JPH05127542A - Device for correcting meandering of transfer belt - Google Patents

Abstract

PURPOSE:To prevent the deviation of a toner image, for example, color slippage in a full color image, and to prevent the deterioration of image quality by detecting the meandering of a transfer belt just before the toner image on a photosensitive body reaches a transfer position and correcting the meandering. CONSTITUTION:In the case of forming a synthesized toner image, for example, in the case of forming the full color image, all the leading ends of three-color toner images must be aligned. Then, all the leading ends of the three-color toner images are set on the leading end part C in a toner image forming area A. The leading end part C of the toner image is detected by a home position sensor TBHPS. And the meandering of the transfer belt 2 is detected by a meandering detecting sensor 25 when a correction area B is opposite to the photosensitive belt 1 and just before the position C as the leading end of the synthesized toner image on the transfer belt 2 reaches the abutting part of the photosensitive body 1 and the transfer belt 2, and then, the transfer belt 2 is moved to a rear side or a front side so as to correct the meandering of the transfer belt 2 in accordance with the detection result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention corrects meandering of a transfer belt in an image forming apparatus for forming a synthetic toner image on the transfer belt by repeating a process of transferring a toner image on a photoconductor to the transfer belt. The present invention relates to a meandering correction device.

[0002]

2. Description of the Related Art For example, when performing a full-color copy in a full-color copying machine, a yellow toner image, a magenta toner image, and a cyan toner image are sequentially formed on a photoconductor and are sequentially transferred to a transfer belt (primary transfer). ) And then transfer (secondary transfer) to the paper. That is, a monochromatic toner image is formed on the photoconductor, and the monochromatic toner images are superposed on the transfer belt to form a full color toner image (composite toner image), which is transferred onto a sheet.

By the way, the transfer belt is formed by forming a dielectric sheet into a belt shape and stretching it between rollers.
Meandering may occur during rotation due to dimensional accuracy of the roller and belt, balance of tension for stretching the belt, uneven rotation of the roller, and the like. If the transfer belt meanders greatly, it interferes with the image forming process, so the design accuracy is such that the meandering is within ± 0.5 mm.

[0004]

However, since a synthetic toner image, for example, a full-color toner image is formed by superposing three color toner images, meandering occurs during superposition of the three color toner images. In that case, even if the deviation is within ± 0.5 mm, there is a deviation in the color superposition, and the quality as a full-color image is significantly deteriorated. In particular, when the number of superimposed toner images increases, the transfer belt rotates a plurality of times from the transfer of the first toner image to the transfer of the final toner image, during which the meandering state of the transfer belt progresses. As a result, the toner image transferred first and the toner image transferred last may be significantly displaced.

An object of the present invention is to prevent deviation of toner images, for example, color deviation in a full-color image, when a toner image on a photoconductor is transferred onto a transfer belt to form a synthetic toner image on the transfer belt. It is an object of the present invention to provide a transfer belt meandering correction device capable of preventing the deterioration of the transfer belt.

[0006]

SUMMARY OF THE INVENTION The present invention includes a transfer belt disposed in contact with a photoconductor, and continuously transferring a toner image formed on the photoconductor to the transfer belt a plurality of times. In an image forming apparatus that forms a synthetic toner image on a belt, the timing immediately before the position on the transfer belt that should be the tip of the synthetic toner image reaches the contact portion between the photoconductor and the transfer belt is the correction timing. A correction timing detection unit for detecting, a meandering detection unit for detecting the meandering state of the transfer belt, a transfer belt meandering correction unit for correcting the meandering of the transfer belt, and a meandering state of the transfer belt when the correction timing is detected. And means for operating the meandering correction means in response thereto.

[0007]

In the present invention, the front end position of the synthetic toner image on the transfer belt reaches the contact portion between the photoconductor and the transfer belt, that is, the position where the toner image on the photoconductor is transferred to the transfer belt. Immediately before, the meandering state of the transfer belt is detected, and the meandering correction is performed. Thus, the meandering correction of the transfer belt is performed immediately before the transfer of the toner image from the photoconductor to the transfer belt is started. For example, when a full-color image is formed, the meandering correction is performed immediately before the transfer of the first color toner image is started, and the meandering correction is performed immediately before the transfer of the second color toner image is started. The meandering correction is also performed immediately before the transfer of the color toner image is started. That is, the meandering correction of the transfer belt is performed several times during the formation of one synthetic toner image, and the meandering of the transfer belt is excessively advanced and the toner image first transferred and the toner image finally transferred are formed. There will be no significant deviation between and.

[0008]

EXAMPLE FIG. 5 is a diagram showing a schematic structure of a full-color copying machine for forming an image using a transfer belt.

A photoconductor belt 1 and a transfer belt 2 are provided in the main body of the copying machine.

The photoconductor belt 1 is a photoconductive photosensitive sheet formed into a sheet and is formed into a belt shape. The belt portion 1a has a length twice as long as the maximum image length that can be copied in this copying machine. Is stretched between the two rollers 1b and 1c. Further, the transfer belt 2 is a belt-shaped dielectric sheet, and has a belt portion 2a having a maximum image length that can be copied in this copying machine and three rollers 2b ,.
It is stretched between 2c and 2d. The transfer belt 2 contacts the photoconductor belt, and the primary transfer roller 21 is arranged at this position. The photoconductor belt 1 and the transfer belt 2 rotate at the same speed, and the toner image on the photoconductor belt 1 is transferred to the transfer belt 2 by the primary transfer roller 21.

An original table 3 made of a transparent glass is placed on the upper surface of the main body of the copying machine, and an original to be copied is placed on the original table 3. Below the document table 3, light sources 4a and 4b and a mirror 4 are provided.
An optical system device 4 including c to 4g, a lens 4h, and a color separation filter 4i is arranged. The optical system device 4 scans a document placed on the document table 3 and guides the reflected light to the photosensitive belt 1. Around the photosensitive belt 1, a charging charger 5, a blank lamp 6, a developing device 7, a transfer belt 2, a cleaner 8 and a discharging lamp 9 are arranged in this order. The developing device 7 includes four types of developing units 7a, 7b,
It has 7c and 7d. The developing unit 7a contains yellow toner, 7b contains magenta toner, 7c contains cyan toner, and 7d contains black toner.

Each of the developing units 7a to 7d operates as necessary to attach toner to the electrostatic latent image formed on the photosensitive belt 1.

A primary transfer roller 2 is provided around the transfer belt 2.
1, secondary transfer roller 22, cleaner 23, static elimination lamp 2
4 are provided. The primary transfer roller 21 is arranged at a position where the photosensitive belt 1 and the transfer belt 2 contact each other, and electrostatically transfers the toner image on the photosensitive belt 1 to the transfer belt 2. Further, the secondary transfer roller 22 is movable to a position where it contacts the transfer belt 2 shown by the solid line in the figure and a position where it does not contact the transfer belt 2 shown by the chain double-dashed line in the figure. At a certain time, the toner image on the transfer belt 2 is transferred onto a sheet.

The sheets are stored in a sheet feeding cassette 10a or 10b or a manual sheet feeding tray 10c provided on the right side surface of the copying machine body. During the copying process, the paper is fed from any one of them and fed to the position of the transfer belt 2. The paper is further sent to the paper discharge tray 12 via the fixing device 11.

A method for forming a full-color image by this copying machine will be briefly described. First, a yellow toner image is formed on the photoconductor belt 1, and this is transferred to the transfer belt 2. The yellow toner image is formed as follows. A light source 4 is a full-color document placed on the document table 3.
a and 4b, the reflected light of the original is reflected by the color separation filter 4
It is guided to the photosensitive belt 1 through the blue filter i.
By this time, the photosensitive belt 1 has been charged by the charging charger 5, and an electrostatic latent image is formed by exposure.
Then, the developing unit 7a containing the yellow toner operates to attach the yellow toner to the electrostatic latent image on the photosensitive belt 1. In this way, a yellow toner image is formed on the photosensitive belt 1, and this is transferred to the transfer belt 2. Similarly, magenta toner is attached to the electrostatic latent image formed by the reflected light of the original through the green filter to form a magenta toner image, which is superposed on the yellow toner image on the transfer belt 2. It
Further, cyan toner is attached to the electrostatic latent image by the reflected light of the original through the red filter to form a toner image, which is superposed on the yellow and magenta toner images on the transfer belt 2. The composite toner image superimposed as described above is transferred by the secondary transfer roller 22 to the paper fed from either the paper feed cassette 10a or 10b or the manual paper feed tray 10c.

As described above, the transfer belt 2 is set to the maximum image length that can be copied by this copying machine.
That is, when the maximum image is formed as shown in FIG. 1, the toner image is formed (transferred) in the toner image forming area A, and the toner image is not transferred to the area B. In the case of an image smaller than the maximum size image, the toner image is formed in an area smaller than the toner image forming area A. By the way, when forming a synthetic toner image, for example, when forming a full-color image, all the front ends of the three-color toner images must be aligned. Therefore, all the leading ends of the toner images of the three colors are set to the leading end portion C of the toner image forming area A. The toner image front end portion C is detected by the home position sensor TBHPS. The area immediately before the toner image front end portion C is a correction area B. The correction area B is an area in which a toner image is not formed even when the maximum size image is formed, and this area B is the photosensitive belt 1.
When the transfer belt 2 is opposed to, the meandering correction of the transfer belt 2 is performed as described later. The timing at which the correction area B faces the photoconductor belt 1 can also be easily obtained from the output of TBHPS.

FIG. 2 is a view for explaining the installation state of the sensor (meandering detection means) 25 for detecting the meandering amount of the transfer belt 2 and the output state of the sensor. The meandering detection sensor 25 is provided on the rear side of the main body of the copying machine and has a light emitting element 25a and a light receiving element 25b.

The light emitting element 25a and the light receiving element 25b are arranged so as to sandwich the end portion of the transfer belt 2 as shown in the side view of FIG. The transfer belt 2 has a meandering amount of ± 0.5 mm.
Since it is set within the range, the light receiving surface of the light receiving element 25b is based on the normal position where the end of the transfer belt 2 should be.
The front side and the rear side are placed 0.5 mm each (see the plan view). As a result, as shown in the sensor output state diagram, the output voltage of the light receiving element 25b is increased when the transfer belt 2 is displaced to the front side, the sensor output is increased, and the transfer belt 2 is displaced to the rear side. When this happens, the amount of light received decreases and the sensor output decreases. Then, the meandering amount (mm) is obtained from the value.

Transfer belt 2 determined by meandering detection sensor 25
The meandering correction of the transfer belt is performed on the basis of the meandering amount of.
FIG. 3 is a diagram showing a configuration example of the meandering correction mechanism. In this meandering correction mechanism, meandering correction is performed by adjusting the tension on the rear side of the belt portion 2a of the transfer belt 2. The belt portion 2a is stretched around three rollers: a drive roller 2b to which a driving force is transmitted, a tension roller 2c for giving a tension to the belt portion 2a, and a pressure contact roller 2d against which a secondary transfer roller is pressed.

If the tension on the rear side of the tension roller 2c is set higher than the tension on the front side, the belt portion 2a shifts to the front side, and conversely, the tension on the rear side is set weaker than the tension on the front side. Then, the belt portion 2a shifts to the rear side. Therefore, the meandering is corrected by weakening the tension on the rear side when the belt portion 2a shifts to the front side and increasing the tension on the front side when the belt portion 2a shifts to the rear side. A meandering correction mechanism is provided at the rear end of the rotating shaft of the tension roller 2c. In the meandering correction mechanism, the rotating shaft 31 of the tension roller 2c is supported by a support plate 32 provided with a rack, and a worm gear 33 is meshed with the rack. The worm gear 33 is rotated by the motor, whereby the rear end of the tension roller 2c is pushed in the direction of arrow F or returned in the direction of arrow R. When the tension roller 2c is pushed in the arrow F direction, the belt portion 2a moves to the front side, and when it is returned in the arrow R direction, the belt portion 2a moves to the rear side.

FIG. 4 is a flowchart showing a processing procedure for correcting the meandering of the transfer belt.

First, when the correction timing is detected based on the output of TBHPS, the meandering amount is read (n1 → n2). The correction timing is when the correction area B faces the photoconductor belt 1 as described above. When it is determined that the transfer belt 2 is meandering based on the read meandering amount, the meandering correction mechanism operates to perform meandering correction, but when it is not meandering, the next correction timing is waited (n3 → n4). ).

Since the meandering correction is performed when the area B where the image is not formed faces the photoconductor belt 1 as described above, the transfer belt 2 may move to the rear front side during the toner image transfer. Therefore, it is possible to prevent the toner image from being rubbed.

In this embodiment, the photosensitive member has a belt shape, but it may have a drum shape. The meandering correction mechanism is not limited to this structure.

[0025]

According to the present invention, when a full-color image, which is a synthetic toner image, is formed, the meandering amount of the transfer belt is detected immediately before the toner image of one color is transferred, and the meandering correction is performed. Done. Therefore, it is possible to perform the meandering correction while the meandering amount is small, and it is possible to prevent the image quality from being significantly deteriorated. That is, in the prior art, meandering correction of the transfer belt was not performed even once during three rotations of the transfer belt, but in the present invention, meandering correction is performed three times during three rotations. . Thus, the meandering of the transfer belt can be corrected at an early stage, and the progress of the meandering can be stopped.

[Brief description of drawings]

FIG. 1 is a side view of a transfer belt.

FIG. 2 is a diagram showing a configuration and an output state of a meandering detection sensor.

FIG. 3 is a configuration diagram of a meandering correction mechanism.

FIG. 4 is a flowchart showing a meandering correction processing procedure.

FIG. 5 is a schematic configuration diagram of a full-color copying machine.

[Explanation of symbols]

 1 Photoconductor Belt 2 Transfer Belt 21 Primary Transfer Roller 2a Belt Part 2c Tension Roller 25 Meandering Detection Sensor 31 Rotating Shaft 32 Support Plate 33 Worm Gear TBHPS Transfer Belt Home Position Sensor

Claims (1)

[Claims] 1. A transfer belt disposed in contact with a photosensitive member, wherein a toner image formed on the photosensitive member is continuously transferred to the transfer belt a plurality of times to form a synthetic toner image on the transfer belt. In the image forming apparatus, a correction timing detection unit that detects, as a correction timing, a timing immediately before the position on the transfer belt, which should be the front end of the synthetic toner image, reaches the contact portion between the photoconductor and the transfer belt, A meandering detection unit that detects the meandering state of the transfer belt, a transfer belt meandering correction unit that corrects the meandering of the transfer belt, and a meandering correction unit that operates according to the meandering state of the transfer belt when the correction timing is detected. A transfer belt meandering correction device, characterized by comprising: