JP2007333852A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which foreign matter such as toner left after transfer and recording medium powder can be removed from an electrostatic latent image carrier without using a cleaner exclusively used for cleaning and abrasive toner. <P>SOLUTION: The image forming apparatus is characterized in that an electrification bias at an image formation period or an electrification bias at a non-image formation period whose peak-to-peak voltage of AC component is larger than that of the electrification bias at the image formation period is selectively applied to an electrifying roller 2 electrifying the electrostatic latent image carrier 1, and in that a toner recovery member 6 that rubs the surface of the electrostatic latent image carrier is arranged upstream from the electrifying roller 2 and downstream from a transfer apparatus (transfer roller 5), and in that a toner recovery bias or a toner discharge bias can be applied to the recovery member 6, and in that the electrification bias at the image formation period is applied to the electrifying roller 2 at a prescribed timing during the non-image formation period, in this case, when the electrostatic latent image carrier surface scheduled to pass through the electrifying roller 2 passes through the toner recovery member 6, the toner recovery bias is applied to the member 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and transfers the toner image to a transfer target. For example, the present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine, or a multifunction machine combining two or more of these.

  In an image forming apparatus such as an electrophotographic system, the surface of an electrostatic latent image carrier (hereinafter also referred to as “image carrier”) that is driven so that the surface moves is charged by a charging device, An electrostatic latent image corresponding to an image to be formed by an electrostatic latent image forming apparatus (such as an image exposure apparatus or an electrostatic recording apparatus) is formed in a charged area, and the electrostatic latent image is developed by a developing device and is visible. An image forming process is performed in which a toner image is formed and the visible toner image is transferred to a transfer target.

Such image forming apparatuses can be roughly classified into a monochrome image forming apparatus and a color image forming apparatus (typically, a full color image forming apparatus) capable of forming an image using two or more colors of toner.
In a monochrome image forming apparatus, a toner image formed on an image carrier is directly transferred and fixed on a recording medium which is a transfer medium using a transfer apparatus, or an intermediate image which is an intermediate transfer medium. The image is primarily transferred to the transfer body by a primary transfer apparatus, and transferred from the intermediate transfer body onto a recording medium, which is the final transfer target, by a secondary transfer apparatus and fixed.

Known color image forming apparatuses include so-called four-cycle color image forming apparatuses and tandem color image forming apparatuses.
A four-cycle color image forming apparatus forms an electrostatic latent image by charging the surface of an image carrier such as a photoconductor and exposing the image to the charged area. Develop to form a toner image. In such toner image formation, a plurality of developing devices containing different color toners are sequentially used to sequentially form different color toner images on the image carrier. Further, the toner images formed on the image carrier are sequentially superposed on the intermediate transfer member by using a primary transfer device, and are primarily transferred onto the intermediate transfer member. A color image can be obtained by secondary transfer and fixing on a recording medium with a secondary transfer device.

  In a tandem type color image forming apparatus, an image carrier such as a photoconductor, a charging device for charging the surface thereof, an electrostatic latent image forming device (for example, an image exposure device), and developing an electrostatic latent image on the image carrier. A plurality of image forming units including a developing device and the like are sequentially arranged along the intermediate transfer body according to the color of the toner, and the toner image formed on the image carrier in each image forming unit is subjected to primary transfer. The image is primarily transferred onto the intermediate transfer body by the apparatus, and the multiple toner images on the intermediate transfer body are secondarily transferred and fixed on the recording medium by the secondary transfer apparatus. The intermediate transfer member in the color image forming apparatus can be said to be a type of transfer target.

  Regardless of whether it is a monochrome image forming device or a color image forming device, there are various types of charging devices that charge the surface of the image carrier prior to electrostatic latent image formation, and corona discharge is typically used. Although a non-contact type corona charging device can be mentioned, a contact type charging device in which a charging member is brought into contact with the surface of the image carrier has been proposed and put into practical use. Compared with a non-contact type charging device, the contact type charging device has advantages in that the amount of ozone generated is small or absent and the power consumption can be kept low.

  Among contact-type charging devices, a charging member that uses a charging roller that rotates in contact with the surface of the image carrier is preferable from the viewpoint of charging stability.

  In the above-described image forming apparatus, when the toner image formed on the image carrier is transferred to the transfer target (recording medium or intermediate transfer member), all the toner is not transferred to the transfer target. In other words, so-called transfer residual toner remains on the image carrier. In general, the transfer residual toner is often removed and discarded by a cleaning cleaner having a cleaning member such as a cleaning blade disposed in contact with the image carrier.

On the other hand, in order to reduce the size and cost of the image forming apparatus, and to eliminate the use of cleaning members such as a cleaning blade, to suppress wear of the image carrier, and to extend the life of the image carrier, only for cleaning A so-called cleanerless type image forming apparatus without a cleaner has also been proposed.
A typical cleanerless type image forming apparatus is an image forming apparatus that collects transfer residual toner with a developing device.

  For example, Japanese Patent Laid-Open No. 2005-181941 discloses that a transfer residual toner charged to a polarity opposite to a normal charging polarity is collected by a charging member of a charging device that contacts an image carrier, and non-image formation (for example, between recording media) In the post-processing operation after image formation, etc., the collected toner is charged to a normal charging polarity, discharged onto the image carrier, and collected by the developing device.

The publication also includes the following description.
Since the transfer residual toner charged to the normal charging polarity passes through the charging member without being collected by the charging member and may appear as a so-called ghost in the next image formation, the transfer device (in the moving direction of the image carrier surface) When there is a primary or secondary transfer device, the image bearing member is loaded with the transfer residual toner charged to the regular charge polarity downstream from the primary transfer device) and upstream from the charging device, and charged to the opposite polarity. It is described that a fixed (non-rotating) conductive brush is provided to return to the top.

  By the way, in the cleanerless type image forming apparatus, since a cleaning member having high cleaning performance such as a cleaning blade is not used, the ability to remove foreign matters such as recording medium powder adhering to the surface of the image carrier is lowered. In an image carrier to which foreign matter such as recording medium powder adheres, substances contained in the foreign matter (for example, calcium carbonate and talc contained in the recording paper) reduce the surface resistance of the image carrier, and therefore charging by a charging device. A lateral flow of electrification tends to occur, and an image flow tends to occur in the formed image, or image noise due to filming tends to occur.

In this respect, the image forming apparatus described in Japanese Patent Application Laid-Open No. 2005-181941 employs a magnetic brush that rubs the surface of the image carrier as a charging member, and has a polishing effect externally added to the toner collected on the magnetic brush. The surface of the image carrier is polished with a certain external additive.
JP 2005-181941 A

  However, in the cleanerless type image forming apparatus described in Japanese Patent Application Laid-Open No. 2005-181941, the polishing of the image carrier relies exclusively on toner external additives. In other words, the image carrier is polished with a toner having polishing properties. However, when image formation that does not consume much toner is repeated, the amount of toner that contributes to polishing is insufficient and the polishing ability of the image carrier is reduced. Therefore, the polishing of the image carrier from the developing device to the image carrier is reduced. Therefore, toner must be replenished, and the degree of effective use of toner for image formation is reduced accordingly.

  In addition, a toner that takes into account the image carrier abradability must be prepared as a toner, and in the preparation, the compatibility between the toner body and an external material having an image carrier abradant must also be considered. With difficulty.

  Therefore, the present invention charges the surface of the electrostatic latent image carrier that is driven so that the surface moves by a charging device, forms an electrostatic latent image in the charged area by an electrostatic latent image forming device, and An image forming apparatus that develops an electrostatic latent image with a developing device to form a toner image, and transfers the toner image to a transfer target with a transfer device, wherein the toner image is transferred from the electrostatic latent image carrier to the transfer target. The transfer residual toner remaining on the subsequent electrostatic latent image carrier can be recovered from the electrostatic latent image carrier and the electrostatic latent image can be collected without causing trouble in image formation without using a cleaner dedicated to cleaning the transfer residual toner. An object of the present invention is to provide an image forming apparatus capable of polishing and removing foreign matters such as recording medium powder adhering to a carrier without causing trouble in image formation without using abrasive toner.

In order to solve the above problems, the present invention provides:
The surface of the electrostatic latent image carrier that is driven so that the surface is moved is charged by a charging device, an electrostatic latent image is formed in the charged area by an electrostatic latent image forming device, and the electrostatic latent image is An image forming apparatus that develops a toner image by a developing device and transfers the toner image to a transfer target by a transfer device,
The charging device includes a charging roller disposed in contact with the surface of the electrostatic latent image carrier, and a first bias applying device that applies a charging bias in which a DC voltage is superimposed on an AC voltage to the charging roller;
A toner recovery member is disposed on the surface of the electrostatic latent image carrier on the downstream side of the transfer device and on the upstream side of the charging device so as to rub against the surface of the electrostatic latent image carrier, A second bias applying device for applying a bias to the toner collecting member is provided;
Further, a control unit for controlling the first bias application device and the second bias application device is provided,
The first bias applying device can selectively apply a charging bias at the time of image formation to the charging roller or a charging bias at the time of non-image formation in which an AC component has a peak-to-peak voltage larger than the charging bias at the time of image formation.
The second bias applying device can selectively apply a toner recovery bias or a toner discharge bias to the toner recovery member,
The control unit applies the charging bias during image formation to the charging roller at least during image formation, and applies the charging bias during non-image formation to the charging roller at a predetermined timing during non-image formation. The controller further controls the first charging bias applying device, and the controller further controls the second bias applying device at least when the charging bias is applied to the charging roller during the non-image formation. The second bias applying device is controlled so that the toner recovery bias is applied to the toner recovery member when the surface portion of the electrostatic latent image carrier passing through the toner recovery member passes upstream of the charging roller. An image forming apparatus is provided.

  The control unit in the image forming apparatus according to the present invention is configured such that, for the second bias applying device, for example, the toner recovery bias is applied to the toner recovery member at least during image formation, and is determined in advance during non-image formation. The toner discharge bias is applied to the toner recovery member at the timing, and even when non-image formation is performed, the electrostatic latent image passing through the charging roller is applied to the charging roller when the non-image formation charging bias is applied. When the surface portion of the image carrier passes through the toner recovery member upstream of the charging roller, the second bias applying device is controlled so that the toner recovery bias is applied to the toner recovery member. be able to.

  However, the toner discharge bias may be a bias (sequential discharge bias) for discharging a small amount of toner that does not cause image noise while collecting the toner on the toner collecting member. With respect to the bias applying device, for example, the surface portion of the electrostatic latent image carrier that passes through the charging roller when the charging bias is applied to the charging roller when the non-image is formed is upstream of the charging roller. The second bias applying device is configured so that the toner collecting bias is applied to the toner collecting member when passing through the collecting member, and the toner discharging bias (sequential discharging bias) is applied at times other than when the toner collecting bias is applied. It may be controlled.

  Here, “a small amount of toner that does not cause image noise” in “a small amount of toner that does not cause image noise while collecting toner on the toner recovery member” means an amount that can be regarded as causing no image noise in practice. Toner.

In any case, according to the image forming apparatus of the present invention, the transfer residual toner on the electrostatic latent image carrier can be collected by the toner recovery member so as not to interfere with image formation at the time of image formation. Even without using a dedicated cleaner, it is possible to suppress the generation of image noise due to the transfer residual toner and form a good image.
The toner discharged from the toner recovery member onto the electrostatic latent image carrier can be recovered by the developing device and reused.

  Further, a charging bias during non-image formation is applied to the charging roller at a predetermined timing during non-image formation. This non-image-forming charging bias is a charging bias in which the peak-to-peak voltage of the AC component is larger than the image-forming charging bias applied to the charging roller during image formation. By improving the rubbing polishing effect, foreign substances can be removed by polishing so as not to hinder image formation.

  In addition, even during non-image formation, the surface portion of the electrostatic latent image carrier that passes through the charging roller when a charging bias is applied to the charging roller at the upstream side of the charging roller. When passing through the recovery member, the toner recovery bias is applied to the toner recovery member.

Therefore, when applying a charging bias during non-image formation where the peak-to-peak voltage of the AC component is large to the charging roller, the amount of toner passing through the charging roller is kept low as much as the residual toner is collected by the toner collecting member. In addition, toner contamination on the surfaces of the charging roller and the electrostatic latent image carrier is suppressed despite the application of a charging bias during non-image formation where the peak-to-peak voltage of the AC component is large.
Note that if the peak-to-peak voltage of the AC component of the charging bias during non-image formation is made larger than the peak-to-peak voltage of the AC component during the image formation, the effect of rubbing and polishing the surface of the electrostatic latent image carrier by the toner recovery member can be obtained. The improvement is confirmed as will be described later with reference to FIG.

  As described above, according to the image forming apparatus of the present invention, the transfer residual toner remaining on the electrostatic latent image carrier after the transfer of the toner image from the electrostatic latent image carrier to the transfer target is transferred to the cleaner for exclusive use of the transfer residual toner cleaning. It is possible to recover from the electrostatic latent image carrier so that there is no hindrance to image formation without using toner, and to remove foreign matter such as recording medium powder adhering to the electrostatic latent image carrier without using abrasive toner. However, the surface of the electrostatic latent image carrier can be refreshed by polishing and removing so as not to hinder image formation.

The image forming apparatus according to the present invention may be the following (1) to (4).
(1) The developing device includes a developing member for supplying and developing toner to the electrostatic latent image formed on the electrostatic latent image carrier, and for applying a bias to the developing member. A third bias applying device is provided;
The third bias applying device selectively applies a developing bias for transferring toner to the electrostatic latent image on the electrostatic latent image carrier or a bias for preventing toner from transferring to the electrostatic latent image carrier to the developing member. Can
The controller is configured such that an electrostatic latent image carrier surface portion passing through the charging roller when the charging bias is applied to the charging roller during non-image formation passes through the developing member upstream of the charging roller. An image forming apparatus that controls the third bias applying device so that the bias is set so that the toner is not transferred to the electrostatic latent image carrier.

  According to this image forming apparatus, the surface portion of the electrostatic latent image carrier that passes through the charging roller when the charging bias is applied to the charging roller when the non-image forming is applied passes through the developing member on the upstream side of the charging roller. In this case, the bias is set so that the third bias applying device for the developing member does not transfer the toner to the electrostatic latent image carrier. As a result, the adhesion of fog toner to the electrostatic latent image carrier is suppressed, and even if the fog toner recovery performance of the toner recovery member deteriorates with repeated use of the image forming apparatus, the toner passes through the toner recovery member and is charged. Since the amount of fog toner reaching the roller is suppressed, if there is fog toner passing through the toner collecting member, a charging roller or electrostatic latent image generated by applying a non-image charging bias having a large peak-to-peak voltage to the charging member. Stain on the surface of the image carrier is suppressed.

(2) The developing device supplies toner to the electrostatic latent image formed on the electrostatic latent image carrier and develops the developing member, and separates the developing member from the electrostatic latent image carrier. A separation device,
The controller is configured such that an electrostatic latent image carrier surface portion passing through the charging roller when the charging bias is applied to the charging roller during non-image formation passes through the developing member upstream of the charging roller. And an image forming apparatus for controlling the separating device so that the developing member is separated from the electrostatic latent image carrier.

  According to this image forming apparatus, the surface portion of the electrostatic latent image carrier that passes through the charging roller when the charging bias is applied to the charging roller when the non-image forming is applied passes through the developing member on the upstream side of the charging roller. When developing, the developing member is separated from the electrostatic latent image carrier. Accordingly, toner transfer from the developing device to the surface portion of the electrostatic latent image carrier scheduled to pass through the charging roller when the charging bias is applied during non-image formation is suppressed, and toner contamination of the charging roller and the electrostatic latent image carrier is suppressed. Is suppressed so much.

(3) The controller is configured such that the surface portion of the electrostatic latent image carrier passing through the charging roller when the non-image-forming charging bias is applied to the charging roller is upstream of the charging roller. An image forming apparatus that stops the developing device when passing through the apparatus.

  According to this image forming apparatus, the surface portion of the electrostatic latent image carrier that passes through the charging roller when the charging bias is applied to the charging roller when the non-image forming is applied passes through the developing device on the upstream side of the charging roller. When doing so, the developing device is stopped. Accordingly, toner transfer from the developing device to the surface portion of the electrostatic latent image carrier scheduled to pass through the charging roller when the charging bias is applied during non-image formation is suppressed, and toner contamination of the charging roller and the electrostatic latent image carrier is suppressed. Is suppressed so much. The configuration (3) may be used in combination with the configuration (2).

(4) The transfer device faces the electrostatic latent image carrier through an intermediate transfer member which is a kind of the transfer target, and applies a transfer voltage to a toner image formed on the electrostatic latent image carrier. A transfer member for transferring to the intermediate transfer member, and a reverse drive device for the transfer member. The reverse drive device causes the intermediate transfer member to be placed on the surface of the electrostatic latent image carrier by the transfer member. The intermediate transfer member can be separated from the surface of the electrostatic latent image carrier by retracting the transfer member from the contact state,
The controller controls the surface of the latent electrostatic image bearing member that passes through the charging roller when the non-image-forming charging bias is applied to the charging roller to face the transfer member upstream of the charging roller. (1), (2) or (3) for controlling the backward driving device so as to retract the transfer member to separate the intermediate transfer member from the electrostatic latent image carrier when passing the position. The image forming apparatus described.

  According to this image forming apparatus, the surface portion of the electrostatic latent image carrier that passes through the charging roller when the non-image-forming charging bias is applied to the charging roller faces the transfer member upstream of the charging roller. When passing through the position, the intermediate transfer member is separated from the electrostatic latent image carrier. Accordingly, the toner on the intermediate transfer member (for example, secondary transfer residual toner left by wiping by the cleaner of the intermediate transfer member) is suppressed from adhering to the surface portion of the electrostatic latent image carrier, and charging during the non-image formation is performed. The amount of toner on the surface portion of the electrostatic latent image carrier that passes through the charging roller when bias is applied is suppressed to a low level, and toner contamination on the charging roller and the electrostatic latent image carrier is suppressed accordingly.

  In this image forming apparatus, when the intermediate transfer member is separated from the surface of the electrostatic latent image carrier, the bias setting in the developing device is set to a bias setting that does not cause the toner to transfer from the developing member to the electrostatic latent image carrier. Alternatively, the developing device is stopped, or the developing member is retracted from the electrostatic latent image carrier, so that toner is supplied from the developing device onto the electrostatic latent image carrier, and the toner is charged when non-image is formed. The situation of passing through the charging roller at the time of application is prevented.

  As described above, according to the present invention, the surface of the electrostatic latent image carrier that is driven so that the surface moves is charged by the charging device, and an electrostatic latent image is formed in the charged area by the electrostatic latent image forming device. The electrostatic latent image is developed with a developing device to form a toner image, and the toner image is transferred to a transfer target with a transfer device. Transfer residual toner remaining on the electrostatic latent image carrier after transferring the toner image to the toner can be recovered from the electrostatic latent image carrier so that there is no problem in image formation without using a cleaner dedicated to cleaning the residual toner. In addition, it is possible to provide an image forming apparatus capable of polishing and removing foreign matter such as recording medium powder adhering to the electrostatic latent image bearing member without causing trouble in image formation without using abrasive toner. .

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an example of a monochrome image forming apparatus according to the present invention.
The image forming apparatus shown in FIG. 1 includes a drum-type rotationally driven photoreceptor 1 as an electrostatic latent image carrier. The photoconductor 1 is a negatively chargeable photoconductor in this example. The photoconductor 1 is rotationally driven clockwise in FIG. 1 by a photoconductor drive motor (not shown in FIG. 1) (see FIGS. 2 to 5).

  Around the photosensitive member 1, a charging roller 2, an image exposure device 3, a developing device 4, a primary transfer roller 5, a brush roller 6 as an example of a toner collecting member, and the like are arranged in this order. In this example, the primary transfer roller 5 faces the photosensitive member 1 via an intermediate transfer belt 7 which is an example of an intermediate transfer member.

  The intermediate transfer belt 7 is also wound around rollers 71, 72, and 73 in addition to the primary transfer roller 5, and one of these rollers (for example, the roller 72) is rotationally driven by a driving unit (not shown). This rotates counterclockwise in the figure.

  The secondary transfer roller 8 faces the belt portion on the roller 73. A secondary transfer residual toner cleaner (belt cleaner) 70 is provided for the belt portion on the roller 71. In FIG. 1, a timing roller pair 9 is provided on the left side (upstream side in the recording medium conveyance direction) of the secondary transfer roller 8, and a fixing device 10 is provided on the right side (downstream side).

  A first bias applying device PW1 for applying a charging bias is connected to the charging roller 2. The bias application device PW1 applies a power supply PW11 for applying a charging bias at the time of image formation to the charging roller 2 for image formation, and applies a charging bias at the time of non-image formation to the charging roller 2 at a later-described timing at the time of non-image formation. And a switch SW1 for switching between the power sources PW11 and PW12. The charging bias is shown as “charging roller bias” in FIGS. 2 to 5 described later.

Each of the power supplies PW11 and PW12 applies an AC charging bias obtained by superimposing an AC voltage on a DC voltage, and the switching of these power supplies is performed by a switching operation of the switch SW1 under the instruction of the control unit Cont described later.
The charging bias at the time of non-image formation by the power source PW12 is such that the peak-to-peak voltage Vpp of the AC component is larger than that at the time of image formation.

  The brush roller 6 is connected to a second bias applying device PW2 for applying a bias. The bias applying device PW2 includes a power source PW21 for applying a toner recovery bias to the brush roller 6 at a later-described timing at the time of non-image formation at least during image formation, and a brush roller 6 at a predetermined timing to be described later at the time of non-image formation. Includes a power supply PW22 for applying a toner discharge bias and a switch SW2 for switching between the power supplies PW21 and PW22. The bias applied to the brush roller 5 from the bias applying device PW2 is shown as “brush bias” in FIGS. 2 to 5 described later.

  A power supply PW21 for applying a toner recovery bias applies an AC bias in which an AC voltage is superimposed on a DC voltage, and a power supply PW22 for applying a toner discharge bias is a DC power supply. Is performed by the switching operation of the switch SW2.

  The charging roller 2 is rotated in the opposite direction to the photosensitive member by the rotation of the photosensitive member 1. The brush roller 6, the belt 7, and the transfer rollers 5 and 8 are rotationally driven in the direction of the arrow in FIG. Note that the rotation direction of the brush roller 6 may be opposite to that shown in FIG.

  The image exposure apparatus 3 performs image exposure on the photoreceptor 1 with laser light in accordance with image information provided from a computer (not shown) or the like.

In this example, the developing device 4 reversely develops the electrostatic latent image using negatively charged toner, and a developing roller 41 for developing the toner by flying the toner onto the electrostatic latent image on the photoreceptor 1. It has. In this example, the developing roller 41 is disposed with a small toner flying gap from the photoreceptor 1, but may be disposed in contact with the photoreceptor.
The developing roller 41 is rotationally driven in a counterclockwise direction in FIG. 1 at a predetermined timing by a developing drive motor (see FIGS. 2 to 5) not shown in FIG. Note that the rotation direction of the developing roller 41 may be opposite to that shown in FIG. A bias can be applied to the developing roller 41 from the third bias applying device PW3. In this example, the bias applying device PW3 includes power supplies PW31 and PW32 and a switch SW3 for switching between the power supplies.

  The power supply PW31 applies a developing bias to the developing roller 41 for developing an electrostatic latent image, and the power supply PW32 applies a bias to the developing roller 41 so that toner does not fly from the developing roller 41 onto the photosensitive member 1. is there. These power sources are switched by a switching operation of the switch SW3 under the instruction of the control unit Cont described later.

  The control unit Cont controls the operation of the entire image forming apparatus. The operation panel PA is equipped with a print key for instructing the start of image formation, a numeric keypad for designating the number of image formations, a key for designating the recording medium size to be used, and the like. Etc. are connected. Switching operation of the switch SW1 for applying a bias to the photosensitive roller driving motor, development driving motor, charging roller 2, switching operation of the switch SW2 for applying a bias to the brush roller 5, and bias application to the developing roller 41 For example, the switching operation of the switch SW3 is performed under the instruction of the control unit Cont.

Next, a case where images for two pages are sequentially formed under the instruction of the control unit Cont using the image forming apparatus of FIG. 1 will be described with reference to the control sequence of FIG.
“Brush to charging” in FIG. 2 indicates the time required for one point on the surface of the photoreceptor 1 to move from the brush roller 6 to the charging roller 2 by the rotation of the photoreceptor, and “exposure to development”, “ "Brush to exposure", "Exposure to brush" and "Exposure to primary transfer", the same description in FIG. 3 to be described later, and "Development to charging", "Brush to development", the same description in FIG. The same description in FIG. 5 and “development to primary transfer” also indicate the time required for one point on the surface of the photoreceptor 1 to reach the developing roller from the exposure position.

  First, the photosensitive member driving motor is turned on to start rotating the photosensitive member 1, the developing driving motor is turned on, and the developing roller 41 is started to rotate. The charging roller 2, the brush roller 6, the intermediate transfer belt 7, and the primary transfer roller 5 are started. The secondary transfer roller 8 and the like are also started to rotate.

  Further, the charging roller 2 is started to apply a charging bias at the time of image formation from the power source PW11, the brush roller 6 is applied with a toner discharge bias from the power source PW22 as a brush bias, and the developing roller 41 is started to apply a developing bias from the power source PW31. In the control example shown in FIG. 2, the power supply PW32 in the developing bias applying device PW3 is not used).

  An image exposure apparatus 3 performs image exposure on the surface of the photoreceptor 1 charged to a predetermined potential by the charging roller 2 to form an electrostatic latent image. At this time, when the surface portion of the photosensitive member 1 passing through the exposure position passes through the brush roller 6 prior to the exposure, a toner recovery bias is applied to the brush roller 6 from the power source PW21 as a brush bias, which hinders image formation. So that there is no. The electrostatic latent image formed in this manner is reversely developed by the developing roller 41 to which a developing bias is applied from the power source PW31, thereby forming a visible toner image.

On the other hand, the recording paper S is supplied to the timing roller pair 9 from a recording medium (recording paper in this example) not shown.
As the toner image on the photoreceptor 1 arrives at the primary transfer position, the recording paper S is supplied to the transfer position by the timing roller pair 9.

  Thus, the toner image on the photoreceptor is primarily transferred onto the intermediate transfer belt 7 by the primary transfer roller 5, and the toner image transferred to the belt 7 is transferred to the recording paper S by the secondary transfer roller 8. At this time, a primary transfer voltage is applied to the primary transfer roller 5 from a primary transfer power supply (not shown), and a secondary transfer voltage is applied to the secondary transfer roller 8 from a secondary transfer power supply (not shown).

The recording paper S to which the toner image has been transferred passes through the fixing device 10 to fix the toner image, and is subsequently discharged to a paper discharge tray (not shown).
The secondary transfer residual toner on the intermediate transfer belt 7 is removed and cleaned by the belt cleaner 70.

  In this way, the image of the first page is formed. In this example, after the formation of the electrostatic latent image of the first page, the time between sheets corresponding to the interval between the first and second recording sheets is set. After the elapse of time, an electrostatic latent image of the second page is subsequently formed, and then an image is formed on the second recording paper as in the case of the first image.

  The photosensitive member following the electrostatic latent image forming region on the second page, which corresponds to the space between the papers corresponding to the non-image formation, passes through the brush roller 6 on the upstream side of the charging roller, and the non-image formation. When a predetermined portion of the surface passes the brush roller 6 on the upstream side of the charging roller (in other words, when the surface portion of the photoconductor scheduled to form the second page has passed the brush roller 6), the image formation is hindered. Therefore, a toner discharge bias is applied to the brush roller 6 from the power supply PW22, and the toner collected by the brush of the roller 6 is discharged onto the photosensitive member 1 to complete the printing operation (image forming operation).

  The toner discharged in this way is adjusted to a normal charging polarity by the charging roller 2 and is collected by the developing device 4 by the developing roller 41 to which a developing bias is applied, and is reused. Therefore, it is possible to suppress the consumption of toner accordingly.

  The post-processing operation is continued after the printing operation. During this post-processing operation belonging to the time of non-image formation, during a predetermined control time Tc, the charging roller 2 is supplied with a peak of AC component from the power supply PW12 to the charge bias during non-image formation, that is, the charge bias during image formation by the power supply PW11. A charging bias having a large two-peak voltage (Vpp) is applied to the charging roller 2, thereby improving the rubbing and polishing effect of the surface of the photoreceptor 1 by the brush roller 6, and may adhere to the surface of the photoreceptor 1. Foreign matter such as recording paper powder is polished and removed so as not to hinder image formation.

  At this time, when the surface portion of the photoreceptor passing through the charging roller 2 to which a charging bias is applied during non-image formation passes through the brush roller 6 before the charging roller, the brush roller 6 is supplied with a toner recovery bias from the power supply PW21. Thus, the toner adhesion on the surface portion of the photosensitive member is suppressed to a low level, and the charging roller 2 and the photosensitive member 2 are exposed even though the charging bias at the time of non-image formation having a large Vpp is applied to the charging roller 2. The surface contamination of the body 1 is suppressed.

  Thus, after the charging bias is applied during non-image formation, the charging bias is returned to the normal charging bias setting during image formation, and the control sequence ends.

Specific examples of some biases in the image formation described above are shown below.
(1) Charging roller bias
(1-1) Charging bias at the time of image formation by the power source PW11 (when the time is other than the time Tc): 1 kHz sine wave of DC component Vdc = −500 V, AC component Vpp = 1.2 kV. Charge to 500V.
(1-2) Charging bias during non-image formation by power source PW12 (at time Tc):
1kHz sine wave with DC component Vdc = -500V, AC component Vpp = 2.0kV
(2) Development bias by power supply PW31:
DC component Vdc = −320V,
AC component Vpp = 1.3kV, duty 35% 2kHz rectangular wave
(3) Primary transfer bias: DC voltage + 800V
(4) Brush bias
(4-1) Toner recovery bias by power supply PW21:
DC component Vdc = −200V,
AC component Vpp = 1kV, duty 50% 1kHz rectangular wave
(4-2) Toner discharge bias by power supply PW22: DC voltage -500V

  In the brush bias control described above, the brush bias applied to the brush roller 6 is exclusively used as the toner collection bias for collecting the transfer residual toner and the toner discharge bias for discharging the toner exclusively. 6 may be a bias for discharging a small amount of toner that does not cause image noise while being collected (sequential discharge bias).

  Here, “a small amount of toner that does not cause image noise” is an amount of toner that can be regarded as causing no image noise in practice, and a toner discharge bias (sequential discharge bias) is applied to the brush roller 6 to apply the toner to the brush roller. If the toner is not discharged while being collected, the amount of toner is less than the amount of toner present on the photoreceptor 1 and going toward the charging roller 2.

An example of bias in this case is described below.
(1) Charging roller bias
(1-1) Charging bias during image formation by the power source PW11:
DC component Vdc = -500V, AC component Vpp = 1.2kV, 1kHz sine wave
(1-2) Charging bias during non-image formation by the power supply PW12:
1kHz sine wave with DC component Vdc = -500V, AC component Vpp = 2.0kV
(2) Development bias by power supply PW31:
DC component Vdc = −320V,
AC component Vpp = 1.3kV, duty 35% 2kHz rectangular wave
(3) Primary transfer bias: DC voltage + 800V
(4) Brush bias
(4-1) Toner recovery bias by power supply PW21 (at time Tb in FIG. 2):
DC component Vdc = −200V,
AC component Vpp = 1kV, duty 50% 1kHz rectangular wave
(4-2) Toner discharge bias by power supply PW22 (Sequential discharge bias at times other than Tb) (In the case of sequential discharge, power supply PW22 is a power supply that can apply the following AC bias)
DC component Vdc = -100V,
AC component Vpp = 300V, duty 50% 100Hz rectangular wave

  In this case, the surface portion of the photosensitive member that passes through the charging roller 2 when a charging bias with a large Vpp is applied to the charging roller 2 passes through the brush roller 6 before the charging roller. In some cases, a toner recovery bias is applied. In other cases, a toner discharge bias (sequential discharge bias) may be applied.

  In the image forming apparatus of FIG. 1, the switching of the bias is performed by using a changeover switch. However, the charging bias power source and the brush bias power source are each one, and the bias is switched by controlling the output of the power source. It may be.

Other examples of the control sequence are shown in FIG. 3, FIG. 4, and FIG.
In the control sequence of FIG. 3, as in the control sequence of FIG. 2, a charging bias at the time of non-image formation with a large Vpp is applied to the charging roller 2 in the post-processing operation at the time of non-image formation, and the charging roller 2 passes through. When the photosensitive member surface portion passes through the brush roller 6 before the charging roller, a toner recovery bias is applied to the brush roller 6, and the photosensitive member surface portion that is scheduled to pass through the charging roller 2 further passes the developing roller 41. When passing, under the instruction of the control unit Cont, a bias is applied to the developing roller 41 from the power source PW32 shown in FIG.

As a result, the adhesion of fog toner to the photosensitive member 1 is suppressed, and even if the fog toner recoverability of the brush roller 6 deteriorates as the image forming apparatus is used repeatedly, it passes through the brush roller 6 and reaches the charging roller 2. Since the amount of fog toner is suppressed, the presence of fog toner passing through the brush roller suppresses contamination on the surface of the charging roller 2 and the photoreceptor 1 which is generated by applying a non-image charging bias having a large Vpp to the charging roller 2. Is done.
Other points are substantially the same as the control of FIG.

The following two examples are shown as bias settings to be applied to the developing roller 41 so that the toner does not fly from the developing roller 41 to the photoreceptor 1.
First example (AC bias)
DC component Vdc = −320V,
AC component Vpp = 700V Duty 35% 2kHz square wave (Vaiasu with reduced Vpp)
Second example (DC bias)
DC voltage -320V (In this case, a single power source capable of applying a bias in which an AC voltage is superimposed on the DC voltage is used as a bias power source for the developing roller 41, the AC component output may be stopped and only the DC output may be used.)

  Regardless of which of the first and second bias examples described above, the toner discharge from the brush roller 6 is not only performed at a predetermined timing during non-image formation, but also in the case of the sequential discharge described above. Applicable.

  In the control sequence of FIG. 4, as in the control sequence of FIG. 2, a charging bias at the time of non-image formation having a large Vpp is applied to the charging roller 2 in the post-processing operation at the time of non-image formation, and passes through the charging roller 2. When the photosensitive member surface portion passes through the brush roller 6 before the charging roller, a toner recovery bias is applied to the brush roller 6, and the photosensitive member surface portion that is scheduled to pass through the charging roller 2 further passes the developing roller 41. When passing, under the instruction of the control unit Cont, the bias application to the developing roller 41 is stopped and the developing drive motor is stopped to stop the developing roller. That is, the developing device 4 is stopped. Other points are substantially the same as the control of FIG.

Also in the control sequence of FIG. 4, the adhesion of fog toner to the photosensitive member 1 is suppressed.
In the control sequence of FIG. 4, the toner discharged from the brush roller 6 onto the photosensitive member 1 when the developing roller 41 is stopped is transferred onto the intermediate transfer belt 7 by the primary transfer roller 5, and the belt cleaner 70. Is processed.

  When the control sequence of FIG. 4 is employed, the developing device 4 may be stopped and the developing roller 41 may be separated from the photoreceptor 1 as described above. For the separation of the developing roller, for example, a separation device D1 is provided as illustrated by a chain line in FIG. 1, and the entire developing device 4 is separated from the photoreceptor 1 by the separation device D1 under the instruction of the control unit Cont. Yes. Further, the developing roller 41 can be disposed at the normal developing position with respect to the photoreceptor 1 by reversely operating the separating device. The separation device D1 can be configured using a conventionally known mechanism such as a cam mechanism or a solenoid utilization mechanism.

  When the developing roller 41 is separated from the photosensitive member 1 in this way, the separation of the toner to the photosensitive member 1 is suppressed by the separation, so that it is not necessary to stop driving the developing roller 41 or stop applying the bias. By stopping, there is an advantage that the life of the developing device 4 is extended accordingly.

  In the control sequence of FIG. 5 as well, as in the control sequence of FIG. 2, a charging bias at the time of non-image formation having a large Vpp is applied to the charging roller 2 in the post-processing operation at the time of non-image formation, and passes through the charging roller 2. When the photosensitive member surface portion passes through the brush roller 6 before the charging roller, a toner recovery bias is applied to the brush roller 6.

In the control sequence of FIG. 5, similarly to the control sequences of FIG. 3 and FIG. 4, after the toner on the brush roller 6 is discharged to the photosensitive member 1 after image formation, the brush bias is set as the toner recovery bias and discharged. After the toner is collected by the developing device 4 (after “brush-development”), the developing device 4 is stopped to prevent toner flying from the developing device 4 to the photosensitive member 1 (toner to the developing roller shown in FIG. 3). The toner may be prevented from flying by switching to a bias for preventing flying or by separating the developing roller from the photosensitive member), and when the surface of the photosensitive member where toner flying is prevented passes through the primary transfer roller 5, the primary transfer is performed. The roller 5 is moved backward to separate the belt 7 from the photoreceptor 1.
Other points are substantially the same as the control of FIG.

  When the surface of the photosensitive member that has passed through the primary transfer region with the transfer belt 7 separated from the photosensitive member 1 passes through the charging roller 2 in this way, a charging voltage at the time of non-image formation having a large Vpp is applied to the charging roller 2. To do.

  According to this control, since the belt 7 is separated from the photosensitive member 1 after the toner flying in the developing device 4 is prevented, the toner to be transferred to the belt 7 is not transferred to the belt 7 but is transferred to the brush roller 6. And the toner passing through the cleaner 70 with respect to the belt 7 is retransferred to the photoreceptor 1 in the primary transfer region and adhered to the photoreceptor 1. be able to.

  In order to retract the primary transfer roller 5 in order to separate the belt 7 from the photoreceptor 1, a reverse drive device D2 for the transfer roller 5 is provided as shown by a chain line in FIG. At the same time, the transfer roller 5 may be moved backward by the driving device D2. The belt 7 can be brought into contact with the photosensitive member 1 again by reversely operating the driving device D2. The drive device D2 can be configured using a conventionally known mechanism such as a cam mechanism or a solenoid utilization mechanism.

  In each of the above control sequences, the timing for applying the charging bias at the time of non-image formation having a large Vpp to the charging roller 2 is set during the post-processing operation after the printing operation. However, the present invention is not limited to this. It may be set during the previous preprocessing operation, or may be set during both the postprocessing operation and the preprocessing operation. Further, during a continuous printing operation in which a plurality of images are formed, the printing operation (image forming operation) may be interrupted, and the charging bias may be applied to the charging roller 2 during non-image formation. The operation panel PA or the like may be provided with a command instruction function, and when the command is executed, a charging bias at the time of non-image formation may be applied to the charging roller 2.

  FIG. 7A shows the relationship between Vpp and the abrasiveness of the photosensitive member 1 by the brush roller 6 by changing the Vpp of the AC component while the DC component in the ba ice applied to the charging roller 2 is constant at Vdc = −500V. The results of the investigation are shown.

  FIG. 7A shows a photoconductor per one rotation obtained by driving the image forming apparatus of the type shown in FIG. 1 for a long time and obtaining the outer diameter difference of the photoconductor 1 before and after driving and the driving rotation speed of the photoconductor 1. The relationship between the amount of wear and Vpp is shown. In FIG. 7A, the wear amount unit [pm / rot] on the vertical axis indicates the wear amount [pm] per rotation of the photoreceptor.

  It can be seen that when Vpp is increased, the amount of wear is also increased, and when Vpp is increased, the photoconductor polishing performance by the brush roller 6 is improved.

  In FIG. 7B, the direct current component in the ba ice applied to the charging roller 2 is made constant at Vdc = −500 V, the alternating current component Vpp is changed, and the relationship between Vpp and the contamination of the surface of the charging roller 2 and the like is examined. Results are shown.

  FIG. 7B shows the results of evaluating the stains on the surfaces of the photoreceptor 1 and the charging roller 2 after driving the image forming apparatus of the type shown in FIG. 1 for a long time without toner collection by the brush roller 6. Show. It can be seen that when Vpp is increased, both the surface of the photoreceptor and the surface of the charging roller become dirty.

  Although the monochrome image forming apparatus employing the intermediate transfer belt has been described above, the present invention can also be applied to a monochrome image forming apparatus not employing an intermediate transfer member, and a so-called four-cycle type, tandem type color image forming apparatus. .

FIG. 6 shows an outline of the configuration of an example of a tandem type color image forming apparatus.
In this color image forming apparatus, a yellow image forming portion Y, a magenta image forming portion M, a cyan image forming portion C, and a black image forming portion K are arranged along an intermediate transfer belt 7 ′ that is rotationally driven.

  Each image forming unit includes a drum-type photosensitive member 1 ′, a charging roller 2 ′ sequentially disposed around the drum-type photosensitive member 1 ′, an image exposure device 3 ′, a developing device 4 ′ having a developing roller 41 ′, a primary transfer roller 5 ′, a toner collecting unit. A brush roller 6 ′, which is an example of a member, is provided.

  The intermediate transfer belt 7 ′ is wound around rollers 71 ′, 72 ′, 73 ′, and can be driven to rotate in the direction of the arrow in the figure by driving any of the rollers. The primary transfer roller 5 ′ of each image forming unit presses the belt 7 ′ against the photoreceptor 1 ′.

The secondary transfer roller 8 'faces the belt portion on the roller 72', and a cleaner 70 'is provided for the belt portion on the roller 73'.
A timing roller pair 9 ′ is disposed on the upstream side of the secondary transfer roller 8 ′, and a fixing device 10 ′ is disposed on the downstream side.

According to this image forming apparatus, a monochrome image can be formed using any one image forming unit under the control of a control unit (not shown), and a color image can be formed using two or more image forming units. It can also be formed.
An example in which a full color image is formed using all the image forming units Y, M, C, and K will be described below.

  First, in the yellow image forming portion Y, the rotationally driven photoreceptor 1 ′ is charged by the charging roller 2 ′, and an electrostatic latent image is formed in the charged area by image exposure from the image exposure device 3 ′. The electrostatic latent image is developed by the developing device 4 ′ to form a yellow toner image, and the toner image is primarily transferred by the primary transfer roller 5 ′ onto the belt 7 ′ that is rotationally driven.

  Similarly, a magenta toner image is formed by the image forming unit M, a cyan toner image is formed by the image forming unit C, and a black toner image is formed by the image forming unit K, and these toner images are sequentially transferred onto the belt 7 ′ in a primary transfer. The The multiple toner image formed in this way is sent from the recording medium supply unit (not shown) to the timing roller pair 9 ′, and is sent to the recording medium S sent to the secondary transfer area in accordance with the arrival of the multiple toner image on the belt. Secondary transfer is performed by the next transfer roller 8 ′, and the image is fixed on the recording medium S by the fixing device 10 ′.

By applying the present invention to this tandem type color image forming apparatus, the control sequence shown in FIG. 2, FIG. 3, FIG. 4 or FIG.
When the primary transfer roller is moved backward as in the control sequence of FIG. 5, the primary transfer roller 5 ′ of each image forming unit may be moved back together by a backward drive device (not shown).

  The present invention does not obstruct image formation even if the transfer residual toner remaining on the electrostatic latent image carrier after the transfer of the toner image from the electrostatic latent image carrier to the transfer target is not used. It is possible to recover from the electrostatic latent image carrier so that there is no problem, and foreign matter such as recording medium powder adhering to the electrostatic latent image carrier is not affected by image formation without using abrasive toner. The present invention can be used to provide an image forming apparatus that can be removed by polishing.

1 is a diagram illustrating an outline of a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an example of a control sequence of the image forming apparatus illustrated in FIG. 1. FIG. 6 is a diagram illustrating another example of a control sequence of the image forming apparatus illustrated in FIG. 1. FIG. 10 is a diagram illustrating still another example of the control sequence of the image forming apparatus illustrated in FIG. 1. FIG. 10 is a diagram illustrating still another example of the control sequence of the image forming apparatus illustrated in FIG. 1. 1 is a diagram showing an outline of a configuration of an example of a tandem type color image forming apparatus to which the present invention can be applied. FIG. 7A is a diagram showing the relationship between the peak-to-peak voltage Vpp of the AC component of the bias applied to the charging roller and the photoconductor polishing property by the toner recovery member (here, a brush roller). FIG. 4 is a diagram showing a relationship between a peak-to-peak voltage Vpp of an AC component of a bias applied to the charging roller and dirt on each surface of the charging roller and the photoreceptor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging roller 3 Image exposure apparatus 4 Developing apparatus 41 Developing roller 5 Primary transfer roller 6 Brush roller (an example of a toner collecting member)
7 Intermediate transfer belts 71, 72, 73 Belt winding roller 70 Belt cleaner 8 Secondary transfer roller 9 Timing roller pair 10 Fixing device Cont Control unit PA Operation panel PW1 First bias applying device PW11 Charging bias power supply PW12 during image formation Non-image Charging bias power supply PW2 During formation Second bias application device PW21 Toner recovery bias power supply PW22 Toner discharge bias power supply PW3 Third bias application device PW31 Development bias power supply PW32 Power supply SW1, SW2, SW3 for toner jump prevention bias setting Switch D1 Development roller Separation device D2 Reverse drive device S for primary transfer roller Recording medium

Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit 1 'Photoconductor 2' Charging roller 3 'Image exposure device 4' Developing device 41 'Developing roller 5' Primary transfer roller 6 'Brush Roller (one example of toner recovery member)
7 'intermediate transfer belts 71', 72 ', 73' belt winding roller 70 'belt cleaner 8' secondary transfer roller 9 'timing roller pair 10' fixing device

Claims (5)

The surface of the electrostatic latent image carrier that is driven so that the surface is moved is charged by a charging device, an electrostatic latent image is formed in the charged area by an electrostatic latent image forming device, and the electrostatic latent image is An image forming apparatus that develops a toner image by a developing device and transfers the toner image to a transfer target by a transfer device,
The charging device includes a charging roller disposed in contact with the surface of the electrostatic latent image carrier, and a first bias applying device that applies a charging bias in which a DC voltage is superimposed on an AC voltage to the charging roller;
A toner recovery member is disposed on the surface of the electrostatic latent image carrier on the downstream side of the transfer device and on the upstream side of the charging device so as to rub against the surface of the electrostatic latent image carrier, A second bias applying device for applying a bias to the toner collecting member is provided;
Further, a control unit for controlling the first bias application device and the second bias application device is provided,
The first bias applying device can selectively apply a charging bias at the time of image formation to the charging roller or a charging bias at the time of non-image formation in which an AC component has a peak-to-peak voltage larger than the charging bias at the time of image formation.
The second bias applying device can selectively apply a toner recovery bias or a toner discharge bias to the toner recovery member,
The control unit applies the charging bias during image formation to the charging roller at least during image formation, and applies the charging bias during non-image formation to the charging roller at a predetermined timing during non-image formation. The controller further controls the first charging bias applying device, and the controller further controls the second bias applying device at least when the charging bias is applied to the charging roller during the non-image formation. The second bias applying device is controlled so that the toner recovery bias is applied to the toner recovery member when the surface portion of the electrostatic latent image carrier passing through the toner recovery member passes upstream of the charging roller. An image forming apparatus. The developing device includes a developing member for supplying and developing toner to the electrostatic latent image formed on the electrostatic latent image carrier, and a third bias for applying a bias to the developing member. An application device is provided,
The third bias applying device selectively applies a developing bias for transferring toner to the electrostatic latent image on the electrostatic latent image carrier or a bias for preventing toner from transferring to the electrostatic latent image carrier to the developing member. Can
The controller is configured such that an electrostatic latent image carrier surface portion passing through the charging roller when the charging bias is applied to the charging roller during non-image formation passes through the developing member upstream of the charging roller. The image forming apparatus according to claim 1, wherein the third bias applying device is controlled so as to set the bias so that the toner is not transferred to the electrostatic latent image carrier. The developing device includes a developing member for supplying toner to the electrostatic latent image formed on the electrostatic latent image carrier and developing it, and a separating device for separating the developing member from the electrostatic latent image carrier. Including
The controller is configured such that an electrostatic latent image carrier surface portion passing through the charging roller when the charging bias is applied to the charging roller during non-image formation passes through the developing member upstream of the charging roller. The image forming apparatus according to claim 1, wherein the separating device is controlled so that the developing member is separated from the electrostatic latent image carrier.   The controller is configured such that the surface portion of the electrostatic latent image carrier passing through the charging roller when the non-image-forming charging bias is applied to the charging roller passes through the developing device on the upstream side of the charging roller. 4. The image forming apparatus according to claim 1, wherein the developing device is stopped when performing the operation. The transfer device faces the electrostatic latent image carrier through an intermediate transfer member, which is a type of the transfer target, and applies a toner voltage formed on the electrostatic latent image carrier to a transfer voltage. A transfer member for transferring to the intermediate transfer member and a reverse drive device for the transfer member. The reverse drive device causes the intermediate transfer member to contact the surface of the electrostatic latent image carrier by the transfer member. The intermediate transfer member can be separated from the surface of the electrostatic latent image carrier by retracting the transfer member from the
The controller controls the surface of the latent electrostatic image bearing member that passes through the charging roller when the non-image-forming charging bias is applied to the charging roller to face the transfer member upstream of the charging roller. 5. The image forming apparatus according to claim 2, wherein the backward drive device is controlled so that the transfer member is moved backward to separate the intermediate transfer member from the electrostatic latent image carrier when passing the position.