JPH04141676A - Erase control method for image forming device - Google Patents

Abstract

PURPOSE:To prevent the degradation of the picture quality by specifying the arrangement of an erase means, a transfer means, and a sheet detecting means and erasing an unnecessary electrification potential at the time of detecting the trailing end of a transfer sheet or after the elapse of a prescribed time. CONSTITUTION:Respective means are arranged to satisfy relations A<=B where A is the distance from the transfer position of a transfer means 20 on a photosensitive body 18 to the erase position of an erase means 30 and B is the distance for which the transfer sheet is carried from the transfer position to the sheet detection position of a sheet detecting means 6. When the trailing end of the transfer sheet is detected by the sheet detecting means 6 or the prescribed time elapses, the erase means 30 is operated. Thus, the unnecessary electrification potential is erased without increasing the cost even if the size of the used transfer sheet cannot be detected, and the degradation of the picture quality is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an erase control method in various image forming apparatuses such as laser printers, copying machines, and facsimile machines.

[Conventional technology]

In an electrophotographic image forming apparatus such as a copying machine, the surface of a photoreceptor charged by a charging charger is exposed to light by a fog light device, toner is applied thereto by a developing device, and the toner is developed. The toner image is transferred onto a transfer sheet from a paper feeding device, and residual toner after transfer is removed by a cleaning unit.

By the way, in such an image forming apparatus, since the outside of the image area on the photoconductor is not exposed to light, the potential charged by the charger remains, and if the image is developed as it is, it will be developed solidly in black, which increases the load on the cleaning unit. At the same time, this leads to a large amount of toner consumption, and furthermore, there is a possibility that a portion of the solid black portion may be transferred to the image on the transfer sheet.

In particular, in copying machines that use a transfer drum to obtain monochrome, full-color, or black images, toner outside the sheet size on the photoreceptor is transferred to the transfer drum (made of polyester film, etc.). Once transferred, the toner remains behind, and when a larger transfer sheet is fed, the remaining toner adheres to the transfer sheet and causes stains on the back and edges, reducing the image quality. There was a problem in that it lowered the value.

In addition, even in image forming apparatuses such as ordinary copying machines and Pfunta that do not use transfer rams, untransferred toner outside the sheet size is cleaned by the cleaning unit, so the increased amount of untransferred toner increases the burden on cleaning. This can lead to poor cleaning and degraded image quality.

Therefore, in order to solve such problems, the special public
As seen in Japanese Patent Publication No. 3752, Japanese Patent Publication No. 62-11347, and Japanese Patent Application Laid-Open No. 63-97985, the size of the transfer sheet to be passed is generally detected by a sheet size detection means, The area on the photoreceptor outside the size is erased by an eraser.

[Problem to be solved by the invention]

However, in cases where the sheet size cannot be detected, for example in an image forming apparatus equipped with a manual feed tray, there are various sizes of transfer sheets fed from the manual feed tray, so it is not possible to detect the sheet size each time. Since static electricity removal is performed using an eraser only for a specific size without using the eraser, if a transfer sheet of a size other than that size is fed from the manual feed tray and image formation is performed, the photoreceptor or transfer drum is Unnecessary toner remains, resulting in problems such as deterioration of image quality as described above.

Therefore, it is conceivable to provide a means for detecting the sheet size in the manual feed tray, but this would increase the size and cost of the apparatus.

This invention was made in view of the above points, and even when the size of the transfer sheet to be used cannot be detected, unnecessary charged potential can be erased without increasing costs, thereby suppressing the deterioration of image quality. The purpose is to do so.

[Means to solve the problem]

In order to achieve the above object, the present invention includes an erase means for erasing unnecessary charged potential on the photoreceptor, and a device disposed downstream of the erase means in the rotational direction of the photoreceptor to transfer the toner image formed on the photoreceptor. In an image forming apparatus equipped with a transfer means for transferring onto a sheet, and a sheet detection means for detecting the presence or absence of the transfer sheet, which is located upstream of the transfer means in the transfer sheet conveyance direction, the transfer position by the transfer means on the photoreceptor is Assuming that the distance from A to the erase position by the erase means is A, and the transfer sheet transport distance from the transfer position to the sheet detection position by the sheet detection means is B, each of the above means is arranged so that A≦B, The erase means is activated when the trailing edge of the transfer sheet is detected by the sheet detection means or after a predetermined period of time has elapsed.

Note that the present invention can also be applied to an image forming apparatus equipped with a transfer drum for full-color image formation.

[For production]

In the image forming apparatus to which the erase control method according to the present invention is applied, the erase means, the transfer means, and the sheet detection means are arranged so that the relationship A≦B holds, and the rear end of the transfer sheet is detected by the sheet detection means. Since the erase means is activated to erase unnecessary charged potential when the transfer sheet is transferred or after a predetermined period of time has elapsed, the deterioration in image quality can be suppressed without increasing costs even when the size of the transfer sheet to be used cannot be detected. I can do it.

In particular, in an image forming apparatus equipped with a transfer drum for full-color image formation, when the toner on the photoreceptor outside the sheet size is transferred to the transfer drum as described above, the toner remains. Although there has been a problem of deterioration of image quality, this invention is very effective because it can solve this problem without increasing costs.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 2 is an overall configuration diagram showing a color copying machine which is an embodiment of the present invention.

To explain the configuration of this copying machine, the transfer sheet P fed from the paper feed cassette 23 is further fed by the intermediate roller 1, and the first... It is guided by the second guide plates 2 and 3 and sent to the nip portion of the pair of registration rollers 4.

At this time, the leading end of the transfer sheet is detected by a sheet sensor (registration sensor) 6 consisting of a photosensor, etc., and after a predetermined period of time, the rotation of the intermediate roller 1 is stopped by disengaging a clutch (not shown). Occasional slack (loop) between intermediate roller 1 and registration roller pair 4
is formed, and the leading end of the paper is reliably held and aligned in the nip portion of the pair of registration rollers 4.

On the other hand, the original on the contact glass 10 (not shown)
On the other hand, illumination scanning is performed by moving the illumination device 11 to the right in the figure together with the first mirror 12. The scanning light image at this time is the second mirror 1 moving in the same direction.
3. It enters the lens 15 via the third mirror 14, and then the fourth mirror 16. The image passes through a filter device 17 and is projected onto a latent image carrier configured as a drum-shaped photoreceptor 18 that rotates clockwise.

The filter device 17 has a plurality of color separation filters, and through one of these filters, an optical image of, for example, a blue component is formed and projected onto the photoreceptor 18, which has already been uniformly charged by the charger 19. , thereby forming an electrostatic latent image on the photoreceptor.

The eraser 30 is composed of light emitting elements such as light emitting diodes arranged in the axial direction of the photoreceptor 18. When the latent image formed on the photoreceptor passes through the eraser 30, the irradiation light causes the paper feeder 23 to Charges (charged potential) in areas outside the size of the transfer sheet (leading edge, side edge, and trailing edge) fed from the transfer sheet are dissipated.

Below the photoreceptor 18 is a yellow developing device 21Y.

A developing device 21 having a magenta developer 21M, a cyan developer 21C, and a blank developer 21B is provided, and the electrostatic latent image is first visualized by the yellow developer 21Y to become a toner image.

The transfer sheet, which has been waiting with its leading edge held between the pair of registration rollers 4, is conveyed by the pair of registration rollers 4 in synchronization with the movement of the toner image on the photoreceptor 18, and is transferred to the clamping section of the transfer drum 22. 22a and rotate together, and the toner image is transferred onto the transfer sheet P by the transfer charger 20.

Similarly, the magenta and cyan images formed on the photoreceptor 18 are transferred to the transfer sheet P and overlapped, and if necessary, a blank image made visible by the black developer 21B is overlapped.

Note that in the case of blank exposure, an ND filter may be used as the filter, but such a filter may not be used in some cases.

After the transfer, the transfer sheet is separated from the transfer drum 22 by the separation charger 24 and the separation claw 25, and the separated transfer sheet passes through the fixing device 26 and is discharged outside the machine as copy paper.

On the other hand, the residual toner on the photoreceptor 18 is removed by the cleaning device 2.
7, and then the photoreceptor is subjected to a static eliminating action by a static eliminating lamp 28.

It is also possible to make black and white copies using only the black developing device 21B by operating a switching means such as a conversion key (not shown).

Here, the photoreceptor 18. Transfer drum 12. Eraser 30.
Transfer charger 20. FIG. 3 shows the arrangement relationship of the seat sensor 6 and the seat sensor 6.

In the figure, A is the distance from the transfer position on the photoreceptor 18 (transfer drum 12) by the transfer charger 20 to the erase position by the eraser 30, and B is the distance on the transfer sheet from the transfer position to the sheet detection position by the sheet sensor 6. The transport distance is shown, and each means is arranged so that the relationship A<B holds.

FIG. 4 is a block diagram showing the control system of this copying machine.
The control unit 40 includes a microcomputer consisting of a CPU, ROM, RAM, timer, Ilo, etc., and inputs key information from the operation panel 41 and detection signals from various sensors and switches 42 including the seat sensor 6. hand,
Illumination device 11 in FIG. Charger 19. Eraser 30,4
Seed developers 21Y, 21M, 21C, 21B, transfer charger 20. 3, which controls copying process equipment 43 such as the fixing device 26 and sequence equipment 44 such as motors, solenoids, clutches, and fixing heaters, and sends display information to the operation panel 41; The eraser operation by the CPU will be explained along the flowchart of FIG.

However, the explanation of the operation for the portion outside the sheet width on the photoreceptor 18 will be omitted.

The second flow starts when called by the main routine (not shown), starts the above-mentioned sheet feeding operation by processing (not shown), and when the sheet sensor 6 is turned on and a preset time has elapsed, the transfer sheet is loaded. is temporarily stopped, whereby the leading edge of the transfer sheet is aligned at the nip portion of the pair of registration rollers 4 as described above.

After the registration roller pair 44 is driven to re-feed the waiting transfer sheet, it is checked whether the sheet sensor 6 shown in FIG. do.

Thereafter, when the trailing edge of the transfer sheet passes the sheet sensor 6 and the sheet sensor 6 is turned off, an internal timer is started.

Next, it is determined whether or not the time amplifier is reached, that is, whether the preset time has elapsed, but since the internal timer has just been started, the program returns directly, and when the time is up, the eraser 30 is turned on. (by causing all the light-emitting elements to emit light), the charges on the portion of the photoreceptor 18 corresponding to the rear end of the transfer sheet and thereafter are erased.

Thereafter, processes not shown are sequentially performed and the process returns to the main routine.

Thus, in this embodiment, the photoreceptor 18, the transfer drum 22 . Eraser 30. Transfer charger 20. and sheet sensor 6 are arranged so that the relationship A<B as shown in FIG.
0 is activated to erase unnecessary charged potentials, toner is prevented from adhering to the portion of the transfer drum 22 corresponding to the rear end of the transfer sheet, regardless of the size of the transfer sheet used. be able to.

Therefore, assuming that this copying machine is equipped with a manual feed tray, it is possible to eliminate unnecessary charged potentials without having to provide a new means for detecting the sheet size on the manual feed tray, which is very effective. It is.

Note that if the respective means have the relationship A=B, the eraser 30 may be activated when the trailing edge of the transfer sheet is detected by the sheet sensor 6.

Further, although an embodiment in which the present invention is applied to a color copying machine has been described, the present invention can also be applied to a monochrome copying machine shown in FIG. 5, for example.

That is, let A be the distance from the transfer position by the transfer charger 51 on the photoreceptor 50 to the erase position by the eraser 52, and let B be the transfer sheet transport distance from the transfer position to the sheet detection position by the sheet sensor 53.
The respective means are arranged so that the relationship A≦B holds, and when the trailing edge of the transfer sheet fed from the paper feed cassette 54 is detected by the sheet sensor 53 or after a predetermined period of time has elapsed, the eraser 52 By operating the , unnecessary charged potential can be erased.

In addition, 55 is a power supply device, 56 is a developing device, 57 is a cleaning device, and 58 is a pair of registration rollers.

59 is a conveyor belt.

Furthermore, this invention is not limited to copiers, but also includes laser link,
It is applicable to various image forming apparatuses such as other optical printers such as LED printers and liquid crystal shutter printers, and facsimile machines.

〔Effect of the invention〕

As described above, according to the present invention, even when the size of the transfer sheet to be used cannot be detected, unnecessary charged potentials can be erased without increasing costs, and deterioration in image quality can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the processing according to the present invention by the control unit shown in FIG. 4, FIG. 2 is an overall configuration diagram showing a color copying machine which is an embodiment of the present invention, and FIG. 3 is a photoconductor of the same. , a diagram for explaining the arrangement relationship of a transfer drum, an eraser, a transfer charger, and a sheet sensor, FIG. 4 is a block diagram showing a control system of the copying machine shown in FIG. 2, and FIG. 5 is another embodiment of the present invention. 1 is a schematic configuration diagram showing an example monochrome copying machine; FIG. 6.53...Sheet sensor 20.5] Transfer charger 21.56...Developing device 22...Transfer tram 24.
55. Charger 30. 52.. Eraser 40.. Control unit 43.. Copying process equipment 44.. Sequence equipment

Claims (1)

[Scope of Claims] 1. An erase means for erasing unnecessary charged potential on the photoreceptor, and a toner image formed on the photoreceptor on the downstream side of the erase means in the rotational direction of the photoreceptor onto a transfer sheet. In an image forming apparatus, the image forming apparatus includes a transfer means for transferring, and a sheet detection means for detecting the presence or absence of a transfer sheet, which is located upstream of the transfer means in a transfer sheet conveying direction. Assuming that the distance from the position to the erase position by the erase means is A, and the transfer sheet transport distance from the transfer position to the sheet detection position by the sheet detection means is B, each of the means is adjusted so that the relationship A≦B holds. and activating the erase means when the trailing edge of the transfer sheet is detected by the sheet detection means or after a predetermined period of time has elapsed. 2. The erase control method according to claim 1 in an image forming apparatus equipped with a transfer drum for full color image formation.