Cleaning apparatus and image forming apparatus

Abstract

To form a good-quality image without density unevenness by preventing uneven attachment of toner and external additive in a main scanning direction of a transfer body.SOLUTION: A belt cleaning device 30 has: a plurality of cleaning units that are disposed along the direction of rotation of an intermediate transfer belt 7, and upon application of a cleaning bias, recover, from the intermediate transfer belt 7, untransferred toner not transferred to a recording material P from the intermediate transfer belt 7; and a control unit 50 that applies a first cleaning bias to the cleaning unit on the upstream side, and subsequently applies a second cleaning bias having a smaller absolute value than the first cleaning bias.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a cleaning device for recovering toner on a transfer body such as an intermediate transfer belt, and an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus using an electrophotographic method or an electrostatic recording method provided with the same.

Background Art

[0002] Conventionally, as an electrophotographic image forming apparatus, an intermediate transfer type image forming apparatus having a rotatable intermediate transfer belt constituted by an endless belt is known. In an intermediate transfer type image forming apparatus, for example, a toner image formed on a photosensitive drum is primarily transferred from the photosensitive drum to the intermediate transfer belt by applying a primary transfer voltage in a primary transfer section. Then, the toner image primarily transferred onto the intermediate transfer belt is secondarily transferred from the intermediate transfer belt to a recording material such as paper by applying a secondary transfer voltage in a secondary transfer section.

[0003] Further, in an intermediate transfer type image forming apparatus, in order to stabilize the image density or correct the color shift, a test pattern such as a detection image or a patch image is formed on the intermediate transfer belt, and a test mode for detecting the test pattern may be executed.

[0004] From this, on the surface of the intermediate transfer belt that has passed through the secondary transfer section, secondary transfer residual toner or an untransferred test pattern that has remained without being transferred to the recording material adheres. Therefore, a belt cleaning device that electrostatically recovers the secondary transfer residual toner or the test pattern adhering to the surface of the intermediate transfer belt is sometimes disposed downstream of the secondary transfer section and upstream of the primary transfer section in the rotational direction of the intermediate transfer belt using electrostatic force.

[0005] Such belt cleaning devices are equipped with cleaning brushes that come into contact with the intermediate transfer belt as cleaning components. For example, a rotatable roller-shaped brush roller can be used as such a cleaning brush. Furthermore, multiple cleaning brushes may be provided in the direction of rotation of the intermediate transfer belt.

[0006] Conventional belt cleaning devices include a brush or roller that contacts the intermediate transfer belt and is supplied with bias, a recovery roller that collects toner removed from the intermediate transfer belt, and a cleaning blade that scrapes off toner from the recovery roller. In a belt cleaning device with such a configuration, a toner layer and an external additive layer are formed at the blade nip, which is the contact point between the recovery roller and the cleaning blade, by a certain amount of toner and an external additive. This makes it possible to moderately reduce the contact friction resistance at the blade nip and maintain cleaning performance.

[0007] In this context, Patent Document 1 discloses an image forming apparatus that improves the cleaning performance for untransferred test patterns. The image forming apparatus of Patent Document 1 provides good cleaning performance by increasing the cleaning voltage applied to the pre-cleaning section, the uppermost of the three intermediate transfer belt cleaning sections, when recovering untransferred toner rather than when recovering residual secondary transfer toner.

[0008] Furthermore, Patent Document 2 discloses a cleaning device that improves the cleaning performance of reverse-charged toner, which has reversed from its normal charging polarity. The cleaning device of Patent Document 2 switches the cleaning bias polarity of at least one of the two downstream cleaning sections among the three intermediate transfer belt cleaning sections. As a result, reverse-charged toner that has not been recovered in the pre-cleaning section and has re-adhered to the intermediate transfer belt can be recovered by at least one of the two downstream cleaning sections. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2014-62981 [Patent Document 2] Japanese Patent Publication No. 2015-138086 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, Patent Documents 1 and 2 do not mention cleaning performance according to the image pattern in the main scanning direction perpendicular to the rotation direction of the intermediate transfer belt.

[0011] In this case, the intermediate transfer belt may continuously transfer images of image patterns or test patterns where the amount of toner is not uniform along the main scanning direction of the intermediate transfer belt. In such cases, according to Patent Documents 1 and 2, longitudinal unevenness occurs in which the toner layer and the external additive layer are not formed uniformly in the longitudinal direction parallel to the main scanning direction of the blade nip.

[0012] In this case, in areas where the toner layer and external additive layer are not formed along the longitudinal direction of the blade nip, the contact edge of the cleaning blade with the recovery roller deforms due to contact friction resistance, creating a tiny space between the recovery roller and the cleaning blade. Then, the external additive with small particle sizes slips through this tiny space between the recovery roller and the cleaning blade unevenly and randomly.

[0013] As a result, in Patent Documents 1 and 2, the external additive that passes through the minute space between the recovery roller and the cleaning blade unevenly and randomly adheres to the intermediate transfer belt, changing the surface properties of the intermediate transfer belt and causing uneven transfer. Therefore, Patent Documents 1 and 2 have the problem that uneven density patterns may occur on the image in the main scanning direction of the intermediate transfer belt.

[0014] An object of the present invention is to provide a cleaning device and an image forming apparatus capable of forming an image with good image quality without density unevenness by suppressing uneven adhesion of toner and external additives in the main scanning direction of a transfer body.

Means for Solving the Problems

[0015] The cleaning device according to the present invention is arranged along the rotation direction of a transfer body, and a plurality of cleaning units that recover untransferred toner that is not transferred from the transfer body to a recording material from the transfer body by applying a cleaning bias. The system comprises an application unit for applying a cleaning bias to the plurality of cleaning units, and control means for controlling the cleaning bias applied by the application unit, and is capable of executing a cleaning mode in which a toner strip for supply to the plurality of cleaning units is formed on the transfer body when not forming an image, wherein the plurality of cleaning units comprises a first cleaning unit and a second cleaning unit arranged downstream of the first cleaning unit in the rotation direction of the transfer body, and the control means controls the cleaning bias applied to the first cleaning unit during the predetermined period in which the toner strip passes through the first cleaning unit, such that the cleaning bias applied to the first cleaning unit is a first cleaning bias, and the cleaning bias applied to the first cleaning unit is a second cleaning bias with an absolute value smaller than the first cleaning bias, or the cleaning bias applied to the first cleaning unit is turned off. It is characterized by this.

Effects of the Invention

[0016] According to the present invention, by suppressing uneven adhesion of toner and external additives in the main scanning direction of a transfer body, an image with good image quality without density unevenness can be formed.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] It is a schematic diagram of a cleaning device according to Embodiment 1 of the present invention. [Figure 3] It is a partially enlarged schematic diagram of a cleaning device according to Embodiment 1 of the present invention. [Figure 4] It is a flowchart of a toner band formation process executed by an image forming apparatus according to Embodiment 1 of the present invention. [Figure 5] It is a timing chart of a cleaning device according to Embodiment 1 of the present invention. [Figure 6] It is a diagram showing an example of display on an operation unit of a cleaning device according to Embodiment 1 of the present invention. [Figure 7] It is a schematic diagram of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 8] It is a schematic diagram of a cleaning device according to Embodiment 2 of the present invention. [Figure 9]It is a flowchart of a toner band formation process executed by an image forming apparatus according to Embodiment 2 of the present invention. [Figure 10] It is a timing chart of a cleaning apparatus according to Embodiment 2 of the present invention.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0019] (Embodiment 1) <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail while referring to FIG. 1.

[0020] The image forming apparatus 100 exemplifies a tandem type multifunction device having functions of a copier, a printer, and a facsimile apparatus that can form a full-color image using an electrophotographic method and adopting an intermediate transfer method here.

[0021] Specifically, the image forming apparatus 100 includes an image forming unit UY, UM, UC, UK, an intermediate transfer belt 7, a secondary transfer roller 8, a resist roller pair 9, a pre-fixing conveyance device 10, a fixing device 11, and a toner sensor 12. Further, the image forming apparatus 100 includes a secondary transfer opposing roller 21, a driving roller 22, an idle roller 23, an idle roller 24, a tension roller 25, a pressing roller 26, and a backup roller 27. Furthermore, the image forming apparatus 100 includes a belt cleaning device 30, a primary transfer power source 41, and a secondary transfer power source 42.

[0022] Image forming unit UY forms a yellow (Y) image. Image forming unit UM forms a magenta (M) image. Image forming unit UC forms a cyan (C) image. Image forming unit UK forms a black (K) image. Image forming units UY, UM, UC, and UK, as image forming sections, are equipped with photosensitive drums 1Y, 1M, 1C, and 1K, charging rollers 2Y, 2M, 2C, and 2K, and exposure devices 3Y, 3M, 3C, and 3K. In addition, image forming units UY, UM, UC, and UK are equipped with developing devices 4Y, 4M, 4C, and 4K, primary transfer rollers 5Y, 5M, 5C, and 5K, and drum cleaning devices 6Y, 6M, 6C, and 6K.

[0023] The photosensitive drums 1Y, 1M, 1C, and 1K are rotatable drum-type (cylindrical) photoreceptors (electrophotographic photoreceptors). Each photosensitive drum 1Y, 1M, 1C, and 1K is constructed by coating the outer surface of an aluminum cylinder with a diameter of 30-80 mm with an organic photoconductor (OPC) layer. The photosensitive drums 1Y, 1M, 1C, and 1K are driven to rotate at a predetermined peripheral speed in the direction of arrow R1 in Figure 1 (counterclockwise in Figure 1). As the drums rotate, their surfaces are uniformly charged to a predetermined potential of a predetermined polarity by roller-type charging rollers 2Y, 2M, 2C, and 2K. Here, a negative polarity is used as an example of the predetermined polarity.

[0024] On the surfaces of the electrostatically charged photosensitive drums 1Y, 1M, 1C, and 1K, an electrostatic image (electrostatic latent image) is formed by scanning exposure by the exposure devices 3Y, 3M, 3C, and 3K. On the photosensitive drums 1Y, 1M, 1C, and 1K on which the electrostatic image has been formed, toner as a developer is supplied by the developing device 4 and developed (visualized) to form a toner image (developer image).

[0025] The charging rollers 2Y, 2M, 2C, and 2K are positioned to contact the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K. During the charging process, a predetermined charging voltage, including a negative DC component, is applied to the core metal (not shown) of the charging rollers 2Y, 2M, 2C, and 2K from a charging power supply (not shown).

[0026] The exposure units 3Y, 3M, 3C, and 3K are laser scanners that scan and expose the photosensitive drums 1Y, 1M, 1C, and 1K by irradiating them with laser light via polygon mirrors or the like, based on image information (image signals).

[0027] The developing units 4Y, 4M, 4C, and 4K are equipped with developing rollers. During the developing process, a predetermined developing voltage containing a negative DC component is applied to the developing rollers of the developing units 4Y, 4M, 4C, and 4K from a developing power supply (not shown). The developing units 4Y, 4M, 4C, and 4K perform inverse developing on the exposed area (image area) on the photosensitive drums 1Y, 1M, 1C, and 1K, whose absolute potential has decreased due to exposure, by depositing toner charged with the same polarity as the charging polarity of the photosensitive drums 1Y, 1M, 1C, and 1K. In this example, the normal charging polarity, which is the charging polarity of the toner during development, is shown as negative polarity.

[0028] The primary transfer rollers 5Y, 5M, 5C, and 5K are roller-type primary transfer members provided on the inner circumferential surface side of the intermediate transfer belt 7, corresponding to each of the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer rollers 5Y, 5M, 5C, and 5K are biased toward the photosensitive drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 7, and bring the photosensitive drums 1Y, 1M, 1C, and 1K into contact with the intermediate transfer belt 7 to form a primary transfer section (primary transfer nip) T1. The distance L5 between adjacent primary transfer sections T1 in the direction of movement of the intermediate transfer belt 7 is 120 mm each.

[0029] The primary transfer rollers 5Y, 5M, 5C, and 5K, in the primary transfer section T1, transfer the toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K onto the rotating intermediate transfer belt 7. For example, when forming a full-color image, the primary transfer rollers 5Y, 5M, 5C, and 5K, in each primary transfer section T1, sequentially transfer the toner images of each color formed on each photosensitive drum 1Y, 1M, 1C, and 1K onto the intermediate transfer belt 7.

[0030] The primary transfer rollers 5Y, 5M, 5C, and 5K are all conductive rollers composed of a core metal (base) (not shown) and an elastic layer formed on the outer circumference of the core metal. The outer diameter of the primary transfer rollers 5Y, 5M, 5C, and 5K is preferably 12 to 25 mm in order to stably form the primary transfer section T1.

[0031] The AskerC hardness of the primary transfer rollers 5Y, 5M, 5C, and 5K is preferably 15 to 35°. The core metal is an 8mm cylindrical metal component. The elastic layer is formed of conductive foamed rubber made of NBR or EPDM, etc., and is formed around the core metal such that the outer diameter of the primary transfer roller 5 is 18mm and the AskerC hardness is 24°. The electrical resistance of the primary transfer roller 5 is preferably 1 × 10⁵ to 1 × 10⁸ Ω (measurement environment: 23℃, 50%RH, applied voltage 1kV), considering the transfer performance and power supply capacity. The electrical resistance of the primary transfer roller 5 is, for example, 1 × 10⁶ Ω (measurement environment: 23℃, 50%RH, applied voltage 1kV).

[0032] The primary transfer rollers 5Y, 5M, 5C, and 5K are pressed against the photosensitive drums 1Y, 1M, 1C, and 1K by a pressing mechanism (not shown) that contacts the intermediate transfer belt 7 from its back side. The primary transfer rollers 5Y, 5M, 5C, and 5K are pressed by the pressing mechanism and are in contact with the intermediate transfer belt 7 over a width of approximately 4 mm in the direction of the intermediate transfer belt 7's movement. Both ends of the primary transfer rollers 5Y, 5M, 5C, and 5K in the direction of their rotational axis are supported by a pressure of 1 kgf.

[0033] The drum cleaning devices 6Y, 6M, 6C, and 6K remove and recover the primary transfer residue toner that remained on the photosensitive drums 1Y, 1M, 1C, and 1K during the primary transfer process and was not transferred onto the intermediate transfer belt 7.

[0034] The intermediate transfer belt 7, acting as a transfer body, is positioned opposite the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 7 is a rotatable intermediate transfer body composed of an endless belt. The intermediate transfer belt 7 is stretched and tensioned across the secondary transfer opposing roller 21, drive roller 22, idler roller 23, idler roller 24, tension roller 25, and pressure roller 26. The intermediate transfer belt 7 is driven by the drive roller 22 and rotates (circulates) at a predetermined peripheral speed (surface movement speed) in the direction of arrow R2 (clockwise) in Figure 1. The intermediate transfer belt 7 rotates at a peripheral speed of 150 to 470 mm / sec. The intermediate transfer belt 7 extends along the alignment direction of each photosensitive drum 1Y, 1M, 1C, and 1K.

[0035] The intermediate transfer belt 7 is composed of a base layer, which is a back layer (not shown), an elastic intermediate layer, and a surface layer. The base layer is made of a material containing an appropriate amount of carbon black as an antistatic agent in a resin such as polyimide or polycarbonate, or various types of rubber.

[0036] The thickness of the base layer is preferably 0.05 to 0.15 mm, considering durability and stability of the transfer surface. The elastic layer is formed from a material containing an appropriate amount of ion conductive agent or carbon black in various types of rubber such as CR rubber, urethane rubber, or silicone rubber. The thickness of the elastic layer is preferably 0.1 to 0.500 mm, considering its ability to conform to the unevenness of the recording material P and its durability. The surface layer is formed from a material in which fluororesin fine particles are dispersed in a resin such as urethane resin or fluororesin. The thickness of the surface layer is preferably 0.002 to 0.020 mm, considering its ability to conform to the unevenness of the recording material P and its durability.

[0037] The intermediate transfer belt 7 is composed of, for example, a polyimide base layer with a thickness of 85 μm, an elastic layer of CR rubber with a thickness of 260 μm containing an ion conductive agent and carbon black, and a surface layer of urethane with a thickness of 2 μm containing PTFE.

[0038] The volume resistivity of the intermediate transfer belt 7 at the start of use is preferably 5 × 10⁸ to 2 × 10⁻¹¹ Ω·cm, taking transferability into consideration (measurement environment: 23°C, 50%RH, measuring instrument: Hi-Resta UPM, CP-HT450, UR probe, applied voltage 1000V, applied time 10 seconds). The hardness of the intermediate transfer belt 7 is preferably 40 to 90° on the MD1 hardness scale, taking into consideration its ability to conform to the unevenness of the recording material P (measurement environment: 23°C, 50%RH). For example, the intermediate transfer belt 7 has a volume resistivity of 5 × 10⁹ Ω·cm and an MD1 hardness of 70°. Although an elastic intermediate transfer belt was used for the intermediate transfer belt 7, it is not limited to this, and a single-layer belt such as a resin belt containing an ion conductive agent may also be used.

[0039] The intermediate transfer belt 7 is pressed onto the photosensitive drums 1Y, 1M, 1C, and 1K by electrical action and pressing force from the primary transfer rollers 5Y, 5M, 5C, and 5K, thereby transferring the toner image on the photosensitive drums 1Y, 1M, 1C, and 1K in the first place.

[0040] The secondary transfer roller 8 is a roller-type secondary transfer member positioned on the outer circumferential surface side of the intermediate transfer belt 7, facing the secondary transfer opposing roller 21. The secondary transfer roller 8 is biased toward the secondary transfer opposing roller 21 via the intermediate transfer belt 7 and contacts the intermediate transfer belt 7 to form a secondary transfer section (secondary transfer nip) T2. The secondary transfer roller 8, together with the intermediate transfer belt 7, grips and transports the recording material P, such as paper, recording media, or sheets. In the secondary transfer section T2, the secondary transfer roller 8 transfers the toner image formed on the intermediate transfer belt 7 onto the recording material P. The secondary transfer roller 8 then transports the recording material P, on which the toner image has been transferred, to the pre-fixing transport device 10.

[0041] Each secondary transfer roller 8 is composed of a core metal (base) (not shown) and an elastic layer made of NBR (nitrile rubber) or EPDM containing an ionic conductive agent such as a metal complex around the core metal. The secondary transfer roller 8 is formed so that the outer diameter of the core metal is 12 mm and 24 mm. The electrical resistance of the secondary transfer roller 8 is 3.0 × 10⁷ to 5.0 × 10⁷ Ω. The electrical resistance of the secondary transfer opposing roller 21 and the intermediate transfer belt 7 in the secondary transfer section T2 is sufficiently smaller than the electrical resistance of the secondary transfer roller 8.

[0042] The secondary transfer roller 8 is separated from the intermediate transfer belt 7 by a separation mechanism (not shown) as the test pattern passes through the secondary transfer section T2. ​​As a result, the test pattern is transported to the belt cleaning device 30 as untransferred toner that has not been transferred from the intermediate transfer belt 7 to the recording material P.

[0043] Each of the registration roller pairs 9 transports the recording material P, which is fed out one sheet at a time from a recording material storage section (not shown) by a pickup roller or the like and transported by a transport roller pair or the like, to the secondary transfer section T2 in time with the toner image on the intermediate transfer belt 7.

[0044] The pre-fixing transport device 10 transports the recording material P, which is transported from the secondary transfer section T2 formed by the secondary transfer roller 8 and the secondary transfer opposing roller 21, toward the fixer device 11.

[0045] The fixing device 11 heats and pressurizes the recording material P, which is carried by the pre-fixing transport device 10 and carries the unfixed toner image, thereby melting and fixing the toner image to the recording material P. The fixing device 11 transports the recording material P with the fixed toner image to a pair of discharge rollers (not shown) and discharges (outputs) it to the outside of the main body of the image forming apparatus 100.

[0046] The toner sensor 12 is located downstream of the primary transfer section T1K and upstream of the secondary transfer section T2 in the rotational direction of the intermediate transfer belt 7, and is positioned to detect a portion of the toner in the main scanning direction perpendicular to the rotational direction of the intermediate transfer belt 7. The toner sensor 12 is an optical sensor that detects a test pattern of a detection image or patch image formed on the intermediate transfer belt 7 at a predetermined timing and outputs the detection result to the control unit 50 described later. Here, the test pattern is a test pattern for image density correction or a test pattern for color shift correction, etc.

[0047] The secondary transfer opposing roller 21 functions as an opposing member (opposing electrode) of the secondary transfer roller 8. The secondary transfer opposing roller 21 is composed of a core metal (base) (not shown) and an elastic layer made of EPDM (ethylene propylene diene rubber) surrounding the core metal. The secondary transfer opposing roller 21 is formed to have an outer diameter of 20 mm and an elastic layer thickness of 0.5 mm, and to have a hardness of, for example, 70° (Asker C). The secondary transfer opposing roller 21 is electrically grounded (connected to ground).

[0048] The secondary transfer section T2 is composed of a secondary transfer roller 8 positioned on the toner image-carrying surface (outer peripheral surface) side of the intermediate transfer belt 7, and a secondary transfer opposing roller 21 positioned on the inner peripheral surface side of the intermediate transfer belt 7.

[0049] The drive roller 22 is driven by a motor (not shown) with excellent constant-speed capabilities, causing the intermediate transfer belt 7 to circulate (rotate).

[0050] Idler rollers 23 and 24 support the intermediate transfer belt 7.

[0051] The tension roller 25 applies a constant tension to the intermediate transfer belt 7. The tension roller 25 is biased from the inner circumferential surface to the outer circumferential surface of the intermediate transfer belt 7 by elastic members (not shown), such as springs, at both ends in the direction of the rotation axis (the direction perpendicular to the plane of the paper in Figure 1).

[0052] The pressing roller 26 causes the intermediate transfer belt 7 to protrude outward near the upstream side of the secondary transfer section T2 in the rotational direction of the intermediate transfer belt 7, thereby improving the adhesion between the secondary transfer roller 8 and the intermediate transfer belt 7.

[0053] The backup roller 27 is positioned opposite the upstream cleaning brush 32a of the belt cleaning device 30, which will be described later, via the intermediate transfer belt 7. The backup roller 27 is electrically grounded. The backup roller 27 rotates in conjunction with the rotation of the intermediate transfer belt 7.

[0054] The belt cleaning device 30, which functions as a cleaning device, is provided on the outer circumferential surface side of the intermediate transfer belt 7. The belt cleaning device 30 is positioned downstream of the secondary transfer section T2 and downstream of the primary transfer section T1Y in the rotational direction of the intermediate transfer belt 7. The belt cleaning device 30 is an electrostatic brush cleaning device that electrostatically removes and recovers secondary transfer residue toner or test patterns that remain on the intermediate transfer belt 7 without being transferred to the recording material P during the secondary transfer process. Details of the configuration of the belt cleaning device 30 will be described later. Here, secondary transfer residue toner or test patterns are untransferred toner that is not transferred from the intermediate transfer belt 7 to the recording material P.

[0055] The primary transfer power supplies 41Y, 41M, 41C, and 41K apply a primary transfer voltage (primary transfer bias), which is a constantly controlled DC voltage, to the primary transfer rollers 5Y, 5M, 5C, and 5K.

[0056] The secondary transfer power supply 42 is a high-voltage power supply circuit that applies a secondary transfer voltage (secondary transfer bias), which is a constant-voltage controlled DC voltage with the normal charge polarity and the opposite polarity of the toner, to the secondary transfer roller 8. Here, the positive polarity is used as an example of the normal charge polarity and the opposite polarity of the toner. The secondary transfer power supply 42 applies a secondary transfer voltage of, for example, +1 to +7kV to the secondary transfer roller 8, and by flowing a secondary transfer current of +40 to +120μA through the secondary transfer roller 8, it transfers the toner image on the intermediate transfer belt 7 onto the recording material P.

[0057] The image forming apparatus 100 having the above configuration adjusts the image forming conditions and corrects the image density based on the detection result of a test pattern for image density correction detected by the toner sensor 12. The image forming apparatus 100 also adjusts the image forming timing and corrects color misalignment based on the detection result of a test pattern for color misalignment correction detected by the toner sensor 12.

[0058] <Configuration of the belt cleaning device> The configuration of the belt cleaning device 30 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 1 and 2.

[0059] The belt cleaning device 30 includes a housing 31a, a housing 31b, an upstream cleaning brush 32a, an intermediate cleaning brush 32b, and a downstream cleaning brush 32c. The belt cleaning device 30 also includes an upstream recovery roller 33a, an intermediate recovery roller 33b, a downstream recovery roller 33c, an upstream cleaning blade 34a, an intermediate cleaning blade 34b, and a downstream cleaning blade 34c. Furthermore, the belt cleaning device 30 includes a cleaning power supply 43a, a cleaning power supply 43b, a cleaning power supply 43c, a voltage detection unit 44a, a voltage detection unit 44b, a voltage detection unit 44c, a control unit 50, and an operation unit 150.

[0060] Here, the upstream cleaning brush 32a, the upstream recovery roller 33a, and the upstream cleaning blade 34a constitute the upstream cleaning section. The intermediate cleaning brush 32b, the intermediate recovery roller 33b, and the intermediate cleaning blade 34b constitute the downstream cleaning section. The downstream cleaning brush 32c, the downstream recovery roller 33c, and the downstream cleaning blade 34c constitute the downstream cleaning section. Furthermore, the above-mentioned upstream and downstream cleaning sections constitute a plurality of cleaning sections arranged along the rotational direction of the intermediate transfer belt 7.

[0061] Furthermore, the upstream cleaning brush 32a, the intermediate cleaning brush 32b, and the downstream cleaning brush 32c will be collectively referred to as cleaning brush 32. Also, the upstream recovery roller 33a, the intermediate recovery roller 33b, and the downstream recovery roller 33c will be collectively referred to as recovery roller 33. In addition, the upstream cleaning blade 34a, the intermediate cleaning blade 34b, and the downstream cleaning blade 34c will be collectively referred to as cleaning blade 34.

[0062] The housing 31a is provided on the outer circumferential surface side of the intermediate transfer belt 7 and is positioned downstream of the secondary transfer section T2 and upstream of the drive roller 22 in the rotational direction of the intermediate transfer belt 7. Inside the housing 31a are an upstream cleaning brush 32a, an upstream recovery roller 33a, and an upstream cleaning blade 34a.

[0063] The housing 31b is provided on the outer circumferential side of the intermediate transfer belt 7, and is positioned downstream of the secondary transfer section T2 in the rotational direction of the intermediate transfer belt 7, and is positioned opposite the drive roller 22. Inside the housing 31b are an intermediate cleaning brush 32b, a downstream cleaning brush 32c, an intermediate recovery roller 33b, a downstream recovery roller 33c, an intermediate cleaning blade 34b, and a downstream cleaning blade 34c.

[0064] The upstream cleaning brush 32a is biased toward the backup roller 27 via the intermediate transfer belt 7. The upstream cleaning brush 32a contacts the intermediate transfer belt 7 to form an upstream contact portion Fa that cleans the surface of the intermediate transfer belt 7. The upstream cleaning brush 32a has the same configuration as the intermediate cleaning brush 32b and the downstream cleaning brush 32c. The upstream cleaning brush 32a is located furthest upstream of the cleaning brushes 32 in the rotational direction of the intermediate transfer belt 7.

[0065] The intermediate cleaning brush 32b is biased toward the drive roller 22 via the intermediate transfer belt 7. The intermediate cleaning brush 32b contacts the intermediate transfer belt 7 to form an intermediate contact portion Fb that cleans the surface of the intermediate transfer belt 7.

[0066] The downstream cleaning brush 32c is biased toward the drive roller 22 via the intermediate transfer belt 7. The downstream cleaning brush 32c contacts the intermediate transfer belt 7 to form a downstream contact portion Fc that cleans the surface of the intermediate transfer belt 7.

[0067] The cleaning brush 32 consists of a rotatable, roller-shaped conductive fur brush (fur brush roller). The fibers of the cleaning brush 32 are made of carbon-dispersed nylon, acrylic, or polyester fibers with a volume resistivity of 3 × 10⁵ to 1 × 10⁻¹⁰ Ω·cm and a fiber thickness of 2 to 15 denier. The cleaning brush 32 is constructed by implanting fibers on a metal roller at a density of 50,000 to 500,000 fibers / inch². The cleaning brush 32 is positioned to maintain an penetration depth of approximately 1.0 to 2.0 mm into the intermediate transfer belt 7.

[0068] The cleaning brush 32 is driven by a drive motor (not shown) to rotate in the opposite direction to the movement direction of the intermediate transfer belt 7 at the point opposite to the intermediate transfer belt 7, in the direction of the arrow in Figure 2. The cleaning brush 32 is rotated at a peripheral speed of 20-80% of the moving speed (conveying speed) of the surface of the intermediate transfer belt 7, and rubs against the surface of the intermediate transfer belt 7. The outer diameter of the cleaning brush 32 is, for example, 18 mm.

[0069] The recovery roller 33 consists of an upstream recovery roller 33a, an intermediate recovery roller 33b, and a downstream recovery roller 33c. The recovery roller 33 is made of a rotatable metal roller formed of a metal such as aluminum. The recovery roller 33 is positioned to maintain an insertion depth of approximately 1.5 to 2.5 mm relative to the cleaning brush 32.

[0070] The recovery roller 33 is driven by a drive motor (not shown) to rotate in the same direction as the cleaning brush 32, at the portion opposite to the cleaning brush 32 in the direction of the arrow in Figure 2. The recovery roller 33 is driven to rotate at a peripheral speed equivalent to the peripheral speed of the cleaning brush 32. The outer diameter of the recovery roller 33 is, for example, 13 mm. The recovery roller 33 supplies cleaning bias applied from cleaning power supplies 43a, 43b, and 43c to the cleaning brush 32.

[0071] The cleaning blade 34, as a blade, consists of an upstream cleaning blade 34a, an intermediate cleaning blade 34b, and a downstream cleaning blade 34c. The cleaning blade 34 is positioned in contact with the recovery roller 33. The cleaning blade 34 is a plate-shaped member made of an elastic material such as urethane rubber. The cleaning blade 34 has a thickness of 1.6 to 2.2 mm and an IRHD hardness of 70 to 78° (23°C, 50% RH), and is positioned to penetrate the recovery roller 33 by approximately 0.5 to 2.0 mm.

[0072] The cleaning power supply 43a is a high-voltage power supply circuit that applies a cleaning bias (cleaning voltage), which is a positive-polarity, constant-current controlled DC voltage, to the upstream cleaning brush 32a via the upstream recovery roller 33a. The cleaning power supply 43a applies the cleaning bias to the upstream cleaning brush 32a so that a cleaning current of, for example, +20 μA flows through it.

[0073] The cleaning power supply 43b is a high-voltage power supply circuit that applies a cleaning bias, which is a negative-polarity, constant-current controlled DC voltage, to the intermediate cleaning brush 32b via the intermediate recovery roller 33b. The cleaning power supply 43b applies a cleaning bias to the intermediate cleaning brush 32b such that a cleaning current of, for example, -15 μA flows through it.

[0074] The cleaning power supply 43c is a high-voltage power supply circuit that applies a cleaning bias, which is a positive-polarity, constant-current controlled DC voltage, to the downstream cleaning brush 32c via the downstream recovery roller 33c. The cleaning power supply 43c applies a cleaning bias to the downstream cleaning brush 32c such that a cleaning current of, for example, +20 μA flows through it.

[0075] The voltage detection unit 44a is provided on the cleaning power supply 43a. The voltage detection unit 44a detects the output voltage value of the cleaning power supply 43a when a cleaning bias is applied from the cleaning power supply 43a to the upstream cleaning brush 32a. The voltage detection unit 44a outputs the detected output voltage value to the control unit 50.

[0076] The voltage detection unit 44b is provided on the cleaning power supply 43b. The voltage detection unit 44b detects the output voltage value of the cleaning power supply 43b when a cleaning bias is applied from the cleaning power supply 43b to the intermediate cleaning brush 32b. The voltage detection unit 44b outputs the detected output voltage value to the control unit 50.

[0077] The voltage detection unit 44c is provided on the cleaning power supply 43c. The voltage detection unit 44c detects the output voltage value of the cleaning power supply 43c when a cleaning bias is applied from the cleaning power supply 43c to the downstream cleaning brush 32c. The voltage detection unit 44c outputs the detected output voltage value to the control unit 50.

[0078] The control unit 50, acting as a control means, is connected to an operation unit 150, such as an operation panel, provided on the image forming apparatus 100; an image reading device (not shown), also provided on the image forming apparatus 100; and an external device 200, such as a personal computer. Based on image information input from the image reading device or the external device 200, and control commands input from the operation unit 150 or the external device 200, the control unit 50 comprehensively controls the image forming apparatus 100 to execute image forming operations.

[0079] The control unit 50 is connected to cleaning power supplies 43a, 43b, and 43c. Based on the detection results of the output voltage values ​​input from the voltage detection units 44a, 44b, and 44c, the control unit 50 controls the operation of cleaning power supplies 43a, 43b, and 43c. The control unit 50 forms a test pattern on the intermediate transfer belt 7 at a predetermined timing and executes a test mode that performs image density correction or color shift correction based on the detection results of the test pattern input from the toner sensor 12.

[0080] The control unit 50 performs the toner strip formation process at the time the main power supply of the image forming apparatus 100 is first turned on, either during the initial setup when the image forming apparatus 100 is first installed or when the belt cleaning device 30 is replaced. By performing the toner strip formation process, the control unit 50 controls the cleaning bias applied to the upstream cleaning brush 32a from the cleaning power supply 43a, thereby adjusting the amount of toner supplied from the intermediate transfer belt 7 to the upstream cleaning brush 32a.

[0081] The control unit 50 includes an arithmetic control unit (not shown), a RAM 51, and a ROM 52.

[0082] RAM51 is a rewritable memory (storage medium). Information or calculation results input from the arithmetic control unit are stored in RAM51. RAM51 and the arithmetic control unit can transfer or read data from each other.

[0083] ROM52 stores the control program and pre-determined data tables, etc. ROM52 and the arithmetic control unit can transfer or read data from each other.

[0084] The operation unit 150, which serves as a mode selection unit, has the functions of a display unit that displays various information to the user or service operator under the control of the control unit 50, and an input unit for the operator to input various settings related to image formation to the control unit 50.

[0085] <Operation of the belt cleaning device> The operation of the belt cleaning device 30 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 1 to 3.

[0086] Here, a blade nip Na is formed at the contact point between the upstream recovery roller 33a and the upstream cleaning blade 34a. A blade nip Nb is also formed at the contact point between the intermediate recovery roller 33b and the intermediate cleaning blade 34b. Furthermore, a blade nip Nc is formed at the contact point between the downstream recovery roller 33c and the downstream cleaning blade 34c. Blade nips Na, Nb, and Nc are collectively referred to as blade nip N.

[0087] A cleaning bias is applied to the cleaning brush 32 from cleaning power supplies 43a, 43b, and 43c. This creates a cleaning electric field between the intermediate transfer belt 7 and the cleaning brush 32 that is suitable for cleaning residual toner or test patterns from the secondary transfer. In addition, residual toner or test patterns adhering to the surface of the intermediate transfer belt 7 are attracted to the cleaning brush 32 and removed from the surface of the intermediate transfer belt 7.

[0088] Specifically, the secondary transfer residue toner or the large amount of normally charged toner that is negatively charged, which is the normal charging polarity in the test pattern, is attracted to and recovered by the upstream cleaning brush 32a, to which a positive polarity cleaning bias is applied, at the upstream contact part Fa.

[0089] Toner with a relatively small amount of negative charge or positive charge that has passed through the upstream contact area Fa is attracted to and recovered by the intermediate cleaning brush 32b, to which a negative cleaning bias is applied, at the intermediate contact area Fb. Toner that has passed through the intermediate contact area Fb and is often made negatively charged by discharge or charge injection at the intermediate contact area Fb is attracted to and recovered by the downstream cleaning brush 32c, to which a positive cleaning bias is applied, at the downstream contact area Fc.

[0090] The toner that is adsorbed and collected by the cleaning brush 32 is further transferred from the cleaning brush 32 to the surface of the collection roller 33 by the cleaning electric field, and scraped off from the surface of the collection roller 33 by the cleaning blade 34. At this time, toner and external additives are supplied to the cleaning blade 34 from the collection roller 33. As a result, a toner layer and an external additive layer (hereinafter referred to as the "blocking layer") are formed on the upstream side in the rotational direction of the collection roller 33 of the blade nip N, which is the contact edge portion between the collection roller 33 and the cleaning blade 34, by toner and external additives, as shown in Figure 3.

[0091] The toner scraped off the surface of the recovery roller 33 is then collected in housings 31a and 31b and transported to a recovery toner container (not shown) for collection.

[0092] In the operation of the belt cleaning device 30 described above, when it is equipped with multiple cleaning brushes 32, the cleaning brushes 32 positioned upstream in the rotational direction of the intermediate transfer belt 7 recover relatively more toner. Therefore, in the belt cleaning device 30, it is necessary to consider that a blocking layer be formed evenly in the longitudinal direction of the blade nip N on the upstream side of the rotational direction of the blade nip N's recovery roller 33. Here, the longitudinal direction of the blade nip N is parallel to the main scanning direction which is perpendicular to the rotational direction of the intermediate transfer belt 7, and is perpendicular to the paper surface in Figures 1 to 3.

[0093] <Toner band formation process> The toner strip formation process performed by the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 4 to 6.

[0094] Here, the test pattern is imaged at a position corresponding to the location where the toner sensor 12 is installed, and is therefore formed unevenly in the main scanning direction, such as in vertical bands parallel to the direction perpendicular to the main scanning direction of the intermediate transfer belt 7. In addition, the secondary transfer residue toner may also be uneven in the main scanning direction of the intermediate transfer belt 7, depending on the image pattern formed. Consequently, in such secondary transfer residue toner or test patterns, a large amount of blocking layer is formed in the vertical band portions, while it is difficult to form a blocking layer in portions other than the vertical band portions.

[0095] The toner band formation process is a process that forms a stop layer over the entire area of ​​multiple blade nips N so as not to cause uneven formation of the stop layer in the longitudinal direction (hereinafter referred to as "longitudinal unevenness"). In the toner band formation process, the amount of toner recovered at the upstream contact area Fa, which recovers a relatively large amount of toner, is adjusted, and toner and external additives are supplied to the intermediate contact area Fb and the downstream contact area Fc.

[0096] The toner band formation process shown in Figure 4 is initiated when the main power of the image forming apparatus 100 is first turned on, either during the initial setup when the image forming apparatus 100 and the belt cleaning device 30 are first installed, or when the belt cleaning device 30 is replaced. The timing at which this toner band formation process is initiated is before longitudinal unevenness occurs in the stop layer on the upstream side in the rotational direction of the recovery roller 33 of the blade nip N.

[0097] First, the control unit 50 starts forming a toner strip based on a control command input from the operation unit 150, which is operated by a user or service representative (S1). As a result, a toner layer and a blocking layer are formed on the upstream side of the rotational direction of the recovery roller 33 of the blade nip N.

[0098] Next, the control unit 50 outputs a predetermined cleaning bias to the cleaning brush 32 via the recovery roller 33 from the cleaning power supply 43a, cleaning power supply 43b, and cleaning power supply 43c (S2).

[0099] At this time, the control unit 50 outputs a cleaning bias (first cleaning bias) from the cleaning power supply 43a to the upstream cleaning brush 32a via the upstream recovery roller 33a so that a cleaning current A0 flows. The control unit 50 also outputs a cleaning bias from the cleaning power supply 43b to the intermediate cleaning brush 32b via the intermediate recovery roller 33b so that a predetermined cleaning current flows. Furthermore, the control unit 50 outputs a cleaning bias from the cleaning power supply 43c to the downstream cleaning brush 32c via the downstream recovery roller 33c so that a predetermined cleaning current flows.

[0100] Next, the control unit 50 determines whether a predetermined time T1 has elapsed since the time when the cleaning bias output was started from the cleaning power supply 43a, cleaning power supply 43b, and cleaning power supply 43c (S3).

[0101] When the predetermined time T1 has not elapsed (step S3: NO), the control unit 50 repeats the process of step S3.

[0102] On the other hand, when the predetermined time T1 has elapsed (step S3: YES), the control unit 50 switches the cleaning current A0 to the cleaning current A1 and causes the cleaning power supply 43a to output a cleaning bias (second cleaning bias) (S4). Here, the absolute value of the cleaning current A1 is smaller than that of the cleaning current A0 and is 0 or more (0 ≦ A1 < A0). At this time, the control unit 50 continues to form the toner band. As a result, a cleaning bias is applied to the upstream cleaning brush 32a so that the cleaning current A1 flows from the cleaning power supply 43a through the upstream recovery roller 33a.

[0103] Next, when the control unit 50 has formed a predetermined amount of the toner band, it ends the formation of the toner band (S5), and then ends the toner band formation process.

[0104] Subsequently, the toner band formation process will be described in more detail with reference to FIG. 5.

[0105] The toner band formed by the toner band formation process is a halftone band of about 10% image duty that forms an image in the entire area 330 [mm] in the main scanning direction where the developing devices 4Y, 4M, 4C, and 4K can develop.

[0106] By executing the toner band formation process, the control unit 50 causes the image forming units UY, UM, UC, and UK to form and develop a toner band in about 180 [sec], and sequentially primary transfers the developed toner band to the intermediate transfer belt 7 in the primary transfer unit T1. In order to send the primarily transferred toner band to the belt cleaning device 30, the control unit 50 separates the secondary transfer roller 8 from the secondary transfer opposing roller 21 by a separation mechanism (not shown) in the secondary transfer unit T2.

[0107] Next, the control unit 50 applies a cleaning bias, which is a positive-polarity constant-current controlled DC voltage, from the cleaning power supply 43a to the upstream cleaning brush 32a located at the uppermost position in the rotational direction of the intermediate transfer belt 7, via the upstream recovery roller 33a. At this time, the cleaning bias is applied to the upstream cleaning brush 32a so that a cleaning current A0 of +30 [μA], the same as the output value for the test pattern, flows from the cleaning power supply 43a.

[0108] Furthermore, the control unit 50 applies a cleaning bias, which is a negative-polarity constant-current controlled DC voltage, to the intermediate cleaning brush 32b from the cleaning power supply 43b via the intermediate recovery roller 33b. At this time, the cleaning bias is applied so that a cleaning current of -10 [μA], the output value for the test pattern, flows through the intermediate cleaning brush 32b.

[0109] Furthermore, the control unit 50 applies a cleaning bias, which is a positive-polarity constant-current controlled DC voltage, to the downstream cleaning brush 32c via the recovery roller 33c downstream of the cleaning power supply 43c. At this time, the cleaning bias is applied so that a cleaning current of the output value for the test pattern + 30 [μA] flows through the downstream cleaning brush 32c.

[0110] The cleaning power supplies 43a, 43b, and 43c apply the cleaning bias described above from the time t1 when the output of the cleaning bias is started until a predetermined time T1 has elapsed. Here, the predetermined time T1 is exemplified as 90 [sec].

[0111] During this process, toner is primarily recovered by the upstream cleaning brush 32a. This uniformly forms a barrier layer in the longitudinal direction of the blade nip Na of the upstream contact area Fa. In addition, only small amounts of toner, such as the remaining toner from the upstream cleaning brush 32a and the toner re-adhered to the intermediate transfer belt 7, are sent to the intermediate cleaning brush 32b and the downstream cleaning brush 32c. Here, the toner re-adhered to the intermediate transfer belt 7 is reverse-charged toner that has been reverse-charged by the discharge between the upstream cleaning brush 32a and the upstream recovery roller 33a, and therefore cannot be recovered with a positive polarity cleaning bias and returns to the intermediate transfer belt 7.

[0112] Next, when a predetermined time T1 has elapsed from time t1, the control unit 50 switches the cleaning current A0 of +30 [μA] to a cleaning current A1 of +5 [μA] and outputs a cleaning bias from the cleaning power supply 43a. As a result, a cleaning bias is applied to the upstream cleaning brush 32a so that a cleaning current A1 of +5 [μA] flows through it.

[0113] In this process, the amount of toner recovered by the upstream cleaning brush 32a is reduced, and the toner that was not recovered by the upstream cleaning brush 32a is supplied to the intermediate cleaning brush 32b and the downstream cleaning brush 32c. This allows for the uniform formation of a blocking layer in the longitudinal direction of the blade nip Nb of the intermediate contact portion Fb and the blade nip Nc of the downstream contact portion Fc.

[0114] In this way, when a predetermined time T1 has elapsed from time t1, the cleaning current output from the cleaning power supply 43a is reduced without turning off the cleaning power supply 43a. This prevents the toner recovery capacity of the upstream cleaning brush 32a from decreasing more than necessary, suppresses a decrease in the electrostatic toner recovery capacity of the entire belt cleaning device 30, and suppresses cleaning defects.

[0115] Subsequently, the control unit 50 turns off the output of each cleaning power supply at time t2 in conjunction with the completion of toner band formation, and terminates the operation of the toner band formation mode.

[0116] Here, cleaning power supplies 43b and 43c constantly apply a cleaning bias so that a constant cleaning current flows during the toner strip formation process. This is because, after a predetermined time T1 has elapsed from time t1, toner that was not recovered by the upstream cleaning brush 32a is supplied, and the output of the cleaning bias predetermined for the test pattern is sufficient, so there is no need to switch.

[0117] The toner band formation process described above is not limited to when the image forming apparatus 100 is first installed or when the belt cleaning device 30 is replaced; it may also be performed at the operator's discretion. For example, the toner band formation process may be performed by the operator pressing the execute button 152 and then the OK button 153 on the mode screen 151 shown in Figure 6, which is displayed on the operation unit 150 as a mode selection unit. In this case, the operation unit 150 can be used to select a toner band formation mode that changes the cleaning bias applied to the cleaning brush 32a upstream of the cleaning power supply 43a.

[0118] Furthermore, the control unit 50 may turn off the cleaning power supply 43a after a predetermined time T1 has elapsed from time t1, thereby stopping the application of the cleaning bias to the upstream cleaning brush 32a. This reduces the amount of toner recovered by the upstream cleaning brush 32a compared to when the cleaning current is switched from A0 to A1. Consequently, in this case, a large amount of toner is supplied to the intermediate cleaning brush 32b and the downstream cleaning brush 32c, allowing for the uniform formation of a blocking layer in the longitudinal direction of the blade nip Nb and blade nip Nc.

[0119] In this embodiment, a cleaning bias is applied to the upstream cleaning brush 32a so that cleaning current A0 flows, and then a cleaning bias is applied so that cleaning current A1 flows. This suppresses uneven adhesion of toner and external additives in the main scanning direction of the intermediate transfer belt 7, thereby enabling the formation of an image with good image quality without density unevenness.

[0120] (Embodiment 2) The configuration of the image forming apparatus according to Embodiment 2 of the present invention is the same as that shown in Figure 1, except that a belt cleaning device 130 is provided instead of a belt cleaning device 30, so its description will be omitted.

[0121] In the first embodiment described above, three upstream contact parts Fa, an intermediate contact part Fb, and a downstream contact part Fc were provided to control the output of the cleaning power supply 43a to the upstream cleaning brush 32a, which is the uppermost upstream in the rotational direction on the intermediate transfer belt 7. In the second embodiment of the present invention, a belt cleaning device 130 equipped with two upstream contact parts Fb and a downstream contact part Fc will be described.

[0122] <Configuration of the belt cleaning device> The configuration of the belt cleaning device 130 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 7 and 8.

[0123] In addition, parts in Figures 7 and 8 that have the same configuration as those in Figures 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0124] The belt cleaning device 130 includes a housing 31b, an upstream cleaning brush 32b, a downstream cleaning brush 32c, an upstream recovery roller 33b, and a downstream recovery roller 33c. The belt cleaning device 130 also includes an upstream cleaning blade 34b, a downstream cleaning blade 34c, and a control unit 50. Furthermore, the belt cleaning device 130 includes a cleaning power supply 143b, a cleaning power supply 143c, a voltage detection unit 144b, a voltage detection unit 144c, and an operation unit 150.

[0125] Furthermore, the upstream cleaning brush 32b has the same configuration as the intermediate cleaning brush 32b of Embodiment 1, although its name is different. Also, the upstream recovery roller 33b has the same configuration as the intermediate recovery roller 33b of Embodiment 1, although its name is different. In addition, the upstream cleaning blade 34b has the same configuration as the intermediate cleaning blade 34b of Embodiment 1, although its name is different.

[0126] Here, the upstream cleaning brush 32b, the upstream recovery roller 33b, and the upstream cleaning blade 34b constitute the upstream cleaning section. The downstream cleaning brush 32c, the downstream recovery roller 33c, and the downstream cleaning blade 34c constitute the downstream cleaning section. Furthermore, the above-mentioned upstream cleaning section and downstream cleaning section constitute a plurality of cleaning sections arranged along the rotational direction of the intermediate transfer belt 7.

[0127] The housing 31b is equipped with an upstream cleaning brush 32b, a downstream cleaning brush 32c, an upstream recovery roller 33b, a downstream recovery roller 33c, an upstream cleaning blade 34b, and a downstream cleaning blade 34c.

[0128] The upstream cleaning brush 32b is biased toward the drive roller 22 via the intermediate transfer belt 7. The upstream cleaning brush 32b contacts the intermediate transfer belt 7 to form an upstream contact portion Fb that cleans the surface of the intermediate transfer belt 7.

[0129] The cleaning brush 32 is driven by a drive motor (not shown) to rotate in the opposite direction to the movement of the intermediate transfer belt 7 at the portion opposite to the intermediate transfer belt 7, which is in the direction of the arrow in Figure 8.

[0130] The recovery roller 33 consists of an upstream recovery roller 33b and a downstream recovery roller 33c. The recovery roller 33 is driven by a drive motor (not shown) to rotate in the direction of movement of the cleaning brush 32 at the part facing the cleaning brush 32, which is in the direction of the arrow in Figure 8.

[0131] The cleaning blade 34 consists of an upstream cleaning blade 34b and a downstream cleaning blade 34c.

[0132] The cleaning power supply 143b is a high-voltage power supply circuit that applies a cleaning bias, which is a positive-polarity, constant-current controlled DC voltage, to the upstream cleaning brush 32b via the upstream recovery roller 33b. The cleaning power supply 143b applies a cleaning bias to the upstream cleaning brush 32b so that a cleaning current of +30 [μA] flows, for example, the same as the output value for a test pattern.

[0133] The cleaning power supply 143c is a high-voltage power supply circuit that applies a cleaning bias, which is a negative-polarity, constant-current controlled DC voltage, to the downstream cleaning brush 32c via the downstream recovery roller 33c. The cleaning power supply 143c applies a cleaning bias to the downstream cleaning brush 32c so that a cleaning current of, for example, an output value of -10 [μA] for a test pattern flows through it.

[0134] The voltage detection unit 144b is provided on the cleaning power supply 143b. The voltage detection unit 144b detects the output voltage value of the cleaning power supply 143b when a cleaning bias is applied from the cleaning power supply 143b to the intermediate cleaning brush 32b. The voltage detection unit 144b outputs the detected output voltage value to the control unit 50.

[0135] The voltage detection unit 144c is provided on the cleaning power supply 143c. The voltage detection unit 144c detects the output voltage value of the cleaning power supply 143c when a cleaning bias is applied from the cleaning power supply 143c to the downstream cleaning brush 32c. The voltage detection unit 144c outputs the detected output voltage value to the control unit 50.

[0136] The control unit 50 is connected to the cleaning power supply 143b and the cleaning power supply 143c. The control unit 50 controls the operation of the cleaning power supply 143b and the cleaning power supply 143c based on the detection results of the output voltage values ​​input from the voltage detection unit 144b and the voltage detection unit 144c.

[0137] The control unit 50 performs the toner strip formation process at the time the main power supply of the image forming apparatus 100 is first turned on, either during the initial setup when the image forming apparatus 100 is first installed or when the belt cleaning device 130 is replaced. By performing the toner strip formation process, the control unit 50 controls the cleaning bias applied to the upstream cleaning brush 32b from the cleaning power supply 143b, thereby adjusting the amount of toner supplied from the intermediate transfer belt 7 to the upstream cleaning brush 32b.

[0138] <Operation of the belt cleaning device> The operation of the belt cleaning device 130 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 7 and 8.

[0139] Here, a blade nip Nb is formed at the contact point between the upstream recovery roller 33b and the upstream cleaning blade 34b. Also, a blade nip Nc is formed at the contact point between the downstream recovery roller 33c and the downstream cleaning blade 34c.

[0140] A cleaning bias is applied to the cleaning brush 32 from cleaning power supplies 143b and 143c. This creates a cleaning electric field between the intermediate transfer belt 7 and the cleaning brush 32 that is suitable for cleaning residual toner or test patterns from the secondary transfer. In addition, residual toner or test patterns adhering to the surface of the intermediate transfer belt 7 are attracted to the cleaning brush 32 and removed from the surface of the intermediate transfer belt 7.

[0141] Specifically, the secondary transfer residue toner or the majority of normally charged toner that is negatively charged, which is the normal charging polarity in the test pattern, is attracted to and recovered by the upstream cleaning brush 32b, to which a positive cleaning bias is applied, at the upstream contact part Fb. Toner with a relatively small amount of negative charge or positively charged toner that has passed through the upstream contact part Fb is attracted to and recovered by the downstream cleaning brush 32c, to which a negative cleaning bias is applied, at the downstream contact part Fc. Note that the operation of the belt cleaning device 130 other than the above is the same as the operation of the belt cleaning device 30, so its explanation is omitted.

[0142] <Toner band formation process> The toner strip formation process performed by the image forming apparatus 100 according to Embodiment 2 of the present invention will be described in detail with reference to Figures 9 and 10.

[0143] The toner band formation process is a process that forms a barrier layer over the entire area of ​​multiple blade nibs N so as not to cause longitudinal unevenness in the longitudinal direction. In the toner band formation process, the amount of toner recovered at the upstream contact section Fb, which recovers a relatively large amount of toner, is adjusted to supply toner and external additives to the downstream contact section Fc.

[0144] The toner strip formation process shown in Figure 9 is initiated when the main power of the image forming apparatus 100 is first turned on, either during the initial setup when the image forming apparatus 100 and the belt cleaning apparatus 130 are first installed, or when the belt cleaning apparatus 130 is replaced.

[0145] First, the control unit 50 starts forming a toner strip based on a control command input from the operation unit 150, which is operated by a user or service representative (S11). As a result, a toner layer and a blocking layer are formed on the upstream side of the rotational direction of the recovery roller 33 of the blade nip N.

[0146] Next, the control unit 50 outputs a predetermined cleaning bias to the cleaning brush 32 via the recovery roller 33 from the cleaning power supply 143b and the cleaning power supply 143c (S12).

[0147] At this time, the control unit 50 outputs a cleaning bias (first cleaning bias) from the cleaning power supply 143b to the upstream cleaning brush 32b via the upstream recovery roller 33b so that a cleaning current B0 flows. The control unit 50 also outputs a cleaning bias from the cleaning power supply 143c to the downstream cleaning brush 32c via the downstream recovery roller 33c so that a predetermined cleaning current flows.

[0148] Next, the control unit 50 determines whether a predetermined time T2 has elapsed since the time when the cleaning bias output was started from the cleaning power supply 143b and the cleaning power supply 143c (S13).

[0149] If the predetermined time T2 has not elapsed (step S13: NO), the control unit 50 repeats the process in step S13.

[0150] On the other hand, when a predetermined time T2 has elapsed (step S13: YES), the control unit 50 switches the cleaning current B0 to the cleaning current B1 and outputs a cleaning bias (second cleaning bias) from the cleaning power supply 143b (S14). Here, the absolute value of the cleaning current B1 is smaller than that of the cleaning current B0 and is 0 or more (0 ≦ B1 < B0). At this time, the control unit 50 continues to form the toner band. As a result, a cleaning bias is applied to the upstream cleaning brush 32b so that the cleaning current B1 flows from the cleaning power supply 143b through the upstream recovery roller 33b.

[0151] Next, when the control unit 50 has formed a predetermined amount of the toner band, it ends the formation of the toner band (S15), and then ends the toner band formation process.

[0152] Subsequently, the toner band formation process will be described in more detail while referring to FIG. 10.

[0153] The control unit 50 applies a cleaning bias, which is a DC voltage with a constant current control of positive polarity, to the upstream cleaning brush 32b located most upstream in the rotation direction of the intermediate transfer belt 7 via the upstream recovery roller 33b from the cleaning power supply 143b. At this time, a cleaning bias is applied to the upstream cleaning brush 32b so that a cleaning current B0 of +30 [μA], which is the same as the output value for the test pattern, flows from the cleaning power supply 143b.

[0154] In addition, the control unit 50 applies a cleaning bias, which is a DC voltage with a constant current control of negative polarity, to the downstream cleaning brush 32c via the downstream recovery roller 33c from the cleaning power supply 143c. At this time, a cleaning bias is applied to the downstream cleaning brush 32c so that a cleaning current B1 of -10 [μA], which is the output value for the test pattern, flows.

[0155] The cleaning power supplies 143b and 143c apply the cleaning bias described above from the time t11 when the output of the cleaning bias is started until a predetermined time T2 has elapsed. Here, the predetermined time T2 is exemplified as 90 [sec].

[0156] During this process, toner is primarily recovered by the upstream cleaning brush 32b. This uniformly forms a barrier layer in the longitudinal direction of the blade nip Nb of the upstream contact portion Fb. Furthermore, only a small amount of toner, such as the remaining toner from the upstream cleaning brush 32b and the toner re-adhered to the intermediate transfer belt 7, is sent to the downstream cleaning brush 32c. Here, the toner re-adhered to the intermediate transfer belt 7 is reverse-charged toner that has been reverse-charged by the discharge between the upstream cleaning brush 32b and the upstream recovery roller 33b, and therefore cannot be recovered with a positive polarity cleaning bias and returns to the intermediate transfer belt 7.

[0157] Next, when a predetermined time T2 has elapsed from time t11, the control unit 50 switches the cleaning current B0 of +30 [μA] to a cleaning current B1 of +5 [μA] and outputs a cleaning bias from the cleaning power supply 43a. As a result, a cleaning bias is applied to the upstream cleaning brush 32b so that a cleaning current B1 of +5 [μA] flows through it.

[0158] In this process, the amount of toner recovered by the upstream cleaning brush 32b is reduced, and the toner that was not recovered by the upstream cleaning brush 32b is supplied to the downstream cleaning brush 32c. This allows for the uniform formation of a blocking layer in the longitudinal direction of the blade nip Nc of the downstream contact portion Fc.

[0159] In this way, when a predetermined time T2 has elapsed from time t11, the cleaning current output from the cleaning power supply 143b is reduced without turning off the cleaning power supply 143b. This prevents the toner recovery capacity of the upstream cleaning brush 32b from decreasing more than necessary, suppresses a decrease in the electrostatic toner recovery capacity of the entire belt cleaning device 130, and suppresses cleaning defects.

[0160] Subsequently, the control unit 50 turns off the output of each cleaning power supply at time t12 in conjunction with the completion of toner band formation, and terminates the operation of the toner band formation mode.

[0161] Here, the cleaning power supply 143c constantly applies a cleaning bias so that a constant cleaning current flows during the toner strip formation process. This is because, after a predetermined time T2 has elapsed from time t11, toner that was not recovered by the upstream cleaning brush 32b is supplied, and the output of the cleaning bias predetermined for the test pattern is sufficient, so there is no need to switch.

[0162] Furthermore, the toner strip formation process described above may be performed at the operator's discretion, not limited to when the image forming apparatus 100 is first installed or when the belt cleaning device 130 is replaced.

[0163] Furthermore, the control unit 50 may turn off the cleaning power supply 143b after a predetermined time T2 has elapsed from time t11, thereby stopping the application of the cleaning bias to the upstream cleaning brush 32b. This reduces the amount of toner recovered by the upstream cleaning brush 32b compared to when the cleaning current is switched from B0 to B1. Consequently, in this case, a larger amount of toner is supplied to the downstream cleaning brush 32c, allowing for the uniform formation of a blocking layer in the longitudinal direction of the blade nip Nc.

[0164] Furthermore, after a predetermined time T2 has elapsed from time t11, a cleaning bias, which is a positive polarity constant voltage controlled DC voltage, may be applied from the cleaning power supply 143c. This increases the amount of negative polarity toner recovered.

[0165] In this embodiment, a cleaning bias is applied to the upstream cleaning brush 32b so that cleaning current B0 flows, and then a cleaning bias is applied so that cleaning current B1 flows. This suppresses uneven adhesion of toner and external additives in the main scanning direction of the intermediate transfer belt 7, thereby enabling the formation of an image with good quality and no density unevenness.

[0166] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention.

[0167] Specifically, in Embodiments 1 and 2 described above, the image forming apparatus is not limited to a tandem-type multifunction device employing an intermediate transfer method, but may also be a single-drum type, a charging method, an electrostatic image forming method, a developing method, a transfer method, or a fixing method.

[0168] Furthermore, while the above-described embodiments 1 and 2 focused primarily on the parts that form and transfer the toner image, the invention is not limited to these. By adding necessary equipment, devices, or housing structures, it can be used for various purposes such as printers, various printing machines, photocopiers, or fax machines.

[0169] Furthermore, in Embodiments 1 and 2 described above, the cleaning bias was applied by constant current control, but the method is not limited to this; the cleaning bias may also be applied by constant voltage control or other high-voltage control methods. [Explanation of Symbols]

[0170] 7. Intermediate transfer belt 12 Toner Sensor 30 Belt cleaning device 32 Cleaning Brushes 33 Recovery Roller 34 Cleaning Blades 43a Cleaning Power Supply 43b Cleaning power supply 43c Cleaning Power Supply 50 Control Unit 100 Image forming apparatus 130 Belt cleaning device 143b Cleaning power supply 143c Cleaning Power Supply 150 Operation section N Blade Nips P recording material UC Image Forming Unit UK Image Forming Unit UM Image Forming Unit UY Image Forming Unit

Claims

1. Multiple cleaning units are arranged along the rotational direction of the transfer body and recover untransferred toner from the transfer body by applying a cleaning bias, An application unit that applies a cleaning bias to the plurality of cleaning units, The system includes control means for controlling the cleaning bias applied by the application unit, During non-image formation, a cleaning mode can be executed in which a toner strip for supplying to the plurality of cleaning units is formed on the transfer body. The aforementioned multiple cleaning units are The system comprises a first cleaning unit and a second cleaning unit located downstream of the first cleaning unit in the rotational direction of the transfer body, The control means is The cleaning bias applied to the first cleaning unit during a predetermined period in which the toner strip passes through the first cleaning unit is controlled such that the cleaning bias is set to a first cleaning bias during that predetermined period, and the cleaning bias applied to the first cleaning unit is set to a second cleaning bias with an absolute value smaller than the first cleaning bias during that predetermined period, or the cleaning bias applied to the first cleaning unit is turned off during that predetermined period. A cleaning device characterized by the following features.

2. The control means is The cleaning mode is executed during the initial installation of the cleaning device or when the transfer body is replaced. The cleaning apparatus according to feature 1.

3. The plurality of cleaning units are In the aforementioned rotational direction, the third cleaning unit is located downstream of the first cleaning unit, The aforementioned application unit is The first cleaning unit applies a cleaning bias of the opposite polarity to the normal charge polarity so that it can collect normally charged toner that has been charged with the normal charge polarity, the second cleaning unit applies a cleaning bias of the same polarity as the normal charge polarity so that it can collect reverse charged toner that has been charged with the opposite polarity to the normal charge polarity, and the third cleaning unit applies a cleaning bias of the opposite polarity to the normal charge polarity so that it can collect normally charged toner that has been charged with the normal charge polarity. The cleaning apparatus according to claim 1 or 2.

4. The control means is During the predetermined period, the first cleaning bias is applied to the first cleaning unit, followed by the second cleaning bias, and the application unit is controlled to keep the cleaning bias applied to the second cleaning unit constant. A cleaning apparatus according to any one of claims 1 to 3.

5. The first cleaning unit is, The toner, which has been charged to the correct polarity, is collected. The second cleaning unit is, The normal charging polarity and the reverse charging toner with the opposite polarity are recovered. The control means is The cleaning bias is continuously applied to the second cleaning unit. A cleaning apparatus according to any one of claims 1 to 4.

6. Having a mode selection unit capable of selectively executing the cleaning mode, The control means is When the cleaning mode is selected by the mode selection unit, the cleaning mode is executed. A cleaning apparatus according to any one of claims 1 to 5, characterized by the following:

7. The cleaning unit is The device comprises a fur brush that contacts the transfer body, a metal roller that supplies the applied cleaning bias to the fur brush, and a blade that removes toner adhering to the metal roller, and electrostatically recovers and removes the untransferred toner from the transfer body. A cleaning apparatus according to any one of claims 1 to 6.

8. A cleaning device according to any one of claims 1 to 7, An image forming unit that forms an image on the recording material, An image forming apparatus characterized by having the following features.

Images