Image forming device

Abstract

To obtain stable cleaning property with a simple configuration when a cleaning device of an intermediate transfer body has three contact members.SOLUTION: First and second position regulation parts 38, 37 provided on a second support 34 for supporting three contact members are engaged with bearing members 251, 251 of two counter rollers 241, 242 of three counter rollers 241, 242, 243 with which the three contact members 311, 312, 313 are in contact with an intermediate transfer body 20 therebetween, thereby determining the position of the second support 34 with respect to a first support 26 for supporting the first, second, and third counter rollers 241, 242, 243.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, for example, electrophotographic image forming apparatuses employ an intermediate transfer system in which toner images formed on multiple photosensitive members are primarily transferred onto an intermediate transfer member, and then secondarily transferred onto a recording material such as paper. An intermediate transfer belt formed of an endless belt is often used as the intermediate transfer member.

[0003] Toner particles (secondary transfer residual toner particles) remaining on the intermediate transfer belt without being transferred to the recording material are removed and collected from the intermediate transfer belt by a cleaning device. This cleaning device is also used to remove unnecessary toner images from the intermediate transfer belt, such as test toner images formed on the intermediate transfer belt for image density control or toner images remaining on the intermediate transfer belt after jam processing. Known cleaning devices include electrostatic cleaning devices (electrostatic cleaning devices) that employ an electrostatic cleaning method to electrostatically collect particles (secondary transfer residual toner particles) from the intermediate transfer belt. An electrostatic cleaning device has a cleaning member (electrostatic cleaning member) such as a brush roller as a contact member that contacts the surface of the intermediate transfer belt. A voltage is applied to the cleaning member or to an opposing member that contacts the cleaning member via the intermediate transfer belt, causing a current to flow between the cleaning member and the opposing member. This electrostatically moves particles (secondary transfer residual toner particles) from the intermediate transfer belt to the cleaning member, removing them from the intermediate transfer belt. Conventionally, electrostatic cleaning devices generally have two cleaning members so as to remove positively charged toner and negatively charged toner from the intermediate transfer belt.

[0004] Recently, with the trend toward higher speeds and higher image quality in image forming devices, electrostatic cleaning devices are being required to have higher cleaning capabilities. Accordingly, it has been proposed to increase the number of cleaning members in order to improve the cleaning capabilities of electrostatic cleaning devices. Patent Documents 1 and 2 propose electrostatic cleaning devices having three cleaning members. Patent Document 2 also proposes a configuration in which a cleaning member and a collection roller that electrostatically collects toner collected by the cleaning member are combined into a subunit, and this subunit is placed inside a casing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5939473 [Patent Document 2] Patent No. 6264650 Summary of the Invention [Problem to be solved by the invention]

[0006] To ensure that the cleaning performance of an electrostatic cleaning device is optimal, it is important that the penetration depth of the cleaning member into the surface of the intermediate transfer belt is consistent with a set value. If this penetration depth is smaller than the set value, the chances of contact between the cleaning member and the surface of the intermediate transfer belt decrease, and the electrostatic force required to move the toner becomes weaker. This can result in lower cleaning performance than expected. Conversely, if this penetration depth is greater than the set value, the force acting between the cleaning member and the intermediate transfer belt increases, potentially accelerating deterioration of the intermediate transfer belt and cleaning member due to wear and other factors. One possible reason for this penetration depth not being consistent with the set value is variations in component size.

[0007] As mentioned above, in the configuration of Patent Document 2, multiple cleaning members are each organized into sub-units and placed inside a casing. This configuration requires a large number of components to determine the positional relationship between the cleaning members and the surface of the intermediate transfer belt, which can lead to significant variations in the amount of penetration of the cleaning members into the intermediate transfer belt. To prevent this and achieve stable cleaning performance, it is necessary to increase the precision of the components, which can lead to increased costs. Furthermore, this configuration is likely to increase costs due to the complexity of the device configuration and the increased number of components.

[0008] Therefore, it is desirable to have a configuration that can determine the positional relationship between the cleaning member and the intermediate transfer belt using as few parts as possible, thereby suppressing variations in the amount of penetration of the cleaning member into the intermediate transfer belt and achieving stable cleaning performance.

[0009] Therefore, an object of the present invention is to obtain stable cleaning performance with a simple configuration when the cleaning device for the intermediate transfer member has three contact members. [Means for solving the problem]

[0010] The above object is achieved by an image forming apparatus according to the present invention. In summary, a typical configuration of the present invention includes an image carrier that carries a toner image, a rotatable intermediate transfer member that transports the toner image that has been primarily transferred from the image carrier at a primary transfer unit so that the toner image can be secondarily transferred to a recording material at a secondary transfer unit, first, second, and third rollers that are arranged on the inner circumferential surface of the intermediate transfer member downstream of the secondary transfer unit and upstream of the primary transfer unit with respect to the rotation direction of the intermediate transfer member, and that contact the inner circumferential surface of the intermediate transfer member along a width direction that is approximately perpendicular to the moving direction of the surface of the intermediate transfer member, a first support that rotatably supports the first, second, and third rollers at at least one end side in the width direction, and a first support that is arranged on the outer circumferential surface of the intermediate transfer member, and that contacts the outer circumferential surface of the intermediate transfer member along the width direction. first, second, and third contact members capable of removing toner from the surface of the intermediate transfer body,a second support member that supports the first, second, and third contact members at least at one end side in the width direction; and a current supply means that supplies current between the first, second, and third contact members and the first, second, and third rollers, respectively. Among the first, second, and third contact members, the third contact member is 、 This is an image forming apparatus characterized in that the absolute value of the current flowing when in contact with the image area on the intermediate transfer body immediately after passing through the secondary transfer portion during image forming operation is the largest, the first roller and the second roller are supported by the first support via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction, the second support is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support relative to the first support is determined by the engagement of the first and second position regulating portions with the first and second bearing members, respectively. Another representative configuration of the present invention includes an image carrier that carries a toner image, a rotatable intermediate transfer body that transports the toner image that has been primarily transferred from the image carrier in a primary transfer section to a recording material in a secondary transfer section for secondary transfer, and first, second, and third rollers that are arranged on an inner circumferential surface side of the intermediate transfer body downstream of the secondary transfer section and upstream of the primary transfer section with respect to the rotation direction of the intermediate transfer body, and that come into contact with the inner circumferential surface of the intermediate transfer body along a width direction that is approximately perpendicular to the moving direction of the surface of the intermediate transfer body, a first support that rotatably supports the first, second, and third rollers at least on one end side in the width direction, and first, second, and third contact members that are arranged on an outer circumferential surface side of the intermediate transfer body, come into contact with the outer circumferential surface of the intermediate transfer body along the width direction, and are capable of removing toner from the surface of the intermediate transfer body, and that come into contact with the inner circumferential surface of the intermediate transfer body via the intermediate transfer body. and a second support body supporting the first, second, and third contact members at least at one end in the width direction, wherein the third contact member of the first, second, and third contact members is disposed at the most downstream position in the direction of movement of the surface of the intermediate transfer body, the first roller and the second roller are supported by the first support body via a first bearing member and a second bearing member, respectively, at least at one end in the width direction, and the second support body is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support body relative to the first support body is determined by the engagement of the first and second position regulating portions with the first and second bearing members, respectively. Another representative configuration of the present invention includes an image carrier that carries a toner image, a rotatable intermediate transfer member that transports the toner image that has been primarily transferred from the image carrier in a primary transfer unit to a recording material in a secondary transfer unit for secondary transfer, and first, second, and third rollers that are arranged on an inner circumferential surface side of the intermediate transfer member downstream of the secondary transfer unit and upstream of the primary transfer unit with respect to the rotation direction of the intermediate transfer member, and that come into contact with the inner circumferential surface of the intermediate transfer member along a width direction that is approximately perpendicular to the moving direction of the surface of the intermediate transfer member, a first support that rotatably supports the first, second, and third rollers at least on one end side in the width direction, and first, second, and third contact members that are arranged on an outer circumferential surface side of the intermediate transfer member, that come into contact with the outer circumferential surface of the intermediate transfer member along the width direction, and that are capable of removing toner from the surface of the intermediate transfer member, and and a third contact member, and a second support body that supports the first, second, and third contact members at least at one end side in the width direction, wherein of the first, second, and third contact members, the first contact member is arranged at the most upstream side in the moving direction of the surface of the intermediate transfer body, and the second contact member is arranged at the most downstream side in the moving direction of the surface of the intermediate transfer body, the first roller and the second roller are supported by the first support body via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction, the second support body is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support body relative to the first support body is determined by the engagement of the first and second position regulating portions with the first and second bearing members, respectively.

[0011] Another representative configuration of the present invention includes an image carrier that carries a toner image, a rotatable intermediate transfer body that transports the toner image that has been primarily transferred from the image carrier in a primary transfer section to a recording material in a secondary transfer section for secondary transfer, first and second rollers that are arranged on the inner circumferential surface side of the intermediate transfer body downstream of the secondary transfer section and upstream of the primary transfer section with respect to the rotation direction of the intermediate transfer body, and that contact the inner circumferential surface of the intermediate transfer body along a width direction that is approximately perpendicular to the moving direction of the surface of the intermediate transfer body, a first support that rotatably supports the first and second rollers at least on one end side in the width direction, and a second support that is arranged on the outer circumferential surface side of the intermediate transfer body and that contacts the outer circumferential surface of the intermediate transfer body along the width direction. and capable of removing toner from the surface of the intermediate transfer body.an image forming apparatus having first, second, and third contact members, one of which contacts the first roller via the intermediate transfer body and the other two of which contact the second roller via the intermediate transfer body, and a second support body that supports the first, second, and third contact members at least at one end side in the width direction, wherein the first roller and the second roller are supported by the first support body via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction, and the second support body is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support body relative to the first support is determined by the first and second position regulating portions engaging with the first and second bearing members, respectively. [Effects of the Invention]

[0012] According to the present invention, when the cleaning device for the intermediate transfer member has three contact members, stable cleaning performance can be obtained with a simple configuration. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] 1 is a schematic cross-sectional view of the periphery of a cleaning device according to a first embodiment. [Figure 3] 3 is a schematic diagram for explaining a power supply mode of the cleaning device of the first embodiment. FIG. [Figure 4] FIG. 2 is a schematic block diagram showing a control mode of the image forming apparatus. [Figure 5] 1 is a schematic perspective view of the periphery of one end of a cleaning device according to a first embodiment. [Figure 6] FIG. 6 is a schematic side view seen in the direction of arrow A in FIG. 5(c). [Figure 7] 10 is a schematic side view of the periphery of one end of a cleaning device according to a modified example of the first embodiment. FIG. [Figure 8]FIG. 10 is a schematic cross-sectional view of the periphery of a cleaning device according to a second embodiment. [Figure 9] FIG. 10 is a schematic perspective view of the periphery of one end of a cleaning device according to a second embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view of the periphery of a cleaning device according to a modified example of the second embodiment. [Figure 11] 10A and 10B are schematic diagrams for explaining another modified example of the positioning configuration. DETAILED DESCRIPTION OF THE INVENTION

[0014] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0015] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a tandem printer that employs an intermediate transfer method.

[0016] Image forming apparatus 100 has four image forming units 1Y, 1M, 1C, and 1K that form images in the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. The four image forming units 1Y, 1M, 1C, and 1K are arranged in a row along the direction of movement of a substantially horizontally disposed flat portion of intermediate transfer belt 20, which will be described later. Image forming apparatus 100 is capable of forming full-color images on recording material S by electrophotography in response to image signals transmitted from an external device such as a personal computer. 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 numerals indicating that the element is for one of the colors. In this embodiment, the image forming unit 1 includes photosensitive drums 11 (11Y, 11M, 11C, 11K), chargers 12 (12Y, 12M, 12C, 12K), exposure devices 13 (13Y, 13M, 13C, 13K), developers 14 (14Y, 14M, 14C, 14K), primary transfer rollers 21 (21Y, 21M, 21C, 21K), and drum cleaning devices 15 (15Y, 15M, 15C, 15K), which will be described later. The order (position) of the image forming units for each color is not limited to that of this embodiment. Furthermore, the number of image forming units and the colors of the images formed are also not limited to those of this embodiment.

[0017] The photosensitive drum 11, a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as an image carrier, is rotated in the direction of arrow R1 (counterclockwise) in FIG. 1 at a predetermined peripheral speed (process speed). 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 serving as charging means. During the charging process, a predetermined charging bias (charging voltage) 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 (laser scanner) 13 serving as exposure means, forming an electrostatic image (electrostatic latent image) on the photosensitive drum 11. The exposure device 13 irradiates the surface of the photosensitive drum 11 with laser light (image light) modulated based on image information from an external device. The electrostatic image formed on the photosensitive drum 11 is developed (visualized) by a developing device 14 serving as developing means, which supplies toner as a developer, thereby forming a toner image on the photosensitive drum 11. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 11 (negative in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 11, which has been uniformly charged and then exposed based on image information to reduce the absolute value of the potential (reverse development method). In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative. During the development process, a predetermined development bias (development voltage) is applied by a development power source (not shown) to the development roller serving as a developer carrier (developing member) provided in the developer 14.

[0018] An intermediate transfer belt 20, which is an endless belt, is disposed facing the four photosensitive drums 11. The intermediate transfer belt 20 is stretched around a plurality of tension rollers 241 to 247 and tensioned with a predetermined tension. A drive roller (e.g., tension roller 243 or tension roller 246), which is one of the tension rollers, is driven to rotate. As a result, the intermediate transfer belt 20 rotates (circularly moves) in the direction of arrow R2 (clockwise direction) in FIG. 1 at a predetermined peripheral speed (process speed) corresponding to the peripheral speed of the photosensitive drums 11. Another of the tension rollers, an inner secondary transfer roller 247, functions as an opposing member (opposite electrode) of an outer secondary transfer roller 23, which will be described later. The inner secondary transfer roller 247 is electrically grounded (connected to ground). Primary transfer rollers 21Y, 21M, 21C, and 21K, which are roller-type primary transfer members serving as primary transfer means, are arranged on the inner circumferential surface of the intermediate transfer belt 20, corresponding to the photosensitive drums 11Y, 11M, 11C, and 11K, respectively. In this embodiment, the primary transfer rollers 21 are arranged at positions where they contact the photosensitive drums 11 via the intermediate transfer belt 20. The primary transfer rollers 21 are pressed against the photosensitive drums 11 and contact the photosensitive drums 11 via the intermediate transfer belt 20, forming a primary transfer portion (primary transfer nip) T1 where the photosensitive drums 11 and the intermediate transfer belt 20 come into contact. Of the multiple tension rollers, the tension rollers other than the drive roller are driven to rotate in accordance with the rotation of the intermediate transfer belt 20. The toner image formed on the photosensitive drum 11 is transferred (primary transfer) onto the rotating intermediate transfer belt 20 at the primary transfer portion T1 by the action of the primary transfer rollers 21. During the primary transfer process, a primary transfer bias (primary transfer voltage), 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 roller 21 by a primary transfer power supply (high-voltage power supply) E1 (FIG. 4). This supplies a primary transfer current to the primary transfer portion T1. For example, during the primary transfer process, a constant voltage controlled primary transfer bias of about +1 to +3 kV is applied to the core of each primary transfer roller 21, and a current of about +20 to +100 μA, as viewed from the primary transfer power supply E1 side, flows through each primary transfer portion T1.For example, when a full-color image is formed, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 11 are sequentially transferred onto the intermediate transfer belt 20 so as to be superimposed on the same image position (image area). The tension rollers 241 to 247 and the primary transfer rollers 21Y, 21M, 21C, and 21K are rotatably supported by a belt frame 26 (FIG. 5) serving as a first support body, which will be described later.

[0019] On the outer peripheral surface of the intermediate transfer belt 20, a secondary transfer outer roller 23, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed at a position facing the inner secondary transfer roller 247. The outer secondary transfer roller 23 is pressed toward the inner secondary transfer roller 247 and abuts against the inner secondary transfer roller 247 via the intermediate transfer belt 20, forming a secondary transfer portion (secondary transfer nip) T2 where the intermediate transfer belt 20 and the outer secondary transfer roller 23 abut. At the secondary transfer portion T2, the toner image formed on the intermediate transfer belt 20 is transferred (secondarily transferred) onto a recording material (transfer material, recording medium, sheet) S, which is being conveyed while being sandwiched between the intermediate transfer belt 20 and the outer secondary transfer roller 23, by the action of the outer secondary transfer roller 23. During the secondary transfer process, a secondary transfer bias (secondary transfer voltage), which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the outer secondary transfer roller 23 by a secondary transfer power source (high-voltage power source) E2 (FIG. 4). This supplies a secondary transfer current to the secondary transfer portion T2. ​​For example, during the secondary transfer process, a constant voltage controlled secondary transfer bias of approximately +1 to +7 kV is applied to the core of the outer secondary transfer roller 23, and a current of approximately +40 to +120 μA is passed through the secondary transfer portion T2 as viewed from the secondary transfer power supply E2 side. Recording material S, such as paper or plastic sheets, is stored in cassettes 61 and 62 serving as recording material storage units. The recording material S is fed one sheet at a time from either cassette 61 or 62 to a feeding path 81 by the rotation of either feed roller 71 or 72 serving as a feeding member. The recording material S is then conveyed to the secondary transfer portion T2 by registration roller 74 serving as a conveying member in synchronization with the toner image on the intermediate transfer belt 20. The positions and number of the recording material storage units are not limited to those in this embodiment. Alternatively, a roller corresponding to the inner secondary transfer roller 247 in this embodiment may be used as the secondary transfer member, and a secondary transfer bias of the opposite polarity to that in this embodiment (the same polarity as the normal charging polarity of the toner) may be applied to it. In this case, a roller corresponding to the outer secondary transfer roller 23 in this embodiment may be used as the opposing member (opposing electrode), which may be electrically grounded.

[0020] The recording material S onto which the toner image has been transferred is conveyed to a fixing device (thermal fixing device) 5 as fixing means. The fixing device 5 applies heat and pressure (thermocompression) to the recording material S carrying the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material S. The recording material S onto which the toner image has been fixed passes through a discharge conveyance path 82 and is discharged (output) to a discharge tray 64 provided outside the main body of the image forming apparatus 100.

[0021] Further, deposits such as toner (primary transfer residual toner) remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 20 are removed and collected from the photosensitive drum 11 by a drum cleaning device 15 serving as a photosensitive body cleaning means. Further, deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 20 without being transferred to the recording material S are removed and collected from the intermediate transfer belt 20 by a cleaning device (belt cleaning device) 30 serving as an intermediate transfer body cleaning means. The cleaning device 30 will be described in more detail later.

[0022] In this embodiment, the intermediate transfer belt 20 is a multi-layer belt having a base layer (backside layer), an elastic layer (intermediate layer), and a surface layer. The base layer is made of a material such as a resin such as polyimide or polycarbonate, or various rubbers containing an appropriate amount of carbon black as an antistatic agent. The elastic layer is made of a material such as various rubbers such as CR rubber, urethane rubber, or silicone rubber containing an appropriate amount of an ion conductive agent. For example, an aliphatic sulfonate salt is used as the ion conductive agent. The surface layer is made of a resin such as a urethane resin or a fluororesin. The volume resistivity of the intermediate transfer belt 20 is, for example, 5×10 8 ~1×10 14 Ω·cm (23° C., 50% RH, 100 V applied). The surface resistivity of the intermediate transfer belt 20 is, for example, 5×10 8 ~1×10 14Ω / □ (23°C, 50% RH, 100 V applied). In this embodiment, the intermediate transfer belt 20, the tension rollers 241 to 247, the primary transfer rollers 21Y, 21M, 21C, and 21K, and the cleaning device 30 integrally constitute an intermediate transfer unit 22 that is detachable from the main body of the image forming apparatus 100.

[0023] 2.Cleaning device 2 is a schematic cross-sectional view of the vicinity of the cleaning device (belt cleaning device) 30 in this embodiment. The cleaning device 30 is disposed downstream of the secondary transfer unit T2 and upstream of the primary transfer unit T1 (the most upstream primary transfer unit T1Y) in the moving direction (rotation direction, conveying direction) of the surface of the intermediate transfer belt 20. Note that, here, positions such as upstream (most upstream), downstream (most downstream), and center in relation to the cleaning device 30 and its elements refer to positions in the moving direction of the surface of the intermediate transfer belt 20, even if not specifically stated.

[0024] In this embodiment, the cleaning device 30 is an electrostatic cleaning device (electrostatic cleaning device) that electrostatically collects toner and other adhering matter on the intermediate transfer belt 20. In particular, in this embodiment, the cleaning device 30 is configured as an electrostatic brush cleaning device that uses a rotatable roller-shaped conductive fur brush (conductive fur brush roller). The cleaning device 30 removes adhering matter from the intermediate transfer belt 20, such as secondary transfer residual toner that remains on the intermediate transfer belt 20 after the secondary transfer. The cleaning device 30 is also used to remove unnecessary toner images from the intermediate transfer belt 20, such as test toner images and toner images remaining after jam clearance.

[0025] In this embodiment, the cleaning device 30 has first, second, and third brushes 311, 312, and 313, which are first, second, and third cleaning members (electrostatic cleaning members, conductive members) serving as first, second, and third contact members. The cleaning device 30 also has first, second, and third collection rollers 321, 322, and 323, which serve as first, second, and third collection members. The cleaning device 30 also has first, second, and third blades 331, 332, and 333, which serve as first, second, and third scraping members. The cleaning device 30 also has a housing 35 that holds the brushes 311, 312, and 313, the collection rollers 321, 322, and 323, and the blades 331, 332, and 333, and that accommodates toner and other toner removed from the intermediate transfer belt 20. The housing 35 is composed of a cleaning frame 34, which will be described later, and other components. Furthermore, the cleaning device 30 has a conveying member 36 such as a screw. A first cleaning unit 301 is made up of a first brush 311, a first collection roller 321, a first blade 331, etc. A second cleaning unit 302 is made up of a second brush 312, a second collection roller 322, a second blade 332, etc. A third cleaning unit 303 is made up of a third brush 313, a third collection roller 323, a third blade 333, etc.

[0026] The first, second, and third brushes 311, 312, and 313 are each composed of a rotatable roller-shaped conductive fur brush (conductive fur brush roller). The first, second, and third brushes 311, 312, and 313 each have an outer diameter of, for example, 21 mm when the brush fibers are not deformed by an external force. The brush fibers of the first, second, and third brushes 311, 312, and 313 each have an electrical resistance of, for example, 3×10 5 ~1×10 13 The brushes 311, 312, and 313 are made of carbon-dispersed nylon fibers, acrylic fibers, or polyester fibers with a fiber thickness of, for example, 2 to 15 denier and a resistivity of, for example, Ω / cm. The brush fibers are planted at a density of, for example, 50,000 to 500,000 fibers per inch. 2In this embodiment, first, second, and third opposing rollers 241, 242, and 243, which are tension rollers for the intermediate transfer belt 20, are arranged at positions facing the first, second, and third brushes 311, 312, and 313, respectively, across the intermediate transfer belt 20. The first, second, and third brushes 311, 312, and 313 are brought into contact with the first, second, and third opposing rollers 241, 242, and 243, respectively, across the intermediate transfer belt 20. In this embodiment, the first, second, and third opposing rollers 241, 242, and 243 are made of rotatable metal (aluminum in this embodiment) rollers (metal rollers). At least one of the first, second, and third opposing rollers 241, 242, and 243 may be a roller (elastic roller) having an elastic layer made of a conductive elastic material formed around a core metal (metallic rotating shaft material). The first, second, and third brushes 311, 312, and 313 are disposed with a penetration depth of, for example, approximately 1.0 to 2.0 mm relative to the intermediate transfer belt 20 backed up by the first, second, and third opposing rollers 241, 242, and 243, respectively. This penetration depth is the difference between the distance between the substrate on which the brush fibers are implanted and the surface of the intermediate transfer belt 20 and the axial length of the brush fibers when not deformed by an external force. In this embodiment, this penetration amount is represented by the value obtained by subtracting the axial distance (distance between the rotation centers) between the brush roller and the opposing roller from the sum of the radius of the brush roller and the radius of the opposing roller (to which the thickness of the belt may also be added) when the brush fibers are not deformed by external force in a cross section approximately perpendicular to the rotation axis direction of the brush roller.

[0027] The first, second, and third brushes 311, 312, and 313 are driven to rotate in the direction of arrow R3 in FIG. 2 (clockwise direction) by a drive motor (not shown) serving as a drive unit. That is, the first, second, and third brushes 311, 312, and 313 rotate so as to move in the opposite direction to the movement direction of the intermediate transfer belt 20 at the contact portion with the intermediate transfer belt 20, thereby rubbing the surface of the intermediate transfer belt 20. The first, second, and third brushes 311, 312, and 313 are driven to rotate at a peripheral speed that is, for example, 20 to 80% of the peripheral speed (surface movement speed) of the intermediate transfer belt 20. The first, second, and third opposing rollers 241, 242, and 243 are driven to rotate in accordance with the rotation of the intermediate transfer belt 20. The first, second, and third brushes 311, 312, and 313 are arranged such that their rotation axes are substantially parallel to a direction (herein also referred to as the "width direction") that is substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 20. In this embodiment, the length of the first, second, and third brushes 311, 312, and 313 in the rotation axis direction is shorter than the length (width) of the intermediate transfer belt 20 in the width direction. Note that the length of the first, second, and third brushes 311, 312, and 313 in the rotation axis direction may be longer than the maximum image formation width on the intermediate transfer belt 20 in the width direction of the intermediate transfer belt 20. Furthermore, the first, second, and third opposing rollers 241, 242, and 243 are arranged such that their rotation axes are substantially parallel to the width direction of the intermediate transfer belt 20. In this embodiment, the lengths of the first, second, and third opposing rollers 241, 242, and 243 in the direction of their rotational axes are equal to the lengths of the first, second, and third brushes 311, 312, and 313 in the direction of their rotational axes. Here, when the opposing rollers are drive rollers for the intermediate transfer belt 20, the length of the opposing rollers in the direction of their rotational axes may be longer than the length of the brushes facing the opposing rollers in the direction of their rotational axes. The length of the drive roller for the intermediate transfer belt 20 in the direction of its rotational axes is longer than the length (width) of the intermediate transfer belt 20 in the width direction. When the opposing rollers are idler rollers, the length of the opposing rollers in the direction of their rotational axes may be equal to the length of the brushes facing the opposing rollers in the direction of their rotational axes.

[0028] The contact portion between the first brush 311 and the intermediate transfer belt 20 is the first contact portion CL1. The contact portion between the second brush 312 and the intermediate transfer belt 20 is the second contact portion CL2. The contact portion between the third brush 313 and the intermediate transfer belt 20 is the third contact portion CL3. The first contact portion CL1 is a cleaning portion where the first brush 311 collects toner from the intermediate transfer belt 20. The second contact portion CL2 is a cleaning portion where the second brush 312 collects toner from the intermediate transfer belt 20. The third contact portion CL3 is a discharge portion where the third brush 313 supplies current to the intermediate transfer belt 20 to even out ion distribution in the intermediate transfer belt 20 (also referred to as "discharge" here), as will be described later. The third contact portion CL3 is also a cleaning portion where the third brush 313 collects at least a portion of toner from the intermediate transfer belt 20. The first, second, and third contact portions CL1, CL2, and CL3 are located downstream of the secondary transfer portion T2 and upstream of the primary transfer portion T1 (the most upstream primary transfer portion T1Y) in the moving direction of the surface of the intermediate transfer belt 20. In this embodiment, the first contact portion CL1 is located upstream of the second contact portion CL2, and the second contact portion CL2 is located upstream of the third contact portion CL3 in the moving direction of the surface of the intermediate transfer belt 20.

[0029] The first, second, and third collection rollers 321, 322, and 323 are rotatable metal rollers (metal rollers) made of aluminum in this embodiment. The first, second, and third collection rollers 321, 322, and 323 are positioned with a penetration depth of, for example, approximately 1.5 to 2.5 mm relative to the first, second, and third brushes 311, 312, and 313, respectively. The first, second, and third collection rollers 321, 322, and 323 are driven to rotate in the direction of arrow R4 (counterclockwise) in FIG. 2 by a drive motor (not shown) serving as a driving means. In other words, the first, second, and third collection rollers 321, 322, and 323 rotate so as to move in the same direction as the first, second, and third brushes 311, 312, and 313 at their contact portions with the first, second, and third brushes 311, 312, and 313. The first, second, and third collection rollers 321, 322, and 323 are rotated at, for example, the same speed (circumferential speed) as the first, second, and third brushes 311, 312, and 313. The first, second, and third collection rollers 321, 322, and 323 are disposed such that their rotational axes are substantially parallel to the width direction of the intermediate transfer belt 20. In this embodiment, the length of the first, second, and third collection rollers 321, 322, and 323 in the rotational axis direction is longer than the length of the first, second, and third brushes 311, 312, and 313 in the rotational axis direction.

[0030] The first, second, and third blades 331, 332, and 333 are disposed in contact with the first, second, and third collection rollers 321, 322, and 323, respectively. The first, second, and third blades 331, 332, and 333 are plate-shaped members formed of a rubber material such as urethane rubber as an elastic member. The first, second, and third blades 331, 332, and 333 each have a predetermined length and a predetermined thickness in the longitudinal direction, which is disposed approximately parallel to the rotational axis direction of the first, second, and third collection rollers 321, 322, and 323, and in the lateral direction, which is approximately perpendicular to the longitudinal direction. The first, second, and third blades 331, 332, and 333 are disposed with a penetration depth of, for example, approximately 0.5 to 2.0 mm relative to the first, second, and third collection rollers 321, 322, and 323, respectively. The first, second, and third blades 331, 332, and 333 are brought into contact with the respective collection rollers so as to be in a counter direction (with their free ends facing upstream in the rotation direction) with respect to the rotation direction of the first, second, and third collection rollers 321, 322, and 323. In this embodiment, the longitudinal lengths of the first, second, and third blades 331, 332, and 333 are shorter than the lengths of the first, second, and third collection rollers 321, 322, and 323 in the rotation axis direction.

[0031] The length relationships among the intermediate transfer belt 20, brushes 311-313, collection rollers 321-323, blades 331-333, and opposing rollers (idler rollers, drive rollers) in the width direction of the intermediate transfer belt 20 may be as follows: brush < blade < opposing roller (idler roller) < intermediate transfer belt < collection roller < drive roller.

[0032] In this embodiment, during image formation (more specifically, during cleaning of secondary transfer residual toner during image formation), secondary transfer residual toner is collected mainly by the first and second brushes 311 and 312, and discharged by the third brush 313. That is, an electric field suitable for cleaning is formed between the first brush 311 and the first opposing roller 241 and between the second brush 312 and the second opposing roller 242. Furthermore, an electric field suitable for discharging is formed between the third brush 313 and the third opposing roller 243. As a result, secondary transfer residual toner on the intermediate transfer belt 20 is attracted mainly to the first and second brushes 311 and 312 and removed from the intermediate transfer belt 20, and is discharged by the third brush 313. Note that at least a portion of the secondary transfer residual toner on the intermediate transfer belt 20 may be removed from the intermediate transfer belt 20 by the third brush 313. That is, the third brush 313 discharges the intermediate transfer belt 20 by injecting or discharging electric charge, and collects less toner than either of the first and second brushes 311 and 312 to which a current flows in the same direction as the third brush 313. The toner attracted to the first, second, and third brushes 311, 312, and 313 is further transferred to the first, second, and third collection rollers 321, 322, and 323 by an electric field, and scraped off by the first, second, and third blades 331, 332, and 333. The toner scraped off from the first, second, and third collection rollers 321, 322, and 323 is contained in the housing 35 and further transported by the transport member 36 toward a collection container (not shown) provided in the image forming apparatus 100.

[0033] FIG. 3 is a schematic diagram illustrating a method for supplying power to the first, second, and third brushes 311, 312, and 313 in this embodiment. In this embodiment, a first brush power supply (high-voltage power supply) E11, which is a DC power supply, applies a positive DC voltage, which is opposite in polarity to the normal charging polarity of the toner, to the first opposing roller 241 under constant current control. In this embodiment, the first brush 311 is electrically floated, and the first collection roller 321 is electrically grounded. In this embodiment, when cleaning residual toner after secondary transfer during image formation, a current of +73 μA (−73 μA) is supplied to the first brush 311, as viewed from the first brush power supply E11 side (as viewed from the first brush 311 side). For example, the current flowing through the first brush 311 as viewed from the first brush power supply E11 side is defined as a positive current flowing from the first brush power supply E11 toward the first brush 311 (the same applies to other currents). Thus, in this embodiment, when a current flowing from the inner circumferential surface side toward the outer circumferential surface side of the intermediate transfer belt 20 is expressed as a positive value, a cleaning current of +73 μA, for example, for collecting toner on the intermediate transfer belt 20 is supplied to the first contact portion CL1.

[0034] In this embodiment, a positive DC voltage, which is opposite in polarity to the normal charging polarity of the toner, is applied to the second collection roller 322 by constant current control from a second brush power supply (high-voltage power supply) E12, which is a DC power supply. In this embodiment, the second brush 312 is electrically floated, and the second opposing roller 242 is electrically grounded. In this embodiment, when cleaning the residual toner after secondary transfer during image formation, a current of, for example, +73 μA flows through the second brush 312 as viewed from the second brush power supply E12. As a result, in this embodiment, when the current flowing from the inner circumferential surface of the intermediate transfer belt 20 to the outer circumferential surface thereof is expressed as a positive value, a cleaning current of, for example, −73 μA is supplied to the second contact portion CL2 for collecting the toner on the intermediate transfer belt 20.

[0035] In this embodiment, a third brush power supply (high-voltage power supply) E13, which is a DC power supply, applies a positive DC voltage, which is opposite to the normal charging polarity of the toner, to the third collection roller 323 under constant current control. In this embodiment, the third brush 313 is electrically floated, and the third opposing roller 243 is electrically grounded. During image formation, a current of +220 μA, for example, is supplied to the third brush 313 when cleaning the residual toner from secondary transfer during image formation. As a result, in this embodiment, a discharge current of −220 μA, for example, is supplied to the third contact portion CL3 to even out the uneven distribution of ions in the intermediate transfer belt 20, when the current flowing from the inner circumferential surface of the intermediate transfer belt 20 to the outer circumferential surface thereof is expressed as a positive value. The discharge current will be described in more detail below.

[0036] The constant current control adjusts the outputs of the first, second, and third brush power supplies E11, E12, and E13 so that the currents flowing through the first, second, and third brush power supplies E11, E12, and E13 are kept substantially constant (approaching the target value). The following method is used to control the outputs of the high-voltage power supplies at constant current. A current detection unit (current detection circuit) is provided between the voltage output unit of the high-voltage power supply and the voltage application target, and the current detection unit detects the current generated by the high-voltage power supply. Based on the detection result from the current detection unit, the output of the high-voltage power supply is adjusted so that the currents generated by the high-voltage power supplies are kept substantially constant (approaching the target value). The first, second, and third brush power supplies E11, E12, and E13 constitute current supply means that supply current between the first, second, and third brushes 311, 312, and 313 and the first, second, and third opposing rollers 241, 242, and 243, respectively.

[0037] As described above, by supplying current to the first and second brushes 311 and 312, an electric field (cleaning electric field) suitable for collecting toner on the intermediate transfer belt 20 is formed between the first and second brushes 311 and 312 and the intermediate transfer belt 20. As a result, the secondary transfer residual toner on the intermediate transfer belt 20 is electrostatically attracted to the first and second brushes 311 and 312 and removed from the intermediate transfer belt 20. Of the secondary transfer residual toner on the intermediate transfer belt 20, mainly toner charged with a positive polarity opposite to the normal charge polarity of the toner (herein also referred to as "reverse polarity toner") adheres to the first brush 311. Furthermore, of the secondary transfer residual toner on the intermediate transfer belt 20, mainly toner charged with a negative polarity opposite to the normal charge polarity of the toner (herein also referred to as "normal polarity toner") adheres to the second brush 312. Furthermore, this toner is transferred from the first and second brushes 311 and 312 to the second and third collection rollers 321 and 322 by an electric field formed between the first and second collection rollers 321 and 322 and the first and second brushes 311 and 312. Furthermore, the toner transferred to the first and second collection rollers 321 and 322 is scraped off the first and second collection rollers 321 and 322 by the first and second blades 331 and 332.

[0038] Here, when cleaning the secondary transfer residual toner during the image formation operation, most of the secondary transfer residual toner is removed from the intermediate transfer belt 20 by the first and second brushes 311 and 312. However, among the relatively small amount of secondary transfer residual toner that has passed through the first and second contact portions CL1 and CL2, negatively charged normal polarity toner is removed from the intermediate transfer belt 20 by the third brush 313. Furthermore, after being temporarily collected by the third brush 313, at least a portion of the normal polarity toner may have its polarity reversed by discharge in the third brush 311, becoming reversely charged toner and re-adhering to the intermediate transfer belt 20. Furthermore, among the relatively small amount of secondary transfer residual toner that has passed through the first and second contact portions CL1 and CL2, positively charged reversely charged toner passes through the third contact portion CL3. The oppositely charged toner that has re-adhered from the third brush 313 or that has passed through the third contact portion CL3 moves to the photosensitive drum 1 at the same time as the primary transfer at the primary transfer portion T1 (for example, the most upstream primary transfer portion T1Y) and is collected by the drum cleaning device 15.

[0039] Note that a power supply method in which a high-voltage power supply is located on the brush side, such as the power supply method for the second and third brushes 312 and 313 in this embodiment, is referred to as "external power supply." Furthermore, a power supply method in which a high-voltage power supply is located on the opposing roller side, such as the power supply method for the first brush 311 in this embodiment, is referred to as "internal power supply." The power supply method (power supply location) for the first, second, and third brushes 311, 312, and 313 is not limited to that described in this embodiment. The power supply method (power supply location) for the first, second, and third brushes 311, 312, and 313 can be selected arbitrarily, taking into account the characteristics of various components such as the intermediate transfer belt 20, the device layout, and the like. In this case, for example, the polarity of the voltage output by the power supply can be appropriately set so that the direction of the current supplied to the first, second, and third contact portions CL1, CL2, and CL3 is the same as in this embodiment.

[0040] The positioning structure of the cleaning device 30 in this embodiment will be described in detail later.

[0041] 3. Discharge current In an intermediate transfer image forming apparatus, the electrical resistance of the intermediate transfer belt may increase due to the application of current during image formation. This phenomenon is particularly pronounced when an ionically conductive belt is used as the intermediate transfer belt. For example, the intermediate transfer belt may have multiple layers, such as a base material, an elastic layer, and a surface layer, and an ionically conductive agent may be used to adjust the electrical resistance of the elastic layer. When an ionically conductive belt is used as the intermediate transfer belt, an electric field generated within the belt by the flow of current exerts a force on cations and anions, which are responsible for ion conductivity. Positively charged cations migrate in the direction of the electric field, while negatively charged anions migrate in the opposite direction. Consider, for example, a case where the normal charge polarity of toner is negative. In this case, for primary transfer, a positive voltage is applied to a primary transfer member in contact with the inner circumferential surface of the intermediate transfer belt, and a current is supplied to the primary transfer section in a direction from the inner circumferential surface of the intermediate transfer belt toward the outer circumferential surface (also referred to as the "outward direction" here). As a result, positive ions migrate toward the outer peripheral surface of the intermediate transfer belt, while negative ions migrate toward the inner peripheral surface of the intermediate transfer belt. For secondary transfer, a positive voltage is applied to a secondary transfer member abutting the outer peripheral surface of the intermediate transfer belt, supplying a current to the secondary transfer section in a direction from the outer peripheral surface of the intermediate transfer belt toward the inner peripheral surface (also referred to as the "inward direction" here). As a result, ions within the intermediate transfer belt migrate in the opposite direction to that during primary transfer (positive ions toward the inner peripheral surface, negative ions toward the outer peripheral surface). If the total charge amounts supplied to the intermediate transfer belt in the outward and inward directions are significantly out of balance, ions within the intermediate transfer belt become unbalanced, causing an increase in the electrical resistance of the intermediate transfer belt. As the electrical resistance of the intermediate transfer belt increases with repeated use, the absolute values ​​of the voltages required for primary and secondary transfer increase, making image defects more likely to occur due to discharge at the primary and secondary transfer sections.

[0042] In order to suppress the increase in electrical resistance of the intermediate transfer belt as described above and extend the life of the intermediate transfer belt, it is effective to supply a current to the intermediate transfer belt so as to even out the uneven distribution of ions in the intermediate transfer belt caused by the image formation operation. A cleaning member (electrostatic cleaning member) of an electrostatic cleaning device can be used as a discharge member for supplying a current to even out the uneven distribution of ions in the intermediate transfer belt ("discharging"). Note that the discharge member does not necessarily have a cleaning function, but for convenience, both a contact member used primarily for cleaning purposes and a contact member used primarily for discharging purposes will be referred to as a cleaning member. A contact member may be used for both cleaning and discharging purposes.

[0043] The current required to sufficiently level the ion distribution in the intermediate transfer belt during image formation is typically greater than the current (also referred to here as the "optimum cleaning current") suitable for recovering residual toner from the intermediate transfer belt after secondary transfer. For example, in a tandem-type full-color image forming apparatus, an outward current flows at four primary transfer stations and an inward current flows at one secondary transfer station, so the outward current tends to be greater than the inward current. Therefore, if a cleaning member is used to supply an inward current to level the ion distribution in the intermediate transfer belt, the current that needs to be supplied to the intermediate transfer belt by the cleaning member is typically greater than the optimal cleaning current.

[0044] Table 1 shows an example of the relationship between the currents supplied to the intermediate transfer belt 20 at each portion (primary transfer portion T1, secondary transfer portion T2, first and second contact portions CL1 and CL2) during the image forming operation in this embodiment.

[0045] [Table 1]

[0046] In Table 1, the value of the current flowing from the inner circumferential surface of the intermediate transfer belt 20 to the outer circumferential surface (outward) is expressed as a positive value, and the value of the current flowing from the outer circumferential surface of the intermediate transfer belt 20 to the inner circumferential surface (inward) is expressed as a negative value. In the example shown in Table 1, when the sum of the currents supplied to the primary transfer portion T1, the secondary transfer portion T2, and the first and second contact portions CL1 and CL2 during image formation operation is calculated, it is found that the outward current is 172 to 252 μA greater in absolute value than the inward current. This can cause an imbalance in the ions within the intermediate transfer belt 20, potentially increasing the electrical resistance of the intermediate transfer belt 20.

[0047] Here, the sum of the current values ​​supplied to the primary transfer unit T1, the secondary transfer unit T2, and the first, second, and third contact units CL1, CL2, and CL3 during image formation is defined as the "current balance" applied to the intermediate transfer belt 20 during image formation. In this embodiment, an inward current of 220 μA, for example, is supplied to the third contact unit CL3 during image formation to make this current balance approximately zero. This discharge current is −220 μA, where a current flowing in the direction from the inner circumferential surface of the intermediate transfer belt 20 to the outer circumferential surface is expressed as a positive value. In this embodiment, supplying such a discharge current to the third brush 311 during image formation can even out the uneven distribution of ions within the intermediate transfer belt 20. This suppresses an increase in the electrical resistance of the intermediate transfer belt 20 and extends its lifespan. The control unit 50 can set the discharge current value for each print job, for example, by referencing a pre-set data table stored in ROM 53. The setting of the discharge current may vary depending on the type of recording material S used in image formation, the environment (at least one of the temperature and humidity inside or outside the image forming apparatus 100), etc. For example, in this embodiment, the absolute value of the discharge current can be changed within a range of 210 to 240 μA depending on the environment, etc.

[0048] On the other hand, in the configuration of this embodiment, it has been found that good cleaning performance can be achieved by setting the current supplied to the first brush 311 during image formation to approximately −60 to −90 μA (typically −73 μA) as viewed from the first brush 311 side, i.e., approximately +60 to +90 μA (typically +73 μA) as viewed from the first brush power supply E11 side. Also, in the configuration of this embodiment, it has been found that good cleaning performance can be achieved by setting the current supplied to the second brush 312 during image formation to approximately +60 to +90 μA (typically +73 μA) as viewed from the second brush 312 side. That is, in the configuration of this embodiment, the absolute value of the optimal cleaning current is approximately 60 to 90 μA, typically 73 μA. If the absolute value of the cleaning current is smaller than the absolute value of the optimal cleaning current, it may not be possible to sufficiently attract and collect toner onto the brush roller. Furthermore, if the absolute value of the cleaning current is larger than the absolute value of the optimal cleaning current, toner that has once adhered to the brush roller may be more likely to re-adhere to the intermediate transfer belt.

[0049] In this way, the absolute value of the current flowing through the third brush 313, which mainly plays a role in discharging toner during image formation, is greater than the absolute value of the current flowing through each of the first and second brushes 311 and 312, which mainly play a role in cleaning toner during image formation. The absolute value of the current flowing through the third brush 313, which mainly plays a role in discharging toner during image formation, is greater than the current (optimum cleaning current) suitable for collecting secondary transfer residual toner on the intermediate transfer belt 20.

[0050] The set value of the discharge current is not limited to that of this embodiment. The discharge current is a current in a direction (inward in this embodiment) that evens out the uneven distribution of ions in the intermediate transfer belt 20 during image formation. The discharge current is typically a current within a range of ±50% of the value that causes the current balance to be zero when applied to the intermediate transfer belt 20 during image formation, preferably within a range of ±30%, and more preferably a current value that causes the current balance to be approximately zero. Note that a current that causes the current balance to be approximately zero refers to a current within a range of ±5% of the value that causes the current balance to be zero. By setting this value, the increase in the electrical resistance of the intermediate transfer belt 20 can be sufficiently suppressed, thereby achieving a sufficiently long service life for the intermediate transfer belt 20. If this current is less than -50% of the value that causes the current balance to be zero, the effect of suppressing the increase in the electrical resistance of the intermediate transfer belt 20 will be insufficient, and the service life of the intermediate transfer belt 20 will not be sufficiently long. On the other hand, if this current is greater than +50% of the value that results in a current balance of 0, ion bias in the opposite direction to the above may occur. Here, for the primary transfer current, secondary transfer current, cleaning current, and discharge current that are controlled at a constant current, the target current value for that constant current control can be used to determine the current balance. Furthermore, for those currents that are controlled by constant voltage applied bias, the average value of the current flowing due to application of the bias or the target current value used to set the target voltage value for the constant voltage control can be used to determine the current balance.

[0051] More specifically, the value of the optimum cleaning current can be represented by the following value when one brush is used alone. That is, it is the value of the cleaning current that can minimize the amount of toner remaining on the intermediate transfer belt 20 after untransferred toner of a toner image with the maximum toner amount on the intermediate transfer belt 20 passes through the cleaning section by that brush. The maximum toner amount on the intermediate transfer belt 20 is expressed as the toner amount (mg / cm), which is the mass of toner per unit area of ​​the toner image that can be formed on the intermediate transfer belt 20 in the image forming apparatus 100. 2 ) is the maximum amount of toner applied to the toner image.

[0052] Furthermore, the values ​​of the currents supplied to the primary transfer portion T1, the secondary transfer portion T2, and the first, second, and third contact portions CL1, CL2, and CL3 during the image forming operation are represented by the values ​​of the currents when the image area on the intermediate transfer belt 20 passes through each of the above-mentioned portions. Here, the image area on the photosensitive drum 1 or the intermediate transfer belt 20 is an area where an image that is transferred to the recording material S and output from the image forming apparatus 100 can be formed, and the non-image area is an area other than the image area.

[0053] Furthermore, for example, during the execution of an adjustment operation other than an image formation operation, there may be a period during which the absolute value of the current supplied to the third contact portion CL3 is not the greatest among the absolute values ​​of the currents supplied to the first, second, and third contact portions CL, CL2, and CL3.

[0054] 4. Control mode 4 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 has a control unit (controller, control circuit) 50. The control unit 50 is configured to have a CPU 51 as an arithmetic control means which is a central element for performing arithmetic processing, memories (storage media) such as RAM 52 and ROM 53 as storage means, and a signal input / output circuit (not shown). The RAM 52, which is a rewritable memory, stores information input to the control unit 50, detected information, arithmetic results, etc., and the ROM 53 stores a control program, a pre-determined data table, etc. The CPU 51 and memories such as RAM 52 and ROM 53 can transfer and read data to and from each other.

[0055] The control unit 50 is connected to an operation unit and image reading unit of the image forming apparatus 100, and external devices such as a personal computer. The control unit 50 comprehensively controls each unit of the image forming apparatus 100 to perform an image formation operation based on instructions from the operation unit of the image forming apparatus 100, image data from the image reading unit, or image formation signals (image data, control commands) from external devices. Figure 4 shows the primary transfer power supply E1, secondary transfer power supply E2, and first, second, and third brush power supplies E11, E12, and E13 as representatives of each unit of the image forming apparatus 100.

[0056] 5. Positioning of cleaning device The cleaning performance of a cleaning device employing an electrostatic cleaning system is influenced by factors such as the voltage applied to the cleaning member (contact member) and the cleaning member's electrical resistance, as well as the cleaning member's penetration depth into the intermediate transfer belt. If this penetration depth is too small, the cleaning member will not come into contact with the intermediate transfer belt, resulting in poor cleaning performance. Alternatively, the cleaning member's electrical resistance may be too low, resulting in excessively high voltage output. If this penetration depth is too large, it may cause leaks, excessive collapse of the brush fibers of the brush roller cleaning member, resulting in the cleaning member not coming into contact with the intermediate transfer belt, and accelerated deterioration of the intermediate transfer belt and cleaning member due to wear. To ensure optimal cleaning performance, it is important that the cleaning member, whose primary role is to clean toner during image formation, has a set penetration depth into the intermediate transfer belt. A cleaning member whose primary role is to discharge toner during image formation requires less precision in its penetration depth into the intermediate transfer belt than a cleaning member whose primary role is to clean toner.

[0057] As mentioned above, in the configuration of Patent Document 2, the subunit having the cleaning member is positioned relative to the casing, and the casing is then positioned relative to the belt unit that holds the intermediate transfer belt. In this configuration, the penetration depth of the cleaning member into the intermediate transfer belt is determined by the position of the casing relative to the belt unit and the position of the counter roller relative to the belt unit. Therefore, a relatively large tolerance is added to the target penetration depth, which can lead to large variations in the penetration depth and reduce the stability of cleaning performance.

[0058] Therefore, it is desirable to minimize the variation in the amount of penetration of the cleaning member by determining the positional relationship between the cleaning member, particularly the cleaning member whose main role is to clean the toner, and the intermediate transfer belt using as few parts as possible.In order to minimize the variation in the amount of penetration of the brush roller as a cleaning member into the intermediate transfer belt, it is desirable to minimize the number of parts to determine the axial distance between the brush roller and the opposing roller.

[0059] Therefore, in this embodiment, the cleaning device is positioned by regulating the axial distance between two of the three brush rollers with high cleaning performance and the opposing roller (the tension roller for the intermediate transfer belt) located opposite them. In this embodiment, the two brush rollers with high cleaning performance are the first and second brushes 311 and 312, which are primarily responsible for cleaning toner during image formation. In this embodiment, the other brush roller is the third brush 313, which is primarily responsible for discharging toner during image formation. In this embodiment, the axial distance between the two brush rollers and the opposing roller is determined using as few components as possible. That is, in this embodiment, two position regulating units are provided on at least one of the frames (supports) that rotatably support both ends of the three brush rollers in the rotational axis direction. These two position regulating units are then engaged with the bearing members of the two opposing rollers located opposite the two brush rollers. This makes it possible to suppress variations in the amount of penetration of the brush roller, particularly the brush roller that mainly plays a role in cleaning the toner, into the intermediate transfer belt, and improves the stability of cleaning performance.

[0060] 6. Details of the positioning configuration of the cleaning device in this embodiment Next, the positioning configuration of the cleaning device 30 in this embodiment will be described in more detail. In this embodiment, the front side of the paper in FIG. 1 is referred to as the front (front face) side, and the back side of the paper in FIG. 1 is referred to as the rear (rear face) side. In this embodiment, the front-to-rear direction connecting the front and rear sides of the image forming apparatus 100 is approximately parallel to the rotation axis direction of the tension rollers of the photosensitive drum 11 and the intermediate transfer belt 20 (a direction approximately perpendicular to the direction of movement of the surfaces of the photosensitive drum 11 and the intermediate transfer belt 20). Furthermore, the up-down direction of the image forming apparatus 100 and its elements refers to the up-down direction relative to the direction of gravity (vertical direction), but does not mean just directly above or directly below, but also includes the upper and lower sides of a horizontal plane passing through a position or element of interest.

[0061] Fig. 5(a) is a schematic perspective view showing the periphery of the front end of the cleaning device 30 in this embodiment. Figs. 5(b) and 5(c) are schematic perspective views showing the cleaning device 30 and the periphery of the attachment portion of the cleaning device 30 in the intermediate transfer unit 22, respectively. Fig. 6 is a schematic side view (illustration of the intermediate transfer belt 20 is omitted) as seen in the direction of arrow A in Fig. 5(c). Note that Fig. 5 only shows the front side configuration of the cleaning device 30 with respect to the positioning configuration of the cleaning device 30, but in this embodiment, the rear side configuration of the cleaning device 30 is similar (substantially symmetrical with respect to a plane passing through approximately the center in the width direction of the intermediate transfer belt 20).

[0062] As described above, the cleaning device 30 has a housing 35 that holds the first, second, and third cleaning portions 301, 302, and 303 and accommodates toner and other particles removed from the intermediate transfer belt 20. In this embodiment, the housing 35 of the cleaning device 30 includes a cleaning frame 34 serving as a second support that rotatably supports both ends of the first, second, and third brushes 311, 312, and 313 in the rotational axis direction. In this embodiment, both ends of the first, second, and third collection rollers 321, 322, and 323 in the rotational axis direction are also rotatably supported by the cleaning frame 34. The first, second, and third brushes 311, 312, and 313 are supported at both ends of their rotational axis direction by the cleaning frame 34 via first, second, and third brush bearing members 311a, 311b, and 311c, respectively. The first, second, and third collection rollers 321, 322, and 323 are supported at both ends in the latitudinal direction of the rotation axes by the cleaning frame 34 via first, second, and third collection roller bearing members 321a, 322a, and 323a, respectively. In this embodiment, the cleaning frame 34 is made of a plate-like member arranged along a plane substantially perpendicular to the rotation axis direction of the first, second, and third brushes 311, 312, and 313. The cleaning frame 34 may be made of any appropriate material, such as metal.

[0063] In this embodiment, first, second, and third opposing rollers 241, 242, and 243, which are tension rollers for the intermediate transfer belt 20, are disposed at positions facing (contacting) the first, second, and third brushes 311, 312, and 313, respectively, with the intermediate transfer belt 20 interposed therebetween. In this embodiment, the first, second, and third opposing rollers 241, 242, and 243 are supported by the belt frame 26 at both ends in the direction of their rotational axes via first, second, and third bearing members 251, 252, and 253, respectively. At least the first and second bearing members 251 and 252 of the first, second, and third bearing members 251, 252, and 253 at least partially protrude outside the belt frame 26 in the direction of the rotational axes of the first and second opposing rollers 241 and 242, respectively. In this embodiment, the first and second bearing members 251 and 252 have substantially cylindrical outer peripheral surfaces 251a and 252a that are substantially circular when viewed in the direction of the rotation axes of the first and second opposing rollers 241 and 242, respectively, and protrude outside the belt frame 26. In this embodiment, the outer peripheral surfaces 251a and 252a of the first and second bearing members 251 and 252 are engageable with the rotation stop slots 38 and positioning holes 37 (described later) of the cleaning frame 34. The first and second bearing members 251 and 252 may be any suitable bearing, such as a ball bearing, a roller bearing, or a plain bearing. The outer peripheral surfaces 251a and 252a of the first and second bearing members 251 and 252 are formed from the outer peripheral surfaces of the outer rings of a ball bearing or a roller bearing, or the outer peripheral surface of a plain bearing. The outer peripheral surfaces 251a and 252a of the first and second bearing members 251 and 252 may be made of any appropriate material such as metal.

[0064] In this embodiment, the cleaning frame 34 is provided with a positioning hole 37 as one of the first and second position restricting portions, and a rotation-stop elongated hole 38 as the other of the first and second position restricting portions. In this embodiment, the positioning hole 37 restricts the axial distance between the second brush 312 and the second opposing roller 242 disposed opposite the second brush 312. In addition, in this embodiment, the rotation-stop elongated hole 38 restricts the axial distance between the first brush 311 and the first opposing roller 241 disposed opposite the first brush 311. As a result, the positioning hole 37 and the rotation-stop elongated hole 38 determine the position of the cleaning device 30 relative to the belt frame 26. In other words, in this embodiment, the cleaning frame 34 constitutes a position restricting member that determines the position of the cleaning device 30 relative to the belt frame 26. In other words, the cleaning frame 34 regulates the axial distance between the first brush 311 and the first opposing roller 241, and the axial distance between the second brush 312 and the second opposing roller 242, thereby determining the position of the cleaning device 30 relative to the belt frame 26.

[0065] In this embodiment, the positioning hole 37 of the cleaning frame 34 is fitted with the second bearing member 252. More specifically, in this embodiment, the positioning hole 37 has a substantially cylindrical inner peripheral surface 37a that is substantially circular when viewed in the direction of the rotation axis of the second opposing roller 242. That is, in this embodiment, the positioning hole 37 is a circular hole (through hole) that is substantially circular in a plan view. The inner peripheral surface 37a of the positioning hole 37 is fitted with the outer peripheral surface 252a of the second bearing member 252. That is, the positioning hole 37 and the second bearing member 252 are engaged with each other so as to be rotatable around the rotation axis of the second opposing roller 242. As a result, the positioning hole 37 regulates the position of the second brush 312 in the interaxial direction between the second brush 312 and the second opposing roller 242.

[0066] In this embodiment, the rotation stop slot 38 of the cleaning frame 34 engages with the first bearing member 251 so as to be movable in a direction intersecting the rotation direction of the second opposing roller 242 about the rotation axis of the second opposing roller 242. More specifically, in this embodiment, the rotation stop slot 38 has a substantially oval cylindrical inner circumferential surface 38a that is elongated in the interaxial direction between the first opposing roller 241 and the second opposing roller 242 when viewed in the direction of the rotation axis of the first opposing roller 241. That is, in this embodiment, the rotation stop slot 38 is an elongated circular hole (through hole) that is substantially oval in plan view. The surface of the inner circumferential surface 38a of the rotation stop slot 38 that extends in the interaxial direction between the first opposing roller 241 and the second opposing roller 242 engages with the outer circumferential surface 251a of the first bearing member 251. As a result, the rotation stop slot 38 absorbs component tolerances in the direction along the axial direction between the first opposing roller 241 and the second opposing roller 242, while restricting the position of the first brush 311 in the rotation direction about the rotation axis of the second opposing roller 242. In other words, the rotation stop slot 38 restricts the position of the first brush 311 approximately in the axial direction between the first brush 311 and the first opposing roller 241.

[0067] After the position of the cleaning device 30 is determined as described above, it may be fixed to the belt frame 26 by any suitable fixing means such as a screw. For example, the cleaning frame 34 and the belt frame 26 may be fixed together using a screw between the positioning hole 37 and the rotation stop slot 38.

[0068] As described above, in this embodiment, the position of the cleaning device 30 relative to the belt frame 26 is determined by the positioning holes 37 and the long rotation stop holes 38 engaging with the second bearing member 252 and the first bearing member 251, respectively. This makes it possible to accurately determine the axial distance between the first brush 311 and the first opposing roller 241, and the axial distance between the second brush 312 and the second opposing roller 242.

[0069] As described above, in this embodiment, the first and second brushes 311 and 312 mainly play a role in cleaning toner off the intermediate transfer belt 20. Therefore, in this embodiment, the precision of the inter-axial distance between the first and second brushes 311 and 312 and the first and second opposing rollers 241 and 242 arranged in opposing positions thereto is increased. This reduces variations in the amount of penetration of the first and second brushes 311 and 312 into the intermediate transfer belt 20, and stabilizes cleaning performance.

[0070] In this embodiment, the position restricting portion that engages with the second bearing member 252 is a positioning portion configured as a round hole, and the position restricting portion that engages with the first bearing member 251 is a rotation preventing portion configured as an elongated round hole. In this embodiment, the second opposing roller 242 is positioned higher than the first opposing roller 241 in the direction of gravity, so the configuration of this embodiment is preferable in consideration of ease of attachment to the belt frame 26 of the cleaning device 30. However, the present invention is not limited to this embodiment, and it is possible to appropriately determine which opposing roller's bearing member is used for positioning and which is used for rotation preventing. Conversely to this embodiment, the position restricting portion that engages with the first bearing member 251 may be a positioning portion configured as a round hole, and the position restricting portion that engages with the second bearing member 252 may be a rotation preventing portion configured as an elongated round hole.

[0071] 7. Variations In this embodiment, the cleaning frame 34 is positioned relative to the first and second bearing members 251 and 252 of the first and second opposing rollers 241 and 242, which are arranged in positions opposing the first and second brushes 311 and 312. That is, in this embodiment, the position of the cleaning frame 34 is determined by engaging the rotation stop slot 38 and the positioning hole 37 provided in the cleaning frame 34 with the first and second bearing members 251 and 252, respectively. However, the present invention is not limited to this embodiment.

[0072] As described above, the stability of cleaning performance can be improved by positioning the cleaning frame 34 relative to the bearing members of the opposing rollers that are disposed opposite the two cleaning members that primarily clean toner from the intermediate transfer belt 20. Therefore, for example, if the cleaning members that primarily clean toner from the intermediate transfer belt 20 are the second and third brushes 312 and 313, the following can be done. That is, the cleaning frame 34 can be positioned relative to the second and third bearing members 252 and 253 of the second and third opposing rollers 242 and 243 that are disposed opposite the second and third brushes 312 and 313. For example, as shown in FIG. 7A, the position of the cleaning frame 34 can be determined by engaging the rotation stop slot 38 and the positioning hole 37 provided in the cleaning frame 34 with the second and third bearing members 252 and 253, respectively. The second and third brushes 312 and 313 are the cleaning members primarily responsible for cleaning the toner on the intermediate transfer belt 20, for example, in the following case. That is, when cleaning the secondary transfer residual toner during image formation, the secondary transfer residual toner is mainly collected by the second and third brushes 312 and 313, and discharged by the first brush 313. In this configuration, an electric field suitable for cleaning is formed between the second brush 312 and the second opposing roller 242, and between the third brush 313 and the third opposing roller 243. In addition, in this configuration, an electric field suitable for discharge is formed between the first brush 311 and the first opposing roller 241.

[0073] Furthermore, for example, when the cleaning members primarily responsible for cleaning toner off the intermediate transfer belt 20 are the first and third brushes 311 and 313, the following can be done. That is, the cleaning frame 34 can be positioned relative to the first and third bearing members 251 and 253 of the first and third opposing rollers 241 and 243, which are disposed opposite the first and third brushes 311 and 313. For example, as shown in FIG. 7B, the position of the cleaning frame 34 can be determined by engaging the rotation stop slots 38 and the positioning holes 37 provided in the cleaning frame 34 with the first and third bearing members 251 and 253, respectively. Note that when the cleaning members primarily responsible for cleaning toner off the intermediate transfer belt 20 are the first and third brushes 311 and 313, the following can be considered, for example. That is, in this configuration, when cleaning the secondary transfer residual toner during image formation operation, the secondary transfer residual toner is collected mainly by the first and third brushes 311 and 313, and discharged by the second brush 312. In this configuration, an electric field suitable for cleaning is formed between the first brush 311 and the first opposing roller 241, and between the third brush 313 and the third opposing roller 243. In addition, in this configuration, an electric field suitable for discharge is formed between the second brush 312 and the second opposing roller 242.

[0074] Generally, the longer the distance between the positioning point and the rotation prevention point, the smaller the positional variation during installation. Therefore, for example, as shown in FIG. 7(b), positioning the cleaning frame 34 relative to the first bearing member 251 and the third bearing member 253 can be said to be preferable from the following viewpoint. In other words, this configuration can suppress the positional variation between the cleaning device 30 and the belt frame 26, and can stabilize the average penetration amount of the three cleaning members into the intermediate transfer belt 20.

[0075] 7(a) and 7(b), as described above, which of the two position restriction portions that engage with the two bearing members, respectively, serves as the positioning portion and which serves as the rotation prevention portion can be set as appropriate. Also, as described above, the power supply method (power source arrangement) for each of the first, second, and third brushes 311, 312, and 313 may be either internal power supply or external power supply.

[0076] Furthermore, in this embodiment, the front and rear sides of the cleaning device 30 are configured similarly (substantially symmetrically) for the positioning configuration of the cleaning device 30, but the present invention is not limited to this. For example, of the front and rear cleaning frames 34, only the front cleaning frame 34 shown in FIG. 5 may be configured to have a positioning hole 37 and a rotation stop slot 38. Furthermore, it is sufficient that at least one of the same ends in the rotation axis direction of the first and second opposing rollers 241, 242 is journaled by bearing members 251, 252 that can engage with the rotation stop slot 38 and the positioning hole 37, respectively, and supported by the belt frame 26 via the bearing members. In this case, for example, as shown in FIG. 11 As shown in (a), at the rear end, a convex portion or the like serving as an engaging portion 39 provided on the cleaning frame 34 on that end side may be fitted into a hole or recess serving as an engaged portion 27 provided on the belt frame 26 on that end side. The engaged portion 27 provided on the belt frame 26 may have one circular hole and the other an elongated circular hole, similar to the positioning holes and rotation-stop slots provided on the cleaning frame 34 in this embodiment. This makes it easy to attach and detach the cleaning device 30 by, for example, pulling it out toward the front of the image forming apparatus 100 with respect to the belt frame 26 and removing it.

[0077] In addition, in this embodiment, the first and second position restricting portions are formed by holes provided in the cleaning frame 34 so as to surround the entire periphery of the bearing member with which they engage, but the present invention is not limited to this. 11As shown in (b), at least one of the first and second position restricting portions may be a groove shape cut out so that at least a portion of the periphery of the bearing member with which it engages is exposed to the outside of the cleaning frame 34. The first and second position restricting portions may be configured to perform functions equivalent to those of the positioning portion and rotation restricting portion provided by the positioning hole 37 and the rotation restricting elongated hole 38 in this embodiment. 11 (b) illustrates an example in which a portion of the circumferential direction of the position regulating portion 37 corresponding to the positioning hole 37 in this embodiment is cut out, and further, a portion of the circumferential direction of the position regulating portion 38 corresponding to the rotation stop long hole 38 in this embodiment is cut out.

[0078] In addition, in this embodiment, the first and second position regulating portions engage with the bearing members on the outside of the belt frame 26 in the width direction of the intermediate transfer belt 20 (the direction of the rotation axis of the opposing roller), but the present invention is not limited to this embodiment. The first and second position regulating portions may also be configured to engage with the bearing members on the inside of the belt frame 26 in the width direction of the intermediate transfer belt 20.

[0079] 8.Effects As described above, in this embodiment, the image forming apparatus 100 includes the image carrier 11 that carries a toner image, the rotatable intermediate transfer body 20 that transports the toner image that has been primarily transferred from the image carrier 11 at the primary transfer portion T1 to be secondarily transferred to the recording material S at the secondary transfer portion T2, the first, second, and third rollers 241, 242, and 243 that are disposed on the inner circumferential surface side of the intermediate transfer body 20 downstream of the secondary transfer portion T2 and upstream of the primary transfer portion T1 in relation to the rotation direction of the intermediate transfer body 20, and that contact the inner circumferential surface of the intermediate transfer body 20 along the width direction that is approximately perpendicular to the moving direction of the surface of the intermediate transfer body 20, and the first, second, and third rollers 241, 242, and 243 that are disposed on at least one end side of the width direction. the first, second, and third contact members 311, 312, and 313 being arranged on the outer peripheral surface side of the intermediate transfer body 20, contacting the outer peripheral surface of the intermediate transfer body 20 along the width direction, and abutting the first, second, and third rollers 241, 242, and 243, respectively, via the intermediate transfer body 20; a second support 34 supporting the first, second, and third contact members 311, 312, and 313 at least on the one end side in the width direction; and current supply means E11, E12, and E13 supplying current between the first, second, and third contact members 311, 312, and 313 and the first, second, and third rollers 241, 242, and 243, respectively. In this embodiment, of the first, second and third contact members 311, 312 and 313, the third contact member 313 has the largest absolute value of the current that flows when it is in contact with the image area on the intermediate transfer body immediately after passing through the secondary transfer portion T2 during the image forming operation, and the first roller 241 and the second roller 242 are supported by the first support 26 via the first bearing member 251 and the second bearing member 252, respectively, at least at one end side in the width direction, and the second support 34 is provided with a first position regulating portion 38 that engages with the first bearing member 251 and a second position regulating portion 37 that engages with the second bearing member 252, and the position of the second support 34 relative to the first support 26 is determined by the engagement of the first and second position regulating portions 38 and 37 with the first and second bearing members 251 and 252, respectively.

[0080] In this embodiment, the third contact member 311 is disposed furthest downstream among the first, second, and third contact members 311, 312, and 313 in the direction of movement of the surface of the intermediate transfer body 20. In this embodiment, the intermediate transfer body 20 is formed as an endless belt, and the first, second, and third rollers 241, 242, and 243 are rollers that tension the intermediate transfer body 20. In this embodiment, one of the first and second position restricting portions is fitted with one of the first and second bearing members 251 and 252 with which it engages so as to allow rotation of the second support body 34 about the rotation axis of the roller supported by that bearing member, and the other of the first and second position restricting portion is engaged with the one of the first and second bearing members 251 and 252 with which it engages so as to restrict the rotation of the second support body 34 and allow movement in a direction intersecting the direction of the rotation. In this embodiment, the second support 34 is provided with a hole 37 that is substantially circular in plan view and that constitutes one of the first and second position restriction portions, and a hole 38 that is substantially oval in plan view and that constitutes the other of the first and second position restriction portions. Also, in this embodiment, the first, second, and third contact members 311, 312, and 313 are each rotatable brush rollers.

[0081] As described above, when the first, second and third contact members are arranged at the most upstream position in the direction of movement of the surface of the intermediate transfer body 20 as the first contact member 311 and the most downstream position is arranged at the most downstream position as the second contact member 313, the first roller 241 and the second roller 243 are supported by the first support 26 via the first bearing member 251 and the second bearing member 253, respectively, at least at one end side in the width direction, and the second support 34 is provided with a first position regulating portion 38 that engages with the first bearing member 251 and a second position regulating portion 37 that engages with the second bearing member 253, and the position of the second support 34 relative to the first support 26 is determined by the engagement of the first and second position regulating portions 38 and 37 with the first and second bearing members 251 and 253, respectively.

[0082] Furthermore, according to this embodiment, when the cleaning device 30 has three contact members, the simple configuration can suppress variations in the amount of penetration of the contact members into the intermediate transfer belt 20, thereby achieving stable cleaning performance.

[0083] [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, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0084] Fig. 8 is a schematic cross-sectional view of the vicinity of the cleaning device 30 in this embodiment. Fig. 9(a) is a schematic perspective view showing the periphery of the front end of the cleaning device 30 in this embodiment. Figs. 9(b) and 9(c) are schematic perspective views showing the cleaning device 30 and the periphery of the attachment portion of the cleaning device 30 in the intermediate transfer unit 22, respectively. Note that Fig. 9 only shows the front side configuration of the cleaning device 30 with respect to the positioning configuration of the cleaning device 30, but in this embodiment, the rear side configuration of the cleaning device 30 is similar (substantially symmetrical with respect to a plane passing through approximately the center in the width direction of the intermediate transfer belt 20).

[0085] In this embodiment, a first opposing roller 241, which is a tension roller for the intermediate transfer belt 20, is disposed at a position facing (contacting) the first brush 311 with the intermediate transfer belt 20 interposed therebetween. Also, in this embodiment, a second opposing roller 242, which is a tension roller for the intermediate transfer belt 20, is disposed at a position facing (contacting) the second and third brushes 312 and 313 with the intermediate transfer belt 20 interposed therebetween. In this embodiment, the first and second opposing rollers 241 and 242 are supported by the belt frame 26 at both ends in the direction of their rotational axes via first and second bearing members 251 and 252, respectively. At least a portion of the first and second bearing members 251 and 252 protrudes outside the belt frame 26 with respect to the direction of the rotational axes of the first and second opposing rollers 241 and 242, respectively. The first and second bearing members 251 and 252 may have the same configuration as that described in the first embodiment.

[0086] As described above, in this embodiment, one of the three brush rollers contacts a counter roller located opposite it via the intermediate transfer belt, while the other two contact a common counter roller located opposite it via the intermediate transfer belt. In this embodiment, the cleaning device is positioned by regulating the axial distance between the one brush roller and the counter roller located opposite it, and the axial distance between the other two brush rollers and the common counter roller located opposite it. In this embodiment, the positions of all three brush rollers relative to the counter rollers located opposite them (the two counter rollers) are regulated. Therefore, any one of the three brush rollers may be the one with the highest cleaning performance (primarily responsible for cleaning toner). Furthermore, in this embodiment, as in the first embodiment, the axial distances between the three brush rollers and the counter rollers are determined using as few components as possible. That is, in this embodiment, two position regulating units are provided on at least one of the frames (supports) that rotatably support both ends of the three brush rollers in the rotational axis direction. These two position regulating units are engaged with the bearing members of the two counter rollers, respectively. This makes it possible to suppress variations in the amount of penetration of the three brush rollers into the intermediate transfer belt, thereby improving the stability of cleaning performance. This will be explained in more detail below.

[0087] In this embodiment, the cleaning frame 34 is provided with a positioning hole 37 as one of the first and second position restricting portions, and a rotation-stop elongated hole 38 as the other of the first and second position restricting portions. In this embodiment, the positioning hole 37 restricts the axial distance between the second and third brushes 312 and 313 and the second opposing roller 242 disposed opposite them. In addition, in this embodiment, the rotation-stop elongated hole 38 restricts the axial distance between the first brush 311 and the first opposing roller 241 disposed opposite them. As a result, the positioning hole 37 and the rotation-stop elongated hole 38 determine the position of the cleaning device 30 relative to the belt frame 26. In other words, in this embodiment, the cleaning frame 34 constitutes a position restricting member that determines the position of the cleaning device 30 relative to the belt frame 26. That is, the cleaning frame 34 regulates the axial distance between the first brush 311 and the first opposing roller 241, and the axial distance between the second and third brushes 312 and 313 and the second opposing roller 242, and determines the position of the cleaning device 30 relative to the belt frame 26. The configurations of the positioning hole 37 and the long rotation stop hole 38 in this embodiment are the same as the configurations of the positioning hole 37 and the long rotation stop hole 38 in the first embodiment, respectively.

[0088] In this embodiment, the positioning hole 37 of the cleaning frame 34 is fitted with the second bearing member 252 so as to be rotatable around the rotation axis of the second opposing roller 242. Also, in this embodiment, the rotation stop slot 38 of the cleaning frame 34 is engaged with the first bearing member 251 so as to be movable in a direction intersecting the rotation direction around the rotation axis of the second opposing roller 242.

[0089] As described above, in this embodiment, the position of the cleaning device 30 relative to the belt frame 26 is determined by the positioning holes 37 and the long rotation stop holes 38 engaging with the second bearing member 252 and the first bearing member 251, respectively. This makes it possible to accurately determine the axial distance between the first brush 311 and the first opposing roller 241, and the axial distance between the second and third brushes 312 and 313 and the second opposing roller 242.

[0090] As described above, in this embodiment, any one of the first, second, and third brushes 311, 312, and 313 may be the brush that primarily plays a role in cleaning toner. In this embodiment, as an example, the first, second, and third brushes 311, 312, and 313 have functions corresponding to the first, second, and third brushes 311, 312, and 313 in the first embodiment, respectively. However, the first, second, and third brushes 311, 312, and 313 may also have functions corresponding to those described in the modified example of the first embodiment.

[0091] In this embodiment, the position restricting portion that engages with the second bearing member 252 is a positioning portion configured as a round hole, and the position restricting portion that engages with the first bearing member 251 is a rotation preventing portion configured as an elongated round hole. In this embodiment, the second opposing roller 242 is positioned higher than the first opposing roller 241 in the direction of gravity, so the configuration of this embodiment is preferable in consideration of ease of attachment to the belt frame 26 of the cleaning device 30. However, as described in the embodiment, the present invention is not limited to this configuration, and it is possible to appropriately determine which opposing roller's bearing member is used for positioning and which is used for rotation preventing. Conversely to this embodiment, the position restricting portion that engages with the first bearing member 251 may be a positioning portion configured as a round hole, and the position restricting portion that engages with the second bearing member 252 may be a rotation preventing portion configured as an elongated round hole.

[0092] 10, the second brush 312 may be disposed at a position facing (in contact with) the first opposing roller 241, rather than the second opposing roller 242, with the intermediate transfer belt 20 interposed therebetween.

[0093] As described in the first embodiment, of the front and rear cleaning frames 34, for example, only the front cleaning frame 34 shown in FIG. 9 may have the first and second position regulating portions.

[0094] Furthermore, as described in Example 1, at least one of the first and second position regulating portions may have a groove shape cut out so as to expose at least a portion of the periphery of the bearing member with which it engages to the outside of the cleaning frame 34.

[0095] As described above, in this embodiment, the image forming apparatus 100 includes the first and second rollers 241, 242, which are disposed on the inner peripheral surface side of the intermediate transfer body 20 downstream of the secondary transfer portion T2 and upstream of the primary transfer portion T1 in the rotation direction of the intermediate transfer body 20, and which contact the inner peripheral surface of the intermediate transfer body 20 along the width direction substantially perpendicular to the moving direction of the surface of the intermediate transfer body 20, the first support 26, which rotatably supports the first and second rollers 241, 242 at least on one end side in the width direction, and the first support 26, which is disposed on the outer peripheral surface side of the intermediate transfer body 20 and which contacts the inner peripheral surface of the intermediate transfer body 20 along the width direction substantially perpendicular to the moving direction of the surface of the intermediate transfer body 20. The transfer roller 31 includes first, second, and third contact members 311, 312, and 313 that contact the outer peripheral surface of the intermediate transfer body 20 along the transfer roller 311, 312, and 313, one of which contacts the first roller 241 via the intermediate transfer body 20, and the other two of which contact the second roller 242 via the intermediate transfer body 20, and a second support 34 that supports the first, second, and third contact members 311, 312, and 313 at least on the one end side in the width direction. In this embodiment, the first roller 241 and the second roller 242 are supported by the first support 26 via a first bearing member 251 and a second bearing member 252, respectively, at least at one end side in the width direction, and the second support 34 is provided with a first position regulating portion 38 that engages with the first bearing member 251 and a second position regulating portion 37 that engages with the second bearing member 252, and the position of the second support 34 relative to the first support 26 is determined by the engagement of the first and second position regulating portions 38, 37 with the first and second bearing members 251, 252, respectively. In this embodiment, of the first, second and third contact members 311, 312, 313, the first contact member 311 is arranged at the most upstream position in the direction of movement of the surface of the intermediate transfer body 20, and the third contact member 313 is arranged at the most downstream position in the direction of movement of the surface of the intermediate transfer body 20, and the first contact member 311 abuts against the first roller 241 via the intermediate transfer body 20, and the second and third contact members 312, 313 abut against the second roller 242 via the intermediate transfer body 20.However, as described above, the first and second contact members 311 and 312 may be configured to contact the first roller 241 via the intermediate transfer body 20, and the third contact member 313 may be configured to contact the second roller 242 via the intermediate transfer body 20. In this embodiment, the intermediate transfer body 20 is configured as an endless belt, and the first and second rollers 241 and 242 are rollers that stretch the intermediate transfer body 20.

[0096] According to this embodiment, the same effects as those of the first embodiment can be obtained, and the device configuration can be further simplified.

[0097] [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.

[0098] In the above-described embodiment, the outputs of the power supplies that supply current to the three contact members are all constant current controlled, but the output of at least one power supply may be constant voltage controlled. Constant current control is a control that adjusts the output of a power supply so that the voltage output by the power supply is approximately constant (so that it approaches a target value).

[0099] In the above-described embodiments, the contact member was a brush roller having a rotatably supported metal rotating shaft and a plurality of raised bristles arranged on the circumferential surface. A brush roller is preferably used as the contact member from the viewpoint of good cleaning performance, but is not limited to this. Depending on other conditions, such as the amount of toner to be removed, the contact member may be an elastic roller such as a rubber roller or sponge roller having a conductive rubber or sponge disposed on the circumferential surface of the rotating shaft. It may also be a brush-like member that rubs against the intermediate transfer body without rotating. In the above-described embodiments, the recovery member was a metal roller. A metal roller is preferably used as the recovery member from the viewpoint of its simple configuration and relatively low cost, but is not limited to this, and may also be a conductive elastic roller similar to the above. In the above-described embodiments, the scraping member was a rubber blade, but is not limited to this, and a blade member made of an elastic material such as a rubber sheet or a PET sheet (resin sheet) can be preferably used.

[0100] Furthermore, the cleaning device may not be provided with a recovery member, and a scraping member may directly rub the surface of the contact member. Furthermore, when the contact member moves the toner on the intermediate transfer body, it need not do so electrostatically, but may instead move it physically. In cases such as this, where the contact members primarily physically move and recover the toner, the contact member located furthest downstream in the direction of movement of the surface of the intermediate transfer body may have the lowest cleaning performance. In other words, in such cases, the two most upstream contact members of the three contact members may have the highest cleaning performance (mainly responsible for cleaning the toner). [Explanation of symbols]

[0101] 1 Image forming unit 11 Photosensitive drum 20 Intermediate transfer belt 26 Belt Frame 30 Cleaning device 34 Cleaning Frame 241, 242, 243 opposing rollers 251, 252, 253 Bearing members 311, 312, 313 cleaning members (contact members)

Claims

1. an image carrier that carries a toner image; a rotatable intermediate transfer member that conveys the toner image that has been primarily transferred from the image carrier at a primary transfer unit to a recording material at a secondary transfer unit for secondary transfer; first, second, and third rollers that are disposed on the inner peripheral surface of the intermediate transfer body downstream of the secondary transfer unit and upstream of the primary transfer unit in relation to the rotation direction of the intermediate transfer body, and that come into contact with the inner peripheral surface of the intermediate transfer body along a width direction that is substantially perpendicular to the moving direction of the surface of the intermediate transfer body; a first support member that rotatably supports the first, second, and third rollers at least at one end side in the width direction; first, second, and third contact members that are arranged on the outer peripheral surface side of the intermediate transfer body, that come into contact with the outer peripheral surface of the intermediate transfer body along the width direction, and that are capable of removing toner from the surface of the intermediate transfer body, and that come into contact with the first, second, and third rollers, respectively, via the intermediate transfer body; a second support member that supports the first, second, and third contact members at least at one end side in the width direction; current supply means for supplying current between the first, second and third contact members and the first, second and third rollers, respectively; and Among the first, second, and third contact members, the third contact member has the largest absolute value of a current that flows when the third contact member is in contact with an image area on the intermediate transfer body immediately after the intermediate transfer body has passed through the secondary transfer portion during an image forming operation; the first roller and the second roller are supported by the first support via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction; An image forming apparatus characterized in that the second support is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support relative to the first support is determined by the first and second position regulating portions engaging with the first and second bearing members, respectively.

2. 2. The image forming apparatus according to claim 1, wherein the third contact member is disposed at the most downstream position of the first, second and third contact members in the direction of movement of the surface of the intermediate transfer body.

3. an image carrier that carries a toner image; a rotatable intermediate transfer member that conveys the toner image that has been primarily transferred from the image carrier at a primary transfer unit to a recording material at a secondary transfer unit for secondary transfer; first, second, and third rollers that are disposed on the inner peripheral surface of the intermediate transfer body downstream of the secondary transfer unit and upstream of the primary transfer unit in relation to the rotation direction of the intermediate transfer body, and that come into contact with the inner peripheral surface of the intermediate transfer body along a width direction that is substantially perpendicular to the moving direction of the surface of the intermediate transfer body; a first support member that rotatably supports the first, second, and third rollers at least at one end side in the width direction; first, second, and third contact members that are arranged on the outer peripheral surface side of the intermediate transfer body, that come into contact with the outer peripheral surface of the intermediate transfer body along the width direction, and that are capable of removing toner from the surface of the intermediate transfer body, and that come into contact with the first, second, and third rollers, respectively, via the intermediate transfer body; a second support member that supports the first, second, and third contact members at least at one end side in the width direction; and Among the first, second, and third contact members, the third contact member is disposed at the most downstream position in a moving direction of the surface of the intermediate transfer body, the first roller and the second roller are supported by the first support via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction; An image forming apparatus characterized in that the second support is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support relative to the first support is determined by the first and second position regulating portions engaging with the first and second bearing members, respectively.

4. an image carrier that carries a toner image; a rotatable intermediate transfer member that conveys the toner image that has been primarily transferred from the image carrier at a primary transfer unit to a recording material at a secondary transfer unit for secondary transfer; first, second, and third rollers that are disposed on the inner peripheral surface of the intermediate transfer body downstream of the secondary transfer unit and upstream of the primary transfer unit in relation to the rotation direction of the intermediate transfer body, and that come into contact with the inner peripheral surface of the intermediate transfer body along a width direction that is substantially perpendicular to the moving direction of the surface of the intermediate transfer body; a first support member that rotatably supports the first, second, and third rollers at least at one end side in the width direction; first, second, and third contact members that are arranged on the outer peripheral surface side of the intermediate transfer body, that come into contact with the outer peripheral surface of the intermediate transfer body along the width direction, and that are capable of removing toner from the surface of the intermediate transfer body, and that come into contact with the first, second, and third rollers, respectively, via the intermediate transfer body; a second support member that supports the first, second, and third contact members at least at one end side in the width direction; and Among the first, second, and third contact members, the first contact member is disposed at the most upstream position in a moving direction of the surface of the intermediate transfer body, and the second contact member is disposed at the most downstream position in the moving direction of the surface of the intermediate transfer body, the first roller and the second roller are supported by the first support via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction; An image forming apparatus characterized in that the second support is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support relative to the first support is determined by the first and second position regulating portions engaging with the first and second bearing members, respectively.

5. 5. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an endless belt, and the first, second, and third rollers are rollers that stretch the intermediate transfer member.

6. an image carrier that carries a toner image; a rotatable intermediate transfer member that conveys the toner image that has been primarily transferred from the image carrier at a primary transfer unit to a recording material at a secondary transfer unit for secondary transfer; a first roller and a second roller that are disposed on the inner peripheral surface of the intermediate transfer body downstream of the secondary transfer unit and upstream of the primary transfer unit in relation to the rotation direction of the intermediate transfer body, and that come into contact with the inner peripheral surface of the intermediate transfer body along a width direction that is substantially perpendicular to the moving direction of the surface of the intermediate transfer body; a first support member that rotatably supports the first and second rollers at least at one end side in the width direction; first, second, and third contact members that are arranged on the outer peripheral surface side of the intermediate transfer body, that come into contact with the outer peripheral surface of the intermediate transfer body along the width direction, and that are capable of removing toner from the surface of the intermediate transfer body, one of the first, second, and third contact members coming into contact with the first roller via the intermediate transfer body, and the other two coming into contact with the second roller via the intermediate transfer body; a second support member that supports the first, second, and third contact members at least at one end side in the width direction; and the first roller and the second roller are supported by the first support via a first bearing member and a second bearing member, respectively, at least at one end side in the width direction; An image forming apparatus characterized in that the second support is provided with a first position regulating portion that engages with the first bearing member and a second position regulating portion that engages with the second bearing member, and the position of the second support relative to the first support is determined by the first and second position regulating portions engaging with the first and second bearing members, respectively.

7. 7. The image forming apparatus according to claim 6, wherein, of the first, second and third contact members, the first contact member is arranged at the most upstream position in the direction of movement of the surface of the intermediate transfer body, the third contact member is arranged at the most downstream position in the direction of movement of the surface of the intermediate transfer body, the first contact member abuts against the first roller via the intermediate transfer body, and the second and third contact members abut against the second roller via the intermediate transfer body.

8. 7. The image forming apparatus according to claim 6, wherein, of the first, second and third contact members, the first contact member is disposed at the most upstream position in the direction of movement of the surface of the intermediate transfer body, the third contact member is disposed at the most downstream position in the direction of movement of the surface of the intermediate transfer body, the first and second contact members abut against the first roller via the intermediate transfer body, and the third contact member abuts against the second roller via the intermediate transfer body.

9. 9. The image forming apparatus according to claim 6, wherein the intermediate transfer member is an endless belt, and the first and second rollers are rollers that stretch the intermediate transfer member.

10. An image forming apparatus according to any one of claims 1 to 9, characterized in that one of the first and second position regulating portions engages with one of the first and second bearing members so as to allow rotation of the second support body around the rotation axis of the roller supported by the bearing member, and the other of the first and second position regulating portions engages with the other of the first and second bearing members so as to regulate the rotation of the second support body and allow movement in a direction intersecting the direction of the rotation.

11. The image forming apparatus according to claim 10, characterized in that the second support body is provided with a hole that is approximately circular in plan view and that constitutes one of the first and second positional regulating portions, and a hole that is approximately oval in plan view and that constitutes the other of the first and second positional regulating portions.

12. 12. The image forming apparatus according to claim 1, wherein the first, second and third contact members are rotatable brush rollers.

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