JP2009186589A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an excellent image by reducing a rotation load generated in an image carrier. <P>SOLUTION: The image forming apparatus includes: a motor 126 and a depressing cam 113 which make an intermediate transfer belt 2 and a transfer roller 7 close to and away from each other; a solenoid 116 with which a transfer section gap forming member 114 is inserted between and removed from between the intermediate transfer belt 2 and both end portions of the transfer roller 7; a registration roller 26 and a registration pressure roller 27 which convey a paper 8 to between the intermediate transfer belt 2 and the transfer roller 7; and a control section 104 which causes the solenoid 116 to insert the transfer section gap forming member 114 between the intermediate transfer belt 2 and both end portions of the transfer roller 7, causes the motor 126 and the depressing cam 113 to make the intermediate transfer belt 2 and the transfer roller 7 close to each other to hold the transfer section gap forming member 114 therebetween then causes the registration roller 26 and the registration pressure roller 27 to convey the paper 8 to between the intermediate transfer belt 2 and the transfer roller 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that employs an image forming method such as an electrophotographic method, an electrostatic recording method, an ionography method, and a magnetic recording method for recording on a single-sheet recording medium. More specifically, the present invention relates to an image forming apparatus that suppresses speed fluctuations of an image carrier and an intermediate transfer member.

  Conventionally, in this type of image forming apparatus, when an image is not formed on the image carrier, at least one of the image carrier and the pressure roll is moved by a driving force from a driving unit that rotationally drives the image carrier. Using the urging force of the urging means that presses the image carrier and the pressure roll in synchronization with the timing at which the recording medium enters between the pressure contact portions of the image carrier and the pressure roll. A device that releases the separation of the press contact portion is known (for example, see Patent Document 1).

  In addition, the recording member enters the pressure contact portion between the image carrier and the transfer member by pushing down the transfer member with a push-down amount corresponding to the thickness of the recording medium to provide a gap between the image carrier and the transfer member. An image carrier that suppresses the speed fluctuation of the image carrier that is sometimes generated is known (for example, see Patent Document 2).

In addition, a concave groove is provided in the image carrier or transfer member, and a gap narrower than the thickness of the recording medium is formed in the pressure contact portion between the image carrier and the transfer member. There is known one that suppresses the speed fluctuation of the image carrier that occurs when the recording medium enters (see, for example, Patent Document 3).
JP-A-6-274051 JP-A-4-242276 Japanese Utility Model Publication No. 56-47639

  However, since the pressure contact portion is separated until the recording medium enters in the one described in Patent Document 1, it can be expected that the rotational load on the image carrier when the recording medium enters is suppressed. When releasing the separation, the image carrier, the recording medium, and the transfer roller collide with each other due to the urging force of the urging means, causing a rotational load on the image carrier and causing image deterioration. It was.

  Further, the one disclosed in Japanese Patent Application Laid-Open No. H10-228707 depresses the transfer member by a depressing amount corresponding to the thickness of the recording medium so that a gap is provided between the image carrier and the transfer member, so that the speed when the recording medium enters is increased. Although it is considered that the effect of reducing fluctuations can be obtained regardless of the thickness of the recording medium, a device for detecting the thickness of the recording medium must be provided, or the adjustment amount must be determined and driven according to the thickness of the recording medium. In other words, there is a problem that the apparatus is expensive and complicated.

  In addition, the one described in Patent Document 3 forms a gap using a concave groove, and it can be expected that the rotational load of the image carrier when the recording medium enters is suppressed. Since the image carrier or the transfer member is in contact with only the provided portion, there is a problem that local stress concentration occurs at the contact portion, and the transfer member may be plastically deformed during long-term use. there were.

  In general, a conventional image forming apparatus adopting an electrophotographic method, which employs a transfer method in which a transfer roller is pressed against an image carrier with a recording sheet sandwiched between them, is a transfer roller. When the leading edge of the recording paper enters the pressure contact portion with the image carrier, a phenomenon that the conveying speed of the image carrier temporarily decreases occurs, and the phenomenon becomes more remarkable as the recording paper is thicker. There is. In particular, in recent years, the distance from the registration roller to the pressure contact portion between the transfer roller and the image carrier has become shorter due to a request for downsizing of the apparatus, and thus the speed fluctuation of the image carrier has become more problematic than before. Yes.

  Due to this phenomenon in which the conveyance speed of the image carrier temporarily decreases, not only the transfer process, but also the linear speed of the cleaning, exposure, and development processes performed on the photosensitive member fluctuate. There is a problem in that image defects called banding such as band-like shading unevenness in the sub-scanning direction and image displacement occur.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reducing the rotational load generated on an image carrier and performing good image formation. And

  An image forming apparatus according to the present invention includes an image carrier that rotates while carrying an image, a transfer member that transfers an image carried by the image carrier to a recording medium, and the image carrier and the transfer member that are close to each other. And a separation / separation means for separating, a gap forming member driving means for inserting / removing a gap forming member between both ends of the image carrier and the transfer member, and a recording medium between the image carrier and the transfer member A gap forming member is inserted between both ends of the image carrier and the transfer member by a gap forming member driving means, and the image carrier and the transfer member by the proximity separating means. And a control means for transporting the recording medium between the image carrier and the transfer member by the recording medium transporting means after the gap forming member is sandwiched between them.

  With this configuration, the gap forming member is sandwiched between the transfer member and the image carrier at both ends, so that the distance between the transfer member and the image carrier can be maintained at a predetermined distance. The difference between the distance between the transfer member and the image carrier before and after entering the body can be reduced, and the fluctuation of the image carrier speed that occurs when the recording medium enters between the transfer member and the image carrier is suppressed. it can. Therefore, it is possible to reduce the rotational load generated on the image carrier and perform good image formation. Also, by inserting the gap forming member in a state where the transfer member is separated from the image carrier, the gap forming member is inserted in a state where the transfer member and the image carrier are in pressure contact with each other. It is possible to reduce the possibility that a rotational load is generated on the image carrier when the gap forming member is inserted. Further, since the gap forming member is inserted and removed between the both ends of the image carrier and the transfer member by the gap forming member driving means, the gap forming member is interposed between the both ends of the image carrier and the transfer member. It is possible to prevent wear and plastic deformation of the gap forming member, the image carrier and the transfer member as compared with the case where the gap forming member is always inserted, and by controlling the gap forming member driving means, the gap forming member can be It can be inserted when the transfer member is separated from the image carrier.

  The image forming apparatus according to the present invention further includes a selection unit that selects whether the gap forming member is inserted between the image carrier and both ends of the transfer member by the gap forming member driving unit. It is characterized by.

  With this configuration, the user can select whether or not to insert a gap forming member between both ends of the image carrier and the transfer member according to the thickness of the recording medium to be used. When the gap forming member is inserted only when the recording medium is a thin sheet of plain paper or the like, sufficient pressure is generated between the image carrier and the transfer member by inserting the transfer portion gap forming member. Therefore, it is possible to prevent the transferability from deteriorating.

  In the image forming apparatus according to the present invention, the gap forming member is formed of a circular sheet-like member having a preset thickness and is sandwiched between the image carrier and the transfer member. In addition, the rotation is driven by contacting at least one of the image carrier or the transfer member with the position outside the space between both ends of the image carrier and the transfer member as a rotation center.

  With this configuration, it is possible to maintain the state in which the gap forming member is sandwiched between both ends of the image carrier and the transfer member while the transfer member and the image carrier are close to each other. A gap corresponding to the thickness of the gap forming member can be formed stably.

  In the image forming apparatus according to the present invention, the rotation plane of the gap forming member is positioned substantially on the same plane as the contact surface between the image carrier and the transfer member brought close to each other by the proximity / separation unit. It is characterized by.

  With this configuration, the rotation plane of the gap forming member is substantially flush with the contact surface between the image carrier and the transfer member, so that when the image carrier and the transfer member are close to each other, Since the image carrier or the transfer member is not in contact with only the surface, the gap between the image carrier and the transfer member can be prevented from becoming larger than the thickness of the gap forming member. A gap corresponding to the thickness of the gap forming member can be stably formed between the member and the member. Further, it can be prevented that the image carrier or the transfer member is in contact with only one surface of the gap forming member and the gap forming member is bent or plastically deformed.

  In the image forming apparatus according to the present invention, the gap forming member driving unit changes the thickness of the gap forming member at a portion inserted between the image carrier and both ends of the transfer member. A gap formation amount control means for controlling the amount of a gap formed between the image carrier and the transfer member; and a gap formation amount selection means for selecting the gap amount controlled by the gap formation amount control means. It is characterized by that.

  With this configuration, the amount of the gap formed between the image carrier and the transfer member can be reduced by changing the thickness of the gap forming member at the portion inserted between the both ends of the image carrier and the transfer member. Since it can be selected and controlled according to the thickness of the recording medium, the speed of the image carrier when the recording medium enters between the transfer member and the image carrier without deteriorating the transferability to the recording medium. Variations can be suppressed.

  Further, in the image forming apparatus according to the present invention, the gap forming member has a thickness distribution with respect to the insertion direction of the gap forming member, and the gap forming amount control means is operated by the gap forming member driving means. The amount of the gap formed between the image carrier and the transfer member is controlled by changing the insertion amount of the gap forming member inserted between the carrier and both ends of the transfer member. And

  With this configuration, gaps of different sizes can be formed between the transfer member and the image carrier without changing the gap forming member, so that transfer to a recording medium can be performed with a simple and low-cost configuration. Without deteriorating, it is possible to suppress the speed fluctuation of the image carrier when the recording medium enters between the transfer member and the image carrier.

  Further, the image forming apparatus according to the present invention is characterized in that the gap forming member driving means is driven by one driving source to insert the gap forming member between both ends of the image carrier and the transfer member. To do.

  With this configuration, a single driving source can insert a gap forming member between both ends of the image carrier and the transfer member to set a plurality of gaps between the image carrier and the transfer member. The cost can be reduced.

  According to the present invention, it is possible to provide an image forming apparatus capable of reducing the rotational load generated on the image carrier and performing good image formation.

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

(First embodiment)
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

  First, the configuration will be described.

  As shown in FIG. 1, the image forming apparatus 50 includes a printer unit 100, a paper feed unit 200, a scanner unit 300, and an automatic document feeder 400.

  The printer unit 100 includes an intermediate transfer unit 101, an exposure device, an image forming unit, a fixing unit, a toner supply device, and the like, and forms an image on a sheet 8 (see FIG. 2) that is a recording medium. The paper feed unit 200 includes a plurality of paper feed cassettes, a paper transport path, and the like, and stores and transports the paper 8. The scanner unit 300 includes a contact glass 301 and reads image information of a document placed on the contact glass 301. The automatic document feeder 400 includes a document tray 401 and conveys a document placed on the document tray 401 onto the contact glass 301. That is, the image forming apparatus 50 shows an example in which the image forming apparatus according to the present invention is applied to a color laser copying machine.

  FIG. 2 is a cross-sectional view of the intermediate transfer portion of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 2, the intermediate transfer unit 101 includes an intermediate transfer belt 2 as an image carrier, a driving roller 3, a driven roller 4, a tension roller 5, a counter roller 6, and a transfer roller 7. The intermediate transfer belt 2 as an image carrier is stretched by a driving roller 3, a driven roller 4, a tension roller 5, and a counter roller 6, and is driven by the driving roller 3 in the clockwise direction in the figure. The intermediate transfer belt 2 carries toner images primarily transferred from the four photosensitive drums 1 corresponding to cyan, magenta, yellow, and black colors, and presses the toner images against the opposing roller 6 and the opposing roller 6. It moves to the transfer roller 7 provided in this way.

  The transfer roller shaft 10 of the transfer roller 7 is supported by a transfer roller support frame 111. The transfer roller support frame 111 is urged toward the opposing roller 6 by the compression spring 9. One end of the transfer roller support frame 111 is supported by a support frame rotation fulcrum 112, and the upper surface of the other end of the transfer roller support frame 111 is in contact with the pressing cam 113.

  The push-down cam 113 pushes the transfer roller support frame 111 downward against the urging force of the compression spring 9 according to the rotation angle.

  The transfer roller support frame 111 swings up and down around the support frame rotation fulcrum 112 as the push cam 113 rotates. Therefore, when the transfer roller support frame 111 is moved downward by the pressing cam 113, the transfer roller 7 is also moved downward, and the transfer roller 7 and the opposing roller 6 are separated from each other. When the transfer roller support frame 111 is moved upward by the compression spring 9, the transfer roller 7 is also moved upward to come close to the opposing roller 6 and contact the intermediate transfer belt 2 below the opposing roller 6. It is designed to rotate.

  In the present embodiment, while a print job is input by the user and process control is performed, the transfer roller support frame 111 moves downward and the transfer roller 7 and the opposing roller 6 are separated from each other, thereby transferring the transfer roller. 7 and the intermediate transfer belt 2 are separated from each other, so that residual toner on the intermediate transfer belt 2 and a toner pattern by process control do not adhere to the transfer roller 7.

  Further, the opposing roller 6 and the transfer roller 7 are configured to secondarily transfer the toner image carried by the intermediate transfer belt 2 onto the paper 8. On the right side of the opposing roller 6 and the transfer roller 7, that is, on the upstream side in the conveyance direction of the paper 8, a registration roller 26 that conveys the paper 8 to a pressure contact portion where the opposing roller 6 and the transfer roller 7 are in pressure contact with the intermediate transfer belt 2. A pressure roller 27 is provided. The registration roller 26 is driven by a motor (not shown), and the registration pressure roller 27 is driven in contact with the registration roller 26.

  Further, the entry of the leading edge of the sheet 8 into the transfer unit 102 is detected in the path downstream of the registration roller 26 and the registration pressure roller 27 in the sheet conveyance direction, and the trailing end of the sheet 8 is removed from the transfer unit 102. A transfer section paper passage detection sensor 19 for detecting the above is provided.

  During the transfer operation, the paper 8 supplied from the paper supply unit 200 stands by at the installation position of the registration roller 26 and the registration pressure roller 27, and when the toner image is transferred to the intermediate transfer belt 2, the registration roller 26 and By the registration pressure roller 27, the opposing roller 6 and the transfer roller 7 are conveyed to a pressure contact portion in pressure contact with the intermediate transfer belt 2 in synchronization with the leading edge of the toner image on the intermediate transfer belt 2. The toner image carried on the intermediate transfer belt 2 is transferred to the paper 8 sandwiched between the intermediate transfer belt 2 and the transfer roller 7 at the press contact portion by the pressure applied by the compression spring 9 and a transfer bias (not shown). As described above, the image forming apparatus 50 conveys the intermediate transfer belt 2 onto which the toner image has been transferred by the primary transfer while being sandwiched by the registration rollers 26, and the toner image is secondarily transferred onto the paper 8 by the transfer roller 7. A transfer method is adopted. The counter roller 6 and the transfer roller 7 constitute a transfer unit 102, and the registration roller 26 and the registration pressure roller 27 constitute a registration unit 103. The image carrier is not limited to the intermediate transfer belt 2 but may be the photosensitive drum 1. That is, FIG. 2 shows an intermediate transfer type configuration in which the intermediate transfer belt 2 and the transfer roller 7 come into contact to perform secondary transfer on the paper 8, but the photosensitive drum 1 and the transfer roller 7 come into contact with each other. Thus, the present invention can be applied even to a direct transfer type configuration in which direct transfer is performed on the paper 8.

  FIG. 3A and FIG. 3B are a top view and a cross-sectional view of the transfer unit during standby of the image forming apparatus according to the first embodiment of the present invention. 4A and 4B are a top view and a cross-sectional view of the transfer unit when the transfer unit gap forming member is inserted in the image forming apparatus according to the first embodiment of the present invention. FIGS. 5A and 5B are a top view and a cross-sectional view of the transfer portion when the image forming apparatus according to the first embodiment of the present invention is pressed against the transfer roller. 3 to 5, the illustration of the intermediate transfer belt 2 is omitted.

  As shown in FIGS. 3 to 5, the transfer unit 102 has a gap between the intermediate transfer belt 2 and the transfer roller 7 at the transfer pressure contact portion 18 where the opposing roller 6 and the transfer roller 7 are pressed against the intermediate transfer belt 2. The transfer section gap forming member 114 to be formed, the transfer section gap forming member support member 115 that supports the transfer section gap forming member 114, and the transfer section gap forming member 114 so that the transfer section gap forming member 114 moves in and out of the transfer pressure contact portion 18. And a solenoid 116 for moving the forming member 114. The solenoid 116 is fixed to the frame 109, and the plunger 116 a of the solenoid 116 is fixed to the transfer part gap forming member support member 115. The transfer part gap forming member support member 115 is urged in a direction away from the transfer pressure contact part 18 by a tension spring 117.

  The solenoid 116 moves the transfer portion gap forming member 114 toward the transfer pressure contact portion 18 against the urging force of the tension spring 117 so that the transfer portion gap forming member 114 is inserted into the transfer pressure contact portion 18. It has become.

  The transfer part gap forming member 114 is formed of a circular sheet-like member, and is sandwiched between the intermediate transfer belt 2 and the transfer roller 7 as shown in FIGS. 4 (a) and 5 (a). In addition, the rotation is driven by contacting at least one of the intermediate transfer belt 2 or the transfer roller 7 with the position outside the interval between both ends of the intermediate transfer belt 2 and the transfer roller 7 as a rotation center. As shown in FIGS. 4B and 5B, the rotation plane of the transfer portion gap forming member 114 is in contact with the transfer roller 7 and the intermediate transfer belt 2 brought close to each other by the motor 126 and the push-down cam 113. It is located on substantially the same plane as the plane.

  The transfer part gap forming member 114 is set in advance to a thickness smaller than the thickness of the thick paper 8 assumed in a thick paper mode to be described later. For this reason, the transfer portion gap forming member 114 prevents a sufficient pressure from being generated between the intermediate transfer belt 2 and the transfer roller 7, thereby preventing the transferability from deteriorating. 3 to 5 show one end sides of the opposing roller 6 and the transfer roller 7, the other end sides of the opposing roller 6 and the transfer roller 7 are also configured in the same manner as described above.

  The transfer portion gap forming member 114 is required to have sufficient flexibility to be in close contact with both rollers when sandwiched between the intermediate transfer belt 2 and the transfer roller 7 and is sandwiched between the intermediate transfer belt 2 and the transfer roller 7. In the standby state where it is not, a certain degree of flatness must be maintained by the restoring force. Therefore, a flexible material is used for the transfer portion gap forming member 114. As the flexible material, for example, polymer materials such as polyethylene terephthalate (PET), polycarbonate (PC), polyamide (nylon), and polyimide (PI) are suitable. In particular, polyimide (PI) has mechanical properties. It is excellent and preferable. In addition, when a material made of a metal material is used as a flexible material, phosphor bronze strips, beryllium copper strips, etc. that are supplied to the market as metal thin plates are suitable, but stainless steel strips have excellent mechanical properties. Therefore, it is more preferable. SUS304-CSP is the most excellent stainless steel strip. Further, as the stainless steel strip, there is precipitation hardening SUS631-CSP, but it is preferable to use austenitic SUS631-CSP in consideration of repeated fatigue. Moreover, the transfer part gap forming member 12 can also be made of nickel foil by an electroforming method that can be easily processed into a desired thickness.

  FIG. 6 is a block diagram showing a control unit of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 6, the control unit 104 rotates the microprocessor 21 to which the detection signal from the transfer unit paper passage detection sensor 19 is input, the solenoid drive circuit 22 that drives the solenoid 116, and the push cam 113. And a motor drive circuit 125 that drives the motor 126. The microprocessor 21 controls the solenoid drive circuit 22 and the motor drive circuit 125 based on various signals including detection signals from the transfer section paper passage detection sensor 19. Further, the control unit 104 receives an operation mode (whether it is a cardboard mode, etc.) selected and input by a user from an operation unit (not shown) and stores the operation mode, and various types of image forming apparatus 50. It is designed to control the operation.

  Next, the operation of the image forming apparatus 50 configured as described above will be described.

  FIG. 7 is a flowchart for explaining the operation of the control unit of the image forming apparatus according to the first embodiment of the present invention. 8 to 12 are sectional views showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series.

  As shown in FIG. 7, the control unit 104 determines whether or not the mode set by the user's instruction is the thick paper mode when waiting for printing (step S1). It is determined whether or not there is a request (step S2).

  At the time of standby in which the determination in step S1 is performed, the transfer roller 7 is separated from the opposing roller 6 by the action of the push-down cam 113 as shown in FIG. Further, the transfer portion gap forming member 114 is in a state of protruding from the nip portion between the transfer roller 7 and the opposing roller 6.

  If it is determined in step S2 that there is a print request, the control unit 104 starts process control or the like (step S3), and determines whether printing of the paper 8 is started (step S4). The determination in step S4 is performed based on the start of the electrophotographic process on the photosensitive drum 1 and the detection of the leading edge of the paper 8 by the transfer portion paper passage detection sensor 19.

  If it is determined in step S4 that printing of the paper 8 has started, the control unit 104 turns on the solenoid 116 to move the transfer unit gap forming member 114 between the transfer roller 7 and the opposing roller 6 as shown in FIG. Insert into the nip (step S5).

  Next, the control unit 104 rotates the push cam 113 to urge the transfer roller 7 against the opposing roller 6 by the compression spring 9 (step S6). At this time, as shown in FIG. 10, the transfer roller 7 and the counter roller 6 are in a state in which the transfer portion gap forming member 114 is sandwiched between both ends, and the transfer roller 7 and the counter roller 6 are not transferred. A gap corresponding to the thickness of the gap forming member 114 is formed. Note that due to the elasticity of the transfer roller 7 and the counter roller 6, the size of the gap in the center in the axial direction between the transfer roller 7 and the counter roller 6 is smaller than the thickness of the transfer unit gap forming member 114.

  Further, when the paper 8 is sandwiched between the transfer roller 7 and the counter roller 6, a gap corresponding to the thickness of the paper 8 is formed between the transfer roller 7 and the counter roller 6, as shown in FIG. It will be in the state.

  Next, the control unit 104 determines whether or not the transfer of the final sheet has been completed (step S7). If it is determined that the transfer of the final sheet has been completed, the control unit 104 rotates the push cam 113 to return to FIG. As shown, the transfer roller 7 is separated from the opposing roller 6 (step S8).

  Next, the control unit 104 turns off the solenoid 116 and moves the transfer unit gap forming member 114 out of the nip portion between the transfer roller 7 and the opposing roller 6 (step S9). When step S9 ends, the transfer unit 102 enters a standby state again.

  When the mode for the normal thickness paper 8 thinner than the thick paper is set, that is, when it is not determined in step S1 that the paper is in the thick paper mode, processes other than steps S5 and S9 are executed. Thus, the transfer portion gap forming member 114 is not inserted into the pressure contact portion of the transfer portion 102.

  As described above, the image forming apparatus according to the present embodiment includes the intermediate transfer belt 2 that rotates while supporting an image, the transfer roller 7 that transfers the image carried by the intermediate transfer belt 2 to the paper 8, and the intermediate transfer. A motor 126 that moves the belt 2 and the transfer roller 7 close to and away from each other, a push cam 113, a solenoid 116 that inserts and removes the transfer portion gap forming member 114 between both ends of the intermediate transfer belt 2 and the transfer roller 7, A transfer roller gap forming member 114 is provided between both ends of the intermediate transfer belt 2 and the transfer roller 7 by a registration roller 26 that conveys the paper 8 between the transfer belt 2 and the transfer roller 7, a resist pressure roller 27, and a solenoid 116. And the intermediate transfer belt 2 and the transfer roller 7 are brought close to each other by the motor 126 and the push-down cam 113 and the transfer portion gap forming member 114 is sandwiched between them. And a control unit 104 that conveys the paper 8 between the intermediate transfer belt 2 and the transfer roller 7 by the registration roller 26 and the registration pressure roller 27, so that the transfer unit gap forming member 114 and the transfer roller 7 are intermediate. By holding the transfer belt 2 at both ends, the distance between the transfer roller 7 and the intermediate transfer belt 2 can be held at a predetermined distance. Therefore, before and after the sheet 8 enters between the transfer roller 7 and the intermediate transfer belt 2. The difference in the distance between the transfer roller 7 and the intermediate transfer belt 2 can be reduced, and the speed fluctuation of the intermediate transfer belt 2 that occurs when the paper 8 enters between the transfer roller 7 and the intermediate transfer belt 2 can be suppressed. . Therefore, it is possible to reduce the rotational load generated on the intermediate transfer belt 2 and perform good image formation. Further, the transfer portion gap forming member 114 is inserted in a state where the transfer roller 7 is separated from the intermediate transfer belt 2, so that the transfer portion gap is kept in contact with the transfer roller 7 and the intermediate transfer belt 2. Compared with the case where the forming member 114 is inserted, it is possible to reduce the possibility that a rotational load is generated on the intermediate transfer belt 2 when the transfer portion gap forming member 114 is inserted. Further, since the transfer portion gap forming member 114 is inserted and removed between the intermediate transfer belt 2 and both ends of the transfer roller 7 by the solenoid 116, the transfer portion gap forming member 114 is transferred to the intermediate transfer belt 2 and the transfer roller 7. It is possible to prevent wear and plastic deformation of the transfer portion gap forming member 114, the intermediate transfer belt 2 and the transfer roller 7 as compared with the case where the roller 7 is always inserted between both ends, and by controlling the solenoid 116. If necessary, the transfer portion gap forming member 114 can be inserted when the transfer roller 7 and the intermediate transfer belt 2 are separated from each other.

  Further, the image forming apparatus according to the present embodiment includes a control unit 104 that selects whether or not the transfer unit gap forming member 114 is inserted between both ends of the intermediate transfer belt 2 and the transfer roller 7 by the solenoid 116. Therefore, the user can select whether or not to insert the transfer portion gap forming member 114 between the both ends of the intermediate transfer belt 2 and the transfer roller 7 according to the thickness of the paper 8 to be used. The transfer portion gap forming member 114 is inserted only when the paper 8 is a thick paper, and the transfer portion gap forming member 114 is inserted when the paper 8 is a thin paper such as plain paper. It can be prevented that sufficient pressure is not generated between the rollers 7 and transferability is deteriorated.

  In the image forming apparatus according to the present embodiment, the transfer portion gap forming member 114 is formed of a circular sheet-like member having a preset thickness, and is sandwiched between the intermediate transfer belt 2 and the transfer roller 7. The roller is driven and rotated in contact with at least one of the intermediate transfer belt 2 or the transfer roller 7 with the position outside the end portion between the intermediate transfer belt 2 and the transfer roller 7 as a rotation center. 7 and the intermediate transfer belt 2 are close to each other, the state in which the transfer portion gap forming member 114 is sandwiched between both ends of the intermediate transfer belt 2 and the transfer roller 7 can be maintained. A gap corresponding to the thickness of the transfer portion gap forming member 114 can be stably formed between the transfer roller 7 and the transfer roller 7.

  Further, in the image forming apparatus according to the present embodiment, the rotation plane of the transfer portion gap forming member 114 is substantially the same as the contact surface between the intermediate transfer belt 2 and the transfer roller 7 that are brought close to each other by the motor 126 and the push-down cam 113. Since the rotation plane of the transfer portion gap forming member 114 is substantially on the same plane as the contact surface between the intermediate transfer belt 2 and the transfer roller 7, the intermediate transfer belt 2 and the transfer roller 7 are located on the same plane. When close to each other, the intermediate transfer belt 2 or the transfer roller 7 does not come into contact with only one surface of the transfer portion gap forming member 114, and the gap between the intermediate transfer belt 2 and the transfer roller 7 forms the transfer portion gap. Since the thickness of the member 114 can be prevented from becoming larger, a gap corresponding to the thickness of the transfer portion gap forming member 114 is stably formed between the intermediate transfer belt 2 and the transfer roller 7. It is possible. Further, it is possible to prevent the intermediate transfer belt 2 or the transfer roller 7 from contacting only one surface of the transfer portion gap forming member 114 and bending or plastically deforming the transfer portion gap forming member 114.

(Second Embodiment)
FIG. 13A and FIG. 13B are a top view and a cross-sectional view of the transfer unit when the image forming apparatus according to the second embodiment of the present invention is on standby. FIGS. 14A and 14B are a top view and a cross-sectional view of the transfer unit when the transfer unit gap forming member corresponding to the medium thickness paper of the image forming apparatus according to the second embodiment of the present invention is inserted. FIG. FIGS. 15A and 15B are a top view and a cross-sectional view of the transfer unit when the transfer unit gap forming member corresponding to the thickest paper of the image forming apparatus according to the second embodiment of the present invention is inserted. FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted.

  As shown in FIGS. 13 to 15, a transfer unit 142 is provided in place of the transfer unit 102 of the first embodiment. The transfer unit 142 is a circular sheet-shaped transfer unit gap forming unit that forms a gap between the intermediate transfer belt 2 and the transfer roller 7 at the transfer pressure contact unit 18 where the opposing roller 6 and the transfer roller 7 are pressed against the intermediate transfer belt 2. Members 114a and 114b, transfer portion gap forming member support member 115 for supporting the transfer portion gap forming members 114a and 114b, and transfer portion gaps so that the transfer portion gap forming members 114a and 114b move in and out of the transfer pressure contact portion 18. And a gap forming member drive cam 119 for moving the forming members 114a and 114b. The gap forming member drive cam 119 is provided on the output shaft of the gap forming member drive motor 120, and the gap forming member drive motor 120 is fixed to the frame 109. The gap forming member driving cam 119 moves the transfer part gap forming member support member 115 toward the transfer pressure contact part 18 according to the rotation angle. Further, the transfer portion gap forming member support member 115 is urged in a direction away from the transfer pressure contact portion 18 by a tension spring 117.

  That is, the gap forming member driving cam 119 moves the transfer part gap forming member support member 115 toward the transfer pressure contact part 18 against the urging force of the tension spring 117 according to the rotation angle thereof, as shown in FIG. As shown in FIG. 15, only the transfer part gap forming member 114a is inserted into the transfer pressure contact part 18 (operation in the medium-thick paper mode), or the transfer part gap forming member 114b and the transfer part gap forming member 114b are Both are inserted into the transfer pressure contact portion 18 (operation in the thickest paper mode).

  Specifically, when only the transfer part gap forming member 114a is inserted into the transfer pressure contact part 18, and when both the transfer part gap forming member 114a and the transfer part gap forming member 114b are inserted into the transfer pressure contact part 18. In each case, a table that associates the movement amount (displacement in the insertion direction) of the transfer portion gap forming member support member 115 and the rotation angle of the gap forming member drive cam 119 is stored in the control unit 105 described later, and a job set by the user is stored. The rotation angle of the gap forming member drive cam 119 by the gap forming member drive motor 120 is controlled depending on whether the medium thick paper mode or the thickest paper mode is selected.

  The transfer portion gap forming member 114a is set to a thickness of 220 μm, and the transfer portion gap forming member 114b is set to a thickness of 180 μm. The transfer part gap forming member 114a and the transfer part gap forming member 114b are overlapped. Further, the outer diameter of the transfer portion gap forming member 114a is larger than the outer diameter of the transfer portion gap forming member 114b, and the outer peripheral portion of the transfer portion gap forming member 114a is larger than the outer peripheral portion of the transfer portion gap forming member 114b. It is close to the transfer pressure contact portion 18. Therefore, when the transfer part gap forming members 114a and 114b are viewed as one member, the transfer part gap forming members 114a and 114b have a thickness distribution with respect to the insertion direction of the transfer part gap forming members 114a and 114b. is doing.

  The materials and materials of the transfer part gap forming members 114a and 114b are the same as those in the first embodiment.

The medium thick paper mode and the thickest paper mode are modes in which the thick paper mode described in the first embodiment is subdivided. Medium thick paper mode is a mode corresponding to 220kg paper (256g / ^{m 2)} or more paper weight of the sheet 8, the uppermost thick paper mode is 309Kg paper (359 g / ^{m 2}
This mode corresponds to the paper 8 having the above paper weight. In the present embodiment, in the middle-thick paper mode, as shown in FIG. 14, only the transfer portion gap forming member 114a is inserted into the transfer pressure contact portion 18 so that the intermediate transfer belt 2 and the transfer roller 7 are close to each other. The gap is held at about 220 μm, which is the thickness of the transfer part gap forming member 114a. In the thickest paper mode, as shown in FIG. 15, the intermediate transfer belt 2 and the transfer roller 7 are moved by inserting both the transfer portion gap forming member 114 a and the transfer portion gap forming member 114 b into the transfer pressure contact portion 18. The gap when approaching is maintained at about 400 μm (220 μm + 180 μm), which is the sum of the thickness of the transfer portion gap forming member 114a and the thickness of the transfer portion gap forming member 114b. The thickness of the transfer portion gap forming member 114a in the medium thick paper mode is 220 μm, which is smaller than the thickness of the medium thick paper 8 assumed in the medium thick paper mode. 400 μm, which is the sum of the thicknesses of the transfer portion gap forming members 114a and 114b in the thickest paper mode, is thinner than the thickness of the thickest paper 8 assumed in the thickest paper mode. For this reason, the transfer portion gap forming members 114a and 114b prevent a sufficient pressure from being generated between the intermediate transfer belt 2 and the transfer roller 7, thereby preventing the transferability from deteriorating.

  FIG. 16 is a block diagram of a control unit that controls the transfer unit of the image forming apparatus according to the second embodiment of the present invention.

  As shown in FIG. 16, the control unit 105 includes a microprocessor 21 to which a detection signal from the transfer unit paper passage detection sensor 19 is input, a gap formation member drive motor drive circuit 127 that drives the gap formation member drive motor 120, and And a motor drive circuit 125 that drives a motor 126 that rotates the push cam 113. The microprocessor 21 controls the gap forming member drive motor drive circuit 127 and the motor drive circuit 125 based on various signals including detection signals from the transfer section paper passage detection sensor 19. Further, the control unit 105 receives an operation mode (whether it is the middle-thick paper mode or the thickest-paper mode, etc.) selected and input by the user from an operation unit (not shown) or the like and stores this operation mode. Various operations of the device 50 are controlled.

  Next, the operation of the image forming apparatus 50 configured as described above will be described.

  17 to 19 are flowcharts for explaining the operation of the control unit of the image forming apparatus according to the second embodiment of the present invention.

  As shown in FIG. 17, the control unit 105 determines whether or not the mode set by the user's instruction is the thick paper mode when waiting for printing (step S11). It is determined whether or not there is a request (step S12).

  At the time of standby during the determination in step S11, as shown in FIGS. 13A and 13B, the transfer roller 7 is separated from the facing roller 6 by the action of the push-down cam 113. ing. In addition, the transfer portion gap forming members 114 a and 114 b are in a state of protruding from the nip portion between the transfer roller 7 and the opposing roller 6.

  If it is determined in step S12 that there is a print request, the control unit 105 starts process control or the like (step S13), and determines whether the thick paper mode set by the user instruction is the thickest paper mode. (Step S14), if it is not determined that the paper is in the thickest paper mode, the middle thick paper mode process shown in FIG. 18 is executed. If it is determined that the paper is in the thickest paper mode, the thickest paper shown in FIG. Perform mode processing.

  As shown in FIG. 18, in the medium-thick paper mode, the control unit 105 determines whether printing of the paper 8 has been started (step S21). The determination in step S21 is performed based on the start of the electrophotographic process on the photosensitive drum 1, the detection of the leading edge of the paper 8 by the transfer portion paper passage detection sensor 19, and the like.

  If it is determined in step S21 that printing of the sheet 8 has started, the control unit 105 drives the gap forming member drive cam 119 by the rotation of the gap forming member drive motor 120, and as shown in FIG. Only the forming member 114a is inserted into the nip portion between the transfer roller 7 and the opposing roller 6 (step S22).

  Next, the control unit 105 rotates the push cam 113 to urge the transfer roller 7 against the opposing roller 6 by the compression spring 9 (step S23). At this time, the transfer roller 7 and the counter roller 6 are in a state where the transfer portion gap forming member 114a is sandwiched between both ends, and the thickness of the transfer portion gap forming member 114a is between the transfer roller 7 and the counter roller 6. A gap corresponding to this is formed. Note that due to the elasticity of the transfer roller 7 and the opposing roller 6, the size of the gap in the center in the axial direction between the transfer roller 7 and the opposing roller 6 becomes a value smaller than the thickness of the transfer portion gap forming member 114a.

  When the paper 8 is sandwiched between the transfer roller 7 and the opposing roller 6, a gap corresponding to the thickness of the paper 8 is formed between the transfer roller 7 and the opposing roller 6.

  Next, the control unit 105 determines whether or not the transfer of the final sheet has been completed (step S24). If it is determined that the transfer of the final sheet has been completed, the control unit 105 rotates the pressing cam 113 to transfer the transfer roller 7. Is separated from the facing roller 6 (step S25).

  Next, the control unit 105 drives the gap forming member driving cam 119 by the rotation of the gap forming member driving motor 120, and moves the transfer unit gap forming member 114a from the nip portion between the transfer roller 7 and the opposing roller 6 (step). S26). When step S26 is completed, the transfer unit 142 enters a standby state again.

  On the other hand, as shown in FIG. 19, in the thickest paper mode, the control unit 105 determines whether printing of the paper 8 has been started (step S31). The determination in step S31 is performed based on the start of the electrophotographic process on the photosensitive drum 1, the detection of the leading edge of the paper 8 by the transfer unit paper passage detection sensor 19, and the like.

  When it is determined in step S31 that printing of the paper 8 has started, the control unit 105 drives the gap forming member drive cam 119 by the rotation of the gap forming member drive motor 120, and as shown in FIG. Both the forming members 114a and 114b are inserted into the nip portion between the transfer roller 7 and the counter roller 6 (step S32).

  Next, the control unit 105 rotates the push cam 113 to urge the transfer roller 7 against the opposing roller 6 by the compression spring 9 (step S33). At this time, the transfer roller 7 and the counter roller 6 are in a state where the transfer portion gap forming member 114a is sandwiched between both ends, and the transfer portion gap forming members 114a and 114b are interposed between the transfer roller 7 and the counter roller 6. A gap corresponding to the total thickness is formed. Note that due to the elasticity of the transfer roller 7 and the counter roller 6, the size of the gap between the transfer roller 7 and the counter roller 6 in the center in the axial direction is smaller than the total thickness of the transfer unit gap forming members 114a and 114b. Become.

  When the paper 8 is sandwiched between the transfer roller 7 and the opposing roller 6, a gap corresponding to the thickness of the paper 8 is formed between the transfer roller 7 and the opposing roller 6.

  Next, the control unit 105 determines whether or not the transfer of the final sheet has been completed (step S34). If it is determined that the transfer of the final sheet has been completed, the control unit 105 rotates the pressing cam 113 to transfer the transfer roller 7. Is separated from the facing roller 6 (step S35).

  Next, the control unit 105 drives the gap forming member driving cam 119 by the rotation of the gap forming member driving motor 120, and moves the transfer unit gap forming members 114 a and 114 b from the nip portion between the transfer roller 7 and the opposing roller 6. (Step S36). When step S36 is completed, the transfer unit 142 enters a standby state again.

  As described above, the image forming apparatus according to the present embodiment transfers a portion inserted between the both ends of the intermediate transfer belt 2 and the transfer roller 7 by the gap forming member driving motor 120 and the gap forming member driving cam 119. Since the control section 105 is provided for selecting and controlling the amount of the gap formed between the intermediate transfer belt 2 and the transfer roller 7 by changing the thickness of the section gap forming members 114a and 114b. The gap formed between the intermediate transfer belt 2 and the transfer roller 7 can be changed by changing the thickness of the transfer portion gap forming members 114 a and 114 b at the portions inserted between the belt 2 and both ends of the transfer roller 7. Since the amount can be selected and controlled in accordance with the thickness of the paper 8, when the paper 8 enters between the transfer roller 7 and the intermediate transfer belt 2 without deteriorating transferability to the paper 8. It is possible to suppress the velocity fluctuation of the intermediate transfer belt 2.

  In the image forming apparatus according to the present embodiment, the transfer part gap forming members 114a and 114b have a thickness distribution with respect to the insertion direction of the transfer part gap forming members 114a and 114b. By changing the insertion amount of the transfer portion gap forming members 114a and 114b inserted between the intermediate transfer belt 2 and both ends of the transfer roller 7 by the forming member drive motor 120 and the gap forming member drive cam 119, the intermediate transfer belt is changed. 2 and the transfer roller 7, the amount of the gap between the transfer roller 7 and the intermediate transfer belt 2 can be changed without changing the transfer portion gap forming members 114a and 114b. Therefore, the sheet 8 can be placed between the transfer roller 7 and the intermediate transfer belt 2 without deterioration in transferability to the sheet 8 with a simple and low-cost configuration. It is possible to suppress the speed fluctuation of the intermediate transfer belt 2 at the time of rush.

(Third embodiment)
FIG. 20A is a top view of the transfer unit of the image forming apparatus according to the third embodiment of the present invention. FIG. 20B is a cross-sectional view of the transfer portion of the image forming apparatus according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. In the second embodiment, the two gap forming members at both ends of the transfer portion can be driven by one driving source in the second embodiment.

  As shown in FIGS. 20A and 20B, the transfer unit 152 includes a transfer unit gap forming member support member 115 that supports the transfer unit gap forming members 114a and 114b, and a transfer unit gap forming member support member 115. And a pinion gear 121 that meshes with the two racks 122 and is driven by the gap forming member drive motor 120. The two racks 122 are arranged so as to sandwich the pinion gear 121 therebetween.

  For this reason, when the gap forming member driving motor 120 rotates the pinion gear 121, the two racks 122 move in directions opposite to each other, so that the transfer unit gap forming member support member 115 is moved in accordance with the movement of the rack 122. The gap forming members 114 a and 114 b can be inserted into the nip portion between the transfer roller 7 and the opposing roller 6, and the transfer portion gap forming members 114 a and 114 b can be brought out of the nip portion between the transfer roller 7 and the opposing roller 6. It is like that. Selection of insertion or non-insertion of the transfer portion gap forming members 114a and 114b into the nip portion between the transfer roller 7 and the opposing roller 6 is performed by controlling the rotation angle of the gap forming member drive motor 120 that drives the pinion gear 121. It is like that.

  As described above, the image forming apparatus according to the present embodiment uses the single gap forming member driving motor 120 as a drive source, and the transfer portion gap forming members 114 a and 114 b between the both ends of the intermediate transfer belt 2 and the transfer roller 7. Is inserted between the both ends of the intermediate transfer belt 2 and the transfer roller 7 by one gap forming member driving motor 120, and the intermediate transfer belt 2, the transfer roller 7 and the transfer roller 7 are inserted. Since a plurality of gaps can be set, a simple configuration can be achieved and cost reduction can be realized.

  As described above, the image forming apparatus according to the present invention has the effect of reducing the rotational load generated on the image carrier and performing good image formation, and performs recording on a single-sheet recording medium. It is useful as an image forming apparatus such as a copying machine, a printer, or a facsimile machine that employs an image forming system such as an electrophotographic system, an electrostatic recording system, an ionography system, or a magnetic recording system.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view of an intermediate transfer unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 3A is a top view of a pressure contact portion of a transfer portion when the image forming apparatus according to the first embodiment of the present invention is on standby. FIG. 3B is a cross-sectional view of the transfer unit during standby of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6A is a top view of the transfer unit when the transfer unit gap forming member is inserted in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6B is a cross-sectional view of the transfer unit when the transfer unit gap forming member is inserted in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3A is a top view of a transfer unit when the image forming apparatus according to the first embodiment of the present invention is pressed against a transfer roller. FIG. 4B is a cross-sectional view of the transfer portion when the image forming apparatus according to the first embodiment of the present invention is in contact with the transfer roller. 2 is a block diagram illustrating a control unit of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. FIG. 5 is a flowchart illustrating an operation of a control unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a side view showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series. FIG. 4 is a cross-sectional view showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series. FIG. 4 is a cross-sectional view showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series. FIG. 4 is a cross-sectional view showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series. FIG. 4 is a cross-sectional view showing the operation of the transfer unit of the image forming apparatus according to the first embodiment of the present invention in time series. FIG. 6A is a top view of a transfer unit during standby of an image forming apparatus according to a second embodiment of the present invention. FIG. 6B is a cross-sectional view of the transfer unit when the image forming apparatus according to the second embodiment of the present invention is on standby. (A) is a top view of the transfer unit when the transfer unit gap forming member corresponding to the medium-thick paper of the image forming apparatus according to the second embodiment of the present invention is inserted. FIG. 6B is a cross-sectional view of the transfer unit when the transfer unit gap forming member corresponding to the medium-thick paper of the image forming apparatus according to the second embodiment of the present invention is inserted. (A) is a top view of the transfer unit when the transfer unit gap forming member corresponding to the thickest paper of the image forming apparatus according to the second embodiment of the present invention is inserted. FIG. 6B is a cross-sectional view of the transfer unit when the transfer unit gap forming member corresponding to the thickest paper of the image forming apparatus according to the second embodiment of the present invention is inserted. 6 is a block diagram illustrating a control unit of an image forming apparatus according to a second embodiment of the present invention. FIG. FIG. 10 is a flowchart illustrating an operation of a control unit of an image forming apparatus according to a second embodiment of the present invention. FIG. 10 is a flowchart illustrating an operation of a control unit of an image forming apparatus according to a second embodiment of the present invention. FIG. 10 is a flowchart illustrating an operation of a control unit of an image forming apparatus according to a second embodiment of the present invention. FIG. 6A is a top view of a transfer unit of an image forming apparatus according to a third embodiment of the present invention. FIG. 6B is a cross-sectional view of a transfer portion of an image forming apparatus according to a third embodiment of the present invention.

Explanation of symbols

2 Intermediate transfer belt (image carrier)
6 Opposing roller 7 Transfer roller (transfer member)
8 paper (recording medium)
18 Transfer pressure contact portion 26 Registration roller (recording medium conveying means)
27 Registration Pressure Roller (Recording Medium Transport Unit)
50 Image forming apparatus 101 Intermediate transfer unit 102, 142, 152 Transfer unit 104, 105 Control unit (control unit, selection unit, gap formation amount control unit, gap formation amount selection unit)
113 Push-down cam (proximity separation means)
114, 114a, 114b Transfer part gap forming member 116 Solenoid (gap forming member driving means)
119 Gap forming member driving cam (gap forming member driving means)
120 Gap forming member driving motor (gap forming member driving means, driving source)
126 Motor (Proximity separation means)

Claims (7)

An image carrier that carries an image and rotates;
A transfer member for transferring an image carried by the image carrier to a recording medium;
Proximity separation means for causing the image carrier and the transfer member to approach and separate from each other;
A gap forming member driving means for inserting and removing a gap forming member between the image carrier and both ends of the transfer member;
Recording medium conveying means for conveying a recording medium between the image carrier and the transfer member;
A gap forming member is inserted between both ends of the image carrier and the transfer member by the gap forming member driving means, and the gap forming member is moved close to the image carrier and the transfer member by the proximity separating means. An image forming apparatus comprising: a control unit that transports a recording medium between the image carrier and the transfer member by the recording medium transport unit after being sandwiched.   2. The image according to claim 1, further comprising selection means for selecting whether or not the gap forming member is inserted between both ends of the image carrier and the transfer member by the gap forming member driving means. Forming equipment.   The gap forming member is a circular sheet-like member having a preset thickness, and when the gap forming member is sandwiched between the image carrier and the transfer member, the image carrier and the transfer member 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is driven to rotate while being in contact with at least one of the image carrier or the transfer member, with a position outside the interval between both ends as a rotation center.   4. The rotation plane of the gap forming member is located on the same plane as the contact surface between the image carrier and the transfer member brought close to each other by the approaching / separating means. The image forming apparatus according to any one of the above. The gap forming member driving means changes the thickness of the gap forming member inserted between the image carrier and both ends of the transfer member, thereby forming the gap between the image carrier and the transfer member. A gap formation amount control means for controlling the amount of gap to be formed;
The image forming apparatus according to claim 1, further comprising a gap formation amount selection unit that selects a gap amount controlled by the gap formation amount control unit. The gap forming member has a thickness distribution with respect to the insertion direction of the gap forming member;
The gap formation amount control means changes the insertion amount of the gap formation member inserted between the image carrier and both ends of the transfer member by the gap formation member driving means, thereby allowing the image carrier and the transfer member to be transferred. 6. The image forming apparatus according to claim 5, wherein an amount of a gap formed between the members is controlled.   The image forming apparatus according to claim 6, wherein the gap forming member driving unit is driven by a single driving source to insert the gap forming member between both ends of the image carrier and the transfer member.

Images