Image forming device

Abstract

To improve the exchangeability of a pressing member in a configuration in which the amount of pressing of the pressing member against a belt is variable.SOLUTION: In an image forming apparatus 100 having a belt unit 3 including a pressing member 70 for a belt 31 and a moving mechanism 2 for the pressing member 70, the moving mechanism 2 includes a support part 71 for the pressing member 70, contact parts 80c for moving the support part 71, and a driving part 81, and an upstream side moving mechanism 2a including the contact parts 80c and the driving part 81 and a downstream side moving mechanism 2b including the support part 71 are separable from each other. The belt unit 3 is detachably attached with a pressing member unit 7 including the pressing member 70 and the downstream side moving mechanism 2b. The image forming apparatus 100 has a separation mechanism 3b for separating the support part 71 and the contact parts 80c from each other. The pressing member unit 7 is configured to be moved along the rotation axis direction of an inner roller 32 and removed from the belt unit 3 with the support part 71 separated from the contact parts 80c by the separation mechanism 3b.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, printing machine, copying machine, facsimile machine, or multifunction machine having multiple functions of these, which uses an electrophotographic system or an electrostatic recording system. [Background technology]

[0002] Conventionally, some image forming apparatuses using electrophotography or the like have a rotatable endless belt (hereinafter simply referred to as a "belt") as an image carrier that carries and transports a toner image. For example, such a belt is an intermediate transfer belt that serves as a second image carrier and transports a toner image that has been primarily transferred from a photosensitive member or the like as a first image carrier onto a sheet-like recording material such as paper for secondary transfer. The following description mainly focuses on an image forming apparatus that employs an intermediate transfer method and has an intermediate transfer belt.

[0003] In an image forming apparatus using an intermediate transfer belt, a toner image formed on a photosensitive element or the like in an image forming unit is primarily transferred to the intermediate transfer belt in a primary transfer unit. The toner image primarily transferred to the intermediate transfer belt is then secondarily transferred to a recording material in a secondary transfer unit. The secondary transfer unit is formed by an inner member (inner secondary transfer member) provided on the inner circumferential surface of the intermediate transfer belt and an outer member (outer secondary transfer member) provided on the outer circumferential surface of the intermediate transfer belt. The inner member is an inner secondary transfer roller, which is one of multiple tension rollers that tension the intermediate transfer belt. The outer member is often an outer secondary transfer roller, which is positioned opposite the inner secondary transfer roller across the intermediate transfer belt and pressed against the inner secondary transfer roller. A voltage of opposite polarity to the toner charge polarity is applied to the outer secondary transfer roller (or a voltage of the same polarity as the toner charge polarity is applied to the inner secondary transfer roller), thereby secondarily transferring the toner image on the intermediate transfer belt to the recording material in the secondary transfer unit. Note that with respect to the recording material, the "leading edge" and "trailing edge" refer to the leading edge and trailing edge, respectively, in the conveyance direction of the recording material. Also, the upstream of the secondary transfer unit in the rotation direction of the intermediate transfer belt (the direction of movement of the surface) is simply referred to as "upstream of the secondary transfer unit."

[0004] To transfer the toner image formed on the intermediate transfer belt to the recording material with high accuracy, the contact length between the intermediate transfer belt and the recording material in the direction of rotation of the intermediate transfer belt upstream of the secondary transfer unit is important. If the contact length is long, image defects may occur due to the toner rubbing against the recording material caused by the speed difference between the intermediate transfer belt and the recording material. On the other hand, if the contact length is short, image defects may occur due to discharge occurring in the gap between the recording material and the intermediate transfer belt. Therefore, the transport orientation of the recording material and the tension layout of the intermediate transfer belt are determined taking into account the contact position of the leading edge of the recording material against the intermediate transfer belt upstream of the secondary transfer unit.

[0005] Meanwhile, in recent years, with the diversification of recording materials, for example, in the commercial printing market, there is a demand for good transfer performance on a wide variety of recording materials, from high-rigidity cardboard to low-rigidity thin paper. In particular, when high-rigidity recording materials such as cardboard are used, the intermediate transfer belt is prone to deformation when the recording material enters the contact position. This can result in the formation of a minute gap between the intermediate transfer belt and the recording material upstream of the secondary transfer unit, which can cause image defects due to electrical discharge in the gap. Therefore, there is a demand for suppressing deformation of the intermediate transfer belt upstream of the secondary transfer unit and for accurately forming the desired shape (posture) of the intermediate transfer belt upstream of the secondary transfer unit.

[0006] Patent Document 1 proposes a configuration in which a flatness correction member is provided upstream of the contact position (tacking position) of the leading edge of the recording material against the intermediate transfer belt in the rotation direction of the intermediate transfer belt, to contact the inner peripheral surface of the intermediate transfer belt and press against the intermediate transfer belt. In Patent Document 1, a flexible baffle plate or an elastic roll is used as the flatness correction member.

[0007] Furthermore, Patent Document 2 proposes a configuration in which the amount of pressure applied to the intermediate transfer belt by a pressing member that contacts the inner circumferential surface of the intermediate transfer belt and presses the intermediate transfer belt is changed depending on the type of recording material. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 9-80926 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-215594 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, by providing a pressing member upstream of the secondary transfer unit that contacts the inner surface of the intermediate transfer belt and presses the intermediate transfer belt, the shape (posture) of the intermediate transfer belt upstream of the secondary transfer unit can be made into a desired shape (posture).

[0010] Because this pressing member may deteriorate due to wear, for example, its lifespan is generally shorter than that of the image forming apparatus itself. Therefore, when operating an image forming apparatus, it is necessary to replace the pressing member, for example, periodically. In an image forming apparatus, the pressing member is included in an intermediate transfer belt unit (hereinafter simply referred to as the "belt unit") that includes an intermediate transfer belt and its tension rollers. Because the lifespan of the pressing member may differ from that of the intermediate transfer belt and its tension rollers, it is desirable for the unit containing the pressing member (herein also referred to as the "pressing member unit") in the belt unit to be replaceable. Furthermore, for example, in image forming apparatuses for commercial printing, the belt unit is large in size and weight due to its characteristics, making it difficult for an operator to remove the belt unit from the image forming apparatus itself. Therefore, it is desirable for the pressing member unit to be replaceable while the belt unit is still installed in the image forming apparatus itself.

[0011] In this case, if a mechanism for adjusting the amount of pressure applied by the pressure member to the intermediate transfer belt is attached to the belt unit, the replacement of the pressure member unit for the belt unit becomes difficult, and there is a risk of damage to the mechanism.

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve the replaceability of a pressing member in a configuration in which the amount of pressing of the pressing member against the belt is variable. [Means for solving the problem]

[0013] The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus including a rotatable endless belt carrying a toner image, a plurality of tension rollers for tensioning the belt, the plurality of tension rollers including an inner roller and an upstream roller disposed adjacent to the inner roller and upstream of the inner roller in the direction of rotation of the belt, a tension applying unit for applying tension to the belt, a pressing member capable of contacting an inner peripheral surface of the belt upstream of the inner roller and downstream of the upstream roller in the direction of rotation of the belt, and a moving unit capable of moving the pressing member so as to change the amount of pressing of the pressing member against the belt. and an outer member disposed opposite the inner roller and forming a transfer section that contacts the outer peripheral surface of the belt to transfer a toner image from the belt to a recording material, the movement mechanism includes a movable support section that supports the pressing member, a movable contact section that contacts the support section to move the support section, and a drive section that moves the contact section, and an upstream movement mechanism including the contact section and the drive section and a downstream movement mechanism including the support section are separable, and the belt unit is configured to move the pressing member and the upstream movement mechanism of the movement mechanism. side Moving mechanism and the downstream side The image forming apparatus is characterized in that a pressing member unit equipped with only the downstream moving mechanism among the moving mechanisms is detachable, the image forming apparatus has a separation mechanism that separates the support portion and the contact portion, and the pressing member unit is configured to be moved along the rotational axis direction of the inner roller and removed from the belt unit when the support portion is separated from the contact portion by the separation mechanism. [Effects of the Invention]

[0014] According to the present invention, it is possible to improve the replaceability of the pressing member in a configuration in which the amount of pressing of the pressing member against the belt is variable. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic perspective view illustrating a support structure for a belt unit. [Figure 3] FIG. 10 is a schematic cross-sectional view of the periphery of a secondary transfer unit when a pressing member is provided. [Figure 4] FIG. 2 is a perspective view of a pressing member and a moving mechanism in the first embodiment. [Figure 5] FIG. 2 is a cross-sectional side view of the periphery of a secondary transfer portion in the first embodiment. [Figure 6] FIG. 2 is a perspective view of a secondary transfer internal unit in the first embodiment. [Figure 7] 4 is a cross-sectional side view for explaining the operation of the moving mechanism in the first embodiment. FIG. [Figure 8] 10 is a cross-sectional side view for explaining the operation of the moving mechanism in the second embodiment. FIG. [Figure 9] FIG. 11 is a perspective view of a pressing member and a moving mechanism in the third embodiment. [Figure 10] FIG. 11 is a cross-sectional side view of the periphery of a secondary transfer portion in a third embodiment. [Figure 11] FIG. 11 is a perspective view of a pressing member and a moving mechanism in a modified example of the third embodiment. [Figure 12] FIG. 11 is a perspective view of a pressing member and a moving mechanism according to another modified example of the third embodiment. [Figure 13] FIG. 2 is a schematic block diagram showing a control mode of a main part of the image forming apparatus. [Figure 14] FIG. 10 is a schematic cross-sectional view of the periphery of the secondary transfer unit when no pressing member is provided. DETAILED DESCRIPTION OF THE INVENTION

[0016] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0017] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotation axis direction of a photosensitive drum 11 and a tension roller for an intermediate transfer belt 31, which will be described later) of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem printer that employs an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a sheet-like recording material P made of paper, plastic, or the like using an electrophotographic method in response to an image signal (image information) transmitted from an external device such as a personal computer.

[0018] Image forming apparatus 100 has four image forming units (stations), namely, image forming units 1Y, 1M, 1C, and 1K, which form images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. These image forming units 1Y, 1M, 1C, and 1K are arranged in a row along the direction of movement of the image transfer surface of intermediate transfer belt 31, which is arranged substantially horizontally, as described below. Elements in each image forming unit 1Y, 1M, 1C, and 1K that have the same or corresponding functions or configurations may be generally described by omitting the Y, M, C, or K suffix to the reference numeral indicating that the element is for one of the colors. In this embodiment, the image forming unit 1 is configured to include photosensitive drums 11 (11Y, 11M, 11C, 11K), chargers 12 (12Y, 12M, 12C, 12K), exposure devices 13 (13Y, 13M, 13C, 13K), developing devices 14 (14Y, 14M, 14C, 14K), primary transfer rollers 37 (37Y, 37M, 37C, 37K), cleaning devices 15 (15Y, 15M, 15C, 15K), etc., which will be described later.

[0019] The image forming apparatus 100 includes a photosensitive drum 11, a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as a first image carrier for carrying a toner image. The photosensitive drum 11 receives a driving force from a drum drive motor (not shown) as a drive source, and is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise) in FIG. 1 . The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charger 12 as a charging means. During charging, a predetermined charging voltage (charging bias) is applied to the charger 12 by a charging power supply (not shown). The charged surface of the photosensitive drum 11 is scanned and exposed by an exposure device 13 as an exposure means in accordance with an image signal, forming an electrostatic image (electrostatic latent image) on the photosensitive drum 11. In this embodiment, the exposure device 13 is a laser scanner that irradiates the photosensitive drum 11 with laser light modulated in accordance with the image signal. The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by the developing device 14 as a developing means, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 11. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 11 (negative polarity in this embodiment) adheres to the exposed portion (image portion) of the photosensitive drum 11, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development method). During development, a predetermined development voltage (developing bias) is applied by a development power supply (not shown) to the developing roller, which serves as a developer carrier, of the developing device 14. In this embodiment, the normal charge polarity of the toner during development is negative polarity.

[0020] An intermediate transfer belt 31, which is a rotatable intermediate transfer body formed of an endless belt and serves as a second image carrier that carries a toner image, is disposed facing the four photosensitive drums 11Y, 11M, 11C, and 11K. The intermediate transfer belt 31 is wound around a plurality of tension rollers (support rollers), including a drive roller 33, a tension roller 34, a secondary pre-transfer roller 35, and a secondary inner transfer roller 32, and is stretched with a predetermined tension. The drive roller 33 transmits a driving force to the intermediate transfer belt 31. The drive roller 33 is driven to rotate by a driving force transmitted from a belt drive motor (not shown) serving as a drive source. As a result, the intermediate transfer belt 31 receives driving force from the drive roller 33 and rotates (moves orbitally) in the direction of arrow R2 in FIG. 1 (clockwise direction) at a peripheral speed (process speed) corresponding to the peripheral speed of the photosensitive drums 11. The tension roller 34 applies a predetermined tension to the intermediate transfer belt 31 and controls the tension of the intermediate transfer belt 31 to a constant level. The tension roller 34 is biased at both ends in the direction of its rotation axis from the inner circumferential surface toward the outer circumferential surface of the intermediate transfer belt 31 by tension springs 36, which are compression coil springs serving as biasing members (elastic members) serving as biasing means. The tension springs 36 constitute a tension applying means (tension applying unit) that applies tension to the intermediate transfer belt 31. The secondary transfer pre-roller 35, which serves as an upstream roller, forms the surface of the intermediate transfer belt 31 near the upstream side of the secondary transfer unit N2 (described later) in relation to the rotation direction (surface movement direction) of the intermediate transfer belt 31. In this embodiment, the secondary transfer inner roller (inner member) 32 functions as a secondary transfer member serving as secondary transfer means. The tension rollers other than the drive roller 33 among the multiple tension rollers are driven to rotate in accordance with the rotation of the intermediate transfer belt 31. Further, primary transfer rollers 37Y, 37M, 37C, and 37K, which are roller-shaped primary transfer members serving as primary transfer means, are arranged corresponding to the photosensitive drums 11Y, 11M, 11C, and 11K on the inner peripheral surface side of the intermediate transfer belt 31. In this embodiment, each primary transfer roller 37 is arranged at a position facing each photosensitive drum 11.The primary transfer roller 37 is pressed against the photosensitive drum 11 and abuts against the photosensitive drum 11 via the intermediate transfer belt 31, forming a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 11 and the intermediate transfer belt 31 come into contact. The primary transfer roller 37 is rotated in accordance with the rotation of the intermediate transfer belt 31. A pressing member 70 is provided on the inner circumferential surface of the intermediate transfer belt 31, upstream of the inner secondary transfer roller 32 and downstream of the pre-secondary transfer roller 35 in terms of the rotation direction of the intermediate transfer belt 31. The pressing member 70 and a movement mechanism 2 (FIG. 4) that changes the position of the pressing member 70 will be described in more detail later.

[0021] The toner images formed on the photosensitive drums 11 are transferred (primary transfer) onto the rotating intermediate transfer belt 31 at the primary transfer portion N1 by the action of the primary transfer rollers 37. During the primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer rollers 37 by a primary transfer power supply (not shown). For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are sequentially primary-transferred so as to be superimposed on the same image position (image area) on the intermediate transfer belt 31. In this embodiment, the primary transfer portion N1 is an image forming position where toner images are formed on the intermediate transfer belt 31. The intermediate transfer belt 31 is an example of a rotatable endless belt that transports the toner images carried at the image forming position.

[0022] A secondary transfer outer roller (external member) 41 is disposed on the outer peripheral surface of the intermediate transfer belt 31 at a position facing the secondary transfer inner roller 32. In this embodiment, the secondary transfer outer roller 41 functions as an opposing member (opposing electrode) of the secondary transfer inner roller 32. The secondary transfer outer roller 41 is pressed toward the secondary transfer inner roller 32 and abuts against the secondary transfer inner roller 32 via the intermediate transfer belt 31, forming a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 31 and the secondary transfer outer roller 41 come into contact. The toner image formed on the intermediate transfer belt 31 is transferred (secondary transfer) onto the recording material P being conveyed while being sandwiched between the intermediate transfer belt 31 and the secondary transfer outer roller 41 at the secondary transfer portion N2. In this embodiment, during secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the same polarity (negative in this embodiment) as the normal charging polarity of the toner, is applied to the inner secondary transfer roller 32 by a secondary transfer power supply (not shown). In this embodiment, the outer secondary transfer roller 41 is electrically grounded (connected to ground). Alternatively, the outer secondary transfer roller 41 may be used as a secondary transfer member and a secondary transfer voltage of the opposite polarity to the normal charging polarity of the toner may be applied to it, and the inner secondary transfer roller 32 may be used as an opposing electrode and electrically grounded.

[0023] Recording material (transfer material, sheet, recording medium, media) P is stored in recording material cassettes 61a to 61c serving as recording material storage units. The recording material P stored in recording material cassettes 61a to 61c is sent to a feeding conveying path 63 by rotationally driving any of feeding rollers 62a to 62c, which are feeding members serving as feeding means. This recording material P is conveyed to a registration roller pair 65, which is also a conveying member serving as conveying means, by a conveying roller pair 64, which is also a conveying member serving as conveying means, and is temporarily stopped. By rotationally driving the registration roller pair 65, this recording material P is sent to the secondary transfer unit N2 in synchronization with the toner image on the intermediate transfer belt 31.

[0024] A conveyance guide (pre-transfer guide) for guiding the recording material P to the secondary transfer portion N2 is provided downstream of the pair of registration rollers 65 and upstream of the secondary transfer portion N2 in the conveyance direction of the recording material P. The conveyance guide 66 includes a first guide member 66a that can contact the front surface of the recording material P (the surface onto which the toner image is transferred immediately after passing through the conveyance guide 66) and a second guide member 66b that can contact the back surface of the recording material P (the surface opposite to the front surface). The first guide member 66a and the second guide member 66b are disposed opposite each other, and the recording material P passes between these two members. The first guide member 66a restricts movement of the recording material P toward the intermediate transfer belt 31. The second guide member 66b restricts movement of the recording material P away from the intermediate transfer belt 31.

[0025] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 5 as fixing means by a conveyor belt (pre-fixing conveying device) 67 or the like. The fixing device 5 heats and pressurizes (thermocompression) the recording material P carrying the unfixed toner image by sandwiching it between a pair of fixing rotors and conveying it, thereby fixing (melting and solidifying) the toner image onto the surface of the recording material P. The recording material P onto which the toner image has been fixed passes through a discharge conveying path 68 and is discharged (output) to a discharge tray 69 provided outside (outside) the apparatus main body 110 of the image forming apparatus 100.

[0026] Meanwhile, deposits such as toner remaining on the photosensitive drum 11 after the primary transfer (primary transfer residual toner) are removed from the photosensitive drum 11 by a cleaning device 15 serving as cleaning means and collected. Also, deposits such as toner remaining on the intermediate transfer belt 31 after the secondary transfer (secondary transfer residual toner) are removed from the intermediate transfer belt 31 and collected by a belt cleaning device 38 serving as intermediate transfer body cleaning means.

[0027] In this embodiment, an intermediate transfer belt unit ("belt unit") 3 is configured with the intermediate transfer belt 31, tension rollers 32 to 35, primary transfer rollers 37, belt cleaning device 38, and a support frame 39 (FIG. 2) described later. In this embodiment, the belt unit 3 is further provided with a pressing member 70 and a movement mechanism 2 (FIG. 4) that changes the position of the pressing member 70. In this embodiment, as will be described in detail later, the belt unit 3 can be pulled out from the apparatus body 110 of the image forming apparatus 100 for maintenance. In this embodiment, the secondary transfer internal unit 7 (FIG. 6) including the pressing member 70 can be attached and detached to and from the belt unit 3 for replacement of the pressing member 70, as will be described in detail later.

[0028] The intermediate transfer belt 31 may be made of a single-layer or multi-layer resin material, or may be made of a multi-layer structure including a resin layer made of a resin material and an elastic layer made of an elastic material. In this embodiment, the inner secondary transfer roller 32 is configured with a metal core (core material) and an elastic layer made of electronically conductive rubber provided on the outer periphery thereof. In this embodiment, the pre-secondary transfer roller 35 is configured with a metal roller. In this embodiment, the outer secondary transfer roller 41 is configured with a metal core (core material) and an elastic layer made of ionically conductive foam rubber provided on the outer periphery thereof. In this embodiment, bearing members (not shown) supporting both ends of the outer secondary transfer roller 41 in the rotational axis direction are slidable toward and away from the inner secondary transfer roller 32. The bearing members are pressed toward the inner secondary transfer roller 32 by a pressure spring 42 (FIG. 3) that is a compression coil spring and serves as a biasing member (elastic member) serving as a biasing means. As a result, the outer secondary transfer roller 41 contacts the inner secondary transfer roller 32 with a predetermined pressure across the intermediate transfer belt 31, forming the secondary transfer portion N2. The rotational axes of the tension rollers of the intermediate transfer belt 31, including the inner secondary transfer roller 32, and the outer secondary transfer roller 41 are substantially parallel to each other.

[0029] 2. Belt unit and its supporting structure Next, the belt unit 3 and the support structure of the belt unit 3 in this embodiment will be described. Note that in this embodiment, the front side of the paper in FIG. 1 is the front (front face) side for the image forming apparatus 100 and its elements, and the back side of the paper in FIG. 1 is the rear (rear face) side. The front-to-rear direction connecting the front side and the rear side is assumed to be approximately parallel to the rotation axis direction of the photosensitive drum 11 and the tension roller of the intermediate transfer belt 31. Also, with regard to the image forming apparatus 100 and its elements, "up" and "down" refer to up and down in the direction of gravity (vertical direction), but do not mean only directly above and directly below, but also include above and below a horizontal plane passing through the element or position of interest.

[0030] FIG. 2 is a schematic perspective view of the image forming apparatus 100, seen from the front, showing the support structure for the belt unit 3 and the intermediate transfer belt 31. As shown in FIG. 2(a), in this embodiment, the apparatus body 110 of the image forming apparatus 100 is provided with a support unit 120 as a holding member. The support unit 120 can hold the belt unit 3 at a first position where the toner image can be transferred from the photosensitive drum 11 to the intermediate transfer belt 31. In the first position, the rotation axes of the tension rollers 32-35 and the primary transfer rollers 37 of the intermediate transfer belt 31 are substantially horizontal. The belt unit 3 has a support frame 39 with front and rear plates 39a and 39b, respectively, on both sides in the width direction (the rotation axis direction of the tension rollers 32-35) that is substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 31. Both ends of each of the tension rollers 32 to 35 and each of the primary transfer rollers 37 in the direction of their rotational axis are rotatably supported by a front plate 39a and a rear plate 39b of the support frame 39 via bearing members. The belt unit 3 can be pulled out forward from a housing 110a of the device body 110 of the image forming apparatus 100, for example, when performing maintenance work such as replacing the intermediate transfer belt 31 or the pressing member 70. In this embodiment, when the belt unit 3 is pulled out from the device body 110, it is held in a tiltable manner relative to the support unit 120 in the direction of arrow f (upward) in FIG. 2(b). The support unit 120 can be pulled out forward from the device body 110 and inserted into the device body 110. That is, the support unit 120 is held by slide rails 111 provided in the device body 110 and can be inserted into and pulled out of the device body 110 along the slide rails 111.

[0031] The support unit 120 has a front support portion 120a provided on the front side, a rear support portion 120b provided on the rear side, and a pair of connecting portions 120c, 120c connecting the front support portion 120a and the rear support portion 120b. The belt unit 3 is disposed in a space surrounded by the front support portion 120a, the rear support portion 120b, and the pair of connecting portions 120c, 120c. During maintenance of the belt unit 3, the support unit 120 holding the belt unit 3 is pulled out to the front from the device main body 110 by a user, a service technician, or other worker, as shown in FIG. 2(a). Then, as shown in FIG. 2(b), the worker tilts the belt unit 3 in the direction of arrow f (upward) relative to the support unit 120 and moves it to the second position. 2(a), the belt unit 3 is supported by the support unit 120 by a hinge 3a so as to be rotatable about one end (rear side) of the intermediate transfer belt 31 in the width direction. As shown in FIG. 2(b), the belt unit 3 can be tilted to a second position where the other end (front side) of the intermediate transfer belt 31 in the width direction is exposed above the front support portion 120a of the support unit 120.

[0032] With the belt unit 3 tilted to the second position, an operator operates the release mechanism 3b to release (loosen) the tension applied to the intermediate transfer belt 31. This allows the intermediate transfer belt 31 to be pulled out from the other end (front) of the intermediate transfer belt 31 in the width direction. In this embodiment, with the tension of the intermediate transfer belt 31 released, the secondary transfer internal unit 7 (FIG. 6) including the pressing member 70 can be pulled out from the other end (front) of the intermediate transfer belt 31 in the width direction. The release mechanism 3b is configured to act on the bearing member of the tension roller 34, for example, to move the tension roller 34 from the outer peripheral surface of the intermediate transfer belt 31 toward the inner peripheral surface thereof against the biasing force of the tension spring 36 (FIG. 1). In this manner, in this embodiment, maintenance work such as replacing the intermediate transfer belt 31 or the pressing member 70 can be performed with the belt unit 3 installed in the device body 110 of the image forming apparatus 100. Therefore, maintenance work such as replacement of the intermediate transfer belt 31 and the pressing member 70 can be easily performed.

[0033] In this embodiment, as described above, a hinge 3a with a built-in damper is provided between the rear plate 39b of the support frame 39, which is disposed on the one end (rear side) of the intermediate transfer belt 31 in the width direction, and the rear support portion 120b of the support unit 120. The hinge 3a is configured to damp the moving speed of the belt unit 3 when the belt unit 3 moves from the tilted second position toward the first position due to gravity. A locking mechanism may be further provided to hold the belt unit 3 at the second position. In this embodiment, the hinge 3a and the locking mechanism constitute a rotational holding portion that can hold the belt unit 3 at the second position. Furthermore, protrusions (not shown) provided on the front plate 39a and the rear plate 39b of the support frame 39 are placed on placement portions (not shown) provided on the front support portion 120a and the rear support portion 120b, so that the belt unit 3 is supported by the support unit 120 at the first position.

[0034] 3. Shape of the intermediate transfer belt upstream of the secondary transfer section Next, the shape (posture) of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 will be described. FIG. 3 is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotational axis direction of the inner secondary transfer roller 32) for explaining the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 in the image forming apparatus 100 of this embodiment. FIG. 14 is a schematic cross-sectional view (a cross-section substantially perpendicular to the rotational axis direction of the inner secondary transfer roller 32) for explaining the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 in a comparative example configuration in which the pressing member 70 is not provided. Note that in the comparative example, elements corresponding to those in this embodiment are assigned the same reference numerals. FIG. 3(a) shows a state before the recording material P moves to the secondary transfer portion N2, FIG. 3(b) shows a state after the recording material P moves to the secondary transfer portion N2, and FIG. 3(c) shows an enlarged view of the vicinity of the secondary transfer portion N2 in FIG. 3(b). 14(a), (b), and (c) are diagrams corresponding to FIGS. 3(a), (b), and (c), respectively, for the comparative example.

[0035] 3, in this embodiment, the shape of the intermediate transfer belt 31 is formed by being stretched between the inner secondary transfer roller 32 and the pre-secondary transfer roller 35 (FIG. 1), and the outer secondary transfer roller 41 is elastically biased by a pressure spring 42 toward the inner secondary transfer roller 32. As a result, the intermediate transfer belt 31 is sandwiched between the inner secondary transfer roller 32 and the outer secondary transfer roller 41, forming a secondary transfer portion N2.

[0036] In this embodiment, as will be described in detail later, a pressing member 70 is provided upstream of the secondary transfer portion N2 and adjacent to the inner secondary transfer roller 32. In this embodiment, during image formation (secondary transfer) in at least one predetermined mode, the image forming apparatus 100 maintains a state in which the tip of the pressing member 70 is in contact with the inner circumferential surface of the intermediate transfer belt 31. The pressing member 70 contacts the inner circumferential surface of the intermediate transfer belt 31 and presses the intermediate transfer belt 31 from the inner circumferential surface side toward the outer circumferential surface side. This allows the pressing member 70 to cause the tension surface of the intermediate transfer belt 31, formed between the inner secondary transfer roller 32 and the pre-secondary transfer roller 35, to protrude from the inner circumferential surface side toward the outer circumferential surface side of the intermediate transfer belt 31. In this embodiment, the pressing member 70 is formed of a resin plate-shaped member, and the pressing member 70 elastically biases the intermediate transfer belt 31 by utilizing its flexural elasticity. Therefore, the shape (amount of deflection, amount of deformation) of the pressing member 70 is determined to be a shape (also referred to here as a "static shape") in which the biasing force of the pressing member 70 biasing the intermediate transfer belt 31 is balanced with the resistance force generated by the tension of the intermediate transfer belt 31. The static shape of the pressing member 70 determines the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2.

[0037] Furthermore, in this embodiment, as will be described in detail later, the image forming apparatus 100 is configured to be able to change the position of the pressing member 70 by the action of the movement mechanism 2 (FIG. 4). As a result, in this embodiment, the image forming apparatus 100 is configured to be able to control the static shape of the pressing member 70, i.e., the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2.

[0038] In this embodiment, a bias voltage of the same polarity as the charge polarity of the toner constituting the toner image on the intermediate transfer belt 31 is applied to the inner secondary transfer roller 32, and the outer secondary transfer roller 41 is connected to ground. This forms a transfer electric field at the secondary transfer portion N2. A recording material P is guided by a conveyance guide 66 and conveyed to the secondary transfer portion N2 where the transfer electric field is formed. As shown in FIG. 3A, the leading edge of the recording material P abuts (contacts) the intermediate transfer belt 31 upstream of the secondary transfer portion N2, and is conveyed toward the secondary transfer portion N2 while still in contact with the toner image formed on the surface of the intermediate transfer belt 31. Then, as shown in FIG. 3B, when the recording material P is conveyed to the secondary transfer portion N2, the toner image is transferred from the intermediate transfer belt 31 to the recording material P due to the pressure action between the inner secondary transfer roller 32 and the outer secondary transfer roller 41 and the electrical action of the transfer electric field.

[0039] For high-precision secondary transfer, the length of contact between the intermediate transfer belt 31 and the recording material P in the rotational direction of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 when the recording material P is transported to the secondary transfer portion N2 (also referred to herein as the "contact length") is important. If the contact length is long, image defects may occur due to friction between the toner image formed on the surface of the intermediate transfer belt 31 and the recording material P. On the other hand, if the contact length is short, the gap (gap) G ( FIG. 3( c) ) between the intermediate transfer belt 31 and the recording material P may become large, and image defects may occur due to discharge occurring in the gap G. In particular, when a recording material P with high stiffness, such as cardboard or coated paper, is used, the intermediate transfer belt 31 is likely to deform when the leading edge of the recording material P enters the contact position between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer portion N2. This makes the gap G more likely to occur, which may lead to image defects due to discharge in the gap G.

[0040] By providing the pressing member 70 as in this embodiment, it becomes easier to appropriately set the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer portion N2. In particular, in this embodiment, the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2 can be controlled by variably controlling the position of the pressing member 70 using a movement mechanism 2 (FIG. 4) described later. This allows for optimization of the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer portion N2, thereby enabling stable secondary transfer of the toner image to the recording material P. Furthermore, even when a recording material P with high stiffness, such as cardboard or coated paper, is used, the elastic biasing effect of the pressing member 70 has the following effect. In other words, deformation of the intermediate transfer belt 31 when the recording material P comes into contact with the intermediate transfer belt 31 is suppressed, and an increase in the gap G between the intermediate transfer belt 31 and the recording material P can be suppressed.

[0041] On the other hand, as shown in FIGS. 14(a) to 14(c), if the pressing member 70 is not provided, when the recording material P is conveyed to the secondary transfer portion N2, the intermediate transfer belt 31 may deform upstream of the secondary transfer portion N2, and the gap G between the intermediate transfer belt 31 and the recording material P may become larger. This may cause variations in the contact length between the recording material P and the intermediate transfer belt 31. Furthermore, the larger gap G may cause discharge, resulting in image defects. As described above, this is likely to occur when a recording material P with high stiffness, such as cardboard or coated paper, is used.

[0042] In this way, the image forming apparatus 100 of this embodiment can provide a finished product with stable image quality due to the action of the pressing member 70. In particular, the image forming apparatus 100 of this embodiment can provide a finished product with high image quality due to the action of the pressing member 70, even when a recording material P with high rigidity, such as cardboard or coated paper, is used.

[0043] The image forming apparatus 100 of this embodiment is an apparatus that achieves high productivity, and the intermediate transfer belt 31 is transported at a speed of 600 mm / s. Furthermore, in the image forming apparatus 100 of this embodiment, the toner has a negative polarity. In the image forming apparatus 100 of this embodiment, a high voltage bias of −10 kV is applied to the inner secondary transfer roller 32 to ensure appropriate transfer performance even at this transport speed of the intermediate transfer belt 31. However, the transport speed of the intermediate transfer belt 31, the polarity of the toner, and the value of the secondary transfer voltage are not limited to these.

[0044] 4. Pressing member and moving mechanism Next, the pressing member 70 in this embodiment and the moving mechanism 2 that changes the position of this pressing member 70 will be described. Fig. 4 is a perspective view of the pressing member 70 and the moving mechanism 2 in this embodiment, viewed from the rear. Fig. 5(a) is a cross-sectional side view of the pressing member 70 and the moving mechanism 2 in this embodiment, viewed from the front along the rotational axis of the inner secondary transfer roller 32. Fig. 5(b) is a cross-sectional side view of the pressing member 70 of the belt unit 3 in this embodiment, viewed from the rear along the rotational axis of the inner secondary transfer roller 32, viewed from the rear.

[0045] <Pressing member> In this embodiment, the image forming apparatus 100 includes a pressing member (backup member) 70 on the inner circumferential surface side of the intermediate transfer belt 31, near the upstream side of the secondary transfer portion N2. The pressing member 70 presses the inner circumferential surface of the intermediate transfer belt 31 near the entrance of the secondary transfer portion N2, causing the intermediate transfer belt 31 to bulge outward toward the outer circumferential surface. The pressing member 70 is disposed upstream of the inner secondary transfer roller 32 and downstream of the pre-secondary transfer roller 35 in the rotation direction of the intermediate transfer belt 31 so as to be able to contact the inner circumferential surface of the intermediate transfer belt 31. In particular, in this embodiment, the pressing member 70 is disposed upstream of the inner secondary transfer roller 32 and downstream of the downstream tip of the conveyance guide 66 (first guide member 66a) in the conveyance direction of the recording material P so as to be able to contact the inner circumferential surface of the intermediate transfer belt 31.

[0046] In this embodiment, the pressing member 70 is configured as a plate-like (sheet-like) member that is generally rectangular in plan view, having a predetermined length in both a longitudinal direction disposed generally parallel to the width direction of the intermediate transfer belt 31 and a lateral direction generally perpendicular to the longitudinal direction, and having a predetermined thickness. The lateral direction of the intermediate transfer belt 31 is generally perpendicular to the direction of movement of the surface of the intermediate transfer belt 31 and is generally parallel to the direction of the rotation axis of the inner secondary transfer roller 32. The longitudinal length of the pressing member 70 is equal to the width length of the intermediate transfer belt 31. A free end (tip) 70a of the pressing member 70, which is one end in the lateral direction (the end downstream in the rotation direction of the intermediate transfer belt 31), can contact the inner circumferential surface of the intermediate transfer belt 31 over substantially the entire width of the intermediate transfer belt 31 and can press the intermediate transfer belt 31. In this embodiment, the pressing member 70 has a fixed end (base end) 70b, which is the other end in the width direction (the end on the upstream side in the rotation direction of the intermediate transfer belt 31), partially fixed to an attachment portion 70c by adhesive or the like. In this embodiment, the attachment portion 70c is made of a metal plate having a plate-like portion that is arranged along the width direction of the intermediate transfer belt 31 (the longitudinal direction of the pressing member 70), and is used to attach the pressing member 70 to the movement mechanism 2, which will be described later.

[0047] In this embodiment, the pressing member 70 is formed using a resin material. In particular, in this embodiment, the pressing member 70 is formed of PPS (polyphenylene sulfide) with a thickness of 0.5 mm. In this embodiment, the pressing member 70 elastically biases the intermediate transfer belt 31 by utilizing its flexural elasticity. Note that in this embodiment, the pressing member 70 may be any material that can elastically bias the intermediate transfer belt 31. For example, the thickness of the pressing member 70 is not limited to 0.5 mm, but is preferably approximately 0.4 to 1.5 mm, and may be, for example, 1.0 mm. Furthermore, the material of the pressing member 70 is not limited to PPS, but may also be PEEK (polyether ether ketone), PET (polyethylene terephthalate), or the like.

[0048] Here, it is desirable that the pressing member 70, more specifically, the end portion (herein simply referred to as the "tip") on the side of the free end portion (tip portion) 70a in the widthwise direction of the pressing member 70, be disposed as close as possible to the inner secondary transfer roller 32. However, the pressing member 70 is disposed so as not to come into contact with the inner secondary transfer roller 32. The pressing member 70 is disposed so as to come into contact with the inner circumferential surface of the intermediate transfer belt 31, for example, at a position that is, for example, about 2 mm or more, typically about 10 mm or more, upstream in the rotation direction of the intermediate transfer belt 31 from the position where the inner secondary transfer roller 32 and the intermediate transfer belt 31 contact each other. The pressing member 70 is also disposed so as to come into contact with the inner circumferential surface of the intermediate transfer belt 31, for example, at a position that is, for example, about 40 mm or less, typically about 25 mm or less, upstream in the rotation direction of the intermediate transfer belt 31 from the position where the inner secondary transfer roller 32 and the intermediate transfer belt 31 contact each other.

[0049] <Movement mechanism> In this embodiment, the image forming apparatus 100 has a movement mechanism 2 that changes the position of the pressing member 70. By changing the position of the pressing member 70, the movement mechanism 2 can control the static shape of the pressing member 70, i.e., the shape of the intermediate transfer belt 31 upstream of the secondary transfer portion N2. In other words, by changing the position of the pressing member 70, the movement mechanism 2 can control the amount of pressure that the pressing member 70 applies to the intermediate transfer belt 31. This allows the movement mechanism 2 to optimize the contact length between the intermediate transfer belt 31 and the recording material P upstream of the secondary transfer portion N2.

[0050] The movement mechanism 2 has a support member 71 as a support portion arranged along the width direction of the intermediate transfer belt 31. The pressing member 70 is supported by the support member 71. In this embodiment, a portion of the pressing member 70 on the side of a fixed end 70b in the short side direction is fixed to an attachment portion 70c over substantially the entire width in the longitudinal direction by adhesive or the like, and this attachment portion 70c is fixed to the support member 71 with screws or the like. The pressing member 70 may also be directly fixed to the support member 71. A rotation shaft 73 is provided at each end of the support member 71 in the longitudinal direction. As will be described in detail later, the support member 71 is supported by a front frame 74 and a rear frame 75 ( FIG. 6 ) of the secondary transfer internal unit 7 via the rotation shaft 73 so as to be rotatable about a rotation axis line substantially parallel to the width direction of the intermediate transfer belt 31 around the rotation shaft 73. In this way, by rotating the support member 71 around a rotation axis that is approximately parallel to the width direction of the intermediate transfer belt 31, the pressing member 70 can be rotated around the rotation axis, thereby changing the position of the pressing member 70.

[0051] The moving mechanism 2 also has a cam shaft 80 formed of a cylindrical member extending along the width direction of the intermediate transfer belt 31. As will be described in detail later, the cam shaft 80 is supported by the support frame 39 of the belt unit 3 so as to be rotatable about a rotation axis substantially parallel to the width direction of the intermediate transfer belt 31. The moving mechanism 2 also has a cam 80c, a drive gear 80a, and a flag 80b. The cam 80c, drive gear 80a, and flag 80b are each fixed to the cam shaft 80. The cam 80c is provided at both ends of the cam shaft 80 in the rotational axis direction. The drive gear 80a is provided at the rear end of the cam shaft 80 in the rotational axis direction. The moving mechanism 2 also has a drive motor 81 formed of a stepping motor as a drive source constituting a drive unit, and first and second transmission gears 82 and 83. The drive motor 81 and the first and second transmission gears 82 and 83 are provided on the rear side of the cam shaft 80 in the rotational axis direction. The drive gear 80a is drivingly connected to a drive motor 81 via first and second transmission gears 82 and 83. That is, the output gear 81a fixed to the output shaft of the drive motor 81 meshes with the first transmission gear 82, the first transmission gear 82 meshes with the second transmission gear 83, and the second transmission gear 83 meshes with the drive gear 80a fixed to the cam shaft 80. As will be described in detail later, the drive motor 81 and the first and second transmission gears 82 are supported by a support frame 39 of the belt unit 3. When the drive motor 81 rotates, the drive is transmitted to the cam shaft 80 via the first and second transmission gears 82 and 83 and the drive gear 80a, and the cam 80c and the flag 80b rotate integrally with the cam shaft 80 around a rotation axis that is substantially parallel to the width direction of the intermediate transfer belt 31.

[0052] The cam 80c as a contacting portion comes into contact with the cam follower 71a as a contacted portion provided on the support member 71. The cam 80c forms a non-stepped surface whose radius from the rotation center changes uniformly depending on the rotation angle of the cam 80c. This non-stepped surface as a contacting surface comes into contact with the contacted surface of the cam follower 71a of the support member 71. The cam followers 71a are provided at both ends of the support member 71 in the longitudinal direction. The cams 80c provided at both ends of the camshaft 80 in the rotational axis direction come into contact with the cam followers 71a. Therefore, when the cam 80c rotates as the drive motor 81 rotates, the rotation of the cam 80c causes the support member 71 to rotate about the pivot shaft 73. That is, the rotational drive of the drive motor 81 is transmitted to the cam 80c via the first and second transmission gears 82 and 83 and the drive gear 80a, and the support member 71 is rotated around the rotation shaft 73 via the non-step surface of the cam 80c. As a result, the movement mechanism 2 can move the pressing member 70 and change the position of the pressing member 70. Here, in this embodiment, changing the position of the pressing member 70 means, more specifically, changing the position of the tip of the pressing member 70 when it is assumed that the intermediate transfer belt 31 does not exist (hereinafter, also simply referred to as the "tip position"). Specifically, in this embodiment, changing the position of the pressing member 70 means changing the position of the support member 71, which is a movable moving part of the movement mechanism 2.

[0053] The moving mechanism 2 also has a position sensor (HP sensor) 89 as position detection means for detecting the position (phase) of the cam 80c in the rotational direction, particularly the home position (HP) in the rotational direction of the cam 80c in this embodiment. The position sensor 89 is supported by the support frame 39 of the belt unit 3. The position sensor 89 and a flag 80b fixed to the cam shaft 80 constitute a photointerrupter. The moving mechanism 2 can set its posture to a preset neutral position by the action of the position sensor 89 and the flag 80b.

[0054] The operation of the movement mechanism 2 will be further described with reference to FIG. 5(a). For example, when the pressing member 70 is moved in a direction to press the intermediate transfer belt 31, the cam 80c is driven by the drive motor 81 to rotate clockwise in the figure. As a result, the support member 71 rotates counterclockwise in the figure about the rotation shaft 73, and the position of the pressing member 70 (more specifically, the tip position) moves toward the outer circumferential surface of the intermediate transfer belt 31. Furthermore, for example, when the pressing member 70 is moved in a direction opposite to the direction in which the intermediate transfer belt 31 is pressed, the cam 80c is driven by the drive motor 81 to rotate counterclockwise in the figure. As a result, the support member 71 rotates clockwise in the figure about the rotation shaft 73, and the position of the pressing member 70 (more specifically, the tip position) moves toward the inner circumferential surface of the intermediate transfer belt 31.

[0055] In this embodiment, the image forming apparatus 100 can control the rotation angle of the cam 80c by controlling the rotation amount of the drive motor 81 using a control unit 50 (FIG. 13), which will be described later. This controls the position of the support member 71 in the rotation direction, thereby controlling the position of the pressing member 70 (more specifically, the tip position). In this embodiment, the control unit 50 controls the drive amount of the drive motor 81 based on the number of pulses input to the drive motor (stepping motor) 81 from the neutral position (home position of the cam 80c) of the movement mechanism 2, which is detected by a position sensor 89. This controls the rotation angle of the cam 80c, thereby controlling the position of the support member 71 in the rotation direction. In this embodiment, the control unit 50 sets the movement mechanism 2 to the neutral position, for example, when the image forming apparatus 100 is in a power-off state or in a standby state where the image forming apparatus 100 is powered on and waiting for a job to be input.

[0056] The specific support structure for each element in the movement mechanism 2 will be described in more detail later.

[0057] 5. Control mode FIG. 13 is a schematic block diagram illustrating the control mode of the main components of the image forming apparatus 100 of this embodiment. The apparatus body 110 of the image forming apparatus 100 is provided with a control unit 50 as a control means. The control unit 50 includes a CPU 51 as a central element for performing arithmetic and control operations, a ROM 52 as a storage means, a RAM 53, and an interface unit (input / output circuit). The CPU 51, in accordance with a control program stored in the ROM 52 and using the RAM 53 as a work area, can comprehensively control each component of the image forming apparatus 100 based on input signals from various sensors provided in the image forming apparatus 100. In this embodiment, the control unit 50 controls the operation of the drive motor 81 of the movement mechanism 2 based on an input signal from a position sensor 89 of the movement mechanism 2, thereby controlling the rotational position (phase) of the cam 80c of the movement mechanism 2. The control unit 50 is also connected to an operation unit (operation panel) 130 provided in the apparatus body 110 of the image forming apparatus 100. The operation unit 130 has a display unit (display means) that displays information under the control of the control unit 50, and an input unit (input means) that inputs information to the control unit 50 through operation by an operator (worker) such as a user or a service representative. The operation unit 130 may be configured with a touch panel that functions as a display means and an input means. Furthermore, the control unit 50 may be connected to an opening / closing sensor 140 that detects the opening / closing of a door provided on the apparatus body 110 of the image forming apparatus 100. Furthermore, the image forming apparatus 100 may be connected to an external device such as a personal computer, an image reading device, etc.

[0058] Here, the image forming apparatus 100 executes a job (print job) that is a series of operations that starts with a single start command and forms and outputs an image on one or multiple recording materials P. A job generally includes an image forming process (image forming operation), a pre-rotation process, a sheet-to-sheet process when forming images on multiple recording materials P, and a post-rotation process. The image forming process is a period during which electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer of the toner image are performed for the image that is actually formed and output on the recording materials P, and this period is referred to as the image formation period. More specifically, the timing of the image formation differs depending on the positions where the electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer are performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. The sheet-to-sheet process is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation). The post-rotation process is a period during which a tidying operation (preparatory operation) is performed after the image formation process. Non-image formation time (non-image formation period) refers to a period other than image formation time, and includes the following periods: standby state, pre-rotation process, sheet interval process, post-rotation process, and even the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when the apparatus returns from a sleep state, as well as the period from the standby state until the pre-rotation process or pre-multiple rotation process is started. In this embodiment, during non-image formation time, the image forming apparatus 100 can perform an operation to set (adjust) the amount of pressure of the pressing member 70 against the intermediate transfer belt 31, i.e., the position of the pressing member 70, depending on the settings for the image formation to be performed thereafter.

[0059] The control unit 50 can control the amount of pressure of the pressure member 70 against the intermediate transfer belt 31, i.e., the position of the pressure member 70, to be changed in accordance with information about the recording material P used in a job. In this case, information (e.g., table data) indicating the relationship between the information about the recording material P and the amount of pressure of the pressure member 70 against the intermediate transfer belt 31, i.e., the position of the pressure member 70, is pre-stored in the ROM 52. Based on this information, the control unit 50 can control the amount of pressure of the pressure member 70 against the intermediate transfer belt 31, i.e., the position of the pressure member 70, to be changed during non-image formation for subsequent image formation. The information about the recording material P includes any information that can distinguish the recording material P, such as attributes based on general characteristics (so-called paper type categories) such as plain paper, thick paper, thin paper, etc., numerical values ​​or numerical ranges for basis weight, thickness, size, stiffness, etc., or brand (including manufacturer, product name, product number, etc.). Each recording material P distinguished by the information about the recording material P can be considered to constitute a type of recording material P. Furthermore, the information about the recording material P may be included in or substituted by information specifying the operation settings of the image forming apparatus 100, such as "plain paper mode" or "thick paper mode." For example, the amount of pressure that the pressing member 70 applies to the intermediate transfer belt 31 may be greater when forming an image on thick paper than when forming an image on thin paper. Alternatively, the amount of pressure that the pressing member 70 applies to the intermediate transfer belt 31 may be freely changed in response to an instruction from an operator (worker) such as a user or service representative via the operation unit 130. In this embodiment, the neutral position of the movement mechanism 2 is set so that the amount of pressure that the pressing member 70 applies to the intermediate transfer belt 31 is a predetermined amount, i.e., so that the position of the pressing member 70 is a predetermined position.

[0060] The amount of pressure applied to the intermediate transfer belt 31 by the pressing member 70 can be expressed, for example, by the amount of penetration of the pressing member 70 into the intermediate transfer belt 31. This penetration amount is roughly the amount by which the pressing member 70 causes the intermediate transfer belt 31 to protrude outward from the tension surface (stretching surface) of the intermediate transfer belt 31 formed by tensioning the intermediate transfer belt 31 between the inner secondary transfer roller 32 or the outer secondary transfer roller 41 and the pre-secondary transfer roller 35. The pre-secondary transfer roller 35 is an example of an upstream roller that is disposed adjacent to the inner secondary transfer roller 32 and upstream of the inner secondary transfer roller 32 in the rotation direction of the intermediate transfer belt 31, among the multiple tensioning rollers.

[0061] 6. Secondary transfer unit As mentioned above, the lifespan of the pressing member may differ from that of the intermediate transfer belt and its tension roller. Therefore, it is desirable for the unit containing the pressing member (the "pressing member unit") in the belt unit to be replaceable. Furthermore, for example, in commercial printing image forming apparatuses, the belt unit is large and heavy due to its characteristics, making it difficult for an operator to remove the belt unit from the main body of the image forming apparatus. Therefore, it is desirable for regularly replaced parts in the belt unit, such as the pressing member unit, to be replaceable while the belt unit is installed in the main body of the image forming apparatus. Note that the state in which the belt unit is pulled out from the main body, as in this embodiment, is also considered to be a state in which the belt unit is installed in the main body. To achieve a configuration in which the amount of pressure applied by the pressing member to the intermediate transfer belt can be varied, a mechanism for adjusting the amount of pressure can be attached to the belt unit. In such a case, for example, in a commercial printing image forming apparatus in which the secondary transfer unit is located below the main body of the image forming apparatus, replacing the pressing member may require the operator to look under the belt unit. In this case, the workability of replacing the pressing member is extremely poor. In this way, when a mechanism that changes the amount of pressure that the pressing member applies to the intermediate transfer belt is attached to the belt unit, the workability of replacing the pressing member unit for the belt unit is poor. This may result in a risk of damage to the mechanism.

[0062] Therefore, in this embodiment, the movement mechanism 2 has an upstream-side movement mechanism 2a (FIG. 4) including a drive motor 81 and a downstream-side movement mechanism 2b (FIG. 4) including a support member 71 that supports the pressing member 70, and the upstream-side movement mechanism 2a and the downstream-side movement mechanism 2b are configured to be drivingly connected to each other. In the belt unit 2, the upstream-side movement mechanism 2a is attached to a fixed-side unit 8 (FIG. 5), which is a unit fixed to the support frame 39 of the belt unit 3, and the downstream-side movement mechanism 2b is attached to a secondary transfer internal unit 7 (FIG. 5), which is a unit ("pressing member unit") including the pressing member 70. In particular, in this embodiment, the secondary transfer internal unit 7 can be moved to the front side of the image forming apparatus 100 and separated from the fixed-side unit 8. The secondary transfer internal unit 7 including the pressing member 70 can be removed from the belt unit 3 by moving it to the front side of the image forming apparatus 100. As a result, in this embodiment, the image forming apparatus 100 can achieve high replaceability of the pressing member 70 while being provided with a mechanism that changes the amount of pressure that the pressing member 70 applies to the intermediate transfer belt 31. This will be described in more detail below.

[0063] 5(a) and 5(b) are cross-sectional side views of the pressing member 70 and the periphery of the moving mechanism 2 in this embodiment as seen from the front and rear, respectively, as described above. Also, Fig. 6 is a perspective view of the secondary transfer internal unit 7, which is the pressing member unit in this embodiment, as seen from the rear.

[0064] In this embodiment, the secondary transfer inner unit 7 includes an upper frame 72 arranged along the width direction of the intermediate transfer belt 31, and a front frame 74 and a rear frame 75 arranged at both longitudinal ends of the upper frame 72. Note that the front frame 74 is not shown in FIG. 5A. The front frame 74 is arranged on the front side of the image forming apparatus 100, and the rear frame 75 is arranged on the rear side of the image forming apparatus 100. The upper frame 72 is arranged above the pressing member 70 and connects the front frame 74 and the rear frame 75. In this embodiment, the secondary transfer inner unit 7 includes the secondary transfer inner roller 32 and a support member 71 to which the pressing member 70 is attached. That is, both ends of the rotation axis of the secondary transfer inner roller 32 are rotatably supported by the front frame 74 and the rear frame 75 via bearing members, respectively. Furthermore, rotation shafts 73 provided at both longitudinal ends of the support member 71 are rotatably supported by the front frame 74 and the rear frame 75, respectively.

[0065] On the other hand, in this embodiment, a drive support plate 86 is fixed to a stay 85 provided on the support frame 39 of the belt unit 3. In this embodiment, the drive support plate 86 is fixed to each of the front side plate 39a and the rear side plate 39b of the support frame 39, but the front drive support plate 86 is not shown in FIG. 5(a). A drive motor 81 is fixed to the drive support plate 86 (rear side). First and second transmission gears 82 and 83 are rotatably supported on the drive support plate 86 (rear side). A camshaft 80 is rotatably supported on the drive support plate 86 (front side and rear side). In this embodiment, the drive support plate 86, drive motor 81, first and second transmission gears 82 and 83, camshaft 80, drive gear 80a, cam 80c, flag 80b, etc. constitute a fixed side unit 8, which is a unit fixed to the support frame 39 of the belt unit 3.

[0066] In this embodiment, guide portions 72a and 72b provided on the upper frame 72 of the secondary transfer internal unit 7 slidably engage with rail portions 84a and 84b fixed to the support frame 39 of the belt unit 3. The guide portions 72a and 72b, serving as first engagement portions, are provided along the longitudinal direction of the upper frame 72, at both ends of the upper frame 72 in the width direction substantially perpendicular to the longitudinal direction. The rail portions 84a and 84b, serving as second engagement portions, are provided so as to connect the front plate 39a and the rear plate 39b of the support frame 39 of the belt unit 3 along the width direction of the intermediate transfer belt 31. This makes it possible to insert or remove the secondary transfer internal unit 7 into or from the belt unit 3 along the width direction of the intermediate transfer belt 31 by releasing the tension of the intermediate transfer belt 31 using the release mechanism 3b (FIG. 2) as described above.

[0067] For example, when replacing the pressing member 70, the secondary transfer inner unit 7 is pulled out toward the front of the image forming apparatus 100 along the width direction of the intermediate transfer belt 31 and removed from the belt unit 3. In this embodiment, the belt unit 3 is pulled out toward the front of the image forming apparatus 100 and tilted upward, as described above, to release the tension on the intermediate transfer belt 31. The secondary transfer outer roller 41 is separated from the intermediate transfer belt 31. The pressing member 70 can be replaced by removing the entire mounting portion 70c from the support member 71. The secondary transfer inner unit 7 may be attached to or detached from the belt unit 3 for maintenance, such as cleaning the pressing member 70. The secondary transfer inner unit 7 may be attached to or detached from the belt unit 3 for maintenance, such as cleaning or replacing the inner secondary transfer roller 32, in addition to or instead of replacing or maintaining the pressing member 70. Furthermore, the entire secondary transfer inner unit 7 may be replaced when, for example, the pressing member 70 reaches the end of its life.

[0068] Furthermore, in this embodiment, positioning protrusions 74a (two in this embodiment) are provided on the rear side of the front frame 74, and positioning protrusions 75a (two in this embodiment) are provided on the rear side of the rear frame 75. When the secondary transfer internal unit 7 is inserted into the rear of the image forming apparatus 100 relative to the belt unit 3 along the width direction of the intermediate transfer belt 31, the following occurs. That is, the front and rear positioning protrusions 74a, 75a are fitted into positioning holes (not shown) provided on the front plate 39a and rear plate 39b of the support frame 39 of the belt unit 3, respectively. This determines the position of the secondary transfer internal unit 7 relative to the belt unit 3. Furthermore, the secondary transfer internal unit 7 may be fixed to the belt unit 3 by any fixing means such as screws.

[0069] Thus, in this embodiment, the upstream moving mechanism 2a of the moving mechanism 2 is configured to have the drive motor 81, first and second transmission gears 82 and 83, the drive gear 80a, the camshaft 80, the flag 80b, and the cam 80c. Also, in this embodiment, the downstream moving mechanism 2b of the moving mechanism 2 is configured to have the support member 71 to which the pressing member 70 is fixed and which is equipped with the cam follower 71a against which the cam 80c can abut. The moving mechanism 2 is configured to have the upstream side Moving mechanism 2a and downstream side The upstream-side moving mechanism 2a and the downstream-side moving mechanism 2b are drivingly connected to each other. In this embodiment, the belt unit 2 is configured so that the fixed-side unit 8 to which the upstream-side moving mechanism 2a is attached and the secondary-transfer internal unit 7 to which the downstream-side moving mechanism 2b is attached are separable. In particular, in this embodiment, the secondary-transfer internal unit 7 is configured so that it can be moved to the front side of the image forming apparatus 100 and separated from the fixed-side unit 8.

[0070] In this embodiment, in order to make the position of the pressing member 70 variable as described above and to reduce the risk of the support member 71 and the cam 80c colliding when the secondary transfer internal unit 7 is inserted into or removed from the belt unit 3, the movement mechanism 2 is configured as follows. That is, during image formation (image creation), the cam 80c and the cam follower 71a of the support member 71 are brought into contact with each other to determine the position of the pressing member 70. On the other hand, when the secondary transfer internal unit 7 is inserted into or removed from the belt unit 3, the cam follower 71a of the support member 71 and the cam 80c are separated from each other. Note that, in relation to the operation of the movement mechanism 2, during image formation (image creation) includes a period during which secondary transfer of an image is being performed, which is transferred onto the recording material P and output from the image forming apparatus 100.

[0071] 7 is a cross-sectional side view of the internal secondary transfer unit 7 and the cam 80c in this embodiment, seen from the front along the rotation axis direction of the internal secondary transfer roller 32. Fig. 7(a) shows an example of the posture of the cam 80c and the support member 71 during image formation, and Fig. 7(b) shows the posture of the cam 80c and the support member 71 when the internal secondary transfer unit 7 is removed from the belt unit 3.

[0072] In this embodiment, the support member 71 is configured such that, in a free state, a moment due to its own weight is generated in the counterclockwise direction in the figure, i.e., in the direction in which the cam follower 71a of the support member 71 moves away from the cam 80c. That is, in this embodiment, in FIG. 7(a), the support member 71 is configured such that the rotation shaft 73 is provided on the right side (cam shaft 80 side) in the horizontal direction with respect to the center of gravity 71G of the support member 71 to which the pressing member 70 is fixed. Note that, in this embodiment, in FIG. 7(a), the cam shaft 80 is disposed above a position overlapping with the rotation shaft 73 in the horizontal direction. Therefore, in the free state, the support member 73 generates a moment due to its own weight in the counterclockwise direction in the figure, i.e., in the direction in which the cam follower 71a of the support member 71 moves away from the cam 80c.

[0073] 7(a), when the image is formed, the tension of the intermediate transfer belt 31 causes the support member 71 to receive a moment in the clockwise direction in the figure from the intermediate transfer belt 31 via the pressing member 70. Then, the cam follower 71a of the support member 71 comes into contact with the cam 80c, and the position of the pressing member 70 is determined.

[0074] In contrast, when the secondary transfer internal unit 7 shown in FIG. 7B is removed from the belt unit 3, the tension on the intermediate transfer belt 31 is released, and the support member 71 is set in a free state, so that the support member 71 receives a moment in the counterclockwise direction in the figure due to its own weight. The cam follower 71a of the support member 71 then separates from the cam 80c. In this embodiment, when the tension on the intermediate transfer belt 31 is released, the belt unit 3 is configured so that the intermediate transfer belt 31 and the pressing member 70 do not come into contact with each other, even when the support member 71 is rotated to its maximum extent in the counterclockwise direction in the figure, as shown in FIG. 7B. In this manner, in this embodiment, the release mechanism 3b of the intermediate transfer belt 31, which sets the support member 71 in a free state, constitutes a separation mechanism that separates the support member 71 from the cam 80c.

[0075] The operation for attaching the secondary transfer internal unit 7 to the belt unit 3 is the reverse of the operation for removing it. That is, with the tension of the intermediate transfer belt 31 released, the secondary transfer internal unit 7 is attached to the belt unit 3 with the support member 71 receiving a moment in the counterclockwise direction in the figure due to its own weight as shown in FIG. 7(b). Then, by applying tension to the intermediate transfer belt 31, the cam follower 71a comes into contact with the cam 80c as shown in FIG. 7(a), and the position of the pressing member 70 is determined.

[0076] As mentioned above, in this embodiment, when the secondary transfer internal unit 7 is removed from the belt unit 3, the front side of the belt unit 3 is rotated upward and tilted, but the operation of the moving mechanism 2 is as described above.

[0077] Furthermore, in the configuration of this embodiment, similarly to the case of the second embodiment described later, the cam 80c may be rotated (retracted) to a position (phase) where it does not come into contact with the support member 71 when inserting or removing the secondary transfer internal unit 7 into or from the belt unit 3. Specifically, as shown in FIG. 7B, for example, the cam 80c may be rotated (retracted) to a position (phase) where the contact surface of the cam 80c that can come into contact with the cam follower 71a faces away from the cam follower 71a. This further reduces the risk of collision between the support member 71 and the cam 80c.

[0078] As described above, the image forming apparatus 100 of this embodiment includes a rotatable, endless belt 31 that carries a toner image, a plurality of tension rollers that tension the belt 31, including an inner roller 32 and an upstream roller 35 that is arranged adjacent to the inner roller 32 upstream of the inner roller 32 in the rotation direction of the belt 31, a tension applying section 36 that applies tension to the belt 31, a pressing member 70 that can contact the inner surface of the belt 31 upstream of the inner roller 32 and downstream of the upstream roller 35 in the rotation direction of the belt 31, and a moving mechanism 2 that can move the pressing member 70 to change the amount of pressure that the pressing member 70 applies to the belt 31, and an external member 41 that is arranged opposite the inner roller 32 and abuts against the outer surface of the belt 31 to form a transfer section N2 that transfers the toner image from the belt 31 to a recording material P. In this embodiment, the moving mechanism 2 includes a movable support portion 71 that supports the pressing member 70, a movable contact portion 80c that contacts the support portion 71 to move the support portion 71, and a drive portion 81 that moves the contact portion 80c, and the upstream moving mechanism 2a including the contact portion 80c and the drive portion 81 and the downstream moving mechanism 2b including the support portion 71 are separable. side Moving mechanism 2a and downstream sideThe pressing member unit 7, which includes only the downstream-side moving mechanism 2b of the moving mechanism 2b, is detachable. In this embodiment, the image forming apparatus 100 also has a separation mechanism (release mechanism 3b) that separates the support portion 71 from the contact portion 80c. In this embodiment, the pressing member unit 7 is configured to be moved along the rotation axis direction of the inner roller 32 and removed from the belt unit 3 in a state in which the support portion 71 is separated from the contact portion 80c by the separation mechanism 3b.

[0079] In this embodiment, the image forming apparatus 100 includes a release mechanism 3b that releases the tension. The support portion 71 is rotatable about a rotation axis that is substantially parallel to the rotation axis of the inner roller 32. The support portion 71 is set in a free state when the tension is released by the release mechanism 3b. The rotation axis is positioned so that the support portion 71 in the free state rotates in a direction away from the contact portion 80c. The release mechanism 3b constitutes the separation mechanism. In this embodiment, the pressing member unit 7 includes first engagement portions 72a, 72b that extend along the rotation axis of the inner roller 32. The belt unit 3 includes second engagement portions 84a, 84b with which the first engagement portion 72a slidably engages. In this embodiment, the pressing member unit 7 is pulled out of the housing 110a of the image forming apparatus 100 and removed from the belt unit 3 that is held in the housing 110a. In this embodiment, the pressing member unit 7 includes an inner roller 32. In this embodiment, the pressing member 70 is arranged with its longitudinal direction substantially parallel to the width direction of the belt 31, and is configured as a plate-like member whose upstream end in the rotation direction of the belt 31 in the lateral direction is fixed to the support portion 71 and whose downstream end in the rotation direction of the belt 31 in the lateral direction can come into contact with the inner circumferential surface of the belt 31. In this embodiment, the belt 31 is an intermediate transfer body that transports the toner image primarily transferred from the image carrier 11 to the recording material P for secondary transfer at the transfer portion N2.

[0080] As described above, according to this embodiment, the position of the pressing member 70 can be varied, and the risk of the support member 71 colliding with the cam 80c can be reduced when the secondary transfer internal unit 7 is inserted into or removed from the belt unit 3. Furthermore, according to this embodiment, it is possible to improve the replaceability of the pressing member 70 in a configuration in which the amount of pressure applied by the pressing member 70 to the intermediate transfer belt 31 is variable.

[0081] [Example 2] Next, another embodiment 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 embodiment 1. Therefore, elements in the image forming apparatus of this embodiment that have the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those in embodiment 1, and detailed descriptions thereof will be omitted.

[0082] The configuration of Example 1 is simple and reduces the risk of the support member 71 and the cam 80c colliding when the secondary transfer internal unit 7 is inserted into or removed from the belt unit 3. However, with the configuration of Example 1, the distance from the rotation shaft 73 of the support member 71 to the tip position of the pressing member 70 is long, which may make it difficult to ensure an arm ratio with respect to the contact surface with the cam 80c. In this case, it is considered that variations in the positional relationship between the cam 80c and the support member 71 will have a greater impact on variations in the tip position of the pressing member 70. Therefore, it is considered that the tip position of the pressing member 70 will be more likely to vary depending on the accuracy of parts, etc. Therefore, in this example, the movement mechanism 2 is configured as follows.

[0083] 8 is a cross-sectional side view of the secondary transfer inner unit 7 and the cam 80c in this embodiment, seen from the front along the rotation axis direction of the secondary transfer inner roller 32. Fig. 8(a) shows an example of the posture of the cam 80c and the support member 71 during image formation, and Fig. 8(b) shows the posture of the cam 80c and the support member 71 when the secondary transfer inner unit 7 is removed from the belt unit 3.

[0084] In this embodiment, the support member 71 is configured such that, in a free state, a moment due to its own weight is generated in the clockwise direction in the figure, i.e., in the direction in which the cam follower 71a of the support member 71 abuts against the cam 80c. That is, in this embodiment, in FIG. 8A, the support member 71 is configured such that the rotation shaft 73 is provided to the left (opposite the cam shaft 80) of the center of gravity 71G of the support member 71 to which the pressing member 70 is fixed in the horizontal direction. Note that in this embodiment, in FIG. 8A, the cam shaft 80 is positioned above and shifted to the right of the rotation shaft 73 in the horizontal direction. Also, in this embodiment, the front frame 74 and the rear frame 75 of the secondary transfer internal unit 7 are each provided with a protrusion 76 as a restricting portion. The protrusion 76 abuts against the support member 71 to restrict the support member 71 from rotating clockwise in the figure by more than a predetermined angle. It should be noted that the protrusion 76 is only required to restrict the rotation of the support member 71 as described above, and may be configured to abut against the attachment portion 70c of the pressing member 70 fixed to the support member 71. The attachment portion 70c of the pressing member 70 can be seen as constituting a support portion that supports the pressing member 70 together with the support member 71.

[0085] 8(a), in addition to the clockwise moment due to its own weight, the support member 71 receives a clockwise moment from the intermediate transfer belt 31 via the pressing member 70 due to tension in the intermediate transfer belt 31. Then, the cam follower 71a of the support member 71 comes into contact with the cam 80c, and the position of the pressing member 70 is determined.

[0086] In contrast, when the secondary transfer internal unit 7 shown in FIG. 8B is removed from the belt unit 3, the support member 71 rotates clockwise in the figure due to a moment caused by its own weight and abuts against the protrusion 76, thereby determining its position. At this time, in this embodiment, the cam 80c rotates (retracts) to a position (phase) where it does not contact the support member 71, which has rotated to a position where it abuts against the protrusion 76. Specifically, the cam 80c rotates (retracts) to a retracted position (phase) where the contact surface of the cam 80c that can contact the cam follower 71a faces away from the cam follower 71a. Therefore, when the support member 71 rotates to a position where it abuts against the protrusion 76, the cam follower 71a of the support member 71 moves away from the cam 80c. Note that in this embodiment as well, as in the first embodiment, the tension of the intermediate transfer belt 31 is released when the secondary transfer internal unit 7 is removed from the belt unit 3. In this manner, in this embodiment, the protrusion 76 and the drive motor 81 and control unit 50 that constitute the retraction mechanism for retracting the cam 80c constitute a separation mechanism that separates the support member 71 from the cam 80c.

[0087] In this embodiment, the neutral position of the moving mechanism 2 is set to a state in which the cam 80c has rotated (retracted) to a position (phase) where it does not contact the support member 71, as shown in FIG. 8B . Therefore, in this embodiment, when the secondary transfer internal unit 7 is removed from the belt unit 3, the cam 80c is rotated (retracted) to a position (phase) where it does not contact the support member 71. However, the present invention is not limited to this embodiment. When an operator removes the secondary transfer internal unit 7 from the belt unit 3, the control unit 50 may set the cam 80c to the retracted state as described above. For example, the control unit 50 can receive a signal indicating that the secondary transfer internal unit 7 is being removed from the belt unit 3 in response to an operation by the operator on the operation unit 130 ( FIG. 13 ). In response to receiving this signal, the control unit 50 can set the cam 80c to the retracted state as described above. Alternatively, the image forming apparatus 100 may be provided with an opening / closing sensor 140 (FIG. 13) that detects the opening / closing of a door provided in the apparatus body 110 that allows an operator to access the belt unit 3. The control unit 50 can acquire a signal indicating that the door has been opened from the opening / closing sensor 140. In response to acquiring this signal, the control unit 50 can set the cam 80c to the retracted state as described above. On the other hand, when the secondary transfer internal unit 7 is properly attached to the belt unit 3 and the belt unit 3 is properly attached to the apparatus body 110, the control unit 50 can rotate the cam 80c to a position where it can contact the support member 71 before the first image formation thereafter.

[0088] The operation for attaching the secondary transfer internal unit 7 to the belt unit 3 is the reverse of the operation for removing it. That is, with the tension of the intermediate transfer belt 31 released, the secondary transfer internal unit 7 is attached to the belt unit 3 with the support member 71 receiving a clockwise moment in the figure due to its own weight and abutting against the protrusion 76 as shown in FIG. 8B. At this time, the cam 80c is rotated (retracted) to a position (phase) where it does not contact the support member 71. Then, by applying tension to the intermediate transfer belt 31 and rotating the cam 80c to a position (phase) where it can contact the support member 71, the cam follower 71a comes into contact with the cam 80c as shown in FIG. 8A, and the position of the pressing member 70 is determined.

[0089] As mentioned above, in this embodiment, when the secondary transfer internal unit 7 is removed from the belt unit 3, the front side of the belt unit 3 is rotated upward and tilted, but the operation of the moving mechanism 2 is as described above.

[0090] In this embodiment, the moving mechanism 2 changes the position of the pressing member 70, thereby changing the state of contact or separation of the pressing member 70 with respect to the intermediate transfer belt 31. That is, as described above, by rotating (retreating) the cam 80c to a position (phase) where it does not contact the support member 71, the support member 71 abuts against the protrusion 76. In this embodiment, the protrusion 76 is provided so that the tip of the pressing member 70 is separated from the inner circumferential surface of the intermediate transfer belt 31, which is tensioned at this time. In this embodiment, since the support member 71 rotates clockwise in the figure due to its own weight as described above, the pressing member 70 can be separated from the intermediate transfer belt 31 without providing a special biasing means such as a spring. The image forming apparatus 100 may be configured so that the tip of the pressing member 70 is separated from the inner circumferential surface of the intermediate transfer belt 31 during image formation (secondary transfer) in at least one predetermined mode.

[0091] As described above, in this embodiment, the image forming apparatus 100 has a retraction mechanism (drive motor 81, control unit 50) that moves the contact portion 80c to a retracted position where it does not contact the support portion 71, the support portion 71 is rotatable around a rotation axis that is approximately parallel to the rotation axis direction of the inner roller 32, and the contact portion 80c becomes free when moved to the retracted position, and the rotation axis is positioned so that the support portion 71 in the free state rotates in a direction toward the contact portion 80c, and the pressing member unit 7 is provided with a regulating portion 76 that abuts against the support portion 71 that has rotated in the free state to regulate the rotation of the support portion 71 and holds the support portion 71 separated from the contact portion 80c, and the retraction mechanisms 81, 50 and the regulating portion 76 constitute a separation mechanism that separates the support portion 71 from the contact portion 80c.

[0092] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the distance from the rotation axis 73 to the tip position of the pressing member 70 can be reduced, and the tip position of the pressing member 70 can be determined with higher accuracy.

[0093] [Example 3] Next, another embodiment 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 embodiment 1. Therefore, elements in the image forming apparatus of this embodiment that have the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those in embodiment 1, and detailed descriptions thereof will be omitted.

[0094] This embodiment differs from the first embodiment mainly in that the upstream including the drive motor 81 in the moving mechanism 2 side The configuration of the moving mechanism 2a (fixed side unit 8) is different.

[0095] Fig. 9 is a perspective view of the pressing member 70 and the moving mechanism 2 in this embodiment as seen from the front side. Fig. 10 is a cross-sectional side view of the pressing member 70, the moving mechanism 2, and their surroundings as seen from the front side along the rotation axis direction of the inner secondary transfer roller 32.

[0096] As in the first embodiment, the pressing member 70 is fixed to a support member 71, and the support member 71 is supported by a front frame 74 and a rear frame 75 (FIG. 6) of the secondary transfer internal unit 7 so as to be rotatable around a rotation shaft 73.

[0097] In this embodiment, the movement mechanism 2 also has a driven pressure link shaft 80d made of a cylindrical member extending along the width direction of the intermediate transfer belt 31. The driven pressure link shaft 80d is supported by the support frame 39 of the belt unit 3 so as to be rotatable about a rotation axis that is approximately parallel to the width direction of the intermediate transfer belt 31. The movement mechanism 2 also has a driven pressure link 80e. The driven pressure link 80e is fixed to the driven pressure link shaft 80d. The driven pressure links 80e are provided at both ends of the driven pressure link shaft 80d in the rotation axis direction. The movement mechanism 2 also has a drive motor 81 made of a stepping motor as a drive source, a drive pressure link 81b, a flag 81c provided on the drive pressure link 81b, and a pressure spring 87 which is a biasing member (elastic member) that serves as biasing means. The drive motor 81, drive pressure link 81b, flag 81c, and pressure spring 87 are provided on the rear side of the driven pressure link shaft 80d in the direction of the rotation axis. The drive pressure link 81b having the flag 81c is fixed to the output shaft of the drive motor 81. The rear driven pressure link 80e and the drive pressure link 81b are connected by the pressure spring 87. In this embodiment, the pressure spring 87 is configured as a tension coil spring, which is a biasing member made of piano wire. The drive motor 81 is supported by the support frame 39 of the belt unit 3.

[0098] The driven pressure link 80e has a contact portion 80f that comes into contact with the contacted portion 71a of the support member 71. The driven pressure link 80e transmits the force of the pressure spring 87 to the pressing member 70 via the contact portion 80f and the contacted portion 71a. The support member 71 then rotates to a point where the force of the pressure spring 87 and the reaction force that the pressing member 70 receives from the intermediate transfer belt 31 are balanced, and the attitude of the support member 71, i.e., the position of the pressing member 70, is determined. In this embodiment, the angle of the drive pressure link 81b changes when the drive motor 81 is driven to rotate, and further, the amount of deformation of the pressure spring 87 changes, which changes the spring force, and the attitude of the support member 71, i.e., the position of the pressing member 70, also changes.

[0099] Also, similar to the first embodiment, the belt unit 3 is provided with a position sensor 89 (not shown in Figures 9 and 10), and the position of the moving mechanism 2 can be set to a preset neutral position by the action of the position sensor 89 and the flag 81c.

[0100] The configuration of the secondary transfer internal unit 7 in this embodiment is substantially the same as that in the first embodiment, and is configured to be insertable into and removable from the belt unit 3 in the same manner as in the first embodiment. In this embodiment, a drive support plate 86 is fixed to a stay 85 provided on the support frame 39 of the belt unit 3. In this embodiment, the drive support plate 86 is fixed to the front side plate 39a and the rear side plate 39b of the support frame 39, respectively; however, the front drive support plate 86 is not shown in FIG. 10 . A drive motor 81 is fixed to the drive support plate 86 (rear side). A driven pressure link shaft 80d is rotatably supported on the drive support plate 86 (front and rear sides). In this embodiment, the drive support plate 86, the drive motor 81, the drive pressure link 81b, the flag 81c, the pressure spring 87, the driven pressure link shaft 80d, and the driven pressure link 80e constitute a fixed unit 8, which is a unit fixed to the support frame 39.

[0101] In this embodiment, the pressing member 70 is made of a plastic material that is less likely to damage the intermediate transfer belt 31 and can also ensure insulation (similar to the first embodiment). However, the elastic modulus of the pressing member 70 made of a plastic material can easily change over time due to the influence of environmental temperature and creep deformation. Therefore, with the configuration of the movement mechanism 2 in the first embodiment, although the orientation of the support member 71 can be maintained at a desired orientation, the position of the tip of the pressing member 70 may change with the change in the elastic modulus.

[0102] In contrast, in the configuration of the movement mechanism 2 in this embodiment, a spring made of piano wire, which changes little over time, is used for the pressure spring 87, and therefore it is possible to achieve a stable contact pressure between the pressure member 70 and the intermediate transfer belt 31. Furthermore, by making the elastic modulus of the pressure spring 87 smaller than that of the pressure member 70, even if the elastic modulus of the pressure member 70 changes over time, the spring force of the pressure spring 87 changes very little, and it is possible to keep the change in the tip position of the pressure member 70 small.

[0103] According to the biasing mechanism of the pressing member 70 in this embodiment, a member formed of a relatively rigid metal plate (sheet metal) may be used as the pressing member 70. By biasing the pressing member 70 with the biasing member, the intermediate transfer belt 31 can be elastically biased by the pressing member 70.

[0104] As described above, in this embodiment, the movement mechanism 2 has an elastically deformable elastic deformation portion 87 between the contact portion 80f and the drive portion 81, and the drive portion 81 can change the amount of deformation of the elastic deformation portion 87. Also, in this embodiment, the pressing member 70 is elastically deformable, and the elastic modulus of the pressing member 70 is Part 8 The elastic modulus is greater than 7.

[0105] As described above, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the influence of the changes over time of the pressing member 70 can be reduced, making it possible to stably maintain the tip position of the pressing member 70 at a desired position.

[0106] It should be noted that the configuration of the secondary transfer internal unit 7, which is substantially the same as that in the second embodiment, may be combined with this embodiment.

[0107] [Example 4] Next, another embodiment 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 embodiment 1. Therefore, elements in the image forming apparatus of this embodiment that have the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those in embodiment 1, and detailed descriptions thereof will be omitted.

[0108] This embodiment is a modification of the third embodiment. In this embodiment, elements having the same or corresponding functions or configurations as those in the third embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Fig. 11 is a perspective view of the pressing member 70 and the moving mechanism 2 in this embodiment, as seen from the front side.

[0109] According to the configuration of the movement mechanism 2 in the third embodiment, it is possible to reduce the influence of changes over time in the pressing member 70 and stably maintain the tip position of the pressing member 70 at a desired position. However, in the configuration of the third embodiment, the contact pressure between the intermediate transfer belt 31 and the pressing member 70 depends on the spring force of the pressing spring 87. Therefore, if the pressing member 70 receives an external force when the recording material P enters the secondary transfer portion N2, the pressing member 70 may undergo deformation that depends on the elastic modulus of the pressing spring 87. As a result, it may not be possible to maintain the tip position of the pressing member 70 appropriately.

[0110] Therefore, in this embodiment, as shown in FIG. 11 , the driven pressure link shaft 80d is connected to the output shaft 88a of the electromagnetic clutch 88 via a coupling 88b. The driven pressure link shaft 80d constitutes a moving part that moves integrally with the contact part 80f. The input shaft 88c of the electromagnetic clutch 88 is fixed to the rear side plate 39b of the support frame 39 of the belt unit 3. In this embodiment, a closed-type electromagnetic clutch 88 is used. When voltage is cut off, the input shaft 88c and the output shaft 88a are connected. When voltage is applied, a built-in spring (not shown) is released, disengaging the input shaft 88c and the output shaft 88a. In this embodiment, a power source (not shown) that applies voltage to the electromagnetic clutch 88 is connected to the control unit 50, and the control unit 50 can control the ON / OFF of the power source output. In this embodiment, the electromagnetic clutch 88 as a clutch mechanism constitutes a fixing means for fixing the position of the pressing member 70.

[0111] In this embodiment, when the drive motor 81 drives and rotates the drive pressure link 81b, the control unit 50 energizes the electromagnetic clutch 88 to allow the driven pressure link shaft 80d to rotate freely. On the other hand, after the drive motor 81 has finished driving and rotating, the control unit 50 fixes the position of the driven pressure link shaft 80d by cutting off the input of voltage to the electromagnetic clutch 88. As a result, even when the recording material P enters the secondary transfer portion N2, the posture of the support member 71 is fixed, and it is possible to maintain the position of the tip of the pressing member 70 as in the first embodiment.

[0112] As described above, according to this embodiment, by using the pressure spring 87 and the electromagnetic clutch 88, it is possible to reduce the influence of changes over time in the pressing member 70, and it is also possible to maintain the tip position of the pressing member 70 at a desired position when it is affected by an external force from the recording material P.

[0113] The fixing means for fixing the position of the pressing member 70 is not limited to the embodiment described above.

[0114] For example, the clutch mechanism connected to the driven pressure link mechanism is not limited to the electromagnetic clutch 88. For example, a one-way clutch (not shown) may be disposed between the driven pressure link shaft 80d and the driven pressure link 80e. In this case, the driven pressure link 80e constitutes a moving part that moves integrally with the contact part 80f. The one-way clutch is disposed relative to the driven pressure link shaft 80d so that the driven pressure link 80e can rotate clockwise in FIG. 10 and is locked in the counterclockwise direction in FIG. 10. This allows the posture of the support member 71 to be maintained even when the recording material P enters the secondary transfer portion N2. Furthermore, to reduce the deformation of the pressure spring 87, the drive motor 81 rotates the drive pressure link 81b clockwise in FIG. 10. At the same time, the driven pressure link shaft 80d is rotated counterclockwise via a transmission gear (not shown), thereby rotating the driven pressure link 80e counterclockwise.

[0115] Furthermore, because the external force generated when the recording material P enters the secondary transfer portion N2 is temporary, it is also possible to obtain a similar effect by using a damper mechanism instead of a clutch mechanism, as shown in Fig. 12. Fig. 11 is a perspective view of the pressing member 70 and the moving mechanism 2 in a modified example of this embodiment that uses a damper mechanism, as seen from the front. In this example, a driven pressure link shaft 80d and an output shaft 90a of a rotary damper 90 serving as a damper mechanism fixed to the rear side plate 39b of the support frame 39 of the belt unit 3 are connected via a coupling 90b.

[0116] Furthermore, the above-mentioned clutch mechanism (electromagnetic clutch 88, one-way clutch) and damper mechanism 90 may be connected to the rotating shaft 73 of the support member 71 instead of the driven pressure link shaft 80d. This also provides the same effect as above. In this case, the rotating shaft 73 constitutes a moving part that moves integrally with the support member 71, which serves as a support part for the pressing member 70.

[0117] In this way, the moving mechanism 2 may have a clutch mechanism 88 connected to the moving part (80d, 80e, 73) that moves integrally with the contact part 80f or the support part 71. This clutch mechanism 88 allows the moving part to move when the drive part 81 moves the support part 71, and restricts this movement when transfer is performed (during image formation). The moving mechanism 2 may also have a damper mechanism 90 connected to the moving part (80d, 80e, 73) that moves integrally with the contact part 80f or the support part 71. This damper mechanism 90 allows the moving part 71 to move when the drive part 81 moves the support part 71, and restricts this movement when transfer is performed (during image formation).

[0118] As described above, according to this embodiment, the same effects as those of the first and third embodiments can be obtained, and the change in the posture of the support member 71 of the pressing member 70 due to the external force when the recording material P enters the secondary transfer section N2 can be suppressed.

[0119] It should be noted that the configuration of the secondary transfer internal unit 7, which is substantially the same as that in the second embodiment, may be combined with this embodiment.

[0120] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0121] In the above-described embodiment, rails and rail guides are provided to enable insertion and removal of the secondary transfer internal unit, but the present invention is not limited to such an embodiment. Any configuration is acceptable as long as the pressing member unit can be removed along the width direction of the belt, typically from the front side of the image forming apparatus. For example, rails and rail guides may not be provided, and the pressing member unit may be removed by moving it along the width direction of the belt after disengaging the positioning protrusion and positioning hole described in the first embodiment.

[0122] In the above-described embodiment, the pressing member unit is provided with a secondary transfer inner roller. However, the present invention is not limited to this configuration. For example, the pressing member unit may essentially be a unit having only a support member to which a pressing member is fixed. However, if the pressing member unit includes a secondary transfer inner roller, the positional accuracy between the secondary transfer inner roller and the pressing member can be improved. Furthermore, the pressing member unit may be configured to have a guide member (conveyance guide, secondary transfer entrance guide) fixed thereto for guiding the recording material being conveyed to the transfer section. In this case, for example, the conveyance guide can be removed first from the pressing member unit before the unit itself can be removed. If the conveyance guide is fixed to the pressing member unit, the positional accuracy between the pressing member and the conveyance guide can be improved.

[0123] The pressing member may be disposed so as to simply contact the inner circumferential surface of the intermediate transfer belt, which also provides some effect of suppressing deformation of the intermediate transfer belt upstream of the secondary transfer portion.

[0124] Furthermore, the belt unit is not limited to a configuration that can be pulled out from the main body of the image forming apparatus and tilted. Even in a configuration in which the pressing member is replaced while the belt unit is substantially housed within the main body of the image forming apparatus, the present invention can improve the replaceability of the pressing member unit. Furthermore, the belt unit may be detachable from the main body of the image forming apparatus for replacement, etc., with the pressing member unit still attached or with the pressing member unit removed.

[0125] The pressing member may also be a roller made of an elastic material such as sponge or rubber, or a roller made of a rigid material such as resin or metal. However, from the viewpoint of arranging the pressing member sufficiently close to the secondary transfer unit, it is preferable that the pressing member be a plate-shaped member as in the above-described embodiment.

[0126] In the above-described embodiment, an outer roller that directly contacts the outer peripheral surface of the intermediate transfer belt is used as the outer member that forms the secondary transfer portion together with the inner roller as the inner member. Alternatively, an outer roller and a secondary transfer belt stretched between the outer roller and another roller may be used as the outer member. The outer roller may then contact the outer peripheral surface of the intermediate transfer belt via the secondary transfer belt. In such a configuration, the intermediate transfer belt and the secondary transfer belt are sandwiched between the inner roller that contacts the inner peripheral surface of the intermediate transfer belt and the outer roller that contacts the inner peripheral surface of the secondary transfer belt, thereby forming the secondary transfer portion.

[0127] In the above embodiment, the belt-shaped image carrier is an intermediate transfer belt, but the present invention can be applied to any image carrier that is an endless belt that transports a toner image carried at an image forming position. Examples of such a belt-shaped image carrier include the intermediate transfer belt in the above embodiment, a photosensitive belt, and an electrostatic recording dielectric belt.

[0128] The present invention can also be implemented in other embodiments in which some or all of the configurations of the above-described embodiments are replaced with alternative configurations. Therefore, as long as the image forming apparatus uses a belt-shaped image carrier, it can be implemented regardless of whether it is a tandem type or a single-drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, or a fixing method. While the above-described embodiment has focused on the main components related to the formation / transfer of a toner image, the present invention can be implemented in a variety of applications, such as printers, various printing machines, copiers, fax machines, and multifunction machines, by adding the necessary devices, equipment, and housing structures. [Explanation of symbols]

[0129] 1 Image forming unit 2 Moving mechanism 3 Belt unit 7 Secondary transfer unit 8 Fixed side unit 31 Intermediate transfer belt 32 Secondary transfer inner roller 70 Pressing member 71 Support member 71a Cam follower 80 Camshaft 80c cam 81 Drive motor

Claims

1. a rotatable endless belt that carries a toner image; a plurality of tension rollers for tensioning the belt, the plurality of tension rollers including an inner roller and an upstream roller disposed adjacent to the inner roller and upstream of the inner roller in the rotation direction of the belt; a tension applying unit that applies tension to the belt; a pressing member that is capable of contacting an inner circumferential surface of the belt upstream of the inner roller and downstream of the upstream roller in a rotation direction of the belt; a movement mechanism that can move the pressing member so as to change the amount of pressing of the pressing member against the belt; a belt unit including: an outer member disposed opposite the inner roller and in contact with the outer peripheral surface of the belt to form a transfer section for transferring a toner image from the belt to a recording material; In an image forming apparatus having the movement mechanism includes a movable support portion that supports the pressing member, a movable contact portion that comes into contact with the support portion to move the support portion, and a drive portion that moves the contact portion, and an upstream movement mechanism including the contact portion and the drive portion and a downstream movement mechanism including the support portion are separable; the belt unit is detachable with a pressing member unit including the pressing member and only the downstream-side moving mechanism of the upstream-side moving mechanism and the downstream-side moving mechanism of the moving mechanism, the image forming apparatus has a separation mechanism that separates the support portion from the contact portion, The image forming apparatus is characterized in that the pressing member unit is configured to be moved along the rotational axis direction of the inner roller and removed from the belt unit when the support portion is separated from the contact portion by the separation mechanism.

2. a release mechanism for releasing the tension, the support portion is rotatable about a rotation axis that is substantially parallel to the rotation axis direction of the inner roller, and is set in a free state when the tension is released by the release mechanism; the rotation axis is positioned so that the support portion in the free state rotates in a direction away from the contact portion, The release mechanism constitutes the separation mechanism.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. a retraction mechanism that moves the contact portion to a retracted position where the contact portion does not contact the support portion, the support portion is rotatable about a rotation axis that is substantially parallel to a rotation axis direction of the inner roller, and is placed in a free state when the contact portion is moved to the retracted position; the rotation axis is positioned so that the support portion in the free state rotates in a direction toward the contact portion, the pressing member unit is provided with a restricting portion that comes into contact with the support portion that has rotated in the free state to restrict the rotation of the support portion and holds the support portion in a state spaced apart from the contact portion, The retraction mechanism and the restriction portion constitute the separation mechanism.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. 4. The image forming apparatus according to claim 1, wherein the pressing member unit has a first engagement portion extending along the rotational axis direction of the inner roller, and the belt unit has a second engagement portion with which the first engagement portion slidably engages.

5. 5. The image forming apparatus according to claim 1, wherein the pressing member unit is pulled out from a housing of the image forming apparatus and detached from the belt unit held by the housing.

6. 6. The image forming apparatus according to claim 1, wherein the pressing member unit includes the inner roller.

7. 7. The image forming apparatus according to claim 1, wherein a guide member for guiding the recording material conveyed to the transfer section is fixed to the pressing member unit.

8. The image forming apparatus according to any one of claims 1 to 7, characterized in that the moving mechanism has an elastic deformation portion between the contact portion and the drive portion that can elastically deform, and the drive portion is capable of changing the deformation amount of the elastic deformation portion.

9. 9. The image forming apparatus according to claim 8, wherein the pressing member is elastically deformable, and the elastic modulus of the pressing member is greater than the elastic modulus of the elastic deformation portion.

10. 10. The image forming apparatus according to claim 8, wherein the moving mechanism includes a clutch mechanism connected to a moving part that moves integrally with the contact part or the support part.

11. 11. The image forming apparatus according to claim 10, wherein the clutch mechanism allows the moving part to move when the drive part moves the support part, and restricts the movement when the transfer is performed.

12. 10. The image forming apparatus according to claim 8, wherein the moving mechanism includes a damper mechanism connected to a moving part that moves integrally with the contact part or the support part.

13. 13. The image forming apparatus according to claim 12, wherein the damper mechanism allows the moving part to move when the driving part moves the support part, and restricts the movement when the transfer is performed.

14. The image forming apparatus according to any one of claims 1 to 13, characterized in that the pressing member is arranged such that its longitudinal direction is approximately parallel to the width direction of the belt, its upstream end in the short direction in the rotation direction of the belt is fixed to the support portion, and its downstream end in the short direction in the rotation direction of the belt is composed of a plate-like member that can contact the inner surface of the belt.

15. 15. The image forming apparatus according to claim 1, wherein the belt is an intermediate transfer member that conveys a toner image that has been primarily transferred from an image carrier to a recording material in the transfer section for secondary transfer.

Images