JP2008089733A - Image forming apparatus with belt meandering correction mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which need not to use a complex mechanism for preventing meandering of a conveying belt and need not to increase the width of the apparatus and is compact. <P>SOLUTION: A primary transfer belt 8 is trained over a drive roller 13 and a follower roller 14. A pair of pressure contact rollers 31 and 32 are disposed between the drive roller 13 and follower roller 14 so as to be journaled by a pressure contact roller shaft 33 that is parallel to the roller shafts 13a and 14a of the drive roller 13 and follower roller 14. The pressure contact rollers 31 and 32 are spaced at both edges of the primary transfer belt 8. The pressure contact rollers 31 and 32 are disposed so that the outer circumferential faces of the pressure contact rollers 31 and 32, disposed in contact with the primary transfer belt 8, project outside or inside from the reference face of the primary transfer belt 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a belt meandering correction mechanism for preventing meandering of an endless belt used in an image forming apparatus or the like.

One of transfer methods in image forming apparatuses such as copying machines and printers is an intermediate transfer method. In this method, after each color toner image is formed on a plurality of photoconductors, each of these color toner images is temporarily transferred to an intermediate transfer member, and then a multiple transfer toner image on the intermediate transfer member with respect to a recording material such as paper. Are collectively transferred to obtain a color image, and a belt conveyance device (primary transfer belt mechanism) is used as an intermediate transfer member.
This belt conveying device hangs a transfer belt on a driving roller and a driven roller, and hangs the transfer belt on a plurality of stretching rollers arranged between these rollers, and circulates and conveys the transfer belt in a predetermined traveling direction. I am letting. In this type of belt conveyance device, the transfer belt does not run straight in the circumferential direction and shifts in the roller axis direction due to various factors such as variations in the outer diameter and parallelism of each roller, and the difference in circumferential length of the transfer belt. A so-called belt meander (shift) occurs.
When the transfer belt meanders, image misregistration occurs, and color misregistration occurs in a color image in which a plurality of colors are superimposed to form a high quality image.

As a prior art for preventing meandering of the transfer belt, there is a technique in which a tension roller is disposed between a driving roller and a driven roller. According to this technique, the right and left end portions of the tension roller are provided with tapered circular tapered portions, and the right and left end edges of the transfer belt are extended to approximately the middle position of the inclined surface of the tension roller taper portion. ing. An end sensor is provided for detecting the meandering of the transfer belt when the tension roller rotates. If the meandering occurs, the tension roller rotation shaft is moved to either the left or right direction by the tension roller axial movement means. A method for moving and correcting the meandering of the belt is described in Patent Document 1 below.
JP 2001-147599 A

However, in the technique of Patent Document 1, the left and right edge portions of the transfer belt are extended to almost the middle position of the inclined surface of the taper portion of the tension roller, and the taper surface protrudes to the left and right sides from both ends of the transfer belt. The tension roller is long in the axial direction. When the transfer belt meanders, the width of the image forming apparatus is increased by offsetting the tension roller to the left and right. Furthermore, according to the technique of Patent Document 1, a sensor or the like is required to detect meandering, and the configuration is complicated.
The present invention has been made in view of such circumstances, and in order to prevent meandering of the endless belt, the present invention is compact without using a complicated mechanism and without increasing the width of the image forming apparatus. An object of the present invention is to provide an image forming apparatus having a belt meandering prevention mechanism for an image forming apparatus.

In order to achieve the above object, an image forming apparatus that swings a belt meandering prevention mechanism according to the present invention includes: a driving roller; a belt meandering prevention mechanism in which an endless belt is hung on a driven roller; A pair of pressure rollers, which are rotatably supported by rotation shafts parallel to the roller shafts, are provided between the driven rollers on the inner peripheral surface of the endless belt, and the pressure rollers are arranged in the width of the endless belt. Positioned so that the contact portion between the pressure roller and the endless belt protrudes above the reference surface of the endless belt connecting the driving roller and the driven roller. Arranged to be.
In the image forming apparatus, the endless belt is a primary transfer belt to which a toner image is transferred from a plurality of color image forming units, and the pressure roller is the drive roller on the side where the image forming unit is not disposed; It is preferable to be disposed between the driven rollers.
The image forming apparatus may be arranged such that an axially outer end surface of the pressure roller coincides with a side edge portion of the endless belt.
In addition, the image forming apparatus can form an arc surface or an inclined surface at a corner portion of the outer peripheral surface on the inner side in the axial direction of the pressure roller.
Further, in the image forming apparatus, the pair of pressure rollers can be disposed at a plurality of locations in the circumferential direction of the endless belt.

An image forming apparatus having a belt meandering prevention mechanism according to the present invention is an image forming apparatus provided with a belt meandering prevention mechanism in which an endless belt is hung on a driving roller and a driven roller, and between the driving roller and the driven roller, A pair of pressure rollers rotatably supported on a rotation shaft parallel to the roller shafts is provided on the inner peripheral surface of the endless belt, and the pressure rollers are arranged at both ends in the width direction of the endless belt. Since the contact portion between the pressure roller and the endless belt is disposed so as to protrude above the reference surface of the endless belt connecting the driving roller and the driven roller, the endless belt is arranged. A difference in peripheral speed between the inner side and the outer side can be provided to prevent meandering of the endless belt.
In the above invention, the endless belt is a primary transfer belt to which toner images are transferred from a plurality of color image forming units, and the driving roller and the driven roller on the side where the image forming unit is not disposed. Since it is disposed between the rollers, color misregistration can be prevented when a color image is printed.
In the image forming apparatus, since the outer end surface in the axial direction of the pressure contact roller is disposed so as to coincide with the side edge portion of the endless belt, it is possible to take an unnecessarily large place in the width direction of the endless belt. Without increasing the size of the apparatus.
In the image forming apparatus, since the circular arc surface or the inclined surface is formed at the corner portion on the inner side in the width direction of the pressure roller, the wear of the endless belt is prevented at the contact portion between the corner portion of the pressure roller and the endless belt. it can. This is particularly effective when the material of the surface of the pressure roller is resin.
In the image forming apparatus, the pair of pressure rollers are arranged at a plurality of locations in the circumferential direction of the endless belt, so that the endless belt can be prevented from meandering.

Hereinafter, an image forming apparatus having a belt meandering preventing mechanism according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an image forming apparatus 1 having a belt meandering prevention mechanism according to the present invention. In the apparatus main body 2 of the image forming apparatus 1 shown in FIG. 1, four sets of image forming units 3 to 6 are arranged in this order from right to left in FIG. 1 of the image forming apparatus 1. In this embodiment, reference numeral 3 is a black image forming unit, reference numeral 4 is a yellow image forming unit, reference numeral 5 is a cyan image forming unit, and reference numeral 6 is a magenta image forming unit.

Among these, the image forming unit 6 is provided with a photosensitive drum 25, and includes a primary transfer roller 24 disposed with a primary transfer belt 8 that is an endless belt sandwiched between the photosensitive drum 25 and the photosensitive drum 25. Is provided with an image forming element including a developing device 26, a charger 27, and a cleaning device 28. Since the image forming units 3 to 6 have basically the same configuration except for the color of the toner, only the upstream image forming unit 6 is given a reference and the configurations of the other image forming units 3 to 5 are the same. The members are omitted for simplification of reference numerals.
In the apparatus main body 2, a primary transfer belt 8 including a linear movement region 7 to which toner images formed by the image forming units 3 to 6 are sequentially superimposed and transferred, and a drive for suspending the primary transfer belt 8 are suspended. A primary transfer belt mechanism 9 having a roller 13 and a driven roller 14, a paper feed cassette 10 for storing paper, and a toner image transferred to the primary transfer belt 8 on a paper P fed by the paper feed cassette 10. A secondary transfer roller 12 as a secondary transfer device for transferring is disposed.
The driving roller 13 located on the left end side of the primary transfer belt and the driven roller 14 located on the right end side are driven to rotate clockwise in FIG. When the drive roller 13 is driven to rotate, the linear movement region 7 of the primary transfer belt 8 is moved from the right side to the left side.

A pickup roller 11 is provided on the discharge side of the paper feed cassette 10, and the pickup roller 11 can discharge the paper placed on the paper feed cassette 10. Between the paper feed cassette 10 and the primary transfer belt mechanism 9, a paper feed conveyance path 15 that guides the paper fed upward from the paper feed cassette 10 toward the uppermost portion is disposed. Separate paper feed roller pairs 16 and 17 are arranged in the paper feed path 15. A fixing device 18 is disposed at the upper end portion in the apparatus main body 2 and on the extension in the downstream direction of the paper feed conveyance path 15. The fixing device 18 is provided with a fixing roller 19 and a pressure roller 20. Discharge roller pairs 21 and 22 are disposed further upstream and downstream of the fixing device 18.
On the upper surface of the apparatus main body 2, a paper discharge tray 23 is disposed for receiving the paper discharged in the horizontal and horizontal directions by the discharge roller pairs 21 and 22.

Next, details of the primary transfer belt 8 according to the present invention will be described.
FIG. 2 is a perspective view of the primary transfer belt 8, and FIG. 3 is a front view of the pressure roller pair 30 attached to the primary transfer belt 8.
The primary transfer belt 8 shown in FIG. 2 has a linear movement region on the lower surface side, and operating units 3 to 6 are disposed. As described above, in the primary transfer belt 8 that is an endless belt, the driving roller 13 is rotatably provided on the left end side by a driving source (not shown), and the driven roller 14 is rotatably provided on the right end side. The driving roller 13 and the driven roller 14 are supported by a support portion (not shown) of the apparatus main body 2.

A pair of pressure rollers 30 that are in contact with the inner peripheral surface of the on-belt conveyance path 8a is disposed inside the primary transfer belt 8 and at a substantially intermediate position in the belt conveyance direction of the primary transfer belt 8.
As shown in FIG. 3, the pressure roller pair 30 includes a pair of cylindrical pressure rollers 31 and 32 positioned at both ends in the width direction of the primary transfer belt 8, and the pressure rollers 31 and 32 are arranged on the pressure roller shaft 33. It is supported. The pressure roller shaft 33 is rotatably supported by a support portion (not shown) of the apparatus main body 2.

As a condition of the position where the pressure rollers 31 and 32 are disposed, the reference surface A of the primary transfer belt 8 where the pressure rollers 31 and 32 should be disposed, that is, as shown in FIG. In a state where it is not arranged, it is necessary to arrange it at a position higher than a reference plane (virtual plane) A connecting the apexes between the driving roller 13 and the driven roller 14 (see FIGS. 2 and 5). For example, as shown in FIG. 4, if the diameters of the driving roller 13, the driven roller 14, and the pressure roller pair 30 are the same, the pressure roller shaft 33 is disposed at a position higher than the driving roller shaft 13a and the driven roller 14a axis. The When another intermediate roller 17 (shown by an imaginary line in FIG. 4) is disposed between the driving roller 13 and the driven roller 14, or between the driving roller 13 and the intermediate roller 17, or It arrange | positions between the driven roller 14 and its intermediate | middle roller 17, and arrange | positions so that it may become a surface rather than the reference surface of those primary transfer belts. However, the image forming units 3 to 6 are not disposed between the rollers on the same surface before and after the image forming units 3 to 6.
The reference surface A is provided on the upper surface side of the primary transfer belt 8 wound around the drive roller 13 and the driven roller 14 in the present embodiment, but the image forming units 3 to 6 are disposed on the upper side. In such an image forming apparatus, the reference surface is provided on the lower surface side, and in the image forming apparatus in which the image forming units 3 to 6 are arranged in the vertical direction, the driving roller and the driven roller are arranged in the vertical direction. Therefore, in such a case, the reference plane is provided on either the left or right side.

Thus, only the pressure roller shaft 33 exists between the pressure rollers 31 and 32. Therefore, when the pressure rollers 31 and 32 are mounted on the primary transfer belt 8, as shown in FIG. Both ends in the width direction of the primary transfer belt 8 protrude outward from the reference surface A of the primary transfer belt 8, and only the center side coincides with the height of the reference surface A. This is the same whether the primary transfer belt 8 is rotating or stopped.
As shown in FIG. 5, the positions of the pressure rollers 31 and 32 in the axial direction are such that the outer end surfaces 31 a and 32 a of the pressure rollers 31 and 32 are flush with the side end surfaces 13 b and 14 b of the driving roller 13 and the driven roller 14. It is preferable, and it arrange | positions in the position which does not protrude outside those side end surfaces 13b and 14b. As an initial condition, in a state where the primary transfer belt 8 is on the correct track, the lengths L1 and L2 at which the primary transfer belt 8 is superimposed on the pressure rollers 31 and 32 need to match each other. The lengths of L1 and L2 are preferably in the range of 5 to 10 mm.

For the material of the pressure rollers 31, 32, resin or rubber can be used. In the case of resin, for example, POM (polyacetal) can be used, and in the case of rubber, EPDM (ethylene propylene rubber) can be used. When the material of the pressure rollers 31 and 32 or the material of the surface of the pressure rollers 31 and 32 is resin, the inner edges 31b and 32b are not damaged by the inner edges 31b and 32b of the pressure roller pair. A chamfer or a curved surface as shown in FIG. 3 may be formed on 32b.
When the material of the pressure rollers 31, 32 or the surface of the pressure rollers 31, 32 is rubber, the pressure rollers 31, 32 are greatly deformed by the tension of the primary transfer belt 8, and the circumference of the central portion of the primary transfer belt 8 is reduced. In order not to eliminate the difference, it is necessary to use a rubber roller having a hard material. If the material is a rubber roller, it is not necessary to form chamfers or curved surfaces formed on the inner edges 31b and 32b as shown in FIG.

In the image forming apparatus 1 configured as described above, the surface of the photosensitive drum 25 uniformly charged by the charger 27 in each of the image forming units 3 to 6 is exposed by the laser beam of the laser scanning unit 29. Thus, an electrostatic latent image is formed, and this electrostatic latent image is developed by the developing device 26 to become a toner image. This toner image is sequentially superimposed and transferred from the toner image formed by the upstream image forming unit 6 on the surface of the linear movement region 7 of the primary transfer belt 8 in the primary transfer belt mechanism 9. The toner image transferred to the surface of the linear movement area 7 of the primary transfer belt 8 is transferred to the surface of the sheet fed from the paper feed cassette 10 through the paper feed conveyance path 15 at the uppermost part of the primary transfer belt 8. Transferred by the roller 12. The color toner image transferred onto the paper is fixed onto the paper while passing between the fixing roller 19 and the pressure roller 20 of the fixing device 18. The sheet on which the color toner image is fixed is discharged to the discharge tray 23 by the discharge roller pair 21 and 22. The toner that is not transferred and remains on the surface of the photosensitive drum 25 is cleaned by the cleaning device 28.

  While the primary transfer belt 8 is rotating, the primary transfer belt 8 may meander in the axial direction of the drive roller 13 and the driven roller 14. In such a case, as shown in FIG. 5, the pressing rollers 31 and 32 of the pressing roller pair 30 are in contact with each other in a protruding state, and thus protrude outward from the reference surface A of the primary transfer belt 8. While the primary transfer belt 8 is rotating, the length of the belt in the circumferential direction of the portion where the pressure rollers 31 and 32 are located is different between the central portion and the outer side in the width direction of the primary transfer belt 8, and the length is short on the central side. The length increases on the outside. Since the belt is the same belt, the belt itself has the same rotation speed, and the primary transfer belt 8 has a lower peripheral speed at the center and a higher peripheral speed at the outer speed. As a result, a force is generated in the inward direction on the side shifted to the outside of the primary transfer belt 8, and the trajectory of the primary transfer belt 8 is always corrected.

Thus, in the present embodiment, the meandering of the primary transfer belt 8 can be prevented with a simple structure only by providing the pair of left and right pressure contact rollers 31 and 32. As a result, the meandering of the primary transfer belt is eliminated, image positional deviation is prevented, and a color image in which a plurality of colors are superimposed to form an image can be formed with no color deviation and a high-quality image can be formed.
Further, since the pressure rollers 31 and 32 are disposed only at both ends of the primary transfer belt 8 and do not need to be disposed in the intermediate region, material costs can be saved. There is no need to project the pressure rollers 31 and 32 outward from both ends of the primary transfer belt 8, no space is required in the width direction, and the apparatus does not increase in size due to the meandering prevention mechanism.
Furthermore, the structure is complicated, but the pressure roller shaft 33 can be moved up and down,
As described in the prior art, a belt meandering sensor is provided so that the pressure roller pair 31 can be brought into contact with and separated from the primary transfer belt 8, and the pressure roller pair 31 is attached to the primary transfer belt 8 only during belt meandering. You may make it press-contact.

While the embodiments of the present invention have been described above, the present invention can of course be modified or changed in various ways based on the technical idea of the present invention.
For example, in the above embodiment, the pressure contact rollers 31 and 32 are formed in a columnar shape, but may be formed in a conical surface that tapers inward in the axial direction. However, the processing cost of a roller becomes high.
Similarly, although the cost increases, two sets (plurality) of pressure rollers 31 and 32 may be provided, one set is arranged on the driving roller 13 and one set is arranged on the driven roller 14 side.

1 is a schematic side view of an image forming apparatus employing a meandering prevention mechanism according to an embodiment of the present invention. FIG. 2 is a perspective view of a primary transfer belt of the image forming apparatus in FIG. 1. FIG. 2 is a front view of a pressure roller pair disposed on the inner peripheral side of the primary transfer belt of the image forming apparatus of FIG. 1. FIG. 2 is a side view of a primary transfer belt of the image forming apparatus in FIG. 1. The right side of the center line is a front view of the primary transfer belt of the image forming apparatus of FIG. 1, and the left side of the center line is a cross-sectional view of a portion where the pressure roller is present.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Apparatus main body 3-6 Image forming unit 8 Primary transfer belt (endless belt)
8b Side edge portion 13 Driving roller 13a, 14a, 33 Roller shaft 13b Side end surface 14 Driven roller 18 Fixing device 25 Photosensitive drum 30 Pressure roller pair 31, 32 Pressure roller 31a, 32a Outer end surface 31b, 32b Inner edge A Reference surface

Claims (5)

In an image forming apparatus having a belt meandering prevention mechanism in which an endless belt is hung on a driving roller and a driven roller.
Between the driving roller and the driven roller, a pair of pressure contact rollers rotatably supported on a rotation shaft parallel to these roller shafts is provided on the inner peripheral surface of the endless belt, and the pressure contact rollers are The endless belt is disposed at both ends in the width direction with a space between them, and the contact portion between the pressure roller and the endless belt is above the reference surface of the endless belt connecting the driving roller and the driven roller. An image forming apparatus having a belt meandering prevention mechanism, wherein the belt meandering prevention mechanism is disposed so as to protrude.   The endless belt is a primary transfer belt to which toner images are transferred from a plurality of color image forming units, and the pressure contact roller is disposed between the driving roller and the driven roller on the side where the image forming unit is not disposed. The image forming apparatus having the belt meandering prevention mechanism according to claim 1, wherein the image forming apparatus has a belt meandering prevention mechanism.   The image forming apparatus having a belt meandering prevention mechanism according to claim 1, wherein an axially outer end face of the pressure roller is disposed so as to coincide with a side edge portion of the endless belt.   The image forming apparatus having a belt meandering prevention mechanism according to any one of claims 1 to 3, wherein an arc surface or an inclined surface is formed at a corner portion of the outer circumferential surface on the axially inner side of the pressure roller.   The image forming apparatus having a belt meandering prevention mechanism according to claim 1, wherein the pair of pressure contact rollers are arranged at a plurality of locations in a circumferential direction of the endless belt.

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