axial direction is eliminated. Good adhesion can be obtained. Further, in this embodiment, the spring material used in the previous series of embodiments is unnecessary, and the bending moment does not act on the roller shaft.

Incidentally, the developers used in the developing unit 6 (FIG. 13) are roughly classified into two types, magnetic developers and non-magnetic developers. By using, even if a magnet body is provided inside the photoconductor, this does not adversely affect image formation, and an image of good quality can be obtained.

Here, in FIG. 10, the three types of rollers, that is, the charging roller 4, the developing roller 7, and the transfer roller 8 are connected to the photoreceptor 33 by the magnetic force of the magnet 34 provided inside the photoreceptor. This embodiment shows an example in which both of them are attracted to each other and brought into close contact with each other. With this configuration, one magnet body can uniformly press all the plurality of image forming rollers onto the surface of the photoreceptor.

The rollers 4, 7, 8 are arranged so as to correspond to the magnetic pole positions of the magnet body 34. When the image forming apparatus is not operating, that is, when the image is not being formed, the magnetic body 34 is rotatable and displaceable so that the magnetic poles are located at positions that do not correspond to the rollers. This driving is possible by connecting a rotary solenoid 36 as shown in FIG. 11 to the magnet body 34, for example.

By thus constructing the magnet body,
At the time of non-image formation, the pressure contact force of the image forming roller with respect to the photoconductor can be weakened or eliminated, so that compression set (creep) of the elastic layer can be made less likely to occur. Regarding the configuration in which the magnet body is rotationally displaced so that the position of the magnetic pole changes,
It can be applied even when the number of image forming rollers is one.

In the embodiment shown in FIG. 8, the roller 28 is attracted to the side of the photoconductor 33 by the magnetic force of the magnet body 34. In order to increase the attraction force, the roller 28 is placed in the elastic body 28B. Alternatively, magnetic particles such as ferrite may be dispersed and mixed. A roller 28 'shown in FIG. 12 is a roller in which such magnetic particles are dispersed and mixed in an elastic body 28B'. If the image forming roller is configured in this way,
The adhesion of the roller can be increased. In any case, the magnetic attraction distance between the magnetic material (magnetic particles) and the magnet body is shortened, and a larger attraction force can be obtained.

In the above-described series of inventions, not only the transfer roller and the charging roller but also the developing roller can be applied as the image forming roller. Further, as an application example, the registration roller portion 9 ( It can also be applied to the roller of FIG. 13). At that time, the developing roller 7
Is uniformly pressed against the image bearing member such as the photoconductor by the configuration of each of the above-described embodiments, and one of the rollers of the registration roller unit 9 is uniformly attached to the other roller by the configuration of each of the above-described embodiments. Press against. In any case, the roller has a low rigidity and can be pressed uniformly against an object such as a photoconductor in this axial direction.

Further, although the drum-shaped photosensitive member is shown as the image bearing member in the above embodiment, it is needless to say that the present invention can be widely applied to an image forming apparatus using a belt-shaped image bearing member.

[0052]

According to the image forming apparatus of the first aspect of the present invention, the image forming roller can be brought into close contact with the image bearing member evenly in the axial direction, so that the axis of charging or transfer can be improved. Since it is performed uniformly in the direction, a higher quality image can be obtained. And, even if the rigidity of the image forming roller tends to be insufficient, such a function is required.
Can be achieved.

According to the image forming apparatus of the second aspect,
The image forming roller can be brought into close contact with the image carrier in the axial direction, and charging and transfer can be performed uniformly in the axial direction, so that a higher quality image can be obtained. be able to. Then, such a function can be achieved even if the rigidity of the image forming roller tends to be insufficient. Also, one set of spring material is sufficient.

According to the image forming apparatus of the third aspect,
The image forming roller can be brought into close contact with the image carrier in the axial direction, and charging and transfer can be performed uniformly in the axial direction, so that a higher quality image can be obtained. be able to. Further, since the spring material is unnecessary, the bending moment does not act on the roller shaft.

According to the image forming apparatus of the fourth aspect,
Since permanent distortion and abrasion of the surface elastic layer of the image forming roller are less likely to occur, the life of the roller can be kept long.

[Brief description of drawings]

FIG. 1 is a diagram showing a pressing component of an image forming roller provided in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of the same pressure component.

FIG. 3 is a side view around the tension spring portion of the same pressure component.

FIG. 4 is a cross-sectional view of an example of an image forming roller.

FIG. 5 is a cross-sectional view of an example of the image forming roller of the above.

FIG. 6 is a view showing a pressure component of another embodiment.

FIG. 7 is a side view of the same pressing component.

FIG. 8 is a view showing a pressure component of still another embodiment.

FIG. 9 is a side cross-sectional view of the same pressing component.

FIG. 10 is a configuration diagram of an embodiment in which a plurality of image forming rollers are attracted toward a photoconductor by a magnet body.

FIG. 11 is a configuration diagram showing an example of a magnetic pole position changing means of a magnet body.

FIG. 12 is a sectional view showing another example of an image forming roller.

FIG. 13 is a schematic configuration diagram of an example of an image forming apparatus used to describe the related art and the present invention.

FIG. 14 is a view showing a conventional pressing component.

FIG. 15 is a side view of the above-mentioned pressing component.

[Explanation of symbols]

 4 Charging Roller as Image Forming Roller 7 Developing Roller as Image Forming Roller 8 Transfer Roller as Image Forming Roller 8A Roller Shaft 21 Compression Spring as First Spring Material 22 Tension Spring as Second Spring Material 24 Bearing Support Member 25 Compression Spring as Spring Material 28 Image Forming Roller 28 'Roller 28A Roller Shaft 31 First Bearing 32 Second Bearing 33 Drum-Shaped Photoreceptor as Image Carrier 34 Magnet

Claims (4)

[Claims] 1. An image forming apparatus comprising: an image carrier; and an image forming roller having a roller shaft at the center thereof and an elastic surface rotating while being in pressure contact with the image carrier. A first spring member that exerts an elastic force on the roller shaft is attached to both end sides of the roller so that the image forming roller is in pressure contact with the image bearing member. At the position outside the material in the axial direction, the first
The image forming apparatus further includes a second spring member that has a lower elastic force than the first spring member and exerts an elastic force on the roller shaft in a direction opposite to the elastic force applying direction of the first spring member. 2. An image forming apparatus comprising: an image bearing member; and an image forming roller having a roller shaft in the center thereof and an elastic surface that rotates while being pressed against the image bearing member.
Both ends of the roller shaft are rotatably supported by first and second bearings arranged in an adjacent positional relationship such that they are inside and outside with respect to the axial direction, and both bearings are a common bearing support member. A spring force of a spring material is applied to the bearing support member such that the image forming roller is in pressure contact with the image carrier, and the action position of this spring force is further than that of the inner bearing. An image forming apparatus, characterized in that the image forming apparatus is set at a position that is located on the inner side in the axial direction. 3. An image forming apparatus comprising: an image bearing member; and an image forming roller having a roller shaft at the center thereof and an elastic surface which rotates while being pressed against the image bearing member. An image forming apparatus characterized in that a magnet body is provided inside the body for magnetically contacting the image forming roller with the outer peripheral surface of the image bearing body in the axial direction. 4. The image forming roller is arranged at a position corresponding to the magnetic pole of the magnet body, and the magnet body is rotated so that the magnetic pole is located at a position not corresponding to the image forming roller during non-image formation. The image forming apparatus according to claim 3, wherein the image forming apparatus is displaceable.