JP2014021465A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in image quality in a transfer area.SOLUTION: An image forming device (U) includes a support member (T2a) for supporting an image holding body (B) holding an image, and a transfer member (T2b) arranged opposite the support member (T2a) across the image holding body (B) to transfer the image of the image holding body (B) to a medium (S) passing between the transfer member and the image holding body (B) with a voltage applied between the transfer member and the support member (T2a). In the transfer member (T2b), when a rear end in a conveyance direction of the medium (S) passes through a transfer area (Q4), a front end in a conveyance direction of the medium (S) is located downstream in the medium conveyance direction with respect to a position where the medium is to be located when conveyed to the transfer area (Q4) where the image is transferred.

Description

  The present invention relates to an image forming apparatus.

  Regarding conventional image forming apparatuses, techniques described in Patent Documents 1 to 3 below are known.

  Japanese Patent Application Laid-Open No. 2011-064917 as Patent Document 1 describes a technique for preventing the trailing edge of a recording medium conveyed to a secondary transfer unit from being flipped up by an intermediate transfer belt. In the configuration described in Patent Document 1, when the recording medium (2) is thick paper, the secondary transfer roller (23) is moved to the downstream side in the medium conveyance direction as compared with the case of plain paper. Next transfer is performed.

  Japanese Patent Application Laid-Open No. 2011-112658 as Patent Document 2 describes a technique for reducing trailing edge transfer blur due to restoration of the trailing edge of a curved recording medium during a transfer process. In the configuration described in Patent Document 2, the posture of the guide member (30) disposed on the upstream side of the secondary transfer roller (19) is changed according to the thickness and rigidity of the recording medium (P) being conveyed. To change the curvature of the recording medium (P).

  Japanese Patent Application Laid-Open No. 2010-139603 as Patent Document 3 discloses a secondary transfer backup roller (at the timing when the trailing edge of the transfer paper separates the guide member (38) disposed on the upstream side of the secondary transfer nip. A configuration is described in which the push-down roller (37) supporting the intermediate transfer belt (10) is moved in the direction away from the intermediate transfer belt (10) on the upstream side of 16). In the configuration described in Patent Document 3, the toner image disturbance due to the collision between the transfer paper and the intermediate transfer belt (10) is suppressed by moving the push-down roller (37) to change the posture of the intermediate transfer belt (10). To do.

JP 2011-064917 A (“0063” to “0081”) JP 2011-112658 A (“0053” to “0058”) JP 2010-139603 A ("0030" to "0031", FIGS. 3 to 5)

  An object of the present invention is to reduce deterioration in image quality in a transfer region.

In order to solve the technical problem, an image forming apparatus according to claim 1 is provided.
An image carrier for holding an image;
A support member for supporting the image carrier;
An image of the image carrier is placed on a medium that is disposed opposite to the support member with the image carrier interposed therebetween, and that passes between the image carrier and a voltage applied between the image carrier and the support member. A transfer member to be transferred;
With
When the rear end of the transfer direction of the medium passes through the transfer region with respect to a position when the front end of the transfer direction of the medium is transferred to the transfer region to which the image is transferred Is located downstream in the conveyance direction of the medium.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The transfer member is moved downstream in the medium conveyance direction after the front end in the medium conveyance direction passes through the transfer area and the rear end in the medium conveyance direction passes through the transfer area. By the moving system to be moved, the rear end of the medium in the transport direction is positioned downstream in the transport direction of the medium when passing through the transfer region.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
When the type of the medium is a preset high-rigidity type, the transfer member is positioned with respect to a position when the front end of the medium in the conveyance direction is conveyed to a transfer area where the image is transferred. The rear end of the medium in the transport direction is located downstream in the transport direction of the medium when passing through the transfer region.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The higher the rigidity of the medium, the larger the amount of movement of the transfer member to the downstream side in the transport direction of the medium.

According to the first aspect of the present invention, it is possible to reduce the deterioration of the image quality in the transfer region as compared with the case where the configuration of the present invention is not provided.
According to the second aspect of the present invention, the moving system can move the transfer member.
According to the third aspect of the present invention, when the transfer member is moved in the case of a type having low rigidity, the transfer member can be moved efficiently when there is a high possibility that the image quality will deteriorate.
According to invention of Claim 4, useless movement can be reduced compared with the case where movement amount is not enlarged, so that rigidity is high.

FIG. 1 is an overall explanatory view of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is an explanatory diagram of a main part of the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is an explanatory diagram of a main part of the secondary transfer region of the first embodiment. FIG. 4 is a block diagram illustrating the functions of the control unit of the image forming apparatus according to the first embodiment. 5A and 5B are explanatory views of the positional relationship between the support member and the transfer member of Example 1, FIG. 5A is an explanatory view of the state moved to the first position, and FIG. 5B is an explanatory view of the state moved to the second position. FIG. FIG. 6 is an explanatory diagram of a flowchart of the transfer member position control process according to the first embodiment. FIG. 7 is an explanatory diagram of a conventional configuration, FIG. 7A is an explanatory diagram of a state in which a transfer member is disposed at a downstream position when the front end of the medium enters the transfer area, and FIG. 7B is a rear end of the medium at the transfer area It is explanatory drawing of the state by which the transfer member was arrange | positioned in the upstream position when passing through. FIG. 8 is an explanatory diagram of the image reading apparatus according to the second embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment. FIG. 9 is a flowchart of the transfer member position control process according to the second embodiment, and corresponds to FIG. 6 according to the first embodiment. FIG. 10 is an explanatory diagram of the image reading apparatus according to the third embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment. FIG. 11 is a flowchart of the transfer member position control process according to the third embodiment, and corresponds to FIG. 6 according to the first embodiment.

Next, examples as specific examples of embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The direction indicated by Z and -Z or the indicated side is defined as the front side, the rear side, the right side, the left side, the upper side, the lower side, or the front side, the rear side, the right side, the left side, the upper side, and the lower side, respectively.
In the figure, “•” in “○” means an arrow heading from the back of the page to the front, and “×” in “○” is the front of the page. It means an arrow pointing from the back to the back.
In the following description using the drawings, illustrations other than members necessary for the description are omitted as appropriate for easy understanding.

(Description of Overall Configuration of Printer U of First Embodiment)
FIG. 1 is an overall explanatory view of an image forming apparatus according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory diagram of a main part of the image forming apparatus according to the first embodiment of the present invention.
1 and 2, a printer U as an example of an image forming apparatus according to the first exemplary embodiment includes a main body U1 of the image forming apparatus and a feeder unit U2 as an example of a supply device that supplies a medium to the main body U1 of the image forming apparatus. And a discharge unit U3 as an example of a discharge device that discharges a medium on which an image is recorded, an interface module U4 as an example of a connection unit that connects between the main body U1 and the discharge unit U3, and a user operation And an operation unit UI.

(Description of Marking Configuration of Example 1)
1 and 2, the main body U1 of the image forming apparatus transmits information connected to the control unit C that controls the image forming apparatus U or a dedicated cable (not shown) outside the image forming apparatus U. A communication unit (not shown) that receives image information transmitted from a print image server COM as an example of the apparatus, a marking unit U1a as an example of an image recording unit that records an image on a medium, and the like. Connected to the print image server COM is a personal computer PC as an example of an image transmission device that is connected through a cable or a line such as a LAN (Local Area Network) and that transmits image information to be printed by the printer U. Yes.
The marking unit U1a is an example of an image holding body for printing photoconductors Py, Pm, Pc, and Pk for Y: yellow, M: magenta, C: cyan, K: black, and photographic images. A photoconductor Po for glossing the image. The photoreceptors Py to Po are composed of a photosensitive dielectric on the surface.

In FIGS. 1 and 2, around the black photosensitive member Pk, along the rotation direction of the photosensitive member Pk, a charger CCk, an exposure device ROSK as an example of a latent image forming device, a developing device Gk, and a primary transfer device. A primary transfer roll T1k as an example of an imager and a photoreceptor cleaner CLk as an example of an image carrier cleaning device are disposed.
Similarly, around the other photoreceptors Py, Pm, Pc, Po, chargers CCy, CCm, CCc, CCo, exposure units ROSy, ROSm, ROSc, ROSo, developing devices Gy, Gm, Gc, Go, primary Transfer rolls T1y, T1m, T1c, T1o, and photoconductor cleaners CLy, CLm, CLc, CLo are disposed.
On an upper part of the marking unit U1a, toner cartridges Ky, Kc, Km, Kk, Ko containing a developer supplied to the developing devices Gy to Go are detachably supported as an example of a storage container.

Below each of the photoconductors Py to Po, an intermediate transfer belt B, which is an example of an intermediate transfer member and an example of an image carrier, is disposed. The intermediate transfer belt B is connected to the photoconductors Py to Po and 1. It is sandwiched between the next transfer rolls T1y to T1o. The back surface of the intermediate transfer belt B includes a drive roll Rd as an example of a drive member, a tension roll Rt as an example of a tension applying member, a walking roll Rw as an example of a meandering prevention member, and a plurality of examples of a driven member. The idler roll Rf, a backup roll T2a as an example of an opposing member for secondary transfer, a plurality of retract rolls R1 as an example of a movable member, and the primary transfer rolls T1y to T1o.
On the surface of the intermediate transfer belt B, a belt cleaner CLB as an example of an intermediate transfer member cleaner is disposed in the vicinity of the drive roll Rd.

A secondary transfer roll T2b as an example of a secondary transfer member is disposed opposite to the backup roll T2a with the intermediate transfer belt B interposed therebetween. Further, a contact roll T2c as an example of a contact member is in contact with the backup roll T2a in order to apply a voltage having a polarity opposite to the charging polarity of the developer to the backup roll T2a. A conveyance belt T2e as an example of a conveyance member is stretched between the secondary transfer roll T2b of Example 1 and a drive roll T2d as an example of a drive member arranged on the lower right.
The backup roll T2a, the secondary transfer roll T2b, and the contact roll T2c constitute the secondary transfer device T2 of Example 1. The primary transfer rolls T1y to T1o, the intermediate transfer belt B, the secondary transfer device T2, and the like. Thus, the transfer devices T1, B, and T2 of Example 1 are configured.

Below the secondary transfer device T2, paper feed trays TR1 and TR2 are provided as an example of a storage unit that stores a recording sheet S as an example of a medium. A pickup roll Rp as an example of a take-out member and a separating roll Rs as an example of a separating member are disposed diagonally to the right of each sheet feeding tray TR1, TR2. A conveyance path SH that conveys the recording sheet S extends from the separation roll Rs, and a plurality of conveyance rolls Rs as an example of a conveyance member that conveys the recording sheet S to the downstream side are arranged along the conveyance path SH. Yes.
As an example of an unnecessary portion removing device, the recording sheet S is set at a preset pressure on the downstream side in the conveyance direction of the recording sheet S with respect to the position where the conveyance paths SH from the two sheet feeding trays TR1 and TR2 merge. A deburring device Bt that removes unnecessary portions of the edge of the recording sheet S, that is, a deburring device Bt is disposed.

On the downstream side of the deburring device Bt, a detection device Jk for measuring the thickness of the recording sheet S passing therethrough and detecting a state in which a plurality of recording sheets S overlap each other, so-called double feeding is disposed. A correction roll Rc that corrects an inclination with respect to the conveyance direction of the recording sheet S, that is, a so-called skew, is disposed on the downstream side of the double-feed detection device Jk as an example of a posture correction device. On the downstream side of the correction roll Rc, a registration roll Rr as an example of an adjustment member that adjusts the conveyance timing of the recording sheet S to the secondary transfer device T2 is disposed.
The feeder unit U2 is also provided with paper feed trays TR1, TR2, paper feed trays TR3, TR4, etc., which are configured in the same manner as the pick-up roll Rp, the pick-up roll Rs, and the transport roll Ra. The conveyance path SH from TR4 merges with the conveyance path SH of the main body U1 of the image forming apparatus U on the upstream side of the double-feed detection device Jk.

A plurality of conveying belts HB that hold the recording sheet S on the surface and convey the recording sheet S to the downstream side are arranged downstream of the conveying belt T2e in the conveying direction of the recording sheet S.
A fixing device F is disposed on the downstream side in the conveyance direction of the recording sheet S with respect to the conveyance belt HB.
A cooling device Co that cools the recording sheet S is disposed on the downstream side of the fixing device F.
On the downstream side of the cooling device Co, a decurler Hd that applies pressure to the recording sheet S to correct the curvature of the recording sheet S, that is, a so-called curl, is disposed.
An image reading device Sc that reads an image recorded on the recording sheet S is disposed on the downstream side of the decurler Hd.

A reversing path SH2 as an example of a transport path branched from the transport path SH extending toward the interface module U4 is formed on the downstream side of the image reading device Sc. A first gate GT1 as an example of the switching member is disposed.
In the reversing path SH2, a plurality of switchback rolls Rb as an example of a conveying member capable of rotating forward and reverse are arranged. On the upstream side of the switchback roll Rb, a connection path SH3 is formed as an example of a transport path that branches off from the upstream portion of the reversing path SH2 and joins the downstream side of the branch section of the transport path SH with the reversing path SH2. Has been. A second gate GT2 as an example of a transfer direction switching member is disposed at a branch portion between the reversing path SH2 and the connection path SH3.

On the downstream side of the reversing path SH2, a folding path SH4 for reversing the conveyance direction of the recording sheet S, that is, for switching back, is disposed below the cooling device Co. In the return path SH4, a switchback roll Rb as an example of a conveying member capable of rotating in the forward and reverse directions is disposed. In addition, a third gate GT3 as an example of a conveyance direction switching member is disposed at the entrance of the return path SH4.
The conveyance path SH on the downstream side of the return path SH4 merges with the conveyance paths SH of the paper feed trays TR1 and TR2.

In the interface module U4, a transport path SH extending toward the discharge unit U3 is formed.
The discharge unit U3 is provided with a stacker tray TRh as an example of a stacking container on which the recording sheets S to be discharged are stacked, and a discharge path SH5 branched from the transport path SH and extending to the stacker tray TRh is provided. Yes. In the conveyance path SH of the first embodiment, when an additional discharge unit and a post-processing device (not shown) are additionally mounted on the right side of the discharge unit U3, the recording sheet S is attached to the added device. It is configured to be transportable.

(Marking operation)
In the image forming apparatus U, when image information transmitted from the personal computer PC is received via the print image server COM, a job which is an image forming operation is started. When the job is started, the photoreceptors Py to Po, the intermediate transfer belt B, and the like rotate.
The photoreceptors Py to Po are rotationally driven by a drive source (not shown).
The chargers CCy to CCo are applied with a preset voltage to charge the surfaces of the photoreceptors Py to Po.
The exposure units ROSy to ROSo output laser light Ly, Lm, Lc, Lk, Lo as an example of light for writing a latent image in accordance with a control signal from the control unit C, and charge the photoconductors Py to Po. An electrostatic latent image is written on the surface.
The developing devices Gy to Go develop the electrostatic latent images on the surfaces of the photoreceptors Py to Po into visible images.
The toner cartridges Ky to Ko replenish the developer consumed with the development in the developing devices Gy to Go.

The primary transfer rolls T1y to T1o are applied with a primary transfer voltage having a polarity opposite to the charging polarity of the developer, and transfer the visible image on the surface of the photoreceptors Py to Po to the surface of the intermediate transfer belt B.
The photoreceptor cleaners CLy to CLo remove and clean the developer remaining on the surfaces of the photoreceptors Py to Po after the primary transfer.
When the intermediate transfer belt B passes through the primary transfer region facing the photoreceptors Py to Po, the images are transferred and stacked in the order of O, Y, M, C, and K, and then transferred to the secondary transfer unit T2. It passes through the opposing secondary transfer region Q4. In the case of a single color image, an image of only one color is transferred and sent to the secondary transfer area Q4.

The pickup roll Rp records from the paper feed trays TR1 to TR4 to which the recording sheet S is supplied according to the size of the received image information, the designation of the recording sheet S, the size and type of the stored recording sheet S, and the like. The sheet S is sent out.
The separating roll Rs separates and separates the recording sheets S sent out from the pickup roll Rp one by one.
The deburring device Bt applies a preset pressure to the passing recording sheet S to remove burrs.
The double feed detection device Jk detects the double feed of the recording sheet S by detecting the thickness of the recording sheet S passing therethrough.
The correction roll Rc corrects the skew by bringing the recording sheet S passing therethrough into contact with a wall surface (not shown).
The registration roll Rr sends out the recording sheet S in accordance with the timing when the image on the surface of the intermediate transfer belt B is sent to the secondary transfer region Q4.

The secondary transfer device T2 records the image of the intermediate transfer belt B on the recording sheet S by applying a secondary transfer voltage having the same polarity as the developer charging polarity set in advance to the backup roll T2a via the contact roll T2c. Transfer to sheet S.
The belt cleaner CLB removes the developer remaining on the surface of the intermediate transfer belt B after the image is transferred in the secondary transfer region Q4 and cleans it.
The conveying belts T2e and HB hold the recording sheet S on which the image has been transferred by the secondary transfer device T2 on the surface and convey the recording sheet S to the downstream side.

The fixing device F includes a heating roll Fh as an example of a heating member and a pressure roll Fp as an example of a pressure member, and a heater as an example of a heat source is accommodated inside the heating roll Fh. Yes. The fixing device F fixes the unfixed image on the surface of the recording sheet S by heating the recording sheet S passing through the region where the heating roll Fh and the pressure roll Fp are in contact with each other while applying pressure.
The cooling device Co cools the recording sheet S heated by the fixing device F.
The decurler Hd applies pressure to the recording sheet S that has passed through the cooling device Co to remove the curvature of the recording sheet S, so-called curl.
The image reading device Sc reads an image on the surface of the recording sheet S that has passed through the decurler Hd.

When double-sided printing is performed, the recording sheet S that has passed through the decurler Hd is transported to the reversing path SH2 by being actuated by the first gate GT1, switched back by the folding path SH4, and then passed through the transport path SH. The image is retransmitted to the registration roll Rr and printing on the second side is performed.
The recording sheet S discharged to the discharge tray TRh is transported through the transport path SH and discharged to the stacker tray TRh. At this time, when the recording sheet S is discharged to the stacker tray TRh with the front and back sides reversed, the recording sheet S is once carried into the reversing path SH2 and the rear end of the recording sheet S in the conveying direction is the second gate GT2. , The second gate GT2 is switched and the switchback roll Rb rotates in the reverse direction, and is conveyed through the connection path SH3 and conveyed to the stacker tray TRh.
On the stacker tray TRh, the recording sheets S are stacked, and the stacking plate TRh1 is automatically raised and lowered so that the uppermost surface has a preset height according to the stacking amount of the recording sheets S.

(Description of Transfer System of Transfer Device of Example 1)
FIG. 3 is an explanatory diagram of a main part of the secondary transfer region of the first embodiment.
In FIG. 3, in the transfer devices T1, B, and T2 according to the first embodiment, the rotary plate 1 as an example of the first moving member is supported at both ends in the axial direction of the backup roll T2a as an example of the support member. Yes. The rotating plate 1 is supported so as to be rotatable about the rotating shaft 2 of the backup roll T2a. A protruding stud 3 is supported at the lower end of the rotating plate 1 as an example of an interlocking portion.
Below the rotating plate 1, a rotated plate 6 as an example of a second moving member is disposed. The rotated plate 6 supports a transport unit 7 including a secondary transfer roll T2b, a drive roll T2d, and a transport belt T2e as an example of a transfer member. In the first exemplary embodiment, even if the transport unit 7 moves with the rotation of the rotating plate 6, the transport of the recording sheet S is not affected by the transport belt HB disposed downstream of the transport unit 7. As shown in FIG.

The rotated plate 6 is formed with a guide groove 6a as an example of a guided portion. The guide groove 6a according to the first embodiment is configured by an arc-shaped groove centered on the rotation shaft 2 of the backup roll T2a. A guide pin 8 as an example of a guide member is fitted in the guide groove 6a. The guide pin 8 is supported by the main body U1 of the image forming apparatus. Therefore, the rotated plate 6 is supported so as to be movable along the guide groove 6a with respect to the main body U1 of the image forming apparatus.
A concave portion 9 as an example of an interlocked portion is formed at the upper end portion of the rotated plate 6 at a position corresponding to the stud 3. The recessed part 9 of Example 1 is formed in the U-shape by which upper direction was open | released. The recessed portion 9 is supported in a state where the stud 3 is fitted.

  On the rotating plate 1, a right end that is one end of a rod 11 as an example of a connecting member is rotatably supported above the rotating shaft 2. The rod 11 according to the first embodiment is formed in a rod shape extending toward the upper left. The rod 11 is formed with a guide hole 11a as an example of a guided portion. The guide hole 11 a according to the first embodiment is configured by a long hole along the direction in which the rod 11 extends. A guide pin 12 as an example of a guide member is fitted in the guide hole 11a. The guide pin 12 is supported by the main body U1 of the image forming apparatus. Therefore, the rod 11 is supported so as to be movable along the guide hole 11a with respect to the main body U1 of the image forming apparatus.

The left end which is the other end of the rod 11 is supported in a state in which an outer peripheral surface of an eccentric cam 13 as an example of an eccentric member is in contact. A gear 14 is supported coaxially with the rotation center 13 a of the eccentric cam 13. The gear 14 meshes with a gear 17 supported on a shaft 16a of a motor 16 as an example of a drive source.
The rod 11, the guide pin 12, the eccentric cam 13, the gears 14 and 17, the motor 16, and the like constitute moving systems 11 to 17 according to the first embodiment.
In the printer U according to the first exemplary embodiment, a sheet sensor SN1 that detects the passing recording sheet S is disposed as an example of a detection member in the vicinity of the registration roll Rr. Further, a sheet guide 19 as an example of a guide member is disposed between the registration roll Rr and the secondary transfer region Q4. The sheet guide 19 is composed of a pair of upper and lower plate-like members, and guides the recording sheet S toward the secondary transfer area Q4.

(Description of the control part of Example 1)
FIG. 4 is a block diagram illustrating the functions of the control unit of the image forming apparatus according to the first embodiment.
In FIG. 4, the control unit C of the main body U1 has an input / output interface I / O for inputting / outputting signals to / from the outside. In addition, the control unit C includes a ROM (read only memory) in which a program for performing necessary processing, information, and the like are stored. In addition, the control unit C includes a random access memory (RAM) for temporarily storing necessary data. The control unit C includes a central processing unit (CPU) that performs processing according to a program stored in a ROM or the like. Therefore, the control part C of Example 1 is comprised by the small information processing apparatus, what is called a microcomputer. Therefore, the control part C can implement | achieve various functions by running the program memorize | stored in ROM etc.

(Signal output element connected to the control unit C of the printer body U1)
The control unit C of the printer body U1 receives an output signal from a signal output element such as the operation unit UI or the sheet sensor SN1.
The operation unit UI includes a power button UI1 as an example of a power-on unit, a display panel UI2 as an example of a display unit, a numeric input unit UI3, an arrow input unit UI4, and the like.
The sheet sensor SN1 detects the recording sheet S that has passed the registration roll Rr.

(Controlled elements connected to the control unit C of the printer body U1)
The control unit C of the printer main body U1 is connected to a drive circuit D1 as a drive source, a power supply circuit E, a drive circuit D2 as a moving system, and other control elements (not shown). The control unit C outputs those control signals to the circuits D1 to D2, E and the like.
D1: Drive circuit of drive source The drive circuit D1 of the drive source rotates and drives the photoreceptors Py to Po, the intermediate transfer belt B, and the like via a main motor M1 as an example of a drive source.
D2: Moving System Drive Circuit The moving system drive circuit D2 moves the transport unit 7 via the motor 16.

E: Power Supply Circuit The power supply circuit E includes a development power supply circuit Ea, a charging power supply circuit Eb, a transfer power supply circuit Ec, a fixing power supply circuit Ed, and the like.
Ea: Power supply circuit for development The power supply circuit Ea for development applies a development voltage to the development rolls of the development devices Gy to Go.
Eb: Charging power supply circuit The charging power supply circuit Eb applies a charging voltage for charging the surfaces of the photoreceptors Py to Po to the chargers CCy to CCo, respectively.
Ec: Power supply circuit for transfer The power supply circuit Ec for transfer applies a transfer voltage to the primary transfer rolls T1y to T1o and the secondary transfer roll T2b.
Ed: Power supply circuit for fixing The power supply circuit for fixing Ed supplies power for heating the heater to the heating roll Fh of the fixing device F.

(Function of the control unit C of the printer body U1)
The control unit C of the printer main body U1 has a function of executing processing according to an input signal from the signal output element and outputting a control signal to each control element. That is, the control unit C has the following functions.
C1: Image Forming Control Unit The image forming control unit C1 controls the driving of each member of the printer U, the application timing of each voltage, and the like according to the image information input from the personal computer PC, thereby performing an image forming operation. Execute the job that is.

C2: Drive Source Control Unit The drive source control unit C2 controls the drive of the main motor M1 via the drive source drive circuit D1 to control the drive of the photoreceptors Py to Po and the like.
C3: Power Supply Circuit Control Unit The power supply circuit control unit C3 controls the power supply circuits Ea to Ed to control the voltage applied to each member and the power supplied to each member.

C4: Medium Information Storage Unit The medium information storage unit C4 stores medium information. The medium information storage unit C4 according to the first exemplary embodiment stores information on the type of the medium such as the size, thickness, basis weight, and material of the recording sheet S regarding the recording sheets S accommodated in the paper feed trays TR1 to TR4. To do. The medium type information stores information input in advance by the user from the operation unit UI. In the first exemplary embodiment, information on a standard size such as “A4”, “A3”, and “B5”, and an irregular size obtained by directly inputting the length in the conveyance direction and the width direction from the operation unit UI as the medium size information. Information is available. In Example 1, as the thickness and basis weight information of the medium, "plain paper" of a basis weight of 50~80 [g / ^{m 2],} a basis weight of 80 [g / ^{m 2]} is greater than "thick" Simple information such as “thin paper” having a basis weight of less than 50 [g / m ² ] or basis weight information directly inputted with numerical values can be used. Furthermore, in the first embodiment, information such as “plain paper”, “thick paper”, “OHP sheet”, “envelope”, etc. can be used as the material of the medium.
In the first embodiment, information such as “plain paper” and “thick paper” is stored as an example of information related to the rigidity of the medium and used for the control described later. However, the present invention is not limited to this. For example, other parameters relating to the rigidity of the medium, that is, the so-called stiffness, can be used.

C5: Medium Passing Time Calculating Means The medium passing time calculating means C5 calculates a passing time t2, which is a time during which the recording sheet S passes through the secondary transfer region Q4. The medium passage time calculation unit C5 according to the first exemplary embodiment uses the length L in the conveyance direction of the recording sheet S and the recording sheet S based on the information on the size of the recording sheet S conveyed to the secondary transfer region Q4. From the transport speed V, t2 = L / V.
C6: Arrival Time Storage Unit The arrival time storage unit C6 stores an arrival time t1 which is a time until the front end of the recording sheet S sent from the registration roll Rr in the conveyance direction reaches the secondary transfer region Q4. . In the first embodiment, the arrival time t1 is set in advance. If the medium conveyance speed can be changed according to the type of the medium, the user's designation, etc., it is calculated each time from the medium conveyance speed and the distance from the sheet sensor SN1 to the secondary transfer area Q4. Can be derived and stored.

TM1: Timer A timer TM1 as an example of a time measuring means measures time.
C7: Transfer Member Control Unit The transfer member control unit C7 includes a first position storage unit C7A, a second position storage unit C7B, a medium determination unit C7C, and a movement timing to the first position. Discriminating means C7D, and discriminating means C7E for the movement timing to the second position. The transfer member control means C7 controls the moving systems 11 to 17 to control the relative positions of the backup roll T2a and the secondary transfer roll T2b. The transfer member control means C7 is an example of a first position in which the secondary transfer roll T2b and the backup roll T2a are set in advance when the front end in the conveyance direction of the recording sheet S is conveyed to the secondary transfer region Q4. As an upstream position. Further, the transfer member control means C7 is configured such that when the rear end in the conveyance direction of the recording sheet S passes through the secondary transfer region Q4, the secondary transfer roll is downstream in the conveyance direction of the recording sheet S from the upstream position. At least one of the secondary transfer roll T2b and the backup roll T2a is moved to the downstream position as an example of the second position located at the position. In Example 1, the moving systems 11 to 17 are controlled to move the secondary transfer roll T2b, and the position of the backup roll T2a is fixed.

5A and 5B are explanatory views of the positional relationship between the support member and the transfer member of Example 1, FIG. 5A is an explanatory view of the state moved to the first position, and FIG. 5B is an explanatory view of the state moved to the second position. FIG.
C7A: First Position Storage Unit The first position storage unit C7A stores upstream positions as an example of first positions of the secondary transfer roll T2b and the backup roll T2a. In FIG. 5, the storage means C7A at the first position in the first embodiment is compared with the lap position 21 where the intermediate transfer belt B starts to be wound around the backup roll T2a when the secondary transfer roll T2b is not present. As shown in FIG. 5A, when the position where the rotation center 2 of the backup roll T2a, the wrap position 21 and the rotation center 22 of the secondary transfer roll T2b are arranged on a straight line is 0 °, The position where the rotation center 22 of the next transfer roll T2b has moved by θ1 ° upstream is stored as the upstream position. The value of θ1 can be arbitrarily changed according to the configuration, specifications, etc., but in the first embodiment, θ1 = 12 ° is set as an example.

C7B: Second Position Storage Unit The second position storage unit C7B stores downstream positions as an example of second positions of the secondary transfer roll T2b and the backup roll T2a. In FIG. 5, the second position storage means C7B of the first embodiment includes, as an example, the rotation center 2 of the backup roll T2a, the wrap position 21, and the rotation center 22 of the secondary transfer roll T2b on a straight line. When the arrangement position is 0 °, the position of θ2 ° is stored as the downstream position. In the first embodiment, as an example, the downstream position is set to θ2 = 0 °.
C7C: Medium Discriminating Unit The medium discriminating unit C7C discriminates the type of the recording sheet S conveyed to the secondary transfer area Q4. The medium discriminating means C7C according to the first embodiment sets the transfer devices T1, B, and T2 as upstream positions when the type of the recording sheet S conveyed to the secondary transfer region Q4 is a preset high-rigidity type. It is determined that the medium is to be moved between the downstream position. Specifically, the medium determination unit C7C according to the first exemplary embodiment determines that the medium is a high-rigidity medium when the medium type corresponds to “thick paper”, “OHP sheet”, or “envelope”.

C7D: Means for Determining the Timing of Movement to the First Position The means for judging C7D for the timing of movement to the first position determines whether it is time to move the secondary transfer roll T2b to the upstream position. The determination means C7D for the movement timing to the first position in Embodiment 1 determines that it is time to move the recording sheet S to the upstream position before it is carried into the secondary transfer area Q4. For example, when a plurality of sheets are printed, it is determined that it is time to move to the upstream position when the trailing edge of the previous recording sheet S passes through the secondary transfer region Q4.
C7E: Means for determining when to move to the second position The means for determining C7E for when to move to the second position determines whether it is time to move the secondary transfer roll T2b to the downstream position. The determination unit C7E for the movement timing to the second position in the first embodiment is a timing for moving the recording sheet S to the downstream position when a predetermined time has elapsed after the front end of the recording sheet S is carried into the secondary transfer region Q4. It is determined that it has become. In Example 1, it is determined that it is time to move the recording sheet S to the downstream position when t2 / 2, which is half the passage time t2, has elapsed since the front end of the recording sheet S was carried into the secondary transfer region Q4. To do.

(Explanation of flowchart of Example 1)
Next, a flow of control in the printer U according to the first embodiment will be described with reference to a flowchart, a so-called flowchart.

(Explanation of Flowchart of Transfer Member Position Control Process)
FIG. 6 is an explanatory diagram of a flowchart of the transfer member position control process according to the first embodiment.
6 is performed according to a program stored in the control unit C of the printer U. This process is executed in parallel with other various processes of the printer U.
The flowchart shown in FIG. 6 is started when the printer U is turned on.

In ST1 of FIG. 6, it is determined whether or not an image forming operation, so-called job, has been started. If yes (Y), proceed to ST2. If no (N), repeat ST1.
In ST2, the type of recording sheet S used in the job is acquired. That is, the type of the recording sheet S accommodated in the paper feed trays TR1 to TR4 where paper is fed is acquired. Then, the process proceeds to ST3.
In ST3, it is determined whether or not the type of the recording sheet S is highly rigid. If no (N), the process proceeds to ST4. If yes (Y), proceed to ST6.
In ST4, the secondary transfer roll T2b is held at the upstream position. Then, the process proceeds to ST5.
In ST5, it is determined whether or not the job is finished. If no (N), repeat ST5. If yes (Y), the process returns to ST1.

In ST6, the passage time t2 is calculated from the size of the recording sheet S. Then, the process proceeds to ST7.
In ST7, the secondary transfer roll T2b is moved to the upstream position. Then, the process proceeds to ST8.
In ST8, it is determined whether or not the recording sheet S has been sent out from the registration roll Rr. If yes (Y), proceed to ST9. If no (N), repeat ST8.
In ST9, arrival time t1 is set in timer TM1. Then, the process proceeds to ST10.
In ST10, it is determined whether or not the timer TM1 has expired. That is, it is determined whether or not the arrival time t1 has elapsed. If yes (Y), proceed to ST11. If no (N), repeat ST10.

In ST11, the timer TM1 is set to half the passage time, that is, t2 / 2. Then, the process proceeds to ST12.
In ST12, it is determined whether or not the timer TM1 has expired. That is, it is determined whether t2 / 2 has elapsed. If yes (Y), the process proceeds to ST13. If no (N), ST12 is repeated.
In ST13, the following processes (1) and (2) are executed. Then, the process proceeds to ST14.
(1) The secondary transfer roll T2b is moved to the downstream position.
(2) Set t2 / 2 to the timer TM1.
In ST14, it is determined whether or not the timer TM1 has expired. That is, it is determined whether t2 / 2 has elapsed. If yes (Y), proceed to ST15. If no (N), ST14 is repeated.
In ST15, it is determined whether or not the job is finished. If no (N), the process returns to ST7. If yes (Y), the process returns to ST1.

(Function of the transfer device of Example 1)
In the printer U according to the first embodiment having the above-described configuration, the transfer devices T1, B, and T2 are configured so that the front end of the recording sheet S is the secondary transfer region Q4 when the recording sheet S to be used is high rigidity such as cardboard. The secondary transfer roll T2b moves to the upstream position when entering the position, and the secondary transfer roll T2b moves to the downstream position before the trailing edge of the recording sheet S leaves the secondary transfer area Q4. That is, when the so-called strong recording sheet S is used, the secondary transfer roll T2b moves from the upstream position to the downstream position while the recording sheet S passes through the secondary transfer region Q4. Therefore, the secondary transfer roll T2b has a rear end in the conveyance direction of the recording sheet S with respect to a position when the front end in the conveyance direction of the recording sheet S is conveyed to the secondary transfer region Q4 to which the image is transferred. When passing through the secondary transfer region Q4, the recording sheet S is located downstream in the conveyance direction.

FIG. 7 is an explanatory diagram of a conventional configuration, FIG. 7A is an explanatory diagram of a state in which a transfer member is disposed at a downstream position when the front end of the medium enters the transfer area, and FIG. 7B is a rear end of the medium at the transfer area It is explanatory drawing of the state by which the transfer member was arrange | positioned in the upstream position when passing through.
7A, when the secondary transfer roll 01 is moved to the downstream position in the case of thick paper or the like as in the conventional configuration described in Patent Document 1, the front end of the recording sheet 03 is placed in the secondary transfer area 02. In the case of thick paper with strong stiffness, the recording sheet 03 has a small curvature. Accordingly, it is difficult for the front end portion of the recording sheet 03 to be sufficiently along the surface of the intermediate transfer belt 04. Therefore, a wedge-shaped gap 06 is formed between the recording sheet 03 and the intermediate transfer belt 04. Therefore, discharge may occur in the wedge-shaped gap 06 with the voltage applied in the secondary transfer region 02. When discharge occurs in the wedge-shaped gap 06, the toner held on the surface of the intermediate transfer belt 04 is scattered. When the toner is scattered, the image transferred to the recording sheet 03 is disturbed, and an image defect called so-called tailing occurs.

  On the other hand, in Example 1, the secondary transfer roll T2b moves to the upstream position before the front end of the recording sheet S enters the secondary transfer region Q4. Accordingly, the recording sheet S is easily bent into a shape along the intermediate transfer belt B by being pushed by the secondary transfer roll T2b on the upstream side of the backup roll T2a with which the contact roll T2c to which a voltage is applied contacts. Therefore, in Example 1, it becomes difficult to form a wedge-shaped gap. Therefore, the occurrence of discharge in the wedge-shaped gap is suppressed, and the occurrence of image defects is reduced.

On the other hand, in FIG. 7B, when the secondary transfer roll 01 is moved to the upstream position, the recording sheet 03 is recorded along with the elastic recovery of the curvature of the recording sheet 03 when the trailing end of the recording sheet 03 passes the sheet guide 07. There is a possibility that the rear end of the sheet 03 may come into contact with the intermediate transfer belt 04. When the recording sheet 03 comes into contact with the intermediate transfer belt 04, the image being transferred may be disturbed due to an impact at the time of contact.
On the other hand, in Example 1, the secondary transfer roll T2b moves to the downstream position sufficiently before the trailing edge of the recording sheet S passes through the secondary transfer region Q4. Therefore, when the trailing edge of the recording sheet S passes through the sheet guide 19, the curvature of the recording sheet S is smaller than when the secondary transfer roll T2b is positioned at the upstream position. Therefore, the impact when the trailing edge of the recording sheet S passes through the sheet guide 19 and the curvature is elastically restored is reduced. Therefore, as compared with the configuration shown in FIG. 7B, disturbance of the image during transfer is reduced.

In the configuration described in Patent Document 2, it is necessary that the guide member is always in contact with the recording sheet S conveyed to the secondary transfer region Q4 to make the curve uniform, and the guide member needs to be precisely controlled. . Therefore, the configuration described in Patent Document 2 has a problem that the configuration is easily complicated and the cost is likely to be high. Further, in the configuration described in Patent Document 2, the guide member is always in contact with the recording sheet S, which causes conveyance resistance of the recording sheet S, and causes the surface of the recording sheet S to become dirty or scratched. There is.
In the configuration described in Patent Document 3, it is necessary to perform control in accordance with the timing at which the trailing edge of the recording sheet S is separated. If the timing is slightly shifted, it is difficult to obtain the intended effect. That is, precise control is required, and the cost tends to be expensive. Further, in the configuration described in Patent Document 3, the posture of the intermediate transfer belt B is changed relatively large by moving the push-down roller. If the posture of the intermediate transfer belt B changes during the transfer of the recording sheet S, the intermediate transfer belt B may slip in the secondary transfer region Q4. Therefore, there is a possibility that transfer defects and image defects may occur, and there is a problem that is not preferable.

  On the other hand, in Example 1, the secondary transfer roll T2b is moved between the upstream position and the downstream position, and precise control is not necessary as compared with Patent Documents 2 and 3. Therefore, the cost increase is suppressed. Further, in the configuration of Example 1, as compared with Patent Document 2, problems such as conveyance resistance of the recording sheet S and scratches are less likely to occur. Further, in the configuration of the first embodiment, the change in the posture of the intermediate transfer belt B is small as compared with the configuration of Patent Document 3 that uses a push-down roller, and the occurrence of a transfer failure or a decrease in image quality is reduced.

FIG. 8 is an explanatory diagram of the image reading apparatus according to the second embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment.
Next, the second embodiment of the present invention will be described. In the description of the second embodiment, the same reference numerals are given to the components corresponding to the components of the first embodiment, and the detailed description thereof will be omitted. . The second embodiment is different from the first embodiment in the following points, but is configured in the same manner as the first embodiment in other points.
In FIG. 8, the control unit C of the printer U according to the second embodiment replaces the transfer member control means C7 and the movement timing determination means C7E according to the first embodiment with the transfer member control means C7 ′. , And a means for discriminating the movement timing to the second position C7E ′.

When the secondary transfer roll T2b is moved from the upstream position to the downstream position, the transfer member control means C7 ′ of Example 2 continuously moves the secondary transfer roll T2b. That is, unlike the first embodiment, when the half of the recording sheet S passes, the secondary transfer roll T2b is moved from the upstream position to the downstream position. Specifically, in Example 2, the secondary transfer roll T2b is moved toward the downstream position by (θ1-θ2) / t2 per unit time after the front end of the recording sheet S reaches the secondary transfer region Q4. Control to move.
Unlike the first embodiment, the determination means C7E ′ for moving the second transfer position to the second position in the second embodiment with the change in the transfer member control means C7 ′ directs the secondary transfer roll T2b to the downstream position. The movement start time is determined to be the time to move to the downstream position when the front end of the recording sheet S reaches the secondary transfer area Q4.

(Explanation of flowchart of Example 2)
FIG. 9 is a flowchart of the transfer member position control process according to the second embodiment, and corresponds to FIG. 6 according to the first embodiment.
Next, the process for controlling the position of the transfer member according to the second embodiment will be described. The same processes as those of the first embodiment are denoted by the same ST numbers, and detailed description thereof is omitted.
In FIG. 9, the transfer member position control process according to the second embodiment is different from the first embodiment in that ST21 and ST22 are executed instead of ST11 to ST14.
In ST21, the following processes (1) and (2) are executed. Then, the process proceeds to ST22.
(1) The secondary transfer roll T2b starts to move toward the downstream position by θ / t2 with respect to the angle θ = θ1-θ2 formed between the upstream position and the downstream position.
(2) The passing time t2 is set in the timer TM1.
In ST22, it is determined whether or not the timer TM1 has expired. That is, it is determined whether or not the passage time t2 has elapsed. If yes (Y), proceed to ST15. If no (N), ST22 is repeated.

(Function of the transfer device of Example 2)
In the transfer devices T1, B, and T2 of the printer U according to the second embodiment having the above-described configuration, the secondary transfer roll is between the time when the front end of the recording sheet S reaches the secondary transfer region Q4 and the time when the rear end is removed. T2b continuously moves from the upstream position toward the downstream position. Therefore, compared to a case where the recording sheet S fluctuates at a specific timing, vibration of the recording sheet S, vibration generated when the secondary transfer roll T2b is moved, and the like are easily reduced. Therefore, in the second embodiment, compared to the first embodiment, the deterioration of the image quality is more easily suppressed.

FIG. 10 is an explanatory diagram of the image reading apparatus according to the third embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment.
Next, the third embodiment of the present invention will be described. In the description of the third embodiment, the same reference numerals are given to the components corresponding to the components of the first and second embodiments, and the detailed description thereof will be given. Omitted. The third embodiment is different from the first and second embodiments in the following points, but is configured in the same manner as the first and second embodiments in other points.
In FIG. 10, the control unit C of the printer U according to the third embodiment includes a first position setting unit C7A ″ instead of the first position storage unit C7A according to the second embodiment.

  The first position setting unit C7A ″ according to the third embodiment sets an upstream position as an example of the first position according to the type of the recording sheet S used. In the third embodiment, the recording used. The upstream angle θ1 is set to be larger as the rigidity of the sheet S is higher, for example, when “plain paper (thick)” is used as the recording sheet S, set θ1 = 6 °. When “thick paper” is used, θ1 = 8 ° is set, and when “thick paper 2” thicker than “thick paper” is used, θ1 = 12 ° is set. For each type of recording sheet S, an optimum upstream position obtained in advance through experiments or the like is set.

(Explanation of flowchart of Example 3)
FIG. 11 is a flowchart of the transfer member position control process according to the third embodiment, and corresponds to FIG. 6 according to the first embodiment.
Next, the process for controlling the position of the transfer member according to the third embodiment will be described. The same processes as those of the second embodiment are denoted by the same ST numbers, and detailed description thereof is omitted.
In FIG. 11, the transfer member position control process of the third embodiment is different in that the following ST31 is executed instead of ST6 of the second embodiment.
In ST31, the following processes (1) and (2) are executed. Then, the process proceeds to ST7.
(1) The passage time t2 is calculated from the size of the recording sheet S.
(2) The angle θ1 of the upstream position corresponding to the type of the recording sheet S is set.

(Function of the transfer device of Example 3)
In the transfer devices T1, B, and T2 of the printer U according to the third embodiment having the above-described configuration, the upstream position is set at an appropriate position according to the stiffness of the recording sheet S, and the upstream position is set. Compared with the case where it is not performed, useless movement of the secondary transfer roll T2b, application of excessive bending to the recording sheet S, and the like are suppressed.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is performed within the range of the summary of this invention described in the claim. It is possible. Modification examples (H01) to (H011) of the present invention are exemplified below.
(H01) In the above-described embodiment, the printer U as an example of the image forming apparatus has been illustrated. However, the present invention is not limited to this. It is also possible to do.
(H02) In the above-described embodiment, the configuration in which the developer of five colors is used as the printer U is illustrated. However, the present invention is not limited to this, and for example, a single-color image forming apparatus, four colors or less, or six colors or more The present invention can also be applied to a multicolor image forming apparatus.

(H03) In the above-described embodiments, the specific numerical values and parameters illustrated can be arbitrarily changed according to the design and specifications.
(H04) In the above-described embodiment, for the medium having low rigidity such as plain paper and thin paper, the effect obtained by moving the secondary transfer roll T2b is small, and thus the configuration in which the medium is fixed at the upstream position is exemplified. It is not limited to. Even in the case of plain paper or the like, there is an improvement effect on the deterioration of image quality by moving the secondary transfer roll T2b. Therefore, even in the case of plain paper or the like, it can be moved between the upstream position and the downstream position.
(H05) In the above-described embodiment, the configuration in which the downstream position is set to the position of 0 ° is exemplified, but the present invention is not limited to this. For example, the position can be arbitrarily changed according to the design, specifications, etc., such as being set to a position such as + 2 °, or a position being set to −2 °. Similarly to the third embodiment, the downstream position can be changed according to the type of the recording sheet S.

(H06) In the first embodiment, the timing for moving to the downstream position can be arbitrarily changed. That is, the position is not limited to the position where the recording sheet S has passed half, but can be changed to the position where 1/3 or 3/4 has passed. Further, the same position can always be set regardless of the size of the recording sheet S. For example, it may be 0.2 seconds after the front edge of the recording sheet S passes. Further, in the second and third embodiments, the timing for starting the movement toward the downstream position is not limited to the timing when the front end arrives, and may be after a preset time has elapsed since the front end arrived. Is possible.
(H07) In the above embodiment, the case where the medium is highly rigid is exemplified as the case of moving between the upstream position and the downstream position, but the present invention is not limited to this. For example, when a high-resistance medium that easily generates electric discharge is used, a configuration in which the medium is moved between the upstream position and the downstream position can be used.

(H08) In the above-described embodiment, the configuration in which the type of the recording medium is input from the operation unit UI is exemplified, but the present invention is not limited to this. For example, it is also possible to arrange a device for measuring the thickness of the medium, automatically detect the thickness of the medium, and move the secondary transfer roll T2b according to the thickness.
(H09) In the above-described embodiment, the secondary transfer roll T2b is preferably moved. However, the present invention is not limited to this. By moving the backup roll T2a side, the secondary transfer roll T2b can be moved to the upstream position or the upstream position relative to the backup roll T2a.

(H010) In the above embodiment, the intermediate transfer belt B as an example of the image carrier is illustrated, but the present invention is not limited to this. For example, the present invention can be applied to an endless belt-shaped image carrier such as a photosensitive belt.
(H011) In the above-described embodiment, the configuration for moving the secondary transfer roll T2b is not limited to the configuration using the exemplified cam 13 and rod 11. For example, it can be moved by an arbitrary method such as using a pinion gear and a rack, or using a spring and a solenoid.

11 to 17 ... moving system,
B: Image carrier,
Q4 ... transfer area,
S ... medium,
T2a: support member,
T2c: transfer member,
U: Image forming apparatus.

Claims (4)

An image carrier for holding an image;
A support member for supporting the image carrier;
An image of the image carrier is placed on a medium that is disposed opposite to the support member with the image carrier interposed therebetween, and that passes between the image carrier and a voltage applied between the image carrier and the support member. A transfer member to be transferred;
With
When the rear end of the transfer direction of the medium passes through the transfer region with respect to a position when the front end of the transfer direction of the medium is transferred to the transfer region to which the image is transferred Is located downstream in the conveyance direction of the medium. The transfer member is moved downstream in the medium conveyance direction after the front end in the medium conveyance direction passes through the transfer area and the rear end in the medium conveyance direction passes through the transfer area. The image forming apparatus according to claim 1, wherein a rear end of the medium in the conveyance direction is positioned downstream of the medium in the conveyance direction when the medium passes through the transfer region. . When the type of the medium is a preset high-rigidity type, the transfer member is positioned with respect to a position when the front end of the medium in the conveyance direction is conveyed to a transfer area where the image is transferred. 3. The image forming apparatus according to claim 1, wherein a rear end of the medium in the conveyance direction is positioned downstream in the medium conveyance direction when passing through the transfer region. 4. The image forming apparatus according to claim 1, wherein the transfer member moves more downstream in the conveyance direction of the medium as the medium has higher rigidity. 5.

Images