JPH06161308A - Image forming device - Google Patents

Abstract

PURPOSE:To remove toner attached to a transfer roller when an image size and a recording paper size are not equal, in an image forming device such as a laser printer. CONSTITUTION:The length of fed recording paper CP in the direction in which it is carried is detected by a paper feed sensor 10, and it is compared with the size of an image formed on a photosensitive drum 1. When their sizes are equal, image formation is carried out as it is. When their sizes are not equal, a part of a toner image formed on the photosensitive drum 1 is attached to a transfer roller 7, resulting in the soiling of the following recording paper, therefore the toner is transferred to the photosensitive drum 1 by applying bias potential having the same polarity as toner to the transfer roller 7, and also a warning of the unexecuted image formaiton is displayed.

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,
In particular, the present invention relates to an electrophotographic image forming apparatus that transfers a toner image formed on a photoconductor onto a recording medium to form an image.

[0002]

2. Description of the Related Art In this type of image forming apparatus, an image is formed as an electrostatic latent image on a charged photosensitive member, and the toner image developed by a toner is visualized as a recording medium. The image is transferred to, and subjected to a heat fixing process to form a completed image, which is provided. There are various methods for transferring a toner image to a recording medium, one of which is by a transfer roller.

In the transfer by the transfer roller, when the transfer roller is arranged in pressure contact with the photosensitive member and the recording medium is passed between the photosensitive member on which the toner image is formed and the transfer roller, Toner
A transfer bias potential having a polarity opposite to that of the charge applied to the transfer roller is applied to the transfer roller, and the toner image on the photoconductor is attracted and transferred to the recording medium.

[0004]

In principle, in such an image forming apparatus, a recording medium having a size suitable for the size of an image to be formed is supplied. There are various sizes of images to be displayed,
It may not always be possible to supply a recording medium suitable for the size of the image. If the size of the image to be formed is smaller than the recording medium, no particular trouble will occur, but in the opposite case,
That is, when the toner image formed on the photoconductor is larger than the recording medium to be transferred, the toner of the part of the toner image on the photoconductor protruding from the recording medium is transferred to the transfer roller. As a result, the recording medium to be fed next may be contaminated, or the transfer bias potential applied to the transfer roller may be substantially reduced, resulting in defective transfer.

Therefore, before and after the printing process of one image, an electric potential having a reverse polarity to that at the time of transfer is applied to the transfer roller to transfer the toner adhering to the transfer roller to the photoconductor, A method of cleaning a transfer roller has been proposed (for example, see Japanese Patent Laid-Open No. 1-292385). Also, in the case of specifying the image size to be formed by the key on the operation panel, the specified image size is compared with the recording medium to be fed, and if they do not match, it is considered that a jam has occurred and the image recording process is performed. It has been proposed to stop the operation and prevent stains due to toner transfer (see Japanese Patent Application Laid-Open No. 4-83272).

However, the former method of cleaning the transfer roller before and after the image printing process results in a long device drive time other than image formation, resulting in a shorter life of the device. Furthermore, if cleaning is performed between image prints, even if the time required to print one image is the same, extra time is required when printing multiple images, resulting in a large amount of time. It will cost.

In the latter method, the image actually formed may fit in the recording medium even if the designated image size and the size of the recording medium do not match. In such a case, the image recording is stopped. Not only is it inconvenient, but also a part of the image (mainly in the peripheral part of the image)
It is not possible to respond to the request to print anyway after being aware of the loss of paper. The present invention is intended to solve the above problems.

[0008]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems and provides an image carrier and a toner image on the image carrier when it is pressed against the image carrier and a recording medium passes between them. A transfer rotator transferred to the recording medium, a cleaning means for cleaning the transfer rotator, and a feeding means for feeding the recording medium between the image carrier and the transfer rotator.
Designating means for designating the size of the image formed on the image carrier, detecting means for detecting the size of the recording medium fed from the feeding means during conveyance, and size of the image designated by the designating means And a comparison means for comparing the size of the recording medium detected by the detection means, and a control for activating the cleaning means of the transfer rotator when the sizes of the two differ based on the comparison result of the comparison means. And means.

Further, the detecting means can detect the size of the recording medium from the length of the recording medium to be conveyed in the conveying direction and the prescribed size information stored in the storage means.

Further, the control means can operate the cleaning means only when the size of the recording medium conveyed is smaller than the size designated by the designating means.

[0011]

As a result of comparison between the size of the image formed on the image carrier and the detected size of the recording medium, the sizes of the two differ and only when the transfer rotator is soiled by the toner, the transfer rotator Activate the cleaning means. As a result, the number of times the cleaning means is activated can be reduced, and the life of the device can be extended.

[0012]

Embodiments of the present invention will be described below.
FIG. 1 is a schematic sectional view for explaining the structure of a laser printer embodying the present invention. 1 is a photoconductor drum, 2 is a semiconductor laser oscillator, 3 is a polygon mirror driving motor, 3a is a polygon mirror driving motor, 4 is a reflection mirror, 5 is a charging brush, 6
Is a developing device, 7 is a transfer roller, and 8 is a cleaning blade. Further, 9 is a paper feed roller, 10 is a paper feed sensor, and 1 is
Reference numeral 1 is a fixing roller, 12 is a paper ejection sensor, and 13 is a paper ejection roller. The CP may be a recording paper stored in a known paper feed cassette, or may be fed from a manual paper feed port.

To briefly explain the operation of the above configuration, first, the surface of the photosensitive drum 1 is charged with a predetermined charge by the charging brush 5. The laser light modulated by the image signal emitted from the semiconductor laser oscillator 2 is scanned in the main scanning direction by the polygon mirror -3, reflected by the reflection mirror -4, and incident on the photoconductor drum 1. Further, scanning in the sub-scanning direction is performed by rotation of the photosensitive drum 1 in the direction of arrow a, and
A latent image is formed on the image. The latent image is developed by the developing device 6 to form a toner image.

On the other hand, the paper feed roller 9 is actuated in response to a paper feed command, the paper feed of the recording paper CP is started, and the paper is fed on the feeding path and temporarily stopped by a timing roller (not shown).
The toner image on the photosensitive drum 1 is conveyed to the transfer position at the timing when the toner image reaches the transfer position. At this time, the transfer roll
Since a bias potential having a polarity opposite to that of the toner on the photoconductor drum 1 is applied to the roller 7, the toner image on the photoconductor drum 1 is transferred to the recording paper CP. The toner image transferred on the recording paper CP is fixed by the fixing roller 11 and then discharged by the paper discharging roller 13. The ejection of the recording paper CP is detected by the paper ejection sensor 12.

The toner remaining on the photosensitive drum 1 after the image transfer is removed by the cleaning blade 8.

FIG. 2 is a block diagram showing the configuration of the control circuit of the laser printer embodying the present invention. 21 is a host computer, 22 is a printer controller, and 23.
Is an operation panel, 24 is an engine control unit for controlling each part of the printer based on a command from the printer controller 22,
The input / output port has a conveyance control unit 25 for controlling the feeding of recording paper, a paper feed sensor 10 arranged on the conveyance path, a paper ejection sensor 12, and a scanner control unit 28 for controlling scanning by a polygon mirror. , A high voltage controller 29 for controlling high voltage such as charging of the photosensitive drum 1, development bias, application of transfer bias to the transfer roller, laser controller 30 for controlling modulation of laser light, etc. Are connected.

From the operation panel 23, printer control information such as recording paper size is input to the printer controller 22. The printer controller 22 is a host computer.
When a print request signal from the printer 21 is received, a command for printing is output to the engine controller 24. As a result, the engine control unit 24 commands the transport control unit 25 to start feeding, and at the same time commands the scaner control unit 28 to prepare for scanning, and also charges the photosensitive drum 1 via the high-voltage control unit 29, and the developing bias. Etc. are set to prepare for printing. Also, a vertical synchronization request signal is output to the printer controller 22, waiting for reception of the vertical synchronization signal, and when the vertical synchronization signal is output, the host computer 21 passes through the printer controller 22 to the relay. The laser light is modulated based on the image signal input to the laser controller 30, and a latent image of the image is formed on the photosensitive drum 1.

In the above operation, when the recording paper CP is stored in the paper feed cassette and the recording paper size is known in advance, control is performed so that the recording paper that matches the image size to be printed is fed. By doing so, no particular problem arises.

However, when the recording paper size is not known in advance, such as when the recording paper is fed from the manual paper feeding port, the printed image size and the recording paper size may not match. If the recording paper size is larger than the printed image size, the problem of partial loss of the image does not occur, but if the recording paper size is smaller than the printed image size, part of the image is lost. Not only complete recording becomes possible, but the toner forming a part of the image directly adheres to the transfer roller 7 and stains the recording paper fed later. The processing in this case will be described below.

First, the determination of the recording paper size will be described. The size of the recording paper is determined from the length of the recording paper in the conveyance direction, but since the length cannot be measured directly, as shown in FIG. 1, the recording paper is fed close to the paper feed roller on the conveyance path. The paper sensor 10 is arranged, and the length of the recording paper in the conveyance direction (dimension of the recording paper in the sub-scanning direction) is determined from the time when the leading edge and the trailing edge of the recording paper pass the paper feed sensor 10. If the length of the recording paper in the conveying direction is determined, the width direction (dimension of the recording paper in the main scanning direction) can also be determined from the standard size of the recording paper.

In this way, the size of the recording paper can be known. At this point, the toner image formed on the photosensitive drum 1 is also transferred to the transfer position after the conveyance of the recording paper is already started. Since it is close and the transfer cannot be stopped, in this case, the size error is processed and the cleaning process for removing the toner adhering to the transfer roller 7 is executed.

FIG. 3 is a timing chart showing the timing of the above-mentioned cleaning processing. First, the main motor is turned on, the photosensitive drum 1 rotates, and the surface thereof has a negative potential (about -1200V) applied to the charging brush 5.
Charged negatively (about -800V). The surface of the photoconductor drum 1 is uniformly exposed to laser light, and the surface potential decreases (about -2).
00V) On the other hand, the transfer roller 7 has a negative bias potential.
Since (about -1000 V) is applied, the toner (negatively charged toner) of the protruding image portion adhering to the transfer roller 7 is transferred to the surface of the photosensitive drum 1. By carrying out this process at least once for one rotation of the transfer roller 7,
The cleaning process of the transfer roller 7 is completed.

FIG. 4 is a timing chart showing the timing of another example of the cleaning process, in which the transfer roller 7 is alternately biased with a positive bias (about +1000 V) and a negative bias every predetermined time. Apply (about -1000V). According to this, the toner of the image portion on the surface of the transfer roller 7 is negatively charged.
Inside a reverse polarity toner (in this case, a positively charged toner).
Thus, even if a small amount is generated when the toner is stirred in the developing device), it can be entirely transferred to the surface of the photosensitive drum 1.

FIG. 5 is a timing chart showing the timing of another example of the cleaning process, in which exposure of the photosensitive drum 1 and application of a negative bias to the transfer roller 7 are performed for a predetermined time. This is an example of intermittently performing each.

FIG. 6 is a flow chart showing the determination of the size of the recording paper executed by the printer controller 22 and the cleaning process of the transfer roller when the image size does not match the size of the recording paper. -It is.

First, it waits for the print request signal to be output (step P1). When the print request signal is output, the paper feed roller is driven to feed the recording paper CP (step P2). Here, it is assumed that the recording paper CP of unknown size is fed.

It is determined whether or not the leading edge of the recording paper CP is detected by the paper feed sensor 10 (step P3). If detected, the recording paper length detection timer starts counting (step P4). Then, it is judged whether or not the trailing edge of the recording paper is detected by the paper feed sensor 10 (step P5), and if detected, the timing by the recording paper length detection timer is ended (step P6), and the recording paper length is determined. The size of the recording paper fed is determined based on the time measured by the size detection timer.

Since the image size formed on the photosensitive drum 1 is recognized by the host computer side before printing, the image size is compared with the recording paper size to determine whether or not it matches the image size. Is determined (step P7). When the image size matches the recording paper size, it is determined that normal printing is possible, and normal transfer operation is executed (step P8).

If it is determined in step P7 that the image size does not match the recording paper size and the image size is larger than the recording paper size, it is determined that normal printing cannot be performed, and preparations are made to print the image again. In order to output a resend request to the host computer (step P10),
Eject all recording paper in the printer (step P1
1).

Then, a bias potential required to remove the toner adhering to the transfer roller 7 is applied to the transfer roller 7, and the toner on the transfer roller 7 is transferred to the photosensitive drum 1. A cleaning process is performed (step P12). After this, the operator displays a size error indicating that the image size does not match the recording paper size and printing is not possible.
A message is displayed (step P13) to end the operation. At this time, unnecessary toner transferred to the photosensitive drum 1
Are removed by the normal cleaning process of the photosensitive drum 1 by the cleaning blade 8. In addition, step P
The processing after 20 will be described later.

The cleaning process for transferring the toner adhering to the transfer roller 7 to the photosensitive drum 1 may be performed immediately after it is determined that the image size does not match the recording paper size. Alternatively, it may be performed after all the recording sheets in the printer are discharged.

Even if the image size does not match the recording paper size, if the image size is smaller than the recording paper size, there is no defect in the image on the print, so normal transfer operation is performed (step P8). ).

When a print request signal is output from the host computer, the print size may be designated. At this time, the specified print size is compared with the detected recording paper size, and if the print size is large, it may be processed as a size error, but if the image size actually formed is smaller than the print size. Therefore, the image size actually formed is treated with priority, the image size is compared with the recording paper size, and only when the image size is larger than the recording paper size,
You may make it perform a cleaning process. By doing this, it is not necessary to execute wasteful cleaning processing.

In the above processing, if the image size does not match the recording paper size, all the recording paper in the printer is ejected and printing is not executed. However, even if the image size does not match the recording paper size, if it is desired to execute printing, a cleaning process for transferring the toner adhering to the transfer roller 7 to the photosensitive drum 1 is incorporated, and the cleaning process is performed. The printing operation may be continuously executed while performing the turning process. This is shown in the flow chart of FIG. 6 as printing execution and size error display after step P20 after step P10. This will be described below.

First, for reference, a normal printing operation in which the image size matches the recording paper size will be described.
FIG. 7 is an example of a timing chart showing the timing for processing two consecutive normal prints when the image size matches the recording paper size. First, the main motor is turned on, the photosensitive drum 1 rotates, and the surface thereof is negatively charged by the charging brush 5.

Next, the first image is exposed on the surface of the photosensitive drum 1 by laser light to form a latent image, which is developed by a toner and visualized. A positive transfer bias potential is applied to the transfer roller 7, and the toner image formed on the photosensitive drum 1 is transferred to the conveyed recording paper (part B).

Next, a second image is exposed on the surface of the photosensitive drum 1 by laser light to form a latent image, which is developed by a toner and visualized. A positive transfer bias potential is applied to the transfer roller 7, the toner image on the photosensitive drum 1 is transferred to the conveyed recording paper, and the normal printing process ends (part D).

On the other hand, when the image size does not match the recording paper size, an example of a timing chart showing the timing for performing the printing process for two sheets (corresponding to step P20 and subsequent steps in FIG. 6). Is shown in FIG.

In FIG. 8, first, the main motor is turned on.
Then, the photosensitive drum 1 rotates, and its surface is negatively charged by the charging brush 5. The surface of the photosensitive drum 1 is
Then, the transfer roller 7 is uniformly exposed, and a negative bias potential is applied to the transfer roller 7 to perform a cleaning process. At this time, needless to say, the developing device does not operate (development bias is OFF), and the recording paper is not conveyed (part A).

Next, the first image is exposed on the surface of the photosensitive drum 1 by laser light to form a latent image, which is developed by a toner and visualized. A positive bias potential is applied to the transfer roller 7, and the toner image formed on the photoconductor drum 1 is transferred to the recording paper conveyed (part B). After this, the surface of the photoconductor drum 1 is laid again.
Then, the transfer roller 7 is uniformly exposed, and a negative bias potential is applied to the transfer roller 7 to perform a cleaning process (part C).

Next, a second image is exposed on the surface of the photosensitive drum 1 by laser light to form a latent image, which is developed by a toner and visualized. A positive bias potential is applied to the transfer roller 7, and the toner image on the photosensitive drum 1 is transferred to the recording paper that has been conveyed (part D).
After that, the surface of the photosensitive drum 1 is again exposed uniformly with laser light, a negative bias potential is applied to the transfer roller 7, and a cleaning process is executed (part E).

As is clear from the comparison between the timing chart shown in FIG. 7 and the timing chart shown in FIG. 8, the cleaning process is not performed in the normal print in which the image size matches the recording paper size. Not executed And
If the image size does not match the size of the recording paper, the cleaning process is performed before image exposure on the photosensitive drum, between the first and second image formation, and after the second image formation. To be executed. The cleaning process is not always required to be performed during image formation, and may be performed at an appropriate time as necessary.

Further, as described in the prior art,
In the normal printing process, in which the process of cleaning the transfer roller 7 for each image formation is incorporated, when the image size is judged not to match the recording paper size, If it is controlled to execute the cleaning processing for a longer time than the cleaning processing of
The cleaning of the transfer roller can be performed more reliably. FIG. 9 is a timing chart showing the timing of the cleaning process in this case. Part A to Part E
Is the same as that of FIG.

[0044]

As described above, according to the present invention, as a result of comparison between the image size formed on the image carrier and the size of the recording medium detected by the detecting means, for example, when the image size is large, both When the sizes are different from each other, the transfer rotator is contaminated by the toner, and only in this case, the cleaning means is operated to remove the toner from the transfer rotator. As a result, the number of times the cleaning means is operated can be reduced as compared with the case of cleaning the transfer rotary member each time image formation is performed as in the conventional apparatus, and thus the time required for image formation can be shortened. The life of devices such as the developing device and the drive mechanism can be extended.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating the configuration of a laser printer to which the invention is applied.

FIG. 2 is a block diagram showing a configuration of a control circuit of a laser printer.

FIG. 3 is a timing chart showing the timing of the cleaning process.

FIG. 4 is a timing chart showing the timing of another example of the cleaning process.

FIG. 5 is a timing chart showing the timing of another example of the cleaning process.

FIG. 6 is a flowchart showing recording paper size determination and cleaning processing executed by a control circuit of a laser printer.

FIG. 7 is a timing chart showing the timing of normal print processing.

FIG. 8 is a timing chart showing the timing of print processing including cleaning processing.

FIG. 9 is a timing chart showing the timing of another example of the printing process including the cleaning process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Semiconductor laser oscillator 3 Polygon mirror 5 Charging brush 6 Developing device 7 Transfer roller 8 Cleaning blade 9 Paper feeding roller 10 Paper feeding sensor 11 Fixing roller 12 Paper ejection sensor 13 Ejection Roller CP Recording Paper 21 Host Computer 22 Printer Controller 23 Operation Panel 24 Engine Control Section

Claims (4)

[Claims] 1. An image carrier, a transfer rotator that is pressed against the image carrier, and transfers a toner image on the image carrier to the recording medium when the recording medium passes between the image carrier and the transfer roller. Cleaning means for cleaning the body, feeding means for feeding the recording medium between the image carrier and the transfer rotator, and designating means for designating the size of the image formed on the image carrier. A detection unit for detecting the size of the recording medium fed from the feeding unit during conveyance, an image size designated by the designation unit, and a recording medium size detected by the detection unit. An image forming apparatus comprising: comparison means for comparing and a control means for activating the cleaning means of the transfer rotary member when the sizes of the two differ based on the comparison result of the comparison means. 2. The image forming apparatus according to claim 1, wherein the detecting means detects the size of the recording medium from the length of the recording medium conveyed in the conveying direction and the prescribed size information stored in the storing means. An image forming apparatus comprising: 3. The image forming apparatus according to claim 1, wherein the control means operates the cleaning means only when the size of the recording medium conveyed is smaller than the size designated by the designating means. An image forming apparatus characterized by. 4. An image carrier, and a transfer rotator which is in pressure contact with the image carrier and applies a bias when the recording medium passes therebetween to transfer the toner image on the image carrier to the recording medium. A cleaning unit for cleaning the transfer rotary member, a feeding unit for feeding the recording medium between the image carrier and the transfer rotary member, and a size of the recording medium on which an image is formed. Designating means for designating, detection means for detecting the length of the recording medium fed from the feeding means in the transport direction, and transporting length of the recording medium defined by the size of the recording medium designated by the designating means And the comparison means for comparing the conveyance direction length of the recording medium detected by the detection means, and when the sizes of the two differ based on the comparison result of the comparison means, the cleaning means of the transfer rotary member is activated. Control means to An image forming apparatus comprising: