JPH10254251A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clean toner with a cleaning means attached to a photoreceptor by transferring toner remaining on an intermediate transfer body to the photoreceptor. SOLUTION: A blade cleaner 7 for mechanically removing the toner on the surface of a photoreceptor belt 1 from the photoreceptor is provided and the residual toner 100 which cannot be removed by a fur brush cleaner 8 for cleaning the toner on an intermediate transfer drum 5 and has a polarity opposite to that of a cleaning bias is transferred to the belt 1 by a bias voltage of a high voltage in the contact part (gap part) 15 of the belt 1 with the drum 5. Thus, residual toner 101 after being transferred to the belt 1 is mechanically removed by the blade cleaner 7.

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 using an electrophotographic process, such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art There are various printing methods in a color image forming apparatus using an electrophotographic technique. For example, a method of forming a color image on a photoreceptor by repeating exposure and development on a photoreceptor, and then collectively transferring the image onto a sheet of paper, wrapping a sheet of paper on a transfer drum, and applying one color from the photoreceptor onto a sheet of paper one by one Transfer the toner image to form a color image, and finally peel off the paper from the transfer drum, using an intermediate transfer body,
There is a method in which a color image is formed on an intermediate transfer member by transferring a toner image one color at a time from a photoreceptor to an intermediate transfer member, and finally, the color images are collectively transferred to paper. Among them, the intermediate transfer member method has an advantage that an image of relatively high quality can be formed and an image can be formed on various types of paper.

[0003]

By the way, in the intermediate transfer system having the above-mentioned advantages, since a toner image is formed on the intermediate transfer body, the residual toner remaining on the intermediate transfer body after being transferred to paper is transferred. Cleaning means for cleaning the surface is required. Generally, for cleaning the toner,
A blade system and a fur brush system are used. The blade method is a method in which an elastic blade such as a rubber blade is pressed against a toner holding member to mechanically scrape off the toner. On the other hand, in the fur brush method, a cylindrical base material on which a bristle brush is adhered is rotated and brought into contact with a partner, and at the same time, a bias voltage having a polarity opposite to that of the toner is applied to the brush, and the toner is mechanically and electrically charged. Cleaning.

In an image forming apparatus of the intermediate transfer type, the cleaning unit must be retracted while the toner image is being superimposed on the intermediate transfer unit. However, if the mechanical load applied to the intermediate transfer member at the time of contact / separation is large, the positions of the toner images of the respective colors are shifted, resulting in thin line dubbing and hue shift. For this reason, as a cleaning unit for cleaning the intermediate transfer member, a cleaning system with a small contact load is suitable. When the above two systems are compared, the fur brush system is more suitable than the blade system. However, the fur brush method has a problem that the process speed is slow and it is difficult to apply the method to a high-speed image forming apparatus.

Since the fur brush system is a system in which toner is electrostatically attracted to the brush for cleaning as described above, toner having a polarity opposite to the voltage applied to the brush is cleaned. However, the polarity of the toner remaining after the toner image on the intermediate transfer body is transferred to the paper may be reversed due to the electric field applied during the transfer. Since the residual toner having the opposite polarity has the same polarity as the bias applied to the brush, it is not cleaned by the fur brush, is output overlapping the image of the next page to be subsequently printed, and causes image defects. As a method of removing the residual toner, a charger for discharging electric charge having a polarity opposite to the bias voltage of the fur brush is provided in the upstream portion of the fur brush, a method of cleaning the toner with the same polarity, or a method of installing two fur brushes. In addition, there is a method in which positive and negative biases are applied to each of them, and toner of both polarities can be cleaned. However, these methods have disadvantages in that the configuration is complicated, which results in an increase in the size of the apparatus and an increase in cost.

The present invention has been made in view of such a background, and an object of the present invention is to provide a cleaning system capable of reducing the contact load for cleaning on an intermediate transfer member and achieving high speed and high image quality. To provide an image forming apparatus.

[0007]

In order to achieve the above object, the present invention relates to a photosensitive member, a developing means for developing a latent image on the photosensitive member, and a high-voltage power supply for the developed toner image. An intermediate transfer member that is transferred by the bias potential difference generated by the transfer device, a transfer unit that transfers the toner image on the intermediate transfer member to a recording medium to output a final image, and an image that is transferred onto the intermediate transfer member without being transferred to the recording medium. In an image forming apparatus provided with a cleaning unit for electrically cleaning remaining toner, a toner removing unit for mechanically removing toner on the surface of the photoconductor from the photoconductor is provided, and a cleaning bias that cannot be removed by the cleaning unit is provided. The residual toner having the opposite polarity is transferred from the intermediate transfer member to the photosensitive member by the bias voltage of the high-voltage power supply at a contact portion between the photosensitive member and the intermediate transfer member, and is transferred to the photosensitive member. It is characterized by eliminating by the toner removing means residual toner lines.

In this case, the number of the developing means may be one or more. If there are a plurality of developing means, the darkest color toner among all the color toners used for image formation is first transferred to the intermediate transfer member. Alternatively, a good image can be obtained by first transferring the color toner having the lowest charge amount among all the color toners used for image formation to the intermediate transfer member.

Further, voltage control means for controlling the output of the high-voltage power supply is further provided, and the voltage control means causes residual toner on the intermediate transfer body to contact the photosensitive body with the intermediate transfer body based on the progress of the printing process. If the output value of the high-voltage power supply is reduced when the toner passes through the section, the transfer of the residual toner to the photoconductor can be promoted. Similarly, a potential control means for controlling the surface potential of the photoreceptor is further provided, and the potential control means allows residual toner on the intermediate transfer body to contact a contact portion between the photoreceptor and the intermediate transfer body based on the progress of the printing process. The transfer of the residual toner can also be promoted by lowering the surface potential of the photoconductor when passing through. The potential control means can be constituted by, for example, an output control circuit for controlling an output of a power supply for a charger of the photoconductor, and an exposure control circuit for exposing the surface of the photoconductor to attenuate the surface potential. And an output control circuit for controlling the output of the exposure unit.

With this configuration, for example, a fur brush cleaner for electrically cleaning the toner on the intermediate transfer member removes only the toner having the polarity opposite to the applied bias. At this time, when a positive bias is applied to the cleaning bias, the polarity of the toner not cleaned by the fur brush becomes positive. Plus toner
After passing through the fur brush, it passes through a contact portion between the photoconductor and the intermediate transfer member. Here, paying attention to the contact portion between the photoconductor and the intermediate transfer body, between the photoconductor and the intermediate transfer body, in order to transfer the negative toner on the photoconductor onto the intermediate transfer body, the photoconductor side Is applied with a negative voltage higher than that of the intermediate transfer member. Therefore, the positive polarity residual toner on the intermediate transfer member is strongly attracted to the photoconductor by the transfer electric field. As a result, the residual toner is transferred to the photoconductor, and the intermediate transfer member can be cleaned without providing a complicated cleaning mechanism. Of course, the residual toner transferred to the photoreceptor is provided with cleaning means for mechanically removing the toner such as a blade cleaner on the photoreceptor, so that it is cleaned irrespective of the polarity and causes no other problem. Therefore,
The opposite polarity toner on the intermediate transfer member does not appear on the image of the next page.

[0011]

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

FIG. 1 is a schematic sectional view of an electrophotographic color image forming apparatus according to an embodiment of the present invention. In FIG. 1, a photosensitive belt 1
And a developing device group 4 and an intermediate drum 5 as an intermediate transfer member are provided with the photoreceptor belt 1 interposed therebetween.

The photosensitive belt 1 is composed of three rotatable photosensitive belt transport rollers 1a, 1 arranged vertically in the center of the main body.
It is stretched between b and 1c. This photoreceptor belt 1 is
It has a two-layer structure of a photosensitive layer (for example, OPC) on the surface and a conductive layer (for example, aluminum) thereunder. The photoreceptor belt 1 runs in the X direction. In the vicinity of the photoreceptor belt 1, a charging device 2, an exposing device 3, and four developing devices 4a, 4b, 4 for toner of four colors are sequentially arranged along the X direction.
c, 4d, an intermediate transfer drum 5, an erase lamp 6, and a photoreceptor cleaner 7 are arranged. A drum cleaner 8 is provided above the intermediate transfer drum 5, and a drum charger 14 is provided below the intermediate transfer drum 5. A paper cassette 9, a pickup roller 10, a transfer roller 11, a peeling device 12, and a fixing device 13 are arranged in this order on the paper transport path along the paper transport direction.

The charger 2 is a scorotron charger,
The surface of the photoreceptor belt 1 is charged to a specified negative potential by discharging the wire. The exposing device 3 includes a laser diode and a lens system, and exposes the photoreceptor belt 1 to form an electrostatic latent image. First to fourth four developing units 4
a, 4b, 4c, and 4d are toners of different colors,
For example, yellow (Y), magenta (M), cyan (C), and black (K) toners are stored, and the electrostatic latent image formed on the photoreceptor belt 1 is developed with the toner of each color. I do. In the image forming apparatus according to this embodiment, the polarity of the toner is negative since the negative charge reversal development method is used. The intermediate transfer drum 5 has a diameter of 80 to
It is a 160 mm cylinder, which is composed of a conductive cylindrical substrate (for example, an aluminum drum) and a surface layer covering the same. The intermediate transfer drum 5 has a nip width of 5 to 5 with the photosensitive belt 1.
20 mm, the toner formed on the photoreceptor belt 1 is charged by a high-voltage power supply 16 applied to the conductive layer of the photoreceptor belt 1.
Is transferred onto the intermediate transfer drum 5 by the bias voltage from The erase lamp 6 removes the residual potential on the photoreceptor belt 1 by light irradiation. The photoconductor cleaner 7 removes the residual toner 100 remaining on the photoconductor belt 1, and uses a blade cleaner. As described above, since the blade cleaner 7 mechanically removes the toner, cleaning is performed regardless of the polarity of the toner.

The drum cleaner 8 removes the toner remaining on the intermediate transfer drum 5 after the sheet is transferred, and retreats upward while the toner image is present on the intermediate transfer drum 5. It has become. As described above, in such an image forming apparatus, the contact of the cleaning unit with the surface of the intermediate transfer drum 5 and the
Since evacuation from the surface is indispensable, a fur brush cleaner with a small contact pressure is used. Below the photoreceptor belt 1, there is a paper cassette 9, from which the paper is pulled out by a pickup roller 10 and then sent to a transfer unit. The transfer roller 11 is for transferring the toner image formed on the intermediate transfer drum 5 onto a sheet, and includes a metal shaft and an elastic layer (1 k to 10 GΩ) having an appropriate resistance value. A polarity opposite to that of the toner, that is, a positive DC voltage in this embodiment, is applied to the metal shaft, and the toner is electrostatically transferred to the sheet by an electric field generated by the voltage.
The transfer roller 11 is retracted so as not to come into contact with the intermediate transfer drum 5 while the toner image is being formed on the intermediate transfer drum 5. The peeling device 12 is provided for removing the transfer charge on the back surface of the paper and peeling the paper. The fixing device 13 heats and melts the toner on the paper,
Establish. Although not shown, a controller for controlling the printer is provided on the back side of the main body, and an image signal processing unit and a print command control unit are built in the controller.

In the image forming apparatus configured as described above,
When a computer print command is input to the controller, the exposure device 3 exposes the surface of the photoreceptor belt 1 charged by the charging device 2 according to input image data, and forms a latent image corresponding to the input image data. Is done. This latent image is first developed with the first developing device 4a, for example, with yellow toner. The toner image developed on the surface of the photosensitive belt 1 is transferred onto the intermediate transfer drum 5 when passing through the nip between the photosensitive belt 1 and the intermediate transfer drum 5. Next, the photosensitive belt 1 is charged and exposed again, and this time, the second developing unit 4 is charged.
b, for example, developing with magenta toner. Then, the developed toner image is transferred onto the intermediate transfer drum 5 so as to overlap the previous toner image (yellow toner image). This process is hereinafter referred to as third and fourth developing devices 4c and 4d (for example,
(A cyan toner and a black toner) to form a plurality of color toner images on the intermediate transfer drum 5.

The toner images of a plurality of colors formed on the intermediate transfer drum 5 are recharged by a drum charger 14 and then transferred onto a sheet by a transfer roller 11 at a time. Thereafter, the paper is peeled by the peeling device 12, and the color image transferred to the paper is fixed by the fixing device 13, and then discharged out of the machine. At this time, of the residual toner remaining after the transfer on the photoreceptor belt 1 and the intermediate transfer drum 5, the residual toner 101 on the photoreceptor belt 1 is mechanically scraped off by a photoreceptor cleaner (blade cleaner) 7, and The residual toner 100 on the intermediate transfer drum 5 is electrically cleaned by the drum cleaner 8.

The details of the cleaning at this time will be described with reference to FIG. FIG. 2 is a diagram showing the configuration around the photosensitive drum 1 and the intermediate transfer drum 5 in detail. In order to transfer the toner image formed on the photoreceptor belt 1 onto the intermediate transfer drum 5, the potential on the photoreceptor belt 1 side must be made deeper than the intermediate transfer drum 5. In this embodiment, this is realized by applying a negative voltage to the photoreceptor belt 1 and setting the base of the intermediate transfer drum 5 to zero potential. The optimal voltage applied to the photoreceptor belt 1 is 400 V in this embodiment.
Of course, the optimum voltage value depends on the amount of charge of the toner, the speed of the process, the nip width between the photosensitive belt 1 and the intermediate transfer drum 5, the thickness of the photosensitive member, and the material and thickness of the surface layer of the intermediate transfer drum. If different, it changes within the range of 200 to 2000V. A positive voltage is applied to the drum cleaner 8 in order to electrically clean the toner on the intermediate transfer drum 5. This voltage value was 300 V in this embodiment. Of course, this voltage value also varies within the range of 200 to 1500 V if the thickness and material of the surface layer of the intermediate transfer drum 5, the length and density of the bristle brush of the drum cleaner 8, or the resistance value are different.

Since the drum cleaner 8 is a fur brush cleaner, it cannot clean toner having the same polarity as the bias applied to the brush. In this case, the positive polarity toner 100 generated when the toner is transferred onto the paper by the transfer roller 11 remains on the intermediate transfer drum 5 and further passes through the drum cleaner 8.
Subsequently, the residual toner 100 reaches a contact portion 15 between the photoreceptor belt 1 and the intermediate transfer drum 5, where the photoreceptor 1
An electric field in a direction for transferring the negative polarity toner formed on the photoreceptor belt 1 to the intermediate transfer drum 5 is generated between the intermediate transfer drum 5 and the intermediate transfer drum 5. This is because the minus toner on the photoreceptor belt 1 described above is transferred to the intermediate transfer drum 5.
The reason for this is that a negative voltage 200 is present in a region where there is no toner image on the surface of the photoreceptor belt 1 due to the transfer voltage for transferring the image on the upper side and the use of the reversal developing method. Accordingly, the residual toner 100 having a positive polarity is attracted to the photoreceptor belt 1 by the electric field and is transferred to the surface of the photoreceptor belt 1. Then, the residual toner 10 transferred to the surface of the photosensitive belt 1
1 is scraped off by the photoreceptor cleaner 7 and cleaned. Since the photoconductor cleaner 7 is a blade cleaner, cleaning is performed regardless of the polarity of the toner.
At this time, since the photoreceptor also has a belt structure instead of a drum, both have elasticity, the sliding resistance between them is reduced, and stable cleaning can be ensured for a long time. With such an apparatus configuration, the cleaning of the toner is reliably performed without providing a complicated cleaning mechanism or a charging member.

By the way, as described in this embodiment, in spite of the fact that the residual toner on the intermediate transfer drum 5 should be transferred to the photosensitive belt 1 electrically, it does not transfer to the photosensitive belt 1 under certain conditions. In some cases, the toner remains on the intermediate transfer drum 5. As a result of the study, it was found that the cause was that the polarity of the residual toner was changed by the discharge generated in the gap upstream of the contact portion between the photosensitive belt 1 and the intermediate transfer drum 5. FIG. 3 shows the details of this phenomenon. The discharge of the air gap occurs when the transfer voltage applied to the photoreceptor belt 1 and the surface potential of the photoreceptor are high. The discharge charge 300 falls on the intermediate transfer drum 5, that is, on the residual toner 100. For this reason, the polarity of the residual toner 100 having a positive polarity becomes negative again (the negative toner is indicated by 400), and even if the residual toner 100 passes through the contact portion 15 between the photosensitive belt 1 and the intermediate transfer drum 5, it remains on the photosensitive belt 1 side. Remains without transfer. If the discharge in the gap can be suppressed, the residual toner on the intermediate transfer drum 5 can be reliably transferred to the photosensitive belt 1.

The suppression of the discharge is realized by adopting the following configuration. One is a method of reducing a bias voltage difference between the photosensitive belt 1 and the intermediate transfer drum 5.
FIG. 4 is a diagram showing an embodiment for reducing the bias voltage difference. In the embodiment shown in FIG. 4, a high-voltage power supply 16 connected to the photoreceptor belt 1 and having a variable output is provided.
And a voltage controller 17 for controlling the output of the high-voltage power supply 16 in accordance with the printing sequence. The residual toner 100 on the intermediate transfer drum 5 passes through the contact portion 15 between the photosensitive belt 1 and the intermediate transfer drum 5. In such a case, the output of the high-voltage power supply is controlled to be reduced.

In this embodiment, 1 is applied to the normal voltage.
It was set to decrease by 50V. Of course, if the device configuration is different, this voltage value is also different. By performing this control, the voltage difference between the photosensitive belt 1 and the intermediate transfer drum 5 is reduced, the discharge is suppressed, and the transfer of the residual toner 100 from the intermediate transfer drum 5 to the photosensitive belt 1 is reliably performed. You will be At this time, at the same timing as the residual toner 100 is copied onto the photosensitive belt 1, the photosensitive belt 1
When the first color toner image of the next image developed above enters the contact portion, the photosensitive belt 1 and the intermediate transfer drum 5
Is considered to decrease the transfer efficiency when the toner image on the photoreceptor belt 1 is transferred to the intermediate transfer drum 5 when the voltage difference between the two is reduced, but by defining the charge amount of the toner to be transferred at this time, A decrease in transfer efficiency can be prevented. In general, when the charge amount of the toner is high, the transfer efficiency tends to decrease, and a high voltage is required to surely perform the transfer. In our study, the toner charge amount was 20μ.
If it is not more than C / g, it was possible to find a condition that high transfer efficiency and no discharge in the void portion occur. Therefore, the charge amount of any of the Y, M, C, and K toners is reduced to 20 μm.
When the first color image is formed with the toner having the lowest charge amount at C / g, the residual toner 10
0 can be shifted to the photosensitive belt 1 side.

The second method for suppressing the discharge in the gap is to lower the surface potential of the photoreceptor belt 1. FIG.
6 shows an embodiment in which the surface potential of the photoreceptor belt 1 is reduced. FIG. 5 shows a power supply 18 for a photoreceptor charger whose output can be varied and a power supply for the photoreceptor charger according to a printing sequence. An output control unit 19 controls the output of the residual toner 10 on the intermediate transfer drum 5.
A control is performed so that the surface potential of the photoreceptor at a portion where the photoreceptor contacts the photoreceptor belt 1 is reduced. Also, FIG.
An exposing device 20 for exposing the surface of the photoreceptor belt 1 to attenuate the surface charge;
The output control unit 21 controls the output of the photosensitive drum 1 to reduce the surface potential by exposing the surface of the photosensitive member where the residual toner 100 on the intermediate transfer drum 5 comes into contact with the photosensitive belt 1. In this embodiment, the potential of the portion where the residual toner 100 contacts the photoreceptor belt 1 is normally -450 V. However, the present control mechanism lowers the potential by 100 V to -35 V.
It is set to 0V. By lowering the surface potential of the photoreceptor belt 1 using such means, the discharge of the gap 15 is suppressed, and the transfer of the residual toner 100 from the intermediate transfer drum 5 to the photoreceptor belt 1 is performed reliably. Become.

Since the present image forming apparatus outputs a color image, the image is formed by developing each color of Y, M, C, and K on the photoreceptor belt 1. Although the toner 100 on the intermediate transfer drum 5 can be generally removed by using the method described above, when the residual toner 100 is on the intermediate transfer drum 5 and is transferred to the photosensitive belt 1, If the first color toner image of the page exists on the photoreceptor belt 1, some inconvenience may occur. As shown in detail in FIG. 5, this inconvenience occurs because the residual toner 100 on the intermediate transfer drum 5 does not move onto the photoreceptor belt 1 when it overlaps with the portion of the photoreceptor belt 1 where the toner image 500 exists. .
This problem is solved by using the darkest color among the color toners required for the image as the color toner to be first transferred to the intermediate transfer drum 5. For example, in an image printed with four color toners of Y, M, C, and K, the photosensitive belt 1
The image to be developed on the intermediate transfer drum 5 is provided with a toner image 500 of K which is the darkest color in the image to be transferred onto the intermediate transfer drum 5. When this image is printed, the remaining toner naturally contains K toner. When continuous printing is performed, if the image formation is performed in the order of Y, M, C, and K, the residual toner 100 on the intermediate transfer drum 5 and the Y toner image 50
In the area where 0 is in contact, the residual toner 100 remains on the intermediate transfer drum 5, and in addition, Y is the lightest color in image formation, and if the residual toner 100 is K or C,
The image of the residual toner 100 is visually recognized as a stain. However, if an image is formed in the order of K, Y, M, and C, even if the residual toner 100 remains, it is invisible because it is black.

In the color image forming apparatus of such an embodiment, since there is almost no image that does not actually include K, by starting writing on the photoreceptor belt 1 from K in any combination of colors, The above problem is solved. what if,
When the color image of Y, M, C, and K is switched to the color image of Y, M, and C, the residual toner image of K of the four-color image printed immediately before the three-color image may be seen. However, in this case, the problem is caused by performing a print sequence control such as copying all the residual toner 100 on the intermediate transfer drum 5 to the photosensitive belt 1 at intervals of one rotation of the drum and then starting writing the next three-color image. Will be resolved.

[0026]

As described above, according to the first aspect of the present invention, there is provided a toner removing means for mechanically removing the toner on the surface of the photoreceptor from the photoreceptor, and the intermediate transfer body which cannot be removed by the cleaning means. The residual toner having a polarity opposite to that of the above cleaning bias is reversely transferred to the photosensitive member side by a bias voltage of a high-voltage power supply for intermediate transfer at a contact portion between the photosensitive member and the intermediate transfer member, and the residual toner transferred to the photosensitive member is removed. Since the toner is removed by the toner removing means, the toner on the intermediate transfer body can be cleaned without providing a complicated cleaning mechanism, and the apparatus can be reduced in size, cost, and image quality can be improved.

According to the second aspect of the present invention, the same effects as those of the first aspect of the invention can be obtained even in the case of a color image having a plurality of developing means.

According to the third aspect of the invention, when a color image is formed, the darkest color toner among all the color toners used for image formation is first transferred to the intermediate transfer member, so that the intermediate transfer member is transferred. Since the toner remaining on the transfer member is hidden in the dark toner and cannot be recognized in the image, a good image can be obtained.

According to the fourth aspect of the present invention, the color toner having the lowest charge amount among all the color toners used for image formation is first transferred to the intermediate transfer body, so that the transfer efficiency is maintained without lowering the transfer efficiency. The toner can be transferred to the photoconductor.

According to the fifth aspect of the present invention, when the residual toner on the intermediate transfer member passes through the contact portion between the photosensitive member and the intermediate transfer member, the voltage control means for controlling the output of the high voltage power supply (transfer bias). Since the output value of the high-voltage power supply is reduced, the voltage difference between the photosensitive member and the intermediate transfer member is reduced, and the discharge in the gap between the two is suppressed, and the transfer of the residual toner from the intermediate transfer member to the photosensitive member is reduced. It is done reliably.

According to the present invention, when the residual toner on the intermediate transfer member passes through the contact portion between the photosensitive member and the intermediate transfer member by the potential control means for controlling the surface potential of the photosensitive member, , The discharge of the gap between the two is suppressed, and the transfer of the residual toner from the intermediate transfer member to the photosensitive member is reliably performed.

According to the seventh aspect of the present invention, since the potential control means is constituted by an output control circuit for controlling the output of the power supply for the charger of the photosensitive member, the effect of the sixth aspect of the invention can be obtained with a simple configuration. be able to.

According to the eighth aspect of the present invention, the potential control means is constituted by the exposure device for exposing the surface of the photoreceptor to attenuate the surface potential and the output control circuit for controlling the output of the exposure device. The effect of the invention described in claim 6 can be obtained with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus including a plurality of developing units according to an embodiment of the present disclosure.

FIG. 2 is an explanatory diagram showing a behavior of a toner at a contact portion between a photosensitive member and an intermediate transfer member.

FIG. 3 is an explanatory diagram showing an enlarged state of a contact portion between a photosensitive member and an intermediate transfer member in FIG. 2;

FIG. 4 is an explanatory diagram showing a configuration for controlling a transfer bias to ensure a transition from an intermediate transfer member to a photosensitive member.

FIG. 5 is an explanatory diagram showing an example of a configuration for controlling a charging potential to ensure a transition from an intermediate transfer member to a photosensitive member.

FIG. 6 is an explanatory diagram showing another example of the configuration for controlling the charging potential to ensure the transfer from the intermediate transfer member to the photosensitive member.

FIG. 7 is an explanatory diagram illustrating a state in which residual toner on an intermediate transfer member is not transferred to a photosensitive belt.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor belt 2 Charger 3 Exposure device 4a-4d Developing device 5 Intermediate transfer drum 6 Erase lamp 7 Photoconductor cleaner (blade cleaner) 8 Drum cleaner (fur brush cleaner) 9 Paper cassette 10 Pickup roller 11 Transfer roller 12 Peeling device DESCRIPTION OF SYMBOLS 13 Fixing device 14 Drum charger 15 Air gap 16 High voltage power supply 17 Voltage control unit 18 Power supply for photoreceptor charger 19 Output control unit 20 Exposure unit 21 Output control unit 100, 101 Residual toner

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Nobuaki Fukasawa 1-1-1, Higashitaga-cho, Hitachi City, Ibaraki Pref.

Claims (8)

[Claims] A photoconductor, a developing means for visualizing a latent image on the photoconductor, an intermediate transfer body on which the visualized toner image is transferred by a bias potential difference generated by a high voltage power supply; An image provided with transfer means for transferring a toner image on an intermediate transfer body to a recording medium to output a final image, and cleaning means for electrically cleaning toner remaining on the intermediate transfer body without being transferred to the recording medium In the forming apparatus, there is provided a toner removing unit for mechanically removing toner on the surface of the photoconductor from the surface of the photoconductor, and a residual toner having a polarity opposite to that of a cleaning bias which cannot be removed by the cleaning unit is transferred to the photoconductor and the intermediate transfer unit. The intermediate transfer body is transferred to the photoconductor by the bias voltage of the high-voltage power supply at a contact portion of the body, and the residual toner transferred to the photoconductor is moved to the front. Image forming apparatus characterized by eliminating the toner removing means. 2. The image forming apparatus according to claim 1, wherein a plurality of said developing units are provided. 3. The image forming apparatus according to claim 2, wherein the darkest color toner among all the color toners used for image formation is first transferred onto the intermediate transfer member. 4. The image forming apparatus according to claim 2, wherein a color toner having the lowest charge amount among all the color toners used for image formation is first transferred to the intermediate transfer member. 5. A voltage control means for controlling an output of the high-voltage power supply, wherein the voltage control means causes residual toner on the intermediate transfer member to contact the photoreceptor with the intermediate transfer member based on a progress of a printing process. 5. The image forming apparatus according to claim 1, wherein an output value of the high-voltage power supply is reduced when the image forming apparatus passes the unit. 6. A potential control means for controlling a surface potential of the photoreceptor, wherein the potential control means removes residual toner on the intermediate transfer body between the photoreceptor and the intermediate transfer body based on the progress of a printing process. The image forming apparatus according to claim 1, wherein a surface potential of the photosensitive member is reduced when the photosensitive member passes through the contact portion. 7. The image forming apparatus according to claim 6, wherein said potential control means comprises an output control circuit for controlling an output of a power supply for a charger of the photosensitive member. 8. The apparatus according to claim 6, wherein said potential control means comprises an exposure device for exposing the surface of the photosensitive member to attenuate the surface potential, and an output control circuit for controlling the output of said exposure device. The image forming apparatus as described in the above.