JPH05107856A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To provide the electrophotograhic copying machine where a copied image with a stable uniformity can be obtained. CONSTITUTION:When a starting switch is turned ON (step ST1), a half tone image is formed on a photosensitive body (step ST2) by having a half tone patch irradiated by light. The quantity of sticking toner of the half tone image formed on the photosensitive body is detected from the end part of a front side and the end part of a rear side of the photosensitive body by a photosensor (step ST3). Judgement of whether the detected quantity of the sticking toner is within a specified allowance range or not is carried out (step ST4). When the detected quantity of the sticking toner is judged to be within the allowance range, the operation is finished and when the quantity of sticking toner is not within the allowed range, the quantity of the sticking toner is made uniform, and impressing of voltage to a destaticizing lamp corresponding to the position of the photosensitive body exceeding the allowance range is requested (step ST5). The photosensitive body is destaticized in this state, and the device is returned to the step ST2 again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine, and more particularly to an electrophotographic copying machine suitable for full-color electrophotographic copying.

[0002]

2. Description of the Related Art In a conventional electrophotographic copying machine, in order to form an image of a document on a recording medium (final recording medium such as paper), the document is first illuminated by a light source lamp or the like, and light reflected from the document is reflected. Is radiated to the uniformly charged photoconductor belt via a mirror, a lens and the like. The photoconductor belt is exposed by being irradiated with the reflected light from the document, and an electrostatic latent image having a pattern corresponding to the document image is formed on the surface of the photoconductor belt.

Then, the electrostatic latent image is visualized as a toner image by the toner, and the toner image is transferred to the transfer belt. The toner image transferred to the transfer belt is transferred to the recording medium. Thereafter, the toner image on the recording medium is fused, and the copying is completed.

By the way, there are the following factors that affect the uniformity (uniformity) of the copied image.

(1) Light distribution uniformity of the optical system, that is, light distribution of the light source lamp itself, characteristics of the mirror and lens system (2) Uniformity of the photosensitive belt and the transfer belt itself (3) Uniformity of development ( 4) Uniformity of transfer (5) Uniformity of charging (6) Uniformity of static elimination In the conventional electrophotographic copying machine, in order to obtain a stable uniform copy image, that is, a copy image having a uniform density,
A light control plate is provided above the light source lamp, and this light control plate is moved to adjust the light distribution of the light source lamp to the original so that the density of the copied image becomes uniform. Has been done.

[0006]

In such a conventional electrophotographic copying machine, in order to obtain a stable uniform copy image, a service man usually moves a light control plate to perform sample copying during maintenance. You have to make adjustments.

Generally, the uniformity of the copied image changes due to replacement of the light source lamp, change of light distribution of the light source lamp due to aging, replacement of the photoconductor or transfer belt, and change of performance of each element due to aging toner scattering. However, even if the uniformity deteriorates, there is a problem in that adjustment by the light control plate cannot be performed on the way until the maintenance.

Further, adjusting uniformity while performing sample copying requires a large amount of sample copying, and there is a problem that adjustment requires time and labor.

Accordingly, the present invention provides an electrophotographic copying machine capable of obtaining a stable uniform copy image by automatically adjusting the toner density of the toner image formed on the photosensitive belt or the transfer belt. Is provided.

[0010]

[Means for Solving the Problems] A photoconductor, a transfer unit for transferring a toner image formed on the photoconductor to a transfer body according to an original image, and a toner image transferred to the transfer body by the transfer unit on a sheet. Image forming means, a charge removing means for removing charge from the photoconductor after the toner image is transferred to the transfer body, and the toner amount of the toner image formed on either the photoconductor or the transfer body. The body is provided with detection means for detecting along one of the widthwise directions, and control means for controlling the voltage applied to the charge eliminating means so that the toner amount detected by the detection means is within a predetermined range. ..

[0011]

The toner image formed on the photosensitive member according to the original image is transferred to the transfer member by the transfer means. The toner image formed on the transfer body is formed as a copy image on a sheet by the image forming unit. When the toner amount of the toner image formed on the photoconductor is detected by the detection unit along the width direction of the photoconductor, the control unit controls the toner on the transfer body so that the detected toner amount is within a predetermined range. After the image is transferred, the voltage applied to the charge eliminating means for eliminating the charge on the photoconductor is controlled. As a result, the toner amount of the toner image formed on the photosensitive member and the toner amount of the toner image transferred to the transfer member are stable, and therefore a stable uniform copy image can be obtained.

Further, when the toner amount of the toner image transferred and formed on the transfer body is detected by the detection means along the width direction of the transfer body, the control means has the detected toner amount within a predetermined range. In this way, the voltage applied to the charge eliminating means for eliminating the charge on the photoconductor is controlled. As a result, the toner amount of the toner image formed on the photosensitive member and the toner amount of the toner image transferred to the transfer member are stable, and therefore a stable uniform copy image can be obtained.

[0013]

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

FIG. 2 is a side view showing the structure of a full-color copying machine which is an embodiment of the electrophotographic copying machine according to the present invention.

As shown in FIG. 2, the full-color copying machine 10 of this embodiment is provided with an original table 11 made of transparent glass on the upper surface of the machine frame.

On the document table 11, a half used for detecting the toner adhesion amount of a toner image formed on a photosensitive member or a transfer intermediate, which will be described later, at a position that does not overlap the position where the document is to be placed. A tone patch 11a is provided.

An exposure optical system 12 is arranged below the document table 11. The exposure optical system 12 includes a light source lamp 12a for irradiating the original 13 placed on the original placing table 11 with light, and the original 13
A plurality of reflecting mirrors 12b, 12c, 12d, 12e for guiding the reflected light from the photoconductor 14 along the optical path indicated by the alternate long and short dash line and
12f, an imaging lens 12g arranged on the optical path, and a color separation filter 12 having color filters of three primary colors of red, green and blue.
contains h and.

The light source lamp 12a and the reflecting mirrors 12b, 12c and 12
d is configured to be movable in parallel with the document placing table 11 along a bidirectional arrow shown in the drawing by a driving device (not shown).

On the optical axis of the exposure optical system 12, there is arranged a belt-shaped photosensitive member 14 made of an organic photosensitive member (OPC) to which a light image subjected to exposure scanning is irradiated.

Below the photoconductor 14, a paper 15 is accommodated.
Two paper feed cassettes 16 and 17 are provided. Paper feed rollers 18 and 19 are provided on the upper surfaces of the paper feed cassettes 16 and 17, respectively.

The paper feed rollers 18 and 19 are configured to eject the paper 15 from the paper feed cassettes 16 and 17, respectively, and send it toward the transfer intermediate 20.

A timing roller 21 is provided on the delivery side of the paper 15 from the paper feed rollers 18 and 19 toward the transfer intermediate 20, and the timing roller 21 rotates in synchronization with the transfer intermediate 20. Is configured.

The transfer intermediate body 20 is constituted so as to be rotationally driven in the clockwise direction (arrow shown in the figure) by the first, second and third rollers 22a, 22b and 22c. It is pressed against a driving roller 23 that is rotationally driven.

A primary transfer charger 24 is provided on the back surface side of the transfer intermediate 20 in the portion where the drive roller 23 is pressed against the transfer intermediate 20.

A secondary transfer roller 26 is disposed in contact with the transfer intermediate body 20 on the surface side of the transfer intermediate body 20 in the portion where the third roller 22c is disposed.

On the side of the secondary transfer roller 26 where the paper 15 is delivered,
The peeling plate 27, the transport belt 28, and the fixing device 29 are
They are arranged in this order.

A photosensor P1 for detecting the toner adhesion amount on the photoconductor 14 is provided on the surface side of the photoconductor 14 in the portion where the drive roller 23 is provided.

The photo sensor P1 is a front side of the photoconductor 14 (belt-shaped photoconductor
It is configured to be movable between an end portion on the front side in the width direction of 14 and an end portion on the rear side (the other side in the width direction of the belt-shaped photoconductor 14).

On the surface side of the transfer intermediate 20 stretched between the third roller 22c and the first roller 22a, a photo sensor P2 for detecting the toner adhesion amount on the transfer intermediate 20.
Is provided.

The photosensor P2 is also driven by a driving device (not shown) to the front end (front side in the width direction of the belt-shaped transfer intermediate 20) of the transfer intermediate 20 and the rear side (belt-shaped). It is configured to be movable between an end portion of the transfer intermediate body 20 (the other side in the drawing in the width direction).

The positions of the photosensors P1 and P2 are not limited to the positions shown in FIG. 2 as long as they can detect the toner adhesion amounts on the photoconductor 14 and the transfer intermediate 20, respectively. Absent.

In this embodiment, the copying machine is configured to detect the toner adhesion amount on the photoconductor 14 and the transfer intermediate 20 by the two photosensors P1 and P2, respectively, but only one photosensor is provided, For example, the copying machine may be configured so that only the photosensor P1 is provided to detect the toner adhesion amount on the photoconductor 14, or only the photosensor P2 is provided to detect the toner adhesion amount on the transfer intermediate 20. The copier may be configured to detect.

The photosensitive member 14 to which the reflected light from the exposure optical system 12 is irradiated is configured to be driven to rotate in the counterclockwise direction (arrow shown in the figure) by the driving roller 23 and the driven roller 30.

In the vicinity of the outer periphery of the driven roller 30, a cleaning device 31 for removing the toner remaining on the photoconductor 14,
Static elimination lamp unit 32 for eliminating static electricity on the photoconductor 14 and the photoconductor 14
A charging charger 33 for charging is disposed in this order along the rotation direction of the photoconductor 14.

The cleaning device 31 is provided with cleaning blades 31a made of, for example, urethane. These cleaning blades 31a are pressed against the photoconductor 14 so as to scrape off, for example, toner remaining on the photoconductor 14. It is configured.

Above the photoconductor 14, a black and white developing tank 43 and color developing tanks 44, 45 and 46 are arranged in a non-contact state with the photoconductor 14. Color developing tanks 44, 45 and
The yellow, magenta, and cyan color developers are contained in 46, respectively.

Next, the operation of the full-color copying machine 10 of this embodiment will be described.

When a copy start switch (not shown) provided in the full-color copying machine 10 is pressed, the copy mode is executed. This copy mode has a copy cycle in which yellow, magenta, and cyan are developed and transferred to the transfer intermediate 20, and when the copy mode is executed, the yellow copy cycle is executed first.

That is, the original document 13 placed on the original document table 11
On the other hand, light is emitted from the light source lamp 12a to perform exposure scanning. The reflected light from the original 13 is passed through the reflecting mirrors 12b, 12c and 12d and the image forming lens 12g, and the color separation filter 12
Separated by h by color component.

The color separation filter 12 is obtained by the above-mentioned exposure scanning.
The light for each color component transmitted through each color filter of h is reflected by the reflecting mirror 12e.
And 12f, the photosensitive member 14 uniformly charged by the charging charger 33 is irradiated, and the photosensitive member 14 is exposed at the P portion.

As a result, a yellow electrostatic latent image corresponding to the image of the original 13 is formed on the photoconductor 14. This electrostatic latent image is developed by a developing magnet roller at a portion facing a developing tank 44 having a yellow developer which is a complementary color of the color separation filter 12h.
The toner image is developed and visualized by the developer supplied by 44a to form a toner image. This toner image is transferred to the transfer intermediate 20 by the primary transfer charger 24.

When this yellow copying cycle ends,
The photoconductor 14 is cleaned by the cleaning device 31 and discharged by the charge eliminating lamp unit 32.

Thereafter, the magenta and cyan toner images are transferred to the transfer intermediate 20 in the same copying cycle as the yellow copying cycle described above.

Therefore, when the yellow, magenta and cyan copying cycles are executed, the toner image for each color component is transferred to the same position on the transfer intermediate 20 by the primary transfer charger 24, and the toner for each color component is transferred. The toner images are completed by superimposing the images.

On the other hand, the papers 15 accommodated in the paper feed cassettes 16 and 17 are fed one by one to the timing roller 21 by the paper feed rollers 18 and 19, and the timing roller 21 is synchronized with the rotational driving of the transfer intermediate body 20. Then, the paper 15 is conveyed between the transfer intermediate 20 and the secondary transfer roller 26.

After the toner image formed on the transfer intermediate body 20 is transferred by the secondary transfer roller 26 to the conveyed paper 15, the peeling plate 27 separates it from the transfer intermediate body 20, and the conveying belt 28 fixes the fixing device. Introduced to 29.

After the toner image is fixed on the paper 15 by the fixing device 29, the paper 15 is ejected to the outside, whereby the one-time copying mode is completed.

Next, the structure of the static elimination lamp unit 32 included in the full-color copying machine 10 will be described.

FIG. 3 is a schematic configuration diagram showing the configuration of the static elimination lamp unit 32.

As shown in the figure, the static elimination lamp unit 32
Is a static elimination lamp 32a, 32b, 32c, 32d, 32e, 32f, 32g each consisting of, for example, 10 fuse lamp bulbs.
, 32h, 32i and 32j.

The static elimination lamps 32a to 32j are provided on the same substrate 35, and are provided parallel to the surface of the photoconductor 14 along the width direction of the belt-shaped photoconductor 14. Static elimination lamp 32
Voltages are individually applied to a to 32j, and the illuminance (light intensity) of each static elimination lamp can be changed by the applied voltage.

Next, a control device included in the full-color copying machine 10 for uniformly controlling the toner adhesion amount in the toner image formed on the photoconductor 14 will be described.

FIG. 4 is a block diagram showing an embodiment of the configuration of this control device.

As shown in the figure, the control device 50 of this embodiment includes an output amplifier 51, a CPU (central processing unit).
52 and a discharge lamp control unit 53.

The output amplifying section 51 is a photo sensor for detecting the toner adhesion amount of the toner image formed on the photoconductor 14 shown in FIG.
It is connected to P1 and is configured to amplify the output signal from the photosensor P1.

The CPU 52 receives the amplified output signal of the photosensor P1 sent from the output amplifier 51, and
A static elimination lamp 32a included in the static elimination lamp unit 32 for static eliminating the photoconductor 14 so that the toner adhesion amount of the toner image formed on the photoconductor 14 becomes uniform based on this output signal.
It is configured to determine the applied voltage to ~ 32j.

The static elimination lamp control unit 53 is a static elimination lamp unit.
32, that is, the charge removal lamp units 32, which are respectively connected to the charge removal lamps 32a to 32j, and which remove the charge from the photoconductor 14 based on a signal corresponding to the voltage applied to the charge removal lamps 32a to 32j from the CPU 52, are controlled. Is configured.

In this embodiment, the control device 50 is a photoreceptor
Although an example is shown, which is connected to the photo sensor P1 that detects the toner adhesion amount of the toner image formed in 14 and is configured to control the charge eliminating lamp unit 32 based on the output signal of the photo sensor P1. The control device 50 is connected to a photo sensor P2 that detects the toner adhesion amount of the toner image formed on the transfer intermediate 20, and is configured to control the static elimination lamp unit 32 based on the output signal from the photo sensor P2. May be.

The photoconductor 14 is an example of the photoconductor of the present invention. The transfer intermediate 20 is an example of the transfer body of the present invention.
The primary transfer charger 24 is an embodiment of the transfer means of the present invention. Secondary transfer roller 26, peeling plate 27, conveyor belt
28 and the fixing device 29 are examples of the image forming means of the present invention. Static elimination lamp unit 32 and static elimination lamp 32a
32j is an embodiment of the charge eliminating means of the present invention. The photo sensor P1 or P2 is an embodiment of the detecting means of the present invention.
The CPU 52 and the static elimination lamp control section 53 are an example of the control means of the present invention.

Next, the operation of the control device 50 will be described.

FIG. 1 shows a control device 50, in particular a control device.
6 is a flowchart showing an operation of a CPU 52 included in 50. FIG. 5 shows the position of the photoconductor 14 in the width direction and the photosensor from the front end to the rear end of the photoconductor 14.
7 is a graph showing an example of a relationship with a sensor output corresponding to the toner adhesion amount detected when P1 scans. FIG. 6 is a graph showing an example of the relationship between the light amount of the static elimination lamp included in the static elimination lamp unit and the charging potential of the photoconductor. Figure 7
Is the relationship between the position in the width direction of the photoconductor 14 and the sensor output corresponding to the toner adhesion amount detected when the photosensor P1 scans from the front end to the rear end of the photoconductor 14. It is a graph which shows another example.

Here, based on the output signal of the photo sensor P1 which detects the toner adhesion amount of the toner image formed on the photoconductor 14, the charge removal lamp unit 32 is set so as to make the toner adhesion amount on the photoconductor 14 uniform. An example of the operation when controlling will be described.

As shown in FIG. 1, first in step ST1, a start switch for executing the detection of the toner adhesion amount is detected via an operation panel (not shown) provided in the full-color copying machine 10 in FIG. It is determined whether or not it has been pressed (turned on). When it is determined that the start switch is turned on, the process proceeds to step ST2, and when it is determined that the start switch is not turned on, the operation ends.

Next, in step ST2, the document table 11
Light source lamp 12a on halftone patch 11a
To radiate light to form a halftone image on the photoconductor 14. At this time, the amount of light emitted from the light source lamp 12a is
The amount of light is such that a halftone image can be obtained on the photoconductor 14.

Next, in step ST3, the toner adhesion amount of the halftone image formed on the photoconductor 14 through the charging, exposure and development of the photoconductor 14 is measured by the photosensor P1 from the front end of the photoconductor 14. Detects up to the rear end.

Next, in step ST4, the photo sensor
It is determined whether the toner adhesion amount detected by P1 is within a predetermined allowable range from the front end of the photoconductor 14 to the rear end. When it is determined that the detected toner adhesion amount is within the predetermined allowable range, the operation is ended, and when it is determined that the toner adhesion amount is not within the predetermined allowable range, the process proceeds to step ST5.

This determination may be made directly based on the toner adhesion amount or based on the sensor output from the photo sensor P1 corresponding to the toner adhesion amount.

For example, as shown in FIG. 5, a photo sensor
The sensor output S1 corresponding to the toner adhesion amount detected by P1 exceeds the allowable range D of uniformity in the range from the position X in the width direction of the photoconductor to the end portion on the rear side. In the range from X to the end on the rear side, the image becomes dark and the uniformity is broken.

The allowable range D of uniformity can be set in advance so that the uniformity of the copied image does not pose a problem.

In the case of this example, it is determined in step ST4 that the detected toner adhesion amount is not within the predetermined allowable range D, and the process proceeds to step ST5.

Next, in step ST5, the light quantity of the static elimination lamps 32a to 32j included in the static elimination lamp unit 32 as shown in FIG. 6 and the charging potential of the photoconductor are adjusted so that the toner adhesion amount becomes uniform. Based on the relationship, among the static elimination lamps 32a to 32j included in the static elimination lamp unit 32, the voltage applied to the static elimination lamp corresponding to the position of the photoconductor exceeding the allowable range D is obtained.

According to the relationship shown in FIG. 6, as the light quantity of the charge eliminating lamp is increased (from LA to LB), that is, as the voltage applied to the charge eliminating lamp is increased, the charging potential of the photoconductor becomes lower (only ΔV). Lower). Using this relationship, the voltage applied to the charge eliminating lamp is determined so that the toner adhesion amount becomes uniform.

A signal corresponding to the voltage applied to the static elimination lamp thus obtained is sent from the CPU 52 to the static elimination lamp control unit 53, and based on this signal, the static elimination lamp control unit 53.
Applies a voltage to the static elimination lamps 32a to 32j included in the static elimination lamp unit 32 for static eliminating the photoconductor 14.

In this state, the photoconductor 14 is destaticized, the process returns to step ST2 again, and the operations from step ST2 to step ST4 are repeated.

By repeating the operation from step ST2 to step ST4, or when the operation of step ST4 is executed for the first time, it is determined that the toner adhesion amount detected by the photosensor P1 is within the predetermined allowable range D. Then, the operation ends.

As shown in FIG. 7, reference numerals A to J shown along the horizontal axis represent sections in the width direction of the photoconductor that are respectively neutralized by the static elimination lamps 32a to 32j, and are indicated by solid lines. The sensor output S1 is similar to the sensor output shown in FIG.

That is, by the above-mentioned operation, in this example, the applied voltages to the charge eliminating lamps 32h, 32i and 32j corresponding to the sections H, I and J of the photoconductor are obtained, and the charge eliminating lamps 32h, 32i and 32j are brightened. By doing so, the charging potentials of the sections H, I, and J are lowered, and the toner adhesion amount is reduced. As a result, the sensor output from the photosensor P1 falls within a predetermined allowable range D such as the sensor output S2 shown by the broken line. Enter inside.

Therefore, the toner adhesion amount of the toner image formed on the photoconductor can be made uniform. As a result, the toner adhesion amount of the toner image transferred to the transfer intermediate 20 is stable, and a stable copy image can be formed.

The control device 50 included in the full-color copying machine 10 is provided with a ROM (read only memory) (not shown) to uniformly control the toner adhesion amount on the photosensitive member shown in FIG. The operation based on the flowchart for is programmed in advance, and its program is stored in this ROM. The program stored in the ROM can be read and executed by the CPU 52.

According to the above-described embodiment, the toner adhesion amount of the toner image formed on the photoconductor is measured by the photosensor from the front end to the rear end along the width direction of the photoconductor. Based on the detection result, the CPU 52 obtains the applied voltage to each of the plurality of charge eliminating lamps included in the charge eliminating lamp unit for eliminating the charge on the photoconductor, and controls the light quantity of the charge eliminating lamp based on the applied voltage. It Therefore, by automatically adjusting the toner density of the toner image formed on the photoconductor or the transfer body, it is possible to obtain a copy image with stable uniformity.

It should be noted that, based on the output signal of the photo sensor P2 for detecting the toner adhesion amount of the toner image formed on the intermediate transfer member 20, the charge eliminating lamp unit 32 is arranged so as to make the toner adhesion amount on the photosensitive member 14 uniform. Regarding the operation when controlling
The operation is basically similar to that described above.

In the electrophotographic copying machine of the above-described embodiment, the toner adhesion amount of the toner image formed on the photoconductor or the intermediate transfer member is detected by the photosensor, and the photoconductor is detected based on the detected toner adhesion amount. The control signal is fed back to the static elimination lamp unit in order to make the above toner adhesion amount uniform, but the control signal is fed back not only to the static elimination lamp unit but to the surface potential of the photoconductor or the developing bias. You may.

[0083]

As described above, according to the present invention, the photoconductor, the transfer means for transferring the toner image formed on the photoconductor according to the original image to the transfer body, and the transfer means transfers the toner image to the transfer body. Image forming means for forming a toner image on a sheet,
A static eliminator that neutralizes the photoconductor after the toner image is transferred to the transfer body, and a toner amount of the toner image formed on either the photoconductor or the transfer body in the width direction on either the photoconductor or the transfer body. And a control means for controlling the voltage applied to the charge eliminating means so that the amount of toner detected by the detection means is within a predetermined range. By automatically adjusting the toner amount of the toner image formed on the body, it is possible to obtain a copy image with stable uniformity.

[Brief description of drawings]

FIG. 1 is a flowchart showing an operation of a CPU included in a control device.

FIG. 2 is a side view showing the configuration of a full-color copying machine which is an embodiment of the electrophotographic copying machine according to the present invention.

FIG. 3 is a schematic configuration diagram showing a configuration of a charge eliminating lamp unit.

FIG. 4 is a block configuration diagram showing an example of a configuration of a control device.

FIG. 5 is an example of a relationship between a position in the width direction of the photoconductor and a sensor output corresponding to the toner adhesion amount detected when the photosensor scans from the front end to the rear end of the photoconductor. It is a graph which shows.

FIG. 6 is a graph showing an example of a relationship between a light amount of a charge eliminating lamp included in the charge eliminating lamp unit and a charging potential of a photoconductor.

FIG. 7 is a diagram showing the relationship between the widthwise position of the photoconductor and the sensor output corresponding to the toner adhesion amount detected when the photosensor scans from the front end to the rear end of the photoconductor. It is a graph which shows the example of.

[Explanation of symbols]

 10 Full-color copier 14 Photoconductor 20 Transfer intermediate 24 Primary transfer charger 26 Secondary transfer roller 27 Separation plate 28 Conveyor belt 29 Fixing device 32 Static elimination lamp unit 32a to 32j Static elimination lamp P1, P2 Photo sensor 50 Control device 52 CPU 53 Static elimination lamp controller

Claims (1)

[Claims] 1. A photoconductor, and transfer means for transferring a toner image formed on the photoconductor to a transfer body according to an original image,
An image forming means for forming a toner image transferred onto the transfer body by the transfer means on a sheet, a charge removing means for removing charge from the photoconductor after the toner image is transferred onto the transfer body, the photoconductor and the Detecting means for detecting the toner amount of the toner image formed on either one of the transfer bodies along the width direction on either the photosensitive body or the transfer body, and the toner amount detected by the detecting means is predetermined. And a control means for controlling the voltage applied to the static elimination means so that the voltage is within the range.