JP2001350353A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable transfer performance and an excellent image regardless of an environmental condition such as humidity. SOLUTION: Toner images formed by respective image forming parts Pa, Pb, Pc and Pd are successively transferred to recording material P carried on the surface of a transfer belt 130 by transfer electrifiers 24a, 24b, 24c and 24d so as to superpose the toner images on the material P. For example, in the case of forming only the black toner image by the image forming part Pd, the toner images are not formed in other three color image forming parts Pa, Pb and Pc. At such a time, in order to prevent faulty transfer occurring because the transfer current of the black image forming part Pd passes the material P and is discharged from the electrifiers 24c, 24b and 24a, transfer current output power sources 70c, 70b and 70a are controlled by a control means 80 so that the electrifiers 24c, 24b and 24a are constant-current controlled.

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 such as an electrophotographic copying machine and a laser printer.

[0002]

2. Description of the Related Art In an image forming apparatus, an endless recording material carrier for carrying and transporting a recording material on its surface, and a plurality of image forming units (for example, A color image forming apparatus including four image forming units for forming yellow, magenta, cyan, and black toner images) is known.

In the above-described image forming apparatus, in each image forming section, a primary charger, an exposing device, and a developing device form a toner image of each color on a photosensitive drum (image carrier). The image is sequentially transferred onto a recording material on a transfer belt (recording material carrier) by applying a transfer bias to a transfer charger provided in each image forming unit, and the images are superimposed. The image is fixed on a recording material to obtain a color image.

In such an image forming apparatus, when the image to be formed is a full-color image, the process equipment such as a primary charger, an exposing unit, and a developing unit is operated in all four image forming units to perform color printing. While the image is formed, if the image to be formed is a black and white image, in each of the image forming units for yellow, magenta, and cyan other than black, the operation of the primary charger and the developing device is stopped, There is an image forming apparatus in which deterioration of a primary charger, a developing device, a photosensitive drum, and the like is reduced to extend the life. Further, for example, the color characteristics of the original image are detected in advance, and among the four image forming units, one to three (1 to 3) that are not used for image formation are used.
In some image forming units, the developing unit is stopped.

[0005]

However, as described above, when performing the entire image formation in a state where the operation of the process equipment is stopped in some image forming units, the transfer charger is required to form a full-color image. Similarly, when operated in all image forming units, memory is generated in the photosensitive drum due to transfer charging in the image forming unit in which the operation of the process device is stopped, or the potential of the transfer belt increases, Image defects sometimes occurred.

Here, in order to prevent this defect, when the operation of the process equipment is stopped, the transfer charger corresponding to the image forming section having the process equipment is grounded. However, in this case, there is a problem that transfer failure occurs in a high humidity environment. This is because the transfer charge in the transfer section of the image forming section for forming an image escapes to the adjacent transfer charger through the recording paper.

In order to solve such a problem, for example, a configuration has been proposed in which a mechanism for contacting and separating the transfer charger is provided, and the transfer charger corresponding to the image forming unit for stopping the process equipment is separated. ing. Similarly, a configuration has been proposed in which a mechanism for contacting and separating the recording material carrier is provided to separate the recording material carrier at a position corresponding to the image forming unit for stopping the process device.

However, such a configuration causes new problems such as an increase in the number of components, an increase in the size of the image forming apparatus main body, and a complicated control. Further, as described above, if the transfer charger and the recording material carrier are separated from each other, it becomes impossible to sandwich the recording material and the conveyance force of the recording material is reduced, which causes a problem of causing a color shift. .

The present invention has been made in view of the above circumstances, and an image forming unit that can select an image forming unit to be used for image formation from a plurality of image forming units and does not perform image formation. It is an object of the present invention to provide an image forming apparatus capable of obtaining a stable image transferability and a good image regardless of environmental conditions such as humidity in the presence of the image forming apparatus.

[0010]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier having a latent image; and a developing means for developing the latent image on the image carrier with a developer. And a transfer unit that electrostatically transfers the developer image formed on the image carrier in the image forming unit to the medium unit by applying a charge by contacting the medium unit; and A current control unit for controlling a current flowing to the transfer unit, wherein the current control unit is used for image formation in an image forming apparatus capable of selecting an image forming unit used for image formation from the plurality of image forming units. The current flowing through the transfer unit corresponding to the image forming unit that is not performed is controlled to be substantially zero.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the current control means includes a power supply for applying a current to the transfer means and a power supply control means for controlling the power supply. Having.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the current control means includes a power supply for applying a current to the transfer means, a nonlinear element having a predetermined withstand voltage, A switching unit for switching between a power supply and the nonlinear element.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the non-linear element is connected to a transfer unit corresponding to an image forming unit not used for image formation. It is characterized by.

According to a fifth aspect of the present invention, there is provided the third or fourth aspect.
Wherein the predetermined withstand voltage is set to a value corresponding to a maximum output voltage of the power supply.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth aspects, the nonlinear element is a varistor or a Zener diode.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the transfer means has conductivity and has a blade shape, a brush shape, or a roller shape. It is characterized by the following.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image forming section has a charging unit for charging the image carrier, and is used for image formation. In an image forming unit that is not operated, at least one of the operation of the charging unit and the operation of the developing unit is stopped.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the medium unit is a transfer material on which the developer images on the plurality of image forming units are directly transferred. Is a transfer material carrier capable of carrying and transporting the same.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the medium unit can directly transfer the developer images on the plurality of image forming units onto the image forming unit. And an intermediate transfer member.

[0020]

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

<Embodiment 1> FIG. 1 shows an example of an image forming apparatus according to the present invention. FIG. 2 is an enlarged view of an image forming unit of the image forming apparatus.

The image forming apparatus shown in FIG. 1 is a four-color full-color laser printer, and has a transfer belt 130 as a transfer material carrier (medium means) for carrying and transporting a recording material P on its surface, and its rotating direction. Four image forming units arranged in order from the upstream side along the (arrow R130 direction), that is, a first (yellow) image forming unit Pa, a second (magenta) image forming unit Pb, and a third (magenta) image forming unit Pb (Cyan) image forming unit Pc and a fourth (black) image forming unit Pd. The transfer belt 130 is stretched around the driving roller 13, the driven roller 15, and the like.

First to fourth image forming units Pa, Pb, P
c and Pd each have a dedicated image carrier, in this embodiment, a drum-type electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 3a, 3b, 3c, 3d, and these photosensitive drums A toner image (developer image) of each color is formed on 3a, 3b, 3c, and 3d.

Exposure lamps 111a, 111b and 111 are provided around the photosensitive drums 3a, 3b, 3c and 3d, respectively.
c, 111d, drum chargers (primary chargers) 2a, 2b, 2c, 2d as charging means, potential sensors 113a, 1d
13b, 113c, 113d, developing device 1 as developing means
a, 1b, 1c, 1d, transfer charger 24 as transfer means
a, 24b, 24c, 24d and cleaners 4a, 4
b, 4c and 4d are provided, and a light source device (not shown) and a polygon mirror 117 are further provided on the upper part of the image forming apparatus main body.
Are arranged.

The laser light emitted from the light source device is scanned by rotating the polygon mirror 117, the light beam of the scanned light is deflected by the reflection mirror, and is scanned on the generatrix of the photosensitive drums 3a, 3b, 3c and 3d by the fθ lens. By exposing and condensing light, an electrostatic latent image corresponding to an image signal is formed on the photosensitive drums 3a, 3b, 3c, and 3d.

The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of yellow, magenta, cyan, and black toner, respectively, as a developer by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the electrostatic latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and develop them as a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image ( Visualization).

The recording material P is accommodated in a recording material cassette 10, supplied from the recording material cassette 10 via a paper feed roller, a plurality of conveying rollers, and a registration roller 12 to a transfer belt 130.
The photosensitive drums 3a, 3b,
The sheets are sequentially sent to the transfer section facing 3c and 3d.

The transfer belt 130 is made of a dielectric resin sheet such as a polyethylene terephthalate resin sheet (PET resin sheet), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet. An endless shape or a seamless (seamless) belt is used. The transfer belt 130 will be further described later.

The above-mentioned transfer belt 130 is driven by the driving roller 13.
When it is confirmed that the recording material P is at a predetermined position, the recording material P is sent out from the registration roller 12 to the transfer belt 130, and is conveyed toward the transfer unit of the first image forming unit Pa. . At the same time, the image write signal is turned on, and the first
The image is formed on the photosensitive drum 3a of the image forming unit Pa. Then, the transfer charger 24a applies an electric field or electric charge in the lower transfer section of the photosensitive drum 3a, so that the first color toner image formed on the photosensitive drum 3a is transferred onto the recording material P. The recording material P is transferred to the transfer belt 1 by this transfer.
The sheet is firmly held on the sheet 30 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter. Note that the recording material P is not electrostatically attracted onto the transfer belt 130 at the same time as the transfer.
Before transfer, it may be adsorbed by the adsorption charger 5.
As the adsorption charger 5, a non-contact charger such as corona discharge or a contact charger using a charging member such as a blade, a roller, or a brush can be used.

As the transfer charger 24a, a contact charger using a transfer charging member such as a blade, a roller, or a brush is used. The contact charger has advantages such as ozonelessness, resistance to temperature and humidity environmental changes, and high image quality. In addition, static elimination needles 7a to 7d may be provided for stabilizing transferability. Static elimination needle 7a
7d are not in contact with the transfer belt 130, but play a role to discharge and release a part of the transfer current. With this configuration, it is possible to prevent discharge due to uneven charging after the recording paper P is peeled from the photosensitive drum.

Image formation and transfer in the second to fourth image forming units Pb to Pd are performed in the same manner as in the first image forming unit Pa. Next, the recording material P on which the four color toner images have been transferred is removed from the end of the transfer belt 130 by being discharged by the separation charger 32 at a downstream portion of the transfer belt 130 in the transport direction and attenuating the electrostatic attraction force. . In particular, in a low-humidity environment, the recording material P dries and the electrical resistance increases, so that the electrostatic attraction force with the transfer belt 130 increases, and the separation charger 3
The effect of (2) becomes large. Usually, the separation charger 32 charges the recording material P in a state where the toner image is not fixed, so that a non-contact charger is used.

The output of the separation charger 32 is the peak-to-peak voltage Vp
An AC voltage having a p of 10 kV and a frequency of about 500 Hz is used. Further, in order to prevent image defects such as toner scattering, in addition to the above-described AC output, a plus of about 100 μA,
Alternatively, a negative DC component may be superimposed.

Recording material P separated from transfer belt 130
Is transported to the fixing device 9 by the transport unit 62. The separation guide 64 stabilizes the leading end behavior of the recording material P.

The fixing device 9 includes a fixing roller 51, a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning these, a fixing roller 51, and a pressure roller 5.
2, roller heaters 56 and 57, an application roller 50 that applies a release agent oil such as dimethyl silicone oil to the fixing roller 51, and an oil reservoir 53.
And a thermistor 58 that detects the temperature of the surface of the pressure roller 52 and controls the fixing temperature.

The recording material P to which the four color toner images have been transferred is
By the fixing, the color mixture of the toner image and the fixation to the recording material P are performed, a full-color image is formed, and the toner image is discharged onto the paper discharge tray 63.

The photosensitive drums 3a, 3b, 3 after the transfer is completed
c, 3d are the respective cleaners 4a, 4b, 4c, 4
The transfer residual toner is cleaned and removed by d, and is subsequently used for the next image formation. The toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing the cleaning blade 20 and the cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130.

In the cleaner section, the recording material P
The charge of the transfer belt 130 remaining after the toner image is separated is removed by the grounding discharging rollers 21 and 22. A configuration may be employed in which a high voltage of about 2 to 4 kV is applied to the charge removing roller 21 to not only remove the charge from the transfer belt 130 but also charge the battery to the opposite potential so that the potential of the transfer belt at the end of transfer is reduced.

The transfer belt 130 used in the image forming apparatus having the above-described structure is a dielectric sheet such as a PET sheet, a polyvinylidene fluoride sheet, or a polyurethane sheet as described above.
Those having ¹³ to 10 ¹⁸ Ω · cm are generally used. Also,
It is known that the transfer charging unit stabilizes an image when the current contributing at the time of transfer is fixed at an appropriate current. Therefore,
Depending on the type (thickness, material, etc.) of the recording material P and moisture absorption conditions,
In general, constant current control is performed so that a constant current can be obtained even when the volume resistance value changes.

In the above-described image forming apparatus, when the image to be formed is a full-color image, the yellow, magenta, cyan, and black toner images are sequentially formed as described above. The operation of at least one of the primary charger (charging unit) and the developing unit (developing unit) is stopped for the color in which only the toner image is formed and the image is not formed. by this,
Long life is achieved by reducing the deterioration of the primary charger, the developing device, the developer and the like and the scratches on the photosensitive drum. Further, for example, there is a case where a color feature of a document image is detected in advance, and a developing device in a single-color, two-color, or three-color image forming unit that is not used for image formation is stopped.

However, in the case where the image forming section which does not form an image is provided as described above, when the transfer charger is operated in all colors as in the case of full-color image formation, the memory of the photosensitive drum by transfer charging, the transfer belt An image defect occurred due to the rise in the potential.

In order to prevent such an image defect, when an image forming section not performing image formation is provided, the corresponding transfer charger is grounded and operated. There was a problem of getting up. The reason is that the transfer charge in the transfer section escapes from the adjacent transfer charger through the recording paper P.

In the present invention, such a problem has been solved as follows.

Here, as the dielectric sheet material for the transfer belt 130, in addition to the above, polyacetal, polyamide, polyvinyl alcohol, polyether ketone,
Polystyrene, polybutylene terephthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide, polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyether imide, aromatic polyimide, etc. Engineering plastic film-shaped sheets are commonly used. In the present embodiment, a polyimide resin is used in terms of mechanical properties, electrical properties, flame retardancy, and the like. A seamless type having a volume resistivity of 10 ¹⁶ Ω · cm and a thickness of 100 μm was used. The transfer chargers 24a, 24b, 24c, and 24d are formed of a rectangular plate-like conductive rubber that extends in a direction (hereinafter, referred to as a “thrust direction”) orthogonal to the conveying direction (the direction of the arrow R) of the recording material P. ing. The plate-shaped conductive rubber is transferred to the photosensitive drums 3a, 3b, 3c, 3 via the transfer belt 130.
d. This transfer charger 2
4a to 24d, the photosensitive drum 3 is charged by charging the toner (minus in the present embodiment) with the opposite polarity (plus) from the back side of the recording material P conveyed to the transfer section.
The toner images on the sides a to 3d are electrostatically transferred to the surface of the recording material P. In this embodiment, the constant current control is performed, and the transfer current is set to 12 μA. Use a black and white manuscript,
A black and white manuscript was output. At this time, yellow, magenta,
In the cyan image forming units Pa, Pb, and Pc, the primary chargers 2a, 2b, 2c, and the developing devices 1a, 1a,
The operations of b, 1c, etc. are stopped.

Now, with the above configuration, the transfer current of the black transfer charger 24d was set to 12 μA, and the transfer current was not grounded to the yellow, magenta, and cyan transfer chargers 24a, 24b, and 24c. The black transfer current did not flow toward the black photosensitive drum 3d, but flowed into the cyan transfer charger 24c, causing an image defect. At this time, the current flowing into the cyan transfer charger 24c was 3 μA.

Therefore, as shown in FIG. 2, the control means (power control means) 80 controls the transfer current output power so that the transfer current flowing through the transfer chargers 24a, 24b and 24c for yellow, magenta and cyan becomes 0 μA. (Power supply) 70
a, 70b and 70c were controlled. That is, the control means 80 and the transfer current output power supply constitute a current control means. With this configuration, a good image was obtained without the black transfer current flowing into the cyan transfer charger 24c.

The transfer current of the transfer charger corresponding to the image forming section of a color in which no image is formed is set to 0 μA not only when forming a single color image but also when forming a two-color image and a three-color image.
By controlling the constant current, a good image was obtained. It should be noted that substantially the same effects as described above could be obtained even when a conductive brush or a conductive roller was used as the transfer chargers 24a, 24b, 24c, and 24d instead of the conductive blade.

The current control value of the transfer means corresponding to the image forming section where image formation is not performed is most preferably 0 μA. However, the present invention can be applied to a transfer means having a substantially zero range in which transfer failure due to escape of transfer charge does not occur. The effect of can be obtained.

Second Embodiment FIG. 3 shows a second embodiment. In the present embodiment, transfer current output power supplies 71a, 71b, 71c, 71d
Separately, varistors (non-linear elements) 72a, 7 having a predetermined withstand voltage
2b, 72c, and 72d are connected, and a switch 73 serving as a switching unit when image formation is not performed.
a, 73b, 73c and 73d connect the transfer charger to the varistor 7 from the transfer current output power supplies 71a to 71d.
By switching to 2a to 72d, the impedance is changed so that the transfer charge from the part where the image is formed does not flow. With respect to the withstand voltage of the varistor, if the maximum value of the output voltage of the transfer charger when forming a three-color image is, for example, 6 kV, the withstand voltage of the varistors 72 a to 72 d is similarly set to 6 kV.

In the configuration of this embodiment, the transfer current of the black transfer charger 24d is set to 12 μA and the transfer current of the yellow, magenta, and cyan transfer chargers 24a, 24b, and 24c is formed when forming a monochrome image. The switch 73 is connected to connect the varistors 72a, 72b, 72c from the power supply.
Switching between a, 73b and 73c is performed by the control means 81.

With this configuration, a good image was obtained without the black transfer current flowing into the cyan transfer charger. Similarly, the transfer chargers corresponding to the image forming units of the colors that do not perform image formation not only at the time of forming a single color image but also at the time of forming a two-color or three-color image are connected.
A good image was obtained by switching from the transfer current output power supply to the varistor. The transfer chargers 24a, 24
As b, 24c, 24d, instead of the conductive blade,
Even when a conductive brush and a conductive roller were used, substantially the same effects as described above could be obtained. Also, a zener diode can be used as a nonlinear element instead of a varistor.

<Embodiment 3> Referring to FIGS. 4 and 5,
Embodiment 3 will be described. This embodiment is characterized in that the present invention is applied to an image forming apparatus provided with an intermediate transfer belt which is an intermediate transfer member (medium means).

First, the overall configuration and functions of the image forming apparatus according to the present embodiment will be described with reference to FIG.

The image forming apparatus according to the present embodiment is provided with an intermediate transfer belt (intermediate transfer belt) as a medium, which is stretched over a driving roller 112a, a driven roller 112b, and a secondary transfer opposing roller 112c and runs in the direction of arrow X. The image forming units (stations) Pa, Pb, Pc, and Pd are arranged in series above the plane part.

The image forming units Pa to Pd form magenta, cyan, yellow, and black toner images, respectively.

The magenta image forming unit Pa includes a primary charger 102a, an exposure unit 110 around a photosensitive drum 101a.
a, a developing device 103a, and a cleaner 104a. The other image forming units Pb to Pd have the same configuration. That is, the other image forming units Pb, Pc, Pd
Photosensitive drums 101b, 101c, 101d, exposure units 110b, 110c, 110d, primary charger 102, respectively
b, 102c, 102d, developing units 103b, 103c,
103d and cleaners 104b, 104c, 104d are provided. A transfer charger (charging roller) 1 as a primary transfer unit is provided at a position corresponding to the photosensitive drums 101b, 101c, and 101d with the transfer belt 190 interposed therebetween.
05b, 105c, and 105d are provided.

The magenta toner image is formed on the photosensitive drum 101a.
When the toner reaches the primary transfer portion where the toner and the intermediate transfer belt 190 come into contact with each other, the image is transferred to the intermediate transfer belt 190 by the first transfer bias applied by the transfer charger 105a as the primary transfer charging means. When the intermediate transfer belt 190 carrying the magenta toner image is conveyed to the next image forming unit Pb, by this time, the image forming unit Pb
The cyan toner image formed on the photosensitive drum 101b in the same process as above is transferred onto the magenta toner image.

Similarly, as the image forming units Pc and Pd progress, the yellow toner image and the black toner image are superimposed and transferred on the toner images in the respective primary transfer units. The recording material P taken out of the sheet supply roller 107 by the sheet feed roller 107 reaches the registration roller 108, and is further synchronized with the toner image to form a secondary transfer facing roller 112c and a secondary transfer device 140 as a secondary transfer charging unit. Are transferred to the secondary transfer unit formed by the printer, and the toner images of the four colors described above are transferred onto the recording material P by the transfer bias applied to the secondary transfer device 140. The recording material P after the transfer of the toner image is further transferred to the fixing device 1.
Then, the toner image is fixed to the surface by applying heat and pressure thereto, and then discharged outside the image forming apparatus main body (outside the machine).

The residual toner remaining on the intermediate transfer belt 190 after being transferred to the recording material P is removed by the cleaning device 1.
13 to be collected. This cleaning device 113
Has a cleaning blade 115 made of, for example, polyurethane rubber, and its edge is brought into contact with the intermediate transfer belt 190 to scrape off and remove attached toner.

FIG. 5 is an enlarged view of the image forming section of the image forming apparatus shown in FIG.

The primary transfer section in this embodiment uses conductive transfer rollers 105a, 105b, 105c, and 105d as primary transfer means (transfer charger). Transfer current output power supplies 170a, 170b, 170c, and 170d are connected to the transfer rollers 105a to 105d, respectively.
Outputs of 0a to 170d are controlled by the control unit 180.

In the image forming apparatus having such a configuration,
For example, when outputting a black image corresponding to a monochrome original, the magenta, cyan, and yellow image forming units P
a, Pb, and Pc do not perform image formation, and the primary charger 1
The operations of 02a to 102c, developing units 103a to 103c, and the like are stopped.

The transfer current of the black transfer roller 105d is controlled to, for example, 10 μA, and the transfer rollers 105a to 105c of magenta, cyan, and yellow are controlled.
Is controlled to be 0 μA. By doing so, the black transfer current does not flow into the adjacent yellow transfer roller 105c,
Good images were obtained.

The transfer current of the transfer roller corresponding to the image forming portion of the color in which no image is formed is set to 0 μA not only when forming a single-color image but also when forming a two-color image and a three-color image.
, A good image was obtained. In addition, as the transfer charger, conductive transfer rollers 105 a to 105
Even when a conductive brush or conductive blade was used instead of d, substantially the same effects as described above could be obtained.

In the present embodiment, a belt-shaped intermediate transfer belt is used as the intermediate transfer body as the medium means.
Instead, a drum-shaped intermediate transfer drum may be used.

The current control value for the transfer roller corresponding to the image forming section where image formation is not performed is most preferably 0 μA. However, the present invention can be applied to a transfer roller having a substantially zero range in which transfer failure due to escape of transfer charge does not occur. The effect of can be obtained.

<Fourth Embodiment> FIG. 6 shows a fourth embodiment. In the present embodiment, in addition to the configuration of the third embodiment, the transfer current output power supplies 171a, 171b, 171c,
Apart from 171d, for example, varistors (non-linear elements) 172a, 172b, 172c, 172 having a predetermined withstand voltage
d is connected and switches 173a, 173b, and 17 as switching means when image formation is not performed.
3c and 173d, the connection of the transfer charger is changed from the transfer current output power supplies 171a to 171d to the varistors 172a to 171d.
Switching to 172d, the impedance is changed, and the transfer charge from the portion where the image is being formed does not flow. The switching of the switching units 173a to 173d and the transfer current output power supplies 171a to 171d are controlled by the control unit 181. With respect to the withstand voltage of the varistor, if the highest value of the output voltage of the transfer roller when forming a three-color image is 6 kV based on another examination result, the withstand voltage of the varistors 172 a to 172 d is 6 kV, which is the highest value of the output voltage. did.

In the configuration of the present embodiment, the control means 181
In the case of forming a monochromatic black image, the transfer current of the black transfer charger 105d is set to 10 μA, and the transfer current output power supplies 171a to 171c of the magenta, cyan, and yellow transfer chargers 105a to 105c are supplied to the varistors 172a to 172c.
The connection is switched to 172c.

With this configuration, a good image was obtained without the black transfer current flowing into the cyan transfer roller 105c. Similarly, not only when forming a single color image, but also when forming a two-color or three-color image, the connection of the transfer roller corresponding to the image forming portion of a color that does not form an image is switched from a transfer current output power supply to a varistor. As a result, a good image was obtained. Note that the above-described conductive transfer rollers 105a, 105b, 1
Even when a conductive brush or a conductive blade was used instead of 05c and 105d, substantially the same effects as described above could be obtained. Also, a varistor 17 is used as a nonlinear element.
Instead of 2a to 172d, a Zener diode can be used.

[0069]

As described above, according to the present invention,
It is possible to select an image forming unit to be used for image forming from among a plurality of image forming units, and when there is an image forming unit that does not perform image forming, stable transferability regardless of environmental conditions such as humidity. And good images can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged view of an image forming unit according to the first embodiment.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment.

FIG. 4 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a third embodiment.

FIG. 5 is an enlarged view of an image forming unit according to a third embodiment.

FIG. 6 is an enlarged view of an image forming unit in the image forming apparatus according to the fourth embodiment.

[Explanation of symbols]

1a, 1b, 1c, 1d, 103a, 103b, 103
c, 103d developing means (developing device) 2a, 2b, 2c, 2d, 102a, 102b, 102
c, 102d Charging means (primary charger) 3a, 3b, 3c, 3d, 101a, 101b, 101
c, 101d Image carrier (photosensitive drum) 24a, 24b, 24c, 24d Transfer unit (transfer charger) 70a, 70b, 70c, 70d, 71a, 71b, 7
1c, 71d, 170a, 170b, 170c, 170
d, 171a, 171b, 171c, 171d power supply (transfer current output power supply) 72a, 72b, 72c, 72d, 172a, 172
b, 172c, 172d Non-linear elements (varistor, Zener diode) 73a, 73b, 73c, 73d, 173a, 173
b, 173c, 173d Switching means (switch) 80, 81, 180, 181 Power supply control means (control means) 105a, 105b, 105c, 105d Transfer means (transfer charger, transfer roller) 130 Medium means (transfer material carrier, Transfer belt) 190 Medium means (intermediate transfer body, intermediate transfer belt) P Transfer material (recording material) Pa, Pb, Pc, Pd image forming section 190 Intermediate transfer body (medium means, intermediate transfer belt)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kiichi Yoichi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H030 AB02 BB42 BB44 BB54 2H200 FA01 GA12 GA23 HA02 HB07 HB12 HB14 HB22 JA02 JA28 JA29 JB07 JB08 JB25 JB45 JC03 JC12 LB02 LB08 LB09 LB13 LB14 MA04 MB04 NA02 NA08 NA16 NA22 PA04 PA23

Claims (10)

[Claims] A plurality of image forming units each having an image carrier that carries a latent image and a developing unit that develops a latent image on the image carrier with a developer; By applying a charge by contacting the developer image formed on the medium means,
A transfer unit that performs electrostatic transfer toward the medium unit; a current control unit that controls a current that flows through the transfer unit;
An image forming apparatus capable of selecting an image forming unit to be used for image formation from the plurality of image forming units, wherein the current control unit controls a current flowing to a transfer unit corresponding to an image forming unit not used for image formation. An image forming apparatus, wherein the image forming apparatus is controlled to be substantially zero. 2. The image forming apparatus according to claim 1, wherein the current control unit includes a power supply for applying a current to the transfer unit, and a power supply control unit for controlling the power supply. 3. The current control unit includes a power supply for applying a current to the transfer unit, a nonlinear element having a predetermined withstand voltage, and a switching unit for switching between the power supply and the nonlinear element. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 3, wherein the non-linear element is connected to a transfer unit corresponding to an image forming unit not used for image formation. 5. The image forming apparatus according to claim 3, wherein the predetermined withstand voltage is set to a value corresponding to a maximum output voltage of the power supply. 6. The image forming apparatus according to claim 3, wherein the non-linear element is a varistor or a Zener diode. 7. The image forming apparatus according to claim 1, wherein the transfer unit has conductivity, and has a shape of a blade, a brush, or a roller. 8. The image forming unit includes a charging unit that charges the image carrier. In an image forming unit that is not used for image formation, at least one of the operation of the charging unit and the operation of the developing unit is performed. The image forming apparatus according to claim 1, wherein one of the steps is stopped. 9. The image forming apparatus according to claim 1, wherein the medium unit is a transfer material carrier capable of carrying and transferring a transfer material on which the developer images on the plurality of image forming units are directly transferred. The image forming apparatus according to any one of the above. 10. The image forming apparatus according to claim 1, wherein the medium unit is an intermediate transfer member capable of directly transferring the developer images on the plurality of image forming units onto the image forming unit. Image forming device.