JP2002202652A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of the occurrence of an abnormal image due to toner color mixing inside downstream developing device and residual toner on a developing roller. SOLUTION: This image forming device processes voltage applying means 107M, 107C, 108M and 108C to apply bias voltage at which normal electrified toner receives force applied from toner carriers 101M and 101C toward the image part of a latent image carrier 15 and also force applied from supply members 102M and 102C toward the toner carriers 101M and 101C in the developing state of developing devices 1M and 1C, and to apply bias voltage at which the normal electrified toner receives force applied from the toner carriers 101M and 101C toward the image part and the non-image part of the latent image carrier 15 and also force applied from the toner carriers 101M and 101C toward the supply members 102M and 102C in the non-developing state of the developing devices 1M, 1C, 1Y and 1K.

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 a copying machine, a printer, a facsimile, etc., in which a plurality of developing devices are arranged around a latent image carrier.

[0002]

2. Description of the Related Art A color image forming apparatus in which a plurality of developing devices are arranged around a latent image carrier has been known. In this image forming apparatus, a plurality of developing devices simultaneously perform development, and when some of the developing devices perform development, the other developing devices are in a non-developing state, and the developing devices in the developing state are sequentially changed. In some cases, the development is performed by moving. In the latter image forming apparatus, one writing unit writes for two or more developing devices (writes for forming two or more electrostatic latent images to be developed by two or more developing devices). This method has the advantage that it is excellent in cost because it also serves as a countermeasure, and unlike the former, it does not require complicated control such as changing the polarity of the toner. However, in the case of performing contact development, one developing device carries the developed latent image. An adverse effect may occur such that the toner image on the body is disturbed by another developing device or the color is mixed.

In order to prevent this problem, several types of image forming apparatuses have been proposed. For example, Japanese Patent Laid-Open No. 4-29 discloses an image forming apparatus in which a developing device can be brought into contact with and separated from a latent image carrier.
Japanese Patent Application Laid-Open No. Hei 10-31342 discloses an image forming apparatus that performs development by causing a toner to fly without bringing a developing device into contact with a latent image carrier. However, the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 4-29678 has a disadvantage that an expensive contact / separation mechanism is required to bring the developing device into and out of contact with the latent image carrier. In the image forming apparatus disclosed in JP-A-31342, the edge effect becomes strong, which causes high image quality to be hindered.

[0004] On the other hand, various types of developing devices have been conventionally known. The one-component developing system includes a contact one-component developing system in which the toner on the developer carrier is brought into contact with the latent image carrier, and a flying toner in which the toner on the developer carrier is not in contact with the latent image carrier. There is a non-contact one-component development method in which development is performed by causing the image to be developed. In the non-contact one-component development method, dot thickening occurs due to an edge effect, thereby hindering high resolution. This is advantageous in terms of higher resolution since development can be performed faithfully with respect to.

However, the one-component developing method has problems such as deterioration of the toner due to continuous stirring of the toner in the developing device, and occurrence of an abnormal image due to the toner sticking to the doctor blade serving as a layer thickness regulating member. There is a drawback that is easy to occur. On the other hand, in a two-component developing method in which a developer consisting of a toner and a carrier is used to perform development by rubbing a magnetic brush that has been raised on a latent image carrier, the two-component developing method is one in terms of durability and stability. It is superior to the one-component development system, but is inferior to the one-component development system in performing development faithful to a latent image.

[0006] As a developing method combining such a one-component developing method and a two-component developing method, a magnetic brush is formed on a supply roller by a two-component developing method, and the magnetic brush is rubbed against a developing roller to develop. There is known a developing method in which a toner layer is formed on a roller and one-component development is performed using the toner image. In this developing method, since the layer thickness regulating member is not used when forming the toner layer on the developing roller, the stress on the developing roller and the doctor blade can be reduced as compared with the conventional one-component developing method. The stirring for charging is performed by the two-component developing method, so that the durability is excellent and the high image quality of the one-component developing method can be achieved.

Japanese Patent Laid-Open No. 10-161 discloses an image forming apparatus in which a plurality of developing devices of the type having both the advantages of the one-component developing method and the two-component developing method are arranged around the latent image carrier.
No. 383. In this image forming apparatus, as shown in FIG. 7, developing devices 102 and 103 are arranged around a photoreceptor 101. Developing device 102, 1
Since the developing device 103 has the same shape, the developing device 103 will be described.
a, an intermediate roller 103b, a developer mixing and stirring device 103c,
A developing roller 103a having a doctor blade 103e
Is disposed facing the photoconductor 101 at a small interval, an AC power supply 103f is connected to the developing roller 103a, and a voltage conversion circuit 103g is connected to the intermediate roller 103b.
Is connected. The voltage conversion circuit 103g includes a power supply 103
h and the power source 103i, the power source 103h is selected by the voltage conversion circuit 103g during development, and a voltage of 200 V is applied to the intermediate roller 103b from the power source 103h.
03i is selected, and a voltage of -200 V from the power supply 103i is applied to the intermediate roller 103b.

In the developing device 103 having such a configuration, at the time of development, the two-component developer is stirred by the developer mixing / stirring device 103c, so that the toner is positively charged and the carrier is negatively charged. The stirred developer is supplied to the intermediate roller 10.
The toner is conveyed to a portion where the developing roller 103a and the intermediate roller 103b face each other by a magnet inside 3b. At this time, the thickness of the developer is regulated by the doctor blade 103e. At a portion where the developing roller 103a and the intermediate roller 103b face each other, the developer forms a magnetic brush 103d, and the toner in the magnetic brush 103d is supplied from the power source 103h to the intermediate roller 10d.
Transfer from the magnetic brush 103d to the developing roller 103a by the voltage to 3b. As a result, the developing roller 103
A toner layer is formed on the developing roller 103a. Since a developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing roller 103a from the power source 103f, the toner on the developing roller 103a is a latent image on the photosensitive member 101. The toner adheres to the portion and development is performed. On the other hand, during non-development, a voltage of -200 V is applied from the power source 103i to the intermediate roller 103b, and development is stopped.

In such an image forming apparatus, since the developing roller 103a is disposed to face the photosensitive member 101 at a small interval, development is performed by the developing device 103 on the upstream side in the circumferential direction of the photosensitive member 101. The photoreceptor 10
There is no possibility that the toner image formed on the developing device 1 will be disturbed by the developing device 102 on the downstream side. However, on the other hand, since the developing roller 103a faces the photoconductor 101 at a small interval, non-contact development is performed, which causes dot thickening due to the edge effect, which is not preferable from the viewpoint of high resolution. . In addition, mechanical accuracy is required to maintain a small distance between the developing roller 103a and the photoconductor 101.

[0010]

In the image forming apparatus, in order to achieve high resolution, it is preferable that the developing device contacts the photosensitive member with only the toner layer interposed therebetween. In the case of contact, the toner image on the photoconductor contacts the downstream development device during development with the upstream development device, and a part of the toner on the photoconductor may adhere to the downstream development device. Occurs. If this happens,
The color of the toner is mixed inside the downstream developing device, thereby shortening the life of the developing device.

In an image forming apparatus having a developing device for performing contact development, if a system as disclosed in JP-A-10-161383 is used, the toner on the developing roller is collected by a magnetic brush during non-development. If a part of the remaining toner remains on the developing roller, the remaining toner may adhere to the toner image on the photoconductor and cause an abnormal image. In order to prevent this, all the toner on the developing roller may be collected through the magnetic brush, but since the magnetic brush generally varies in height,
It is difficult to recover 100% of the toner.

Further, not all of the toner is uniformly charged by stirring or the like, and depending on the stirring state, some toner may be charged to the opposite polarity. In this case, when the developing bias for developing and for non-developing is switched by a method as disclosed in Japanese Patent Application Laid-Open No. 10-161383 in a developing device that performs contact development, the oppositely charged toner is supplied to the developing roller during non-developing. And the oppositely charged toner on the developing roller adheres to the non-image area on the photoconductor.

The present invention provides an image forming apparatus capable of preventing the above problems, achieving high resolution at low cost and high durability, and reducing the occurrence of abnormal images due to color mixing. The purpose is to do.

[0014]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a toner carrier which comes into contact with a latent image carrier; and a supply member which supplies toner to the toner carrier. An image forming apparatus, wherein a plurality of developing devices in which the rotation directions of the toner carrier and the latent image carrier are in the same direction at a contact portion of each other are arranged around the latent image carrier. In an image forming apparatus that performs development by sequentially changing developing devices in the developing state so that when some of the developing devices are in the developing state, the other developing devices are in the non-developing state. In the developing state of the developing device, a bias is applied such that normally charged toner receives a force from the toner carrier toward the image portion of the latent image carrier and a force from the supply member toward the toner carrier. Apply voltage In the non-development state of the developing device, the force from the toner carrier to the image portion and the non-image portion of the latent image carrier, and the force from the toner carrier to the supply member are normally charged toner. And a voltage applying means for applying a bias voltage as received by the device.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the switching of the bias voltage at the time of transition between the developing state and the non-developing state is performed by changing a voltage applied to the toner carrier. This is done by switching.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the toner carrier is moved from a point at which the recording member feeds the toner to the toner carrier. A relationship of R1> R2 is established between a distance R2 where the toner on the toner carrier moves to a position where the toner carrier contacts the latent image carrier.

The invention according to claim 4 is the invention according to claim 1 or 2
In the image forming apparatus described in the above, the recording medium transport interval R1
And the peripheral length R3 of the toner carrier, the relationship of R1> R3 holds.

According to a fifth aspect of the present invention, a plurality of developing devices having a toner carrier in contact with the latent image carrier and a supply member for supplying toner to the toner carrier are provided around the latent image carrier. An image forming apparatus, wherein when some of the plurality of developing devices are in the developing state, the developing devices in the developing state are sequentially arranged so that the other developing devices are in the non-developing state. In an image forming apparatus that performs development by changing, in a developing state of the developing device, a force directed from the toner carrier to an image portion of the latent image carrier,
And applying a first-level bias voltage to the toner carrier such that the normally charged toner receives a force from the supply member toward the toner carrier, wherein the toner carrier is in a non-developed state of the developing device. A bias voltage of the second level such that the normally charged toner receives a force from the toner carrier toward the image portion and the non-image portion of the latent image carrier and a force from the toner carrier toward the supply member. First voltage applying means for applying a voltage to the body, and a third level bias voltage such that normally charged toner receives a force from the supply member toward the toner carrier in a developing state of the developing device. And a fourth level at which the normally charged toner receives a force from the toner carrier toward the supply member in the non-developing state of the developing device. Those having a second voltage applying means for applying a bias voltage to the supply member.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, when each of the developing devices shifts from a developing state to a non-developing state, the supply member is first controlled by the second voltage applying means. To the first level, and after a lapse of a predetermined time T1, the first level
The bias voltage of the second level is applied to the toner carrier by the voltage applying means, and the toner carrier contacts the latent image carrier from a position where the supply member supplies the toner to the toner carrier. When the time required for the toner carried on the toner carrier to move to the location is T2, a relationship of T1> T2 is established between T1 and T2.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, each of the developing devices controls a linear velocity Vs of the toner carrier in a non-developing state. 0.9 Vpc with respect to the linear velocity Vpc of the latent image carrier.
≦ Vs ≦ 1.5 Vpc.

[0021]

FIG. 2 shows an outline of a first embodiment of the present invention. Intermediate transfer belt 10 as an intermediate transfer member
Is stretched between a driving roller 11 and a driven roller 12, and is driven to run in the direction of arrow a by being driven to rotate by a driving source (not shown). A first image station 13 and a second image station 14 are arranged on the lower traveling surface of the intermediate transfer belt 10 at a constant interval along the traveling direction of the intermediate transfer belt 10. The length L of the intermediate transfer belt 10 is longer by the non-image area α than the length m in the moving direction of the maximum size recording medium used in the image forming apparatus of the present embodiment. That is, L = m + α
In a relationship.

The first image station 13 includes a charger 16 composed of a roller for uniformly charging the surface of a drum-shaped photosensitive member (photosensitive drum) 15 as a latent image carrier, and a charged surface of the photosensitive member 15. Writing means 17 for writing data with a light beam modulated by an image signal based on a document
, A cyan (hereinafter referred to as C) color developing device 1C, a magenta (hereinafter referred to as M) color developing device 1M, and a cleaning unit 1
8 mainly.

The second image station 14 has substantially the same configuration as the first image station 13, and includes a drum-shaped photosensitive member 19 as a latent image carrier, a charger 20, a writing means 21, and a yellow (Y) ) It mainly comprises a color developing device 1Y, a black (K) color developing device 1K, and a cleaning means 22. The second image station 14 is mounted on the apparatus main body of the present embodiment in the same posture as the first image station 13.

Each of the photoconductors 15 and 19 is rotationally driven by a drive source (not shown), and its rotation is synchronized with the running of the intermediate transfer belt 10. It is determined to match. In addition, as the charging unit, a charging unit using a corona discharger or a brush can be employed instead of the chargers 16 and 20.

The C color developing device 1C contains a cyan toner, and the M color developing device 1M contains a magenta toner. The Y color developing device 1Y contains yellow toner,
The K color developing device 1K contains black toner. These developing devices 1C, 1M, 1Y and 1K are provided with chargers 16 and 20 respectively.
Then, the electrostatic latent images formed on the respective photoconductors 15 and 19 by the known methods by the writing means 17 and 21 are developed. In this embodiment, the toners are all non-magnetic toners,
The toner is normally charged when negatively charged and reversely charged when positively charged. Each developing device 1C, 1M, 1Y, and 1K contains a magnetic carrier in addition to the toner. Note that the present invention is applicable even if the charging polarity of the toner is opposite to that described above.

A first transfer brush 23 and a second transfer brush 24 as transfer means to which a bias voltage for transfer is applied from a power source can freely contact with and separate from the intermediate transfer belt 10 on each of the photoconductors 15 and 19 (moving forward and backward). The transfer roller 25 as a transfer unit to which a bias voltage for transfer is applied is provided on the drive roller 11 so as to be able to freely contact and separate from the intermediate transfer belt 10. A transfer roller can be used instead of the transfer brushes 23 and 24, and the transfer roller 2
A transfer brush can be used instead of 5. Also,
The transfer brushes 23 and 24 and the transfer roller 25 may employ a corona discharger. Further, a transfer unit 2 for transferring a color image by the drive roller 11 and the transfer roller 25
6 are constituted.

Each of the photoconductors 15 and 19 is slightly separated from the intermediate transfer belt 10 slightly downward, and the first transfer brush 23 and the second transfer brush 24 are slightly separated upward from the intermediate transfer belt 10. is seperated. Each photoconductor 15, 19
In the step of transferring the upper toner image to the intermediate transfer belt 10, the intermediate transfer belt 10 comes into contact with the photoconductor 15 and / or 19 by pressing the first transfer brush 23 and / or the second transfer brush 24.

The intermediate transfer belt 10 is placed on the driven roller 12.
Cleaning device 2 for removing toner remaining on the surface of
7 is provided on the intermediate transfer belt 10 so as to be able to freely contact and separate therefrom.
The cleaning device 27 is driven by a contact / separation driving unit of an intermediate transfer body cleaning device (not shown).
The approach / separation from zero is controlled.

Below the first image station 13 and the second image station 14, a paper feeder for feeding the stacked recording media 28 one by one is arranged. A manual feed tray 29 for feeding a recording medium to the printer is disposed. Here, the recording medium is an object on which an image is ultimately formed, such as recording paper or an OHP.
One recording medium sent out from the sheet feeding device or the manual feed tray 29 is fed to the transfer unit 26 by a feed roller pair 30 and a pair of registration rollers 31. A fixing device including a heating roller 32 and a pressure roller 33 that rotates while being pressed against the heating roller 32 is disposed diagonally above the transfer unit 26. The heating roller 32 includes the heating roller 3
A roller (not shown) for applying the anti-offset liquid to the surface of No. 2 abuts as required.

The photoconductor 15 in the first image station 13 and the photoconductor 1 in the second image station 14
9 is exactly the same in shape, size and material. The photoconductor 15 and the photoconductor 19 are driven at the same linear speed. In an image forming apparatus having a configuration in which paper is discharged above the apparatus as in the present embodiment, if the first image station 13 and the second image station 14 are configured to be below the intermediate transfer belt 10, the Transfer belt 1
This is particularly desirable because the distance required for the toner image on zero to reach the transfer unit 26 can be short.

If the first image station 13 and the second image station 14 are arranged above the intermediate transfer belt 10, the full-color image formed on the intermediate transfer belt 10 is The recording medium is moved to the discharge section above the apparatus after the full-color toner image is transferred to the recording medium while transferring the recording medium downward in the transfer section 26, or more than a half turn on the transfer belt 10. In each case, which is disadvantageous in terms of time. However, the first image station 1
3. The second image station 14 is the intermediate transfer belt 10
The present invention can be applied to a configuration that is located above.

In the image forming apparatus having the configuration described above, the image forming operation is performed according to the following (1) to (5). (1) On the photoreceptor 15 of the first image station 13, an electrostatic latent image corresponding to the M-color developing device 1M is formed by a latent image forming unit including a charging unit 16 and a writing unit 17, that is, the charging unit Writing is performed by a light beam that is uniformly charged by 16 and modulated by an image signal by a writing unit 17 to form an electrostatic latent image.
The magenta toner image is obtained by being visualized by the M color developing device 1M. The magenta toner image is transferred to the intermediate transfer belt 10 by the first transfer brush 23, and the photoconductor 15 is cleaned by the cleaning unit 18.

(2) On the other hand, arrow a of the intermediate transfer belt 10
As the magenta toner image on the intermediate transfer belt 10 approaches the second image forming unit 14,
The photoreceptor 19 is charged with Y by the charger 20 and the writing means 21.
An electrostatic latent image corresponding to the color developing device 1Y is formed.
The writing is performed by the light beam modulated by the image signal in 1 to form an electrostatic latent image.
The image is visualized by the color developing device 1Y to obtain a yellow toner image. This yellow toner image is superimposed on the magenta toner image obtained on the intermediate transfer belt 10 at the first image station 13 by the second transfer brush 24, and the photoconductor 19 is cleaned by the cleaning unit 22.

(3) The superimposed image of the magenta toner image and the yellow toner image forms the first image as the intermediate transfer belt 10 travels.
While approaching the image station 13, the electrostatic latent image corresponding to the C color developing device 1C is formed on the photoreceptor 15 by the charger 16 and the writing means 17, and this electrostatic latent image is visualized by the C developing device 1C. It is imaged to obtain a cyan toner image. The cyan toner image is superimposed and transferred by the first transfer brush 23 onto the superimposed image of the magenta toner image and the yellow toner image obtained by the second image forming unit 14 on the intermediate transfer belt 10, and the photoconductor 15 is cleaned. The cleaning is performed by the means 18. (4) The superimposed image of the magenta toner image, the yellow toner image, and the cyan toner image travels along the intermediate transfer belt 10,
While approaching the second image station 14, the photoconductor 19
Then, an electrostatic latent image corresponding to the K-color developing device 1K is formed by the charger 20 and the writing means 21, and the electrostatic latent image is visualized by the K-color developing device 1K to obtain a black toner image. The black toner image on the intermediate transfer belt 10
The second image is added to the superimposed image of the magenta toner image, the yellow toner image, and the cyan toner image obtained by the first image station 13.
The transfer brush 24 overlaps and transfers to form a full-color image, and the photoconductor 19 is cleaned by the cleaning unit 22. (5) When a full-color image is formed on the intermediate transfer belt 10 by the second transfer brush 24, the recording medium sent from the sheet feeding device is sent to the transfer unit 26 by the pair of registration rollers 31, and here The transfer roller 25 transfers a full-color image on the intermediate transfer belt 10 to a recording medium. The full-color image transferred to the recording medium is fixed on the recording medium by a fixing device, and is discharged by a discharge roller pair 34 to a discharge tray 35.
Is sent out as an image formed product. On the other hand, the intermediate transfer belt 10 that has finished transferring the color image is
7 removes the remaining toner.

When obtaining a plurality of image-formed products, when the superimposed image of the magenta toner image and the yellow toner image is transferred to the intermediate transfer belt 10 at the second image station 14, the first image station 13 Subsequently, the magenta toner image formed in the same manner as described above is transferred to the intermediate transfer belt 10.
And the steps (1) to (5) are repeated. In the present embodiment, a developing device which is a characteristic portion thereof will be described in detail below. Since the configurations of the first image station 13 and the second image station 14 are substantially the same,
Only the image station 13 will be described. However, each developing device has a different color of toner.

FIG. 1 is an enlarged view of the photoconductor 15, the C color developing device 1C and the M color developing device 1M in the first image station 13. In FIG. 1, C color developing devices 1C and M
Although the configuration of the color developing device 1M is different in the arrangement on the layout and the color of the toner, the configuration and function of each element are the same, so that the configuration will be described below focusing on the M color developing device 1M.

The M color developing device 1M includes a developing roller 101M as a toner carrier and a supply roller 10 as a supply member.
2M, a stirring means 103M, a doctor blade 106M as a layer thickness regulating agent, a sleeve 105M of a developing roller 101M, a supply roller 102M, and a stirring means 10
3M is rotationally driven by a rotational drive mechanism (not shown).
The surface of the developing roller 101M is elastic and forms a predetermined nip with the photoconductor 15 to make contact therewith. The peripheral speed Vs of the developing roller 101M is 1.1 with respect to the linear speed Vpc of the photoconductor 15 in the developing state.
It is set so as not to exceed the range of 05 Vpc ≦ Vs ≦ 2.0 Vpc. In the present embodiment, since the amount of toner carried on the developing roller 101M is 0.7 to 1.5 layers, it is preferable to set Vs in this range from the viewpoint of developing ability. In the present embodiment, in the developing state, the developing roller 101
The peripheral speed Vs of M is set to be 250 mm / sec, which is 1.25 times the peripheral speed Vpc of the photoconductor 15 = 200 mm / sec.

In the non-development state, the peripheral speed Vs of the developing roller 101M is 0.9 to the linear speed Vpc of the photosensitive member 16.
It is set so as not to exceed the range of Vpc ≦ Vs ≦ 1.5 Vpc. If the peripheral speed Vs of the developing roller 101M exceeds this range, the non-developing developing roller 101M disturbs other color images, which is not preferable. Ideally, the peripheral speed Vs of the developing roller 101M is desirably equal to the linear speed Vpc of the photoconductor 15 so that the developing roller 101M does not disturb other color images in the non-developing state. In the present embodiment, the peripheral speed Vs of the developing roller 101M in the non-developing state is set to be equal to the peripheral speed Vpc of the photoconductor 15 and 200 mm / sec. The photoconductor 15 has a charging potential (non-image portion potential)
Is -500 V, and the potential after exposure (image portion potential) is -100 V. On the other hand, the developing roller 101
M is connected to a power supply 108M as a voltage applying means, and is adjusted so that the voltage applied from the power supply 108M has a potential of -250V during development and the voltage applied from the power supply 108M has a potential of -650V during non-development. Have been. In order to form a stable contact state between the developing roller 101M and the photoreceptor 15, the developing roller 10
1M desirably has elasticity.

The supply roller 102M is provided at a distance of 0.4 mm from the developing roller 101M. The supply roller 102M is provided with a sleeve 105M made of a non-magnetic material such as aluminum, brass, stainless steel, or a conductive resin in a cylindrical shape by a rotation drive mechanism (not shown) at a peripheral speed of 650 mm / sec in the direction of the arrow, ie, clockwise. It is provided so that it can be rotated. In the sleeve 105M, a supply magnetic pole 104M that forms a magnetic field so as to make the developer stand on the surface of the sleeve 105M is fixedly provided.

Further, inside the supply roller 102M, a transport magnetic pole (not shown) for transporting the developer is provided in addition to the supply magnetic pole 104M.
The developer is transported to 4M, and after passing the supply magnetic pole 104M, the developer is transported to the stirring means 103M side. A layer thickness regulating member which regulates the amount of the developer after passing in the upstream direction of the supply magnetic pole in the developer conveying direction, that is, the clockwise direction, to be 0.03 to 0.05 mg per square centimeter. Doctor blade 106M is the supply roller 102M
Are spaced 0.55 mm apart from each other. Further, the supply roller 102M is connected to a power supply 107M as a voltage application unit, and the voltage applied from the power supply 107M is adjusted to a potential of -350V. The stirring means 103M is provided to pump the developer in the developing device 1M to the supply roller 104M side while stirring.

The C color developing device 1C includes a developing roller 101C as a toner carrier and a supply roller 10 as a supply member.
2C, a stirring means 103C, a doctor blade 106C as a layer thickness regulating agent, a sleeve 105C of a developing roller 101C, a supply roller 102C, and a stirring means 10
3C is rotationally driven by a rotational drive mechanism (not shown). C
The color developing device 1C differs from the M-color developing device 1M in the layout and toner color, but has the same configuration and function of each element. The supply roller 102C is
It is connected to the power supply 107C, and the voltage applied from the power supply 107C is adjusted to -350V. Developing roller 1
01C is connected to a power supply 108C, and a power supply 10C during development.
The voltage applied from 8C is adjusted to -250V, and the voltage applied from the power supply 108C is adjusted to -650V during non-development.

The operation of the developing devices 1M and 1C having such a configuration will be described below. The description is (1a) at the time of M-color development in which the electrostatic latent image on the photoconductor 15 is visualized into an M toner image, and (2a) development / non-development for switching between the developing state and the non-developing state of the developing devices 1M and 1C. The description will be made in the order of (3a) the C color development in which the electrostatic latent image on the photoconductor 15 is visualized into a C toner image when the development is switched.

(1a) At the time of M color development At this time, since the M color developing device 1M is in the developing state and the C color developing device 1C is in the non-developing state, the developing roller 101M is supplied with a voltage of -250 V from the power source 108M. Then, a voltage of -650 V is applied to the developing roller 101C from the power supply 108C.

(1a-1) Operation of M Color Developing Apparatus 1M In the M color developing apparatus 1M, the carrier is positively charged by the stirring of the developer by the stirring means 103M, and the M toner is negatively charged. It is pumped onto the supply roller 102M by a transport magnet (not shown) in the supply roller 102M. The developer on the supply roller 102M is conveyed to the supply magnetic pole 104M while the layer thickness is regulated by the doctor blade 106M, and the carrier constituting the developer is supplied to the supply magnetic pole 104M.
Sleeve 10 along the lines of magnetic force emitted from M
5M, the magnetic brush 109M is formed by attaching the charged M toner to the carrier having the chain-formed ears. The magnetic brush 109M is transferred in the same direction as the sleeve 105M, that is, clockwise with the rotational transfer of the sleeve 105M. In this embodiment, since the peripheral speed of the supply roller 102M is higher than the peripheral speed of the developing roller 101M, a number of magnetic brushes 109M are provided for one location of the developing roller 101M.
Are rubbed, and a sufficient amount of M toner contacts the developing roller 101M. Since the potential of the developing roller 101M is -250V and is set higher than the potential of -350V of the supply roller 102M, the negatively charged M toner is
To the developing roller 101M side. At this time, even if the oppositely charged M toner exists in the developer, the M toner does not move to the developing roller 101M side because the M toner receives the electrostatic force toward the supply roller 102M side.

The M toner on the developing roller 101M is conveyed to the photosensitive member 15 with the rotation of the developing roller 101M, and is transferred to the photosensitive member 15 at a nip formed by the contact between the developing roller 101M and the photosensitive member 15. Contact. Here, the potential of the photoreceptor 15 is set to a non-image portion -500 V and an image portion-
100V, while the potential of the developing roller 101M is −
Since the voltage is 250 V, the negatively charged M toner
The development is performed by adhering only to the upper image portion. Photoconductor 15
The upper M toner moves as the photoconductor 15 rotates, passes through a nip formed between the intermediate transfer belt 10 and the photoconductor 15, and is transferred to the intermediate transfer belt 10.

(1a-2) Operation of C Color Developing Apparatus 1C In the C color developing apparatus 1C, the carrier is positively charged by the stirring of the developer by the stirring means 103C, and the C toner is negatively charged. It is pumped onto the supply roller 102C by a transport magnet (not shown) in the supply roller 102C. The developer on the supply roller 102C is transported to the supply magnetic pole 104C while the layer thickness is regulated by the doctor blade 106C, and the carrier constituting the developer is supplied to the supply magnetic pole 104C.
C along the line of magnetic force emitted from C
5C, the magnetic brush 109C is formed by attaching the charged C toner to the carrier raised in a chain shape, and the carrier raised in the chain shape. The magnetic brush 109C is transferred in the same direction as the sleeve 105C, that is, clockwise with the rotational transfer of the sleeve 105C. The potential of the developing roller 101C is -650V
Since the potential of the supply roller 102C is set to be lower than -350V, the negatively charged C toner does not move from the magnetic brush 109C to the developing roller 101C side, but moves toward the root of the magnetic brush 109C. . At this time,
When the reversely charged toner exists in the developer, the toner moves to the developing roller 101C side.

Since there is no toner on the developing roller 101C, the developing is not performed with the C toner in the nip formed by the contact between the developing roller 101C and the photosensitive member 15. However, when the oppositely-charged toner is present on the developing roller 101C, the oppositely-charged toner comes into contact with the photoreceptor 15, but the potential of the photoreceptor 15 −100 to −100.
Since the potential of the developing roller 101C at −650 V is lower than 500 V, the oppositely charged toner receives the electrostatic force toward the developing roller 101C and does not adhere to the photoconductor 16.

On the other hand, the M toner on the photoconductor 15 moves with the rotation of the photoconductor 15 and passes through the nip formed by the developing roller 101C of the C color developing device 1C and the photoconductor 15. In the section, the developing roller 101C has −6
The voltage is adjusted to 50 V, and 200
It is rotating at a peripheral speed of mm / sec. Therefore, the negatively charged toner receives an electrostatic force from the developing roller 101C toward the photoconductor 15 side.
The M toner image on the photoconductor 15 is not disturbed by the peripheral speed difference between the photoconductor 15 and the developing roller 101C without moving to the 1C side.

(2a) Switching between development and non-development When the development of the M color is completed, the output voltages of the power supplies 108M and 108C are switched, and the development roller 101M is switched from the power supply 108M.
Is -650 V, and the voltage from the power supply 108C to the developing roller 101C is -250V. Therefore, the C color developing device 1C shifts from the non-development state to the development state, and the M color development device 1M shifts from the development state to the non-development state.

(2a-1) Operation of the M Color Developing Apparatus 1M When the output voltages of the power supplies 108M and 108C are switched, the potential of the developing roller 101M becomes -650V,
5 becomes -500V. Therefore, the developing roller 1
The negatively charged toner on the photoconductor 01M receives electrostatic force toward the photoconductor 15, and the photoconductor 1
Move to side 5. Therefore, the toner on the upstream side of the nip portion between the developing roller 101M and the photosensitive member 15 in the moving direction of the developing roller 101M and on the downstream side of the magnetic brush 109M adheres to the photosensitive member 15. Thereby, the power supply 108
M and 108C when the output voltage is switched
A magenta toner image continues to be formed on the photoconductor 15 while the area of the magnetic brush 109M on M that has been rubbed has passed through the nip between the developing roller 101M and the photoconductor 15. That is, as shown in FIG. 3, a band 42 of the magenta image having a constant width is formed on the photoreceptor 15 after the image (magenta toner image) 41. The intermediate transfer belt 10 of this belt 42
The length in the moving direction is equal to the length of the magnetic brush 10 as shown in FIG.
N2 is the length of 9M rubbing against the developing roller 101M, n1 is the length of the nip formed by the photoreceptor 15 and the developing roller 101M, and rubbing is that the magnetic brush 109M finishes rubbing on the developing roller 101M. From the boundary, the photoconductor 15 and the developing roller 10
Assuming that the distance to the entrance of the nip formed by 1M is K, the width is K to K + n1 + n2. Where n1, n2, K
Are the lengths measured on the surface of the developing roller 101M in the moving direction of the developing roller 101M. Further, it is difficult to collect 100% of the toner on the developing roller 101M by the magnetic brush 109M.
After the band 42 of K + n1 + n2 is formed, the developing roller 10
Until 1M completes one rotation, that is, the radius of the developing roller 101M is r, the toner that cannot be completely collected by the magnetic brush 109M is thin through the photoconductor 15 until the surface of the developing roller 101M advances by a distance of 2πr. 10
May adhere to the The length K + n1 + n2 portion on the developing roller 101M, or more safely the length 2
Since the portion of πr is an area where an image cannot be formed, the length of the intermediate transfer belt 10 needs to be increased by the length m of the area where the image cannot be formed in addition to the length m of the recording medium having the maximum size. There is. In this embodiment, for security, a portion having a length of 2πr is set as a non-image area. In addition, in order to allow the transfer roller 25 and the cleaning device 27 to contact and separate from each other with a margin, a predetermined interval A is further provided between the rear end of the image 41 and the band 42, and the image forming operation is continuously performed. It is desirable to provide a predetermined interval B between the rear end of the band 42 and the next image. In summary, the length L of the intermediate transfer belt 10 is longer than the length m of the recording medium of the maximum size used in the image forming apparatus of the present embodiment in the moving direction by the non-image area α. Although the relationship of m + α has been described above, in more detail, in the present embodiment, when one image is formed by the entire intermediate transfer belt 10, the length α of the non-image portion of the intermediate transfer belt 10 is α ≧ max (J | A +
It is desirable to satisfy the relationship of 2πr + B). Where J
Is the conveyance interval between the recording media when the band 42 is not formed, and max (a | b) is an expression meaning that a larger number is selected from a and b. The relation of this relationship with the time axis is the time axis on the right side of FIG. Power supply 108 at time T1
When the output voltage of M and 108C is switched, the distance n1 + K +
While the intermediate transfer belt 10 moves n2,
2 is formed, and then the distance 2πr is
Until 0 moves, a band 43 of relatively low density is formed by the uncollected toner. Each developing device 1C, 1M, 1M
When the diameters of the developing rollers are not equal in Y and 1K, it is necessary to select the developing device having the largest diameter among the developing devices 1C, 1M, 1Y and 1K so as to satisfy the relationship α = A + 2πr + B. is there. When a plurality of (x) images are formed on the entire intermediate transfer belt 10, only one band 42 or 43 is formed after the formation of the x images. , 43 only need to be spaced by A + 2πr + B. In the present embodiment, the controller of the present embodiment uses this relationship, and when the size of the recording medium in the moving direction of the intermediate transfer belt 10 is j, L ≧ xx (j + J) + max (J | A + 2πr + B) −J. The upper limit of the number x of images to be formed on the intermediate transfer belt 10 at one time is determined so that the relationship is established.

On the other hand, the magnetic brush 109M is
In an area where the developing roller 101M is rubbed with 01M, the potential of the supply roller 102M is -350V and the potential of the developing roller 101M is -650V.
Therefore, the toner in the magnetic brush 109M does not move to the developing roller 101M side. Therefore, the toner on the downstream side of the nip portion between the developing roller 101M and the photoconductor 15 in the moving direction of the developing roller 101M and on the upstream side of the magnetic brush 109M is collected by the magnetic brush 109M. As described above, in the developing device 1M of the present embodiment, the power sources 108M,
08C, the toner on the developing roller 101M receives both the force of being collected by the supply roller 102M and the force of being moved to the photoconductor 15 by the switching of the output voltage of the developing roller 10M.
Excluded from 1M above. However, if there is the oppositely charged toner, it adheres to the developing roller 101M.

(2a-2) Operation of C Color Developing Apparatus 1C When the output voltages of the power supplies 108M and 108C are switched, the potential of the supply roller 102C becomes -350V and the potential of the developing roller 101C becomes -250V. The negatively charged toner moves from the magnetic brush 109C, and the developing roller 101C
The negatively charged toner adheres to the surface. This developing roller 101C
The toner adhering to the developing roller 101C reaches the nip portion between the developing roller 101C and the photoconductor 15 by the rotation of the developing roller 101C,
It becomes ready for development. That is, the power supply 108M, 10
When the output voltage of 8C is switched, the area where the magnetic brush 109C on the developing roller 101C rubs is the developing roller 10C.
After a lapse of time to reach the nip portion between 1C and the photoreceptor 16, development is possible. However, strictly, there is a delay corresponding to the time required for the toner that has been subjected to the force pressed against the root of the magnetic brush 109C to return to the surface of the magnetic brush 109C. At the same time, if there is an oppositely charged toner on the developing roller 101C, it is collected by the magnetic brush 109C.

(3a) At the time of C-color development At this time, since the M-color developing device 1M is in the non-developing state and the C-color developing device 1C is in the developing state, a voltage of -650 V is applied to the developing roller 101M from the power source 108M. The voltage of -250 V is applied to the developing roller 101C from the power supply 108C.

(3a-1) Operation of the M Color Developing Apparatus 1M In the M color developing apparatus 1M, the carrier is positively charged by the stirring of the developer by the stirring means 103M, and the M toner is negatively charged. It is pumped onto the supply roller 102M by a transport magnet (not shown) in the supply roller 102M. The developer on the supply roller 102M is conveyed to the supply magnetic pole 104M while the layer thickness is regulated by the doctor blade 106M, and the carrier constituting the developer is supplied to the supply magnetic pole 104M.
Sleeve 10 along the lines of magnetic force emitted from M
The magnetic brush 109M is formed on the carrier that is raised in a chain shape on the 5M, and the charged M toner adheres to the carrier that is raised in the chain shape. The magnetic brush 109M is transferred in the same direction as the sleeve 105M, that is, clockwise with the rotational transfer of the sleeve 105M. The potential of the developing roller 101M is −65.
0V, which is lower than the potential of the supply roller 102M -350M, so that the negatively charged M toner does not move from the magnetic brush 109M to the developing roller 101M side, and conversely to the root direction of the magnetic brush 109M. Moving. At this time, if a reversely charged toner is present in the developer, the toner moves to the developing roller 101M side. Since no toner exists on the developing roller 101M, the developing roller 1M
No development is performed with the M toner in the nip formed by the contact between 01M and the photoconductor 15. However, when the oppositely charged toner is present, the oppositely charged toner comes into contact with the photoconductor 15, but the potential of the photoconductor 15 is −100 to −100.
The potential of the developing roller 101M is −650V than −500V.
, The oppositely charged toner receives an electrostatic force toward the developing roller 101M and does not adhere to the photoconductor 15.

(3a-2) Operation of C Color Developing Apparatus 1C In the C color developing apparatus 1C, the carrier is positively charged by the stirring of the developer by the stirring means 103C, and the C toner is negatively charged. It is pumped onto the supply roller 102C by a transport magnet (not shown) in the supply roller 102C. The developer on the supply roller 102C is transported to the supply magnetic pole 104C while the layer thickness is regulated by the doctor blade 106C, and the carrier constituting the developer is supplied by the supply magnetic pole 104C.
C along the line of magnetic force emitted from C
5C, the magnetic brush 109C is formed by attaching the charged C toner to the carrier raised in a chain shape, and the carrier raised in the chain shape. The magnetic brush 109C is transferred in the same direction as the sleeve 105C, that is, clockwise with the rotational transfer of the sleeve 105C. In the present embodiment, the supply roller 102
Since the peripheral speed of C is higher than the peripheral speed of developing roller 101C, a number of magnetic brushes 1
09C rubs, and a sufficient amount of C toner is supplied to the developing roller 101.
Touch C. The potential of the developing roller 101C is -250V
Since the potential of the supply roller 102C is set higher than -350V, the negatively charged C toner moves from the magnetic brush 109C to the developing roller 101C. At this time, even if a reversely charged toner exists in the developer, the toner does not move to the developing roller 101C side because the toner receives an electrostatic force toward the supply roller 102C side. The toner on the developing roller 101C is conveyed to the photoconductor 15 with the rotation of the developing roller 101C, and comes into contact with the photoconductor 15 at a nip formed by the contact between the developing roller 101C and the photoconductor 15. Here, the potential of the photosensitive member 15 is -500 V for the non-image portion and -100 V for the image portion, while the potential of the developing roller 101C is -250 V. Therefore, the negatively charged C toner is applied to the image portion on the photosensitive member 15. Only the adhesion is carried out and development is performed. The M toner on the photoconductor 15 is
It moves with the rotation of the photoconductor 15 and is transferred to the intermediate transfer belt 10.

As shown in the above (1a) to (3a), the developing device of the present embodiment can obtain a toner image faithful to a latent image because the developing roller contacts the photosensitive member. In addition, when the potential is switched, a force acts to pull the toner from the developing roller to the supply roller during non-development and a force acts to transfer the toner on the developing roller to the photoconductor. No toner is present. Also,
Since the force for pressing the negatively charged toner from the developing device in the non-developing state toward the photoconductor acts, the toner on the photoconductor is also prevented from adhering to the developing device in the non-developing state. Also,
The bias voltage for switching the developing device between the developing state and the non-developing state may be applied only to the developing roller, so that it is not necessary to provide a plurality of voltage applying means. Further, in the present embodiment, L
≧ x × (j + J) + max (J | A + K + n1 + n2 + B) −In order to determine the upper limit of the number x of sheets for forming an image on the intermediate transfer member at a time, the transfer roller and the like should be separated from each other. It is possible to do.

Further, in the developing device of the present embodiment, even if the oppositely charged toner is present, the oppositely charged toner is attracted to the developing roller side, so that an abnormal image due to the oppositely charged toner can be prevented.

As described above, the image forming apparatus according to the present embodiment includes the developing rollers 101M and 101C as the toner carriers contacting the photoconductors 15 and 19 as the latent image carriers, and the developing rollers 101M and 101C. A developing device 1M having supply rollers 102M and 102C as supply members for supplying the toner, wherein the rotation directions of the developing rollers 101M and 101C and the photoconductors 15 and 19 are the same in the contact portions with each other.
An image forming apparatus in which a plurality of developing devices 1M, 1C, and 1K are disposed around photoconductors 15 and 19, respectively.
When some of the developing devices in Y and 1K are in the developing state, an image forming apparatus that performs development by sequentially changing the developing devices in the developing state so that the other developing devices are in the non-developing state. In the developing state of each of the developing devices 1M, 1C, 1Y, and 1K, the developing roller 101M, 101C to the photosensitive member 15,
19 and the supply roller 102
In the non-developing state of the developing devices 1M, 1C, 1Y, and 1K, a bias voltage is applied so that the normally charged toner receives a force from M, 102C to the developing rollers 101M, 101C. 15 and 19 as a voltage applying means for applying a bias voltage such that the normally charged toner receives the force toward the image portion and the non-image portion and the force toward the supply rollers 102M and 102C from the developing rollers 101M and 101C. Power supply 107M, 10
7C, 108M and 108C.

As a result, the toner is prevented from adhering to the photoreceptor from the developing device in the non-developed state, and low cost, high durability, high image quality can be achieved, and occurrence of abnormal images due to color mixing is reduced. . The “normally charged toner” means a toner charged to a target charge polarity, and is a reversely charged toner or a toner that has not been charged (a toner having a charge amount of 0).
Does not apply. Switching of the bias voltage at the time of transition between the developing state and the non-developing state is performed by the developing roller 101.
This is performed by switching the voltage applied to M and 101C. This makes it possible to switch between the developing state and the non-developing state by a single voltage applying unit.

Further, the conveyance interval R1 of the recording medium and the supply rollers 102M and 102C are changed to the developing rollers 101M and 101C.
The developing rollers 101M, 10M
The developing roller 1 is moved to a position where 1C contacts the photoconductors 15 and 19.
The relationship of R1> R2 is established between the distance R2 of the toner on 01M and 101C and the distance R2. This prevents the occurrence of an abnormal image due to the toner that moves from the developing device to the photoconductor when shifting from the developing state to the non-developing state.

Furthermore, the conveyance interval R1 of the recording medium,
R1> between the circumferential length R3 of the developing rollers 101M and 101C
The relationship R3 holds. As a result, the occurrence of an abnormal image due to the toner moving from the developing roller to the photoconductor when shifting from the developing state to the non-developing state is further reliably prevented.

The image forming apparatus according to the second embodiment of the present invention basically has the configuration shown in FIG. 2 similarly to the image forming apparatus according to the first embodiment. Only the part for switching the non-development potential is different from the first embodiment.

FIG. 5 shows a first image station in the image forming apparatus of this embodiment. The developing devices 1M, 1C, 1Y, and 1K of the present embodiment include not only power supplies 108M and 108C connected to the developing rollers 101M and 101C, but also power supplies 110M and 110C connected to the supply rollers 102M and 102C.
1 is different from the developing device in the first embodiment shown in FIG. 1 in that the potential is switched between during development and during non-development. That is, the voltage applied to the supply rollers 102M and 102C during development is −25.
0 V, but the supply roller 102
The voltage applied to M and 102C is set to -100V.

The operation of the image forming apparatus of this embodiment having the above-described configuration will be described below. Here, among the (1a) M color development, (2a) development / non-development switching, and (3a) C color development described in the first embodiment, (1a)
Since a) and (3a) do not differ between the first embodiment and the second embodiment, only (2a) will be described.

(2a) Switching between development and non-development When the development of the M color is completed, unlike the first embodiment, first, the output voltages of the power supplies 110M and 110C are switched, and the supply roller 102M applies the voltage applied from the power supply 110M. Is -10
0V, and the voltage applied from the power supply 110C to the supply roller 102C becomes a potential of -250V. After a lapse of a predetermined time, the voltages of the power supplies 108M and 108C are switched, the voltage applied from the power supply 108M to the developing roller 101M becomes -650 V, and the developing roller 101C is
The voltage applied from 8C is -250V. Here, when the voltages of the power supplies 110M and 110C are switched and the power supply 10
As shown in FIG. 4, the time interval between the switching of the voltages of 8M and 108C is n2 as long as the magnetic brush 109M is rubbing the developing roller 101M, and the photosensitive member 15 and the developing roller 101M are formed. Where n1 is the length of the nip portion, and K is the distance from the rubbing boundary at which the magnetic brush 109M finishes rubbing the developing roller 101M to the entrance of the nip portion formed by the photoconductor 15 and the developing roller 101M. Is set to be equal to the time required for one point on the surface of the developing roller 101M to move by the distance n1 + n2 + K. Power supply 1
When the voltages of 08M and 108C are switched, the C color developing device 1C shifts from the non-development state to the development state, and the M color development device 1M shifts from the development state to the non-development state.

(2a-1) Operation of the M Color Developing Apparatus 1M When the voltage of the power supply 110M is switched, first, the potential of the supply roller 102M becomes -100V, and the developing roller 101M
Becomes -250V. For this reason, the magnetic brush 10
The negatively charged toner inside 9M receives an electrostatic force from the developing roller 101M toward the supply roller 102M, and
The toner is collected from 1M to the supply roller 102M. Then, after the surface of the developing roller 101M rotates by the distance n1 + n2 + K, the voltage of the power supply 108M is switched, and the voltage of the developing roller 101M becomes -650V, and
The charging voltage (non-image portion potential) of No. 5 is -500V. As a result, the negatively charged toner that has not been completely collected on the developing roller 101M receives an electrostatic force toward the photoconductor 15, and
In the nip portion between the developing roller 101M and the photoconductor 15, the photoconductor 15 moves to the photoconductor 15 side. If there is the oppositely charged toner, it moves onto the developing roller 101M.

Since the magenta toner that has not been completely recovered is transferred onto the photoreceptor 15, a band 44 of a magenta image having a constant width is formed on the intermediate transfer belt 10 after the image 41 as shown in FIG. . The intermediate transfer belt 10 of this belt 44
The length in the movement direction has a width of 2πr as in the first embodiment. Since most of the toner is collected by the supply roller 102M by making the developing roller 101M make one rotation before forming the band 44, the density of the band 44 is reduced unlike the first embodiment. Since it is difficult to completely recover the toner, the density of the band 44 cannot always be set to zero. For this reason, similarly to the first embodiment, the band 44 is an area where image formation is impossible, so that the length of the intermediate transfer belt 10 is added to the length m of the recording medium having the maximum size, and It is necessary to increase K + n1 + n2 + 2πr, which is the sum of the length n1 + K + n2 for collecting the toner on the roller 101M and the length 2πr for one rotation of the developing roller 101M. In addition, in order to allow the transfer roller 25 and the cleaning device 27 to contact and separate with a sufficient margin, the image 4
A predetermined interval A is further provided between the rear end of the band 44 and the next image, considering that the image forming operation is continuously performed. Is desirable. The length L of the intermediate transfer belt 10 is longer than the length m in the moving direction of the recording medium having the maximum size used in the image forming apparatus of the present embodiment by the non-image area α, and L = m +
Although the relationship of α is described above, in more detail, when a single image is formed on the entire intermediate transfer belt 10 in the present embodiment, the length α of the non-image portion of the intermediate transfer belt 10 is α.
It is desirable to satisfy the relationship of ≧ max (J | A + K + n1 + n2 + 2πr + B). Here, J is the conveyance interval between the recording media when the band 44 is not formed, and max (a | b) is an expression meaning that a larger number is selected from a and b. The relationship between this relationship and the time axis is the time axis on the right side of FIG. At time T1, the voltage of the power supply 110M is switched, the toner is collected from the developing roller 101M to the supply roller 102M, and then at time T2, the potential of the power supply 108M is switched. A low density band 44 is formed by the toner that cannot be collected. When the diameter of the developing roller is not equal in each of the developing devices 1M, 1C, 1Y, and 1K, the developing device 1M,
It is necessary to select a roller having the largest developing roller diameter from 1C, 1Y, and 1K so as to satisfy the relationship of α = A + n1 + K + n2 + 2πr + B. Further, when a plurality of (x) images are formed on the entire intermediate transfer belt 10, only one band 44 is formed after the formation of the x images, so that the band 44 is formed. A + K + n1 only for the part
It is sufficient if there is an interval of + n2 + 2πr + B. The controller of this embodiment uses this relationship, and when the size of the recording medium in the moving direction of the intermediate transfer belt 10 is j, L ≧ xx (j
+ J) + max (J | A + K + n1 + n2 + 2πr + B) −J The upper limit of the number x of images to be formed on the intermediate transfer belt 10 at one time is determined.

(2a-2) Operation of C Color Developing Apparatus 1C When the voltage of the power supply 107C is switched, the potential of the supply roller 102C becomes -350V, so that the negatively charged toner moves from the magnetic brush 109C, and the developing is performed. Roller 101C
The negatively charged toner adheres to the surface. Thereafter, when the potential of the power supply 108C is switched, the potential of the developing roller 101C becomes -2.
The voltage becomes 50 V, and it becomes a state in which development is possible. At the same time, if there is the oppositely charged toner on the developing roller 101C, the magnetic brush 109C
Will be collected.

The image forming apparatus of this embodiment has a longer non-image portion on the intermediate transfer belt 10 than the image forming device of the first embodiment, but has a smaller amount of toner adhering to the non-image portion. Thus, wasteful consumption of toner can be suppressed.

As described above, according to the present embodiment, the developing rollers 101M and 101C as the toner carriers contacting the photoconductors 15 and 19 as the latent image carriers,
Developing devices 1M, 1C having supply rollers 102M, 102C as supply members for supplying toner to the toner supply devices 01M, 101C.
An image forming apparatus in which a plurality of C, 1Y, and 1K are arranged around photoconductors 15 and 19, and a plurality of developing devices 1M, 1C, and 1K
When some of the developing devices in Y and 1K are in the developing state, an image forming apparatus that performs development by sequentially changing the developing devices in the developing state so that the other developing devices are in the non-developing state. In the developing state of the developing devices 1M, 1C, 1Y, and 1K, the photosensitive members 15, 1C are moved from the developing rollers 101M and 101C.
9 and the supply roller 102
A first level bias voltage is applied to the developing rollers 101M and 101C so that the normally charged toner receives a force from the M and 102C to the developing rollers 101M and 101C, and the developing devices 1M, 1C, 1Y, and 1K are in a non-developed state. , The force from the developing rollers 101M and 101C to the image portions and non-image portions of the photoconductors 15 and 19, and the developing roller 101
Power supplies 108M and 108C as first voltage applying means for applying a second level bias voltage to the developing rollers 101M and 101C such that the normally charged toner receives a force from the M and 101C to the supply rollers 102M and 102C; In the developing state of the developing devices 1M, 1C, 1Y, and 1K, a third level bias voltage is applied to the supply rollers 102M and 102C so that the normally charged toner receives a force from the supply rollers 102M and 102C to the development rollers 101M and 101C. Apply
In the non-developing state of the developing devices 1M, 1C, 1Y, and 1K, the supply rollers 102M,
Supply rollers 102M and 102C to supply a bias voltage of the fourth level such that the normally charged toner receives a force toward 02C.
Power supply 110M as a second voltage applying means for applying voltage to
110C. This reduces the amount of toner that migrates from the developing device to the latent image carrier when shifting from the developing state to the non-developing state, thereby achieving low cost, high durability, and high image quality. Image generation is reduced.

When each of the developing devices 1M, 1C, 1Y, and 1K shifts from the developing state to the non-developing state, first, the power supply 110
M, 110C to apply the fourth level bias voltage to the supply rollers 102M, 102C, and then for a predetermined time T
After the lapse of 1, the second level bias voltage is applied to the developing rollers 101M and 101C by the power supplies 108M and 108C, and the supply rollers 102M and 102C
Assuming that the time required for the toner carried on the developing rollers 101M and 101C to move from the point where the toner is supplied to the developing rollers 101M and 101C to the point where the developing rollers 101M and 101C contact the photoconductors 15 and 19 is T2, T between T1 and T2
1> T2 holds. This further reduces the amount of toner transferred from the developing device to the latent image carrier when shifting from the developing state to the non-developing state.

Further, in each embodiment, each developing device 1
In the non-developed state, M, 1C, 1Y, and 1K are such that the linear velocity Vs of the developing rollers 101M and 101C is in the range of 0.9Vpc ≦ Vs ≦ 1.5Vpc with respect to the linear velocity Vpc of the photoconductors 15 and 19. And This is preferable from the viewpoint of the developing ability of the developing device.

As described above, according to the present invention, low cost, high durability, high image quality can be achieved, and occurrence of abnormal images due to color mixing can be reduced.

Although the image forming apparatus of the above embodiment has a configuration in which two developing devices are provided for each of the two photoconductors, the present invention is not limited to the image forming apparatus having this configuration, and the present invention is not limited thereto. Is applicable, for example, when four developing devices are provided around one photoconductor. When four developing devices are arranged around one photoconductor, only one developing device is in the developing state, and the other three developing devices are only in the non-developing state. Each developing device in the developing state may perform the same operation as in the present embodiment.
Further, the developing device is not always in the developing state, but can be applied to, for example, a configuration in which two of the four developing devices are in the developing state and the other two developing devices are in the non-developing state. It is. Further, the present invention is also applicable to an image forming apparatus in which a toner image is superimposed on a photosensitive member instead of an intermediate transfer member.

[0075]

As described above, according to the first aspect of the present invention, high image quality can be achieved at low cost and high durability, and the occurrence of abnormal images due to color mixing can be reduced. According to the second aspect of the present invention, it is possible to switch between the developing state and the non-developing state of the developing device by a single voltage applying unit. According to the third aspect of the invention, it is possible to prevent the occurrence of an abnormal image due to the toner transferred from the developing device to the latent image carrier when shifting from the developing state to the non-developing state.

According to the fourth aspect of the invention, it is possible to more reliably prevent the occurrence of an abnormal image due to the toner transferred from the developing roller to the latent image carrier when shifting from the developing state to the non-developing state. According to the fifth aspect of the present invention, high image quality can be achieved at low cost and high durability, and the occurrence of abnormal images due to color mixing can be reduced. According to the sixth aspect of the present invention, the amount of toner transferred from the developing device to the latent image carrier when shifting from the developing state to the non-developing state can be further reduced. According to the seventh aspect of the present invention, it is preferable from the viewpoint of the developing ability of the developing device.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view illustrating a photoconductor, a C color developing device, and an M color developing device of a first image station according to the first embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the first embodiment.

FIG. 3 is a diagram illustrating a developing device according to the first embodiment.

FIG. 4 is a schematic diagram illustrating a photoconductor, a developing roller, and a magnetic brush according to the first embodiment.

FIG. 5 is an enlarged cross-sectional view illustrating a photoconductor, a C color developing device, and an M color developing device of a first image station according to a second embodiment of the present invention.

FIG. 6 is a view for explaining a developing device according to the second embodiment.

FIG. 7 is a schematic diagram illustrating a conventional image forming apparatus.

[Explanation of symbols]

1M, 1C, 1Y, 1K Developing device 15, 19 Photoconductor 101M, 101C Developing roller 102M, 102C Supply roller 107M, 107C, 108M, 108C, 110M, 11
0C power supply

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Saito 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Katsuichi Ota 1-3-6 Nakamagome, Ota-ku, Tokyo・ F-term in Ricoh Co., Ltd. (reference) 2H027 DA04 DA17 DA38 DA41 DC03 DE01 DE09 EA05 EA15 EA18 EB04 EC06 EC09 ED02 ED09 ED16 EE03 2H030 AA04 AB02 AD05 AD17 BB24 BB34 BB71 2H073 AA01 BA02 AD09 BA13 AD04 BA03 DB08 DB14 DB16 GA13

Claims (7)

[Claims] A toner carrier that contacts the latent image carrier; and a supply member that supplies toner to the toner carrier.
An image forming apparatus comprising: a plurality of developing devices in which rotation directions of the toner carrier and the latent image carrier are the same at contact portions with each other; and a plurality of developing devices arranged around the latent image carrier. An image forming apparatus that performs development by sequentially changing developing devices in a developing state so that other developing devices are in a non-developing state when some of the developing devices are in a developing state; In the developing state of the developing device, a bias voltage is applied such that the normally charged toner receives a force from the toner carrier toward the image portion of the latent image carrier and a force from the supply member toward the toner carrier. When the developing device is in the non-developing state, the force from the toner carrier to the image portion and the non-image portion of the latent image carrier, and the force from the toner carrier to the supply member An image forming apparatus, comprising a voltage application means for applying a bias voltage as normal charged toner is subjected. 2. The image forming apparatus according to claim 1, wherein the switching of the bias voltage at the time of transition between the developing state and the non-developing state is performed by switching a voltage applied to the toner carrier. Characteristic image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the toner carrier is transferred to the latent image carrier from a conveyance interval R1 of the recording medium and a point where the supply member supplies the toner to the toner carrier. An image forming apparatus, wherein a relationship of R1> R2 is established between a distance R2 at which the toner on the toner carrier moves to a contact position. 4. The image forming apparatus according to claim 1, wherein a relationship of R1> R3 is established between a conveyance interval R1 of the recording medium and a circumferential length R3 of the toner carrier. Image forming device. 5. An image forming apparatus comprising: a plurality of developing devices each having a toner carrier in contact with a latent image carrier and a supply member for supplying toner to the toner carrier; When some of the developing devices are in the developing state, the developing devices in the developing state are sequentially changed so that the other developing devices are in the non-developing state. In the image forming apparatus performing the developing, in the developing state of the developing device, the force from the toner carrier toward the image portion of the latent image carrier and the force from the supply member toward the toner carrier are charged normally. Applying a first level bias voltage to the toner carrier as received by the toner, and a force from the toner carrier to the image portion and the non-image portion of the latent image carrier in the non-developing state of the developing device. , A first voltage applying means for applying a second level bias voltage to the toner carrier such that the normally charged toner receives a force from the toner carrier toward the supply member; and a developing state of the developing device. A bias voltage of a third level is applied to the supply member such that the normally-charged toner receives a force from the supply member toward the toner carrier. An image forming apparatus comprising: a second voltage applying unit configured to apply a fourth level bias voltage to the supply member such that the normally charged toner receives a force toward the supply member. 6. An image forming apparatus according to claim 5, wherein when each of said developing devices shifts from a developing state to a non-developing state, said second voltage applying means first applies said fourth level to said supply member. A bias voltage is applied, and after a lapse of a predetermined time T1, a bias voltage of the second level is applied to the toner carrier by the first voltage applying means, and the supply member supplies toner to the toner carrier. When the time that the toner carried on the toner carrier moves from the portion where the toner carrier is in contact with the latent image carrier to the location where the toner carrier comes into contact with the latent image carrier is T2, T1 is between T1 and T2.
An image forming apparatus, wherein a relationship of 1> T2 is satisfied. 7. The image forming apparatus according to claim 1, wherein each of the developing devices is configured such that, in a non-developing state, the linear velocity Vs of the toner carrier is set to the latent image carrier. An image forming apparatus, wherein the linear velocity Vpc is in a range of 0.9 Vpc ≦ Vss ≦ 1.5 Vpc.