JPH0643766A - Cleanerless image forming device - Google Patents

Abstract

PURPOSE:To provide a cleanerless image forming device where sudden load fluctuation is not caused in the case a recording paper advances to a photosensitive drum and withdraws therefrom. CONSTITUTION:(A) shows a state where the leading edge of the recording paper 11 comes near to a feeding roller 26 after a paper feeding sensor 25 detects the leading edge of the recording paper 11. A timer is started from the point of time when the leading edge is detected. When and after the leading edge of the recording paper 11 passes the transfer position of a transfer device 8, the power source of the transfer device 8 is turned on as shown by (B). (C) shows the point of time when the power source of the transfer device 8 is turned off. This point of time is before the trailing edge of the recording paper 11 passes. At the point of time when the trailing edge of the recording paper passes the transfer position, the transfer potential is substantially extinguished and does not influence the surface potential of the photosensitive drum 1.

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 of the type which exposes an image bearing member to form an electrostatic latent image, develops it with a coloring powder, and transfers it to a recording medium, and more particularly to a memory removing member. The present invention relates to a cleanerless image forming apparatus used.

[0002]

2. Description of the Related Art A conventional image forming process using a photosensitive drum as an image carrier will be described. The process is started by uniformly charging the photosensitive drum with a charger, and then an electrostatic latent image is formed by the exposing means. The exposure is performed by slit exposure using an optical system, a laser beam modulated by an image signal, or the like. Next, a latent image is developed with a toner, which is a colored powder, in a developing device, and is transferred to recording paper by a transfer device to form an image. The toner remaining on the photosensitive drum after the transfer is cleaned with a cleaner. A blade is used as a cleaner, and residual toner is scraped off and sent to an external toner recovery box using a conveying screw or the like.

Such a blade-type scraping-type cleaner requires a space for the recovery box and must monitor the fullness of the toner recovery box. Further, there is also a problem that the surface of the photosensitive drum is easily scratched by the blade, which shortens the life of the photosensitive drum.

A memory removing member is used in the image forming apparatus described in Japanese Patent Laid-Open No. 64-20587, in which a cleaning method using no scraping blade has been proposed. FIG. 5 is a schematic configuration diagram around the image carrier. In the figure, 1 is a photosensitive drum, 2 is a charger, and 3
Is an exposing unit, 4 is a developing roller, 5 is a bias power source for a developing device, 6 is a memory removing member, 7 is a memory removing unit power source, 8 is a transfer device, 8a is a corona wire, 8b is a grid, 9 is a high voltage power source, 10 Is a varistor, and 11 is a recording paper.

To perform recording, a print start signal
The photosensitive drum 1 rotates and is charged by the charger 2. The charging potential is V0 shown in FIG. 7, for example, -700V. The exposure unit 3 scans and exposes the photosensitive drum 1 with the laser beam modulated by the dot image data to form an electrostatic latent image.

FIG. 6A is an explanatory diagram of a charged state when the residual toner remains on the photosensitive drum 1.
Since the photosensitive drum 1 is charged to the charging potential V0, the residual toners a and b are also charged to the same potential V0. The photoconductors under the residual toners a and b are also charged to the same potential V0.

FIG. 6B is an explanatory diagram of an exposure state.
Since the exposed portion forms an electrostatic latent image having the exposure potential VC in FIG. 7, the residual toner b in that portion also has the exposure potential V.
It becomes C. When the residual toner in the exposed portion is dispersed in a small area, for example, one by one, the photoconductor under the residual toner is also exposed. When the photoconductors under a large area are aggregated and present, underexposure occurs. However, when the underexposed portion is filled with the toner adhering to the surrounding exposed portion, the residual toner is not a problem. Therefore, as will be described later, by the memory removal member,
If the residual toner is dispersed to the extent that exposure does not matter, the residual toner will be substantially negligible.

The developing device 4 has a developing potential VB, for example, -4.
Develop the latent image at 50V. As shown in FIG. 6C, the toner in the developing device is developed and attached to the exposed portion. The residual toner b in the exposed portion remains,
No problem. The residual toner a in the non-exposed portion returns to a developing device (not shown), and cleaning can be achieved. The difference between the charging potential V0 and the developing potential VB, VCL = VB-V0, is called the cleaning potential.

In this example, transfer is performed using a scorotron type charger. By using the scorotron type, the corona wire 8a has a high voltage power supply 9
Therefore, a voltage of 5 kV or more can be applied, and the discharge can be stabilized. The varistor 10 is provided on the grid 8b.
Is connected to generate a constant voltage, for example, 560V, by a part of the corona current. Therefore, the grid potential is 560V. The toner developed by the transfer potential is transferred to the recording paper 11, the transferred toner is fixed by a fixing device (not shown), and the recording paper is ejected. By the transfer, the photosensitive drum becomes the post-transfer potential VT, for example, 100 V in the exposed portion. In addition, the non-exposed portion is about 0 to -80V.

Next, the memory removal potential VB is applied to the photosensitive drum 1 by the memory removal member 6 connected to the memory removal section power supply 7. The memory removal potential VB is 10
0-700V is suitable. A brush is used as the memory removing member 6. The memory removing member 6 electrostatically adsorbs the residual toner once, and then spontaneously ejects the residual toner to the photosensitive drum 1 to change the adhesion position on the photosensitive drum 1, so that the residual toner pattern is diffused. Is brought.

Due to this action, as described above, the residual toner does not interfere with the next exposure, and
Further, the residual toner in the non-exposed portion is collected in the developing device at the same time as the development, and as a result, the cleaning is performed.

Further, when such a residual toner collecting system is adopted, charging of the photosensitive member by the transfer device 8 becomes a problem.
The potential of the photoconductor that has passed through the transfer unit 8 is affected by the presence or absence of recording paper. The potential after transfer VT0 is 10 when there is recording paper
If the voltage is 0V, if there is no recording paper, the post-transfer potential VT
Is about 400V. The photosensitive drum is VT 4
If it is charged to about 00V, the toner adhering to the memory removing member 6 will be developed on the photoconductor.
The toner produced by this development does not form a dispersed pattern and thus becomes an obstacle in the next exposure step.

Therefore, in the cleaning method described in the above publication, the power applied to the corona wire of the transfer device 8 is turned on only when the recording paper is passing under the transfer device, and the recording paper is turned on. In order to prevent the exposed portions of the photosensitive drum before and after the sheet from being positively charged, the recording paper enters the photosensitive drum as shown in the timing of the aligning sensor and the transfer charger shown in FIG. The power of the charging transfer device is turned on, and the power of the charging transfer device is turned off after the recording paper leaves the photosensitive drum.

However, it has been found that the problem cannot be solved by simply avoiding the positive charge on the exposed portion of the photosensitive drum. That is, there is a problem in that when the recording paper enters the photosensitive drum and when the recording paper leaves the photosensitive drum, a sudden load change occurs and the potential on the photosensitive drum is abnormally touched. In the cleanerless system, the toner from the memory removing brush adheres to this potential fluctuation of the photosensitive drum due to the load fluctuation, and black streaks are generated on the print. Further, the method described in the above publication also has a problem that the start-up time and the fall time when the power supply is turned on and off are not taken into consideration.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a rapid load change occurs when a recording sheet enters the photosensitive drum and when the recording sheet exits the photosensitive drum. It is an object of the present invention to provide a cleanerless image forming apparatus.

[0016]

SUMMARY OF THE INVENTION According to the present invention, a charging means for charging an image carrier, an exposing means for forming an electrostatic latent image on the image carrier, and the electrostatic latent image by a colored powder are used. In an image forming apparatus having a developing means for developing, a transferring means for transferring the developed colored powder to a recording medium, and a memory removing member which is in contact with the image carrier and disturbs the residual colored powder, the front end of the recording medium is The power of the transfer means is turned on after passing through the transfer means, and the power of the transfer means is turned off so that the power of the transfer means disappears before the rear end of the recording medium passes through the transfer means. It is characterized in that a control means for controlling the above is provided.

[0017]

According to the present invention, the power source of the transfer means is turned on after the front end of the recording medium passes through the transfer means, and the power source of the transfer means is turned off before the rear end of the recording medium passes through the transfer means. By controlling to turn off the power source of the transfer means, it is possible to avoid a sudden load change when the recording medium enters the photosensitive drum and when it leaves the photosensitive drum.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic block diagram of an embodiment of an image forming apparatus of the present invention. In the figure, 1 is a photosensitive drum, 2 is a charger, 3 is an exposure unit, 4 is a developing roller, 6 is a memory removing member, 8 is a transfer device, 11 is recording paper, 12 is a discharge lamp,
3 is a cleaning brush, 14 is a developing device, 15 is a toner case,
16 is an agitator, 17 is toner, 18 is a paper feed cassette, 1
9 is a push-up lever, 20 is a push-up spring, 21 is a push-up plate, 22 is a separating claw, 23 is a paper feed roller, 24 is a paper guide, 25 is a paper feed sensor, 26 is a feed roller, 27 is a guide roller, and 28 is heating. Roller 29 is pressure roller 30
Is a paper discharge sensor, 31 is a feed roller, 32 is a stacker, 3
3 is a device case. Further, to the exposure unit 3, an appropriate exposure unit such as a method using a laser beam scan or a method using a liquid crystal shutter is applied. The memory removing member 6 may be a fixed brush, a rotating brush, a roller, or a plate-like body made of porous material, fiber material, or the like.

The processes of charging, exposing, developing, transferring, and removing the memory are the same as those described with reference to FIGS. The developing device 14 includes a toner case 15 containing the toner 17 and the developing roller 4, and is provided with a stirring tool 16 for stirring the toner 17. In addition, the static elimination lamp 12
Is for exposing the outer peripheral surface of the photosensitive drum 1 after transfer to remove the charge. The cleaning brush 13 is provided to remove the paper dust and the like attached to the photosensitive drum 1 after transfer.

The transfer operation of the recording paper in FIG. 1 will be described. The recording paper 11 is stored in a paper feed cassette 18, and the front part is placed on a push-up plate 21. Push-up plate 21
Is urged upward by a push-up spring 20 and a push-up lever 19 to bring the recording paper 11 into contact with the lower surface of the paper feed roller 23. Further, the leading end of the recording paper 11 is pressed by the separation claw 22.

During the recording operation, charging, exposure, development,
The uppermost recording paper is taken out from the paper feed cassette 18 by the rotation of the paper feed roller 23 at the timing of the transfer operation, guided by the paper guide 24, and fed by the feed roller 2.
From 6 to the guide roller 27, the toner is closely attached to the photosensitive drum 1, and the electric field from the transfer unit 8 transfers the image-formed toner onto the recording paper. Then, the transferred toner is fixed on the recording paper by the fixing device including the heating roller 28 and the pressure roller 29, and is discharged from the feed roller 31 to the stacker 32.

In this embodiment, two sensors are provided in the recording paper feeding path to monitor the passage of the recording paper. The paper feed sensor 25 detects the leading end of the fed recording paper.
When the detection signal from the paper feed sensor 25 cannot be obtained from the paper feed command within a predetermined time, a paper feed jam signal is issued. The paper discharge sensor 30 detects the leading end and the trailing end of the recording paper after fixing. The trailing edge is detected by the disappearance of the detection signal from the paper discharge sensor 30. If the leading edge signal is not detected from the paper discharge sensor 30 within a predetermined time after the leading edge signal is detected from the paper feed sensor 25,
If the trailing edge signal is not detected from the paper discharge sensor 30 within a predetermined time after the leading edge signal is detected, the jam occurs due to a paper jam.

Further, the paper feed sensor 25 causes the photosensitive drum 1 to move.
A detection signal for detecting the position of the recording paper introduced to the transfer position of is obtained. Of course, the sensor for detecting the position of the recording paper at the transfer position may be provided separately from the paper feed sensor 25.

FIG. 2 is a block diagram of the control system. In the figure, 2 is a charger, 3 is an exposure unit, 6 is a memory removing member, 8
Is a transfer device, 12 is a discharge lamp, 14 is a developing device, 25 is a paper feed sensor, 30 is a paper discharge sensor, 34 is a CPU, and 35 is R.
AM, 36 ROM, 37 timer, 38 photosensitive drum drive motor, 39 paper feed roller drive motor, 40-
Reference numerals 47 are drivers, respectively.

When the CPU 34 receives the print command signal,
The program stored in the ROM 36 is read out, the driving of the photosensitive drum drive motor 38 is started, and the charger 2, the discharge lamp 12, the exposure unit 3, the developing unit 14, the transfer unit 8, the memory removing member 6 and the like are set in a predetermined manner. It drives in sequence, and drives the paper feed roller drive motor 39 in synchronization with it. Also,
Signals from the paper feed sensor 25 and the paper discharge sensor 30 and the timer 3
The output of 7 makes a judgment and monitors the occurrence of jam. When a jam occurs, the image formation is stopped and the jam is displayed or an alarm is issued.

FIG. 3 is an explanatory diagram of operating states of the recording paper and the transfer device in the cleanerless image forming apparatus described with reference to FIGS. In the figure, the portions corresponding to those in FIG. When the print command signal is input to the CPU, the photosensitive drum drive motor is turned on, and at the same time, the charger and the discharging lamp are turned on. When the photosensitive drum drive motor reaches a predetermined rotation speed, the developing bias power source of the developing device is turned on, and a cleaning potential is applied to the memory removing member. The recording paper 11 is fed in synchronization with the rotation of the photosensitive drum 1, and the paper feed sensor 25 causes the recording paper 1 to be fed.
The exposure timing and the power on / off timing of the transfer device 8 are determined from the time point when the leading edge of 1 is detected. FIG. 3A shows a state in which after the paper feed sensor 25 detects the leading edge of the recording paper 11, the leading edge of the recording paper 11 approaches the feed roller 26. In the specific example, the distance between the detection position of the paper feed sensor 25 and the feed roller 26 is about 2 cm, and the feed roller 2
The distance between 6 and the transfer position of the transfer device 8 is about 5 cm, and the feeding speed is 35 mm / sec.

FIG. 3B shows a state in which the power of the transfer device 8 is turned on. The power of the transfer device 8 is turned on after the leading edge of the recording paper 11 has passed the transfer position of the transfer device 8. In the specific example, as shown in FIG.
Is the time point when 1 mm has passed the transfer position. This time is performed by a timer that measures the time from the time when the paper feed sensor 25 detects the leading edge of the recording paper 11. Instead of using a timer, the photosensitive drum 1 and the feed roller 2
The encoder 6 may be provided with an encoder, a pulse generator that generates a pulse for each predetermined rotation angle, and the rotation angle may be integrated to detect the position of the recording paper.

After a short time has passed from FIG. 3B, the power source of the transfer device 8 is turned on. In this example, as shown in FIG. 4, if 4 mm from the front end 11a of the recording paper 11 is passed, the transfer device 8
The power supply of is sufficient to rise. Therefore, at this point, the exposure from the exposure unit is started so that the first recording line comes to the transfer position.

FIG. 3C shows the time when the power of the transfer device 8 is turned off. This time is also determined by the timer that counts the elapsed time from the time when the paper feed sensor 25 detects the trailing edge of the recording paper 11. In the specific example, this time is, as shown in FIG. 4, 5 mm before the rear end 11b of the recording paper 11. The exposure in the exposure unit is designed to end at this position. With this configuration, when the line 1 mm before the rear end 11b of the recording paper 11 passes the transfer position, the transfer potential is substantially extinguished due to the fall of the power supply of the transfer device 8, and the photosensitive drum 1 It does not affect the surface potential of.

The above voltage values are examples, and
An appropriate voltage value is set according to the characteristics of the toner. In the above description, the OPC for negative charging is used as the photosensitive drum, and the potential relationship is described on the assumption that the photosensitive drum is negatively charged. Therefore, the magnitude relation of the potentials should not be understood in the usual sense, and in the case of using positively charged OPC, the magnitude relation of the potentials in this specification is opposite to that described above. Should be understood as.

[0031]

As is apparent from the above description, according to the present invention, in the cleanerless image forming apparatus, the photosensitive drum does not undergo a sudden load change due to the entry and exit of the recording paper in the transfer area. Therefore, it is possible to prevent the black stripes from being printed on the recording paper and improve the recording quality.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a cleanerless image forming apparatus of the present invention.

FIG. 2 is a block diagram of a control system of the cleanerless image forming apparatus of FIG.

FIG. 3 is an explanatory diagram of operating states of a recording sheet and a transfer device in the cleanerless image forming apparatus described in FIGS.

FIG. 4 is an explanatory diagram of a recording state on recording paper.

FIG. 5 is a schematic configuration diagram around an image carrier of a cleanerless image forming apparatus.

FIG. 6 is an explanatory diagram of a cleaning action of the memory removing member.

FIG. 7 is an explanatory diagram of potential distribution.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device, 3 Exposure part 4 Developing roller 6 Memory removing member 8 Transfer device 14 Developing device 25 Paper feeding sensor 28 Heating roller 30 Paper ejection sensor

Claims (1)

[Claims] 1. A charging means for charging an image carrier, an exposing means for forming an electrostatic latent image on the image carrier, a developing means for developing the electrostatic latent image with colored powder, and a developing means. In an image forming apparatus having a transfer means for transferring the colored powder to the recording medium and a memory removing member for contacting the image carrier and disturbing the residual colored powder, Control means is provided for turning on the power supply of the transfer means and for turning off the power supply of the transfer means so that the power supply of the transfer means disappears before the trailing edge of the recording medium passes through the transfer means. A cleanerless image forming apparatus characterized by the above.