JP4603868B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copier using an electrophotographic system.

  Conventionally, an image forming apparatus using an electrophotographic method generally scrapes toner (transfer residual toner) remaining on a photoconductor after the toner image is transferred from the electrophotographic photoconductor (photoconductor) to the transfer target. In order to drop, it has a cleaning device with a cleaning blade. There has also been proposed a cleanerless system in which the transfer residual toner is collected by, for example, a developing device, thereby omitting the cleaning device.

  In an image forming apparatus having a cleaning device, the photoconductor is rotated in reverse (Patent Document 1) or two-component development in order to prevent the transfer residual toner from adhering to the photoconductor at the edge of the cleaning blade. In a cleanerless image forming apparatus using this method, charging is performed after an emergency stop operation when an abnormality such as a jam (paper jam) occurs or after an instantaneous power interruption (forcibly turning off the power due to a power failure, etc.). In order to prevent the untransferred toner from adhering to a portion or the like, it has been proposed to reversely rotate the photosensitive member during the return operation (Patent Document 2). In this way, the photoconductor may be rotated in reverse as necessary.

  In addition, in an intermediate transfer type image forming apparatus that transfers an image on a photosensitive member to an intermediate transfer member and then transfers it to a transfer material, the photosensitive member and the intermediate transfer member are rotated when the photosensitive member is rotated reversely according to the above-described requirements. In order to prevent such rubbing, the intermediate transfer member may also be rotated in reverse in accordance with the operation of the photosensitive member.

  However, when the photosensitive member or the intermediate transfer member is rotated in the reverse direction, the transfer residual toner on the downstream side of the transfer unit in the normal rotation direction on the photosensitive member or the intermediate transfer member, or the transfer residual toner accumulated in the cleaning unit, It may return to the transfer section. The toner returning to the transfer portion may adhere to transfer means using a sponge roller or the like in many cases, and may stain the back surface of the transfer material during subsequent image formation.

The problem is that, for example, in an image forming apparatus using an intermediate transfer member, the transfer member (secondary transfer member) opposing member also serves as the opposing member of the intermediate transfer member cleaning unit. When the toner is close, a large amount of untransferred toner returns to the transfer portion, which may be particularly serious.

For example, by providing a separation mechanism that separates the transfer unit from the photosensitive member or the intermediate transfer member, the transfer unit is separated when the photosensitive member or the intermediate transfer member is rotated in the reverse direction, thereby preventing the toner from adhering to the transfer unit. It is considered possible. However, providing such a separating mechanism for the transfer means leads to an increase in the cost of the apparatus.
JP 2003-015471 A JP 2003-015481 A

An object of the present invention is to form an image capable of preventing toner from adhering to the secondary transfer member when the intermediate transfer member is moved in the direction opposite to that when transferring the toner image from the intermediate transfer member to the transfer material. Is to provide a device.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a rotatable image carrier that carries a toner image, a developing unit that develops a toner image on the image carrier, a rotatable intermediate transfer member, and an intermediate from the image carrier. A primary transfer member that primarily transfers a toner image to a transfer member; a first cleaning unit that collects toner that is not transferred to the intermediate transfer member by the primary transfer member; A secondary transfer member that secondarily transfers a toner image to a transfer material; and a second cleaning unit that collects toner remaining on the intermediate transfer member that is not transferred to the transfer material by the secondary transfer member. The image carrier and the intermediate transfer member can be rotated in a direction opposite to that at the time of image formation. The image carrier is rotated in the reverse direction, and the toner on the image carrier is collected by the developing unit. Collection mode can be executed In the image forming apparatus, the image forming apparatus includes a bias output unit that outputs a bias voltage to the secondary transfer member, and when the recovery mode is executed, the first stage of rotating the intermediate transfer member in the reverse direction; And a second stage in which the intermediate transfer member is rotated in the same direction as that during image formation after the first stage, and the bias output means includes both the first stage and the second stage. An image having a polarity opposite to a bias voltage output to the secondary transfer member when the toner image is secondarily transferred from the intermediate transfer member to the transfer material is output to the secondary transfer member. Forming device .

According to the present invention, it is possible to prevent toner from adhering to the secondary transfer member when the intermediate transfer member is moved in the direction opposite to that when the toner image is transferred from the intermediate transfer member to the transfer material.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
FIG. 1 shows a schematic cross section of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type image forming apparatus that employs a two-component development method and an intermediate transfer method. That is, the image forming apparatus 100 of this embodiment, an image bearing member as an image bearing member configured to bear a toner image formed by toner after the electrostatic image is formed is supplied, the image bearing this And an intermediate transfer member carrying a toner image transferred from the member . The image forming apparatus 100 is a full-color image on a transfer material (recording paper, OHP sheet, cloth, etc.) by electrophotography in accordance with an image information signal from a host device such as a personal computer connected to the image forming apparatus body or an image reading apparatus. Can be formed.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, third, and fourth image forming units PY, PM, PC, and PK that respectively form yellow, magenta, cyan, and black color images. Have In the present embodiment, the configuration and operation of each image forming unit are substantially the same except for different development colors, and hence belong to the image forming unit for any color unless otherwise distinguished. The subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements will be omitted for general explanation.

The image forming apparatus 100 forms a monochromatic toner image on a cylindrical electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier based on an image signal in each image forming portion P. the single-color toner image Gabe belt-shaped intermediate transfer body (hereinafter referred to as "intermediate transfer belt".) superimposed on 50 multi-color toner image is formed. Then, after the multicolor toner image is transferred from the intermediate transfer belt 50 to the transfer material S, the multicolor toner image is fixed on the transfer material S.

  More specifically, the image forming unit P includes a charger 2 as a charging unit, a laser scanner 3 as an exposure unit, and a developing unit 4 as a developing unit around the photosensitive drum 1. A transfer unit 5 including an intermediate transfer belt 50 is provided so as to face the photosensitive drum 1 of each image forming unit P.

  In this embodiment, the photosensitive drum 1 is configured by applying an organic optical transmission layer on the outer periphery of an aluminum cylinder. The photosensitive drum 1 rotates by receiving a driving force of a driving motor (not shown) as driving means. The drive motor can rotate the photosensitive drum 1 forward and backward, and at the time of normal image formation, that is, at the time of forming an image to be transferred to the transfer material S and output, the photosensitive drum 1 according to the image forming operation. Is rotated in the direction of the arrow F1 (counterclockwise) (hereinafter referred to as “forward rotation”).

  During normal image formation, the rotating photosensitive drum 1 is uniformly charged by the charger 2. In this embodiment, the charger 2 is a charging roller that contacts the photosensitive drum 1 and rotates following the rotation of the photosensitive drum 1. A DC voltage having a predetermined polarity (negative polarity in this embodiment) is applied to the charging roller 2 as a charging bias from a charging bias power source (not shown).

  The charged photosensitive drum 1 is scanned and exposed by a laser scanner 3 in accordance with an image signal. As a result, an electrostatic image (latent image) is formed on the photosensitive drum 1. The exposure light is sent from a laser scanner 3 driven by an image formation control unit (not shown) according to a signal converted by an image processing unit (not shown) based on the image signal. By selectively exposing the surface of the photosensitive drum 1 with this light, an electrostatic image is formed on the photosensitive drum 1.

  The electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the developing device 4. In this embodiment, the developing device 4 contains a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as developers. Further, the developing device 4 includes a developing sleeve 41 that is rotatably provided as a developer carrying member. The developing sleeve 41 is made of a nonmagnetic metal and incorporates a magnet roll (not shown) as a magnetic field generating means. The magnet roll has a plurality of magnetic poles along the peripheral surface, and is fixedly arranged with respect to the developing device 4.

  The two-component developer accommodated in the developing device 4 is carried on the surface of the developing sleeve 41 by the magnetic force of the magnet roll. The amount of the two-component developer carried on the developing sleeve 41 is regulated by a developer regulating member (not shown), and the developing sleeve 41 rotates to an area (developing area) facing the photosensitive drum 1. Be transported. The two-component developer on the developing sleeve 41 forms spikes (magnetic brushes) in the developing region by the magnetic field formed by the magnetic poles in the vicinity of the developing region of the magnet roll. In this embodiment, the magnetic brush is brought into contact with the photosensitive drum 1. The developing sleeve 41 is applied with a developing bias power source (not shown) in which both components of a DC voltage having a predetermined polarity (negative polarity in this embodiment) / potential and an AC voltage are superimposed. The Thus, the toner in the two-component developer is supplied to the photosensitive drum 1 according to the electrostatic image on the photosensitive drum 1.

  In this embodiment, the electrostatic image on the photosensitive drum 1 is reversely developed, that is, the toner charged to the same polarity (negative polarity in this embodiment) as the charged polarity of the photosensitive drum 1 is used as an exposed portion on the photosensitive drum 1. It develops by making it adhere to (the part where electric potential attenuate | damped). The developing device 4 is detachably attached to the image forming apparatus main body. The developing device 4 is connected to a toner cartridge 11 as a replenishing developer container that can be attached to and detached from the image forming apparatus main body. Then, a replenishment developer including toner corresponding to the amount consumed by development is replenished from the toner cartridge 11 to the developing device 4 as needed.

  The developing device 4 of this embodiment also serves as a cleaning unit that removes transfer residual toner on the photosensitive drum 1 as will be described later.

The toner image formed on the photosensitive drum 1 is transferred (primary transfer) to an intermediate transfer belt 50 provided in the transfer unit 5. In this embodiment, the intermediate transfer belt 50 is wound around three rollers 53, 54, and 55 and rotates (rotates) in contact with the photosensitive drum 1 of each image forming unit P. The intermediate transfer belt 50 rotates when a driving force of a driving motor (not shown) as driving means is transmitted to the driving roller 53 among the three rollers. The drive motor can rotate the drive roller 53 forward and backward to rotate the intermediate transfer belt 50 forward and backward. During normal image formation, the intermediate transfer belt 50 is rotated in the direction indicated by the arrow F2 (clockwise). Rotate (hereinafter referred to as “forward rotation”). A primary transfer roller 51, which is a primary transfer member serving as a primary transfer unit , is pressed against the photosensitive drum 1 via the intermediate transfer belt 50, thereby forming a nip (primary transfer portion) n1 where the intermediate transfer belt 50 and the photosensitive drum 1 are in contact with each other. Has been.

  For example, during the formation of a full-color image, the intermediate transfer belt 50 rotates as each photosensitive drum 1 rotates, and each primary transfer roller 51 has a polarity opposite to the normal charging polarity of toner (negative polarity in this embodiment). A bias (primary transfer bias) (positive transfer in this embodiment) is applied from a primary transfer bias power source (not shown). As a result, the single color toner images on the respective photosensitive drums 1 are sequentially transferred to the intermediate transfer belt 50 at the primary transfer portion n1.

Thereafter, the multi-color toner image on the intermediate transfer belt 50 is transferred (secondary transfer) to the transfer material S all at once. In this embodiment, the transfer material S is nipped and conveyed by an intermediate transfer belt 50 and a secondary transfer roller 52 which is a secondary transfer member as a secondary transfer unit. In addition, a bias (secondary transfer bias) having a polarity (positive polarity in this embodiment) opposite to the normal charging polarity (negative polarity in this embodiment) of the toner is applied to the secondary transfer roller 52. Applied from (FIG. 3). As a result, the multicolor toner image on the intermediate transfer belt 50 is transferred to the transfer material S. The secondary transfer roller 52 is disposed so as to face a counter roller 53 as a counter member among the rollers on which the intermediate transfer belt 50 is stretched. The secondary transfer roller 52 is always pressed toward the intermediate transfer belt 50, and a nip (secondary transfer portion) n2 where the intermediate transfer belt 50 and the secondary transfer roller 52 are always in contact is formed.

  Here, the transfer material S is fed one by one from the cassette 9a or the manual feed tray 9b as the transfer material supply unit, and then synchronized with the multicolor toner image on the intermediate transfer belt 50 by the registration roller 10. It is conveyed to the secondary transfer unit n2.

  The transfer material S onto which the multicolor toner image has been transferred is separated from the intermediate transfer belt 50 and conveyed to a fixing unit 7 as a fixing unit. The fixing unit 7 includes a fixing roller 71 that heats the transfer material S and a pressure roller 72 that presses the transfer material S against the fixing roller 71. Both rollers 71 and 72 are formed in a hollow shape and incorporate heaters 73 and 74, respectively. The fixing unit 7 melts and fixes the multicolor toner image transferred onto the transfer material S by nipping and conveying the transfer material S between the fixing roller 71 and the pressure roller 72. That is, the transfer material S holding the multicolor toner image is conveyed by the fixing roller 71 and the pressure roller 72, and heat and pressure are applied to fix the toner on the surface.

  Thereafter, the transfer material S on which the toner image is fixed is discharged to a discharge tray (not shown) by a discharge roller (not shown).

  The transfer residual toner remaining on the photosensitive drum 1 in the primary transfer step is simultaneously cleaned by the developing device 2. That is, the untransferred toner remaining on the photosensitive drum 1 in the primary transfer process changes to positive polarity due to the influence of the primary transfer bias. When the transfer residual toner passes through a nip formed between the charging roller 2 and the photosensitive drum 1, it is again negatively charged by the charging bias applied to the charging roller 2. Further, when the toner is conveyed by the rotation of the photosensitive drum 1 and passes through the developing region, the developing bias returns to the developing sleeve 41 side in the non-image portion and the photosensitive drum 1 in the image portion, as with the toner in the developing device 4. Adhere to. Thus, in this embodiment, the cleaner 4 system is realized by providing the developing device 4 with a function of collecting and reusing the transfer residual toner. That is, in this embodiment, the development area is the cleaning portion CL1 of the photosensitive drum 1.

  On the other hand, the transfer residual toner remaining on the intermediate transfer belt 50 in the secondary transfer process is cleaned by an intermediate transfer body cleaner 8 as a cleaning unit. The intermediate transfer body cleaner 8 includes a cleaning blade 81 as a cleaning member that scrapes off the transfer residual toner on the intermediate transfer belt 50, and a scoop sheet 82 that collects the scraped toner. In the cleaning blade 81, the edge portion on the free end side comes into contact with the surface of the intermediate transfer belt 50 and scrapes off the transfer residual toner on the intermediate transfer belt 50. That is, in this embodiment, the contact portion of the cleaning blade 81 with the intermediate transfer belt 50 becomes the cleaning portion CL2 of the intermediate transfer belt 50. The transfer residual toner removed from the intermediate transfer belt 50 by the cleaning blade 81 is stored in a waste toner container (not shown). In this embodiment, the cleaning blade 81 is always pressed toward the intermediate transfer belt 50.

  Note that the image forming apparatus 100 can naturally form a single color or a multicolor image using a single or a plurality of image forming units for a desired color.

[Return operation]
In this embodiment, the image forming apparatus 100 performs an emergency stop operation when an abnormality such as a jam (paper jam) occurs. Examples of the emergency stop operation include stopping the rotation of the photosensitive drum 1 and the intermediate transfer belt 50, and stopping the supply of bias to the charging roller 2, the developing sleeve 41, the primary transfer roller 51, the secondary transfer roller 52, and the like.

Then, after such an emergency stop operation or after a momentary power interruption (forcibly turning off the power due to a power failure or the like), when the image forming apparatus 100 becomes operable again, the image is displayed. The forming apparatus 100 is in a state where image formation can be resumed after performing a predetermined return operation (collection mode) .

  That is, when the photosensitive drum 1 is stopped during an emergency stop operation due to a jam (paper jam) or when the power supply is instantaneously cut off, the charging roller 2 and the primary transfer roller 51 are interposed as shown in FIG. In some cases, untransferred toner t may remain. For this reason, in this embodiment, after the emergency stop operation as described above or during the return operation after a momentary power interruption, as shown in FIG. And a recovery bias (for example, a bias having a polarity opposite to that during normal image formation) is applied to the developing sleeve 41 of the developing device 4 in the illustrated arrow B1 direction (clockwise) (hereinafter referred to as “reverse rotation”). The toner is applied and untransferred toner is collected in the developing device 4. This prevents the untransferred toner t from adhering to the charging roller 2.

  By the way, at the time of the returning operation, in order to prevent the surface of the photosensitive drum 1 or the intermediate transfer belt 50 from being worn by the intermediate transfer belt 50 disposed in contact with the photosensitive drum 1 being rubbed against the photosensitive drum 1. The intermediate transfer belt 50 also needs to be rotated (hereinafter referred to as “reverse rotation”) in the direction of the arrow B2 (counterclockwise) in the direction opposite to that during normal image formation in accordance with the movement of the photosensitive drum 1. .

  However, if the distance from the secondary transfer roller 52 to the cleaning unit CL2 in the forward rotation direction F2 of the intermediate transfer belt 50 is L, the intermediate transfer belt cleaner 8 accumulates when the intermediate transfer belt 50 is rotated backward by a distance L or more. The transferred untransferred toner t returns to the secondary transfer portion n2.

  At this time, particularly in the configuration in which the secondary transfer roller 52 is always in contact with the intermediate transfer belt 50, the transfer residual toner t returned to the secondary transfer portion n2 adheres to the secondary transfer roller 52, and the subsequent printing is performed. Sometimes the back surface of the transfer material S is easily soiled. Even when the distance for reversely rotating the transfer belt 50 is L or less, the transfer residual toner t remaining on the intermediate transfer belt 50 in a small amount may adhere to the secondary transfer roller 52.

Therefore, in this embodiment, in the image forming apparatus 100, the secondary transfer bias power source 56 as a bias output unit that outputs a bias to the secondary transfer roller 52 outputs the first bias, and the intermediate transfer belt 50 is the first transfer belt 50. In the first direction (forward rotation direction) F2 and the toner image on the intermediate transfer belt 50 is transferred to the transfer material P, and the secondary transfer bias power source 56 outputs the second bias and intermediate The second operation (the first stage of the recovery mode ) in which the transfer belt 50 moves in the second direction (reverse rotation direction) B2 is performed, and the polarities of the first bias and the second bias are made different. The configuration.

  In this embodiment, the first operation is performed at the time of normal image formation. At this time, the transfer bias power source 56 uses the secondary transfer bias at the time of normal image formation as the first bias, that is, normal charging of toner. A bias (hereinafter referred to as “normal polarity bias”) having a polarity opposite to the polarity (positive polarity in this embodiment) is output (FIG. 3). On the other hand, in the present embodiment, the second operation is performed during the return operation. At this time, the transfer bias power source 56 has a polarity opposite to that of the secondary transfer bias during normal image formation as the second bias, that is, toner. A bias (hereinafter referred to as “reverse polarity bias”) having the same polarity as the normal charging polarity (negative polarity in this embodiment) is output (FIG. 4).

  More specifically, FIG. 3A shows the secondary transfer portion n2 during normal image formation, and FIG. 3B shows the rotation of the intermediate transfer belt 50 and the bias applied to the secondary transfer roller 52 at that time. The schematic control chart of is shown. In this embodiment, during normal image formation, the intermediate transfer belt 50 rotates forward (in the direction of arrow F2), and a normal polarity bias (positive polarity in this embodiment) is applied to the secondary transfer roller 52.

  On the other hand, FIGS. 4A and 4B are views similar to FIGS. 3A and 3B when the intermediate transfer belt 50 is reversely rotated during the return operation. In this embodiment, when the intermediate transfer belt 50 is rotated reversely (in the direction of arrow B2) during the return operation, the secondary transfer roller 52 has a reverse polarity bias, that is, the same polarity as the normal charging polarity of the toner, and A bias (negative polarity in this embodiment) having a polarity opposite to that at the time of normal image formation is applied. Accordingly, it is possible to suppress the transfer residual toner t from adhering to the secondary transfer roller 52 due to the electric repulsive force.

  Here, as shown in FIG. 4B, it is preferable to start the application of the reverse polarity bias before starting the reverse rotation of the intermediate transfer belt 50 and to end the application of the reverse polarity bias after the end of the reverse rotation. . Thereby, it is possible to more reliably prevent the transfer residual toner from adhering to the secondary transfer roller 52.

In this embodiment, in order to prepare for the next image forming operation in the returning operation, after the photosensitive drum 1 is rotated in the reverse direction as described above, the photosensitive drum 1 is rotated in the forward direction to perform a preparatory operation (in the collection mode). ( Second stage) is performed (for example, charging and exposure are performed for several rotations of the photosensitive drum 1). At this time, for the same reason as described above, the intermediate transfer belt 50 also rotates forward in the same manner.

  FIGS. 5A and 5B are views similar to FIGS. 3A and 3B when the intermediate transfer belt 50 is rotated in the reverse direction after the intermediate transfer belt 50 is rotated in the reverse operation. In this embodiment, when the intermediate transfer belt 50 is rotated forward again during the return operation, the reverse transfer bias (negative polarity in this embodiment) is applied to the secondary transfer roller 52 for a predetermined time or longer after the forward rotation is started. Applied.

That is, in this embodiment, during the return operation, the intermediate transfer belt 50 is rotated in the reverse direction, and the transfer bias power source 56 outputs the second bias (reverse polarity bias) ( second operation in the recovery mode). Then, after the second operation, a third operation (second stage of the collection mode) is performed in which the intermediate transfer belt 50 is continuously rotated forward. In the third operation, the transfer bias power source 56 outputs the third bias (reverse polarity bias) for a predetermined time or more after the forward rotation of the intermediate transfer belt 50 is started.

  A second bias output from the secondary transfer bias power source 56 when the intermediate transfer belt 50 rotates in the reverse direction and a third bias output from the secondary transfer bias power source 56 when the intermediate transfer belt 50 rotates forward. The values may be the same or different.

  Here, for the predetermined time, the transfer residual toner that has passed through the secondary transfer portion n2 by reversely rotating the intermediate transfer belt 50 (such as that carried from the cleaning portion CL2) rotates the intermediate transfer belt 50 forward again. Thus, it is desirable that the time is longer than the time required to finish passing through the secondary transfer portion n2. That is, the predetermined time is preferably a time required for forward rotation of the intermediate transfer belt 50 by the third operation by a distance that is the reverse rotation of the intermediate transfer belt 50 by the second operation.

  As described above, when the intermediate transfer belt 50 is rotated forward after being reversely rotated, a reverse polarity bias (negative polarity in this embodiment) is applied to the secondary transfer roller 52 for a predetermined time or longer after the forward rotation is started. Apply. As a result, the transfer residual toner once moved to the upstream side in the forward rotation direction F2 of the intermediate transfer belt 50 from the secondary transfer portion n2 adheres to the secondary transfer roller 52 by rotating the intermediate transfer belt 50 forward. This can be suppressed.

  Further, when the secondary transfer means has a roller shape as in the present embodiment, the predetermined time is set to be longer than the time necessary for one rotation of the roller, so that the toner is temporarily placed on the outer periphery of the secondary transfer roller 52. Even when the toner adheres, the toner can be returned to the secondary transfer belt 50 by the electric repulsive force, and contamination can be suppressed over the entire circumference of the roller.

  Further, as shown in FIG. 5B, when the intermediate transfer belt 50 is rotated forward after being reversely rotated, it is preferable to start applying the reverse polarity bias before starting the forward rotation. Thereby, it is possible to more reliably prevent the transfer residual toner from adhering to the secondary transfer roller 52.

  In this embodiment, as a control unit, the controller 12 of the image forming control unit that performs overall control of the operation of the image forming apparatus 100 includes the photosensitive drum 1, the rotation of the intermediate transfer belt 50, the charging roller 2, the developing sleeve 41, and the primary transfer roller. 51, control of application of a bias to the secondary transfer roller 52, and the like. During normal image formation, the controller 12 forms and outputs an image on the transfer material S by causing each part of the image forming apparatus 100 to perform a sequence operation in accordance with an image forming program stored in a ROM serving as a storage unit. When the controller 12 detects an abnormality such as a jam (paper jam) during a normal image forming operation, the controller 12 urgently stops the operation of the image forming apparatus 100. Then, after detecting that the fault that caused the emergency stop of the image forming apparatus 100 has been removed, the controller 12 performs the above-described recovery operation according to the recovery operation program stored in the ROM (for example, power failure) The same applies to the case where the power is turned on again after the power is unexpectedly shut off by, for example.

  During the return operation, the controller 12 controls the drive motor to rotate the photosensitive drum 1 and the intermediate transfer belt 50 forward and backward at a predetermined timing. As shown in FIGS. 3 to 5, the secondary transfer bias power source 56 includes a switching unit 56a for switching the polarity of the bias to be output. The controller 12 switches the polarity of the bias output from the secondary transfer bias power source 56 by operating the switching unit 56a at a predetermined timing during the return operation.

  As described above, when the intermediate transfer belt 50 is reversely rotated by a distance L from the secondary transfer roller 52 to the cleaning unit CL2 in the forward rotation direction F2 of the intermediate transfer belt 50, the transfer residual conveyed from the cleaning unit CL2 is transferred. When the toner t reaches the secondary transfer roller 52, the adhesion of the toner to the secondary transfer roller 52 becomes more remarkable. Therefore, for example, when the reverse transfer amount of the intermediate transfer belt 50 is variable during the above-described return operation, the reverse transfer to the secondary transfer roller 52 is performed only when the intermediate transfer belt 50 is rotated reversely by a distance L or more. A polar bias may be applied. In this case, the timing for starting the application of the reverse polarity bias to the secondary transfer roller 52 is a predetermined timing before starting the reverse rotation of the intermediate transfer belt 50 or when the reverse transfer of the intermediate transfer belt 50 is started. For example, a predetermined timing before the position on the intermediate transfer belt 50 in the cleaning portion CL of the intermediate transfer body cleaner 8 reaches the secondary transfer portion n2 can be set.

  As described above, according to the present exemplary embodiment, a mechanism for separating the intermediate transfer belt 50 and the secondary transfer roller 52 is not required, and a simple configuration is used, for example, after a jam (paper jam) or during a return operation after an instantaneous power interruption. In addition, it is possible to suppress contamination of the secondary transfer roller 52 when the intermediate transfer belt 50 is rotated in the reverse direction and at the start of the forward rotation thereafter.

Example 2
Next, another embodiment of the present invention will be described. FIG. 6 is a schematic cross-sectional view of a main part of the image forming apparatus 200 of this embodiment. In the image forming apparatus according to the present exemplary embodiment, elements having substantially the same or corresponding functions and configurations as those of the image forming apparatus 100 according to the first exemplary embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The image forming apparatus 200 of this embodiment employs a one-component development method. That is, the developing device 4 develops the electrostatic image formed on the photosensitive drum 1 as a toner image by using a developer (which may include an external additive or the like) substantially consisting only of toner particles. . The developing operation by the developing device 4 is substantially the same as that of the first embodiment, and the toner is carried on the developing sleeve 41 as a developer carrying member and conveyed to the developing region, whereby an electrostatic image on the photosensitive drum 1 is formed. In response, toner is supplied to the photosensitive drum 1 to develop the electrostatic image as a toner image.

  The image forming apparatus 200 according to the present exemplary embodiment includes a photoconductor cleaner 6 as a cleaning unit that scrapes off transfer residual toner on the photoconductive drum 1. In this embodiment, the photoconductor cleaner 6 has a cleaning blade 61 that contacts the photosensitive drum 1 as a cleaning member. In the cleaning blade 61, the edge portion on the free end side comes into contact with the surface of the photosensitive drum 1 and scrapes off the transfer residual toner on the photosensitive drum 1. Further, the transfer residual toner scraped off by the cleaning blade 61 is collected by the scooping sheet 62. In the present embodiment, the contact portion of the photosensitive cleaner 6 with the cleaning blade 61 on the photosensitive drum 1 is the cleaning portion CL1 of the photosensitive drum 1.

  Further, in the image forming apparatus 200 of this embodiment, the intermediate transfer belt 50 is wound around two rollers 53 and 54. In this embodiment, the secondary transfer roller 52 and the intermediate transfer cleaner 8 are arranged to face the opposing roller (opposing member) 53 among the rollers on which the intermediate transfer belt 50 is stretched as the opposing member. . That is, the opposing member of the secondary transfer roller 52 that transfers the toner image on the intermediate transfer belt 50 to the transfer material S also serves as the opposing member of the intermediate transfer body cleaner 8 that scrapes off the transfer residual toner on the intermediate transfer belt 50. The secondary transfer roller 52 and the intermediate transfer body cleaner 8 face the same member with the intermediate transfer belt 50 interposed therebetween. In this embodiment, the secondary transfer roller 52 and the cleaning blade 81 of the intermediate transfer body cleaner 8 are always in contact with the intermediate transfer belt 50. The contact portion of the cleaning blade 81 with the intermediate transfer belt 50 becomes the cleaning portion CL2 of the intermediate transfer belt 50.

  Other configurations of the image forming apparatus 200 according to the present exemplary embodiment are substantially the same as those of the image forming apparatus 100 according to the first exemplary embodiment.

  In the image forming apparatus 200 of this embodiment, the transfer residual toner t on the photosensitive drum 1 is scraped off by the cleaning blade 61 of the photoconductor cleaner 6, so that the transfer residual toner t at the edge of the cleaning blade 61 receives pressure and aggregates. Then, a certain amount of untransferred toner continues to stay. When the operation of the photosensitive drum 1 is stopped, the transfer residual toner t thus aggregated remains on the edge portion of the cleaning blade 61 as shown in FIG. In particular, in a high-temperature and high-humidity environment, the transfer residual toner t tends to adhere to the edge portion of the cleaning blade 61 and the photosensitive drum 1, and may cause cleaning failure or image defect.

  In order to prevent the transfer residual toner t from adhering to the edge portion of the cleaning blade 61 of the photoconductor cleaner 6 as described above, the photosensitive drum 1 is reversely rotated as shown in FIG. It is effective to release the pressure at the edge portion of the cleaning blade 61 and smooth the transfer residual toner t (toner sticking prevention operation).

  Further, in order to increase the effect of leveling the transfer residual toner, an operation of stopping or forwardly rotating the photosensitive drum 1 may be sandwiched between reverse rotations of the photosensitive drum 1, and this may be repeated several times.

  The toner sticking prevention operation can be performed every time the image forming operation ends, but can also be performed periodically or when the environment detection sensor detects that the environment is a high temperature and high humidity environment.

  As described in the first embodiment, when the photosensitive drum 1 is rotated in the reverse direction and further stopped or forwardly rotated between the reverse rotations, the photosensitive drum 1 and the intermediate transfer belt 50 are prevented from being worn due to rubbing. The intermediate transfer belt 50 needs to be reversely rotated, or reversely rotated and stopped or forwardly rotated in accordance with the movement of the photosensitive drum 1.

  However, as described in the first embodiment, when the intermediate transfer belt 50 is rotated reversely, the transfer residual toner t accumulated in the intermediate transfer body cleaner 8 returns to the secondary transfer portion n2. In particular, as in this embodiment, the secondary transfer roller 50 and the intermediate transfer body cleaner 8 face the same member, and the distance between the secondary transfer portion n2 and the cleaning portion CL2 of the intermediate transfer body cleaner 8 is as follows. If it is shorter, when the intermediate transfer belt 50 is rotated in the reverse direction, the untransferred toner t conveyed from the cleaning unit CL2 immediately reaches the secondary transfer unit n2. For this reason, in the configuration in which the secondary transfer roller 52 is always in contact with the intermediate transfer belt 50, the transfer residual toner t adheres to the secondary transfer roller 52, so that the back surface of the transfer material S is soiled during subsequent image formation. It becomes easy.

  Therefore, in the image forming apparatus 200 of the present embodiment, as in the first embodiment, by applying a reverse polarity bias to the secondary transfer roller 52, the transfer residual toner adheres to the secondary transfer roller 52 due to the electric repulsive force. To suppress.

  More specifically, in this embodiment, as the toner sticking prevention operation, the reverse rotation and stop of the photosensitive drum 1 and the intermediate transfer belt 50 are repeated a plurality of times.

  According to this embodiment, as shown in FIGS. 8A and 8B, the intermediate transfer belt 50 is sandwiched between when the intermediate transfer belt 50 is reversely rotated (in the direction of arrow B2) and between the reverse rotations of the intermediate transfer belt 50. When the operation is stopped, the secondary transfer roller 52 has a reverse polarity bias, that is, a bias having the same polarity as the normal charging polarity of the toner and a reverse polarity (negative polarity in the present embodiment) as in normal image formation. Applied. In this embodiment, the reverse polarity bias is continuously applied to the secondary transfer roller 52 during a series of operations in which the intermediate transfer belt 50 is repeatedly rotated and stopped. As a result, the transfer residual toner t can be prevented from adhering to the secondary transfer roller 52.

  That is, in the present embodiment, the second operation in which the secondary transfer bias power source 56 outputs the second bias (reverse polarity bias) and the intermediate transfer belt 50 moves in the second direction (reverse rotation direction) B2 is as follows. This is performed during the toner sticking prevention operation. Further, in this embodiment, when performing the second operation at least twice during the toner sticking prevention operation, the intermediate transfer belt 50 is stopped or sequentially stopped between the second operation and the second operation. A fourth operation that rotates (especially stops in this embodiment) is performed, and in this fourth operation, the secondary transfer bias power source 56 applies a fourth bias having the same polarity as the second bias (reverse polarity bias). Output.

  The secondary transfer bias power source 56 outputs a secondary bias when the intermediate transfer belt 50 rotates in the reverse direction, and the secondary transfer bias power source when the intermediate transfer belt 50 stops or rotates forward (particularly in this embodiment). The value of the fourth bias output by 56 may be the same or different.

  As shown in FIGS. 9A and 9B, as in the first embodiment, when the intermediate transfer belt 50 is rotated again in the forward direction (third operation), the intermediate transfer is performed by the second operation. It is preferable to apply a reverse polarity bias (negative polarity in this embodiment) to the secondary transfer roller 52 for a time required to forwardly rotate the intermediate transfer belt 50 by a distance obtained by reversely rotating the belt 50. As a result, the transfer residual toner that has once moved to the upstream side in the forward rotation direction F2 of the intermediate transfer belt 50 from the secondary transfer portion n2 is prevented from adhering to the secondary transfer roller 52.

  In this embodiment, the intermediate transfer belt is stopped between the reverse rotations of the intermediate transfer belt 50 as the fourth operation, but the intermediate transfer belt 50 is used instead of or in addition to the stop operation as the fourth operation. The intermediate transfer belt 50 can be rotated forward between the reverse rotations.

  As in the first embodiment, in this embodiment, the controller 12 of the image forming control unit that performs overall control of the operation of the image forming apparatus 100 includes the photosensitive drum 1, the rotation of the intermediate transfer belt 50, the charging roller 2, Application of bias to the developing sleeve 41, the primary transfer roller 51, and the secondary transfer roller 52 is controlled. During normal image formation, the controller 12 forms and outputs an image on the transfer material S by causing each part of the image forming apparatus 100 to perform a sequence operation in accordance with an image forming program stored in a ROM serving as a storage unit. In addition, the controller 12 stores the image data in the ROM after the normal image forming operation is completed (for example, every time one job (a series of image forming operations for one or a plurality of transfer materials according to one image forming start instruction) is completed). According to the stored toner sticking prevention operation program, the return operation as described above is performed.

  During the toner sticking prevention operation, the controller 12 controls the drive motor to rotate the photosensitive drum 1 and the intermediate transfer belt 50 in the forward and reverse directions and stop at a predetermined timing. In addition, the controller 12 switches the polarity of the bias output from the secondary transfer bias power source 56 by operating the switching unit 56a at a predetermined timing during the toner sticking prevention operation.

  As described above, according to the present exemplary embodiment, a mechanism for separating the intermediate transfer belt 50 and the secondary transfer roller 52 is not required, and a simple configuration can be used only when the intermediate transfer belt 50 is rotated reversely at the time of toner sticking prevention operation or the like. By applying a reverse polarity bias to the secondary transfer roller 52 even when stopped between the reverse rotation operations, contamination of the secondary transfer roller 52 can be reliably suppressed.

Example 3
Next, still another embodiment of the present invention will be described.

  In each of the above embodiments, the case where the present invention is applied to an intermediate transfer type image forming apparatus has been described. However, the present invention is not limited to this. The present invention relates to an image forming apparatus in which a toner image is directly transferred to a transfer material from an image carrier that is a latent image carrier that carries a toner image formed by supplying toner after an electrostatic image is formed. It is equally applicable to the above.

  For example, in FIG. 10, the toner image is directly transferred from the photosensitive drum 1 to the transfer material S by applying a transfer bias to a transfer roller 51 as a transfer unit provided facing the photosensitive drum 1 in the transfer unit n. 2 shows a schematic cross section of a main part of an image forming apparatus 300. In the image forming apparatus 300 illustrated in FIG. 10, elements having substantially the same or corresponding functions and configurations as those of the image forming apparatus 100 according to the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the image forming apparatus 300 shown in FIG. 10, similarly to the second embodiment, the transfer residual toner on the photosensitive drum 1 is scraped off by the cleaning blade 61 in the photosensitive member cleaner 6 and collected by the rake sheet 62. In this embodiment, the contact portion of the cleaning blade 61 with respect to the photosensitive drum 1 of the photoreceptor cleaner 6 is the cleaning portion CL.

  In such a configuration, similarly to the second embodiment, by performing the toner sticking prevention operation at a predetermined timing, it is possible to prevent the transfer residual toner from sticking to the edge portion of the cleaning blade 61. However, when the photosensitive drum 1 is rotated in the opposite direction (arrow B direction) to the rotation direction (arrow F direction) during normal image formation in the toner sticking prevention operation, the photosensitive drum 1 starts from the edge of the cleaning blade 61. The transfer residual toner t returned to the top easily adheres to the transfer roller 51. This is similar to the secondary transfer portion n2 in each of the above embodiments, in particular, the photosensitive drum 1 is reversely rotated more than the distance from the cleaning portion CL to the transfer portion n in the reverse rotation direction (arrow B direction) of the photosensitive drum 1. It becomes remarkable when making it.

  Therefore, in this embodiment, as in the case of the second transfer roller 52 in the second embodiment, the reverse polarity is applied to the transfer roller 51 when the photosensitive drum 1 is reversely rotated during the toner sticking prevention operation. A bias (that is, negative polarity in this embodiment) having a polarity that is the same as the normal charging polarity of the toner and opposite to that during normal image formation is applied from the transfer bias power source 56. Thereby, it is possible to prevent the transfer residual toner from adhering to the transfer roller 51 from the photosensitive drum 1.

  Similarly to the second embodiment, when the stop or forward rotation is sandwiched between the reverse rotations of the photosensitive drum 1, the reverse polarity bias (negative polarity in this embodiment) is also applied to the transfer roller 51 during the stop or forward rotation operation. Can be applied. As a result, it is possible to more reliably suppress the transfer residual toner from adhering to the transfer roller 51.

  FIG. 11 shows another example of an image forming apparatus that directly transfers a toner image from the photosensitive drum 1 to the transfer material S. In the image forming apparatus 400 of FIG. 11, the transfer roller 51 is pressed against the photosensitive drum 1 via a conveyance belt 90 as a transfer material conveyance unit. The transfer roller 51 and the conveyance belt 90 constitute a transfer unit in the transfer portion n where the conveyance belt 90 pressed by the transfer roller 51 and the photosensitive drum 1 abut. The toner image on the photosensitive drum 1 is transferred onto the transfer material S carried on the conveyance belt 90 by the action of a transfer bias applied by the transfer bias power source 56 via the transfer roller 51 and the conveyance belt 90. .

  Also in the image forming apparatus 400 having such a configuration, as in the image forming apparatus 300 of FIG. 10, for example, when the photosensitive drum 1 rotates in the reverse direction during the toner sticking prevention operation (at this time, the transport belt 90 also rotates in the reverse direction). By applying a reverse polarity bias (negative polarity in this embodiment) to the transfer roller 51 at the time of stopping between the reverse rotations or the forward rotation operation, adhesion of the transfer residual toner to the conveyance belt 90 can be suppressed.

  Further, in the image forming apparatus 400 of FIG. 11, a plurality of image forming units (photosensitive drum 1, charging roller 2, developing device 4, photoconductor cleaner 6, transfer roller 51) along the transport direction of the transfer material S by the transport belt 60. The present invention can be equally applied to each transfer portion n.

  The image forming apparatuses 300 and 400 shown in FIGS. 10 and 11 have other characteristics described in the first and second embodiments, for example, the reverse polarity bias applied to the transfer roller 51 before the reverse rotation of the photosensitive drum 1 is started. When the application of the reverse polarity bias to the transfer roller 51 is stopped after the reverse rotation of the photosensitive drum 1 is stopped, or when the photosensitive drum 1 is reversely rotated and then forward rotated again, For example, applying a reverse polarity bias to the transfer roller 51 for a predetermined time or more can also be applied.

  In the image forming apparatuses 300 and 400 shown in FIGS. 10 and 11, the transfer bias power source 56 as a bias output unit is controlled in the same manner as the secondary transfer bias power source 56 in the second embodiment.

  As is clear from the above, in the primary transfer portion n1 of the image forming apparatus 200 of the first and second embodiments, in the same manner as that performed for the transfer roller 51 of the image forming apparatuses 300 and 400 shown in FIGS. For example, a reverse polarity bias may be applied to the primary transfer roller 51 during the return operation or the toner sticking prevention operation. Accordingly, it is possible to prevent the untransferred toner or the transfer residual toner from adhering to the intermediate transfer belt 50 constituting the transfer unit by applying the primary transfer bias via the primary transfer roller 51 in the primary transfer unit n1. .

  As described above, also in the image forming apparatuses 300 and 400 that directly transfer the toner image from the photosensitive drum 1 to the transfer material S, it is possible to prevent the toner from adhering to the transfer roller 51 and causing the recording material S to become dirty. Can do.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the aspect of each said Example. For example, in each of the above embodiments, the normal charging polarity of the toner is described as negative, and the polarity of the transfer bias during normal image formation is described as positive. However, when the normal charging polarity of the toner is positive However, the present invention is naturally applicable, and the same effect can be obtained by reversing the bias control in the above embodiments.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus to which the present invention can be applied. It is a schematic diagram for demonstrating return operation | movement. FIG. 6 is a schematic diagram for explaining a rotation operation of an intermediate transfer belt and an output bias of a secondary transfer bias power source during normal image formation. FIG. 10 is a schematic diagram for explaining the rotation operation of the intermediate transfer belt and the output bias of the secondary transfer bias power source during the return operation. FIG. 10 is a schematic diagram for explaining the rotation operation of the intermediate transfer belt and the output bias of the secondary transfer bias power source during the return operation. It is a principal part schematic sectional drawing of the other Example of the image forming apparatus which can apply this invention. FIG. 6 is a schematic diagram for explaining a toner adhesion preventing operation. FIG. 6 is a schematic diagram for explaining the rotation operation of the intermediate transfer belt and the output bias of the secondary transfer bias power source during the toner sticking prevention operation. FIG. 6 is a schematic diagram for explaining the rotation operation of the intermediate transfer belt and the output bias of the secondary transfer bias power source during the toner sticking prevention operation. It is a principal part schematic sectional drawing of the other Example of the image forming apparatus which can apply this invention. It is a principal part schematic sectional drawing of the other Example of the image forming apparatus which can apply this invention.

Explanation of symbols

1 Photosensitive drum (image carrier )
2 Charging roller (charging means)
3 Laser scanner (exposure means)
4 Developer (Developer)
6 Photoconductor cleaner (cleaning means)
8 Intermediate transfer body cleaner (cleaning means)
51 primary transfer row La (primary transfer member)
52 Secondary transfer roller ( secondary transfer member )
50 Intermediate transfer belt ( intermediate transfer member )
56 secondary transfer bias supply (bias output means)

Claims (6)

  A rotatable image carrier for carrying a toner image, a developing unit for developing the toner image on the image carrier, a rotatable intermediate transfer member, and a primary transfer of the toner image from the image carrier to the intermediate transfer member A primary transfer member that collects toner remaining on the image carrier that is not transferred to the intermediate transfer member by the primary transfer member, and a secondary toner image from the intermediate transfer member to the transfer material. A secondary transfer member to be transferred; and a second cleaning unit for collecting toner remaining on the intermediate transfer body that is not transferred to the transfer material by the secondary transfer member, and the image carrier and the intermediate The transfer member can be rotated in the opposite direction to that during image formation, and a recovery mode in which the toner on the image carrier is recovered by the developing means by rotating the image carrier in the reverse direction can be executed. For image forming equipment Stomach,
  A bias output means for outputting a bias voltage to the secondary transfer member, and when executing the recovery mode, a first stage of rotating the intermediate transfer member in the reverse direction; and There is a second stage in which the intermediate transfer member is rotated in the same direction as that at the time of image formation later, and the bias output means transfers the intermediate transfer member from the intermediate transfer member in both the first stage and the second stage. An image forming apparatus, wherein a voltage having a polarity opposite to a bias voltage output to the secondary transfer member when a toner image is secondarily transferred to a material is output to the secondary transfer member. It said secondary transfer member, an image forming apparatus according to claim 1, characterized in that it always abuts on the intermediate transfer body. In the second stage, the bias output means outputs the reverse polarity voltage to the secondary transfer member for a predetermined time or more after the intermediate transfer member starts to rotate in the same direction. the first stage Oite the intermediate transfer member by a distance moved more to the rotation of the reverse, to move more of Oite the intermediate transfer member to the second stage to the rotation of the same direction the image forming apparatus according to claim 1 or 2, characterized in that the time required. The image forming apparatus according to claim 3, wherein the secondary transfer member has a roller shape, and the predetermined time is a time required for one rotation of the roller-shaped secondary transfer member . In the second step , the bias output means starts outputting the reverse polarity voltage to the secondary transfer member before the intermediate transfer member starts rotating in the same direction. The image forming apparatus according to any one of claims 1 to 4 . Oite the first stage, the intermediate transfer body, the more rotation in the reverse direction, the second cleaning means is a secondary transfer portion where the cleaning unit secondary transfer is performed to recover the toner The image forming apparatus according to claim 1, wherein the image forming apparatus moves more than a distance between them .

Images