JP2004219710A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain good monochrome and full color images by recovering scattered toner or fogged toner in an image forming apparatus. <P>SOLUTION: The image forming apparatus comprises a fixed (jumping) developing device, a scattered toner collecting device and a plurality of (two components) developing devices disposed in a rotary device in this order from the upstream side of drum rotation. Bias applied to a roll provided to the scattered toner collecting device is controlled variably according to the image forming state, and the scattered toner and fogged toner on the roll are adsorbed and recovered. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a developing device used for developing a latent image formed on a latent image carrying member in a copying apparatus, an image forming and recording apparatus, a printer, a facsimile, and the like, and particularly to a color image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus that forms a color image by superimposing toner images of a plurality of colors, conventionally, for the purpose of obtaining a color image without color shift, an image forming apparatus using an intermediate transfer member as shown in FIG. A device has been proposed.
[0003]
This image forming apparatus is a copying machine or a laser beam printer using an electrophotographic process. Hereinafter, the configuration and operation of the image forming apparatus shown in FIG. 1 will be briefly described.
[0004]
A rotating drum type electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 1 as a latent image holding member is disposed inside the apparatus main body (hereinafter, referred to as “inside machine”). Here, an amorphous silicon photosensitive member is used, and a schematic diagram thereof is shown in FIG. Reference numeral 101 denotes a conductive support such as Al, 104 denotes the conductive support, and a charge injection blocking layer 102 for preventing charge injection from the 101 is made of at least an amorphous silicon-based material. 103, a surface protective layer for protecting the photoconductive layer 102; and 105, a long-wavelength light absorbing layer for preventing reflection from the conductive support 101.
[0005]
The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1, and each image forming process described later is repeatedly performed on the surface thereof.
[0006]
The photosensitive drum 1 is charged to a predetermined polarity and a predetermined surface potential by a charger 2 such as a corona discharger in the course of rotation in the direction of the arrow R1, and then exposed to an exposure unit 3 (imaging based on color separation of a color original image). A color component image of a target color image by receiving an image exposure L by an exposure optical system or a scanning exposure optical system by a laser scanner that outputs a laser beam modulated according to a time-series electric digital pixel signal of image information. (For example, an electrostatic latent image corresponding to an M (magenta) component image) is formed.
[0007]
An intermediate transfer belt is used as the intermediate transfer member. The intermediate transfer belt 5 is suspended between one conductive roller 6 and four turn rollers 7a, 7b, 7c, 7d, for a total of five rollers. The conductive roller 6 holds the intermediate transfer belt 5 in pressure contact with the photosensitive drum 1 with a predetermined pressing force. The intermediate transfer belt 5 is driven to rotate at the same peripheral speed as the photosensitive drum 1 in the direction of arrow R5, and a formed toner image (hereinafter referred to as a “toner image”) on the photosensitive drum 1 is supplied to the conductive roller 6 by a bias power supply. ), A transfer bias having a polarity (plus) opposite to the toner charge polarity (minus in this embodiment) is applied.
[0008]
The intermediate transfer belt 5 is, for example, a dielectric film such as polyester or polyethylene, or a composite layer type dielectric film such as a medium resistance rubber in which the back surface (inner surface side) is lined with a conductor. The first color magenta toner image formed and carried on the surface of the photosensitive drum 1 passes through the transfer section by an electric field formed by application of a transfer bias to the conductive roller 6, and the intermediate transfer belt 5 Are sequentially transferred to the outer surface of the substrate.
[0009]
The image forming apparatus includes a developing device 4a having a black (Bk) developing device (hereinafter, referred to as “Bk developing device”) 401 fixedly arranged on the upstream side in the rotation direction (the direction of the arrow R1) of the photosensitive drum 1. And a rotary developing device 4b having developing devices for other three colors rotatably arranged on the downstream side. The rotary developing device 4b includes a rotating body that rotates in the direction of the arrow R4b, and three developing devices supported by the rotating body, that is, toners of respective colors of magenta (M), cyan (C), and yellow (Y), respectively. Are stored (hereinafter, referred to as “M developing device 402, C developing device 403, and Y developing device 404”, respectively).
[0010]
The Bk developing device 401 is fixedly arranged between the upstream exposure unit 3 and the downstream rotary developing device 4b so as to separate them.
[0011]
The Bk developing device 401 shown in FIGS. 3A and 3B will be described.
[0012]
The developing container 40 has an opening extending in the longitudinal direction of the apparatus (perpendicular to the plane of FIG. 1), and the developing sleeve 41 is installed in the opening. The developing sleeve 41 is made of a material such as aluminum or SUS. The developing sleeve 41 has a substantially semi-peripheral left surface protruding into the container and a substantially semi-peripheral right surface exposed to the outside of the container 40 when viewed from the view of the opening. Have been. A slight minute gap: S-Dgap is provided between the developing sleeve 41 and the photosensitive drum 1 by an abutting roller 46, and the developing sleeve 41 is rotationally driven in the direction of the arrow R <b> 4 a with respect to the rotational direction R <b> 1 of the photosensitive drum 1. Is done.
[0013]
In the developing sleeve 41, a magnet 42 is provided as a magnetic field generating means. In the present embodiment, the magnet 42 is made of a permanent magnet. The magnet 42 is non-rotatably disposed within the developing sleeve 41 so that a fixed magnetic field can be generated regardless of the rotation of the developing sleeve 41.
[0014]
In the vicinity of the developing sleeve 41 in the developing container 40, a plate-shaped magnetic blade 43 having a fixed end supported by the opening of the developing container and having a free end facing the developing sleeve 41 is provided as a developer regulating member, One magnetic pole of the magnet 42 is positioned so as to substantially face the magnetic blade 43.
[0015]
The magnetic toner 45 carried on the developing sleeve 41 by the stirring member 44 is thereafter conveyed to the developing sleeve opposing portion of the magnetic blade 43 as the developing sleeve 41 rotates. Then, after the thickness of the magnetic layer 43 is regulated by the magnetic regulation: S-Bgap formed in the gap between the magnetic blade 43 and the developing sleeve 41, the layer is formed in a thin layer on the developing sleeve 41, and the regulating section: S-Bgap is formed. And a small gap S-Dgap is opened between the photosensitive drum 1 and the photosensitive drum 1, and the photosensitive drum 1 is conveyed to the opposing developing area. By applying an alternating voltage in which DC and AC are superimposed as a developing bias between the developing sleeve 41 and the photosensitive drum 1 in the developing area, the toner 45 on the developing sleeve 41 becomes an electrostatic latent image on the photosensitive drum 1. The electrostatic latent image is visualized and developed as a toner image by transferring and adhering opposingly.
[0016]
Next, image formation by the Bk developing device 401 will be described.
[0017]
First, the surface of the photosensitive drum 1 is uniformly charged by the primary charger 2 to a drum surface potential Vd = + 400V. Next, exposure L is performed by PWM with a semiconductor laser having a wavelength of 680 μm at 600 dpi to form an electrostatic latent image on the photosensitive drum 1. The laser power at this time is set so that the electrostatic latent image becomes Vl = + 50V.
[0018]
Subsequently, development is performed by a Bk developing device 401 with S-Bgap: 250 μm and S-Dgap: 250 μm to visualize as a toner image.
[0019]
The developer used in this embodiment is a negatively charged magnetic toner. The developing bias Vdc is obtained by superimposing a DC voltage of +200 V with an AC voltage of 2700 Hz, 1500 Vpp, and 50% duty to realize jumping development. This is because the Bk development contrast Vcont in the normal development is set to 200 V, and the fog removal contrast Vback is set to +150 V (FIG. 4).
[0020]
The rotary developing device 4b rotates the developing device (M developing device 402 in FIG. 1) for development by rotating in the direction of the arrow R4b, thereby disposing the developing device at a developing position facing the surface of the photosensitive drum 1. The rotation direction R4 of the rotary developing device 4b is the same as the rotation direction R1 of the photosensitive drum 1, and is opposite to the rotation direction of the intermediate transfer belt 5 (the direction of arrow R5).
[0021]
If the rotation direction of the rotary developing device 4b is set in the direction of the arrow R4b, and the developing order of the four colors is, for example, M → C → Y → Bk in the same manner as in the conventional example, The arrangement of the M developing unit 402, the C developing unit 403, and the Y developing unit 404 is such that the M developing unit 402, the Y developing unit 403, and the C developing unit are arranged along the rotation direction (the direction of the arrow R4) of the rotary developing device 4b as shown in FIG. The order of the developing device 404 is as follows.
[0022]
Hereinafter, the image forming operation in the image forming apparatus of the present embodiment shown in FIG. 1 will be described by dividing it into processes (1) to (5). FIG. 1 shows a state in which the M developing device 402 of the three developing devices in the rotary developing device 4b is on standby at the current position.
[0023]
(1) First, a latent image of the M image of the first color is formed on the photosensitive drum 1 and development is performed in the state shown in FIG. The M toner image on the photosensitive drum 1 that has been made visible with the M toner by the developing unit 402 is sequentially transferred onto the outer peripheral surface of the intermediate transfer belt 5 while rotating in the direction of the arrow R1 (counterclockwise). After the transfer of the first color M toner image onto the intermediate transfer belt 5, the surface of the photosensitive drum 1 is cleaned by the cleaning device 8.
[0024]
(2) Subsequently, a latent image of the C image as the second color is formed. In order to perform the C development, the rotary developing device 4b rotates in the direction of arrow R4 (the same counterclockwise as the photosensitive drum 1). And similarly,
(3) C development → C toner development on the intermediate transfer belt 5 → intermediate transfer of the C image to the intermediate transfer belt 5 → cleaning of the surface of the photosensitive drum 1 by the cleaning device 8.
[0025]
(4) Then, similarly to (2) and (3), the Y phenomenon → the intermediate transfer of the Y image to the intermediate transfer belt 5 → the cleaning of the surface of the photosensitive drum 1 by the cleaning device 8.
[0026]
(5) Next, image exposure L corresponding to the fourth Bk component image → development with Bk toner in Bk developing device 401 → intermediate transfer of Bk toner image to intermediate transfer belt 5 → cleaning device 8 for photosensitive drum 1 surface Cleaning.
[0027]
By sequentially executing the above processes (1) to (5), the above-described four toner images (magenta, cyan, yellow, and black toner images) are superimposed and transferred on the outer surface of the intermediate transfer belt 5. Thus, a composite color toner image (mirror image) corresponding to the target color image is formed.
[0028]
Next, the transfer material (sheet) P is separated and conveyed one by one from the paper supply cassette 9 by the paper supply roller 10, passes through the registration roller pair 11 and the transfer guide 12, and is transferred to the transfer device 13 (corona charger) and turn. The sheet is fed at a predetermined timing to a transfer section formed by the roller 13a.
[0029]
Here, to the conductive roller 6, a bias (in this example, minus) which is the same as the charging polarity of the toner opposite to the transfer process and which is 0 V is applied from a bias power supply. Further, when a toner image is transferred onto the transfer material P fed at a predetermined timing, a transfer bias having a polarity opposite to the toner charging polarity (minus in this example) and a polarity opposite to the positive polarity (plus) is applied by the bias power supply. 13 is applied.
[0030]
By repeating the above-described series of image forming processes, the transfer-combined color images are sequentially transferred onto the intermediate transfer belt 50 in sequence, and the color toner images thus transferred are successively sent to the transfer unit. Is finally transferred to the transfer material P.
[0031]
When the transfer process is completed, a transfer bias (minus) of 0 V or the same polarity (minus in this example) as the toner charging polarity is applied to the intermediate transfer belt 5.
[0032]
The transfer material P on which the toner image on the intermediate transfer belt 5 has been transferred through the transfer unit is introduced into the fixing device 15 via the conveyance guide 14, and the fixing roller 15a and the pressure roller 15b, which are heated and controlled to predetermined values, are heated. As a result, the toner image is subjected to a fixing process by being heated and pressed, and is output as a final color image formed product.
[0033]
On the other hand, the intermediate transfer belt 5 after the transfer of the toner image is cleaned by the belt cleaning device 16. The belt cleaning device 16 is a cleaning device for the intermediate transfer belt 5, and is normally kept in an inactive state with respect to the intermediate transfer belt 5, but when the transfer of the toner image onto the transfer material P is completed, When the cleaning device 16 operates on the outer surface of the transfer belt 5, the outer surface of the intermediate transfer belt 5 is cleaned.
[0034]
Incidentally, depending on the outer peripheral length of the transfer belt 5, it is also possible to carry two or more transfer materials P at one time and to form two images collectively by one rotation.
[0035]
[Problems to be solved by the invention]
However, in the case where color developing devices are disposed downstream as in the present configuration, toner scattered from other developing devices or the like is mixed therein, and the image quality is impaired not only in black and white images but also in full-color images. . In particular, in full-color image formation (for example, yellow halftone), image defects such as scattering and fogging due to Bk are more likely to appear than other colors. Further, in this configuration, since the Bk developing device is fixed at the position facing the photosensitive drum, it tends to be more remarkable for a color developing device that can be rotated and separated.
[0036]
On the other hand, the color development in the rotary developing device 4b is good in terms of the appearance of scattering and fogging, but has problems such as contamination in the main body due to the provision of three types of developing devices.
[0037]
SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus capable of suppressing and collecting adverse effects due to toner scattering of each color and providing a good black-and-white and full-color image. .
[0038]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
A latent image carrying member that carries and rotates an electrostatic latent image, a first developing device positioned with respect to the latent image carrying member, a rotating device rotatably supporting two or more developing devices, A scattered developer collecting device provided between the first developing device and the rotating device, the scattered developer collecting device is an image forming apparatus having a rotating roller-shaped member,
It is preferable that the bias Vc is variably applied to the roller member.
[0039]
It is preferable that the first developing device is located upstream of the rotating device in the rotation direction of the latent image holding member.
[0040]
It is preferable that the developer used in the first developing device comprises only a magnetic toner.
[0041]
It is preferable that the first developing device is held in non-contact with the latent image carrying member.
[0042]
It is preferable that the thickness of the developer layer on the developer carrying member in the first developing device is smaller than the gap between the developer carrying member and the latent image carrying member in the developing section.
[0043]
It is preferable that the gap between the first developing device and the latent image carrying member is regulated by a contact member for the latent image carrying member attached to the first developing device.
[0044]
It is preferable to apply a bias Va on which a DC voltage and an AC voltage are superimposed to the developer carrying member of the first developing device.
[0045]
The developer used in the developing device provided in the rotating device preferably comprises a carrier and a non-magnetic toner.
[0046]
It is preferable to apply a bias Vb in which a DC voltage and an AC voltage are superimposed on a developer carrying member of the developing device provided in the rotating device.
[0047]
It is preferable that the toners in the first developing device and the developing device provided in the rotating device have the same polarity.
[0048]
The applied bias DC component Vda of the first developing device, the applied bias DC component Vdb of the developing device disposed on the rotating device, and the bias Vc applied to the scattered developer collecting device are:
| Vc |> | Vda |, | Vc |> | Vdb |
It is preferred that
[0049]
It is preferable that the roller member length of the scattered developer collecting device includes a contact position of a contact member that regulates a gap between the first developing device and the latent image carrying member.
[0050]
It is preferable that the switching of the variable application of the bias Vc be performed according to the cumulative image forming period of the first developing device.
[0051]
It is preferable that the switching of the variable application of the bias Vc be performed in accordance with the image forming period of the developing device provided in the rotating device.
[0052]
It is preferable that the switching of the variable application of the bias Vc is performed between the image formation of the first developing device and the image forming of the developing device arranged in the rotating device.
[0053]
Switching of the variable application of the bias Vc is preferably performed at the start of the image forming process.
[0054]
Switching of the variable application of the bias Vc is preferably performed at the end of the image forming process.
[0055]
BEST MODE FOR CARRYING OUT THE INVENTION
[0056]
First Embodiment of the Invention
In the first embodiment, a scattering prevention device 4c (FIG. 4) is provided between the developing device 4a and the rotary developing device 4b, and a proposal is made, and details thereof will be described below (FIG. 5).
[0057]
The scattering prevention device 4c is provided with a bias roller 47 for applying a bias having the same polarity as that of the toner (here, -1000 V). The bias roller 47 rotates in the direction R4c, which is opposite to the rotation direction R1 of the photosensitive drum when the image is formed by the Bk developing device.
[0058]
Here, since the scattering prevention device 4c has a very large electric field in the vicinity of the developing device, the toner having the regular negative polarity repels the bias roller 47, and both the Bk and the color Y, M, and C toners are used. Suppress the scattering in the direction. Conversely, the minutely inverted positive polarity toner is attracted to the bias roller 47 by a strong electric field and then stripped and collected by the scraper 48.
[0059]
As a result, the fog image due to the scattered Bk toner in the color image and the density fluctuation due to the mixing of the color toner in the Bk development were significantly improved.
[0060]
Second Embodiment of the Invention
In this embodiment, in addition to the previous embodiment, it is proposed that the bias applied to the roller is variably controlled in accordance with image formation (FIG. 6).
[0061]
In the previous embodiment, good Bk fog (2.0% or less) is obtained in the case of Bk single color. However, as described above, Bk fog tends to appear on an image in a full-color image, so that further improvement in image quality is necessary ( (Target: 1.0% or less).
[0062]
The fog image is formed by the normally charged negative toner and the inverted positive toner, but the situation changes as the toner deteriorates. As shown in FIG. 7, in the image forming durability test using the Bk developing device of 1000 thousand sheets without using the scattering prevention device 4c, the ground fog by the regular toner is dominant at the beginning and gradually decreases. Conversely, reversal fog is scarcely present at the initial stage, but starts to increase after 100,000 sheets, and Bk fog generally remains at less than 2.0% through a durability test of 1,000,000 sheets.
[0063]
Accordingly, FIG. 8 shows the result of switching the bias application to the bias roller 47 to +1000 V at the initial stage and to -1000 V at the time of 100,000 sheets in the same durability test with the scattering prevention device 4c. As a result, in addition to suppressing the scattering of the Bk toner to the rotary developing device 4b, the target Bk fog of 1.0% was achieved by actively collecting the fog toner, and a good full-color image was obtained.
[0064]
Third Embodiment of the Invention
As described above, contamination in the main body by the color toner in the rotary developing device 4b is also a serious problem.
[0065]
In the first embodiment, bidirectional toner movement with the Bk developing device can be suppressed by the repulsive electric field of the bias roller 47, but the scattering itself is not reduced. Therefore, the intermediate transfer belt 5 and the fixing device 15 around the rotary developing device 4b are contaminated with the color toner without being directly exposed on the image, and are indirectly exposed.
[0066]
Therefore, in this embodiment, in order to collect the scattered color toner by the scatter prevention device 4c, it is proposed to apply a bias to the bias roller 47 even during the color image formation in addition to the second embodiment. Specifically, as shown in FIG. 9, a voltage of 1000 V is applied to the + bias roller 47 to attract the negatively charged color toner during the color image formation as in the Bk image formation. Further, it is peeled and collected by the scraper 48 by driving the bias roller. In addition, based on the second embodiment, after 100,000 images are formed, the voltage is switched to -1000 V during Bk development.
[0067]
In order to confirm these effects, the following experiment was performed every 5,000 sheets until the life of the color developing device reached 30,000 sheets.
[0068]
-Remove the Bk developing device from the main body and perform color development using only the rotary developing device 4b.
[0069]
-For every 5,000 sheets, measure the amount of toner on the photosensitive drum per sheet by forming an image of each color.・ ・ ・ ▲ 1 ▼
-Measure the toner bottle consumption of each color every 5,000 sheets. ... ▲ 2 ▼
The amount of toner collected by the scattering prevention device 4c is measured every 5,000 sheets.・ ・ ・ ▲ 3 ▼
From the above, the amount of scattered toner is set to (2)-(1) × 5000... (4) and the recovery rate is set to (3) / (4), and the result is as shown in FIG. Was confirmed to be effective in reducing scattering of color toner.
[0070]
【The invention's effect】
As described above, according to the present invention, in an image forming apparatus that performs multicolor image formation using a fixed developing device and a rotary developing device, fog and toner scattering are suppressed and collected, and a good full-color image is provided. It is possible to provide a developing method and an electrophotographic image forming apparatus capable of performing the above.
[Brief description of the drawings]
FIG. 1 is an external schematic view of a conventional image forming apparatus main body.
FIG. 2 is a schematic sectional view of an amorphous silicon photosensitive member used in the present invention.
FIGS. 3A and 3B are schematic diagrams of a developing device in a fixed developing device used in the present invention.
FIG. 4 is a schematic diagram of an image forming apparatus main body used in Embodiment 1 of the present invention.
FIG. 5 is a schematic sectional view of a scattered developer collecting device used in Embodiment 1 of the present invention.
FIG. 6 shows a bias application sequence of the scattered developer collecting device used in Embodiment 2 of the present invention.
FIG. 7 is a view showing a fog characteristic by Bk development of a conventional configuration.
FIG. 8 is a fog characteristic diagram by Bk development of a configuration used in Embodiment 2 of the present invention.
FIG. 9 is a bias application sequence of the scattered developer collecting device used in Embodiment 3 of the present invention.
FIG. 10 is a scattered developer collection characteristic diagram of the configuration used in Example 3 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charger 3 Exposure part 4a Developing device 4b Rotary developing device 4c Shatter prevention device 5 Intermediate transfer belt 6 Conductive rollers 7a, 7b, 7c, 7d Turn roller 8 Cleaning device 9 Paper feed cassette 10 Feed roller 11 Resist Roller pair 12 Transfer guide 13 Transfer device (corona charger)
13a turn roller 40 developing container 41 developing sleeve 42 magnet 43 magnetic blade 44 stirring member 45 magnetic toner 46 butting roller 47 bias roller 48 scraper 401 Bk developing device 402 M developing device 403 C developing device 404 Y developing device

Claims (17)

A latent image carrying member that rotates while carrying an electrostatic latent image, a first developing device positioned with respect to the latent image carrying member, a rotating device rotatably supporting two or more developing devices, A scattered developer collecting device provided between the first developing device and the rotating device, and an image forming apparatus having a roller-shaped member around which the scattered developer collecting device rotates,
An image forming apparatus, wherein a bias Vc is variably applied to a roller member. The image forming apparatus according to claim 1, wherein the first developing device is located upstream of the rotating device in a rotation direction of the latent image holding member. The image forming apparatus according to claim 1, wherein a developer used in the first developing device includes only a magnetic toner. The image forming apparatus according to claim 1, wherein the first developing device is held in a non-contact state with the latent image holding member. The developer layer thickness on the developer carrying member in the first developing device is smaller than a gap between the developer carrying member and the latent image carrying member in the developing section. An image forming apparatus according to claim 1. The gap between the first developing device and the latent image carrying member is regulated by a contact member provided on the first developing device for contacting the latent image carrying member. An image forming apparatus according to claim 1. 7. The image forming apparatus according to claim 1, wherein a bias Va on which a DC voltage and an AC voltage are superimposed is applied to the developer carrying member of the first developing device. 3. The image forming apparatus according to claim 1, wherein the developer used in the developing device provided in the rotating device includes a carrier and a non-magnetic toner. 9. The image forming apparatus according to claim 1, wherein a bias Vb in which a DC voltage and an AC voltage are superimposed is applied to a developer carrying member of the developing device provided in the rotating device. apparatus. The image forming apparatus according to any one of claims 1 to 9, wherein the toners in the first developing device and the developing device provided in the rotating device have the same polarity. The applied bias DC component Vda of the first developing device, the applied bias DC component Vdb of the developing device disposed on the rotating device, and the bias Vc applied to the scattered developer collecting device are:
| Vc |> | Vda |, | Vc |> | Vdb |
The image forming apparatus according to claim 1, wherein: The roller member length of the scattered developer collecting device includes a contact position of a contact member that regulates a gap between the first developing device and the latent image holding member. An image forming apparatus according to claim 1. 13. The image forming apparatus according to claim 1, wherein the switching of the variable application of the bias Vc is performed according to an accumulated image forming period of the first developing device. 13. The image forming apparatus according to claim 1, wherein the switching of the variable application of the bias Vc is performed according to an image forming period of a developing device provided in the rotating device. 13. The image forming apparatus according to claim 1, wherein the switching of the variable application of the bias Vc is performed between an image forming operation of the first developing device and an image forming operation of the developing device disposed in the rotating device. . 13. The image forming apparatus according to claim 1, wherein the switching of the variable application of the bias Vc is performed at the start of the image forming process. 13. The image forming apparatus according to claim 1, wherein the switching of the variable application of the bias Vc is performed at the end of the image forming process.

Images