JP6107482B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a guide member for guiding paper.

  In general, in an image forming apparatus, when a toner image on an image carrier is transferred to a sheet at a nip portion of a transfer unit, the image forming apparatus is configured to have a guide member for guiding the sheet to the nip unit. It has been.

In such an image forming apparatus, the toner on the image carrier is held on the image carrier by electrostatic and physical adhesion, but a part of the toner is scattered to form an image carrier on the guide member. Accumulated on the surface facing the body. When toner continues to accumulate and reaches the end of the guide member, and the toner wraps to the surface of the guide member on the side where the paper is passed, the wrap-around toner touches the paper and the paper May get dirty.
An image forming apparatus that solves such a problem is described in, for example, the following patent documents.

JP 2002-229347 A

  In Patent Document 1 described above, a toner removing member is provided in the apparatus main body, and when the transfer roller unit is pulled out from the apparatus main body, the toner removing member comes into light contact with the upper surface of the guide member (pre-transfer guide). . Therefore, the toner on the guide member can be collected on the toner receiver by the toner removing member in conjunction with the sliding operation when the transfer roller unit is taken out from the apparatus main body.

  However, when the toner on the guide member is removed when the transfer roller unit is manually removed from the apparatus main body as in the image forming apparatus described in Patent Document 1, the transfer roller unit is once taken out and next time. Until the toner is taken out, the toner on the guide member is accumulated without being removed. That is, when the operation of taking out for a long period of time is not performed, there is a case where the sheet is stained with accumulated toner as described above.

  On the other hand, in order to surely prevent the paper from being soiled by the toner accumulated in the guide member, the user takes out the transfer roller unit each time when the take-out operation is performed at an appropriate timing and the toner on the guide member is removed. There is a problem that the load on the user becomes large.

  The present invention has been made in view of such problems, and an object thereof is to remove toner on a guide member at an appropriate timing without giving a load to a user.

The present invention provides the following means. That is,
An image carrier for carrying a toner image;
A nip portion is formed in contact with the image carrier, and a transfer portion that transfers a toner image carried on the image carrier to a sheet in the nip portion;
A guide member for guiding the conveyed paper to the nip portion;
A moving member for moving the guide member;
An electric field generator for generating an electric field between the image carrier and the guide member;
A control unit that controls at least the operation of the moving member and the electric field generation unit,
The controller is
The moving member is controlled to move the guide member to a second position closer to the image carrier than a first position for guiding the sheet to the nip portion, and the guide member is moved to the second position. The image forming apparatus, wherein the electric field generating unit is controlled to generate an electric field for moving the toner on the guide member onto the image carrier.

  According to the image forming apparatus of the present invention, it is possible to remove the toner on the guide member at an appropriate timing without imposing a load on the user.

1 is an overall configuration diagram illustrating a configuration example of an image forming apparatus according to the present invention. It is a figure explaining the structure of a secondary transfer nip part and its periphery. 6 is a flowchart illustrating a control method in image forming operation and cleaning control. FIG. 4 is a diagram illustrating a state of a secondary transfer nip portion and its periphery during an image forming operation. FIG. 6 is a diagram for explaining a state of a secondary transfer nip portion and its periphery in a state where toner stains are accumulated on an upper guide member. FIG. 5 is a diagram for explaining a state of a secondary transfer nip portion and its periphery during cleaning control. FIG. 10 is a diagram for explaining a state of a secondary transfer nip portion and its surroundings at the time of cleaning control when another control method 1 is executed. It is a figure explaining an example of other Embodiment 1. FIG.

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

[Configuration of image forming apparatus]
FIG. 1 is an overall configuration diagram showing a configuration example of an image forming apparatus according to the present invention. As shown in FIG. 1, the image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and has four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). This is a tandem color image forming apparatus that superimposes toner. The image forming apparatus 1 includes a document conveying unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer unit 50, a secondary transfer unit 60, a fixing unit 80, and a control. Part 110.

  The document transport unit 10 includes a document feeder 11 on which a document is set, a plurality of rollers 12, a transport drum 13, a transport guide 14, a document discharge roller 15, and a document discharge tray 16. The documents G set on the document feeder 11 are conveyed one by one to the reading position of the image reading unit 30 by the plurality of rollers 12 and the conveying drum 13. The conveyance guide 14 and the document discharge roller 15 discharge the document G conveyed by the plurality of rollers 12 and the conveyance drum 13 to the document discharge tray 16.

  The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 31 and generates image data. Specifically, the image of the original G is irradiated by the lamp L. The reflected light from the document G is guided in the order of the first mirror unit 32, the second mirror unit 33, and the lens unit 34 and forms an image on the light receiving surface of the image sensor 35. The image sensor 35 photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as image data by A / D conversion.

  The image reading unit 30 has an image reading control unit 36. The image reading control unit 36 performs processing such as shading correction, dither processing, and compression on the image data created by the A / D conversion, and stores the processed data in the RAM of the control unit 110. The image data is not limited to data output from the image reading unit 30 and may be data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus.

  The paper storage unit 20 is disposed in the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size and type of the paper S. The sheet S is fed by the sheet feeding unit 21 and sent to the transport unit 23, and is transported by the transport unit 23 to the secondary transfer unit 60 that is a transfer position. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP sheet is sent to the transfer position.

  An image forming unit 40 and an intermediate transfer unit 50 are disposed between the image reading unit 30 and the paper storage unit 20.

  The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk). . The image forming unit 40 forms a printing image at a position corresponding to the sheet S on the intermediate transfer belt 51.

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, only the first image forming unit 40Y will be described here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 disposed around the photoconductor 41, an exposure unit 43, a developing unit 44, and a photoconductor cleaning unit 45. Yes.

  The photoreceptor 41 is rotated by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The exposure unit 43 performs an exposure operation on the surface of the photoconductor 41 based on image data read from the original G or image data transmitted from an external device, thereby forming an electrostatic latent image on the photoconductor 41. Form.

The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41. As a result, a yellow printing image is formed on the surface of the photoreceptor 41. The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.
The photoconductor cleaning unit 45 removes toner remaining on the surface of the photoconductor 41.

  The printing image formed on the photoconductor 41 is transferred to an intermediate transfer belt 51 showing an example of an intermediate transfer member. The intermediate transfer belt 51 is formed in an endless shape, and is stretched around a plurality of rollers including a driven roller 52 and a secondary transfer counter roller 62 shown in FIG. The intermediate transfer belt 51 is rotationally driven in a direction opposite to the rotation (movement) direction of the photoconductor 41 by a drive motor (not shown).

  A primary transfer portion 53 is provided at a position on the intermediate transfer belt 51 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 53 transfers the printing image formed on the photoreceptor 41 to the intermediate transfer belt 51 by applying a polarity opposite to that of the toner to the intermediate transfer belt 51.

  Then, when the intermediate transfer belt 51 is rotationally driven, printing images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 51. As a result, on the intermediate transfer belt 51, yellow, magenta, cyan, and black toner images are overlapped to form a color printing image.

  An intermediate transfer belt cleaning unit 54 faces the intermediate transfer belt 51. The intermediate transfer belt cleaning unit 54 cleans the surface of the intermediate transfer belt 51 that has finished transferring the printing image onto the paper S.

  A secondary transfer unit 60 is disposed in the vicinity of the intermediate transfer belt 51 and downstream of the transport unit 23 in the sheet transport direction. The secondary transfer unit 60 forms a secondary transfer nip N while facing the intermediate transfer belt 51 and facing the secondary transfer counter roller 62 with the intermediate transfer belt 51 interposed therebetween (see FIG. 2). The secondary transfer unit 60 transfers the printing image carried on the outer peripheral surface of the intermediate transfer belt 51 to the paper S sent by the transport unit 23 at the secondary transfer nip N. A secondary transfer belt cleaning unit 61 is opposed to the secondary transfer unit 60.

  A fixing unit 80 is provided on the discharge side of the sheet S in the secondary transfer unit 60. The fixing unit 80 pressurizes and heats the paper S to fix the transferred printing image on the paper S. The fixing unit 80 includes, for example, a pair of fixing upper rollers 81 and a fixing lower roller 82 which are a pair of fixing members. The upper fixing roller 81 and the lower fixing roller 82 are arranged in pressure contact with each other, and a fixing nip portion is formed as a pressing portion between the upper fixing roller 81 and the lower fixing roller 82.

  A heating unit is provided inside the fixing upper roller 81. The roller portion of the fixing upper roller 81 is warmed by the radiant heat from the heating portion. Then, the heat of the roller portion of the fixing upper roller 81 is transmitted to the paper S, whereby the printing image on the paper S is heat-fixed.

  The sheet S is conveyed so that the surface (fixed target surface) onto which the printing image is transferred by the secondary transfer unit 60 faces the fixing upper roller 81, and passes through the fixing nip portion. Accordingly, the sheet S that passes through the fixing nip portion is pressed by the upper fixing roller 81 and the lower fixing roller 82 and heated by the heat of the roller portion of the upper fixing roller 81.

  A switching gate 24 is disposed downstream of the fixing unit 80 in the sheet conveyance direction. The switching gate 24 switches the transport path of the paper S that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper S straight when performing face-up paper discharge in single-sided image formation. As a result, the paper S is discharged by the pair of paper discharge rollers 25. The switching gate 24 guides the paper S downward when face-down paper discharge and double-sided image formation in single-sided image formation.

  When face-down paper discharge is performed, the paper S is guided downward by the switching gate 24, and then the front and back sides are reversed by the paper reverse conveyance unit 26 and conveyed upward. As a result, the paper S whose front and back are reversed is discharged by the pair of paper discharge rollers 25.

  When double-sided image formation is performed, the sheet S is guided downward by the switching gate 24, the front and back sides are reversed by the sheet reversing conveyance unit 26, and sent again to the transfer position by the refeed path 27.

  A post-processing device that folds the paper S or performs a stapling process or the like on the paper S may be disposed on the downstream side of the pair of paper discharge rollers 25.

  The controller 110 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory) (not shown). The ROM holds a program for operating the image forming apparatus 1. The RAM is used as a temporary storage area for programs read from the ROM, input information from the display unit, and the like. The CPU reads a program held in the ROM and executes processing according to the program. For example, a cleaning operation is executed by reading a program for executing the cleaning control described later.

[Secondary transfer nip and surrounding area]
FIG. 2 is a diagram illustrating the configuration of the secondary transfer nip portion N and its periphery. In the secondary transfer nip N and its periphery, there are an intermediate transfer belt (image carrier) 51, a driven roller 52, a secondary transfer unit 60, a secondary transfer counter roller (opposing member) 62, and an upper guide member (guide member). 71, a lower guide member 72, a cleaning facing roller 73, and a power supply unit 90 are provided.

  As described above, the secondary transfer unit 60 forms the secondary transfer nip N while facing the intermediate transfer belt 51 and facing the secondary transfer counter roller 62 with the intermediate transfer belt 51 interposed therebetween. The driven roller 52 rotates following the rotation of the intermediate transfer belt 51.

The upper guide member 71 and the lower guide member 72 are provided on the upstream side of the secondary transfer nip portion N in the transport direction of the paper S.
The upper guide member 71 and the lower guide member 72 have a function of guiding the sheet S conveyed to the secondary transfer nip N by the conveyance unit 23 to the secondary transfer nip N. As a result, the sheet S comes into contact with the intermediate transfer belt 51 on the upstream side of the secondary transfer nip portion N, and the printing image carried on the intermediate transfer belt 51 is damaged or the sheet S is stained. Can be prevented.

  The upper guide member 71 includes a moving member 71a, and is configured such that the downstream portion can rotate around the upstream position in the transport direction of the sheet S (arrow in FIG. 2). A). That is, the control part 110 can rotate the upper guide member 71 by controlling the moving member 71a.

  In the present embodiment, the “upper” guide member 71 includes the moving member 71a, but the embodiment of the present invention is not limited to this. In other words, the guide member that contacts the surface of the sheet close to the intermediate transfer belt 51 and guides it to the secondary transfer nip N only needs to have a moving member. For example, the sheet on which the intermediate transfer belt 51 is conveyed In the image forming apparatus configured to be positioned on the lower side, it is sufficient that the guide for guiding the lower surface of the sheet to the secondary transfer nip portion is rotatable. Further, it is not always necessary to provide two members for guiding the sheet, that is, “upper side” and “lower side”.

  The cleaning facing roller 73 sandwiches the intermediate transfer belt 51 with respect to the position of the downstream end of the upper guide member 71 in the transport direction of the paper S when the upper guide member 71 contacts the intermediate transfer belt 51. Are provided at opposite positions. The cleaning counter roller 73 is grounded by a ground member 73a.

  The power supply unit 90 is connected to the upper guide member 71 and can apply a bias voltage. The power supply unit 90 may be provided for the upper guide member 71 separately from the power supply for the main body of the image forming apparatus 1, but it is more preferable that the power supply section 90 is also used as the power supply for the main body of the image forming apparatus 1.

  The grounding member 73a of the cleaning counter roller 73 and the power supply unit 90 constitute an electric field generation unit.

  The upper guide member 71 and the cleaning counter roller 73 are desirably conductive, and may have a volume resistivity of, for example, 2 to 5 log Ω · cm.

[Control Method in Image Forming Operation and Cleaning Control]
A control method in the image forming operation and cleaning control in the image forming apparatus according to the present embodiment will be described below with reference to the flowchart shown in FIG. 3 and the explanatory diagrams shown in FIGS.

  When a job is input, the control unit 110 controls each unit of the image forming apparatus 1 to execute the image forming operation related to the input job (S301), and the image is output until the image forming operation related to the job is completed. A forming operation is executed (S302).

  The state of the secondary transfer nip N and its periphery during the image forming operation (S301, S302) will be described with reference to the explanatory view shown in FIG.

  During the image forming operation, the control unit 110 controls the upper guide member 71 so that the upper guide member 71 is located at a position (first position) indicated by P1 in FIG.

  When the image forming operation starts, the sheet S is conveyed to the secondary transfer nip N by the conveyance unit 23. At this time, the sheet S is guided to the secondary transfer nip N by the upper guide member 71 and the lower guide member 72.

  Then, the secondary transfer unit 60 transfers the printing image carried on the outer peripheral surface of the intermediate transfer belt 51 to the sheet S sent by the transport unit 23 at the secondary transfer nip N.

When the image forming operation is performed by the operation method described above, the toner on the intermediate transfer belt 51 is held on the intermediate transfer belt 51 by electrostatic and physical adhesion, but some toners are Scattered and accumulated as toner stain T on the upper guide member 71 (see FIG. 5). When toner continues to accumulate and reaches the end of the upper guide member 71 and the toner wraps around the surface on which the paper S is transported, the paper S is contaminated by the wrapping toner. Therefore, in order to prevent the sheet S from being stained by the toner on the upper guide member 71, cleaning control described below is executed.
Note that after the image forming operation is completed (S302; Yes), the intermediate transfer belt 51 may stop operating or may continue to rotate (post-rotating operation).

  When the image forming operation is completed (S302; Yes), the control unit 110 determines whether or not to execute the cleaning control (S303). For example, when it is determined that the cleaning control is to be performed when an image forming operation is performed on a predetermined number of sheets or more, the predetermined number of sheets and the number of sheets on which the image forming operation has been performed so far are determined. In comparison, it is determined whether or not to execute the cleaning control. When it is determined that the cleaning control is to be executed (S303; Yes), the cleaning control described below is executed (S304 to S308). On the other hand, if it is determined that the cleaning control is not to be executed (S303; No), the job is terminated.

  If it is determined that the cleaning control is to be executed (S303; Yes), the control unit 110 controls the moving member 71a to rotate the upper guide member 71 closer to the intermediate transfer belt 51 and to contact the intermediate transfer belt 51. Then, the upper guide member 71 is moved (S304). FIG. 6 shows the state of the secondary transfer nip N and its periphery at this time. The upper guide member 71 is located at a position (second position) indicated by P2 in FIG.

  Thereafter, the control unit 110 controls the power supply unit 90 to apply the bias voltage Vc when performing the cleaning control to the upper guide member 71 in a state where the upper guide member 71 is in the second position (S305). . As a result, a current flows between the upper guide member 71 connected to the power supply unit 90 and the grounded cleaning counter roller 73, and a potential difference is generated between the upper guide member 71 and the cleaning counter roller 73. it can. That is, the electric field E that moves the toner on the upper guide member 71 onto the intermediate transfer belt 51 is generated by the electric field generating unit 120 including the grounding member 73 a of the cleaning counter roller 73 and the power supply unit 90. With this electric field E, the toner on the upper guide member 71 can be moved onto the intermediate transfer belt 51.

  For example, when the toner is negatively charged, the control unit 110 controls the electric field generation unit 120 so as to hold the upper guide member 71 at a negative potential with respect to the ground potential. As a result, a current flows from the cleaning counter roller 73 toward the upper guide member 71, and the potential of the cleaning counter roller 73 becomes a positive potential with respect to the potential of the upper guide member 71. The toner on the upper guide member 71 moves onto the intermediate transfer belt 51 by the force received from the electric field E generated by the potential difference between the upper guide member 71 and the cleaning counter roller 73.

  The upper guide member 71 is brought into contact with the intermediate transfer belt 51, and a bias voltage is applied for a predetermined time (S306). After the predetermined time has elapsed (S306; Yes), the control unit 110 applies the bias voltage to the upper guide member 71. The electric field generator 120 is controlled so as to cut the bias (S307), and the moving member 71a is moved so as to move the upper guide member 71 to the position during image forming operation (position P1 shown in FIG. 4). After the control (S308), the job is terminated.

  The toner that has moved onto the intermediate transfer belt 51 is removed from the intermediate transfer belt 51 by, for example, further rotating the intermediate transfer belt 51 and being removed from the intermediate transfer belt 51 by the intermediate transfer belt cleaning unit 54 without providing an additional configuration. The toner on the intermediate transfer belt 51 can be removed.

  As described above, according to the image forming apparatus of the present embodiment, the control unit moves the upper guide to the second position closer to the intermediate transfer belt than the first position for guiding the sheet to the nip portion. The moving member is controlled to move the member, and the electric field generating unit is controlled to generate an electric field for moving the toner on the upper guide member to the intermediate transfer belt in a state where the upper guide member is in the second position. (Cleaning control). Accordingly, the toner on the upper guide member is moved onto the intermediate transfer belt, and the toner on the guide member can be removed at an appropriate timing without applying a load to the user.

  Further, by configuring the cleaning counter roller 73 to be grounded by the ground member 73a, the cleaning counter roller 73 is kept at the ground potential. For this reason, by controlling only the potential of the upper guide member 71 by the electric field generator 120, an electric field E that moves the toner on the upper guide member 71 onto the intermediate transfer belt 51 can be generated, and the cleaning counter roller 73 There is no need to provide a separate power source for controlling the potential of the. Therefore, the effects of the present invention can be obtained with a simple configuration.

[Other control methods in cleaning control]
The control method in the cleaning control described above is an example, and the present invention is not limited to this, and a control method as described below can be executed.

(Other control method 1)
In the control method described above, in step S304 in FIG. 3, the control unit 110 rotates the upper guide member 71 to approach the intermediate transfer belt 51 and moves the moving member 71a so as to contact the intermediate transfer belt 51. I have control. That is, the position where the upper guide member 71 contacts the intermediate transfer belt 51 is set as the second position. However, instead of this, the controller 110 rotates the upper guide member 71 closer to the intermediate transfer belt 51 and does not contact the intermediate transfer belt 51, so that the upper guide member 71 and the intermediate transfer belt 51 are not in contact with each other. The moving member 71a may be controlled so as to be close to each other with a gap having a certain distance. That is, the position where the upper guide member 71 has a gap of a certain distance from the intermediate transfer belt 51 may be set as the second position.

  FIG. 7 shows the state of the secondary transfer nip N and its surroundings during cleaning control when this control method is executed. The controller 110 controls the moving member 71a so as to move the upper guide member 71 to the position P2 (second position). At this time, the upper guide member 71 is close to the intermediate transfer belt 51 with a gap having a distance D therebetween. In addition, the control unit 110 controls the electric field generation unit 120 so as to apply a bias voltage Vcs when performing cleaning control to the upper guide member 71. In this state, no current flows between the upper guide member 71 and the cleaning counter roller 73, but an electrostatic field Es is generated between the upper guide member 71 and the cleaning counter roller 73. With this electrostatic field Es, the toner on the upper guide member 71 can be moved onto the intermediate transfer belt 51.

  In this control method, the distance D between the upper guide member 71 and the intermediate transfer belt 51 and the value of the bias voltage Vcs to be applied to the upper guide member 71 differ depending on the resistance value of each member and the like. It is specifically determined by etc.

(Other control method 2)
In the control method described above, the control unit 110 controls the electric field generating unit 120 so as not to generate an electric field during the image forming operation. Instead, the intermediate transfer belt 51 is used during the image forming operation. The electric field generator 120 may be controlled so as to generate an electric field that prevents the upper toner from moving onto the upper guide member 71. That is, the controller 110 may control the electric field generator 120 so as to generate an electric field Ei that moves the toner on the upper guide member 71 onto the intermediate transfer belt 51 even during the image forming operation.

  By controlling in this way, it is possible to reduce the amount of toner scattered from the intermediate transfer belt 51 onto the upper guide member 71 during the image forming operation, and in addition to this, by executing the cleaning control described above. The toner on the upper guide member 71 can be removed more reliably.

  Further, the electric field Ei for preventing the toner on the intermediate transfer belt 51 from moving onto the upper guide member 71 is compared with the electric field E for moving the toner on the upper guide member 71 onto the intermediate transfer belt 51. The objective can be achieved even if the absolute value is small.

  Therefore, in this control method, the electric field Ei generated by the electric field generator 120 during the image forming operation has a smaller absolute value than the electric field E generated by the electric field generator 120 during the cleaning control. desirable. By controlling in this way, the toner on the upper guide member 71 can be more reliably removed, and an increase in power consumption due to the generation of an electric field during the image forming operation can be reduced. .

(Other control method 3)
In the control method described above, the electric field generator 120 applies a constant DC voltage Vc as a bias voltage to the upper guide member 71 in a state where the upper guide member 71 is in the second position during cleaning control. However, instead of this, in the state where the upper guide member 71 is in the second position during the cleaning control, the electric field generator 120 applies a voltage obtained by superimposing the AC voltage Vca on the DC voltage Vcd as the bias voltage. The electric field generator 120 may be controlled so as to be applied to the upper guide member 71. By controlling in this way, an oscillating electric field Ea can be generated between the intermediate transfer belt 51 and the upper guide member 71, and the fixing force of the toner dirt T fixed on the upper guide member 71 can be increased. Can be reduced. Thus, the toner on the upper guide member 71 can be moved onto the intermediate transfer belt 51 more reliably during cleaning control.

(Other control method 4)
In the control method described above, the cleaning control is executed (steps S303 and S304 to 308 in FIG. 3) after the image forming operation is completed (step S302 in FIG. 3). However, the present invention is not limited to this. If the printing image is not carried on the intermediate transfer belt 51, the cleaning control may be executed at any timing. For example, the timing from when a certain printing image is transferred by the secondary transfer unit 60 to when the next printing image is transferred by the secondary transfer unit 60 before the image forming operation is started or during execution of the job. Cleaning control can be performed at the timing. Note that it is more preferable to perform the cleaning control after the image forming operation is completed, because a decrease in productivity of the image forming operation can be prevented.

(Other control method 5)
In the control method described above, it is determined that the cleaning control is executed when an image forming operation is performed on a predetermined number of sheets or more (step S303 in FIG. 3), but the present invention is not limited to this. Whether or not to execute the cleaning control can be determined in consideration of various conditions.

  For example, the cleaning timing can be determined in accordance with the type of image on which the image forming operation is performed and the operating environment of the image forming operation. Specifically, when a toner image having a high printing rate is carried on the intermediate transfer belt 51 and transferred onto the paper S, the amount of toner scattered from the intermediate transfer belt 51 onto the upper guide member 71 increases. It is desirable to increase the frequency of performing the cleaning control. In addition, when the image forming operation is performed in a low temperature and low humidity environment, the toner charge amount increases, and the amount of toner scattered from the intermediate transfer belt 51 onto the upper guide member 71 increases. Even when it is detected that the environment is a low temperature and low humidity environment, it is desirable to increase the frequency of performing the cleaning control.

[Other Embodiments]
The embodiment of the image forming apparatus 1 described above is an example, and the present invention is not limited to this. The embodiment described below can also be used.

(Other embodiment 1)
In the embodiment described above, the upper guide member 71 is configured so that the downstream portion can be rotated around the upstream position in the transport direction of the paper S by the moving member 71a. However, the present invention is not limited to this, and it is sufficient that the upper guide member 71 is configured to be able to approach the intermediate transfer belt 51.

  An example of this embodiment is shown in FIG. The upper guide member 71 has a moving member 71b, and is configured to be able to translate in a direction approaching the intermediate transfer belt 51 (see arrow B in FIG. 8). That is, the control unit 110 can translate the upper guide member 71 by controlling the moving member 71b.

  In this embodiment, during the image forming operation, the control unit 110 controls the moving member 71b to move the upper guide member 71 to the position P4 (first position) in FIG. Guides the paper S to the secondary transfer nip N. On the other hand, during the cleaning control, the control unit 110 controls the moving member 71b so as to move the upper guide member 71 to the position P2 (second position) in FIG. 7 so that the upper guide member 71 is moved to the second position. In a certain state, the electric field generator 120 is controlled to generate an electric field that moves the toner on the upper guide member 71 onto the intermediate transfer belt 51 and moves the toner on the upper guide member 71 onto the intermediate transfer belt 51. As a result, the toner on the upper guide member 71 is removed. That is, according to this embodiment, the effect of the image forming apparatus according to the present invention can be obtained as in the above-described embodiment.

(Other embodiment 2)
Since the end of the upper guide member 71 on the downstream side in the transport direction of the paper S may come into contact with the intermediate transfer belt 51, it is desirable that the upper guide member 71 is configured not to damage the intermediate transfer belt 51. For example, it is preferable that the upper guide member 71 includes a rotatable roller at a position in contact with the intermediate transfer belt 51.

  It is also preferable that the upper guide member 71 includes a slidable member having slidability on the surface at a position where the upper guide member 71 is in contact with the intermediate transfer belt 51. Specifically, the slidable member may be provided with a Teflon (registered trademark) member imparted with conductivity by carbon or the like at a position in contact with the intermediate transfer belt 51, or may be conductive by carbon or the like. The Teflon sheet provided with the above may be attached to a position in contact with the intermediate transfer belt 51.

  If the upper guide member 71 is not controlled so as to contact the intermediate transfer belt 51, the configuration as in this embodiment is not necessarily required.

(Other embodiment 3)
Similar to the upper guide member 71, the cleaning facing roller 73 is preferably configured so as not to damage the intermediate transfer belt 51 because it contacts the intermediate transfer belt 51. In the embodiment described above, the configuration including the roller as the facing member facing the upper guide member 71 has been described. However, the slidable member as described above is provided at a position where the facing member contacts the intermediate transfer belt 51. You may prepare.

(Other embodiment 4)
In the above description, the embodiment in which the image carrier that carries the toner image is the intermediate transfer belt 51 has been described. However, the present invention is not limited to this, and a photosensitive drum may be used as the image carrier. In this embodiment, the photosensitive drum is grounded by the grounding member, and the electric field generating unit is configured by the power supply unit and the grounding member.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 51 Intermediate transfer belt 60 Secondary transfer part 62 Secondary transfer opposing roller 71 Upper guide member 71a, 71b Moving member 72 Lower guide member 73 Cleaning opposing roller 73a Grounding member 90 Power supply part 120 Electric field generation part S Paper N Secondary transfer nip T Toner contamination E Electric field Es Electrostatic field D Distance between upper guide member and intermediate transfer belt

Claims (12)

An image carrier for carrying a toner image;
A nip portion is formed in contact with the image carrier, and a transfer portion that transfers a toner image carried on the image carrier to a sheet in the nip portion;
A guide member for guiding the conveyed paper to the nip portion;
A moving member for moving the guide member;
An electric field generator for generating an electric field between the image carrier and the guide member;
A control unit that controls at least the operation of the moving member and the electric field generation unit,
The controller is
The moving member is controlled to move the guide member to a second position closer to the image carrier than a first position for guiding the sheet to the nip portion, and the guide member is moved to the second position. The image forming apparatus, wherein the electric field generating unit is controlled to generate an electric field for moving the toner on the guide member onto the image carrier. The control unit controls the electric field generation unit to generate an electric field that prevents toner on the image carrier from moving onto the guide member during an image forming operation. The image forming apparatus described. The control unit controls the electric field generation unit so as to generate an electric field having an absolute value smaller than an electric field generated when the guide member is in the second position during an image forming operation. The image forming apparatus according to claim 2. In the state where the guide member is in the second position, the control unit generates an electric field that causes the toner on the guide member to move onto the image carrier. The image forming apparatus according to claim 1, wherein the electric field generation unit is controlled to apply a voltage on which the voltage is superimposed to the guide member. The control unit moves the toner on the guide member onto the image carrier while controlling the moving member to bring the guide member closer to the image carrier after the image forming operation is completed. The image forming apparatus according to claim 1, wherein the electric field generation unit is controlled so as to generate an electric field. The control unit controls the moving member to move the guide member to the second position in accordance with the type of image formed in the image forming operation or the operating environment of the image forming apparatus, and the second member The timing for controlling the electric field generation unit is changed so as to generate an electric field for moving the toner on the guide member onto the image carrier at the position. The image forming apparatus described in 1. The said guide member is comprised so that a downstream part can rotate centering | focusing on the position of the upstream with respect to the conveyance direction of a sheet | seat. Image forming apparatus. The image forming apparatus according to claim 1, wherein the control unit controls the moving member so that the guide member is brought into contact with the image carrier. The image forming apparatus according to claim 8, wherein the guide member includes a rotatable roller or a slidable member having slidability on a surface at a position in contact with the image carrier. The image carrier is an intermediate transfer belt;
The image forming apparatus according to claim 1, further comprising a facing member that faces the guide member with the intermediate transfer belt interposed therebetween. The image forming apparatus according to claim 10, wherein the facing member is grounded by a grounding member. The image forming apparatus according to claim 10, wherein the facing member is a rotatable roller, or includes a slidable member having slidability at a position in contact with the image carrier. apparatus.

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