JP2021117265A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can improve transferability for each of a plurality of types of recording materials different in rigidity.SOLUTION: An image forming apparatus has: a first position changing mechanism 1 that changes the position of at least either one of an inner roller 32 or an outer roller 41, changes the relative positions of the inner roller 32 and the outer roller 41 with respect to a circumferential direction of the inner roller 32, and changes the position of a transfer unit N2; a second position changing mechanism 2 that changes the position of a pressing member 39; and a control unit 150 that controls the first position changing mechanism 1 and the second position changing mechanism 2. The control unit 150 controls the second position changing mechanism 2 such that, when an offset amount X is a first offset amount X1, the pressing member 39 presses an inner peripheral surface of a belt 31, and when the offset amount X is a second offset amount X2 (>0) larger than the first offset amount X1, the pressing member 39 is separated from the inner peripheral surface of the belt 31.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile apparatus using an electrophotographic system or an electrostatic recording system.

Conventionally, some image forming apparatus using an electrophotographic method or the like has an endless belt (hereinafter, also simply referred to as “belt”) as an image carrier for supporting a toner image. Such a belt includes, for example, a second belt that transports a toner image primaryly transferred from a photoconductor or the like as a first image carrier for secondary transfer to a sheet-like recording material such as paper. There is an intermediate transfer belt as an image carrier. Hereinafter, an image forming apparatus adopting an intermediate transfer method having an intermediate transfer belt will be mainly described as an example.

In the image forming apparatus of the intermediate transfer method, the toner image formed on the photoconductor or the like in the image forming portion is first transferred to the intermediate transfer belt in the primary transfer portion. Further, the toner image primaryly transferred to the intermediate transfer belt is secondarily transferred to the recording material by the secondary transfer unit. Intermediate transfer is performed by an inner member (secondary transfer inner member) provided on the inner peripheral surface side of the secondary transfer belt and an outer member (secondary transfer outer member) provided on the outer peripheral surface side of the secondary transfer belt. A secondary transfer nip as a secondary transfer portion, which is a contact portion between the belt and the outer member, is formed. As the inner member, an inner roller, which is one of a plurality of tension rollers for tensioning the intermediate transfer belt, is used. As the outer member, an outer roller arranged at a position facing the inner roller with the intermediate transfer belt interposed therebetween is often used. Then, for example, by applying a secondary transfer voltage having a polarity opposite to the charging polarity of the toner to the outer roller, the toner image on the intermediate transfer belt is secondarily transferred onto the recording material at the secondary transfer nip. Generally, a transport guide for guiding the recording material to the secondary transfer nip is provided upstream of the secondary transfer nip in the transport direction of the recording material.

Here, depending on the shape of the secondary transfer nip, the behavior of the recording material in the vicinity of the upstream or the downstream of the secondary transfer nip changes with respect to the transport direction of the recording material. Further, in recent years, it has been required to deal with various recording materials having different rigidity depending on the difference in thickness and surface property. The behavior of the recording material changes in the vicinity of the downstream. For example, when the recording material is "thin paper", which is an example of a recording material having a low rigidity, the intermediate transfer belt and the recording material are stuck in the vicinity of the downstream of the secondary transfer nip in the transport direction of the recording material, and the intermediate transfer is performed. Jam (paper jam) may occur due to poor separation of the recording material from the belt. This phenomenon becomes remarkable when the rigidity of the recording material is small because the recording material is easily attached to the intermediate transfer belt due to the weak stiffness of the recording material. On the other hand, for example, when the recording material is "thick paper" which is an example of a recording material having high rigidity, when the rear end of the recording material in the transport direction passes through the transport guide, the rear end portion of the recording material in the transport direction May collide with the intermediate transfer belt. Then, the posture of the intermediate transfer belt near the upstream of the secondary transfer nip is disturbed with respect to the transport direction of the recording material, and an image defect (a streak extending in a direction substantially orthogonal to the transport direction of the recording material) is formed at the rear end of the transport direction of the recording material. Image distortion, etc.) may occur. This phenomenon becomes remarkable when the rigidity of the recording material is high because the rear end portion of the recording material in the transport direction tends to collide with the intermediate transfer belt with a strong force due to the strong stiffness of the recording material. To solve such a problem, a configuration has been proposed in which the width of the secondary transfer nip in the rotation direction of the intermediate transfer belt is changed according to the type of recording material (Patent Document 1).

In addition, there are other issues such as the following. That is, the posture of the recording material transferred from the transfer guide to the secondary transfer nip changes depending on the rigidity of the recording material. For example, when the recording material is "thick paper", a gap is likely to occur between the intermediate transfer belt and the recording material in the vicinity of the entrance of the secondary transfer nip due to the high rigidity of the recording material. Then, due to the influence of the transfer electric field, electric discharge may occur in the voids, and the toner image may scatter and image defects (“scattering”) may occur. To solve such a problem, a configuration has been proposed in which a pressing member that contacts the inner peripheral surface of the intermediate transfer belt near the inlet of the secondary transfer nip is provided to reduce the gap near the inlet of the secondary transfer nip. (Patent Document 2).

Japanese Unexamined Patent Publication No. 2014-134718 Japanese Unexamined Patent Publication No. 2002-82543

As described above, in order to improve the separability of the recording material from the intermediate transfer belt and suppress image defects due to the collision of the rear end of the recording material with the intermediate transfer belt in the transport direction, the type of recording material is used. It is effective to change the width of the secondary transfer nip (position of the secondary transfer nip) with respect to the rotation direction of the intermediate transfer belt. To change the width of the secondary transfer nip, the inner roller or the outer roller is moved to change the relative position between the inner roller and the outer roller with respect to the circumferential direction of the inner roller, and the position of the secondary transfer nip is changed. Can be done by

On the other hand, in order to suppress image defects (“scattering”) due to electric discharge near the inlet of the secondary transfer nip, it is effective to provide a pressing member that contacts the inner peripheral surface of the intermediate transfer belt near the inlet of the secondary transfer nip. Is.

However, as a result of the examination by the present inventor, it is attempted to improve the separability, suppress the image defect due to the collision, and suppress the image defect (“scattering”) due to the discharge by adopting both of the above means. , It turned out that there are the following problems. That is, for example, when the recording material is switched from "thick paper" to "thin paper", the intermediate transfer belt on the upstream side of the secondary transfer nip with respect to the transport direction of the recording material is changed due to the change in the relative position between the inner roller and the outer roller. The contact area with the recording material becomes large. As a result, image defects, so-called "roughness", in which the toner image on the intermediate transfer belt is mechanically disturbed by friction between the toner image and the recording material may occur.

In the above, the conventional problem has been described by taking the secondary transfer portion, which is the transfer portion of the toner image from the intermediate transfer belt to the recording material, as an example, but from another belt-shaped image carrier such as a photoconductor to the recording material. There is a similar problem with the transfer portion of the toner image of.

Therefore, an object of the present invention is to provide an image forming apparatus capable of improving transferability for each of a plurality of types of recording materials having different rigidity.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises a rotatable endless belt that conveys a toner image and a plurality of tension rollers that stretch the belt, the inner roller and the inner roller with respect to the direction of rotation of the belt. A plurality of tension rollers including an upstream roller arranged adjacent to the inner roller upstream of the inner roller, and a plurality of tension rollers arranged to face the inner roller, contacting the outer peripheral surface of the belt, and from the belt. The outer roller forming the transfer portion for transferring the toner image to the recording material can contact the inner peripheral surface of the belt upstream of the inner roller and downstream of the upstream roller in the rotation direction of the belt. A pressing member capable of pressing the belt from the inner peripheral surface side to the outer peripheral surface side, and the inner roller and the outer roller in relation to the circumferential direction of the inner roller by changing the position of at least one of the inner roller or the outer roller. A first position changing mechanism for changing the position of the transfer portion, a second position changing mechanism for changing the position of the pressing member, the first position changing mechanism, and the first position changing mechanism. A control unit that controls the position changing mechanism of No. 2 is provided, and in a cross section substantially orthogonal to the rotation axis direction of the inner roller, the inner roller on the side on which the belt is hung and the upstream roller are common. The tangent line is the reference line L1, the straight line passing through the rotation center of the inner roller and substantially orthogonal to the reference line L1 is the inner roller center line L2, and the straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is the outer roller. The distance between the center line L3, the inner roller center line L2, and the outer roller center line L3 is offset by an offset amount X (however, the outer roller center line L3 is in the direction of rotation of the belt with respect to the inner roller center line L2. When the value is positive when it is on the upstream side), when the offset amount X is the first offset amount X1, the pressing member presses the inner peripheral surface of the belt, and the offset When the amount X is a second offset amount X2 (> 0) larger than the first offset amount X1, the second position changing mechanism is separated from the inner peripheral surface of the belt so that the pressing member is separated from the inner peripheral surface of the belt. It is an image forming apparatus characterized by controlling.

According to another aspect of the present invention, there is a rotatable endless belt for transporting a toner image and a plurality of tension rollers for tensioning the belt, the inner roller and the inner roller with respect to the rotation direction of the belt. A plurality of tension rollers including an upstream roller arranged adjacent to the inner roller upstream of the roller and a plurality of tension rollers arranged to face the inner roller and abutting on the outer peripheral surface of the belt to abut the belt. The outer roller forming the transfer portion for transferring the toner image from the recording material to the recording material can come into contact with the inner peripheral surface of the belt upstream of the inner roller and downstream of the upstream roller in the rotation direction of the belt. The inner roller and the outer roller with respect to the circumferential direction of the inner roller are changed by changing the positions of at least one of the pressing member capable of pressing the belt from the inner peripheral surface side to the outer peripheral surface side and the inner roller or the outer roller. A first position changing mechanism that changes the position of the transfer portion by changing the relative position with, a second position changing mechanism that changes the position of the pressing member, the first position changing mechanism, and the above. It has a control unit that controls a second position changing mechanism, and is common to the inner roller and the upstream roller on the side where the belt is hung in a cross section substantially orthogonal to the rotation axis direction of the inner roller. The tangent line is the reference line L1, the straight line passing through the rotation center of the inner roller and substantially orthogonal to the reference line L1 is the inner roller center line L2, and the straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is outside. The distance between the roller center line L3, the inner roller center line L2, and the outer roller center line L3 is offset by an offset amount X (however, the outer roller center line L3 is in the rotation direction of the belt rather than the inner roller center line L2). When the offset amount X is the first offset amount X1, the control unit sets the penetration amount Y of the pressing member into the belt as the first penetration. When the amount Y1 is set and the offset amount X is a second offset amount X2 (> 0) larger than the first offset amount X1, the intrusion amount Y is larger than the first intrusion amount Y1. An image forming apparatus is provided, which controls the second position changing mechanism so as to be smaller.

According to the present invention, it is possible to improve the transferability for each of a plurality of types of recording materials having different rigidity.

It is a schematic cross-sectional view of an image forming apparatus. It is a schematic side view which shows the offset mechanism and the pressing mechanism. It is a schematic side view which shows the offset mechanism and the pressing mechanism. It is a schematic side view which shows the disconnection mechanism of an outer roller. It is a schematic block diagram which shows the control mode of the main part of an image forming apparatus. It is a flowchart which shows the outline of the procedure of a job operation. It is a schematic side view which shows the offset mechanism and the pressing mechanism of another example. It is the schematic side view which shows the other example of the outer member. It is a schematic diagram for demonstrating the behavior of the recording material in the vicinity of a secondary transfer nip. It is the schematic sectional drawing for demonstrating the offset amount. It is the schematic sectional drawing for demonstrating the intrusion amount.

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

[Example 1]
1. 1. Overall Configuration and Operation of the Image Forming Device FIG. 1 is a schematic cross-sectional view of the image forming device 100 of the present embodiment. The image forming apparatus 100 of this embodiment is a tandem type multifunction device (having the functions of a copying machine, a printer, and a facsimile machine) that employs an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a sheet-shaped recording material (transfer material, sheet material) S such as paper by using an electrophotographic method in response to an image signal transmitted from an external device, for example. can.

The image forming apparatus 100 has four image forming units 10Y and 10M that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units (stations), respectively. It has 10C and 10K. These image forming portions 10Y, 10M, 10C, and 10K are arranged in series along the moving direction of the image transfer surface which is arranged substantially horizontally of the intermediate transfer belt 31, which will be described later. For elements having the same or corresponding functions or configurations in each image forming unit 10Y, 10M, 10C, and 10K, Y, M, C, and K at the end of the code indicating that the elements are for any color are omitted. And there is a general explanation. In this embodiment, the image forming unit 10 includes a photosensitive drum 11 (11Y, 11M, 11C, 11K), a charger 12 (12Y, 12M, 12C, 12K), and an exposure device 13 (13Y, 13M, 13C, 13K), which will be described later. ), Developer 14 (14Y, 14M, 14C, 14K), primary transfer roller 35 (35Y, 35M, 35C, 35K), cleaning device 15 (15Y, 15M, 15C, 15K) and the like. ..

The photosensitive drum 11, which is a rotatable drum-shaped (cylindrical) photoconductor (electrophotographic photosensitive member) as the first image carrier that carries the toner image, is oriented in the direction of arrow R1 (counterclockwise) in the drawing. It is driven to rotate. The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential having a predetermined polarity (negative electrode property in this embodiment) by the charging device 12 as a charging means. The surface of the charged photosensitive drum 11 is scanned and exposed by an exposure device 13 as an exposure means (electrostatic image forming means) according to an image signal, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 11. It is formed. In this embodiment, the exposure apparatus 13 is composed of a laser scanner apparatus that irradiates the photosensitive drum 11 with a laser beam modulated according to an image signal. The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by supplying toner as a developer by the developer 14 as a developing means, and a toner image (developer image) is formed on the photosensitive drum 11. Will be done. In this embodiment, the exposed portion (image portion) on the photosensitive drum 11 whose absolute potential value is lowered by being exposed after being uniformly charged has the same polarity as the charging polarity of the photosensitive drum 11 (this embodiment). In the example, the charged toner adheres to the negative electrode (negative electrode property) (reversal development).

An intermediate transfer belt, which is a rotatable intermediate transfer body composed of an endless belt as a second image carrier that supports a toner image so as to face the four photosensitive drums 11Y, 11M, 11C, and 11K. 31 is arranged. The intermediate transfer belt 31 is hung around a drive roller 33 as a plurality of tension rollers (support rollers), a tension roller 34, a secondary transfer pre-roller 37, and an inner roller (secondary transfer opposed roller, inner member) 32. It is stretched with a predetermined tension. The drive roller 33 transmits a driving force to the intermediate transfer belt 31. The tension roller 34 applies a predetermined tension to the intermediate transfer belt 31. The secondary transfer pre-roller 37 forms a surface of the intermediate transfer belt 31 near the upstream of the secondary transfer nip N2 (described later) with respect to the rotation direction (traveling direction) of the intermediate transfer belt 31. The inner roller 32 functions as an opposing member (opposing electrode) of the outer roller 41 (described later). The intermediate transfer belt 31 is rotated (rotated) in the direction of arrow R2 (clockwise) in the drawing by rotationally driving the drive roller 33. In this embodiment, as an example, the intermediate transfer belt 31 is rotationally driven so that the peripheral speed is 400 mm / sec. Of the plurality of support rollers, the support rollers other than the drive roller 33 rotate in a driven manner as the intermediate transfer belt 31 rotates. On the inner peripheral surface side of the intermediate transfer belt 31, the primary transfer rollers 35Y, 35M, which are roller-shaped primary transfer members as the primary transfer means, correspond to the photosensitive drums 11Y, 11M, 11C, 11K. 35C and 35K are arranged. The primary transfer roller 35 presses the intermediate transfer belt 31 toward the photosensitive drum 11 to form a primary transfer nip N1 as a primary transfer portion which is a contact portion between the photosensitive drum 11 and the intermediate transfer belt 31. .. As described above, the toner image formed on the photosensitive drum 11 is primarily transferred onto the rotating intermediate transfer belt 31 by the action of the primary transfer roller 35 in the primary transfer nip N1. At the time of primary transfer, the primary transfer roller 35 is subjected to a primary transfer voltage (not shown), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner (charging polarity of the toner during development). A transfer voltage is applied. For example, when forming a full-color image, the toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are sequentially superimposed on the same image forming region on the intermediate transfer belt 31. Next transcribed. In this embodiment, the primary transfer nip N1 is an image forming position for forming a toner image on the intermediate transfer belt 31. The intermediate transfer belt 31 is an example of a rotatable endless belt that conveys a toner image supported at an image forming position.

On the outer peripheral surface side of the intermediate transfer belt 31, an outer roller (secondary transfer roller, outer member) 41, which is a roller-shaped secondary transfer member as a secondary transfer means, is arranged at a position facing the inner roller 32. ing. The outer roller 41 is pressed toward the inner roller 32 via the intermediate transfer belt 31 to form a secondary transfer nip N2 as a secondary transfer portion that is a contact portion between the intermediate transfer belt 31 and the outer roller 41. The toner image formed on the intermediate transfer belt 31 as described above is a recording material that is sandwiched and conveyed between the intermediate transfer belt 31 and the outer roller 41 by the action of the outer roller 41 in the secondary transfer nip N2. Secondary transfer is performed on S. In this embodiment, during the secondary transfer, a secondary transfer voltage (not shown), which is a DC voltage opposite to the normal charging polarity of the toner, is applied to the outer roller 41 by the secondary transfer power supply (not shown). .. In this embodiment, the inner roller 32 is electrically grounded (connected to the ground). The inner roller 32 is used as a secondary transfer member, a secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the inner roller 32, and the outer roller 41 is used as a counter electrode to be electrically grounded. May be good.

The recording material S is conveyed to the secondary transfer nip N2 at the same timing as the toner image on the intermediate transfer belt 31. That is, the recording material S stored in the recording material cassettes 61, 62, 63 is sent out by rotating any one of the feeding rollers 71, 72, 73. The recording material S is conveyed to a resist roller (resist roller pair) 74, which is a transfer member as a transfer means, through a supply transfer transfer path 81, and is temporarily stopped. Then, in the recording material S, the resist roller 74 is rotationally driven so that the toner image on the intermediate transfer belt 31 and the desired image forming region on the recording material S coincide with each other in the secondary transfer nip N2. It is sent to the secondary transfer nip N2. Regarding the transport direction of the recording material S, a transport guide 83 for guiding the recording material S to the secondary transfer nip N2 is provided downstream of the resist roller 74 and upstream of the secondary transfer nip N2. The transport guide 83 includes a first guide member 83a that can come into contact with the front surface of the recording material S (the surface on which the toner image is transferred immediately after passing through the transport guide 83) and the back surface (front surface) of the recording material S. Is configured to have a second guide member 83b, which can come into contact with the opposite surface). The first guide member 83a and the second guide member 83b are arranged so as to face each other, and the recording material S passes between the two members. The first guide member 83a regulates the movement of the recording material S in the direction approaching the intermediate transfer belt 31. The second guide member 83b regulates the movement of the recording material S in the direction away from the intermediate transfer belt 31.

The recording material S to which the toner image is transferred is conveyed to the fixing device 50 as the fixing means by the transport belt 42. The fixing device 50 fixes (melts, fixes) the toner image on the surface of the recording material S by heating and pressurizing the recording material S carrying the unfixed toner image. After that, the recording material S on which the toner image is fixed is discharged (output) to the discharge tray 64 provided outside the device main body 100a of the image forming device 100 through the discharge transfer path 82.

On the other hand, the toner remaining on the photosensitive drum 11 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 11 by the cleaning device 15 as a cleaning means and recovered. Further, the toner (secondary transfer residual toner) remaining on the intermediate transfer belt 31 after the secondary transfer and the deposits such as paper dust adhering from the recording material S are intermediated by the belt cleaning device 36 as the intermediate transfer body cleaning means. It is removed from the transfer belt 31 and recovered.

In this embodiment, an intermediate transfer belt 31 stretched on a plurality of tension rollers, each primary transfer roller 35, a belt cleaning device 36, a frame supporting these, and the like are provided as a belt transfer device. The intermediate transfer belt unit 30 is configured. The intermediate transfer belt unit 30 is detachable from the apparatus main body 100a for maintenance or replacement.

Here, as the intermediate transfer belt 31, a belt made of a resin-based material having a single-layer or multi-layer structure can be used. Further, as the intermediate transfer belt 31, a belt having a thickness of 40 μm or more, a Young's modulus of 1.0 GPa or more, and a surface resistivity of 1.0 × 10 ^{9 to} 5.0 × 10 ¹³ Ω / □ is preferably used. Can be done.

Further, in this embodiment, the inner roller 32 is configured by providing an elastic layer (rubber layer) formed of a rubber material as an elastic material on the outer periphery of a metal core metal (base material). This elastic layer can be formed of, for example, EPDM rubber (which may contain a conductive agent). In this embodiment, the inner roller 32 is formed so that its outer diameter is 20 mm and the thickness of the elastic layer is 0.5 mm. Further, in this embodiment, the hardness of the elastic layer of the inner roller 32 is set to, for example, 70 ° (JIS-A). The inner roller 32 may be composed of a metal roller made of a metal material such as SUM or SUS. The secondary transfer pre-roller 37 can have the same configuration as the inner roller 32.

Further, in this embodiment, the outer roller 41 is a conductive elastic layer (solid rubber layer) formed on the outer periphery of a metal core metal (base material) with a conductive rubber material as a conductive elastic material. Alternatively, it may be a sponge layer (foam elastic layer)). This elastic layer can be formed of, for example, a metal complex, NBR rubber containing a conductive agent such as carbon, EPDM rubber, or the like. In this embodiment, the outer roller 41 is formed so that the outer diameter of the core metal is 12 mm, the thickness of the elastic layer is 6 mm, and the outer diameter of the outer roller 41 is 24 mm. Further, in this embodiment, the hardness of the elastic layer of the outer roller 41 is set to, for example, 28 ° (Asker C). Further, in the present embodiment, the outer roller 41 is predetermined with respect to the inner roller 32 with the intermediate transfer belt 31 sandwiched by the pressing spring 44 (FIG. 2) which is an urging member (elastic member) as an urging means. It is urged to abut with pressure.

In this embodiment, the rotation axis directions of the tension roller and the outer roller 41 of the intermediate transfer belt 31 including the inner roller 32 are substantially parallel to each other. The support configuration of the inner roller 32 and the outer roller 41 will be further described later.

2. Offset FIG. 9A is a schematic cross-sectional view (cross section substantially orthogonal to the rotation axis direction of the inner roller 32) for explaining the behavior of the recording material S in the vicinity of the secondary transfer nip N2. In FIG. 9A, the same reference numerals are given to the elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment.

As described above, depending on the shape of the secondary transfer nip N2 (position of the secondary transfer nip N2) and the rigidity of the recording material S, recording in the vicinity of the upstream side or the downstream side of the secondary transfer nip N2 with respect to the transport direction of the recording material S. The behavior of the material S changes. Then, for example, when the recording material S is "thin paper" which is an example of the recording material S having a low rigidity, a jam (paper jam) may occur due to poor separation of the recording material S from the intermediate transfer belt 31. .. This phenomenon becomes remarkable when the rigidity of the recording material S is small because the recording material S tends to stick to the intermediate transfer belt 31 due to the weak stiffness of the recording material S.

That is, in the cross section shown in FIG. 9A, the line indicating the tensioning surface of the intermediate transfer belt 31 formed by being stretched by the inner roller 32 and the secondary transfer pre-roller 37 is referred to as a tension wire T. The secondary transfer pre-roller 37 is an example of an upstream roller arranged adjacent to the inner roller 32 upstream of the inner roller 32 in the rotation direction of the intermediate transfer belt 31 among the plurality of tension rollers. Further, in the same cross section, a straight line passing through the rotation center of the inner roller 32 and the rotation center of the outer roller 41 is defined as the nip center line Lc. Further, in the same cross section, a line substantially orthogonal to the nip center line Lc is referred to as a nip line Ln. In FIG. 9A, the rotation center of the outer roller 41 is offset to the upstream side in the rotation direction of the intermediate transfer belt 31 from the rotation center of the inner roller 32 in the direction along the overhead wire T. Indicates the state.

At this time, when the recording material S is sandwiched between the inner roller 32 and the outer roller 41 by the secondary transfer nip N2, the recording material S tends to maintain its posture substantially along the nip line Ln. Therefore, in general, when the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are close to each other in the direction along the catenary T, the recording material S is discharged as shown by the broken line A in FIG. 9A. The angle θ becomes smaller. That is, the tip of the recording material S in the transport direction is in such a posture that when it is discharged from the secondary transfer nip N2, it is discharged near the intermediate transfer belt 31. This makes it easier for the recording material S to stick to the intermediate transfer belt 31. On the other hand, in general, the center of rotation of the outer roller 41 is located upstream of the center of rotation of the inner roller 32 in the direction along the overhead wire T in the direction of rotation of the intermediate transfer belt 31. As shown by the solid line in a), the discharge angle θ of the recording material S becomes large. That is, the tip of the recording material S in the transport direction is in such a posture that when it is discharged from the secondary transfer nip N2, it is discharged in a direction away from the intermediate transfer belt 31. As a result, the recording material S is less likely to adhere to the intermediate transfer belt 31.

On the other hand, as described above, for example, when the recording material S is "thick paper" which is an example of the recording material S having high rigidity, when the rear end of the recording material S in the transport direction passes through the transport guide 83. , The rear end portion of the recording material S in the transport direction may collide with the intermediate transfer belt. As a result, image defects may occur at the rear end of the recording material S in the transport direction. This phenomenon becomes remarkable when the rigidity of the recording material S is high because the rear end portion of the recording material S in the transport direction tends to collide with the intermediate transfer belt 31 with a strong force due to the strong stiffness of the recording material S. ..

That is, as described above, in the cross section shown in FIG. 9A, when the recording material S is sandwiched between the inner roller 32 and the outer roller 41 by the secondary transfer nip N2, the recording material S is substantially on the nip line Ln. Tends to maintain posture along. Therefore, in general, the nip line Ln is arranged so that the rotation center of the outer roller 41 is located upstream of the rotation center of the inner roller 32 in the rotation direction of the intermediate transfer belt 31 with respect to the direction along the tension line T. It becomes a shape that bites into T. As a result, when the rear end of the recording material S in the transport direction passes through the transport guide 83, as shown by the broken line B in FIG. 9A, the rear end of the recording material S in the transport direction is the intermediate transfer belt. It will collide with 31 and image defects are likely to occur at the rear end of the recording material S in the transport direction. On the other hand, in general, if the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are close to each other in the direction along the catenary T, when the rear end of the recording material S in the transport direction comes out of the transport guide 83. Collision with the intermediate transfer belt 31 is suppressed. As a result, image defects at the rear end of the recording material S in the transport direction are less likely to occur.

As a countermeasure against such a problem, it is effective to change the relative positions of the inner roller 32 and the outer roller 41 with respect to the circumferential direction of the inner roller 32 (rotational direction of the intermediate transfer belt 31) according to the type of the recording material S. Is. FIG. 10 is a schematic cross-sectional view of the vicinity of the secondary transfer nip N2 for explaining the definition of the relative positions of the inner roller 32 and the outer roller 41 (cross section substantially orthogonal to the rotation axis direction of the inner roller 32). Is. In FIG. 10, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are designated by the same reference numerals.

In the cross section shown in FIG. 10, the common tangent line between the inner roller 32 and the secondary transfer pre-roller 37 on the side on which the intermediate transfer belt 31 is hung is defined as the reference line L1. The reference line L1 corresponds to the above-mentioned overhead wire T when the intermediate transfer belt 31 is not projected toward the outer peripheral surface side by the pressing member 39 described later. Further, in the same cross section, a straight line passing through the rotation center of the inner roller 32 and substantially orthogonal to the reference line L1 is defined as the inner roller center line L2. Further, in the same cross section, a straight line passing through the rotation center of the outer roller 41 and substantially orthogonal to the reference line L1 is defined as the outer roller center line L3. At this time, the distance (vertical distance) between the inner roller center line L2 and the outer roller center line L3 is set to the offset amount X (however, the outer roller center line L3 is in the rotation direction of the intermediate transfer belt 31 rather than the inner roller center line L2). When it is on the upstream side of, it is defined as a positive value). The offset amount X can take a negative value, 0, or a positive value. By increasing the offset amount X, the width of the secondary transfer nip N2 with respect to the rotation direction of the intermediate transfer belt 31 is widened to the upstream side in the rotation direction of the intermediate transfer belt 31. That is, the rotation of the intermediate transfer belt 31 in the contact region between the outer roller 41 and the intermediate transfer belt 31 is larger than the upstream end in the rotation direction of the intermediate transfer belt 31 in the contact region between the inner roller 32 and the intermediate transfer belt 31. The end on the upstream side in the direction will be located on the upstream side. In this way, the position of at least one of the inner roller 32 and the outer roller 41 is changed, and the relative positions of the inner roller 32 and the outer roller 41 are changed with respect to the circumferential direction of the inner roller 32 to change the secondary transfer nip (transfer). Part) The position of N2 can be changed.

In FIG. 10, the outer roller 41 is represented so as to virtually contact the reference line L1 (overhead line T) without being deformed. However, as described above, the material of the outermost layer of the outer roller 41 is an elastic body such as rubber or sponge, and is actually pressed by the pressing spring 44 in the direction toward the inner roller 32 (in the direction of the white arrow in the figure). It is deformed. The outer roller 41 is offset with respect to the inner roller 32 on the upstream side in the rotation direction of the intermediate transfer belt 31, and is pressed by the pressing spring 44 so as to sandwich the intermediate transfer belt 31 with the inner roller 32. Then, a substantially S-shaped secondary transfer nip N2 is formed. Then, the posture of the recording material S guided and sent by the transport guide 83 is also determined according to the shape of the secondary transfer nip N2. The larger the offset amount X, the more the recording material S is bent. Therefore, as described above, for example, when the recording material S is "thin paper", the offset amount X is increased to separate the recording material S from the intermediate transfer belt 31 after passing through the secondary transfer nip N2. The sex can be improved. However, when the offset amount X is large, as described above, for example, when the recording material S is "thick paper", the recording material S is transported when the rear end of the recording material S in the transport direction passes through the transport guide 83. The rear end portion in the direction will collide with the intermediate transfer belt 31. This causes a factor of deteriorating the image quality of the rear end portion of the recording material S in the transport direction. Therefore, in this case, the offset amount X may be reduced.

3. 3. Pressing member FIG. 9B is a schematic cross-sectional view (cross section substantially orthogonal to the rotation axis direction of the inner roller 32) for explaining the transport posture of the recording material S in the vicinity of the secondary transfer nip N2. .. In FIG. 9B, the same reference numerals are given to the elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment. Note that FIG. 9B shows a state in which the rotation center of the inner roller 32 and the rotation center of the outer roller 41 are arranged at substantially the same position in the direction along the overhead wire T.

As described above, the posture of the recording material S transported from the transport guide 83 to the secondary transfer nip N2 changes depending on the rigidity of the recording material S. Then, for example, when the recording material S is "thick paper", a gap G is likely to be generated between the intermediate transfer belt 31 and the recording material S in the vicinity of the inlet of the secondary transfer nip N2, and "scattering" is likely to occur. ..

That is, in FIG. 9B, the intermediate transfer belt 31 is recorded along the moving direction of the intermediate transfer belt 31 in the vicinity of the inlet of the secondary transfer nip N2 (near the upstream of the inner roller 32 with respect to the rotation direction of the intermediate transfer belt 31). The distance in contact with the material S is defined as the contact distance D. More specifically, the contact distance D is the contact start position between the inner roller 32 and the intermediate transfer belt 31 and the contact start position between the recording material S and the intermediate transfer belt 31 with respect to the moving direction of the intermediate transfer belt 31. The distance between. For example, when the recording material S is “thick paper”, the contact distance D becomes small because the recording material S has a high rigidity and is difficult to bend near the inlet of the secondary transfer nip N2. Therefore, a gap G is generated between the intermediate transfer belt 31 and the recording material S, and a discharge occurs in the gap G due to the influence of the transfer electric field, and the toner image may scatter and image defects (“scattering”) may occur. ..

As a countermeasure against such a problem, the gap G in the vicinity of the inlet of the secondary transfer nip N2 is reduced by providing a pressing member that contacts the inner peripheral surface of the intermediate transfer belt 31 near the inlet of the secondary transfer nip N2. Is valid.

FIG. 11 is a schematic cross-sectional view (cross section substantially orthogonal to the rotation axis direction of the inner roller 32) for explaining the definition of the amount of penetration of the pressing member into the intermediate transfer belt 31. In FIG. 11, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of this embodiment are designated by the same reference numerals.

In the example shown in FIG. 11, the image forming apparatus 100 is in the form of a sheet that presses the inner peripheral surface of the intermediate transfer belt 31 near the inlet of the secondary transfer nip N2 to project the intermediate transfer belt 31 toward the outer peripheral surface side. A pressing member (backup sheet) 39 is provided. The pressing member 39 is arranged so as to come into contact with the inner peripheral surface of the intermediate transfer belt 31 in the rotation direction of the intermediate transfer belt 31 upstream of the inner roller 32 and downstream of the secondary transfer pre-roller 37. .. The pressing member 39 presses the intermediate transfer belt 31 from the inner peripheral surface side toward the outer peripheral surface side, and causes the intermediate transfer belt 31 to project toward the outer peripheral surface side. That is, the pressing member 39 comes into contact with the intermediate transfer belt 31 with a predetermined amount of penetration with respect to the intermediate transfer belt 31. The amount of penetration is roughly the tension wire T indicating the tensioning surface of the intermediate transfer belt 31 formed by the pressing member 39 being stretched by the inner roller 32 or the outer roller 41 and the secondary transfer pre-roller 37. On the other hand, it is an amount that causes the intermediate transfer belt 31 to project outward. The definition of the penetration amount (the penetration amount of the pressing member 39 with respect to the intermediate transfer belt 31) Y differs depending on whether the offset amount X is positive or 0 or negative. FIG. 11A shows a case where the offset amount X is 0 or a negative value (particularly a negative value), and FIG. 11B shows a case where the offset amount X is a positive value.

First, a case where the offset amount X is 0 or a negative value will be described. As shown in FIG. 11A, in a cross section substantially orthogonal to the rotation axis direction of the inner roller 32, a common tangent line between the inner roller 32 on the side on which the intermediate transfer belt 31 is hung and the secondary transfer pre-roller 37. Is the reference line L1. Further, in the same cross section, the tangent line of the intermediate transfer belt 31 that contacts the outer peripheral surface of the intermediate transfer belt 31 in the region where the pressing member 39 contacts the intermediate transfer belt 31, which is substantially parallel to the reference line L1, is defined as the pressing portion tangent line L4. .. At this time, when the offset amount X is 0 or a negative value, the distance (vertical distance) between the reference line L1 and the tangent line L4 of the pressing portion is set to the intrusion amount Y of the pressing member 39 with respect to the intermediate transfer belt 31 (however, pressing). It is defined as a positive value when the partial tangent line L4 is closer to the outer peripheral surface side of the intermediate transfer belt 31 than the reference line L1). The intrusion amount Y can take a positive value of 0.

Next, a case where the offset amount X is a positive value will be described. As shown in FIG. 11B, in a cross section substantially orthogonal to the rotation axis direction of the inner roller 32, a common tangent line between the outer roller 41 on the side on which the intermediate transfer belt 31 is hung and the secondary transfer pre-roller 37. Is the reference line L1'. Further, in the same cross section, the tangent line of the intermediate transfer belt 31 that contacts the outer peripheral surface of the intermediate transfer belt 31 in the region where the pressing member 39 contacts the intermediate transfer belt 31, which is substantially parallel to the reference line L1', is tangent to the pressing portion L4'. And. At this time, when the offset amount X is a positive value, the distance (vertical distance) between the reference line L1'and the pressing portion tangent line L4'is set as the intrusion amount Y of the pressing member 39 with respect to the intermediate transfer belt 31 (however, however). It is defined as (a positive value when the tangent line L4'of the pressing portion is closer to the outer peripheral surface side of the intermediate transfer belt 31 than the reference line L1'). The intrusion amount Y can take a positive value of 0.

As shown in FIGS. 11A and 11B, the intermediate transfer belt 31 is projected toward the outer peripheral surface side by the pressing member 39 to increase the contact distance D and to increase the contact distance D in the middle near the inlet of the secondary transfer nip N2. The gap G between the transfer belt 31 and the recording material S can be reduced. As a result, "scattering" can be suppressed.

4. Problem and Outline of Configuration of This Example While obtaining good transportability of the recording material S in the vicinity of the secondary transfer nip N2 for a wide variety of recording materials S having different rigidity such as "thin paper" and "thick paper". In order to suppress image defects that occur in the vicinity of the secondary transfer nip N2 and form a good image, the offset amount X is changed according to the type of the recording material S, and the vicinity of the inlet of the secondary transfer nip N2. It is considered effective to provide a pressing member 39 that comes into contact with the inner peripheral surface of the intermediate transfer belt 31 of the above.

However, as shown in FIG. 11B, for example, when the recording material S is "thin paper", the offset amount X is increased and the intermediate transfer belt 31 is projected toward the outer peripheral surface side by the pressing member 39. If this is the case, the contact distance D becomes too large, and the toner image is mechanically disturbed by the friction between the toner image on the intermediate transfer belt 31 and the recording material S, so-called “roughness” occurs. There is.

Therefore, in the present embodiment, when the position of at least one of the inner roller 32 and the outer roller 41 is changed to greatly change the offset amount X, the image forming apparatus 100 changes the position of the pressing member 39 and the intrusion amount Y. The intrusion amount Y is changed so that In particular, in this embodiment, the image forming apparatus 100 is configured to change the position of the inner roller 32 to change the offset amount X. Further, in the present embodiment, the image forming apparatus 100 is configured to synchronize the change of the offset amount X and the change of the penetration amount Y based on the information regarding the type of the recording material S related to the rigidity of the recording material S. And.

For example, when the recording material S is "thick paper", the inner roller 32 is arranged at the position of the first inner roller where the offset amount X is the first offset amount X1, and the penetration amount Y is the first penetration amount Y1. The pressing member 39 is arranged at the position of the first pressing member. Then, for example, when the recording material S is "thin paper", the following is performed. The inner roller 32 is arranged at the second inner roller position where the offset amount X is larger than the first offset amount X1 and becomes the second offset amount X2, and the intrusion amount Y is smaller than the first intrusion amount Y1. The pressing member 39 is arranged at the position of the second pressing member, which is the intrusion amount Y2 of 2. The first offset amount X1 may be a positive value, 0, or a negative value, and the second offset amount X2 is typically a positive value. Further, the first intrusion amount Y1 may be a positive value, and the second intrusion amount Y2 may be 0, which is a positive value.

Note that changing the offset amount X and the intrusion amount Y in synchronization means the following. Typically, when an image is formed on a recording material S, if the offset amount X is changed before the recording material S reaches the secondary transfer nip N2, the recording material has a secondary transfer nip. It means that the intrusion amount Y is also changed before reaching N2. Further, as another example, when a predetermined adjustment operation such as applying a secondary transfer voltage for controlling the secondary transfer voltage is performed, the offset amount X is changed before the start of the adjustment operation. Means that the intrusion amount Y is also changed before the start of the adjustment operation. Further, for example, the case where the recording material S is "thin paper" and "thick paper" means, more specifically, the case where "thin paper" and "thick paper" are passed through the secondary transfer nip N2, respectively.

5. Configuration related to secondary transcription The configuration related to secondary transcription in this example will be described in more detail. Here, for the sake of simplicity, a case where information on the basis weight of the paper as the recording material S is used as information on the type of the recording material S mainly related to the rigidity of the recording material S will be described as an example. Then, "thin paper" is used as an example of the recording material S having a small rigidity, and "thick paper" is used as an example of the recording material S having a large rigidity. However, as will be described later, the information regarding the type of the recording material S related to the rigidity of the recording material S is not limited to the information on the basis weight of the recording material S.

2 and 3 show that the vicinity of the secondary transfer nip N2 in this embodiment is viewed from one end side (front side of the paper surface in FIG. 1) of the inner roller 32 in the rotation axis direction substantially parallel to the rotation axis direction. It is a schematic side view of a part. FIG. 2 is a diagram mainly for explaining the configuration and operation of the offset mechanism 1 described later, and for ease of understanding, some configurations relating to the pressing mechanism 2 described later are shown by alternate long and short dash lines. There is. Further, FIG. 3 is a diagram mainly for explaining the configuration and operation of the pressing mechanism 2 described later, and for ease of understanding, some configurations relating to the offset mechanism 1 described later are shown by alternate long and short dash lines. Has been done. 2 (a) and 3 (a) show the state in the case of "thick paper", and FIGS. 2 (b) and 3 (b) show the state in the case of "thin paper".

5-1. Offset mechanism The offset mechanism 1 in this embodiment will be described with reference to FIGS. 2 (a) and 2 (b). In this embodiment, the image forming apparatus 100 changes the offset amount X by changing the relative position of the inner roller 32 with respect to the circumferential direction of the outer roller 41, and the offset mechanism (offset amount changing means) as the first position changing mechanism. ) Has 1. 2 (a) and 2 (b) show the configuration of one end of the inner roller 32 in the rotation axis direction, but the configuration of the other end is the same (with respect to the center of the inner roller 32 in the rotation axis direction). (Approximately symmetric).

Both ends of the inner roller 32 in the direction of the rotation axis are rotatably supported by the inner roller holder 38 as a support member. The inner roller holder 38 is supported by a frame or the like of the intermediate transfer belt unit 30 so as to be rotatable about the first rotation shaft 38a. In this way, by rotating the inner roller holder 38 around the first rotation shaft 38a and rotating the inner roller 32 around the first rotation shaft 38a, the inner roller 32 with respect to the outer roller 41 The offset amount X can be changed by changing the relative position of.

The inner roller holder 38 is configured to rotate by the action of the first cam 111 as an operating member. The first cam 111 is supported by a frame or the like of the intermediate transfer belt unit 30 so that it can rotate about the cam rotation shaft 110. More specifically, in this embodiment, the cam rotating shaft 110 is rotatably supported by the frame of the intermediate transfer belt unit 30 or the like, and the first cam 111 is fixed to the cam rotating shaft 110. The first cam 111 can rotate about the cam rotation shaft 110 by being driven by the position change motor 113 as a drive source. More specifically, in the present embodiment, the cam rotation shaft 110 is driven by the position change motor 113 to rotate, so that the first cam 111 fixed to the cam rotation shaft 110 is integrated with the cam rotation shaft 110. Rotate. Further, the first cam 111 is in contact with the first cam follower 38b provided on the inner roller holder 38. Further, the inner roller holder 38 is composed of a tension spring or the like which is an urging member (elastic member) as an urging means so that the first cam follower 38b rotates in the direction of engaging with the first cam 111. It is urged by the first rotating spring 114 that has been urged. The tension of the intermediate transfer belt 31 or the pressing by the outer roller 41 may provide a sufficient moment to rotate the inner roller holder 38 in the direction in which the first cam follower 38b engages with the first cam 111. be. In this case, the first rotating spring 114 may not be provided.

As described above, in this embodiment, the offset mechanism 1 is configured by having the inner roller holder 38, the first cam 111, the cam rotation shaft 110, the position change motor 113, the first rotation spring 114, and the like. ..

As shown in FIG. 2A, in the case of "thick paper", the first cam 111 is driven by the position change motor 113 and rotates clockwise. As a result, the inner roller holder 38 rotates counterclockwise around the first rotation shaft 38a, and the relative position of the inner roller 32 with respect to the outer roller 41 is determined. As a result, the inner roller 32 is arranged at the position of the first inner roller, which is the first offset amount X1 in which the offset amount X is relatively small. As a result, as described above, deterioration of the image quality of the rear end portion of the "thick paper" in the transport direction can be suppressed.

Further, as shown in FIG. 2B, in the case of "thin paper", the first cam 111 is driven by the position change motor 113 and rotates counterclockwise. As a result, the inner roller holder 38 rotates clockwise around the first rotation shaft 38a, and the relative position of the inner roller 32 with respect to the outer roller 41 is determined. As a result, the inner roller 32 is arranged at the position of the second inner roller, which is the second offset amount X2 in which the offset amount X is relatively large. As a result, the separability of the "thin paper" from the intermediate transfer belt 31 after passing through the secondary transfer nip N2 is improved as described above.

5-2. Pressing Mechanism The pressing mechanism 2 in this embodiment will be described with reference to FIGS. 3 (a) and 3 (b). In this embodiment, the image forming apparatus 100 changes the position of the pressing member 39 to change the intrusion amount Y in synchronization with the operation of the offset mechanism 1 described above, and the pressing mechanism as a second position changing mechanism ( It has an intrusion amount changing means) 2. In particular, in this embodiment, the pressing mechanism 2 changes the position of the pressing member 39 to change the intrusion amount Y in conjunction with the operation of the offset mechanism 1 described above. 3 (a) and 3 (b) show the configuration of one end of the inner roller 32 in the rotation axis direction, but the configuration of the other end is the same (with respect to the center of the inner roller 32 in the rotation axis direction). (Approximately symmetric).

In this embodiment, the image forming apparatus 100 has a sheet-shaped pressing member (backup sheet) 39 similar to that described with reference to FIG. The pressing member 39 presses the inner peripheral surface of the intermediate transfer belt 31 in the vicinity of the inlet of the secondary transfer nip N2 to cause the intermediate transfer belt 31 to project toward the outer peripheral surface side. The pressing member 39 is arranged so as to come into contact with the inner peripheral surface of the intermediate transfer belt 31 in the rotation direction of the intermediate transfer belt 31 upstream of the inner roller 32 and downstream of the secondary transfer pre-roller 37. .. In particular, in this embodiment, the pressing member 39 is located upstream of the inner roller 32 and downstream of the tip of the transport guide 83 (first guide member 83a) on the downstream side in the transport direction of the recording material S. It is arranged so as to come into contact with the inner peripheral surface of the intermediate transfer belt 31 corresponding to the above. The pressing member 39 can be formed by using a resin material. As the resin material for forming the pressing member 39, for example, a polyester resin such as PET resin can be preferably used. In this embodiment, the pressing member 39 is arranged in a longitudinal direction substantially parallel to the width direction of the intermediate transfer belt 31 (a direction substantially orthogonal to the moving direction of the surface) and a lateral direction substantially orthogonal to the longitudinal direction. , Each of which has a predetermined length and is composed of a plate-shaped member having a predetermined thickness. The length of the pressing member 39 in the longitudinal direction is equivalent to the length of the intermediate transfer belt 31 in the width direction. Then, the free end portion of the pressing member 39, which is one end portion in the lateral direction (the end portion on the downstream side in the rotation direction of the intermediate transfer belt 31), extends over substantially the entire width of the intermediate transfer belt 31 and is the intermediate transfer belt 31. It can contact the inner peripheral surface and can press the intermediate transfer belt 31. Further, as an example, the thickness of the pressing member 39 is 0.4 mm to 0.6 mm. For example, when a PET resin sheet is used as the pressing member 39, if a PET resin sheet having too low electrical resistance is used, a current flows through the pressing member 39 as the secondary transfer voltage is applied to the outer roller 41, resulting in transfer failure. May occur. On the other hand, if a PET resin sheet having too high electrical resistance is used, static electricity (triboelectric charging) is generated due to friction between the pressing member 39 and the intermediate transfer belt 31, and the intermediate transfer belt 31 is adsorbed on the pressing member 39 to attract the intermediate transfer belt 31. It may interfere with the rotation of 31. Therefore, as the pressing member 39, it is preferable to use a PET resin sheet adjusted to have a medium resistance electrical resistance (for example, a volume resistivity of 1 × 10 ⁵ to 1 × 10 ^{9 Ω · cm).}

The pressing member 39 is supported by a pressing member holder 40 as a supporting member. The pressing member 39 has a fixed end that is one end in the lateral direction (the end on the upstream side in the rotation direction of the intermediate transfer belt 31) and is fixed to the pressing member holder 40 over substantially the entire width in the longitudinal direction. The pressing member holder 40 is supported by a frame or the like of the intermediate transfer belt unit 30 so that the pressing member holder 40 can rotate about the second rotating shaft 40a. In this way, the position of the pressing member 39 is changed by rotating the pressing member holder 40 around the second rotating shaft 40a and rotating the pressing member 39 around the second rotating shaft 40a. The intrusion amount Y can be changed.

The pressing member holder 40 is configured to rotate by the action of the second cam 112 as an operating member. The second cam 112 can rotate coaxially with the first cam 111 constituting the offset mechanism 1 described above and in conjunction with the first cam 111. More specifically, in this embodiment, the second cam 112 is fixed to the cam rotation shaft 110 rotatably supported by the frame of the intermediate transfer belt unit 30 or the like. Then, in the present embodiment, the cam rotation shaft 110 is driven by the position change motor 113 to rotate, so that the first cam 111 and the second cam 112 fixed to the cam rotation shaft 110 rotate. .. Further, the second cam 112 is in contact with the second cam follower 40b provided on the pressing member holder 40. Further, the pressing member holder 40 is composed of a tension spring or the like which is an urging member (elastic member) as an urging means so that the second cam follower 40b rotates in the direction of engaging with the second cam 112. It is urged by the second rotating spring 115 that has been urged.

Here, the first cam 111 and the second cam 112 are in phase with respect to the cam rotation shaft 110 so that the inner roller 32 and the pressing member 39 can be moved in conjunction with each other in a predetermined relationship. Is fixed and provided. As a result, the pressing mechanism 2 can change the intrusion amount Y in conjunction with the operation of the offset mechanism 1 described above. As described above, in this embodiment, the offset amount X and the intrusion amount Y can be changed in synchronization with one (common) drive source. That is, in this embodiment, the offset mechanism 1 and the pressing mechanism 2 can be driven by one (common) actuator. Therefore, it is possible to simplify the configuration of the device and reduce the cost.

As described above, in this embodiment, the pressing mechanism 2 includes the pressing member holder 40, the second cam 112, the cam rotating shaft 110, the position changing motor 113, the second rotating spring 115, and the like. ..

As shown in FIG. 3A, in the case of "thick paper", the inner roller 32 is arranged at the first inner roller position (first offset amount X1) by the offset mechanism 1, and the inner roller 32 is arranged at the first inner roller position (first offset amount X1). The second cam 112 is driven by the position change motor 113 and rotates clockwise. As a result, the pressing member holder 40 rotates counterclockwise around the second rotating shaft 40a to reach the position of the first pressing member, which is the first intrusion amount Y1 in which the intrusion amount Y is relatively large. , The pressing member 39 is arranged. In this embodiment, at this time, the tip of the pressing member 39 comes into contact with the inner peripheral surface of the intermediate transfer belt 31 near the inlet of the secondary transfer nip N2, and the intermediate transfer belt 31 is projected toward the outer peripheral surface side (first). Penetration amount Y1> 0 mm). As a result, as described above, the contact distance D between the intermediate transfer belt 31 and the recording material S in the vicinity of the inlet of the secondary transfer nip N2 can be increased, and "scattering" can be suppressed.

Further, as shown in FIG. 3B, in the case of "thin paper", the offset mechanism 1 interlocks with the inner roller 32 being arranged at the second inner roller position (second offset amount X2). The second cam 112 is driven by the position change motor 113 and rotates counterclockwise. As a result, the pressing member holder 40 rotates clockwise around the second rotating shaft 40a, and the intrusion amount Y is moved to the second pressing member position, which is the second intrusion amount Y2, which is relatively small. The pressing member 39 is arranged. In this embodiment, at this time, the tip of the pressing member 39 is separated from the inner peripheral surface of the intermediate transfer belt 31 (second penetration amount Y2 = 0 mm).

Here, while the pressing member 39 is temporarily arranged at the position of the first pressing member (first penetration amount Y1) shown in FIG. 3A, the inner roller 32 is the second one shown in FIG. 3B. Consider the case where the rollers are arranged at the inner roller position (second offset amount X2). In this case, as shown in FIG. 3A, the contact distance D is such that the inner roller 32 is at the first inner roller position (first offset amount X1) and the pressing member 39 is at the first pressing member position (first pressing member position). It becomes even larger than the contact distance D in the state of being arranged in the intrusion amount Y1). Therefore, the friction between the toner image on the intermediate transfer belt 31 and the recording material S causes the toner image to be mechanically disturbed, resulting in image defects, so-called “roughness”. On the other hand, in the present embodiment, as shown in FIG. 3B, the inner roller 32 is arranged at the second inner roller position (second offset amount X2), but is synchronized (particularly in the present embodiment). The pressing member 39 is arranged at a position separated from the second pressing member position (second intrusion amount Y2), particularly the intermediate transfer belt 31. As a result, the contact distance D can be prevented from becoming larger than necessary, and "roughness" can be suppressed.

In this embodiment, the pressing member 39 is a resin sheet-like member, but the pressing member 39 is not limited to this. The pressing member 39 may be, for example, a sheet-like member made of a thin metal plate. Further, the pressing member 39 may be, for example, an elastic body (pad-shaped or the like) such as a sponge or rubber. Further, the pressing member 39 may be a rigid body such as a rotatable resin or metal roller. Further, the pressing member 39 is not limited to the one that is arranged at a predetermined position and comes into contact with the intermediate transfer belt 31 as in the present embodiment. For example, when a rigid body such as the rotatable roller is used as the pressing member 39, the pressing member 39 may be urged toward the intermediate transfer belt 31 by a spring or the like as an urging means.

5-3. Separation mechanism The separation mechanism 3 of the outer roller 41 in this embodiment will be described. FIG. 4 is a schematic view showing a schematic configuration of the disconnection mechanism 3. FIG. 4 shows the configuration of one end portion of the inner roller 32 in the rotation axis direction, but the configuration of the other end portion is also the same (substantially symmetrical with respect to the center of the inner roller 32 in the rotation axis direction).

Both ends of the outer roller 41 in the direction of the rotation axis are rotatably supported by the bearing 43. The bearing 43 is supported by a frame or the like of the apparatus main body 100a so that the bearing 43 can slide and move in a direction toward the inner roller 32 and in the opposite direction along a predetermined direction (for example, a direction substantially orthogonal to the above-mentioned reference line L1). There is. The bearing 43 is pressed toward the inner roller 32 by a pressing spring 44 composed of a compression spring which is an urging member (elastic member) as an urging means. As a result, the outer roller 41 abuts on the inner roller 32 with the intermediate transfer belt 31 sandwiched between them to form the secondary transfer nip N2.

Then, in this embodiment, the image forming apparatus 100 has a disengagement mechanism (disengagement means) 3 for separating and abutting the outer roller 41 with respect to the intermediate transfer belt 31. As shown in FIG. 4, the disengagement mechanism 3 includes an arm 122, a disengagement cam 121, a disengagement motor 123, and the like. The arm 122 is supported by a frame or the like of the apparatus main body 100a so as to be rotatable about the arm rotation shaft 122a, and is engaged with the bearing 43. Further, the arm 122 is configured to rotate by the action of the disengagement cam 121 as an operating member. The detachable cam 121 is supported by a frame or the like of the apparatus main body 100a so as to be rotatable about the detachable cam rotation shaft 120. The disengagement cam 121 can rotate about the disengagement cam rotation shaft 120 by receiving a drive from the disengagement motor 123 as a drive source. Further, the disengagement cam 121 is in contact with the disengagement cam follower 122b provided on the arm 122. Further, the arm 122 is urged by the pressing spring 44 so that the disengagement cam follower 122b rotates in the direction in which the disengagement cam follower 122b engages with the disengagement cam 121.

The disengagement mechanism 3 moves the outer roller 41 in the direction away from and in the direction toward the inner roller 32. As shown by the solid line in FIG. 4, when the outer roller 41 is separated from the intermediate transfer belt 31, the disengagement cam 121 is driven by the disengagement motor 123 and rotates counterclockwise, for example, to cause the arm 122. Rotates clockwise. As a result, the arm 122 moves the bearing 43 away from the inner roller 32 (downward) against the urging force of the pressing spring 44, and separates the outer roller 41 from the intermediate transfer belt 31. On the other hand, as shown by the alternate long and short dash line in FIG. 4, when the outer roller 41 is brought into contact with the intermediate transfer belt 31, the disengagement cam 121 is driven by the disengagement motor 123 to rotate, for example, clockwise. , The arm 122 is rotated counterclockwise by the urging force of the pressing spring 44. As a result, the arm 122 moves the bearing member 43 in the direction (upward) closer to the inner roller 32, and brings the outer roller 41 into contact with the intermediate transfer belt 31.

In this embodiment, in the disengagement mechanism 3, the toner that is not transferred to the recording paper S such as a test image (patch) for image density correction or color shift correction formed on the intermediate transfer belt 31 is transferred to the surface of the outer roller 41. The outer roller 41 is separated from the intermediate transfer belt 31 in order to avoid adhering to the intermediate transfer belt 31. Further, when the jam (paper jam) is processed, the disengagement mechanism 3 separates the outer roller 41 from the intermediate transfer belt 31. Further, if the outer roller 41 continues to be pressed toward the inner roller 32 after the job (described later) is completed, the inner roller 32 and the outer roller 41 may be deformed. Therefore, in the present embodiment, the disconnection mechanism 3 separates the outer roller 41 from the intermediate transfer belt 31 when the job is completed and the image forming apparatus 100 is in the standby state waiting for the next job. The outer roller 41 is maintained in a state of being separated from the intermediate transfer belt 31 even when the image forming apparatus 100 is in the sleep state (described later) or the main power supply is turned off.

In this embodiment, the outer roller 41 performs intermediate transfer in the operation of changing the offset amount X by the offset mechanism 1 and changing the intrusion amount Y by the pressing mechanism 2 (here, it is also simply referred to as “position change operation”). This may be performed in either a state of being in contact with the belt 31 or a state in which the outer roller 41 is separated from the intermediate transfer belt 31. Further, in the present embodiment, the position changing operation may be performed in either a state in which the intermediate transfer belt 31 is stopped or a state in which the intermediate transfer belt 31 is rotating. From the viewpoint of reducing wear of the intermediate transfer belt 31 and the outer roller 41, driving load of the position changing operation, and the like, it is advantageous to perform the position changing operation in a state where the outer roller 41 is separated from the intermediate transfer belt 31. In this case, the position change operation is typically performed with the intermediate transfer belt 31 stopped. On the other hand, when the position change operation is performed while the intermediate transfer belt 31 is rotated in the paper-to-paper process (described later), the outer roller 41 is intermediate in the position change operation from the viewpoint of shortening the time required for the position change operation. It is advantageous to carry out the operation in contact with the transfer belt 31.

5-4. Specific examples of offset amount and intrusion amount-Specific example 1
In this embodiment (Specific Example 1), based on the basis weight M of the recording material S, the pattern of the combination of the offset amount X (X1, X2) and the intrusion amount Y (Y1, Y2) is, for example, as follows. It is set to have two patterns.
(A) M ≧ 52 g / m ² : X1 = −1.3 mm Y1 = 1.5 mm
(B) M <52 g / m ² : X2 = 2.5 mm Y2 = 0 mm (separation)

As in the present embodiment, when the material of the pressing member 39 is resin and the shape thereof is a sheet shape, the positions of the inner roller 32 and the pressing member 39 in the above setting (b) are set as the home position. Is preferable. This is to prevent the pressing member 39 from being creep deformed by being continuously subjected to the pressure due to the tension of the intermediate transfer belt 31 for a long period of time. When the pressing member 39 changes its creep, for example, the penetration amount Y1 in the case of "thick paper" may become smaller than the above-mentioned setting of 1.5 mm due to a change with time. Here, the home position refers to a position when the image forming apparatus 100 is in a sleep state or a state in which the main power supply is turned off.

In this embodiment, the pressing member 39 can be separated from the inner peripheral surface of the intermediate transfer belt 31, but the present invention is not limited to this. When the intrusion amount Y is 0, the pressing member 39 may be in contact with the intermediate transfer belt 31. Further, the second intrusion amount Y2 may be smaller than the first intrusion amount Y1, and the intrusion amount Y may not be 0. For example, when the pressing member 39 is a thin metal plate or a rotatable roller, and the influence of creep deformation is sufficiently small or absent, it is easy to configure the structure so that the penetration amount Y does not take zero. For example, based on the basis weight M of the recording material S, the pattern of the combination of the offset amount X (X1, X2) and the intrusion amount Y (Y1, Y2) is set to be the following two patterns. May be good.

・ Specific example 2
(A) M ≧ 52 g / m ² : X1 = −1.3 mm Y1 = 1.5 mm
(B) M <52 g / m ² : X2 = 2.5 mm Y2 = 0.5 mm

Further, in the above specific examples 1 and 2, the case where the value of the intrusion amount Y1 is a constant value for each offset amount X (X1, X2) has been described as an example, but the present invention is not limited to this. For example, in each offset amount X (X1, X2), the intrusion amount Y may be changed according to the basis weight. Specifically, the intrusion amount Y may be set as follows.

・ Specific example 3
(A) M ≧ 300 g / m ² : X1 = −1.3 mm Y1 = 1.5 mm
(B) 52 g / m ² ≤ M <300 g / m ² : X1 = -1.3 mm Y1 = 0.5 mm
(C) M <52 g / m ² : X2 = 2.5 mm Y2 = 0 mm (separation)

・ Specific example 4
(A) M ≧ 300 g / m ² : X1 = −1.3 mm Y1 = 1.5 mm
(B) 100 g / m ² ≤ M <300 g / m ² : X1 = -1.3 mm Y1 = 0.5 mm
(C) 52 g / m ² ≤ M <100 g / m ² : X2 = 2.5 mm Y2 = 0.1 mm
(D) M <52 g / m ² : X2 = 2.5 mm Y2 = 0 mm (separation)

When the value of the intrusion amount Y1 is changed for each offset amount X (X1, X2) as in the specific example 4, the maximum value of the intrusion amount Y set when the offset amount X2 (> 0) is set. (Here, Y2 = 0.1 mm) has a relation smaller than the minimum value of the intrusion amount Y (here, Y1 = 0.5 mm) set when the offset amount X1.

The offset amount X and the intrusion amount Y, and the type of the recording material S assigned to each combination of the offset amount X and the intrusion amount Y (here, the basis weight of the recording material S) are limited to the above-mentioned specific examples. It's not a thing. These can be appropriately set through experiments and the like from the viewpoint of improving the separability of the recording material S from the intermediate transfer belt 31 and suppressing image defects occurring in the vicinity of the secondary transfer nip N2 as described above. Although not limited to this, the offset amount X is preferably about -3 mm to +3 mm. Further, although not limited to this, the pressing member 39 is the intermediate transfer belt 31 within 25 mm from the region where the inner roller 32 and the intermediate transfer belt 31 come into contact to the upstream side in the rotation direction of the intermediate transfer belt 31. It is preferable to arrange it so that it can come into contact with the inner peripheral surface. With such a setting, good transferability can be obtained. Further, although not limited to this, the penetration amount Y is preferably about 3.5 mm or less. When the penetration amount Y is larger than 3.5 mm, the load applied to the contact surface between the pressing member 39 and the intermediate transfer belt 31 increases, so that the intermediate transfer belt 31 may not rotate smoothly.

Further, in this embodiment, the switching of the offset amount X (position of the inner roller 32) has been described by taking the case of two steps as an example, but the switching is not limited to this. The offset amount X (position of the inner roller 32) may be changed in three or more steps or steplessly.

When the offset amount X can be changed in three or more steps, the intrusion amount Y does not necessarily have to be reduced as the offset amount X increases. For example, when the change amount of the offset amount X is small or when the offset amount X is changed in the negative range, the fluctuation of the contact distance D described above is small. In this case, the intrusion amount Y does not necessarily have to be reduced.

Further, when there is a setting in which the intrusion amount Y is 0 in the setting in which the offset amount X is changed in three or more stages, it is preferable to set the setting as the home position setting for the same reason as described above. The setting may be a setting that is not used at the time of image formation and is used only in a sleep state of the image forming apparatus 100 or a state in which the main power is turned off.

6. Control mode FIG. 5 is a schematic block diagram showing a control mode of a main part of the image forming apparatus 100 of this embodiment. The control unit 150 as a control means includes a CPU 151 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage medium) 152 such as a ROM and a RAM as a storage means, and an interface unit 153. Will be done. The RAM, which is a rewritable memory, stores the information input to the control unit 150, the detected information, the calculation result, and the like, and the ROM stores the control program, the data table obtained in advance, and the like. Data can be transferred and read from each other between the CPU 151 and the memory 152. The interface unit 153 controls the input / output (communication) of signals between the control unit 150 and the device connected to the control unit 150.

Each part of the image forming apparatus 100 (an image forming unit 10, an intermediate transfer belt 31, a driving device of a member related to the transfer of the recording material S, various power sources, etc.) is connected to the control unit 150. In relation to the present embodiment, in particular, the control unit 150 is connected to the position change motor 113 which is the drive source of the offset mechanism 1 and the pressing mechanism 2, the disengagement motor 123 which is the drive source of the disengagement mechanism 3, and the like. ing. Further, an operation unit (operation panel) 160 provided in the image forming apparatus 100 is connected to the control unit 150. The operation unit 160 includes a display unit as a display means for displaying information under the control of the control unit 150, and an input unit as an input means for inputting information to the control unit 150 by an operation by an operator such as a user or a service person. Have. The operation unit 160 may be configured to have a touch panel having the functions of a display unit and an input unit. Further, the control unit 150 includes an external device 200 such as an image reading device (not shown) provided in the image forming device 100 or connected to the image forming device 100, or a personal computer connected to the image forming device 100. May be connected.

The control unit 150 controls each unit of the image forming apparatus 100 based on the job information to perform image forming. The job information includes information (command signal) regarding image formation conditions such as a start instruction (start signal) input from the operation unit 160 and the external device 200, and a type of recording material S. Further, the job information includes image information (image signal) input from the image reading device or the external device 200. Information on the type of recording material (also simply referred to as "information on recording material") is an attribute based on general characteristics such as plain paper, woodfree paper, glossy paper, coated paper, embossed paper, thick paper, and thin paper. (So-called paper type category), numerical values such as basis weight, thickness, size, numerical range, or brand (including manufacturer, product number, etc.), etc., which includes arbitrary information that can distinguish the recording material. be. In this embodiment, the information regarding the type of the recording material S includes information regarding the type of the recording material S related to the rigidity of the recording material S, and in particular, information on the basis weight of the recording material S as an example.

Here, the image forming apparatus 100 executes a job which is a series of operations of forming and outputting an image on a single or a plurality of recording materials S, which is started by one start instruction. The job generally includes an image forming step (printing operation), a front rotation step, a paper-to-paper step when forming an image on a plurality of recording materials S, and a back rotation step. The image forming step is a period during which an electrostatic image of an image actually formed and output on the recording material S is formed, a toner image is formed, a primary transfer of the toner image is performed, and a secondary transfer is performed, and the image is formed (image). The formation period) means this period. More specifically, the timing at the time of image formation differs depending on the position where each of the steps of forming the electrostatic image, forming the toner image, and performing the primary transfer and the secondary transfer of the toner image is performed. The pre-rotation step is a period during which the preparatory operation before the image forming step is performed from the input of the start instruction to the actual start of forming the image. The inter-paper process is a period corresponding between the recording material S and the recording material S when image formation is continuously performed on the plurality of recording materials S (continuous image formation). The post-rotation step is a period during which the rearranging operation (preparation operation) is performed after the image forming step. The non-image forming period (non-image forming period) is a period other than the image forming period, and is from the pre-rotation process, the inter-paper process, the post-rotation process, and further, when the power of the image forming apparatus 100 is turned on or in the sleep state. It includes a pre-multi-rotation process, which is a preparatory operation at the time of recovery. The sleep state (hibernate state) is, for example, a state in which the supply of power to each part of the image forming apparatus 100 other than the control unit 150 (or a part thereof) is stopped, and the power consumption is less than that in the standby state. Is. In this embodiment, the above-mentioned "position change operation" is executed at the time of non-image formation.

7. Control procedure FIG. 6 is a flowchart showing an outline of a job control procedure in this embodiment. Here, it is assumed that the types of recording materials S used for image formation in one job are the same. Further, here, a case where the operator causes the image forming apparatus 100 to execute a job from the external device 200 will be described as an example. Note that FIG. 6 shows an outline of a control procedure focusing on a position changing operation, and many other operations normally required for executing a job and outputting an image are omitted.

When job information (image information, image formation condition information, start instruction) is input from the external device 200, the control unit 150 inputs information on the type of recording material S used for image formation included in the job information. Acquire (S101). In this embodiment, the information regarding the type of the recording material S includes at least the information on the basis weight of the recording material S. The control unit 150 acquires information regarding the type of the recording material S directly input (including selecting from a plurality of options) from the external device 200 (or the operation unit 160) by the operation of the operator. be able to. Further, the control unit 150 uses the recording material S based on the information of the cassettes 61, 62, and 63 that send the recording material S in the job, which is input from the external device 200 (or the operation unit 160) by the operation of the operator. You can also get information about the types of. In this case, the control unit 150 uses the recording material S from the information regarding the type of the recording material S stored in the cassettes 61, 62, 63, which are stored in the memory 152 in advance in relation to the cassettes 61, 62, 63. Information on the type of S can be obtained. Here, when registering the information regarding the type of the recording material S, the corresponding one from the list of the types of the recording material S stored in the storage device connected to the control unit 150 through the memory 152 or the network in advance. May be selected.

The control unit 150 has a pattern of a combination of the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (intrusion amount Y) based on the information regarding the type of the recording material S acquired in S101 (here, the intrusion amount Y). It is also simply referred to as a "position pattern") (S102). In the memory 152, information on the position pattern according to the basis weight of the recording material S is stored in advance as in the specific example described above. Therefore, the control unit 150 determines the position pattern corresponding to the recording material S used in the current job from the position pattern information stored in the memory 152 based on the information regarding the type of the recording material S acquired in S101. do.

As a specific example, in the present embodiment (Specific Example 1), information of a predetermined threshold value (52 g / m ² described above as an example) of the basis weight of the recording material S is stored in the memory 152. Then, when the basis weight of the recording material S used in this job is equal to or greater than the threshold value, the control unit 150 invades the position of the first inner roller, which is the first offset amount X1 in which the offset amount X is relatively small. The position of the first pressing member, which is the first intrusion amount Y1 in which the amount Y is relatively large, is determined. Further, when the basis weight of the recording material S used in this job is less than the threshold value, the control unit 150 enters the second inner roller position, which is the second offset amount X2 in which the offset amount X is relatively large. The position of the second pressing member, which is the second intrusion amount Y2 in which the amount Y is relatively small, is determined. As described above, when three or more position patterns are set, for example, the basis weight corresponding to each position pattern set so that the intrusion amount Y decreases as the offset amount X increases. Information of a plurality of threshold values may be set so as to define a range.

Next, the control unit 150 determines whether or not it is necessary to change the position pattern with respect to the current position patterns of the inner roller 32 and the pressing member 39 based on the position pattern determined in S102 (S103). As described above, in the present embodiment, the position pattern in which the second offset amount X2 in which the offset amount X is relatively large and the second intrusion amount Y2 in which the intrusion amount Y is relatively small is set as the home position. Has been done. Therefore, for example, when the image forming apparatus 100 goes to sleep after the previous job, the position pattern is the home position regardless of the position pattern in the previous job. The control unit 150 uses the current position pattern information of the inner roller 32 and the pressing member 39 as the position pattern information stored in the memory 152 at the end of the previous job or the like, or information on whether or not the sleep state has occurred. It can be obtained from such as.

When the control unit 150 determines in S103 that the change is necessary, the control unit 150 sends a control signal to the position change motor 113 to change the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (intrusion amount Y). ("Position change operation") (S104). On the other hand, when the control unit 150 determines in S103 that the change is not necessary, the processing of S105 is performed without changing the position of the inner roller 32 (offset amount X) and the position of the pressing member 39 (penetration amount Y). Proceed to. Then, the control unit 150 performs a printing operation with a position pattern corresponding to the recording material S used in this job (S105). The position change operation is completed by the time the recording material S reaches the secondary transfer nip N2. As described above, the position changing operation may be performed in either a state in which the outer roller 41 is in contact with the intermediate transfer belt 31 or in a state in which the outer roller 41 is separated from the intermediate transfer belt 31. Further, as described above, the position changing operation may be performed in either the state where the intermediate transfer belt 31 is stopped or the state where the intermediate transfer belt 31 is rotating. When starting the job, typically, the outer roller 41 is separated from the intermediate transfer belt 31 and the intermediate transfer belt 31 is stopped before the feeding of the recording material S is started. The position change operation is performed. Further, for example, when a plurality of types of recording materials S are mixed in the recording material S used in one job, the position changing operation can be performed in the inter-paper process. In this case, typically, in a state where the outer roller 41 is in contact with the intermediate transfer belt 31 and the intermediate transfer belt 31 is rotating, the preceding recording material S finishes passing through the secondary transfer nip N2. The position change operation is performed until the subsequent recording material S reaches the secondary transfer nip N2.

8. Effect As described above, according to the present embodiment, in the case of "thick paper", while improving the separability of the recording material S from the intermediate transfer belt 31 in the case of "thin paper" and suppressing "roughness". It is possible to suppress the "scattering" of. Therefore, for a wide variety of recording materials S, good transportability of the recording material S in the vicinity of the secondary transfer nip N2 is obtained, and image defects occurring in the vicinity of the secondary transfer nip N2 are suppressed, which is good. Images can be formed. That is, good transfer performance for various recording materials S can be obtained.

[Example 2]
Next, other examples of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of the present embodiment, the elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof will be given. Omit. Further, in this embodiment, as in the case of the first embodiment, a case where "thin paper" is used as an example of the recording material S having a small rigidity and "thick paper" is used as an example of the recording material S having a large rigidity will be described as an example.

In the first embodiment, the image forming apparatus 100 is configured to change the offset distance X by changing the position of the inner roller 32. On the other hand, in the present embodiment, the image forming apparatus 100 is configured to change the offset amount X by changing the position of the outer roller 41.

7 (a) and 7 (b) show that the vicinity of the secondary transfer nip N2 in this embodiment is substantially parallel to the rotation axis direction from one end side (front side of the paper surface in FIG. 1) of the inner roller 32 in the rotation axis direction. It is a schematic side view of the main part seen in. 7 (a) and 7 (b) show the configuration of one end of the inner roller 32 in the rotation axis direction, but the configuration of the other end is the same (with respect to the center of the inner roller 32 in the rotation axis direction). (Approximately symmetric). FIG. 7 (a) shows the state in the case of “thick paper”, and FIG. 7 (b) shows the state in the case of “thin paper”.

In this embodiment, the outer roller 41 is directed toward the inner roller 32 along a predetermined first direction (for example, a direction substantially orthogonal to the reference line L1 described above) as in the first embodiment (FIG. 7A). , (B) In the direction of the white arrow) and in the opposite direction. Further, in the present embodiment, the outer roller 41 is independent of the first direction and has a predetermined second direction intersecting the first direction (for example, a direction substantially parallel to the reference line L1 described above). The recording material S can be slidably moved in the direction toward the downstream side in the transport direction (direction of the middle black arrow in FIG. 7 (a)) and the opposite direction (direction of the middle black arrow in FIG. 7 (b)).

In this embodiment, the support member 132 that supports the bearing 43 of the outer roller 41 so as to be slidable along the first direction is the frame of the apparatus main body 100a so that the support member 132 can be slidably slidable in the second direction. It is supported by such as. Further, the support member 132 is configured to slide and move by the action of the third cam 131 as an operating member. The third cam 131 is supported by a frame or the like of the apparatus main body 100a so as to be rotatable about the third cam rotation shaft 130. The third cam 131 can rotate about the third cam rotation shaft 130 by receiving a drive from the offset motor 133 as a drive source. Further, the third cam 131 is in contact with the third cam follower 132a provided on the support member 132. Further, the support member 132 is composed of a compression spring or the like which is an urging member (elastic member) as an urging means so that the third cam follower 132a slides in the direction of engaging with the third cam 131. It is urged by the offset spring 134. As described above, in this embodiment, the offset mechanism 1 includes a support member 134, a third cam 131, a third cam rotation shaft 130, an offset motor 133, an offset spring 134, and the like.

In this embodiment, as in the first embodiment, the pressing mechanism 2 includes a pressing member holder 40, a second cam 112, a second cam rotating shaft (corresponding to the cam rotating shaft in the first embodiment) 110, and a pressing motor. (Corresponding to the position change motor in the first embodiment) 113 and the like are included. Further, in this embodiment, the control unit 150 sends a control signal to the pressing motor 113 and the offset motor 133 to execute the position changing operation. In this way, the offset mechanism 1 and the pressing mechanism 2 can be driven by separate actuators.

As shown in FIG. 7A, in the case of "thick paper", the third cam 131 is driven by the offset motor 133 and rotates, for example, counterclockwise. Then, the support member 132 slides in the direction toward the downstream side in the transport direction of the recording material S (in the direction of the black arrow in the figure) by the urging force of the offset spring 134, and the relative position of the outer roller 41 with respect to the inner roller 32 is determined. Be done. As a result, the outer roller 41 is arranged at the position of the first outer roller, which is the first offset amount X1 in which the offset amount X is relatively small. As a result, as described in the first embodiment, deterioration of the image quality of the rear end portion of the "thick paper" in the transport direction can be suppressed. Further, in synchronization with the operation of the offset mechanism 1, the pressing mechanism 2 operates in the same manner as in the first embodiment, and at the position of the first pressing member, which is the first intrusion amount Y1 in which the intrusion amount Y is relatively large. , The pressing member 39 is arranged. In this embodiment, at this time, the tip of the pressing member 39 comes into contact with the inner peripheral surface of the intermediate transfer belt 31 near the inlet of the secondary transfer nip N2, and the intermediate transfer belt 31 is projected toward the outer peripheral surface side (first). Penetration amount Y1> 0 mm). As a result, as described in Example 1, "scattering" can be suppressed.

Further, as shown in FIG. 7B, in the case of "thin paper", the third cam 131 is driven by the offset motor 133 and rotates, for example, clockwise. Then, the support member 132 slides in the direction toward the upstream side (black arrow in the figure) of the recording material S against the urging force of the offset spring 134, and the position of the outer roller 41 relative to the inner roller 32. Is decided. As a result, the outer roller 41 is arranged at the position of the second outer roller, which is the second offset amount X2 in which the offset amount X is relatively large. As a result, as described in Example 1, the separability of the "thin paper" from the intermediate transfer belt 31 after passing through the secondary transfer nip N2 is improved. Further, in synchronization with the operation of the offset mechanism 1, the pressing mechanism 2 operates in the same manner as in the first embodiment, and at the position of the second pressing member, which is the second intrusion amount Y2 in which the intrusion amount Y is relatively small. , The pressing member 39 is arranged. In this embodiment, at this time, the tip of the pressing member 39 is separated from the inner peripheral surface of the intermediate transfer belt 31 (second penetration amount Y2 = 0 mm).

Here, tentatively, the outer roller 41 is the second pressing member shown in FIG. 7 (b) while the pressing member 39 is arranged at the position of the first pressing member (first intrusion amount Y1) shown in FIG. 7 (a). Consider the case where it is arranged at the outer roller position (second offset amount X2). In this case, the distance between the pressing member 39 and the outer roller 41 becomes shorter, and the intermediate transfer belt 31 and the recording material S are sandwiched between the pressing member 39 and the outer roller 41. As a result, image defects, so-called “roughness”, occur in which the toner image is disturbed by frictional force before the recording material S rushes into the secondary transfer nip N2. On the other hand, in this embodiment, as shown in FIG. 7B, the pressing member is synchronized with the outer roller 41 being arranged at the second outer roller position (second offset amount X2). 39 is arranged at the position of the second pressing member (second penetration amount Y2), particularly at a position away from the intermediate transfer belt 31. As a result, the outer roller 41 and the pressing member 39 do not sandwich the intermediate transfer belt 31 and the recording material S, and "roughness" can be suppressed.

As described in the first embodiment, the pressing member 39 is not limited to the sheet-shaped member, and the offset amount X and the intrusion amount Y are not limited to those of the present embodiment. do not have.

As described above, the same effect as that of the first embodiment can be obtained by the configuration of the present embodiment. However, in this embodiment, since the outer roller 41 needs to be movable in two directions, the configuration of the first embodiment is more advantageous for simplification and miniaturization of the configuration of the apparatus than the configuration of the present embodiment. It can be said that.

[Example 3]
Next, other examples of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of the present embodiment, the elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof will be given. Omit.

In the first embodiment, the outer roller 41 that directly contacts the outer peripheral surface of the intermediate transfer belt 31 is used as the outer member that forms the secondary transfer nip N2 together with the inner roller 32 as the inner member. On the other hand, in this embodiment, an outer roller and a secondary transfer belt stretched between the outer roller and another roller are used as the outer member.

FIG. 8 is an outline of a main part in which the vicinity of the secondary transfer nip N2 in this embodiment is viewed from one end side (front side of the paper surface in FIG. 1) of the inner roller 32 in the rotation axis direction substantially parallel to the rotation axis direction. It is a side view. In this embodiment, the image forming apparatus 100 has, as an outer member, a tension roller 46, an outer roller 41, and a secondary transfer belt 45 stretched between these rollers. Then, the outer roller 41 comes into contact with the outer peripheral surface of the intermediate transfer belt 31 via the secondary transfer belt 45. That is, the intermediate transfer belt 31 and the secondary transfer belt 45 are sandwiched between the inner roller 32 that contacts the inner peripheral surface of the intermediate transfer belt 31 and the outer roller 41 that contacts the inner peripheral surface of the secondary transfer belt 45. The secondary transfer nip N2 is formed by. In this embodiment, the contact portion between the intermediate transfer belt 31 and the secondary transfer belt 45 is the secondary transfer nip N2 as the secondary transfer portion.

Also in this embodiment, the offset amount X is defined by the relative position of the inner roller 32 and the outer roller 41 as in the first embodiment. Further, the penetration amount Y is also the reference line L1 formed by the inner roller 32 and the pre-secondary transfer roller 37 and the tangent line L4 of the pressing portion, or the reference line L1 formed by the outer roller 41 and the pre-secondary transfer roller 37. 'And the tangent line L4' of the pressing portion are defined in the same manner as in the first embodiment. Further, the configuration and operation of the offset mechanism 1 and the pressing mechanism 2 in this embodiment are the same as those in the first embodiment. Further, also in this embodiment, as in the first embodiment, the outer roller 41 is moved in the direction away from and closer to the inner roller 32 to separate and abut the secondary transfer belt 45 with respect to the intermediate transfer belt 31. A disengagement mechanism 3 may be provided.

Even when the outer roller and the secondary transfer belt stretched between the outer roller and another roller are used as the outer member as in the present embodiment, the outer roller 32 is external to the inner roller 32 as in the second embodiment. The offset amount X can be changed by changing the position of the material.

As described above, the same effects as those of Examples 1 and 2 can be obtained by the configuration of this Example. Further, in this embodiment, it is possible to improve the transportability of the recording material S passing through the secondary transfer nip N2.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

In the above-described embodiment, the information on the basis weight of the recording material is used as the information regarding the type of the recording material related to the rigidity of the recording material, but the information is not limited thereto. If the paper type category (for example, paper type category based on surface properties such as plain paper and coated paper) or brand (including manufacturer, product number, etc.) is the same, the basis weight of the recording material and the thickness of the recording material Are often in a substantially proportional relationship (the larger the thickness, the larger the basis weight). Further, when the paper type category or brand is the same, the rigidity of the recording material and the basis weight or thickness of the recording material are often in a substantially proportional relationship (the larger the basis weight or thickness, the greater the rigidity. ). Therefore, for example, for each paper type category, each brand, or for each combination of the paper type category and the brand, the position pattern (combination of offset amount and penetration amount) is based on the basis weight, thickness, or rigidity of the recording material. Pattern) can be set. Then, the control unit responds to the recording material based on the information such as the paper type category and brand input from the operation unit or the external device and the information such as the basis weight, thickness, and rigidity of the recording material. The offset mechanism and the pressing mechanism can be operated in synchronization so as to have a vertical position pattern. Further, the information regarding the type of recording material is not limited to using, for example, quantitative information such as the basis weight, thickness, or rigidity of the recording material. As information on the type of recording material, for example, only qualitative information such as a paper type category, a brand, or a combination of a paper type category and a brand can be used. For example, a position pattern is set according to the paper type category, the brand, or the combination of the paper type category and the brand, and the control unit uses the information such as the paper type category and the brand input from the operation unit or the external device. The position pattern can be determined accordingly. In this case as well, the position pattern is assigned based on the difference in the rigidity of each recording material. The rigidity of the recording material can be represented by Garley rigidity (MD / vertical grain) [mN], and can be measured with a commercially available Garley rigidity tester. For example, the Garley rigidity (MD) of an example of "thin paper" as a recording material having a basis weight threshold of ^{less than 52 g / m 2 in the above-described embodiment may be about 0.3 mN.} Further, the Garley rigidity (MD) of an example of "plain paper" ( ^{about 80 g / m 2} ) as a recording material having a basis weight threshold of 52 g / m ^{2 or more in the above-described embodiment is about 2 mN, "thick paper".} The Garley rigidity (MD) of an example (with a basis weight of ^{about 200 g / m 2) may be about 20 mN.}

Further, in the above-described embodiment, the control unit has been described as acquiring information on the type of recording material based on the input from the operation unit or the external device operated by the operator, but the information on the type of recording material has been described. It may be acquired based on the input of the detection result of the detection means for detecting. For example, a basis weight sensor can be used as a basis weight detecting means for detecting an index value that correlates with the basis weight of the recording material. As the basis weight sensor, for example, a basis weight sensor using the attenuation of ultrasonic waves is known. This basis weight sensor has an ultrasonic wave generating unit and an ultrasonic wave receiving unit arranged so as to sandwich the transport path of the recording material. Then, the basis weight sensor receives the ultrasonic waves generated from the ultrasonic wave generating unit and attenuated by passing through the recording material at the ultrasonic wave receiving unit, and the basis weight of the recording material is based on the attenuation amount of the ultrasonic waves. Detects an index value that correlates with. The basis weight detecting means may be any one that can detect an index value that correlates with the basis weight of the recording material, and is not limited to the one using ultrasonic waves, for example, the one using light. May be good. Further, the index value that correlates with the basis weight of the recording material is not limited to the basis weight itself, and may be a thickness corresponding to the basis weight. Further, a surface sensor can be used as a smoothness detecting means for detecting an index value that correlates with the smoothness of the surface of the recording material that can be used for detecting the paper type category. As a surface sensor, a specularly reflected light sensor is known in which a recording material is irradiated with light and the intensity of the specularly reflected light and the diffusely reflected light is read by a light amount sensor. When the surface of the recording material is smooth, the specularly reflected light becomes strong, and when it is rough, the diffusely reflected light becomes strong. Therefore, the surface sensor can detect an index value that correlates with the smoothness of the surface of the recording material by measuring the amount of specularly reflected light and the amount of diffusely reflected light. The smoothness detecting means may be any as long as it can detect an index value that correlates with the smoothness of the surface of the recording material, and is not limited to the one using the above-mentioned light amount sensor. For example, an image sensor is used. It may have been. The index value that correlates with the smoothness of the surface of the recording material is not limited to the value converted into a value that conforms to a predetermined standard such as Beck smoothness, but is a value that correlates with the smoothness of the surface of the recording material. Anything is fine. These detection means can be arranged adjacent to the transport path of the recording material upstream of the resist roller in the transport direction of the recording material, for example. Further, for example, a media sensor in which the basis weight sensor, surface sensor and the like are configured as one unit may be used.

Further, in the above-described embodiment, an actuator for operating the movable portion by a cam is used as the offset mechanism, the pressing mechanism, and the detaching mechanism, but the present invention is not limited to this. The offset mechanism, the pressing mechanism, and the detaching mechanism may be any one that can realize the operation according to the above-described embodiment, and for example, an actuator that operates the movable portion by using a solenoid may be used.

Further, in the above-described embodiment, the configuration in which either the inner roller or the outer roller is moved has been described, but both the inner roller and the outer roller may be moved to change the offset amount.

Further, in the above-described embodiment, the case where the belt-shaped image carrier is an intermediate transfer belt has been described, but the image carrier is composed of an endless belt that conveys the toner image supported at the image forming position. If so, the present invention can be applied. Examples of such a belt-shaped image carrier include a photoconductor belt and an electrostatic recording dielectric belt, in addition to the intermediate transfer belt in the above-described embodiment.

The present invention can also be implemented in another embodiment in which a part or all of the configuration of the above-described embodiment is replaced with an alternative configuration thereof. Therefore, if it is an image forming apparatus using a belt-shaped image carrier, it can be carried out without distinction between a tandem type / 1 drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, and a fixing method. In the above-described embodiment, the main part related to the formation / transfer of the toner image has been mainly described, but the present invention includes a printer, various printing machines, a copying machine, and a fax machine by adding necessary equipment, equipment, and a housing structure. , Multifunction machine, etc., can be implemented in various applications.

1 Offset mechanism 2 Pressing mechanism 3 Separation mechanism 31 Intermediate transfer belt 32 Inner roller 37 Secondary transfer pre-roller 39 Pressing member 41 Outer roller 83 Transport guide S Recording material X Offset amount Y Intrusion amount

Claims (19)

A rotatable endless belt that conveys the toner image,
A plurality of tensioning rollers for tensioning the belt, including an inner roller and an upstream roller arranged adjacent to the inner roller upstream of the inner roller in the rotation direction of the belt. With a tension roller,
An outer roller, which is arranged to face the inner roller and abuts on the outer peripheral surface of the belt to form a transfer portion for transferring a toner image from the belt to a recording material.
With a pressing member capable of contacting the inner peripheral surface of the belt with respect to the rotation direction of the belt upstream of the inner roller and downstream of the upstream roller, and pressing the belt from the inner peripheral surface side to the outer peripheral surface side. ,
First, the position of the transfer portion is changed by changing the position of at least one of the inner roller or the outer roller to change the relative position between the inner roller and the outer roller with respect to the circumferential direction of the inner roller. Position change mechanism and
A second position changing mechanism for changing the position of the pressing member and
A control unit that controls the first position change mechanism and the second position change mechanism, and
Have,
In a cross section substantially orthogonal to the rotation axis direction of the inner roller, the common tangent line between the inner roller and the upstream roller on the side on which the belt is hung passes through the reference line L1 and the rotation center of the inner roller, and the reference. A straight line substantially orthogonal to the line L1 is the inner roller center line L2, a straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is the outer roller center line L3, the inner roller center line L2 and the outer roller center line. When the distance from L3 is an offset amount X (however, a positive value when the outer roller center line L3 is on the upstream side of the inner roller center line L2 in the rotation direction of the belt),
When the offset amount X is the first offset amount X1, the control unit presses the inner peripheral surface of the belt, and the offset amount X is larger than the first offset amount X1. When the second offset amount X2 (> 0), the image forming apparatus is characterized in that the second position changing mechanism is controlled so that the pressing member is separated from the inner peripheral surface of the belt. The image forming apparatus according to claim 1, wherein when the offset amount X is the first offset amount X1, the penetration amount Y of the pressing member with respect to the belt is changeable. A rotatable endless belt that conveys the toner image,
A plurality of tensioning rollers for tensioning the belt, including an inner roller and an upstream roller arranged adjacent to the inner roller upstream of the inner roller in the rotation direction of the belt. With a tension roller,
An outer roller, which is arranged to face the inner roller and abuts on the outer peripheral surface of the belt to form a transfer portion for transferring a toner image from the belt to a recording material.
With a pressing member capable of contacting the inner peripheral surface of the belt with respect to the rotation direction of the belt upstream of the inner roller and downstream of the upstream roller, and pressing the belt from the inner peripheral surface side to the outer peripheral surface side. ,
First, the position of the transfer portion is changed by changing the position of at least one of the inner roller or the outer roller to change the relative position between the inner roller and the outer roller with respect to the circumferential direction of the inner roller. Position change mechanism and
A second position changing mechanism for changing the position of the pressing member and
A control unit that controls the first position change mechanism and the second position change mechanism, and
Have,
In a cross section substantially orthogonal to the rotation axis direction of the inner roller, the common tangent line between the inner roller and the upstream roller on the side on which the belt is hung passes through the reference line L1 and the rotation center of the inner roller, and the reference. A straight line substantially orthogonal to the line L1 is the inner roller center line L2, a straight line passing through the rotation center of the outer roller and substantially orthogonal to the reference line L1 is the outer roller center line L3, the inner roller center line L2 and the outer roller center line. When the distance from L3 is an offset amount X (however, a positive value when the outer roller center line L3 is on the upstream side of the inner roller center line L2 in the rotation direction of the belt),
When the offset amount X is the first offset amount X1, the control unit sets the penetration amount Y of the pressing member to the belt to the first penetration amount Y1, and the offset amount X is the first offset amount X. When the second offset amount X2 (> 0) is larger than the offset amount X1, the second position changing mechanism is controlled so that the intrusion amount Y is smaller than the first intrusion amount Y1. An image forming apparatus characterized in that. When the offset amount X is the first offset amount X1, the intrusion amount Y is configured to be changeable.
The control unit is set when the offset amount X is the second offset amount X2 and the intrusion amount Y is set when the offset amount X is the first offset amount X1. The image forming apparatus according to claim 3, wherein the second position changing mechanism is controlled so as to be smaller than the minimum value of the intrusion amount Y. The image forming apparatus according to any one of claims 1 to 4, wherein the first offset amount X1 is a negative value. It has an input unit for inputting information about the recording material, and has an input unit.
Any of claims 1 to 5, wherein the control unit controls the first position changing mechanism and the second position changing mechanism based on the information about the recording material input by the input unit. The image forming apparatus according to claim 1. Based on the information on the basis weight of the recording material input by the input unit, the control unit has the offset amount X as the first offset amount when the basis weight of the recording material is the first basis weight. X1, when the basis weight of the recording material is a second basis weight smaller than the first basis weight, the first position change mechanism is provided so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 6, wherein the image forming apparatus is controlled. Based on the information on the thickness of the recording material input by the input unit, the control unit has the offset amount X being the first offset amount when the thickness of the recording material is the first thickness. X1, when the thickness of the recording material is a second thickness smaller than the first thickness, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 6. Based on the information on the rigidity of the recording material input by the input unit, the control unit sets the offset amount X to the first offset amount X1 when the rigidity of the recording material is the first rigidity. When the rigidity of the recording material is the second rigidity smaller than the first rigidity, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 6. Based on the information of the category of the recording material input by the input unit, the control unit has the offset amount X of the first offset amount X1 when the category of the recording material is the first category. When the category of the recording material is the second category having a rigidity smaller than that of the recording material of the first category, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 6, wherein the image forming apparatus is used. Based on the information of the brand of the recording material input by the input unit, the control unit has the offset amount X of the offset amount X1 and the recording material when the brand of the recording material is the first brand. When the brand is a second brand having a rigidity smaller than that of the recording material of the first brand, the first position changing mechanism is controlled so that the offset amount X becomes the second offset amount X2. The image forming apparatus according to claim 6. The image forming apparatus according to any one of claims 1 to 11, wherein the outer roller directly abuts on the outer peripheral surface of the belt. One of claims 1 to 11, wherein the outer roller comes into contact with the outer peripheral surface of the belt via another endless belt stretched between the outer roller and the other roller. The image forming apparatus according to. When the image forming apparatus is in the sleep state or the main power supply is turned off, the position of the pressing member is set to the position when the offset amount is the second offset amount X2. The image forming apparatus according to any one of claims 1 to 13. The first position changing mechanism is characterized in that the position of the inner roller is changed to change the relative position between the inner roller and the outer roller with respect to the circumferential direction of the inner roller. The image forming apparatus according to any one of the following items. The image forming apparatus according to claim 15, wherein the first position changing mechanism and the second position changing mechanism are driven by one drive source. A rotatable first support member that supports the inner roller and a first cam that rotates the first support member, which constitute the first position change mechanism.
A rotatable second support member that supports the pressing member, a second cam that rotates the second support member, and a second cam that constitutes the second position change mechanism.
A rotatable rotating shaft to which the first and second cams are fixed, which constitutes the first and second position changing mechanisms, and
Have,
The image forming apparatus according to claim 16, wherein the drive source generates a driving force for rotating the rotation shaft. The invention according to any one of claims 1 to 17, wherein a guide member for guiding the recording material is provided in the transfer portion upstream of the transfer portion in the transport direction of the recording material. Image forming device. The belt is characterized in that it is an intermediate transfer body that transports a toner image primaryly transferred from an image carrier for secondary transfer to a recording material by the transfer unit. The image forming apparatus according to any one of 18.

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