JPH10161440A - Transfer belt device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent transferred image by always securing a fit nip width and pressurizing force, and further to obtain the excellent image over a long period by making a transfer belt away from a photoreceptor during nonuse, thereby preventing the deterioration of the transfer belt and photoreceptor in an image forming device using the transfer belt. SOLUTION: In this image forming device provided with the transfer belt 12 whose belt surface is arranged in proximity to the surface of the photoreceptor 11 and a transfer roller 16 for applying a bias to a transfer paper passing through a transferring nip part as the contact part of the transfer belt 12 with the photoreceptor 11, to transfer a toner image on the photoreceptor onto the transfer paper, an elastic body 15 for bringing the surface of the transfer belt into contact with the photoreceptor by pressurization is arranged at the position being inside the transfer belt 12 and corresponding to the transferring nip part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to an improvement of an electrophotographic image forming apparatus such as a facsimile apparatus, and particularly to an image forming apparatus of a type in which a toner image on an image carrier is transferred onto a transfer sheet conveyed by a transfer belt. The present invention relates to an image forming apparatus having improved transfer performance.

[0002]

2. Description of the Related Art Heretofore, a part of a belt surface of a transfer belt (having, for example, medium resistance) stretched endlessly has been arranged close to the outer peripheral surface of a photosensitive drum, and is provided inside the transfer belt. Transfer roller (bias roller) placed
2. Description of the Related Art An image forming apparatus of a type that transfers a toner image on a photoconductor onto a transfer paper passing through a nip between a photoconductor drum and a transfer belt by applying a transfer bias from a photoconductor drum is widely used. In a contact transfer device using such a transfer belt, in order to obtain a good transfer image, a configuration in which a part of the transfer belt is brought into contact with a photoconductor at the time of transfer is often adopted. The contact portion is called a transfer nip portion. The length of the transfer nip portion (the length in the transport direction) and the quality of the adjustment of the pressing force at the time of contact greatly affect the quality of the transferred image. Many image forming apparatuses using a transfer belt have been proposed. For example, in an apparatus manufactured by Ricoh Co., Ltd. and an apparatus disclosed in Japanese Patent Application Laid-Open No. 5-249842, the transfer belt is exposed to light with the transfer unit. The transfer nip is obtained by abutting the body. FIGS. 7 (a) and 7 (b) are schematic views of such a conventional example, in which a transfer belt 2 is disposed at a position where the transfer belt 2 can be brought into contact with the outer peripheral surface of a photosensitive drum 1, and rollers 3 for extending the transfer belt endlessly. The upper surface of the belt is brought into contact with or separated from the peripheral surface of the drum 1 by moving one of the four 4 as a rotation axis and moving the other 4 up and down. Reference numeral 5 denotes a bias roller, and P denotes a transfer sheet. As described above, in this type of transfer device, the adjustment of the nip width A and the pressing force is important for maintaining image quality.

Further, for example, Japanese Patent Application Laid-Open No. Hei 5-107953 discloses a technique for easily adjusting the pressure contact force of a transfer surface in a transfer conveyance device using a transfer roller and a circulating belt. The nip between the photosensitive member and the belt is obtained by vertically moving a transfer roller disposed inside the belt on the upstream side of the transfer unit. In each of these prior arts, the nip between the photosensitive drum and the transfer drum is obtained by utilizing the elasticity of the transfer belt.However, when a hard paper or a thick paper is passed, the paper itself is hardly deformed. A sufficient nip width A cannot be obtained only by the elasticity of the transfer belt, and as a result, poor transfer may occur due to poor adhesion. Also, JP-A-5-107958 and JP-A-5-289.
In the technique described in Japanese Patent Application Publication No. 541, a bias roller (transfer roller) is provided on a peripheral surface of a photosensitive drum via a transfer belt.
When the transfer is performed by applying a bias in the vicinity of the photoconductor, a strong discharge is likely to be generated toward the photoconductor, and the photoconductor is deteriorated and small scratches are formed. For example, there is a problem that the transfer current easily leaks therefrom, which may cause disturbance of an image or malfunction of the apparatus. In general, the transfer belt is configured to abut on the entire width of the photoconductor, but the voltage applied to the bias roller is controlled so that the current flowing through the photoconductor is constant over the entire width direction. Have been. Therefore,
When a sheet smaller than the width of the photoreceptor is passed, a large amount of current flows to the photoreceptor from outside the width of the sheet. Was. On the other hand, the present applicant has solved this problem by increasing the value of the transfer current flowing when using small-size paper. There are problems such as the tendency to occur.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and more specifically, in an image forming apparatus using a transfer belt, an appropriate nip width and pressure are always ensured. To obtain a better transfer image, to separate the transfer belt and the photoconductor when not in use, to prevent deterioration of the transfer belt and the photoconductor, to obtain a good image for a long time, and to contact the inner surface of the transfer belt. By adjusting the position and direction of the elastic body to make the nip with the photoreceptor appropriate, it is possible to obtain good transfer and good transportability, and to use a transfer belt when passing small-sized paper. It is an object of the present invention to obtain a good transfer image with less power by bringing only the portion into contact with the outer peripheral surface of the photoreceptor.

[0005]

In order to achieve the above object, the present invention is directed to a transfer belt in which a belt surface is arranged close to the surface of a photoreceptor, and a transfer portion which is a contact portion between the transfer belt and the photoreceptor. A transfer roller for applying a bias to the transfer paper passing through the nip to transfer the toner image on the photoconductor onto the transfer paper;
The image forming apparatus according to claim 1, wherein an elastic body is provided at a position inside the transfer belt corresponding to the transfer nip portion so as to press the transfer belt surface toward the photosensitive member to make contact therewith. According to a second aspect of the present invention, the elastic member is configured to be movable forward and backward so as to be able to contact and separate from the photosensitive member. According to a third aspect of the present invention, the elastic body is arranged at a position where the leading end of the transfer paper discharged from the transfer nip after the transfer process is pressed against the transfer belt surface. According to the fourth aspect of the present invention, the elastic member is constituted by an elastic piece divided into a plurality of pieces along the width direction of the transfer belt, and at least one elastic piece is operated independently and independently of the other elastic pieces. The nip width between the transfer belt and the photoreceptor is changed according to the width of the transfer paper.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings. 1 (a) and 1 (b) are explanatory views of a main part of an image forming apparatus according to an embodiment of the present invention, wherein (a) shows a state at the time of non-transfer and (b) shows a state at the time of transfer. An image forming unit of the electrophotographic image forming apparatus includes a transfer belt (transfer and conveyance belt) 12 stretched endlessly by rollers 13 and 14 below a photosensitive drum 11 rotating in the direction of an arrow.
And the photoreceptor belt 11 and the transfer belt 1
The elastic member 15 is located at the belt inner position corresponding to the nip portion between
Has been arranged. Reference numeral 16 denotes a bias roller (transfer roller) that operates by a bias current from a power supply V to transfer a toner image on a photosensitive member onto transfer paper. The elastic body 15 is, for example, a roller as shown in the drawing, and the elastic body is configured to have a length extending over the entire length of the photoconductor 11 in the width direction, for example. The elastic body 15 is configured to be able to advance and retreat between a retracted position (non-transfer position) shown in (a) and a contact position (transfer position) shown in (b). In the above configuration,
At the time of non-transfer, the transfer belt 12 is not in contact with the photosensitive member 11 because the elastic body 15 is retracted downward as shown in FIG. At this time, the elastic body 15 installed inside the transfer belt 12
Lifts the transfer belt 12 and the nip width A required for transfer
And pressure can be obtained. The material of the elastic body 15 is set such that a sufficient nip width and a sufficient pressure can be obtained in response to the passage of thick paper or hard paper. Elastic body 15
An elastic roller such as a rubber roller or a sponge roller, or a leaf spring-shaped roller may be used. In the present embodiment, since the voltage required for transfer is applied from the bias roller 16, there is no need to apply a voltage at the transfer nip portion, and there is an advantage that there are few restrictions on the material and shape. Further, there is an advantage that the force required for pressing is smaller than that of the conventional example in which the transfer unit is lifted, and the size and cost of the mechanism can be reduced.

Various methods can be considered as a vertical movement mechanism for moving the elastic body 15 between the transfer position and the non-transfer position. In this embodiment, as shown in FIGS. The intermediate portion of the lever 18 whose one end extends to the outside of the belt unit is used as a rotation shaft 19, and the elastic body 15 supported on the tip of the lever is pushed up by pushing down the end of the lever 18. The elastic body 1 shown in FIG.
Reference numeral 5 denotes a roller, and the elastic body 15 in (b) is an elastic plate.
The transfer paper P that has been transferred to the transfer nip and has been transferred is conveyed to a fixing unit (not shown) by the transfer belt 12, and FIGS. 3A to 3C show examples of the discharge direction of the transfer paper after the transfer. Represents For example, when the upper surface of the transfer belt is horizontal and the elastic body 15 is pressed against the photoreceptor 11 from directly below, the transfer nip becomes as shown in FIG. 3A, and the transfer paper P discharged from the transfer nip is Is the transfer belt 12 as indicated by the arrow.
Therefore, good transferability cannot be obtained with such a configuration of the transfer nip portion. On the other hand, FIGS. 3B and 3C show examples of the arrangement of the elastic body in the case of the present embodiment, in which the elastic body 15 is displaced from the position immediately below the photoconductor 11 by a predetermined distance to the upstream side and the photosensitive body is exposed. By bringing the transfer paper P into contact with the body, the moving direction of the discharged transfer paper P becomes the direction pressed against the upper surface of the transfer belt 11 as illustrated. As a result, good transportability can be obtained.

Next, when the small-size transfer paper is passed through the transfer nip as described above, there is a problem that a large amount of current easily flows to the outer portion during the transfer, but in order to prevent this problem, It is effective to divide the elastic body into a plurality of parts along the width direction and move each elastic body part up and down individually according to the width of the transfer paper. However, when a mechanism for lifting a part of the transfer belt is employed as described above, if a roller-shaped rotary elastic body is used as the pressing means, the structure becomes very complicated and it is difficult to realize. In another embodiment of the present invention, the width of the transfer nip portion can be changed according to the width of the transfer paper with a simple configuration by using the plate-shaped elastic body 15. 4 (a), 4 (b) and 4 (c) are a schematic diagram showing an example of the configuration of the elastic body of this embodiment, and a cross-sectional view taken along line X-X of FIG. c) Outer elastic pieces 15A, 15B located on the outer side in the width direction as shown in (c).
And an intermediate elastic piece 15C located between the outer elastic pieces 15A and 15B. Each elastic piece is individually operated by an operating mechanism as shown in FIG. In this example, since the sheet is conveyed on the basis of the center, the two outer elastic pieces 15A and 15B are integrally and independently moved up and down with respect to the intermediate elastic piece 15C.
In the case of the one-side reference, the elastic piece and the remaining elastic pieces may be moved up and down independently on the reference side.

In the state shown in FIG. 4 (b), all the elastic pieces are separated from the belt 12, but in the state shown in FIG. 4 (c), only the intermediate elastic piece 15C is in contact with the belt 12. Suitable for transfer. That is, since the bias current flows through the transfer paper only for the width of the intermediate elastic piece 15C, there is no possibility that the current flows from the outside of the width of the transfer paper to the photoconductor. FIGS. 5 (a) and 5 (b) are structural diagrams of the operation mechanism, and FIG.
As shown in the figure, the intermediate elastic piece 1 is attached to the hollow cylindrical outer shaft 20.
5C are integrated, and outer elastic pieces 15A and 15A are provided at both ends of an inner shaft 21 which passes through the outer shaft 20 in the axial direction.
5B are integrated. One outer elastic piece 15A is fixed to an inner shaft end protruding from the outer shaft 20, and the other outer elastic piece 15B is fixed to a part of the inner shaft exposed from a hole 20a formed in the outer shaft 20. The two outer elastic pieces 15
The inner portions of A and 15B are bent and extend below the intermediate elastic piece 15C, and push up the intermediate elastic piece when the outer elastic piece rises. Lever 22, 23 extends from the end of each shaft 20, 21, respectively, and the end of each lever 22, 23 is individually pushed down or released by the cam mechanism shown in FIG. 5 (b). As a result, the intermediate elastic piece 15C and the outer elastic pieces 15A and 15B can be independently operated. That is, this cam mechanism is composed of two cam pieces 30 and 31 fixed to one shaft 25 at intervals of 120 degrees as shown in (b), and the shaft 25 receives power from, for example, a drive motor of a photosensitive drum. 1/3 not shown
It is rotated by 120 degrees by the rotating clutch.

At the time of non-transfer shown in FIG. 4 (a), each of the cam pieces 30, 31 is stopped at its respective position (retracted position), so that neither lever 22, 23 is pressed (initial state). It has become. On the other hand, when only the lever 23 is pressed, the cam piece 30 is at the position and the cam piece 31 is at the position (pressed position) as shown in FIG. In this case, since the outer elastic pieces 15A and 15B are simultaneously pushed up, the intermediate elastic piece 15C is also pushed up,
As a result, the entire elastic body 15 is in a state in which the belt is pushed up (at the time of transfer of large-size transfer paper = first pressed state). When the cam piece 30 is at the pressing position and the cam piece 31 is at the retracted position, only the lever 22 is pushed down, so that only the intermediate elastic piece 15C is pushed up as shown in FIG. (At the time of transfer of small-size transfer paper = second pressing state). In this embodiment, the size correction of the elastic body can be performed in two stages. However, this is an example, and three or more stages may be performed.

FIG. 6 is a view for explaining the operation of the operating mechanism during the transfer operation in this embodiment. Before the transfer operation is started, all the elastic pieces 15A, 15B and 15C are lowered. When the transfer operation is started in step 2, the process moves to the first state as in step 3, and all the elastic pieces 15A, 15B, 15C are raised. Step 4
If the size of the transfer paper is smaller than the normal size set in advance in step (2), the second state is set as shown in step 5, and only the intermediate elastic piece 15C is raised. As a result,
An extra current is prevented from flowing from the transfer belt to the photoconductor at the time of image transfer.

[0012]

As described above, according to the first aspect of the present invention,
An elastic body that separates the transfer belt from the inside of the transfer belt and contacts the photoreceptor is provided separately from the transfer roller. And a pressing force, and a good transfer image can be obtained. According to the invention of claim 2,
Since the elastic body for bringing the transfer belt into contact with the photoreceptor has the function of separating the transfer belt from the photoreceptor except during transfer, deterioration of the photoreceptor and the transfer belt can be prevented, and good transfer can be performed for a long time. Images can be obtained. According to the third aspect of the present invention, the contact position of the elastic body is determined so that the transfer paper conveyed through the transfer nip portion is discharged at an angle that can be reliably pressed against the transfer belt surface. Therefore, a good transfer image can be obtained, and at the same time, good transportability can be obtained. According to the fourth aspect of the present invention, a function of changing the width of the transfer belt in contact with the photoreceptor in accordance with the size of the transfer paper to be transferred is provided. A transfer image can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory views of a main part of an image forming apparatus according to an embodiment of the present invention, wherein FIG. 1A shows a state during non-transfer and FIG. I have.

FIGS. 2A and 2B are views showing an example of a mechanism for operating an elastic body.

FIGS. 3 (a), (b) and (c) show examples of arrangement of elastic bodies;
(a) is a diagram showing an inappropriate case, and (b) and (c) are diagrams showing examples of proper arrangement.

4 (a), (b) and (c) are a schematic configuration diagram of an elastic body according to another embodiment of the present invention, and a cross-sectional view taken along line XX.

FIG. 5A is a perspective view of an example of an elastic body operating mechanism, and FIG.
3 is a configuration diagram of a cam mechanism.

FIG. 6 is a flowchart illustrating an operation procedure according to an embodiment of the present invention.

7A and 7B are explanatory diagrams of a conventional example.

[Explanation of symbols]

11 photoreceptor drum, 12 transfer belt, 13, 14
Roller, 15 elastic body, 15A, 15B outer elastic piece,
15C intermediate elastic piece, 16 bias roller (transfer roller), 18 lever, 19 rotating shaft, 20 outer shaft, 21
Inner shaft, 22, 23 lever, 30 cam pieces.

Claims (4)

[Claims] A bias is applied to a transfer belt having a belt surface disposed close to a surface of a photoreceptor and a transfer paper passing through a transfer nip portion which is a contact portion between the transfer belt and the photoreceptor to apply a toner to the toner on the photoreceptor. An image forming apparatus having a transfer roller for transferring an image onto transfer paper, wherein the transfer belt surface is pressed toward the photoconductor at a position inside the transfer belt corresponding to the transfer nip portion. A transfer belt device comprising an elastic member. 2. The transfer belt device according to claim 1, wherein the elastic member is configured to be able to move forward and backward so as to be able to contact and separate from the photosensitive member. 3. The elastic body according to claim 1, wherein the elastic body is arranged at a position where the leading end of the transfer paper discharged from the transfer nip after the transfer process is pressed against the transfer belt surface. 3. The transfer belt device according to 2. 4. The transfer device according to claim 1, wherein the elastic member is formed of a plurality of elastic pieces divided along a width direction of the transfer belt, and at least one elastic piece is operated independently of the other elastic pieces. 4. The transfer belt device according to claim 1, wherein the nip width between the transfer belt and the photosensitive member is changed according to the width of the paper.