JPH07121065A - Image forming device - Google Patents

Abstract

PURPOSE:To prolong the life of an image forming device by actuating a cleaning means when the size of an image and a recording medium is different and the size of the recording medium is designated to be changed. CONSTITUTION:The size of the image is compared with the detected size of a recording paper. Since a transfer roller 7 need not be cleaned when the size of the image is larger than the size of the recording paper and the printing of only one sheet is executed, a routine is returned to the main routine. When the printing of one or more sheets is executed, it is decided by a recording paper existence detection sensor 17a (17b and 17c) whether there is the recording paper CP or not in a cassette loaded in a designated paper supply port. When there is the paper CP in the cassette loaded in the paper supply port, it is decided whether the paper supply port is changed or not. Then, when there is not the paper CP in the cassette, such cleaning processing that toner attached on the roller 7 is transferred to a photoreceptor drum 1, is executed by impressing a bias potential required for eliminating the toner attached on the roller 7 on the roller 7. Then, the routine is returned to the main routine.

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.

In such an image forming apparatus, it is a principle to supply a recording medium having a size suitable for the size of an image to be formed. For example, in a laser printer or the like, the size of the image to be formed is large. There are various types, and it may not always be possible to supply a recording medium suitable for the size of an image. If the size of the formed image is smaller than the recording medium, no particular trouble occurs, 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 photosensitive The toner of the portion of the toner image on the body, which protrudes from the recording medium, is transferred onto the transfer roller, and the recording medium to be fed next is stained or added to the transfer roller. The transfer bias potential is substantially lowered, 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 for cleaning a transfer roller (for example, Japanese Patent Laid-Open No. 1-
No. 292385), or a method of periodically cleaning the transfer roller is proposed.

[0006]

However, in the method of cleaning the transfer roller before and after each print processing of one image, the time for driving the apparatus other than for the print processing is increased. Will result in longer life and shorter life of the device. Furthermore, if cleaning is performed every time one image is printed, even if the time required to print one image is the same, extra time is required for cleaning when printing multiple images. As a result, it takes a long time for the printing process, and the work efficiency is reduced. The present invention is intended to solve the above problems.

[0007]

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 rotating member for transfer which is transferred to a recording medium, a cleaning means for cleaning the rotating member for transfer, and a recording medium feeding for feeding the recording medium between the image carrier and the rotating member for transfer. Means, designating means for designating the size of an image formed on the image carrier, detecting means for detecting the size of the recording medium fed from the recording medium feeding means during conveyance, and designating by the designating means Comparing means for comparing the size of the recorded image with the size of the recording medium detected by the detecting means, and after completion of printing on at least one recording medium, the result of the comparison by the comparing means,
The image forming apparatus and the recording medium are different from each other in size, and the control unit operates the cleaning unit when the size change of the recording medium is designated.

Further, when the size of the image is larger than the size of the recording medium as a result of the comparison by the comparing unit, the control unit records on the recording medium feeding unit after printing on at least one recording medium is completed. It is also possible to control the cleaning means to be activated when the absence of the medium is detected.

[0009]

Operation: The size of the image formed on the image carrier after the completion of printing on at least one recording medium is compared with the detected size of the recording medium, and the two sizes are different and the size change of the recording medium is designated. If the size of the image is larger than the size of the recording medium as a result of the comparison by the comparing means, the recording medium feeding means has no recording medium after printing on at least one recording medium. Is detected, the cleaning means for cleaning the transfer rotary member is operated.

As a result, the number of times the cleaning means is operated can be reduced, the life of the apparatus can be extended, and the printing process of a plurality of sheets can be efficiently performed.

[0011]

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, 10 is a paper feed sensor, 11 is a fixing roller,
Reference numeral 12 is a paper discharge sensor, and 13 is a paper discharge roller.

Further, this laser printer is equipped with three paper feed portions, a first paper feed portion 15a, a second paper feed portion 15b, and a third paper feed portion 15c, which feed recording papers of different sizes. In addition, each paper feed unit can be equipped with a paper feed cassette for accommodating recording paper of a predetermined size, a universal cassette for accommodating recording paper of any size, or the like at each paper feeding port. In addition, each paper feed unit has a paper feed roller 16a, 16
b, 16c, and recording paper presence / absence detection sensors 17a, 17b, 17c for detecting the presence / absence of the recording paper CP in each paper feeding unit.

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 photosensitive 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, one of the first sheet feeding section 15a to the third sheet feeding section 15c is selected by the sheet feeding command.
Here, if the first paper feed unit 15a is selected, the paper feed roller 16a of the paper feed unit 15a operates and the feeding of the recording paper CP is started.

The recording paper CP is transported on the transport path and is temporarily stopped by a timing roller (not shown), and then is transported to the transfer position at the timing when the toner image on the photosensitive drum 1 reaches the transfer position. At this time, a bias potential having a reverse polarity to the charge of the toner on the photoconductor drum 1 is applied to the transfer roller 7, so that the toner image on the photoconductor drum 1 is transferred to the recording paper CP. The toner image transferred onto the recording paper CP is fixed by the fixing roller 11 and then discharged by the discharging roller 13.
Is discharged by. The discharge of the recording paper CP is detected by the paper discharge sensor 12
Detected in.

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

After the recording paper CP is fed from the first paper feeding unit 15a to the third paper feeding unit 15c, the presence or absence of the recording paper is detected by the recording paper presence / absence detection sensors 17a to 17c. Then, when the recording paper is exhausted after the print processing of the first sheet, and when the paper feeding unit is changed (for example, first the first paper feeding unit 15a
If the selected item is changed to the third sheet feeding portion 15c), a cleaning process for removing the toner adhering to the transfer roller 7 is executed. This will be described in detail later.

FIG. 2 is a circuit block diagram showing an example of the configuration of the recording paper presence / absence detection sensors 17a to 17c. The recording paper presence / absence detection sensor 17 (17a to 17c) is a recording paper CP.
It is composed of a contactor contacting the upper side, a light emitting diode LED, and a photo interrupter including a phototransistor PT.

When there is a recording sheet in the paper feed section 15a to the paper feed section 15c, a contactor is inserted between the light emitting diode LED and the phototransistor PT to block light, and the phototransistor PT is non-conductive. Although there is no recording paper in the paper feeding section, the contactor is separated from between the light emitting diode LED and the phototransistor PT, and the light from the light emitting diode LED is incident on the phototransistor PT. The phototransistor PT becomes conductive. The output signal of the phototransistor PT indicating the presence / absence of recording paper in the paper supply unit is input to the engine control unit 24 of the control circuit described below.

FIG. 3 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 paper feed sensor 10, a paper discharge sensor 12, and a recording paper presence / absence detection sensor 17 arranged on the conveyance path.
a, 17b, 17c, a conveyance control unit 25 for controlling the feeding of recording paper, a scanner control unit 28 for controlling the scanning by the polygon mirror, a charging to the photosensitive drum 1, a developing bias,
A high-voltage control unit 29 that performs high-voltage control such as application of a transfer bias to the transfer roller, a laser control unit 30 that performs modulation control of laser light, and the like are connected.

Printer control information such as recording paper size is input to the printer controller 22 from the operation panel 23. Upon receiving the print request signal from the host computer 21, the printer controller 22 outputs a command for printing to the engine control unit 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 size is known in advance, no particular problem occurs by controlling so that the recording paper that matches the image size to be printed is fed.

However, if the recording paper size is not known in advance due to the universal cassettes being attached to the first to third paper feeding units, the image size to be printed and the recording paper size May not match. If the recording paper size is larger than the printed image size, the problem of partial image loss 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 conveying direction, but since the length cannot be measured directly, as shown in FIG. 10 is arranged, and the leading and trailing edges of the recording paper are the paper feed sensor 10.
The length of the recording paper in the conveying direction (dimension of the recording paper in the sub-scanning direction) is determined from the time when the recording paper passes. 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. It is so close that transcription cannot be stopped. For this reason, when it is determined that the detected recording paper size is smaller than the image size, it is processed as a size error and a cleaning process for removing the toner adhering to the transfer roller 7 is executed. Therefore, the recording paper that will be fed later will not be soiled.

However, if it is found that the detected recording paper size is smaller than the image size and the cleaning process is executed each time, the throughput is lowered,
That is, the time required for the printing process becomes long.

Therefore, according to the present invention, even when the detected recording paper size is smaller than the image size, the clearing is performed.
When no inconvenience occurs without performing the cleaning process, for example, when a plurality of prints are made using the same size recording paper, the cleaning process is controlled not to be performed.

First, the timing of the cleaning process of the transfer roller will be described.

FIG. 4 is a timing chart showing the timing of the cleaning process. First, the main motor is turned on, the photosensitive drum 1 is rotated, and the surface thereof is negatively charged (about -800V) by the negative potential (about -1200V) applied to the charging brush 5. The surface of the photosensitive drum 1 is
The light is uniformly exposed to light and the surface potential drops (about -100V). On the other hand, the transfer roller 7 has a negative bias potential (about -100
(0V) is applied, the toner (negatively charged toner) in the protruding image portion adhered on the transfer roller 7 is
Transferred to the surface of the photosensitive drum 1. By performing this process at least once for one rotation of the transfer roller 7, the transfer roller is
The cleaning process of LA7 is completed.

FIG. 5 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, even when a small amount of positively charged toner having a reverse polarity is attached to the surface of the photosensitive drum 1 during the cleaning process, when a positive bias is applied to the transfer roller 7. Since the toner of the opposite polarity transfers to the surface of the photoconductor drum 1, all the negatively charged toner and the toner of the opposite polarity positively charged can be transferred to the surface of the photoconductor drum 1.

FIG. 6 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. 7 shows 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 is larger than the size of the recording paper. A flow chart will be described.

First, the output of the print request signal is waited (step P1), and when the print request signal is output, one of the first to third paper feed units is designated and the paper feed is performed. The recording paper CP is fed by driving the paper feed roller of the paper mouth (step P2). Here, it is assumed that the recording paper CP of unknown size has been fed from the universal monkey cassette attached to the designated paper feed port.

It is judged whether or not the leading edge of the recording paper CP is detected by the paper feed sensor 10 (step P3), and 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, this image size is compared with the detected recording paper size, and the image size is the recording paper. It is determined whether the size is larger than the size (step P7). If the image size is not larger than the recording paper size, normal transfer operation is possible, and therefore the process returns to the main routine without executing the cleaning process of the transfer roller.

If the image size is larger than the recording paper size in step P7, it is determined whether or not one or more sheets have been printed (step P8). If one or more sheets have not been printed, the transfer roller is determined. There is no need to clean the soybeans, so that the main routine is immediately returned to.

If one or more sheets have been printed in the judgment at step P8, it is determined whether or not the recording paper of the cassette loaded in the designated paper feed port is exhausted, the recording paper presence / absence detection sensor 17a (17b, 17c). ) To determine (step P9),
If there is a recording sheet in the cassette attached to the paper feed port, it is determined whether or not the paper feed port has been changed (step P1).
0).

If there is no recording paper in the cassette attached to the paper feed port designated by the judgment of step P9, and if the paper feed port is changed by the judgment of step P10, then it is attached to the transfer roller 7. The cleaning roller 7 is applied with a bias potential necessary for removing the toner thus formed, and a cleaning process for transferring the toner on the transfer roller 7 to the photosensitive drum 1 is performed (step P11). Return to the main routine.

This is because when the cassette mounted in the paper feed port runs out of recording paper, recording paper is newly replenished, but the recording paper size may change at that time. Even if the paper feed port is changed, the size of the recording paper may be changed, and it is expected that the toner attached to the transfer roller 7 will contaminate the recording paper in the next printing process. is there.

If it is determined in step P10 that the paper feed port is not changed, the image size is larger than the recording paper size, but the size of the recording paper fed from the cassette attached to the paper feed port is Since there is no change, the toner adhered to the transfer roller 7 does not stain the recording paper even if the printing process is continued, and the cleaning routine returns to the main routine without performing the cleaning process.

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 is larger than the recording paper size. This will be described below.

First, for reference, the printing operation when the recording paper size is not changed will be described. FIG. 8 shows two consecutive prints when the recording paper size is not changed.
It is an example of a timing chart showing the timing for processing a single sheet. 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).

Further, a second image is exposed on the surface of the photosensitive drum 1 by laser light to form a latent image,
The toner is developed 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 printing process ends (part D).

On the other hand, when the image size does not match the recording paper size, the printing operation and the cleaning process are performed when the recording paper size is changed after the print processing of two sheets. Timing chart
An example of the above is shown in FIG.

In FIG. 9, first, the main motor is turned on, the photosensitive drum 1 is rotated, and the surface thereof is the charging brush 5.
Is charged negatively. The surface of the photoconductor drum 1 is exposed with a laser beam to expose the first image 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, and the toner image on the photosensitive drum 1 is transferred to the recording paper that has been conveyed (part D).

With the above, the print processing of two sheets is completed.
After this, since the recording paper size was changed, the surface of the photosensitive drum 1 was uniformly exposed by laser light, and a negative bias potential (about -1000V) was applied to the transfer roller 7 to clear it. The training process is executed. At this time, needless to say, the developing device does not operate (the developing bias is OFF), and the recording paper is not conveyed (part E).

Next, a third 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 conveyed recording paper (part F). After this, the surface of the photoconductor drum 1 is laid again.
Then, the transfer roller 7 is exposed uniformly, and a negative bias potential is applied to the transfer roller 7 to perform a cleaning process (part G).

As is clear from the comparison between the timing chart shown in FIG. 8 and the timing chart shown in FIG. 9, even when the image size does not match the recording paper size, the recording paper size remains the same. In this case, the cleaning process is not executed. When the recording paper size is changed, the cleaning process is executed before the image exposure on the photosensitive drum, that is, between the second and third image formation and after the third image formation. To be done. This cleaning process does not always have to be performed during image formation,
You may make it perform at an appropriate time as needed.

Since the printing operation is interrupted during the cleaning process, it is preferable to display on the operation panel that the cleaning process is in progress.

In the embodiment described above, when the paper feed port is changed, it is determined that the recording paper size is changed and the cleaning process is performed. However, the recording paper size is directly changed. May be detected and the cleaning processing may be performed.

Although the embodiment in which the present invention is applied to a laser printer has been described above, the present invention can be applied not only to a laser printer but also to a normal electrophotographic copying machine. For example, it is easy to understand if it is assumed that only part of an A4 size original image is copied.
When an A5 size copy sheet is fed to copy an A4 size original, the toner of the original image protruding from the A5 size copy sheet adheres to the transfer roller.
As long as the 5 size copy paper is fed, the copy paper is not contaminated and therefore the cleaning process is not performed. Then, when the size of the copy paper is changed during the copying operation, for example, when the size is changed from A5 size to B5 size, the cleaning process may be controlled.

[0054]

As described above, when the image size formed on the image carrier in the image forming apparatus is larger than the size of the recording medium, the transfer rotary member is soiled by the toner. According to this, when the image size formed on the image carrier is different from the size of the recording medium, when the size of the recording medium is changed after one or more image forming operations are executed, and when the image size is different from that of the recording medium. If it is larger than the size, the cleaning means is operated to remove the toner from the rotary member for transfer only when there is no recording medium to be fed next. 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 circuit block diagram showing an example of the configuration of a recording paper presence / absence detection sensor.

FIG. 3 is a block diagram showing the configuration of a control circuit of a laser printer.

FIG. 4 is a timing chart for explaining the timing of the cleaning process.

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

FIG. 6 is a timing chart for explaining the timing of another example of the cleaning process.

FIG. 7 is a flowchart showing a recording paper size determination and a cleaning process executed by a control circuit of a laser printer.
To.

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

FIG. 9 is a timing chart for explaining 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 Paper discharge rollers 17a, 17b, 17c Recording paper presence / absence detection sensor CP recording paper 21 Host computer 22 Printer controller 23 Operation panel 24 Engine control unit 25 Transport control unit 28 Scanner control unit 29 High voltage control unit 30 relay -The control unit

Claims (2)

[Claims] 1. An image carrier, a transfer rotary member 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 them, and the transfer rotary member. A cleaning unit for cleaning the member, a recording medium feeding unit for feeding the recording medium between the image carrier and the transfer rotary member, and a size of an image formed on the image carrier are designated. Specifying means, detection means for detecting the size of the recording medium fed from the recording medium feeding means during conveyance, image size designated by the designating means and recording medium detected by the detecting means The size of the recording medium is different from the size of the recording medium after the completion of printing on at least one or more recording media after the comparison by the comparing unit. size When further the designation is made, the chestnut - image forming apparatus characterized by comprising a control device for activating the training means. 2. An image carrier, a transfer rotary member 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 through the image carrier, and the transfer rotary member. A cleaning unit for cleaning the member, a recording medium feeding unit for feeding the recording medium between the image carrier and the transfer rotary member, and a size of an image formed on the image carrier are designated. Specifying means, detection means for detecting the size of the recording medium fed from the recording medium feeding means during conveyance, image size designated by the designating means and recording medium detected by the detecting means Comparing means for comparing the size of the recording medium with the size of the recording medium, and as a result of the comparison by the comparing means, when the size of the image is larger than the size of the recording medium, the recording medium feeding means is connected to the recording medium feeding means after printing on at least one recording medium When the absence of the recording medium is detected, the chestnut - image forming apparatus characterized by comprising a control device for activating the training means.